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Editor Work2008 Vol. 16, No. 3
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2008, 16(3): 291-297.
Abstract
There are a lot of large-scale loose complex Quaternary deposits originated from landslide deposits, weathering residues, alluvial and flood deposits, drifts and glacial deposits etc. prevail in the west mountainous regions of China. These multi-origin deposits of a transitional type geological-body are distinctly differing from the single-origin loose deposits in the East plain regions of China. Based on the study of contrast analysis of deposits, this paper summarizes the basic features, main types and distribution rule. Lastly, this paper analyzes the geological origin of deposits from a coupling idea, and puts forward a coupling model of the Earth's geological processes of large-scale loose deposits of river valley. The analysis shows that the large-scale complex deposits belong to multi-order, complex composite geological body of the coupling of Earth's endogenic and exogenic geological processes. This study can provide with theory evidences for environment, geological hazards and project security.
There are a lot of large-scale loose complex Quaternary deposits originated from landslide deposits, weathering residues, alluvial and flood deposits, drifts and glacial deposits etc. prevail in the west mountainous regions of China. These multi-origin deposits of a transitional type geological-body are distinctly differing from the single-origin loose deposits in the East plain regions of China. Based on the study of contrast analysis of deposits, this paper summarizes the basic features, main types and distribution rule. Lastly, this paper analyzes the geological origin of deposits from a coupling idea, and puts forward a coupling model of the Earth's geological processes of large-scale loose deposits of river valley. The analysis shows that the large-scale complex deposits belong to multi-order, complex composite geological body of the coupling of Earth's endogenic and exogenic geological processes. This study can provide with theory evidences for environment, geological hazards and project security.
2008, 16(3): 298-303.
A hydroelectric power station at Lan-Cang river locates the east brim zone of Qing-Zhang tableland. This site is at alpine canyon, has high tectonic stress circumstance and rock mass unload cranny development, and toppling deformation. They become the most important facts which effect the stability of project slope as rock mass quality, rupture action and seismicty. Deformation discrete element method can be used. This paper develops two discrete element models. One model is a theoretical excavation model and the other is a actual slope excavation model. The results of the theoretical model show that the destroying mechanism is the cutting deformation in ebb toppling deformation, fracturing deformation, strain-shear rupture in the lay of strong toppling rock mass and break rupture in strong rupture rock mass and the deformation range, excavation face, reinforce method and so on. Comparing the results of the project slope excavation model with the results of the site geological investigation show that calculated results and field data are basically similar.
A hydroelectric power station at Lan-Cang river locates the east brim zone of Qing-Zhang tableland. This site is at alpine canyon, has high tectonic stress circumstance and rock mass unload cranny development, and toppling deformation. They become the most important facts which effect the stability of project slope as rock mass quality, rupture action and seismicty. Deformation discrete element method can be used. This paper develops two discrete element models. One model is a theoretical excavation model and the other is a actual slope excavation model. The results of the theoretical model show that the destroying mechanism is the cutting deformation in ebb toppling deformation, fracturing deformation, strain-shear rupture in the lay of strong toppling rock mass and break rupture in strong rupture rock mass and the deformation range, excavation face, reinforce method and so on. Comparing the results of the project slope excavation model with the results of the site geological investigation show that calculated results and field data are basically similar.
2008, 16(3): 304-310.
As a kind of representative landslide, accumulative stratum landslides in horizontal stratum have special forming causes and deforming-destructing characteristics. This paper studies the accumulative stratum landslide in Wanzhou and then analyzes the characteristics of the accumulative stratum landslide, sources of matter, causes, forming mode and deforming-destructing characteristics of the accumulative stratum landslide in horizontal stratum. The characteristics of landslide body and bed are then summarized. Falling accumulation is primary and diluvium and alluvium are subordinate to the accumulative stratum landslides in horizontal stratum. The forming mode have six steps: a) cliffy forming, b) landslide bed forming, c) bottom matter of landslide body forming, d) soil and stone forming and, e) the surface matter forming and disaggregating. The deforming-destructing characteristics are as follows: several shear zones can exist in the accumulative stratum landslides. At the same time, deforming velocity and accumulating deformation in different areas are various in the accumulative stratum landslides.
As a kind of representative landslide, accumulative stratum landslides in horizontal stratum have special forming causes and deforming-destructing characteristics. This paper studies the accumulative stratum landslide in Wanzhou and then analyzes the characteristics of the accumulative stratum landslide, sources of matter, causes, forming mode and deforming-destructing characteristics of the accumulative stratum landslide in horizontal stratum. The characteristics of landslide body and bed are then summarized. Falling accumulation is primary and diluvium and alluvium are subordinate to the accumulative stratum landslides in horizontal stratum. The forming mode have six steps: a) cliffy forming, b) landslide bed forming, c) bottom matter of landslide body forming, d) soil and stone forming and, e) the surface matter forming and disaggregating. The deforming-destructing characteristics are as follows: several shear zones can exist in the accumulative stratum landslides. At the same time, deforming velocity and accumulating deformation in different areas are various in the accumulative stratum landslides.
