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Editor Work2018 Vol. 26, No. 4
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2018, 26(4): 835-843.
Abstract
10751KB
Gently inclined layered rock masses display different mechanical behaviors at different strength of beddings in uniaxial compression tests. Particle flow code(PFC) is used to establish numerical models for uniaxial compression in gently inclined layered rock masses based on the results of laboratory uniaxial compression tests on protoliths. The variations in the strength and failure modes of layered rocks under different strength of beddings are characterized. The development and evolution of micro-cracks and meso particles' displacement during uniaxial compression in gently inclined layered rocks with different strength of beddings are analyzed. The results show that when the strength of beddings is far smaller than that of the intact rock between beddings, the beddings reduce the strength of overall layered rock mass to a certain extent. The macroscopic fracture surface is a polyline type surface along the beddings and through the beddings. When the strength of beddings is similarly equal to that of the intact rock between beddings, the macroscopic fracture surface is a smooth slope that obliquely passes through a number of beddings. When the strength of beddings is far bigger than that of the intact rock between beddings, the strength of the rock is mainly determined by the strength of the latter. The macroscopic fracture surface is a X-type conjugate failure surface.
Gently inclined layered rock masses display different mechanical behaviors at different strength of beddings in uniaxial compression tests. Particle flow code(PFC) is used to establish numerical models for uniaxial compression in gently inclined layered rock masses based on the results of laboratory uniaxial compression tests on protoliths. The variations in the strength and failure modes of layered rocks under different strength of beddings are characterized. The development and evolution of micro-cracks and meso particles' displacement during uniaxial compression in gently inclined layered rocks with different strength of beddings are analyzed. The results show that when the strength of beddings is far smaller than that of the intact rock between beddings, the beddings reduce the strength of overall layered rock mass to a certain extent. The macroscopic fracture surface is a polyline type surface along the beddings and through the beddings. When the strength of beddings is similarly equal to that of the intact rock between beddings, the macroscopic fracture surface is a smooth slope that obliquely passes through a number of beddings. When the strength of beddings is far bigger than that of the intact rock between beddings, the strength of the rock is mainly determined by the strength of the latter. The macroscopic fracture surface is a X-type conjugate failure surface.
2018, 26(4): 844-851.
Nine groups of floor-friction simulations are designed to investigate the effect of different angle cracks to the anti-dipped rock slopes. They are divided into no fissure group, a steep fissure group and a group of a steep fissure and a gentle fissure. The effect of different crack angles on the fracture surface is examined. The following conclusions are obtaine. The change of the dip angle of the steep fissure has an obvious regular influence on the deformation of rock slope and the morphology of the main fracture surface. For the steeper dip angle of the steep fissures, the initial site of destruction gradually is shallower, and the damage area is relatively reduced, and the fracture surface can gradually change from the near line to the near arc. Because of the existence of the gentle dip crack, the process that steep dip fissure along the tip of the steep fissures and communicating with each other to form a penetrating fracture surface is quicker. In the event of toppling deformation, stratified rock on the main rupture surface produces reverse bending breaking in the middle area. Through quantitative analysis, it is found that with the increase of fissure dip angle, the failure amplitude of toppling deformation on rock slopes is reduced. Besides, for the main fracture surface, both the length and the fractal dimension of trace complexity decreases accordingly.
Nine groups of floor-friction simulations are designed to investigate the effect of different angle cracks to the anti-dipped rock slopes. They are divided into no fissure group, a steep fissure group and a group of a steep fissure and a gentle fissure. The effect of different crack angles on the fracture surface is examined. The following conclusions are obtaine. The change of the dip angle of the steep fissure has an obvious regular influence on the deformation of rock slope and the morphology of the main fracture surface. For the steeper dip angle of the steep fissures, the initial site of destruction gradually is shallower, and the damage area is relatively reduced, and the fracture surface can gradually change from the near line to the near arc. Because of the existence of the gentle dip crack, the process that steep dip fissure along the tip of the steep fissures and communicating with each other to form a penetrating fracture surface is quicker. In the event of toppling deformation, stratified rock on the main rupture surface produces reverse bending breaking in the middle area. Through quantitative analysis, it is found that with the increase of fissure dip angle, the failure amplitude of toppling deformation on rock slopes is reduced. Besides, for the main fracture surface, both the length and the fractal dimension of trace complexity decreases accordingly.
