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Editor Work2017 Vol. 25, No. 3
Previous Issue
2017, 25(3): 577-581.
Abstract
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Sandstone and limestone specimens were carried out on uniaxial compression tests, and the similarities among stress-strain curves were remarkable except peak strength and elastic modulus. Further tests on artificial solid materials, including gypsum, concrete and ginger nut cemented with quartz sands, showed striking similarity and tendency in stress-strain curves. General summery of those sigmoid curves contained three curves and connected by two inflection points. The results indicated strong universal regularity for solid material under uniaxial compression test. This regularity has significant guidance to evaluation and prediction of deformation and failure process on geological engineering.
Sandstone and limestone specimens were carried out on uniaxial compression tests, and the similarities among stress-strain curves were remarkable except peak strength and elastic modulus. Further tests on artificial solid materials, including gypsum, concrete and ginger nut cemented with quartz sands, showed striking similarity and tendency in stress-strain curves. General summery of those sigmoid curves contained three curves and connected by two inflection points. The results indicated strong universal regularity for solid material under uniaxial compression test. This regularity has significant guidance to evaluation and prediction of deformation and failure process on geological engineering.
2017, 25(3): 582-591.
In this paper, two concepts are proposed—namely, the ground sensing system and the ground sensing engineering. First, the basic composition, sensing requirements and related techniques of the ground sensing system is discussed based on the characteristics of geological media and geological materials. Then, the distributed fiber optic sensing technique is highlighted and introduced, and its technical system, sensing principles, and advantages and disadvantages are summarized. Finally, the meaning of the ground sensing engineering is elaborated, followed by corresponding installation techniques, and some issues to be addressed in this field. The implications of this paper may be of great importance for structuring of ground sensing system, geoengineering monitoring, and prevention and treatment of a variety of geological hazards.
In this paper, two concepts are proposed—namely, the ground sensing system and the ground sensing engineering. First, the basic composition, sensing requirements and related techniques of the ground sensing system is discussed based on the characteristics of geological media and geological materials. Then, the distributed fiber optic sensing technique is highlighted and introduced, and its technical system, sensing principles, and advantages and disadvantages are summarized. Finally, the meaning of the ground sensing engineering is elaborated, followed by corresponding installation techniques, and some issues to be addressed in this field. The implications of this paper may be of great importance for structuring of ground sensing system, geoengineering monitoring, and prevention and treatment of a variety of geological hazards.
2017, 25(3): 592-597.
The safety and durability of the soil slope can be threatened when the strength of soil is deteriorated due to wetting-drying cycles. Experimental studies are undertaken on an undisturbed residual soil from southeast of Fujian area. It aims to discuss the variation of shear strength with the change of water contain and the cyclic number under wetting-drying cycles. It is shown that the cohesion of granite residual soil decreases in different degrees with increasing number of cycles and finally reaches to a constant state. However, the friction angle of granite residual soil keeps a stable with little influence of the wetting-drying effects. On the basis of the relationship between the amount of strength attenuation and cyclic number, the S-shaped function is adopted for fitting. The results show that the S-shaped function can well describe the attenuation rules of cohesion with the change of cyclic number. The results also have an important reference value for further reveal the influence of wetting-drying cycles on deterioration mechanism of granitic residual soil and long-term stability of residual soil slope in southeast of Fujian.
The safety and durability of the soil slope can be threatened when the strength of soil is deteriorated due to wetting-drying cycles. Experimental studies are undertaken on an undisturbed residual soil from southeast of Fujian area. It aims to discuss the variation of shear strength with the change of water contain and the cyclic number under wetting-drying cycles. It is shown that the cohesion of granite residual soil decreases in different degrees with increasing number of cycles and finally reaches to a constant state. However, the friction angle of granite residual soil keeps a stable with little influence of the wetting-drying effects. On the basis of the relationship between the amount of strength attenuation and cyclic number, the S-shaped function is adopted for fitting. The results show that the S-shaped function can well describe the attenuation rules of cohesion with the change of cyclic number. The results also have an important reference value for further reveal the influence of wetting-drying cycles on deterioration mechanism of granitic residual soil and long-term stability of residual soil slope in southeast of Fujian.
2017, 25(3): 598-604.
Niuchang ancient underground Caverns in City Longyou were built in Southern Song Dynasty and is an important part of national key cultural relics protection unit from Xiao Nanhai cave(the Longyou Grotto).They have old excavation history, rare slanting sidewall-roof structure in No.2 Cavern and plug topside structure in No.1 Cavern. The two cavern chambers get great attentions. But, serious deformation and failure happen in their roofs and slopes at the entrances of both caverns. In order to preserve the relics, this paper has carried a detailed investigation and analyzation about deformation and failure from aspect of engineering geological conditions. It shows that the long-term weathering, especially biological and thin roof composed of gentle-dip red clastic rocks are the main reasons of their deformation and failure.
Niuchang ancient underground Caverns in City Longyou were built in Southern Song Dynasty and is an important part of national key cultural relics protection unit from Xiao Nanhai cave(the Longyou Grotto).They have old excavation history, rare slanting sidewall-roof structure in No.2 Cavern and plug topside structure in No.1 Cavern. The two cavern chambers get great attentions. But, serious deformation and failure happen in their roofs and slopes at the entrances of both caverns. In order to preserve the relics, this paper has carried a detailed investigation and analyzation about deformation and failure from aspect of engineering geological conditions. It shows that the long-term weathering, especially biological and thin roof composed of gentle-dip red clastic rocks are the main reasons of their deformation and failure.
2017, 25(3): 612-618.
There are drought and harsh natural environment in northwest China, and the surface weathering causes most earthen sites here disappearing gradually. The paper uses glutinous rice slurries and SH as injecting paste materials to reinforce the weak weathering layers on the top of earthen sites in site. After this reinforcement, the mechanical strength and durability are measured via a mini-penetrometer, an infrared imaging device and an acoustic-waves-monitor, adding to a simulation rain test. In addition, some supplementary tests have been done indoor to make remolded samples in order to compare with the experiment results of uniaxial resist compression, wave velocity, disintegration and field tests. The experiment results show that the SH reinforcement effects on strength and resistance to water-erosions of earthen sites' surface are better than those reinforced by glutinous rice slurries. When the grouting aperture reaches 25mm, the maximum infiltration radius can be obtained. After using concentration of 2% of SH to reinforce, the strength is improved by 2.6 times, and the ability to resist disintegration is improved by 1.63 times. So the concentration of 2% of SH is the optimum to be the anti-weathering material.
There are drought and harsh natural environment in northwest China, and the surface weathering causes most earthen sites here disappearing gradually. The paper uses glutinous rice slurries and SH as injecting paste materials to reinforce the weak weathering layers on the top of earthen sites in site. After this reinforcement, the mechanical strength and durability are measured via a mini-penetrometer, an infrared imaging device and an acoustic-waves-monitor, adding to a simulation rain test. In addition, some supplementary tests have been done indoor to make remolded samples in order to compare with the experiment results of uniaxial resist compression, wave velocity, disintegration and field tests. The experiment results show that the SH reinforcement effects on strength and resistance to water-erosions of earthen sites' surface are better than those reinforced by glutinous rice slurries. When the grouting aperture reaches 25mm, the maximum infiltration radius can be obtained. After using concentration of 2% of SH to reinforce, the strength is improved by 2.6 times, and the ability to resist disintegration is improved by 1.63 times. So the concentration of 2% of SH is the optimum to be the anti-weathering material.
WEATHERING MECHANISM AND PREVENTION METHODS OF ANCIENT BRICK IN PINGYAO CITY, SHANXI PROVINCE, CHINA
2017, 25(3): 619-629.
Due to natural and anthropogenic forcing, the ancient blue bricks in walls and dwellings of Pingyao ancient city have suffered a serious weathering diseases. They are in badly need of protection and restoration. This field investigation finds that all weathering diseases occur in the range of rising height of capillary water(1~3m higher than the ground surface).Main weathering types of the blue bricks include contour scaling, flaking, powdering, salt crystallization. Laboratory tests determines the mineral composition, major elements, physical properties, mechanical strength, as well as performance of resistance to salt crystallization and frost. The weathering reason of the ancient brick is the salts carried by capillary water when rises. The process is aggravated by frost also due to rising of the capillary water. Salts are derived from the soluble salts carried by capillary water when rises. Due to evaporation of capillary water and/or decrease in temperature, the soluble salts in the pores of the ancient bricks become crystal salt, in the meantime the capillary water is captured and transformed to crystal water. The process can generate powerful expansive pressure in the brick pores, leading to brick failure. Methods to prevent further weathering diseases are demonstrated. They are capillary water-proofing, salt-eliminating and brick-strengthening. Technical process and analysis method, presented by the paper on weathering mechanism and weathering prevention for the ancient brick, can provide references for protection and restoration of related buildings of cultural heritage.
Due to natural and anthropogenic forcing, the ancient blue bricks in walls and dwellings of Pingyao ancient city have suffered a serious weathering diseases. They are in badly need of protection and restoration. This field investigation finds that all weathering diseases occur in the range of rising height of capillary water(1~3m higher than the ground surface).Main weathering types of the blue bricks include contour scaling, flaking, powdering, salt crystallization. Laboratory tests determines the mineral composition, major elements, physical properties, mechanical strength, as well as performance of resistance to salt crystallization and frost. The weathering reason of the ancient brick is the salts carried by capillary water when rises. The process is aggravated by frost also due to rising of the capillary water. Salts are derived from the soluble salts carried by capillary water when rises. Due to evaporation of capillary water and/or decrease in temperature, the soluble salts in the pores of the ancient bricks become crystal salt, in the meantime the capillary water is captured and transformed to crystal water. The process can generate powerful expansive pressure in the brick pores, leading to brick failure. Methods to prevent further weathering diseases are demonstrated. They are capillary water-proofing, salt-eliminating and brick-strengthening. Technical process and analysis method, presented by the paper on weathering mechanism and weathering prevention for the ancient brick, can provide references for protection and restoration of related buildings of cultural heritage.
2017, 25(3): 630-636.