2008, 16(3): 311-318.
The problem of a deposit slope is encountered in construction of hydropower projects in Southwest China. The study combines geology phenomena and drill core data, bases on site geology survey, historical seism, rainfall data, and so on. The thought of engineering geology qualitative analysis and back-analysis is applied to study the slope stability. The results show that the slope is stable. The formation mechanism for deposit slope is as follows: on account of joints and weathering, the dip direction of top stratums is opposite to the slope, which results in toppling and falling. After rock failure, the cracked rock masses rolled and accumulated. Durative depositing, rainwater infiltration, and the geology environmental disturbance brought on deposits' concretion and compacting. Aiming at spatial structure features of deposits slope, the quantitative analysis is adopted to compute factors of the whole and partial stability under natural conditions. The possible failure patterns depending on the spatial structure features of the slope are analyzed. The whole slide is along the interface between deposits and bedrocks, and internal partial arc slide. The above discussions offer reasonable evidence to constructions of the project and partial reinforcements of the slope.
The problem of a deposit slope is encountered in construction of hydropower projects in Southwest China. The study combines geology phenomena and drill core data, bases on site geology survey, historical seism, rainfall data, and so on. The thought of engineering geology qualitative analysis and back-analysis is applied to study the slope stability. The results show that the slope is stable. The formation mechanism for deposit slope is as follows: on account of joints and weathering, the dip direction of top stratums is opposite to the slope, which results in toppling and falling. After rock failure, the cracked rock masses rolled and accumulated. Durative depositing, rainwater infiltration, and the geology environmental disturbance brought on deposits' concretion and compacting. Aiming at spatial structure features of deposits slope, the quantitative analysis is adopted to compute factors of the whole and partial stability under natural conditions. The possible failure patterns depending on the spatial structure features of the slope are analyzed. The whole slide is along the interface between deposits and bedrocks, and internal partial arc slide. The above discussions offer reasonable evidence to constructions of the project and partial reinforcements of the slope.
2008, 16(3): 319-326.
This paper is based on the configuration characteristics and topographical changes of the seabed landslide and the results of geophysical exploration and engineering geological prospecting. The structural deterioration characteristics are recognised. A comprehensive analysis of the sliding mechanism is carried out using the following factors: topography, stratum, hydrodynamic conditions and the landslide structure. For different landslide factors, different stability evaluation methods are adopted n. For the submarine landslide, the limiting equilibrium method is adopted; for the posterior landslide, the arc slice method is used. The parameters of the undisturbed and remoulded soft soil samples taken from the submarine landslide are used in calculation. It is found that this submarine landslide was caused by the integrated effect of natural geology, human activity, gravitation and ocean dynamics. The stability factor is far below 1. The findings provide a qualitative and quantitative scientific basis for the landslide remediation.
This paper is based on the configuration characteristics and topographical changes of the seabed landslide and the results of geophysical exploration and engineering geological prospecting. The structural deterioration characteristics are recognised. A comprehensive analysis of the sliding mechanism is carried out using the following factors: topography, stratum, hydrodynamic conditions and the landslide structure. For different landslide factors, different stability evaluation methods are adopted n. For the submarine landslide, the limiting equilibrium method is adopted; for the posterior landslide, the arc slice method is used. The parameters of the undisturbed and remoulded soft soil samples taken from the submarine landslide are used in calculation. It is found that this submarine landslide was caused by the integrated effect of natural geology, human activity, gravitation and ocean dynamics. The stability factor is far below 1. The findings provide a qualitative and quantitative scientific basis for the landslide remediation.
2008, 16(3): 327-331.
The shear strength mechanisms of joint and rock bridge are analyzed in this paper. Though introducing deformation compatibility equation in normal direction, the direct shear strength formulation is deducted based on the Mohr-Coulomb theory. According to the model test, tensile-shear complex failure is the main failure mode on the shear plane. Many tensile micro-cracks are formed in the test sample. There are five typical stages in the failure process. They are the linear elastic increment, the slippage of the joints, the steady development of post-cracking, the coalescence failure of discontinuous joints and the residual strength. The theoretical calculated results coincide well with experimental results.
The shear strength mechanisms of joint and rock bridge are analyzed in this paper. Though introducing deformation compatibility equation in normal direction, the direct shear strength formulation is deducted based on the Mohr-Coulomb theory. According to the model test, tensile-shear complex failure is the main failure mode on the shear plane. Many tensile micro-cracks are formed in the test sample. There are five typical stages in the failure process. They are the linear elastic increment, the slippage of the joints, the steady development of post-cracking, the coalescence failure of discontinuous joints and the residual strength. The theoretical calculated results coincide well with experimental results.