2018, 26(4): 852-860.
Geogrid has been extensively used in reinforced soil engineering such as embankments, slopes, retaining walls. Analysis on the interfacial mechanical interaction between the reinforcement and the soil is a key factor for understanding action mechanisms. This paper aims to investigate the actual shear stress-displacement relationship of the pull-out test. The elastic-exponential softening model is established, which considers the progressive failure mechanism and the nonlinear characteristic of the interface according to the stress state of the geogrid subjected to pull-out loads. It is shown that most of the existing calculating models estimate the shear stress of the interfaces. Combined with the governing equation of the interface, the theoretical solutions of the stress state of the geogrid at different stages are deduced. The evolution and distribution law of the interface friction was analyzed in detail. The influence of design parameters on the interfacial shear resistance was investigated. The design parameters include shear stiffness, tensile stiffness, length of reinforcement and exponential attenuation coefficient. The results show that when the interface is in the elastic stage of the pulling process of geogrids, the non-uniformity of interfacial shear stress and the maximum shear stress increases with the increase of shear stiffness, while the modulus of elasticity is opposite. In the softening stage, the longer reinforcement length has more obvious softening of the interface. The shorter reinforcement length may cause the uniform distribution of the interfacial shear stress. The greater exponential attenuation coefficient, the more obvious interfacial shear stress fluctuation. The interfacial shear stress would move to the pulling end of geogrids. After entering the residual stage, the interfacial shear stress increases from the pulling end to the free one and tends to reach the residual stress gradually. For the reinforced soil engineering, the corresponding conclusions as a theoretical basis for understanding reinforcement mechanisms can be applied to the principle of the selection of geogrid.
Geogrid has been extensively used in reinforced soil engineering such as embankments, slopes, retaining walls. Analysis on the interfacial mechanical interaction between the reinforcement and the soil is a key factor for understanding action mechanisms. This paper aims to investigate the actual shear stress-displacement relationship of the pull-out test. The elastic-exponential softening model is established, which considers the progressive failure mechanism and the nonlinear characteristic of the interface according to the stress state of the geogrid subjected to pull-out loads. It is shown that most of the existing calculating models estimate the shear stress of the interfaces. Combined with the governing equation of the interface, the theoretical solutions of the stress state of the geogrid at different stages are deduced. The evolution and distribution law of the interface friction was analyzed in detail. The influence of design parameters on the interfacial shear resistance was investigated. The design parameters include shear stiffness, tensile stiffness, length of reinforcement and exponential attenuation coefficient. The results show that when the interface is in the elastic stage of the pulling process of geogrids, the non-uniformity of interfacial shear stress and the maximum shear stress increases with the increase of shear stiffness, while the modulus of elasticity is opposite. In the softening stage, the longer reinforcement length has more obvious softening of the interface. The shorter reinforcement length may cause the uniform distribution of the interfacial shear stress. The greater exponential attenuation coefficient, the more obvious interfacial shear stress fluctuation. The interfacial shear stress would move to the pulling end of geogrids. After entering the residual stage, the interfacial shear stress increases from the pulling end to the free one and tends to reach the residual stress gradually. For the reinforced soil engineering, the corresponding conclusions as a theoretical basis for understanding reinforcement mechanisms can be applied to the principle of the selection of geogrid.
2018, 26(4): 861-865.
Through consolidated undrained triaxial compression test, the influence of confining pressure, consolidation ratio and dry density on the static liquefaction characteristics of saturated silt soil are analyzed. The test results show that when the dry density is lower, the deviatoric stress-strain curves of saturated silt soil exhibit obvious strain softening characteristics. With the increase of axial strain, the excess pore water pressure increases and the effective stress decreases, which results in static liquefaction. When the dry density reaches to 1.58 g·cm-3, the deviatoric stress-strain curves of saturated silt soil exhibit strain hardening characteristics, and the excess pore water pressure is negative or close to zero. So there is a critical value of dry density of static liquefaction. As other conditions are constant, with the increase of confining pressure, consolidation ratio or dry density, the peak value of deviatoric stress and the residual strength increase and the static liquefaction potential decreases. According to the effective stress path, the flow liquefaction is established as the interface of the stable zone and the unstable zone of saturated silt soil.