A new nonlinear dynamic constitutive model of the loess is presented based on the arc-tangent function. In order to get the loess dynamic stress-strain curve and the theoretical curve of the proposed constitutive model of the loess, dynamic triaxial tests of Xi'an loess are conducted. Comparison between the theoretical and experimental results indicates that, compared with the H-D model, the new dynamic constitutive mode proposed in this paper is more suitable to describe the strength and deformation characteristics of Xi'an loess under the triaxial stress condition. The results obtained in this paper show that, with the same loading frequency and moisture content, the dynamic shear modulus of Xi'an loess increases with decrease of the moisture content. With the same confining pressure and loading frequency, dynamic shear modulus of Xi'an loess is increasing with increase of the confining pressure. With the same confining pressure and moisture content, dynamic shear modulus of Xi'an loess increases with the increase of loading frequency.
A new nonlinear dynamic constitutive model of the loess is presented based on the arc-tangent function. In order to get the loess dynamic stress-strain curve and the theoretical curve of the proposed constitutive model of the loess, dynamic triaxial tests of Xi'an loess are conducted. Comparison between the theoretical and experimental results indicates that, compared with the H-D model, the new dynamic constitutive mode proposed in this paper is more suitable to describe the strength and deformation characteristics of Xi'an loess under the triaxial stress condition. The results obtained in this paper show that, with the same loading frequency and moisture content, the dynamic shear modulus of Xi'an loess increases with decrease of the moisture content. With the same confining pressure and loading frequency, dynamic shear modulus of Xi'an loess is increasing with increase of the confining pressure. With the same confining pressure and moisture content, dynamic shear modulus of Xi'an loess increases with the increase of loading frequency.
2017, 25(3): 637-647.
Imbricate reverse fault is a kind of fault combination in crust. This paper aims to reveal the crustal stress distributed between imbricate reverse faults under different combinations. It takes Longmenshan fault as research background. The large physical simulation tests are carried out. Crustal stress distributing and changing laws are got as follows.(1) There are two parallel imbricate reverse fault distributions in research area. Their trends are penperdicular to tectonic compression direction. The fault near the compressing part can fail firstly. Meanwhile, it can result in stress release. However, there can be a sudden stress increasing around underlying fault in depth.(2) There are not only two parallel imbricate reverse faults, but also, a thrust fault distributed between them. The tectonic compression direction is perpendicular to imbricate reverse fault. The shallow crustal stress changes early. Crust may break along imbricate thrust fault.(3) There are not only imbricate reverse fault, but also another thrust fault distributed between them. The tectonic compression direction and strike of imbricate thrust fault are skew. The crust may break along thrust fault which distributes between imbricate thrust faults.(4) When there are only imbricate thrust faults, the crustal stress distributes uniformly. However, stress concentration phenomenon appears at the end or intersection of several faults. The research has certain guiding significance to regional stability evaluation and earthquake prediction.
Imbricate reverse fault is a kind of fault combination in crust. This paper aims to reveal the crustal stress distributed between imbricate reverse faults under different combinations. It takes Longmenshan fault as research background. The large physical simulation tests are carried out. Crustal stress distributing and changing laws are got as follows.(1) There are two parallel imbricate reverse fault distributions in research area. Their trends are penperdicular to tectonic compression direction. The fault near the compressing part can fail firstly. Meanwhile, it can result in stress release. However, there can be a sudden stress increasing around underlying fault in depth.(2) There are not only two parallel imbricate reverse faults, but also, a thrust fault distributed between them. The tectonic compression direction is perpendicular to imbricate reverse fault. The shallow crustal stress changes early. Crust may break along imbricate thrust fault.(3) There are not only imbricate reverse fault, but also another thrust fault distributed between them. The tectonic compression direction and strike of imbricate thrust fault are skew. The crust may break along thrust fault which distributes between imbricate thrust faults.(4) When there are only imbricate thrust faults, the crustal stress distributes uniformly. However, stress concentration phenomenon appears at the end or intersection of several faults. The research has certain guiding significance to regional stability evaluation and earthquake prediction.
2017, 25(3): 648-656.
This paper is based on the enlargement project of Jinjishan Tunnel in Fuzhou 2nd ring road. A 1/30 downscale model for the large section tunnel is fabricated. The earthquake-simulating tests with 21 loading cases are carried out. The seismic responses of acceleration and normal pressure upon the tunnel model are focused. The PGA amplification coefficient is defined as the ratio between peak seismic acceleration and peak ground acceleration. The PGA amplification coefficients upon tunnel model increase logarithmically with ground elevation. The ground elevation effect distinguishes from other regular grounds. With the augment of ground motion amplitude, the PGA amplification coefficients upon tunnel model decrease gradually, and the influence of frequency characteristic on the ground elevation effect vanishes gradually. The PEP oscillation coefficient is defined as the ratio between peak seismic and static normal pressures. With the augment of ground motion amplitude, the PEP oscillation coefficients upon sidewall and arch increase linearly in general, while the PEP oscillation coefficients upon crown and invert always remain in a small range. In the aseismic design of larger section tunnel, these results can provide some reference to the evaluation of contact pressure between the lining and the ground.
This paper is based on the enlargement project of Jinjishan Tunnel in Fuzhou 2nd ring road. A 1/30 downscale model for the large section tunnel is fabricated. The earthquake-simulating tests with 21 loading cases are carried out. The seismic responses of acceleration and normal pressure upon the tunnel model are focused. The PGA amplification coefficient is defined as the ratio between peak seismic acceleration and peak ground acceleration. The PGA amplification coefficients upon tunnel model increase logarithmically with ground elevation. The ground elevation effect distinguishes from other regular grounds. With the augment of ground motion amplitude, the PGA amplification coefficients upon tunnel model decrease gradually, and the influence of frequency characteristic on the ground elevation effect vanishes gradually. The PEP oscillation coefficient is defined as the ratio between peak seismic and static normal pressures. With the augment of ground motion amplitude, the PEP oscillation coefficients upon sidewall and arch increase linearly in general, while the PEP oscillation coefficients upon crown and invert always remain in a small range. In the aseismic design of larger section tunnel, these results can provide some reference to the evaluation of contact pressure between the lining and the ground.
2017, 25(3): 657-670.
An increasing number of large engineering projects is being carried out in the hilly loess areas in China. In order to obtain sufficient usable area in limited space, it is usually necessary to dig a mountain to fill the ditch and to form a large number of high fill slopes of more than 40m in height. Their geological conditions are complex. Their mechanical properties are very different. Their construction is difficult. The deformation and stability problems of high fill slopes is prominent. High fill slope engineering has become one of the most dangerous human engineering activities in the loess area, which seriously affect the economic construction and urbanization process in the loess area. This paper takes a high fill slope as the research object, combines the field investigation and investigation data, understands the geological profile of the study area and establishes the generalized model of the loading process of the high fill slope. It studies deformation and monitoring analysis of the backfill structure of the high fill slope. It analyzes the mechanical-deformation response characteristics of high fill slope during loading process by numerical simulation. It is of great theoretical and engineering significance to study the deformation of the anti-slide pile and the inter-pile retaining structure and the stress analysis of the anchor cable on the high embankment slope of loess. The study of deformation and monitoring analysis of the backfill structure of the high fill slope is of great theoretical and engineering significance to study the mechanics and deformation response characteristics of the loading process and to study the deformation of the anti-slide pile, the inter-pile retaining structure and the force of the anchor cable.
An increasing number of large engineering projects is being carried out in the hilly loess areas in China. In order to obtain sufficient usable area in limited space, it is usually necessary to dig a mountain to fill the ditch and to form a large number of high fill slopes of more than 40m in height. Their geological conditions are complex. Their mechanical properties are very different. Their construction is difficult. The deformation and stability problems of high fill slopes is prominent. High fill slope engineering has become one of the most dangerous human engineering activities in the loess area, which seriously affect the economic construction and urbanization process in the loess area. This paper takes a high fill slope as the research object, combines the field investigation and investigation data, understands the geological profile of the study area and establishes the generalized model of the loading process of the high fill slope. It studies deformation and monitoring analysis of the backfill structure of the high fill slope. It analyzes the mechanical-deformation response characteristics of high fill slope during loading process by numerical simulation. It is of great theoretical and engineering significance to study the deformation of the anti-slide pile and the inter-pile retaining structure and the stress analysis of the anchor cable on the high embankment slope of loess. The study of deformation and monitoring analysis of the backfill structure of the high fill slope is of great theoretical and engineering significance to study the mechanics and deformation response characteristics of the loading process and to study the deformation of the anti-slide pile, the inter-pile retaining structure and the force of the anchor cable.
2017, 25(3): 671-677.
Shaking table test is an effective method to study the effect of seismic conditions on engineering practice at present. The selection of appropriate material ratio is the key to successful simulation of the prototype project. Based on Zhoujiawan Bridge of the Chongqing-Guizhou high-speed railway, the orthogonal test is used to study the rock material according to the separation similar design method and secondary refinement test. In this study, barite powder, quartz sand, iron powder, gypsum and rosin alcohol solution are used as proportion materials. The rock mass density, gravity acceleration and geometrical size are regarded as control indexes. By the method of extreme difference analysis, the influence of material contend of model test on simulating the main parameters of rock is studied. Then the second test for refining the analysis and determining the final material mix is conducted. The results show the follows. (1) The proportion of materials affects the main parameters such as deformation modulus, cohesion and internal friction angle on different emphasis and different degrees. (2) The similarity design method can be used to select the main parameters of each component in the similar test. The orthogonal test and the secondary refinement test can quickly and efficiently design and test the main parameters. Finally the parameters are obtained to meet the requirements of the model test.
Shaking table test is an effective method to study the effect of seismic conditions on engineering practice at present. The selection of appropriate material ratio is the key to successful simulation of the prototype project. Based on Zhoujiawan Bridge of the Chongqing-Guizhou high-speed railway, the orthogonal test is used to study the rock material according to the separation similar design method and secondary refinement test. In this study, barite powder, quartz sand, iron powder, gypsum and rosin alcohol solution are used as proportion materials. The rock mass density, gravity acceleration and geometrical size are regarded as control indexes. By the method of extreme difference analysis, the influence of material contend of model test on simulating the main parameters of rock is studied. Then the second test for refining the analysis and determining the final material mix is conducted. The results show the follows. (1) The proportion of materials affects the main parameters such as deformation modulus, cohesion and internal friction angle on different emphasis and different degrees. (2) The similarity design method can be used to select the main parameters of each component in the similar test. The orthogonal test and the secondary refinement test can quickly and efficiently design and test the main parameters. Finally the parameters are obtained to meet the requirements of the model test.
2017, 25(3): 678-685.