2008, 16(3): 332-337.
In June 2003, a continuous rainstorm triggered many landslides along the main road between Yunxi to Manchuanguan in northwestern Hubei province. According to rock constituents and structures of slopes, storm-induced landslides are categorized as five typical failure models. They are (a) slip of shallow colluvial soil, (b) bedding slip along weak surfaces, (c) water split of cutting-bedding slopes, (d) failure along arc track of cataclastic rock and (e) wedge slip of block fracture slopes. The evaluation methods are proposed correspondingly in accordance with the failure modes and its effect. The shallow landslides are found to occur at ease when the water content of colluvial soil reached 85%-100% of liquid limit. Their stabilities are calculated with the infinite-slope-analysis method. The limit equilibrium method of rigid body is adopted to calculate the stability of bedding slips along weak surfaces and wedge slips of block fracture slopes. High-angle cracks of cutting-bedding slopes experienced the process from unloading, expending, water splitting to run-through failure. The split criterion of I type cracks is used for the stability analysis of cutting-bedding slopes. The stability of cataclastic rock slopes with failure trace of similar arc is calculated through Bishop's method.
In June 2003, a continuous rainstorm triggered many landslides along the main road between Yunxi to Manchuanguan in northwestern Hubei province. According to rock constituents and structures of slopes, storm-induced landslides are categorized as five typical failure models. They are (a) slip of shallow colluvial soil, (b) bedding slip along weak surfaces, (c) water split of cutting-bedding slopes, (d) failure along arc track of cataclastic rock and (e) wedge slip of block fracture slopes. The evaluation methods are proposed correspondingly in accordance with the failure modes and its effect. The shallow landslides are found to occur at ease when the water content of colluvial soil reached 85%-100% of liquid limit. Their stabilities are calculated with the infinite-slope-analysis method. The limit equilibrium method of rigid body is adopted to calculate the stability of bedding slips along weak surfaces and wedge slips of block fracture slopes. High-angle cracks of cutting-bedding slopes experienced the process from unloading, expending, water splitting to run-through failure. The split criterion of I type cracks is used for the stability analysis of cutting-bedding slopes. The stability of cataclastic rock slopes with failure trace of similar arc is calculated through Bishop's method.
2008, 16(3): 338-341.
This paper aims to present a back-analysis method on parameter of soil nonlinear elastic constitutive models. . The study is based on the coincident optimization theory of the genetic algorithm, and the commonly used foundation loading experiment. A parameter back analysis method is established on the nonlinear elastic constitutive models of soils by means of joining together the forward computation and the genetic optimization algorithm. Meanwhile, the data from the foundation load experiment of loess stratum are used. To implement the progress of the parameter back-analysis for the nonlinear elastic constitutive model of loess stratum. The results show that the proposed method can accomplish the coincident optimization of much relative parameters in the nonlinear elastic constitutive model of soil. It does give a good estimation without imposing any stringent requirements on the initial values of parameters. Therefore, for analyzing the deformation characteristics and the interaction characteristic of soils and the structures, the paper provides a good method to define the constitutive model parameters of the soils.
This paper aims to present a back-analysis method on parameter of soil nonlinear elastic constitutive models. . The study is based on the coincident optimization theory of the genetic algorithm, and the commonly used foundation loading experiment. A parameter back analysis method is established on the nonlinear elastic constitutive models of soils by means of joining together the forward computation and the genetic optimization algorithm. Meanwhile, the data from the foundation load experiment of loess stratum are used. To implement the progress of the parameter back-analysis for the nonlinear elastic constitutive model of loess stratum. The results show that the proposed method can accomplish the coincident optimization of much relative parameters in the nonlinear elastic constitutive model of soil. It does give a good estimation without imposing any stringent requirements on the initial values of parameters. Therefore, for analyzing the deformation characteristics and the interaction characteristic of soils and the structures, the paper provides a good method to define the constitutive model parameters of the soils.
2008, 16(3): 342-347.
This paper presents a design of a geo-hazard early warning model. It can analyze the influence factors including terrain, physiognomy, hydrology, etc. It is based on the features of variety, randomicity and variability of geo-hazards and use the map algebra and GIS technologies. Considering the features of influential factors, the principal components are selected to quantitatively identify and measure the influence of each factor. And then the levels of potential hazards are calculated by the data and information collected from the station. On this basis, using the Thiessen interpolation method, the surface data are generated with the levels of hazards according to the site-based hazards information. Based on the daily effective rainfall and intensity records, the occurrence of probability of geo-hazard is calculated. After overlaying the level map of hazards, the surface data with the levels of hazards and with rainfall map, the occurrence of geo-hazard can be predicted based on the weather confidence method and the functionality of geo-hazard early warning model can be realized. The case study in Guangdong province shows that the geo-hazard early warning model can predict the occurrence of geo-hazards with high spatial resolution. The framework itself is logic while the predicted results are reliable. So in some sense, this method could be extended to other case studies. The research results in Guangdong are bearing more significance for the guideline of preventing and controlling the occurrences of geo-hazards.