Through consolidated undrained triaxial compression test, the influence of confining pressure, consolidation ratio and dry density on the static liquefaction characteristics of saturated silt soil are analyzed. The test results show that when the dry density is lower, the deviatoric stress-strain curves of saturated silt soil exhibit obvious strain softening characteristics. With the increase of axial strain, the excess pore water pressure increases and the effective stress decreases, which results in static liquefaction. When the dry density reaches to 1.58 g·cm-3, the deviatoric stress-strain curves of saturated silt soil exhibit strain hardening characteristics, and the excess pore water pressure is negative or close to zero. So there is a critical value of dry density of static liquefaction. As other conditions are constant, with the increase of confining pressure, consolidation ratio or dry density, the peak value of deviatoric stress and the residual strength increase and the static liquefaction potential decreases. According to the effective stress path, the flow liquefaction is established as the interface of the stable zone and the unstable zone of saturated silt soil.
2018, 26(4): 866-873.
The bias topography has a great negative influence on the deformation of surrounding rocks and the forces of supporting structure of a large span tunnel. A scientific selection of excavation method is an important prerequisite to ensure the safety of tunnel construction. The Hoek-Brown strength criterion takes account of the influence of rock mass structure surface, rock mass strength and construction disturbance on rock mass deterioration. This can better reflect the deformation of surrounding rock during tunneling. Therefore, this paper selects a typical engineering project relying on No. 2 tunnel in Qichong village, Huancheng Road, Guiyang City, determines the Hoek-Brown strength parameters based on site investigations and empirical method as well as used, and simulates the excavation processes with both three-step method and double-wall guide method. Compared with the field data of rock deformation and the axial force of steel arch, the double-wall guide method can better control the development of the plastic zone and the deformation of surrounding rock. It can also better alleviate the adverse effect of bias load on the surrounding rock. But the force acting on steel arches is more uneven, which is not conducive to the stability of supporting structure. Considering the construction safety and construction progress, the double-side wall guide method should be used to construct the tunnel outlet and the entrance section with relatively broken rock, while the three-step method can be used for the remainder with more integral rock.
The bias topography has a great negative influence on the deformation of surrounding rocks and the forces of supporting structure of a large span tunnel. A scientific selection of excavation method is an important prerequisite to ensure the safety of tunnel construction. The Hoek-Brown strength criterion takes account of the influence of rock mass structure surface, rock mass strength and construction disturbance on rock mass deterioration. This can better reflect the deformation of surrounding rock during tunneling. Therefore, this paper selects a typical engineering project relying on No. 2 tunnel in Qichong village, Huancheng Road, Guiyang City, determines the Hoek-Brown strength parameters based on site investigations and empirical method as well as used, and simulates the excavation processes with both three-step method and double-wall guide method. Compared with the field data of rock deformation and the axial force of steel arch, the double-wall guide method can better control the development of the plastic zone and the deformation of surrounding rock. It can also better alleviate the adverse effect of bias load on the surrounding rock. But the force acting on steel arches is more uneven, which is not conducive to the stability of supporting structure. Considering the construction safety and construction progress, the double-side wall guide method should be used to construct the tunnel outlet and the entrance section with relatively broken rock, while the three-step method can be used for the remainder with more integral rock.
2018, 26(4): 874-881.