Consolidation calculations for prefabricated vertical drains(PVds) are approximately equivalent to sand well model at home and abroad. PVds are equivalent to the flat oval cylinder in this paper. Consolidation solution for PVD foundation is derived with linear load according to equal strain assumption with confocal elliptical coordinate. The correctness of present theory is verified by ADINA finite element calculation and the existing results. The present theory is closer to Long & Covo model "dw=0.5b+0.7δ" in two-dimensional consolidation theory. The "shape effect" of flat rectangular cross is better than circular cross-section. Equivalent model for PVds in "Code for design of sea dike project(GB/T 51015-2014)" and "Technical Specification for Vacuum preloading Technique to Improve Soft Soils(JTS147-2-2009)" overestimates the capacity of PVds while considering well resistance. In addition, the longer of linear loading time, the slower rate of consolidation rate, and significant difference with the plummeted loading conditions.
Consolidation calculations for prefabricated vertical drains(PVds) are approximately equivalent to sand well model at home and abroad. PVds are equivalent to the flat oval cylinder in this paper. Consolidation solution for PVD foundation is derived with linear load according to equal strain assumption with confocal elliptical coordinate. The correctness of present theory is verified by ADINA finite element calculation and the existing results. The present theory is closer to Long & Covo model "dw=0.5b+0.7δ" in two-dimensional consolidation theory. The "shape effect" of flat rectangular cross is better than circular cross-section. Equivalent model for PVds in "Code for design of sea dike project(GB/T 51015-2014)" and "Technical Specification for Vacuum preloading Technique to Improve Soft Soils(JTS147-2-2009)" overestimates the capacity of PVds while considering well resistance. In addition, the longer of linear loading time, the slower rate of consolidation rate, and significant difference with the plummeted loading conditions.
SIMULATION TEST STUDY ON LINEAR EXPANSIVE RATIO FOR DETERMINATION OF WEAK EXPANSIVE SOIL IN SUBGRADE
2017, 25(3): 686-691.
This paper studies the variety ways of loading that affect the linear expansive ratio of expansive soil. It simulates the load variety ways of subgrade to do the test of linear expansive ratio. The results show that the higher load and initial dry density can lead to higher linear expansive ratio. It compares the linear expansive ratio test results from specification and simulation under subgrade loading. The result shows that there is great difference in linear expansive ratios of specification and simulation under subgrade loading. With the decreasing of unload and initial dry initial, the variety of loading ways has the more effect on the linear expansive ratio. It indicates that it has some influence on linear expansive ratio which does not consider the load variety ways of actual engineering. It has some influence on deformation forecast of subgrade used expansive soil. It is needed to consider the effect of load variety ways on linear expansive ratio during its determination. It is suggested to combine the load variety ways into the test of linear expansive ratio.
This paper studies the variety ways of loading that affect the linear expansive ratio of expansive soil. It simulates the load variety ways of subgrade to do the test of linear expansive ratio. The results show that the higher load and initial dry density can lead to higher linear expansive ratio. It compares the linear expansive ratio test results from specification and simulation under subgrade loading. The result shows that there is great difference in linear expansive ratios of specification and simulation under subgrade loading. With the decreasing of unload and initial dry initial, the variety of loading ways has the more effect on the linear expansive ratio. It indicates that it has some influence on linear expansive ratio which does not consider the load variety ways of actual engineering. It has some influence on deformation forecast of subgrade used expansive soil. It is needed to consider the effect of load variety ways on linear expansive ratio during its determination. It is suggested to combine the load variety ways into the test of linear expansive ratio.
2017, 25(3): 692-698.
This paper designs single pile model box test in soft clay to simulate the pile settlement of progressive loading. It measures the change of the excess pore water pressure, surface settlement and pile axial force measurement. The influence of the lateral mode resistance of the pile foundation and the change of the position of the neutral point are analyzed when the soft clay is in the stage of secondary consolidation. The research shows that the settlement caused by the soil in the secondary consolidation stage has a certain effect on the negative skin frictional resistance. Along the pile, the negative skin frictional resistance is first increased and then decreased. When the load level is up to a certain degree, the neutral point can move up as the consolidation time of the soil around the pile increases, the settlement caused during the secondary consolidation stage is related to the load level applied to the soil around the pile. As the load level of the pile increases, the proportion of the total settlement of the secondary-consolidation stage decreases gradually. The creep effect of the pile is gradually weakened.
This paper designs single pile model box test in soft clay to simulate the pile settlement of progressive loading. It measures the change of the excess pore water pressure, surface settlement and pile axial force measurement. The influence of the lateral mode resistance of the pile foundation and the change of the position of the neutral point are analyzed when the soft clay is in the stage of secondary consolidation. The research shows that the settlement caused by the soil in the secondary consolidation stage has a certain effect on the negative skin frictional resistance. Along the pile, the negative skin frictional resistance is first increased and then decreased. When the load level is up to a certain degree, the neutral point can move up as the consolidation time of the soil around the pile increases, the settlement caused during the secondary consolidation stage is related to the load level applied to the soil around the pile. As the load level of the pile increases, the proportion of the total settlement of the secondary-consolidation stage decreases gradually. The creep effect of the pile is gradually weakened.
2017, 25(3): 699-705.
When unclosed waterproof curtain is used for pit dewatering, some defects may exist in the curtain. Bursting issues caused by water-head rise in the pit have been recorded multiple times. In the subway airshaft discussed in this article, at the end of the excavation process, large inflow occurred at west side of the pit. A three-dimensional numerical model with anisotropic permeability into consideration of unsteady flow of underground water is built to simulate and analyze seepage field under seven working conditions. They are no defect on the waterproof curtain, defect at 28~33m deep with/without increased water drawing volume, defect at 33~38m deep with/without increased water drawing volume, defect at 38~43m deep with/without increased water drawing volume. The research shows that when the waterproof curtain has no defect, the waterproof curtain inside and outside water-head difference is largest at top of aquifer and the difference decreases with depth. Contours are dense near the seepage path near the defect. The water inflow raises water-head in the pit and lower water-head outside the pit. Seepage vectors of the water coming into the pit through the defect are mainly horizontal. When the defect is at the aquifer of high permeability, the corresponding water inflow is large. Increasing water drawing volume decreases impact area of the water-head rise, but excessive drawing can incur soil-piping flow. The larger the vertical distance between the defect and bottom of the curtain, the larger the rising potential is, and vice versa. The results provide guidance to incident mechanism analysis, predication and dynamic risk assessment of soil burst at down-side place of foundation pit.
When unclosed waterproof curtain is used for pit dewatering, some defects may exist in the curtain. Bursting issues caused by water-head rise in the pit have been recorded multiple times. In the subway airshaft discussed in this article, at the end of the excavation process, large inflow occurred at west side of the pit. A three-dimensional numerical model with anisotropic permeability into consideration of unsteady flow of underground water is built to simulate and analyze seepage field under seven working conditions. They are no defect on the waterproof curtain, defect at 28~33m deep with/without increased water drawing volume, defect at 33~38m deep with/without increased water drawing volume, defect at 38~43m deep with/without increased water drawing volume. The research shows that when the waterproof curtain has no defect, the waterproof curtain inside and outside water-head difference is largest at top of aquifer and the difference decreases with depth. Contours are dense near the seepage path near the defect. The water inflow raises water-head in the pit and lower water-head outside the pit. Seepage vectors of the water coming into the pit through the defect are mainly horizontal. When the defect is at the aquifer of high permeability, the corresponding water inflow is large. Increasing water drawing volume decreases impact area of the water-head rise, but excessive drawing can incur soil-piping flow. The larger the vertical distance between the defect and bottom of the curtain, the larger the rising potential is, and vice versa. The results provide guidance to incident mechanism analysis, predication and dynamic risk assessment of soil burst at down-side place of foundation pit.
2017, 25(3): 706-714.
At present, the main soil swelling force measuring methods include swelling-consolidation method, pressure swelling method, balance pressure method, constant volume method. Based on the constant volume method of measuring soil swelling force, the TST-55-type permeameter, high-precision pressure sensors and data acquisition system are used to improves measuring method of soil swelling force, and to study the expansion characteristics of expansive soil. Test results show that the initial water content and dry density of soil sample have a significant influence to limit swelling force. The paper establishes the equation for their relation with limit swelling forces. At lower initial water content, when soil sample's limit swelling force of different dry density reaches a peak, it has a different rate of decrease. The value along with increasing of the dry density can be decreased. A linear relationship exists in the double logarithmic coordinate axis about the reduction value of limit swelling force and the dry density. At higher initial water content, when soil sample's limit swelling force of different dry density reaches a peak, it will remain stable trend. There is a good linear relationship between the logarithm of limit swelling force and initial water content. There is also a good linear relationship between the logarithm of water absorption of soil sample and initial water content or dry density.
At present, the main soil swelling force measuring methods include swelling-consolidation method, pressure swelling method, balance pressure method, constant volume method. Based on the constant volume method of measuring soil swelling force, the TST-55-type permeameter, high-precision pressure sensors and data acquisition system are used to improves measuring method of soil swelling force, and to study the expansion characteristics of expansive soil. Test results show that the initial water content and dry density of soil sample have a significant influence to limit swelling force. The paper establishes the equation for their relation with limit swelling forces. At lower initial water content, when soil sample's limit swelling force of different dry density reaches a peak, it has a different rate of decrease. The value along with increasing of the dry density can be decreased. A linear relationship exists in the double logarithmic coordinate axis about the reduction value of limit swelling force and the dry density. At higher initial water content, when soil sample's limit swelling force of different dry density reaches a peak, it will remain stable trend. There is a good linear relationship between the logarithm of limit swelling force and initial water content. There is also a good linear relationship between the logarithm of water absorption of soil sample and initial water content or dry density.
2017, 25(3): 715-722.