This paper presents a design of a geo-hazard early warning model. It can analyze the influence factors including terrain, physiognomy, hydrology, etc. It is based on the features of variety, randomicity and variability of geo-hazards and use the map algebra and GIS technologies. Considering the features of influential factors, the principal components are selected to quantitatively identify and measure the influence of each factor. And then the levels of potential hazards are calculated by the data and information collected from the station. On this basis, using the Thiessen interpolation method, the surface data are generated with the levels of hazards according to the site-based hazards information. Based on the daily effective rainfall and intensity records, the occurrence of probability of geo-hazard is calculated. After overlaying the level map of hazards, the surface data with the levels of hazards and with rainfall map, the occurrence of geo-hazard can be predicted based on the weather confidence method and the functionality of geo-hazard early warning model can be realized. The case study in Guangdong province shows that the geo-hazard early warning model can predict the occurrence of geo-hazards with high spatial resolution. The framework itself is logic while the predicted results are reliable. So in some sense, this method could be extended to other case studies. The research results in Guangdong are bearing more significance for the guideline of preventing and controlling the occurrences of geo-hazards.
2008, 16(3): 348-353.
The mechanical characteristics on the deformation, pore pressure and shear strength of undisturbed soft clay samples are studied with cyclic axial shear tests. The effects of confining pressure, cyclic stress ratio, frequency of cyclic loading and cyclic numbers are considered. The study results show that the pore pressure and axial strain took on a fluctuant increasing process under cyclic shear loading. The amplitudes of pore pressure increased notably with the increase of cyclic stress ratio, and the residual pore pressure also increased obviously. In the meantime, the pore pressure also increased with the increase of confining pressure. More cyclic numbers were needed under a high frequency of cyclic loading than a low frequency of cyclic loading in order that the residual pore pressure could achieve the same value. However, the effect of frequency was not obvious with the increase of cyclic numbers.
The mechanical characteristics on the deformation, pore pressure and shear strength of undisturbed soft clay samples are studied with cyclic axial shear tests. The effects of confining pressure, cyclic stress ratio, frequency of cyclic loading and cyclic numbers are considered. The study results show that the pore pressure and axial strain took on a fluctuant increasing process under cyclic shear loading. The amplitudes of pore pressure increased notably with the increase of cyclic stress ratio, and the residual pore pressure also increased obviously. In the meantime, the pore pressure also increased with the increase of confining pressure. More cyclic numbers were needed under a high frequency of cyclic loading than a low frequency of cyclic loading in order that the residual pore pressure could achieve the same value. However, the effect of frequency was not obvious with the increase of cyclic numbers.
2008, 16(3): 354-359.
The stress-strain relationship and pore pressure characteristics are studied with stress-controlled axial shear tests. Furthermore, the determination method of deformation modulus is obtained. Two kinds of laboratory tests are accomplished under a deviator confining pressure. One is that the lateral pressure is unloaded when axial pressure maintains constant. The other is that the lateral and axial pressures are simultaneously unloaded. The test results show that the stress-strain relationship took on a hyperbolic function. Moreover, the shear strength was increasing with the increase of the lateral confining pressure. In the unloading process, with the increase of deviator stress and the strain, the soil sample took on a dilatancy trend and showed a large negative pore pressure. Besides, the undrained shear strength was increased slightly due to the negative pore pressure.
The stress-strain relationship and pore pressure characteristics are studied with stress-controlled axial shear tests. Furthermore, the determination method of deformation modulus is obtained. Two kinds of laboratory tests are accomplished under a deviator confining pressure. One is that the lateral pressure is unloaded when axial pressure maintains constant. The other is that the lateral and axial pressures are simultaneously unloaded. The test results show that the stress-strain relationship took on a hyperbolic function. Moreover, the shear strength was increasing with the increase of the lateral confining pressure. In the unloading process, with the increase of deviator stress and the strain, the soil sample took on a dilatancy trend and showed a large negative pore pressure. Besides, the undrained shear strength was increased slightly due to the negative pore pressure.
2008, 16(3): 360-364.
The effects of parameters in the finite element analysis of Biot consolidation with Dun-Chang model on consolidation of the soft ground are studied by the method of orthogonal experiment. All the parameters are selected randomly in the analysis. The conclusions are: k、c、G、 and F play vital roles during consolidation procedure; Pc has an important effect at the beginning; Rf has little effect on consolidation if variations of the other parameters are high. The constant coefficient of permeability Kz has prominent influence at the initial stage. The results can be used as reference for test of model parameters, back analysis, stochastic study and estimation of the soft consolidation.