Stability of the slurry trench in complex stratum determines the quality of the diaphragm wall during the construction progress. It is of great significant to study the influence of the unit weight of slurry and soil characters to the local stability of slurry trench. Base on the instability mechanics of the slurry trench, damage-instability model for the trench is presented using the maximum limit analysis method. Both local factor and critical height of the slurry trench are proposed, which combines the nonlinear M-C failure criterion and strength reduction method. This approach is compared to other two methods with applying them to a project practice. The relationships between the local factor, critical height and the unit weight of the slurry, and character parameters of the soil are obtained. Results calculated by all the methods show that, safety factor increases as the increment of unit weight of slurry, cohesion and compressive stress of the soft soil, and decreases as the increment of thickness and unit weight of the soft intercalated layer. However, the calculated results by this approach is sensitive to the change of unit weight of the slurry, which is closed to the phenomenon in site. The local factor is generally the minimum to the others. Furthermore, Comparison of this approach with the method on the basis of the M-C criterion indicates that the nonlinear character of the soft soil only affects the size of local failure area, not to its basic shape.
Stability of the slurry trench in complex stratum determines the quality of the diaphragm wall during the construction progress. It is of great significant to study the influence of the unit weight of slurry and soil characters to the local stability of slurry trench. Base on the instability mechanics of the slurry trench, damage-instability model for the trench is presented using the maximum limit analysis method. Both local factor and critical height of the slurry trench are proposed, which combines the nonlinear M-C failure criterion and strength reduction method. This approach is compared to other two methods with applying them to a project practice. The relationships between the local factor, critical height and the unit weight of the slurry, and character parameters of the soil are obtained. Results calculated by all the methods show that, safety factor increases as the increment of unit weight of slurry, cohesion and compressive stress of the soft soil, and decreases as the increment of thickness and unit weight of the soft intercalated layer. However, the calculated results by this approach is sensitive to the change of unit weight of the slurry, which is closed to the phenomenon in site. The local factor is generally the minimum to the others. Furthermore, Comparison of this approach with the method on the basis of the M-C criterion indicates that the nonlinear character of the soft soil only affects the size of local failure area, not to its basic shape.
2018, 26(4): 882-890.
Studies of volumetric deformations of shear bands are important to obtain a full understanding of the deformation and failure mechanisms. To study distributions of volumetric strains in shear bands, some monitored lines are arranged at clay specimens in uniaxial compression according to positions of higher local volumetric strains in shear bands when microcracks just occur. Smooth local volumetric strains at these lines are obtained through interpolation from strains based on a digital image correlation method. The evolution of the mean and standard deviation of local volumetric strains along these lines are obtained. The concept of the local dilational angle is proposed. The following results are obtained. Generally, with an increase of the longitudinal strain, the contractive deformation is converted into the dilational deformation in shear bands, while in this process several reciprocal cases may occur. Although specimens in compression continuously undergo contraction in total, local volumetric dilatancy occurs earlier at the longitudinal strain of 0.04~0.09. If the condition for local volumetric dilatancy is regarded as the occurrence of the positive mean of the local volumetric strain at monitored lines, then the local volumetric dilatancy occurs at the longitudinal strain of 0.06~0.14. The migration velocity of the peak local volumetric strain can reach (3.77~8.48)×10-5 m·s-1. If monitored lines are determined according to positions of higher local volumetric strains, then the maximum local dilational angle rapidly increases from 13.47°to 56.26° after the mean of the local volumetric strain at monitored lines is changed from negative to positive values, although specimens undergo entire contraction. If monitored lines are determined according to positions of longer shear bands, then the averaged local dilational angle rapidly increases from 16.60°to 45.79°. For specimens undergoing contraction in total, local volumetric dilatancy occurring in shear bands cannot be explained using the traditional dilational angle.