A large deep foundation pit, located on the bank of lower reaches of Yangtze River, is of a typical dual structural stratum. An impermeable layer between two confined aquifers involved in the pit excavation is partial loss so that the two confined aquifers have a very close hydraulic connection. Because the condition of the formation under the pit site is very complex, and foundation pit dewatering has a direct influence on the safety of foundation pit engineering. The pit is divided into three zones for separate dewatering design. Here is the detailed plan. The hydraulic connection to the outside is cut off by the retaining structure in the two confined aquifers at Region Ⅰ and the first confined aquifer at zone Ⅱ. Unwatering wells are used in these layers. The second confined aquifer in zone Ⅱ is not cut off, and the two confined aquifers in zone Ⅲ where the impermeable layer is lost, have a close hydraulic connection. Two dewatering schemes are designed for these two regions. In scheme 1, wells are set in zone Ⅱ to pump the groundwater of the second confined aquifer, and in zone Ⅲ to pump the groundwater of the first aquifer. However, in scheme 2, wells are only set in zone Ⅲ and pump the groundwater of the first aquifer. For a better comparison between the two schemes and verifying their feasibility, a numerical simulation is conducted. The results show that both of the schemes are feasible and can lower the groundwater level to 1m below the bottom of the foundation pit. So the two schemes can both meet the requirement of dewatering. But scheme 2 needs less wells and results in smaller water table decline of aquifers outside the foundation pit, so that it has less impact on the environment surroundings, and it's more suitable than scheme 1.
A large deep foundation pit, located on the bank of lower reaches of Yangtze River, is of a typical dual structural stratum. An impermeable layer between two confined aquifers involved in the pit excavation is partial loss so that the two confined aquifers have a very close hydraulic connection. Because the condition of the formation under the pit site is very complex, and foundation pit dewatering has a direct influence on the safety of foundation pit engineering. The pit is divided into three zones for separate dewatering design. Here is the detailed plan. The hydraulic connection to the outside is cut off by the retaining structure in the two confined aquifers at Region Ⅰ and the first confined aquifer at zone Ⅱ. Unwatering wells are used in these layers. The second confined aquifer in zone Ⅱ is not cut off, and the two confined aquifers in zone Ⅲ where the impermeable layer is lost, have a close hydraulic connection. Two dewatering schemes are designed for these two regions. In scheme 1, wells are set in zone Ⅱ to pump the groundwater of the second confined aquifer, and in zone Ⅲ to pump the groundwater of the first aquifer. However, in scheme 2, wells are only set in zone Ⅲ and pump the groundwater of the first aquifer. For a better comparison between the two schemes and verifying their feasibility, a numerical simulation is conducted. The results show that both of the schemes are feasible and can lower the groundwater level to 1m below the bottom of the foundation pit. So the two schemes can both meet the requirement of dewatering. But scheme 2 needs less wells and results in smaller water table decline of aquifers outside the foundation pit, so that it has less impact on the environment surroundings, and it's more suitable than scheme 1.
2017, 25(3): 723-730.
River sand resource is increasingly scarce compared with dramatic abundance of sea sand resource in Hainan island. Most of coastal engineering projects are sea sand foundation. But so far, there are limited systematically research results on physical and mechanical properties of sea sand in Hainan. This paper deals with a comparative study on physical and mechanical properties of sea sand. Laboratory tests are conducted on samples from 13 bays around Hainan. The results show follows, the silt content of all sand samples satisfy the standard of sand for construction. Most of samples are poorly graded except the grain composition of Yulinzhou is well graded. All the samples from the eastern beach belong to the medium sand and fine sand, while the main ingredient of west beach is coarse sand. Every sample compactness can achieve dense state under smaller preloading(50kPa), but more than half ones just have changes slightly under preloading pressure between 50kPa to 100kPa. They change a lot when the preloading increase from 100kPa to 200kPa. The internal friction angles of samples fluctuate about 25% from 39.24°to 48.24°. The trend of fluctuations is consistent with the mean grain size. The difference of salt content between samples is huge. The maximum one of Jinhai Bay, 3.1g·kg-1, is almost eight times of that of Lingshui Bay, 0.4g·kg-1(the minimum value).Besides the sand of Qingshui Bay, all sample salt contents of other bays are much higher than the national standard of six over ten thousand. So they must be desalinated if they are used as construction sand.
River sand resource is increasingly scarce compared with dramatic abundance of sea sand resource in Hainan island. Most of coastal engineering projects are sea sand foundation. But so far, there are limited systematically research results on physical and mechanical properties of sea sand in Hainan. This paper deals with a comparative study on physical and mechanical properties of sea sand. Laboratory tests are conducted on samples from 13 bays around Hainan. The results show follows, the silt content of all sand samples satisfy the standard of sand for construction. Most of samples are poorly graded except the grain composition of Yulinzhou is well graded. All the samples from the eastern beach belong to the medium sand and fine sand, while the main ingredient of west beach is coarse sand. Every sample compactness can achieve dense state under smaller preloading(50kPa), but more than half ones just have changes slightly under preloading pressure between 50kPa to 100kPa. They change a lot when the preloading increase from 100kPa to 200kPa. The internal friction angles of samples fluctuate about 25% from 39.24°to 48.24°. The trend of fluctuations is consistent with the mean grain size. The difference of salt content between samples is huge. The maximum one of Jinhai Bay, 3.1g·kg-1, is almost eight times of that of Lingshui Bay, 0.4g·kg-1(the minimum value).Besides the sand of Qingshui Bay, all sample salt contents of other bays are much higher than the national standard of six over ten thousand. So they must be desalinated if they are used as construction sand.
THE MICRO-MECHANISM OF STRENGTH CHANGE OF BRECCIA SOIL IN OUTWASH DEPOSIT UNDER RAINFALL AT HUANXIPO
2017, 25(3): 731-739.
The micro-mechanism of strength change of breccia soil in outwash deposit at Huanxipo under rainfall is examined using field shear test, X-ray powder diffraction, scanning electron microscope and soil-water chemical effect test. Rainfall has a significant effect on the shear strength of breccia soil in Huanxipo outwash deposit. When it is saturated, the cohesion and internal friction angle are 64.3% and 22.5%lower than those at natural water content. After soaked by the rain, the microstructure of soil become loose and its cohesion decreases. The micro-mechanism of strength attenuation can be summarized as the swelling of clay minerals, the dissolution of calcium-magnesium cement, the ion's exchange and adsorption and the microscopic action of the breccia and water. Their mean performances are as follow. First, the clay minerals swell after absorbing water, causing its intergranular pores to increase and its form to turn from flocculent to layered or dispersed. Then, the dissolution of calcium-magnesium cement causes a significant increase in the concentration of calcium and magnesium ions in the solution. Then, ion exchange leads to an increase of sodium ion concentration, the thickening of diffusion layer in clay particle surface and the reduction of intergranular gravitational force. Lastly, the micro-physicochemical action of the breccia and water leads to a decrease in the interfacial contact surface roughness.
The micro-mechanism of strength change of breccia soil in outwash deposit at Huanxipo under rainfall is examined using field shear test, X-ray powder diffraction, scanning electron microscope and soil-water chemical effect test. Rainfall has a significant effect on the shear strength of breccia soil in Huanxipo outwash deposit. When it is saturated, the cohesion and internal friction angle are 64.3% and 22.5%lower than those at natural water content. After soaked by the rain, the microstructure of soil become loose and its cohesion decreases. The micro-mechanism of strength attenuation can be summarized as the swelling of clay minerals, the dissolution of calcium-magnesium cement, the ion's exchange and adsorption and the microscopic action of the breccia and water. Their mean performances are as follow. First, the clay minerals swell after absorbing water, causing its intergranular pores to increase and its form to turn from flocculent to layered or dispersed. Then, the dissolution of calcium-magnesium cement causes a significant increase in the concentration of calcium and magnesium ions in the solution. Then, ion exchange leads to an increase of sodium ion concentration, the thickening of diffusion layer in clay particle surface and the reduction of intergranular gravitational force. Lastly, the micro-physicochemical action of the breccia and water leads to a decrease in the interfacial contact surface roughness.
2017, 25(3): 740-746.
Prestressed anchor cable technology as one of the most effective reinforcement technology has been widely used in railway, highway, water conservancy and hydropower, industrial and civil construction projects. Because of the influence of geological factors and technical factors in practical engineering construction of anchor cable and hole inclination and prone to bending problems, especially in the big tonnage-long hole deep anchor drilling the problem is particularly prominent. To obtain the force characteristic of anchor cable channel bending case, carried out under the condition of channel bend of the full-scale model test indoor, with a certain strength of concrete to simulate rock mass, and embed have certain radian of anchor cable components, through classifying tensioning prestressed anchor rope to measure under the condition of bending stress in the process of hole anchor rope around shear stress, axial stress and earth pressure strength. Test results show that in the case of bend channel, inner side and outside of the cable anchorage segment of shear stress distribution is not exactly same and the anchoring bend the inside of the shear stress is larger than the lateral shear stress values when tension load at the same level; axial force along the anchor length direction from large to small, until to 0; soil pressure outside the grouting body on both sides of the same change rule in addition to the compression of the medial, lateral tension.
Prestressed anchor cable technology as one of the most effective reinforcement technology has been widely used in railway, highway, water conservancy and hydropower, industrial and civil construction projects. Because of the influence of geological factors and technical factors in practical engineering construction of anchor cable and hole inclination and prone to bending problems, especially in the big tonnage-long hole deep anchor drilling the problem is particularly prominent. To obtain the force characteristic of anchor cable channel bending case, carried out under the condition of channel bend of the full-scale model test indoor, with a certain strength of concrete to simulate rock mass, and embed have certain radian of anchor cable components, through classifying tensioning prestressed anchor rope to measure under the condition of bending stress in the process of hole anchor rope around shear stress, axial stress and earth pressure strength. Test results show that in the case of bend channel, inner side and outside of the cable anchorage segment of shear stress distribution is not exactly same and the anchoring bend the inside of the shear stress is larger than the lateral shear stress values when tension load at the same level; axial force along the anchor length direction from large to small, until to 0; soil pressure outside the grouting body on both sides of the same change rule in addition to the compression of the medial, lateral tension.
2017, 25(3): 747-754.
This paper is based on the discussion of the framework of sands with fines and the interaction between coarse and fine particles. It shows the intergranular state variables for a particular host sand mixed with different amounts of nonplastic fines. It presents large strain undrained shear strength (Sus) data and steady state line in triaxial compression for the samples. Results indicate that when Drs >>0 (which is defined as intergranular relative density), the undrained shear strength of the composited soil of sand-silt is similar to that of homogeneous sand with e=ec, which is high. When Drs→0, the undrained characteristic of the samples is uncertain, but it is obvious that the undrained shear strength of the composited soil is lower than that of the homogeneous sand. When Drs < 0, the composited soil exhibits the contractive behaviour caused by shear stress, and the Sus is lower than the others. In this research, the particular host sand mixed with nonplasitc fine is from Nanjing sand. The comparison between the test result and the predicted situation is done, and both of them is anastomose. The steady state lines in ec-logSus increases with the amount of the fines, and are parallel. The intergranular state variables can reflect the interaction between sand and fine particles, defined as force chain in cohesionless soil. This research is presented for the choice for the microstructure of sand mixed with fines.