The effects of parameters in the finite element analysis of Biot consolidation with Dun-Chang model on consolidation of the soft ground are studied by the method of orthogonal experiment. All the parameters are selected randomly in the analysis. The conclusions are: k、c、G、 and F play vital roles during consolidation procedure; Pc has an important effect at the beginning; Rf has little effect on consolidation if variations of the other parameters are high. The constant coefficient of permeability Kz has prominent influence at the initial stage. The results can be used as reference for test of model parameters, back analysis, stochastic study and estimation of the soft consolidation.
2008, 16(3): 365-370.
As the increasing economic developments in China, the reinforcements of large-size slopes are frequently encountered during the constructions of hydraulic and hydroelectric power, transportation, mining, and national defense projects. Three main factors influencing the choice of slope reinforcement methods, are chosen to be slope dimensions, engineering geological conditions and project importance, and classified by three grades. It is analyzed that present slope reinforcement methods have some limitations and defects for the reinforcement of important slope characterized by worse engineering geological conditions. For this reason, the authors have developed a new reinforcement method, i.e., underground beam-pile frame structure system. This system is applicable to the reinforcements of large-scale slopes. By connecting adjacent piles and beams, a spatial frame structure will be constructed. The slope parts with a lower stability can be closely jointed with stable rock masses in depth. This is helpful for exerting the self-sustaining capacity of the rock masses. Not only existent tunnels (e. g. investigation adits, testing tunnels) can be utilized for constructing the structure system, but also drainage and monitoring for slopes can be easily and efficiently realized.
As the increasing economic developments in China, the reinforcements of large-size slopes are frequently encountered during the constructions of hydraulic and hydroelectric power, transportation, mining, and national defense projects. Three main factors influencing the choice of slope reinforcement methods, are chosen to be slope dimensions, engineering geological conditions and project importance, and classified by three grades. It is analyzed that present slope reinforcement methods have some limitations and defects for the reinforcement of important slope characterized by worse engineering geological conditions. For this reason, the authors have developed a new reinforcement method, i.e., underground beam-pile frame structure system. This system is applicable to the reinforcements of large-scale slopes. By connecting adjacent piles and beams, a spatial frame structure will be constructed. The slope parts with a lower stability can be closely jointed with stable rock masses in depth. This is helpful for exerting the self-sustaining capacity of the rock masses. Not only existent tunnels (e. g. investigation adits, testing tunnels) can be utilized for constructing the structure system, but also drainage and monitoring for slopes can be easily and efficiently realized.
2008, 16(3): 371-375.
This paper presents a new method to address some problems in slope hazard control projects just as urgent construction period, limited construction location and so on. The new method is a new style of reinforcement structure that is named framework of cable and tube reinforcement. The paper describes composition and feature of framework of cable and tube reinforcement, also analyzes the adaptability of it on the type of slope hazard. According to the computation principle and method of Winkler beam on elastic foundation, an analytic model of framework of cable and tube reinforcement is proposed. A computing program of elastic bar system FEM has been written. The structure is used to the treatment of a backfill slope hazard along west-east gas transmission pipeline. The results show that the model can agree well with practical stress and deformation of framework of cable and tube reinforcement. Certainly safe operation of gas transmission pipeline is ensured.
This paper presents a new method to address some problems in slope hazard control projects just as urgent construction period, limited construction location and so on. The new method is a new style of reinforcement structure that is named framework of cable and tube reinforcement. The paper describes composition and feature of framework of cable and tube reinforcement, also analyzes the adaptability of it on the type of slope hazard. According to the computation principle and method of Winkler beam on elastic foundation, an analytic model of framework of cable and tube reinforcement is proposed. A computing program of elastic bar system FEM has been written. The structure is used to the treatment of a backfill slope hazard along west-east gas transmission pipeline. The results show that the model can agree well with practical stress and deformation of framework of cable and tube reinforcement. Certainly safe operation of gas transmission pipeline is ensured.
2008, 16(3): 376-382.
This paper is based on the slope limit equilibrium theory and the circular sliding failure model of prestressed anchor and grillage supporting structures. It considers the effects of grillage and anchor on the stability of soil slope, and uses the idea of circular slice method. The calculation model for internal global safety factor and the search model for the most dangerous sliding surface are established respectively by applying integration method. The centre coordinates of sliding surface are regarded as geometrical controlling parameters. The function relation for variables in the calculation expression of safety factor and the centre coordinates of sliding surface is derived. Then the function relations among the geometrical controlling parameters of sliding surface and the internal stability safety factor are deduced. The centre coordinates of the most dangerous sliding surface of grillage supporting structure with prestressed anchor have been dynamically searched and solved using mesh method. Finally, the calculation program for stability analysis of the grillage supporting structure with prestressed anchor is compiled with the language Matlab. An engineering example is used to check the stability of the calculation program. The applicable conditions of the proposed method are discussed. The results show that this method is concise and applicable, which is more reasonable than the conventional empirical analysis methods.