Studies of volumetric deformations of shear bands are important to obtain a full understanding of the deformation and failure mechanisms. To study distributions of volumetric strains in shear bands, some monitored lines are arranged at clay specimens in uniaxial compression according to positions of higher local volumetric strains in shear bands when microcracks just occur. Smooth local volumetric strains at these lines are obtained through interpolation from strains based on a digital image correlation method. The evolution of the mean and standard deviation of local volumetric strains along these lines are obtained. The concept of the local dilational angle is proposed. The following results are obtained. Generally, with an increase of the longitudinal strain, the contractive deformation is converted into the dilational deformation in shear bands, while in this process several reciprocal cases may occur. Although specimens in compression continuously undergo contraction in total, local volumetric dilatancy occurs earlier at the longitudinal strain of 0.04~0.09. If the condition for local volumetric dilatancy is regarded as the occurrence of the positive mean of the local volumetric strain at monitored lines, then the local volumetric dilatancy occurs at the longitudinal strain of 0.06~0.14. The migration velocity of the peak local volumetric strain can reach (3.77~8.48)×10-5 m·s-1. If monitored lines are determined according to positions of higher local volumetric strains, then the maximum local dilational angle rapidly increases from 13.47°to 56.26° after the mean of the local volumetric strain at monitored lines is changed from negative to positive values, although specimens undergo entire contraction. If monitored lines are determined according to positions of longer shear bands, then the averaged local dilational angle rapidly increases from 16.60°to 45.79°. For specimens undergoing contraction in total, local volumetric dilatancy occurring in shear bands cannot be explained using the traditional dilational angle.
2018, 26(4): 891-897.
The lattice framed anchor structure is one of popular prevention technologies in the slope and landslide engineering. The local damage generally occurs to the lattice beam in long-term service, which would have impact on the long-term stability of slope or landslide. For this purpose, attaching carbon fiber cloth to the lattice beams is the most proven effective measure to repair the defects of lattice beams. This paper simulated the landslide mass by way of filling clay in the tank of indoor model test, designed the lattice beams with a similarity ratio of 1:10, and conducted model experiment of carbon fiber cloth applying to the repairing technology of lattice defects by using the lifting jack to exert the landslide load, so as to monitor the parameters including the soil pressure at the bottom of lattice beam, stress of lattice beam and displacement of lattice beam, and analyzed the load bearing ratio between the lattice beam and the carbon fiber cloth before and after repair by using carbon fiber cloth, improvement of steel stress and laws of previous and present change in the bending moment of lattice beam. It showed through analysis of experimental data that the load bearing ratio between the carbon fiber cloth and the lattice beam was improved. When the landslide load acted on the composite of carbon fiber cloth and lattice beam, the carbon fiber cloth sustained the load ahead of the lattice beam, and the load sustained by the carbon fiber cloth was greater than that sustained the lattice beam, with the load bearing ratio of about 83% for the carbon fiber cloth. The lattice beam was damaged by tension first and then compression. In the model test, the strain gages were stuck in the surface of steel to monitor the strain of steel and that the stress in the steel was improved after the damage was repaired, and the maximum stress in steel after repaired was approximately 1/8 of that before repaired. This paper studied the change in bending moment of lattice beam before and after the lattice beam was repaired, which found that the bending moment of lattice beam was significantly decreased upon repair using the carbon fiber cloth, about 1/10-1/3 of what it was before repairing. In consideration of the research results above, it is remarkably effective for the carbon fiber cloth to be used to repair and reinforce the defective lattice beam engineering.
The lattice framed anchor structure is one of popular prevention technologies in the slope and landslide engineering. The local damage generally occurs to the lattice beam in long-term service, which would have impact on the long-term stability of slope or landslide. For this purpose, attaching carbon fiber cloth to the lattice beams is the most proven effective measure to repair the defects of lattice beams. This paper simulated the landslide mass by way of filling clay in the tank of indoor model test, designed the lattice beams with a similarity ratio of 1:10, and conducted model experiment of carbon fiber cloth applying to the repairing technology of lattice defects by using the lifting jack to exert the landslide load, so as to monitor the parameters including the soil pressure at the bottom of lattice beam, stress of lattice beam and displacement of lattice beam, and analyzed the load bearing ratio between the lattice beam and the carbon fiber cloth before and after repair by using carbon fiber cloth, improvement of steel stress and laws of previous and present change in the bending moment of lattice beam. It showed through analysis of experimental data that the load bearing ratio between the carbon fiber cloth and the lattice beam was improved. When the landslide load acted on the composite of carbon fiber cloth and lattice beam, the carbon fiber cloth sustained the load ahead of the lattice beam, and the load sustained by the carbon fiber cloth was greater than that sustained the lattice beam, with the load bearing ratio of about 83% for the carbon fiber cloth. The lattice beam was damaged by tension first and then compression. In the model test, the strain gages were stuck in the surface of steel to monitor the strain of steel and that the stress in the steel was improved after the damage was repaired, and the maximum stress in steel after repaired was approximately 1/8 of that before repaired. This paper studied the change in bending moment of lattice beam before and after the lattice beam was repaired, which found that the bending moment of lattice beam was significantly decreased upon repair using the carbon fiber cloth, about 1/10-1/3 of what it was before repairing. In consideration of the research results above, it is remarkably effective for the carbon fiber cloth to be used to repair and reinforce the defective lattice beam engineering.