This paper is based on the discussion of the framework of sands with fines and the interaction between coarse and fine particles. It shows the intergranular state variables for a particular host sand mixed with different amounts of nonplastic fines. It presents large strain undrained shear strength (Sus) data and steady state line in triaxial compression for the samples. Results indicate that when Drs >>0 (which is defined as intergranular relative density), the undrained shear strength of the composited soil of sand-silt is similar to that of homogeneous sand with e=ec, which is high. When Drs→0, the undrained characteristic of the samples is uncertain, but it is obvious that the undrained shear strength of the composited soil is lower than that of the homogeneous sand. When Drs < 0, the composited soil exhibits the contractive behaviour caused by shear stress, and the Sus is lower than the others. In this research, the particular host sand mixed with nonplasitc fine is from Nanjing sand. The comparison between the test result and the predicted situation is done, and both of them is anastomose. The steady state lines in ec-logSus increases with the amount of the fines, and are parallel. The intergranular state variables can reflect the interaction between sand and fine particles, defined as force chain in cohesionless soil. This research is presented for the choice for the microstructure of sand mixed with fines.
2017, 25(3): 755-761.
Soft soil subgrade is commonly reinforced with rigid piles now in order to control the stability of the embankment. The broken mechansim of piles is introduced to analyse the instability and failure mode of soft soil subgrade reinforced with rigid piles using the finit element software ABAQUS.Compared to the traditional numerical simulation method, this theory shows that progressive failure occurs among rigid piles subjected to embankment loading. On this basis, considering the likely occurrence of bending failure, the critical ratio n is proposed as the critical value for judging shearing failure or bending failure of pile. It occurs preferentially also as termination criterion for the broken mechansim of piles. The large errors of quantitative calculation using numerical simulation software can be avoided reasonably. Finally, the proposed numerical simulation is compared with the traditional numerical simulation and the numerical simulation of equivalent sand pile method. The results reflect the rationality and reliability of the proposed method. In engineering, the stability of embankment can be improved by limiting the horizontal displacement or increasing the bending strength of the front piles.
Soft soil subgrade is commonly reinforced with rigid piles now in order to control the stability of the embankment. The broken mechansim of piles is introduced to analyse the instability and failure mode of soft soil subgrade reinforced with rigid piles using the finit element software ABAQUS.Compared to the traditional numerical simulation method, this theory shows that progressive failure occurs among rigid piles subjected to embankment loading. On this basis, considering the likely occurrence of bending failure, the critical ratio n is proposed as the critical value for judging shearing failure or bending failure of pile. It occurs preferentially also as termination criterion for the broken mechansim of piles. The large errors of quantitative calculation using numerical simulation software can be avoided reasonably. Finally, the proposed numerical simulation is compared with the traditional numerical simulation and the numerical simulation of equivalent sand pile method. The results reflect the rationality and reliability of the proposed method. In engineering, the stability of embankment can be improved by limiting the horizontal displacement or increasing the bending strength of the front piles.
2017, 25(3): 762-771.
This paper uses the aerial images before and after the 6.12 Xintan Landslide and digital terrain as the information source. It adopts digital landslide technique, and takes a broader view of space-time. It aims to have more accurate geographical registration and more intuitive and clear expression. From the angle of one of the typical layer landslide types, it analyzes the characteristics of the 6.12 Xintan Landslide activities again in macro view. It suggests that the landslide is a piecewise partition activity. In the meantime, the size of each section, the activity way and the direction of each part are different. The landslide is driven by partition period of multistage movement. It is found that bedrock fissure control the landslide activities to a certain extent. Landslide activity of Jiangjiapo-Xintan slope can happen continuously and is difficult to stop completely. In addition to detailed investigation of geological environment of Xintan Landslide, the key method of digital landslide technique for identify initial failure of this type of layer landslide is to monitor the Jiangjiapo-Xintan slope. The main monitoring contents should include the follow three work. (1) The collapse activities of the main landslide material source areas, the change of the collapse debris accumulation below, and acquiring the warning(maximum) area size of the accumulate debris before slip. (2) The activities of each section on each stage, especially the activities of driving section. (3) The change of bedrock fissure shown on the debris accumulation slope. Because the geological and topography environment of Jiangjiapo-Xintan slope, long-term and successive monitoring is strongly recommended.
This paper uses the aerial images before and after the 6.12 Xintan Landslide and digital terrain as the information source. It adopts digital landslide technique, and takes a broader view of space-time. It aims to have more accurate geographical registration and more intuitive and clear expression. From the angle of one of the typical layer landslide types, it analyzes the characteristics of the 6.12 Xintan Landslide activities again in macro view. It suggests that the landslide is a piecewise partition activity. In the meantime, the size of each section, the activity way and the direction of each part are different. The landslide is driven by partition period of multistage movement. It is found that bedrock fissure control the landslide activities to a certain extent. Landslide activity of Jiangjiapo-Xintan slope can happen continuously and is difficult to stop completely. In addition to detailed investigation of geological environment of Xintan Landslide, the key method of digital landslide technique for identify initial failure of this type of layer landslide is to monitor the Jiangjiapo-Xintan slope. The main monitoring contents should include the follow three work. (1) The collapse activities of the main landslide material source areas, the change of the collapse debris accumulation below, and acquiring the warning(maximum) area size of the accumulate debris before slip. (2) The activities of each section on each stage, especially the activities of driving section. (3) The change of bedrock fissure shown on the debris accumulation slope. Because the geological and topography environment of Jiangjiapo-Xintan slope, long-term and successive monitoring is strongly recommended.
2017, 25(3): 772-783.
Zemuhe fault zone has characteristics of strong tectonic activity, seismic activity, and severe secondary geological disasters. This article takes Ezhang River as example and analyzes the activity characteristics of the fracture, distribution of development and long-term activity of geological disasters and its cause, morphological evolution and so on. The preliminary insights obtained are as follows:(1) The evolution of geological environment is depended on the activity characteristics of Zemuhe breaking. The neotectonic movement determines the local strain imbalance in fault zone. Fault activities frequently induce earthquakes. The different movements of the uplifts and depressions of the fault blocks shapes the ground topography. Different deposition environments impact the erosion and sedimentation of rock and soil. Fault tilting movements control water system and geothermal migration. (2) Active faults have control effect on geological hazards. The disaster distribution has the time-space effect. In space, the disaster is distributed along the fault zone and linear distribution along the river. Lithology has marked corresponding relationship with the development of geohazards, which concentrated in the soft rock of broken band, its corresponding relationship with micro-landform. In time, the existing geology disaster is caused by coupling effect under seismic disturbance and strong rainfall. In addition, Ezhang River has a high frequency of debris flows. (3) Active faults influence the cause of disaster mechanism and disaster type and failure mode. Fragile geological environment in the coupling effect of earthquake persistent disturbance and extreme rainfall is the root causes of disasters. Disasters can be divided into three major categories and 7 minor categories according to the disaster mechanism, with typical failure mode of slope cracking shock. (4) The interaction between active faults and geological hazards determines the landform evolution. Debris flows of Ezhang River form accumulation fans, but have an influence on geomorphic migration of the Qionghai Lake. The comparison of the height caused by tectonic uplift and denudation thickness caused by disaster indicates that Ezhang River in uplift area and Qionghai Lake in sedimentation area. From here we see that, the Zemuhe fault controls regional geological environment evolution by new tectonic movement. Its forms a large number of geological disasters. At the end, uplift and depression are caused by tectonic movements. Erosion and sedimentation are caused by seismic hazard. Their combinations determine the existing landscape.
Zemuhe fault zone has characteristics of strong tectonic activity, seismic activity, and severe secondary geological disasters. This article takes Ezhang River as example and analyzes the activity characteristics of the fracture, distribution of development and long-term activity of geological disasters and its cause, morphological evolution and so on. The preliminary insights obtained are as follows:(1) The evolution of geological environment is depended on the activity characteristics of Zemuhe breaking. The neotectonic movement determines the local strain imbalance in fault zone. Fault activities frequently induce earthquakes. The different movements of the uplifts and depressions of the fault blocks shapes the ground topography. Different deposition environments impact the erosion and sedimentation of rock and soil. Fault tilting movements control water system and geothermal migration. (2) Active faults have control effect on geological hazards. The disaster distribution has the time-space effect. In space, the disaster is distributed along the fault zone and linear distribution along the river. Lithology has marked corresponding relationship with the development of geohazards, which concentrated in the soft rock of broken band, its corresponding relationship with micro-landform. In time, the existing geology disaster is caused by coupling effect under seismic disturbance and strong rainfall. In addition, Ezhang River has a high frequency of debris flows. (3) Active faults influence the cause of disaster mechanism and disaster type and failure mode. Fragile geological environment in the coupling effect of earthquake persistent disturbance and extreme rainfall is the root causes of disasters. Disasters can be divided into three major categories and 7 minor categories according to the disaster mechanism, with typical failure mode of slope cracking shock. (4) The interaction between active faults and geological hazards determines the landform evolution. Debris flows of Ezhang River form accumulation fans, but have an influence on geomorphic migration of the Qionghai Lake. The comparison of the height caused by tectonic uplift and denudation thickness caused by disaster indicates that Ezhang River in uplift area and Qionghai Lake in sedimentation area. From here we see that, the Zemuhe fault controls regional geological environment evolution by new tectonic movement. Its forms a large number of geological disasters. At the end, uplift and depression are caused by tectonic movements. Erosion and sedimentation are caused by seismic hazard. Their combinations determine the existing landscape.
2017, 25(3): 784-793.
Ground fissure disaster is one of the main environmental geological hazards in Xi'an, which influence the using and planning of land in the urban construction. In order to research the characteristics of the dynamic effects of ground fissures, this paper chooses the F6 ground fissure site as the research object. After finishing the field test and the spectrum analysis of micro-tremors, we analyze the acceleration amplitude, excellent frequency, amplification effect and other dynamic response characteristics of the ground fissures. The research shows that there is no obvious relationship between the frequency of the test site and the position of the measuring point. The excellent frequency of the Fourier spectrum is around 2.79Hz, and the excellent frequency of the response spectrum is around 4.17Hz. Nearby the ground fissure region, the dynamic response of ground fissure site has obvious amplification effect. The influence range of hanging wall and footwall is around 15m. The amplification factor of hanging wall is greater than that of footwall, in which the amplification ratios of the Fourier peak are 1.92 and 1.81, the amplification ratios of the response spectrum peak are 1.68 and 1.63.