This paper is based on the slope limit equilibrium theory and the circular sliding failure model of prestressed anchor and grillage supporting structures. It considers the effects of grillage and anchor on the stability of soil slope, and uses the idea of circular slice method. The calculation model for internal global safety factor and the search model for the most dangerous sliding surface are established respectively by applying integration method. The centre coordinates of sliding surface are regarded as geometrical controlling parameters. The function relation for variables in the calculation expression of safety factor and the centre coordinates of sliding surface is derived. Then the function relations among the geometrical controlling parameters of sliding surface and the internal stability safety factor are deduced. The centre coordinates of the most dangerous sliding surface of grillage supporting structure with prestressed anchor have been dynamically searched and solved using mesh method. Finally, the calculation program for stability analysis of the grillage supporting structure with prestressed anchor is compiled with the language Matlab. An engineering example is used to check the stability of the calculation program. The applicable conditions of the proposed method are discussed. The results show that this method is concise and applicable, which is more reasonable than the conventional empirical analysis methods.
2008, 16(3): 383-387.
The method of structural mechanics for multi-row piles that are commonly used in bridges of roads and railways is introduced to the double-row anti-sliding piles for slope stabilization. The difference is the soil body above the slide surface. However, above the scour-line of bridge, it doesn't consider the influence that the soil- body to the m method of under the slide surface. In this paper, the perfect m-method 1 and the perfect m-method 2 are presented and they consider the effect of the sliding soil body. And in this paper, the soil pressures in the back of front-row pile and in the front of back-row pile above the slide surface are researched in project application. The results are gained that the soil pressure in the front of back-row pile could be equal to the rest soil pressure, and that the soil pressure in the back of front-row pile could be equal to the summation of the rest soil pressure and the slide force caused by the slide body between the double-row anti-sliding pile. At the same time, the finite bar element method is used to analyze the influence of connect-girder rigidity. The rigidity ratio of beam and column equal to 0.48 is found to be appropriate when the distance between double-row pile is not less than the value presented by criterion JTJ024-85 or 464-2005. The increase of the rigidity ratio is not significant. It is considered that the double-row piles are cost saving and have strong capability of resisting deformation. It's worthy of further investigation and extensive application.
The method of structural mechanics for multi-row piles that are commonly used in bridges of roads and railways is introduced to the double-row anti-sliding piles for slope stabilization. The difference is the soil body above the slide surface. However, above the scour-line of bridge, it doesn't consider the influence that the soil- body to the m method of under the slide surface. In this paper, the perfect m-method 1 and the perfect m-method 2 are presented and they consider the effect of the sliding soil body. And in this paper, the soil pressures in the back of front-row pile and in the front of back-row pile above the slide surface are researched in project application. The results are gained that the soil pressure in the front of back-row pile could be equal to the rest soil pressure, and that the soil pressure in the back of front-row pile could be equal to the summation of the rest soil pressure and the slide force caused by the slide body between the double-row anti-sliding pile. At the same time, the finite bar element method is used to analyze the influence of connect-girder rigidity. The rigidity ratio of beam and column equal to 0.48 is found to be appropriate when the distance between double-row pile is not less than the value presented by criterion JTJ024-85 or 464-2005. The increase of the rigidity ratio is not significant. It is considered that the double-row piles are cost saving and have strong capability of resisting deformation. It's worthy of further investigation and extensive application.
2008, 16(3): 388-392.
In order to work well the ecological protection of the side-slopes of Tangtun expressway, some investigations on the side-slopes soil were carried out. They include soil sampling, pH mensurating, main nutrient index and main trace elements index analyzing. These results shows that the soil was acidic, low organic, lack of phosphor and excessive of copper. Ecological protection of the slopes have the characteristics of steep slope, destruction of original vegetation, leanness of soil, lack of water and fertilizer, drought and heat stress of ecoclimate, severity of soil and water loss. Considered essential principles such as traffic security, environmental harmonization and economical and practical, a new plant configuration of the side slopes was proposed. The herbages were main measure in the slope ecological protection. The herb, the shrub, and the vine were combined as necessary organic supplement. Aiming at rock slopes, fractured rock slopes, and the soil slopes, the coping ,edge and bench of slope, different plant designs were suggested in the paper.