2018, 26(4): 898-904.
Classical Rankine and Coulomb earth pressure theories are both calculated on the basis of limit equilibrium state. Thus they are not appropriate for foundation pit engineering because the displacements must be strictly controlled. Cohesive soil slope supported by flexible retaining structure is studied. It considers the influence of the soil arching effects, the value of the internal friction angle and cohesive force between flexible retaining structure and soil, and the value of the internal friction angle and cohesive force between soil and soil. The potential slope sliding surface is searched. The formulas of the passive earth pressure of cohesive soil under nonlimit state against flexible retaining structure is derived via Mohr circle of stress, micro layer analysis method and static equilibrium. The difference between the theory in this paper and Rankine theory is researched from analysis of engineering example. The passive earth pressure calculated by the theory in this paper is smaller. The location impacted by resultant force of the passive earth pressure is lower. The distance from the location to the bottom of the pile is 1.5 percent smaller than that of Rankine theory. The potential sliding surface is a curved surface of horizontal angles decrease with depth. The scope of potential sliding surface is less than the scope of sliding surface under Rankine limit state.
Classical Rankine and Coulomb earth pressure theories are both calculated on the basis of limit equilibrium state. Thus they are not appropriate for foundation pit engineering because the displacements must be strictly controlled. Cohesive soil slope supported by flexible retaining structure is studied. It considers the influence of the soil arching effects, the value of the internal friction angle and cohesive force between flexible retaining structure and soil, and the value of the internal friction angle and cohesive force between soil and soil. The potential slope sliding surface is searched. The formulas of the passive earth pressure of cohesive soil under nonlimit state against flexible retaining structure is derived via Mohr circle of stress, micro layer analysis method and static equilibrium. The difference between the theory in this paper and Rankine theory is researched from analysis of engineering example. The passive earth pressure calculated by the theory in this paper is smaller. The location impacted by resultant force of the passive earth pressure is lower. The distance from the location to the bottom of the pile is 1.5 percent smaller than that of Rankine theory. The potential sliding surface is a curved surface of horizontal angles decrease with depth. The scope of potential sliding surface is less than the scope of sliding surface under Rankine limit state.
2018, 26(4): 905-914.
Xijipangwan of Ningxia province is the intensive landslide area caused by the famous Haiyuan earthquake. Its loess is chosen as the research object. The dynamic triaxial tests are carried out on the undisturbed loess and the remolded loess under different water contents and different stress states. This paper examines the changes of microscopic images before and after dynamic triaxial tests. It discusses the action mechanism of confining pressure and moisture on loess soil particles and explains their influence characteristics on dynamic behaviors of loess from the perspective of the microstructure. The results indicate as follows. The relationship curve of dynamic shear modulus and dynamic shear strain can be regressed by derivation of the H-D model. With the increase of water content or the decrease of confining pressure, the value of parameter a and b increase. It is founded that there are some differences between the influence of water to undisturbed samples and remolded samples. With the increase of water content, dynamic shear modulus decreases, damping ratio increases. The dynamic characteristic parameters of remolded samples are transformed quickly before they are slow. Those parameters of undisturbed samples change slowly before they are quick. Besides the influence of external conditions(such as moisture and confining pressure), the microscopic characteristics of soil samples(such as pore size distribution, particle size, inter-particle spacing, connection mode and density) have great influence on the macroscopic behaviors(such as dynamic shear modulus and damping ratio) of loess.