Ground fissure disaster is one of the main environmental geological hazards in Xi'an, which influence the using and planning of land in the urban construction. In order to research the characteristics of the dynamic effects of ground fissures, this paper chooses the F6 ground fissure site as the research object. After finishing the field test and the spectrum analysis of micro-tremors, we analyze the acceleration amplitude, excellent frequency, amplification effect and other dynamic response characteristics of the ground fissures. The research shows that there is no obvious relationship between the frequency of the test site and the position of the measuring point. The excellent frequency of the Fourier spectrum is around 2.79Hz, and the excellent frequency of the response spectrum is around 4.17Hz. Nearby the ground fissure region, the dynamic response of ground fissure site has obvious amplification effect. The influence range of hanging wall and footwall is around 15m. The amplification factor of hanging wall is greater than that of footwall, in which the amplification ratios of the Fourier peak are 1.92 and 1.81, the amplification ratios of the response spectrum peak are 1.68 and 1.63.
2017, 25(3): 794-805.
An earthquake can change the geological environment and show the geohazard effect within 5 to 10 years or even longer. The development numbers of debris flows in Pingwu County change a lot before and after Wenchuan earthquake. According to a series of investigation, by collecting and analyzing all kinds of data in the past 8 years, this paper tries to do a comparative research of the development situation and characteristics of debris flows before and after the earthquake in Pingwu County. It analyzes the basic features and debris flow mechanism and the evolution in recent years and engineering control effects. Then it finally gets the following conclusions. (1) About 85% debris flow disasters caused by the Wenchuan earthquake in Pingwu County are stable and have no potential safety hazard within 5 years after the earthquake. (2) Because of its extremely rich source, the small main channel of longitudinal slope, the large watershed area and the large number of branches, there is still big debris flow risk in Xingping ditch. (3) The effect of debris flow prevention engineering in Xingping ditch is good. (4) Prevention and control recommendations are to build an unilateral protection embankment in the Dasha dam(from entrance of the ditch 1.1km) and to stabilize Zhengjiashan Landslide.Engineering management in time, in order to strengthen the management of the provenance farmland and waste slag and protect the catchment vegetation.
An earthquake can change the geological environment and show the geohazard effect within 5 to 10 years or even longer. The development numbers of debris flows in Pingwu County change a lot before and after Wenchuan earthquake. According to a series of investigation, by collecting and analyzing all kinds of data in the past 8 years, this paper tries to do a comparative research of the development situation and characteristics of debris flows before and after the earthquake in Pingwu County. It analyzes the basic features and debris flow mechanism and the evolution in recent years and engineering control effects. Then it finally gets the following conclusions. (1) About 85% debris flow disasters caused by the Wenchuan earthquake in Pingwu County are stable and have no potential safety hazard within 5 years after the earthquake. (2) Because of its extremely rich source, the small main channel of longitudinal slope, the large watershed area and the large number of branches, there is still big debris flow risk in Xingping ditch. (3) The effect of debris flow prevention engineering in Xingping ditch is good. (4) Prevention and control recommendations are to build an unilateral protection embankment in the Dasha dam(from entrance of the ditch 1.1km) and to stabilize Zhengjiashan Landslide.Engineering management in time, in order to strengthen the management of the provenance farmland and waste slag and protect the catchment vegetation.
2017, 25(3): 806-814.
All of the MS8.0 Wenchuan, MS7.0 Lushan, and MS6.5 Ludian earthquakes have triggered a large number of landslides. Due to differences in magnitude, geology, and topographical conditions, the distribution of seismic landslides vary widely. In this study, existing research results are combined to perform a contrastive analysis of seismic landslide distribution patterns based on three aspects:earthquake characteristics, geology, and topography. The following results are obtained. (1) The number and density of landslides due to the three earthquakes increase with the increase of peak ground acceleration(PGA) and magnitude. The number of landslides shows an increasing trend following an increase of intensity during the Wenchuan and Ludian earthquakes. However, the area affected by the relatively low-intensity Lushan earthquake also develops numerous landslides. (2) The maximum distance of influence of a geological fault on landslide distribution increases with the increase of magnitude. Within the range of 0.2 times of the maximum distance of influence, the Wenchuan earthquake has an 80% landslide distribution, whereas the other two earthquakes have only 30%. Moreover, the number of landslides decreases exponentially with distance of the Wenchuan earthquake from geological faults. (3) The distribution of seismic landslides is strongly influenced by topography. In the Ⅶ or higher intensity regions, the relief depth increases and earthquake-triggered landslides in high concentration areas have relatively higher relief. Furthermore, the slopes gradient with concentrated landslides can subsequently increase. Seismic landslides occur more frequently along mountain ridges and deep slopes in areas of higher relief, which may be related to the topographic amplification effect.
All of the MS8.0 Wenchuan, MS7.0 Lushan, and MS6.5 Ludian earthquakes have triggered a large number of landslides. Due to differences in magnitude, geology, and topographical conditions, the distribution of seismic landslides vary widely. In this study, existing research results are combined to perform a contrastive analysis of seismic landslide distribution patterns based on three aspects:earthquake characteristics, geology, and topography. The following results are obtained. (1) The number and density of landslides due to the three earthquakes increase with the increase of peak ground acceleration(PGA) and magnitude. The number of landslides shows an increasing trend following an increase of intensity during the Wenchuan and Ludian earthquakes. However, the area affected by the relatively low-intensity Lushan earthquake also develops numerous landslides. (2) The maximum distance of influence of a geological fault on landslide distribution increases with the increase of magnitude. Within the range of 0.2 times of the maximum distance of influence, the Wenchuan earthquake has an 80% landslide distribution, whereas the other two earthquakes have only 30%. Moreover, the number of landslides decreases exponentially with distance of the Wenchuan earthquake from geological faults. (3) The distribution of seismic landslides is strongly influenced by topography. In the Ⅶ or higher intensity regions, the relief depth increases and earthquake-triggered landslides in high concentration areas have relatively higher relief. Furthermore, the slopes gradient with concentrated landslides can subsequently increase. Seismic landslides occur more frequently along mountain ridges and deep slopes in areas of higher relief, which may be related to the topographic amplification effect.
2017, 25(3): 815-823.
Material Point Method(MPM)belongs to one of the meshless numerical analysis methods. It is able to integrate a variety of constitutive models and consider the fluid-solid coupling behavior within soils, so as to effectively simulate the large and extra-large deformation of landslides. This paper introduces the fundamental principles of MPM, the governing equations and the solving formats. Based on the 5 types of porous media characterization models of MPM, we briefly review the state-of-the-art of run-out process simulation of soil landslides using MPM.Subsequently, we simulate the run-out process of Shenzhen "12·20" landfill landslide using MPM with the single-layer and sing-phase material point model. Linear loading is applied to identify the initial stress field. Elasto-palstic constitutive models using Drucker-Prager yield criterion, GIMP algorithm and MUSL solving format are also used, respectively. The simulation results show that the maximal sliding distance reaches 510m, after the slope losing its stability. Moreover, the longitudinal distance of the landslide scope is 1050m and the minimal landslide angle is 5.95°, both agreeing well with the observed results. The evolution trends of the equivalent plastic strain zone within the soil exhibit that the landslide mechanism is progressive failure. Specifically, shear failure of the soil occurs at the slope toe initially, and tensile fracture occurs at the slope top subsequently, with both plastic zones extending toward the interior of the slope along the bedrock. The extra-large deformation occurs once the sliding surface is cut-through to accelerate the sliding. The MPM simulation for the run-out process of landslides can shed light on the hazardous behaviors of landslides and provide assistants for landslide prevention.
Material Point Method(MPM)belongs to one of the meshless numerical analysis methods. It is able to integrate a variety of constitutive models and consider the fluid-solid coupling behavior within soils, so as to effectively simulate the large and extra-large deformation of landslides. This paper introduces the fundamental principles of MPM, the governing equations and the solving formats. Based on the 5 types of porous media characterization models of MPM, we briefly review the state-of-the-art of run-out process simulation of soil landslides using MPM.Subsequently, we simulate the run-out process of Shenzhen "12·20" landfill landslide using MPM with the single-layer and sing-phase material point model. Linear loading is applied to identify the initial stress field. Elasto-palstic constitutive models using Drucker-Prager yield criterion, GIMP algorithm and MUSL solving format are also used, respectively. The simulation results show that the maximal sliding distance reaches 510m, after the slope losing its stability. Moreover, the longitudinal distance of the landslide scope is 1050m and the minimal landslide angle is 5.95°, both agreeing well with the observed results. The evolution trends of the equivalent plastic strain zone within the soil exhibit that the landslide mechanism is progressive failure. Specifically, shear failure of the soil occurs at the slope toe initially, and tensile fracture occurs at the slope top subsequently, with both plastic zones extending toward the interior of the slope along the bedrock. The extra-large deformation occurs once the sliding surface is cut-through to accelerate the sliding. The MPM simulation for the run-out process of landslides can shed light on the hazardous behaviors of landslides and provide assistants for landslide prevention.
2017, 25(3): 824-832.
This paper is based on the analysis of 29 karst sinkholes in Wuhan. Their system structure is determined from three elements, i.e.karst, cover and groundwater. The sinkhole mechanism of rainfall, drilling and pile constructing importing karst system is discussed via field monitoring and numerical simulating. The results are as follows. (1) The geological conditions developing sinkhole include the following three aspects. The cover structure is upper clay and lower sand. The shallow karst is developed. The hydraulic connection between pore water-karst water is good. (2) In natural environment, the cave in cover soil has two developing stage that is from hydraulic corrosion to stress failure. (3) Drilling and pile constructing often trigger sinkhole that is from two aspects of structure changing. The covering soil has high hydraulic gradient at the moment of drill connecting pore water and karst water. The head difference of two groundwater is more than 15m during pile constructing.