In order to work well the ecological protection of the side-slopes of Tangtun expressway, some investigations on the side-slopes soil were carried out. They include soil sampling, pH mensurating, main nutrient index and main trace elements index analyzing. These results shows that the soil was acidic, low organic, lack of phosphor and excessive of copper. Ecological protection of the slopes have the characteristics of steep slope, destruction of original vegetation, leanness of soil, lack of water and fertilizer, drought and heat stress of ecoclimate, severity of soil and water loss. Considered essential principles such as traffic security, environmental harmonization and economical and practical, a new plant configuration of the side slopes was proposed. The herbages were main measure in the slope ecological protection. The herb, the shrub, and the vine were combined as necessary organic supplement. Aiming at rock slopes, fractured rock slopes, and the soil slopes, the coping ,edge and bench of slope, different plant designs were suggested in the paper.
2008, 16(3): 393-400.
This field test used the supporting structure for excavation of foundation pit at the PANDA annular island subway station in Beijing. The supporting structure combined pre-stressed ground anchor and soil nails. The field test results included the axial force variation of the soil nails with time, the axial force distribution of the soil nails along its length, the maximum axial force distribution of the soil nails, the pre-stress variation of the cable and so on. The principle of the pre-stressed composite soil nailed reinforcement structure is studied from the aspect of mechanical mechanisms. The results show that: (1) The tensile force in soil nails is variable with time and excavation; (2) The development and distribution of the axial force in soil nails are relevant to the potential slide trend of the foundation pit; (3) The influence of the pre-stress ground anchor on the axial force distribution of the soil nails is rather large; (4) The usage of the pre-stress ground anchor can reduce the displacement and improve the stress state of the pit slope, as well as reduce the axial force of the soil nails; (5) in the initial stage of being used, the variation of the load condition in the soil nailing has less effect on that of pre-stress ground anchor. They function independently.
This field test used the supporting structure for excavation of foundation pit at the PANDA annular island subway station in Beijing. The supporting structure combined pre-stressed ground anchor and soil nails. The field test results included the axial force variation of the soil nails with time, the axial force distribution of the soil nails along its length, the maximum axial force distribution of the soil nails, the pre-stress variation of the cable and so on. The principle of the pre-stressed composite soil nailed reinforcement structure is studied from the aspect of mechanical mechanisms. The results show that: (1) The tensile force in soil nails is variable with time and excavation; (2) The development and distribution of the axial force in soil nails are relevant to the potential slide trend of the foundation pit; (3) The influence of the pre-stress ground anchor on the axial force distribution of the soil nails is rather large; (4) The usage of the pre-stress ground anchor can reduce the displacement and improve the stress state of the pit slope, as well as reduce the axial force of the soil nails; (5) in the initial stage of being used, the variation of the load condition in the soil nailing has less effect on that of pre-stress ground anchor. They function independently.
2008, 16(3): 401-407.
The current design concept of pile-anchor and soil nailing wall composite support structure is to separate pile-anchor and soil nailing wall and to design each of them independently. According to this design concept and the actual construction process of composite support structure, three different numerical simulation models are constructed separately for the upper soil nailing wall, the pile-anchor structure under the upper soil nailing wall and the whole composite support structure. Through numerical simulations of different designing methods for the structure, the following results are found: the composite simulation method can consider both the upper soil nailing wall and the pile-anchor structure in the same time, and satisfies the actual construction process so that its results are more reasonable; compared with the results of the composite simulation method, in the single simulation model for soil nailing wall the horizontal displacement, subsidence and axial force of soil nails are more less, if support design is based on these results the soil nailing wall will be insecure; on the contrary in the single simulation for pile-anchor support structure the magnitudes of anchor forces, subsidence and moment of pile are bigger than the results of composite simulation. Thus the single design for pile -anchor structure will make the support conservative.
The current design concept of pile-anchor and soil nailing wall composite support structure is to separate pile-anchor and soil nailing wall and to design each of them independently. According to this design concept and the actual construction process of composite support structure, three different numerical simulation models are constructed separately for the upper soil nailing wall, the pile-anchor structure under the upper soil nailing wall and the whole composite support structure. Through numerical simulations of different designing methods for the structure, the following results are found: the composite simulation method can consider both the upper soil nailing wall and the pile-anchor structure in the same time, and satisfies the actual construction process so that its results are more reasonable; compared with the results of the composite simulation method, in the single simulation model for soil nailing wall the horizontal displacement, subsidence and axial force of soil nails are more less, if support design is based on these results the soil nailing wall will be insecure; on the contrary in the single simulation for pile-anchor support structure the magnitudes of anchor forces, subsidence and moment of pile are bigger than the results of composite simulation. Thus the single design for pile -anchor structure will make the support conservative.
2008, 16(3): 408-414.
The soft soils which contain high organic matters usually lead to a low-strength cement-soil. This paper mainly studies the influence of fly ash as an additive on cement-soil. By comparing the unconfined compressive strength of the cement fly-ash soil mixtures with different cement contents, fly ash content and concreting time, the strength and deformation behavior of the mixtures are analyzed. Moreover, the improving mechanism of the organic soil is discussed. The results show that the unconfined compressive strength of the mixtures changed slightly at the beginning. However, the unconfined compressive strength increased remarkably after concreting. The optimal content of the fly ash was about 12%. At this fly ash content, the failure strain and E50 reached the smallest and maximum value, respectively. If the fly ash content exceeded 12%, the unconfined compressive strength of the mixtures decreased.