This paper is based on the analysis of 29 karst sinkholes in Wuhan. Their system structure is determined from three elements, i.e.karst, cover and groundwater. The sinkhole mechanism of rainfall, drilling and pile constructing importing karst system is discussed via field monitoring and numerical simulating. The results are as follows. (1) The geological conditions developing sinkhole include the following three aspects. The cover structure is upper clay and lower sand. The shallow karst is developed. The hydraulic connection between pore water-karst water is good. (2) In natural environment, the cave in cover soil has two developing stage that is from hydraulic corrosion to stress failure. (3) Drilling and pile constructing often trigger sinkhole that is from two aspects of structure changing. The covering soil has high hydraulic gradient at the moment of drill connecting pore water and karst water. The head difference of two groundwater is more than 15m during pile constructing.
2017, 25(3): 833-840.
The use of anti-slide pile to reinforce the slope is a common method for landslide control. This paper considers the performance of a homogeneous isotropic slope reinforced with one row of piles. The strength reduction finite element method is used to analyze the effect of anti-slide pile reinforcement of several factors on the slope stability. It calculates the anti-slide pile bending moment, shear force, displacement and safety factor of the slope under the process of slope grading load. The results reveal the influence of pile position, pile length and other factors on the stability of slope. For each of these parameters, the safety factor of the slope, the optimal pile position and the critical length measure of the pile are assessed. The results provide reference basis for optimizing design of the pile row. Furthermore, the body stress and deformation characteristics of pile and laws under the grading loading are analyzed. It finds that the horizontal displacement of pile head under the step loading with exponential function forms of development. It then puts forward the deformation prediction mathematical model to provide basis for the deformation control of pile.
The use of anti-slide pile to reinforce the slope is a common method for landslide control. This paper considers the performance of a homogeneous isotropic slope reinforced with one row of piles. The strength reduction finite element method is used to analyze the effect of anti-slide pile reinforcement of several factors on the slope stability. It calculates the anti-slide pile bending moment, shear force, displacement and safety factor of the slope under the process of slope grading load. The results reveal the influence of pile position, pile length and other factors on the stability of slope. For each of these parameters, the safety factor of the slope, the optimal pile position and the critical length measure of the pile are assessed. The results provide reference basis for optimizing design of the pile row. Furthermore, the body stress and deformation characteristics of pile and laws under the grading loading are analyzed. It finds that the horizontal displacement of pile head under the step loading with exponential function forms of development. It then puts forward the deformation prediction mathematical model to provide basis for the deformation control of pile.
2017, 25(3): 841-852.
Much of relevant materials of 463 old landslides which had significant deformation in Three Gorges Reservoir Area are collected from June 2003 to June 2015. This paper studies the evolution models and slip-surface shapes of some typical old landslides. It concludes that there are 4 typical slip-surface shapes of circular, polyline, rectilinear and chair shape. Results of macroscopic analysis of wading extent and deformation time distribution can be summarized as follows. (1) The hydrodynamic pressure has obvious effect on the stability of the circular and rectilinear slip-surface landslides. Most of these two types of landslides deform at the lowering stage of water level when the front or middle is waded, especially after the first time to the highest water level. (2) A small part of the rectilinear slip-surface landslides is deformed at the stage of low water level after the drop because of lags in response. (3) The deformation occurs in the chair-shaped and polygonal line slip-surface landslides at the increasing stage of water level owing to effect of buoyancy weight loss, especially to the first 135m and 175m storage. Most of the chair-shaped slip-surface landslides are deformed when the front is waded as well as the rear wading extent of the polygonal line slip-surface landslides is higher than other 3 types. At last, the research results have a certain reference meaning for wading old landslides prevention in Three Gorges Reservoir Area.
Much of relevant materials of 463 old landslides which had significant deformation in Three Gorges Reservoir Area are collected from June 2003 to June 2015. This paper studies the evolution models and slip-surface shapes of some typical old landslides. It concludes that there are 4 typical slip-surface shapes of circular, polyline, rectilinear and chair shape. Results of macroscopic analysis of wading extent and deformation time distribution can be summarized as follows. (1) The hydrodynamic pressure has obvious effect on the stability of the circular and rectilinear slip-surface landslides. Most of these two types of landslides deform at the lowering stage of water level when the front or middle is waded, especially after the first time to the highest water level. (2) A small part of the rectilinear slip-surface landslides is deformed at the stage of low water level after the drop because of lags in response. (3) The deformation occurs in the chair-shaped and polygonal line slip-surface landslides at the increasing stage of water level owing to effect of buoyancy weight loss, especially to the first 135m and 175m storage. Most of the chair-shaped slip-surface landslides are deformed when the front is waded as well as the rear wading extent of the polygonal line slip-surface landslides is higher than other 3 types. At last, the research results have a certain reference meaning for wading old landslides prevention in Three Gorges Reservoir Area.
2017, 25(3): 853-857.
The industrial development of shale gas requires the volume fracturing of tight reservoir. Multilevel staged fracturing technique is one of the key techniques for the successful development of shale gas reservoirs. Shale reservoir, under the combined effect of in-situ stress and fracturing pressure, breaks through the shale matrix, and communicates with the weak structural plane of natural fracture, which forms a high conductivity network system. The release of free gas and adsorbed gas exists in shale reservoirs, improves initial shale gas production and ultimate recovery. According to the engineering geological characteristics of shale reservoir in east Chongqing, combined with YuyeA-2HF well and YuyeB-2HF well field fracturing construction data, this paper explores the suitable fracturing technology of shale reservoir in east Chongqing. The results show that the use of prehydrochloric acid treatment to keep the near well with diversion capacity, can protect the follow-up large displacement construction pressure window. Low sand ratio powder sand section of the multi-stage filter to achieve "controlled near and far", can increase the volume of the reservoir fracturing. Abnormal pressure layer glue front, made full hydraulic fracture, for the subsequent slickwater can carry proppant into the reservoir to create favorable conditions.
The industrial development of shale gas requires the volume fracturing of tight reservoir. Multilevel staged fracturing technique is one of the key techniques for the successful development of shale gas reservoirs. Shale reservoir, under the combined effect of in-situ stress and fracturing pressure, breaks through the shale matrix, and communicates with the weak structural plane of natural fracture, which forms a high conductivity network system. The release of free gas and adsorbed gas exists in shale reservoirs, improves initial shale gas production and ultimate recovery. According to the engineering geological characteristics of shale reservoir in east Chongqing, combined with YuyeA-2HF well and YuyeB-2HF well field fracturing construction data, this paper explores the suitable fracturing technology of shale reservoir in east Chongqing. The results show that the use of prehydrochloric acid treatment to keep the near well with diversion capacity, can protect the follow-up large displacement construction pressure window. Low sand ratio powder sand section of the multi-stage filter to achieve "controlled near and far", can increase the volume of the reservoir fracturing. Abnormal pressure layer glue front, made full hydraulic fracture, for the subsequent slickwater can carry proppant into the reservoir to create favorable conditions.
2017, 25(3): 858-866.
In mining process, the height of water flowing fractured zone is significance in preventing mine water and gas. This paper further researchs the failure characteristic of the overlying strata. It takes certain coalmine with 5.82m mining height as the experimental face. It uses water injection and televiewer methods in drillholes, ground penetrating radar, and microseismic monitoring system in underground coalmine. It monitors the height of water flowing fractured zone of fully-mechanized top caving. It conducts numerical simulation experiment on the failure process and similarity simulation experiment on the cracks evolution at the same time. It modifies the empirical formula. The results show that:The heights of caving and fractured zones are respectively 43.1m and 86.7m in fully mechanized sub-level caving mining. The data difference of each test method of caving zone, fractured zone and water flowing fractured zone is respectively less than 4.5%, 7.1%, and 9.0%.The degree of fracture development is low before mining. The number of fissures is obviously increased after mining. The degree of fracture development is increased. The fracture cluster region mainly focuses near the coal wall. The fracture density distribution curves of overlying strata like sanke-shapes. The new empirical formula of water flowing fractured zone height is proposed and can adapt to certain coalmine geological conditions.
In mining process, the height of water flowing fractured zone is significance in preventing mine water and gas. This paper further researchs the failure characteristic of the overlying strata. It takes certain coalmine with 5.82m mining height as the experimental face. It uses water injection and televiewer methods in drillholes, ground penetrating radar, and microseismic monitoring system in underground coalmine. It monitors the height of water flowing fractured zone of fully-mechanized top caving. It conducts numerical simulation experiment on the failure process and similarity simulation experiment on the cracks evolution at the same time. It modifies the empirical formula. The results show that:The heights of caving and fractured zones are respectively 43.1m and 86.7m in fully mechanized sub-level caving mining. The data difference of each test method of caving zone, fractured zone and water flowing fractured zone is respectively less than 4.5%, 7.1%, and 9.0%.The degree of fracture development is low before mining. The number of fissures is obviously increased after mining. The degree of fracture development is increased. The fracture cluster region mainly focuses near the coal wall. The fracture density distribution curves of overlying strata like sanke-shapes. The new empirical formula of water flowing fractured zone height is proposed and can adapt to certain coalmine geological conditions.
2017, 25(3): 867-872.
Natural outcrop of groundwater in karst mountainous countryside is an important water supply source. Its flow dynamic changes in the degree of security of water supply play a decisive role. This paper takes Yantang springs as an example and analyzes the spring flow rate. Using the change law of the SARIMA model, it established a fitting prediction model. The analysis results show that the Yantang springs flow has seasonal changes over the years. Fitting and predicted results show that SARIMA model is applicable to short-term prediction with high accuracy. But its precision is reduced for long-term forecast. Between the measured value, it is still in the 95% of the predicted range, which indicates that the model can be used for short-term forecast. The long-term predicted results can provide reference for natural outcrop of groundwater development and utilization.
Natural outcrop of groundwater in karst mountainous countryside is an important water supply source. Its flow dynamic changes in the degree of security of water supply play a decisive role. This paper takes Yantang springs as an example and analyzes the spring flow rate. Using the change law of the SARIMA model, it established a fitting prediction model. The analysis results show that the Yantang springs flow has seasonal changes over the years. Fitting and predicted results show that SARIMA model is applicable to short-term prediction with high accuracy. But its precision is reduced for long-term forecast. Between the measured value, it is still in the 95% of the predicted range, which indicates that the model can be used for short-term forecast. The long-term predicted results can provide reference for natural outcrop of groundwater development and utilization.
2017, 25(3): 879-885.
In the construction of modern urban rail transit, more and more overlapping subway shield tunnels are used. The overlapping shield tunnels are interacted with each other. The collapse arch of overlapping tunnels is multiple superposed during digging. The traditional analytical method is difficult to calculate the pressure of tunnel surrounding rock. At present, there is no effective way to calculate the stress of overlapping tunnel surrounding rock. In order to study the stress and the segments reinforcement of overlapping shield tunnels, this paper takes the overlapping shield tunnels in Nanluoguxiang station to Dongsi station of Beijing Metro Line 6 as an example. The arch collapse multiple superposed is calculated by simulation of tunnels excavation process using the elastic-plastic theory. The plastic zone area of the tunnels is calculated using the strength reduction method. Then the collapse arch height and surrounding rock pressure are calculated from the plastic zone area. According to the theory of thick wall cylinder, the additional stress of the lower tunnel by shell in construction and by train in running is calculated. From above analysis, the internal force of overlapping shield tunnels is calculated and the segments reinforcement of lower shield tunnel segment is designed.
In the construction of modern urban rail transit, more and more overlapping subway shield tunnels are used. The overlapping shield tunnels are interacted with each other. The collapse arch of overlapping tunnels is multiple superposed during digging. The traditional analytical method is difficult to calculate the pressure of tunnel surrounding rock. At present, there is no effective way to calculate the stress of overlapping tunnel surrounding rock. In order to study the stress and the segments reinforcement of overlapping shield tunnels, this paper takes the overlapping shield tunnels in Nanluoguxiang station to Dongsi station of Beijing Metro Line 6 as an example. The arch collapse multiple superposed is calculated by simulation of tunnels excavation process using the elastic-plastic theory. The plastic zone area of the tunnels is calculated using the strength reduction method. Then the collapse arch height and surrounding rock pressure are calculated from the plastic zone area. According to the theory of thick wall cylinder, the additional stress of the lower tunnel by shell in construction and by train in running is calculated. From above analysis, the internal force of overlapping shield tunnels is calculated and the segments reinforcement of lower shield tunnel segment is designed.
2017, 25(3): 886-891.
From October 20 to 24, 2016, the International Symposium on Marine Engineering Geology was successfully held in Qingdao, China. It was the first symposium on marine engineering geology sponsored by the Marine Engineering Geology Commission of International Association for Engineering Geology and the Environment. The theme of this symposium was marine engineering geology and geo-environmental safety. Six topics were set for this symposium, including engineering characteristics of marine soil, regional engineering geology and offshore geohazards, coastal engineering geology, marine engineering geological survey technology and data analysis, submarine soil-structure interaction, and marine engineering geology in offshore new energy development. It had 13 plenary reports, 57 ordinary oral reports and 15 poster reports. It provided a board platform for domestic and foreign experts to communicate with each other deeply and widely, and reflected our country's academic position and appeal in the international academia of marine engineering geology. Though great progress has been made in marine engineering geology, it was still in their infancy both in China and around the world. Researchers on marine engineering geology should concentrate on the new difficulties and hotspots in ocean engineering, responding to the demand of national strategies.
From October 20 to 24, 2016, the International Symposium on Marine Engineering Geology was successfully held in Qingdao, China. It was the first symposium on marine engineering geology sponsored by the Marine Engineering Geology Commission of International Association for Engineering Geology and the Environment. The theme of this symposium was marine engineering geology and geo-environmental safety. Six topics were set for this symposium, including engineering characteristics of marine soil, regional engineering geology and offshore geohazards, coastal engineering geology, marine engineering geological survey technology and data analysis, submarine soil-structure interaction, and marine engineering geology in offshore new energy development. It had 13 plenary reports, 57 ordinary oral reports and 15 poster reports. It provided a board platform for domestic and foreign experts to communicate with each other deeply and widely, and reflected our country's academic position and appeal in the international academia of marine engineering geology. Though great progress has been made in marine engineering geology, it was still in their infancy both in China and around the world. Researchers on marine engineering geology should concentrate on the new difficulties and hotspots in ocean engineering, responding to the demand of national strategies.
2017, 25(3): 892-900.
With the rapid development of the infrastructure construction in southwestern mountainous areas in China. High-fill foundations of the Airport, Highways, Railways and other construction projects increase day by day. During the construction period, the large deformation of the fill area and long-term slow deformation of the post-construction stage directly affect the normal use of the construction site. Especially the fill works with the free faces of slope, slope and horizontal deformation of the filled soil are related to the overall stability of slope. This paper takes a high-fill slope in Anning city in Yunnan province as a case. The site survey and the monitoring data during the filling process was used in the deformation analysis. The numerical simulation software was used to study the deformation characteristics of the fill slope. The results show that the total deformation of the slope is dominated by subsidence, and the maximum occurs in the interior of the slope. Most of the deformation occurs during the construction. The settlement after construction is very small. The maximum vertical displacement of the slope occurs at the interface between the filling body and the original foundation soil. The contour of settlement is elliptical. The maximum of horizontal displacement of the slope occurs in the original soil. Horizontal displacement contour map is overall strip-like. It extends from the bottom to the earth of the slope. The horizontal displacement that changes greatly is consistent with the position of the actual surface crack. The research results have certain reference value and guiding significance to the construction process of the fill work with free face, the prediction and control of the deformation after construction and the study on crack disease on the upper part of slope.
With the rapid development of the infrastructure construction in southwestern mountainous areas in China. High-fill foundations of the Airport, Highways, Railways and other construction projects increase day by day. During the construction period, the large deformation of the fill area and long-term slow deformation of the post-construction stage directly affect the normal use of the construction site. Especially the fill works with the free faces of slope, slope and horizontal deformation of the filled soil are related to the overall stability of slope. This paper takes a high-fill slope in Anning city in Yunnan province as a case. The site survey and the monitoring data during the filling process was used in the deformation analysis. The numerical simulation software was used to study the deformation characteristics of the fill slope. The results show that the total deformation of the slope is dominated by subsidence, and the maximum occurs in the interior of the slope. Most of the deformation occurs during the construction. The settlement after construction is very small. The maximum vertical displacement of the slope occurs at the interface between the filling body and the original foundation soil. The contour of settlement is elliptical. The maximum of horizontal displacement of the slope occurs in the original soil. Horizontal displacement contour map is overall strip-like. It extends from the bottom to the earth of the slope. The horizontal displacement that changes greatly is consistent with the position of the actual surface crack. The research results have certain reference value and guiding significance to the construction process of the fill work with free face, the prediction and control of the deformation after construction and the study on crack disease on the upper part of slope.
2017, 25(3): 605-611.
The previous research theory of consolidation of unsaturated soil free drainage well foundation, both the permeability coefficient within the searched area and the non-searched area are considered equal. This assumption is not consistent with the actual engineering. The permeability coefficient can be variable within the smear zone in this paper. It gives the analysis of the regularity in pressure of excess pore water and air. It is based on Fredlund one-dimensional consolidation theory, Darcy's law and the law of Fick. It examines finite thickness on the linear elastic unsaturated soil with sand drain foundation, and large area uniform transient load conditions. The change of permeability coefficient is considered in smear zone soil. It uses Laplace transformation and the introduction of Bessel function. It is accomplished by means crump Laplace inverse transformation. The excess pore-air and pore-water pressure with semi-analytical solutions are got for unsaturated soil free drain wells. It calculates typical examples in different radius, smear zone radius and under the condition of different smear zone, and obtains air excess pore pressure and excess pore water pressure with the change rule of the time. The dissipation rates of air excess pore pressure and excess pore water pressure are much slower when the smear effect is considered. The greater the smear zone radius and the higher level of smear, then much slower and the more quickly conversely. This study enriches the theory of consolidation of unsaturated soil free drainage wells. The characteristics of the unsaturated soil consolidation of sand drain has certain reference value in engineering.
The previous research theory of consolidation of unsaturated soil free drainage well foundation, both the permeability coefficient within the searched area and the non-searched area are considered equal. This assumption is not consistent with the actual engineering. The permeability coefficient can be variable within the smear zone in this paper. It gives the analysis of the regularity in pressure of excess pore water and air. It is based on Fredlund one-dimensional consolidation theory, Darcy's law and the law of Fick. It examines finite thickness on the linear elastic unsaturated soil with sand drain foundation, and large area uniform transient load conditions. The change of permeability coefficient is considered in smear zone soil. It uses Laplace transformation and the introduction of Bessel function. It is accomplished by means crump Laplace inverse transformation. The excess pore-air and pore-water pressure with semi-analytical solutions are got for unsaturated soil free drain wells. It calculates typical examples in different radius, smear zone radius and under the condition of different smear zone, and obtains air excess pore pressure and excess pore water pressure with the change rule of the time. The dissipation rates of air excess pore pressure and excess pore water pressure are much slower when the smear effect is considered. The greater the smear zone radius and the higher level of smear, then much slower and the more quickly conversely. This study enriches the theory of consolidation of unsaturated soil free drainage wells. The characteristics of the unsaturated soil consolidation of sand drain has certain reference value in engineering.
2017, 25(3): 873-878.
Toppling deformation has obvious characteristics of partition and is common in rock slopes of one hydropower. The quantitative classification of toppling deformation degree with geophysical properties is infrequent. Based on the discrepancy of resistivity driving by different degrees of deformation, this paper classifies the degree of toppling deformation of the slopes at the right abutment of Miaowei hydropower station with the HDRM(High-Density Resistivity Method).To remove the influence of the ground resistivity caused by the rock itself, this paper gets the law of ground resistivity distribution through forward simulation of a 2D model. Then it gets properties a related with the degree of toppling deformation by dividing the metrical resistivity with ground resistivity. Finally, comparing with the geological survey method, this method has improved the reliability and accuracy. It can quantify the toppling deformation classification successfully.
Toppling deformation has obvious characteristics of partition and is common in rock slopes of one hydropower. The quantitative classification of toppling deformation degree with geophysical properties is infrequent. Based on the discrepancy of resistivity driving by different degrees of deformation, this paper classifies the degree of toppling deformation of the slopes at the right abutment of Miaowei hydropower station with the HDRM(High-Density Resistivity Method).To remove the influence of the ground resistivity caused by the rock itself, this paper gets the law of ground resistivity distribution through forward simulation of a 2D model. Then it gets properties a related with the degree of toppling deformation by dividing the metrical resistivity with ground resistivity. Finally, comparing with the geological survey method, this method has improved the reliability and accuracy. It can quantify the toppling deformation classification successfully.
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