The soft soils which contain high organic matters usually lead to a low-strength cement-soil. This paper mainly studies the influence of fly ash as an additive on cement-soil. By comparing the unconfined compressive strength of the cement fly-ash soil mixtures with different cement contents, fly ash content and concreting time, the strength and deformation behavior of the mixtures are analyzed. Moreover, the improving mechanism of the organic soil is discussed. The results show that the unconfined compressive strength of the mixtures changed slightly at the beginning. However, the unconfined compressive strength increased remarkably after concreting. The optimal content of the fly ash was about 12%. At this fly ash content, the failure strain and E50 reached the smallest and maximum value, respectively. If the fly ash content exceeded 12%, the unconfined compressive strength of the mixtures decreased.
2008, 16(3): 415-421.
One of the key issues in soil mechanics modeling is to correctly define the dilatancy function. Dense and medium dense sands dilate under drained conditions and develop negative excess pore water pressure when sheared under undrained conditions. A phase transformation line is present for dense and medium dense sand and characterizes the state from contractive to dilative. The phase transformation line is affected by the original void ratio and the effective confining pressure. In the proposed model, the state parameter which makes the phase transformation line as reference line is introduced into the stress-dilatancy equation. The plastic hardening modulus expression is used to develop a new dilatant constitutive model for sand within the general framework of bounding surface plasticity. The present model simulates, with a single set of model constants, both the contractive and the dilative responses of granular soils over a wide range of variations in stress and material internal states. The model can be used for both monotonic and cyclic loading paths under either drained or undrained conditions. It has been shown that the calculated results fit well with the test results.
One of the key issues in soil mechanics modeling is to correctly define the dilatancy function. Dense and medium dense sands dilate under drained conditions and develop negative excess pore water pressure when sheared under undrained conditions. A phase transformation line is present for dense and medium dense sand and characterizes the state from contractive to dilative. The phase transformation line is affected by the original void ratio and the effective confining pressure. In the proposed model, the state parameter which makes the phase transformation line as reference line is introduced into the stress-dilatancy equation. The plastic hardening modulus expression is used to develop a new dilatant constitutive model for sand within the general framework of bounding surface plasticity. The present model simulates, with a single set of model constants, both the contractive and the dilative responses of granular soils over a wide range of variations in stress and material internal states. The model can be used for both monotonic and cyclic loading paths under either drained or undrained conditions. It has been shown that the calculated results fit well with the test results.
2008, 16(3): 422-426.
This paper, describes the RIC construction technology and its equipments, introduces construction process and compaction scheme, analyzes parameters of uncompacted fill soil and gravel-soil, compacted fill soil, and abutment backside soil, and reviews detection method. At the end, the paper also introduces some applications of RIC construction technology to the Zhengzhou to Shaolinsi highway. The paper is valuable to design and construction of compaction of road embankment fill soil.
This paper, describes the RIC construction technology and its equipments, introduces construction process and compaction scheme, analyzes parameters of uncompacted fill soil and gravel-soil, compacted fill soil, and abutment backside soil, and reviews detection method. At the end, the paper also introduces some applications of RIC construction technology to the Zhengzhou to Shaolinsi highway. The paper is valuable to design and construction of compaction of road embankment fill soil.
2008, 16(3): 427-431.
According to pile foundation, a closed diaphragm wall has a relatively large stiffness. Because of the great stiffness difference between ferroconcrete and soil, under horizontal load, two types of failure form. Their mechanism can be found via numerical emulation and in-situ test. One is rotary failure, which is associated with rigid short piles. The other is flexible failure, which is associated with elastic long piles. Inside certain buried depth of a diaphragm wall, the buried depth of diaphragm wall notably affects the horizontal load-carrying capability of closed diaphragm wall foundation. Under the same geological condition, when the buried depth of diaphragm wall exceeds 30 m, the buried depth does not notably control the horizontal load-carrying capability of the foundation.
According to pile foundation, a closed diaphragm wall has a relatively large stiffness. Because of the great stiffness difference between ferroconcrete and soil, under horizontal load, two types of failure form. Their mechanism can be found via numerical emulation and in-situ test. One is rotary failure, which is associated with rigid short piles. The other is flexible failure, which is associated with elastic long piles. Inside certain buried depth of a diaphragm wall, the buried depth of diaphragm wall notably affects the horizontal load-carrying capability of closed diaphragm wall foundation. Under the same geological condition, when the buried depth of diaphragm wall exceeds 30 m, the buried depth does not notably control the horizontal load-carrying capability of the foundation.
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