Xijipangwan of Ningxia province is the intensive landslide area caused by the famous Haiyuan earthquake. Its loess is chosen as the research object. The dynamic triaxial tests are carried out on the undisturbed loess and the remolded loess under different water contents and different stress states. This paper examines the changes of microscopic images before and after dynamic triaxial tests. It discusses the action mechanism of confining pressure and moisture on loess soil particles and explains their influence characteristics on dynamic behaviors of loess from the perspective of the microstructure. The results indicate as follows. The relationship curve of dynamic shear modulus and dynamic shear strain can be regressed by derivation of the H-D model. With the increase of water content or the decrease of confining pressure, the value of parameter a and b increase. It is founded that there are some differences between the influence of water to undisturbed samples and remolded samples. With the increase of water content, dynamic shear modulus decreases, damping ratio increases. The dynamic characteristic parameters of remolded samples are transformed quickly before they are slow. Those parameters of undisturbed samples change slowly before they are quick. Besides the influence of external conditions(such as moisture and confining pressure), the microscopic characteristics of soil samples(such as pore size distribution, particle size, inter-particle spacing, connection mode and density) have great influence on the macroscopic behaviors(such as dynamic shear modulus and damping ratio) of loess.
2018, 26(4): 915-929.
Since the impoundment of the Three Gorges Reservoir, thousands of reservoir earthquakes associated with reservoir storage occurred in Badong County. The largest recorded magnitude is 5.1. In recent years, about 50 related papers have been published, which focused on the aspects including the focal mechanism solutions of reservoir earthquake and the relationship with water level in the front dam, and the genetic mechanism of single reservoir earthquake and the micro earthquake swarms. There is a lack of research on reservoir earthquake time periodicity and spatial expansion regularity. On the basis of the field geological survey(including the spring flow survey) and the literature published in recent years, this paper presents a deep study on the earthquake evolution process of reservoir part in Badong County. Results are as follows:(1)The outbreak of Badong reservoir earthquake has specific temporal periodicity, which is shown as long and short cycles. (2)Reservoir earthquakes of karst collapses manifested as linear distribution, and their formation mechanism is closely related to higher pores water pressure and dynamic water pressure process. (3)Field investigation results of spring water also indicate that the reservoir earthquakes of Badong section in Three Gorges Reservoir area have close pertinence with karst collapses, and its spatial expansion mechanism is proposed in the paper.
Since the impoundment of the Three Gorges Reservoir, thousands of reservoir earthquakes associated with reservoir storage occurred in Badong County. The largest recorded magnitude is 5.1. In recent years, about 50 related papers have been published, which focused on the aspects including the focal mechanism solutions of reservoir earthquake and the relationship with water level in the front dam, and the genetic mechanism of single reservoir earthquake and the micro earthquake swarms. There is a lack of research on reservoir earthquake time periodicity and spatial expansion regularity. On the basis of the field geological survey(including the spring flow survey) and the literature published in recent years, this paper presents a deep study on the earthquake evolution process of reservoir part in Badong County. Results are as follows:(1)The outbreak of Badong reservoir earthquake has specific temporal periodicity, which is shown as long and short cycles. (2)Reservoir earthquakes of karst collapses manifested as linear distribution, and their formation mechanism is closely related to higher pores water pressure and dynamic water pressure process. (3)Field investigation results of spring water also indicate that the reservoir earthquakes of Badong section in Three Gorges Reservoir area have close pertinence with karst collapses, and its spatial expansion mechanism is proposed in the paper.
2018, 26(4): 930-938.
Loess landslides occurred frequently due to continued diversion irrigation in South Jingyang Platform, Shanxi Province. A loess landslide occurred near Miaodian Village on May 26, 2015, which destroyed several acres of farmland. In this paper, we regarded "5.26" landslide as a typical case study. Through detailed field investigation, mapping, investigation and so on, analysing its triggering factors, motion and accumulation characteristics. The results showed that:(1)The sliding distance was 278 m, the width of scarp is 222 m with a difference of 40 m in elevation, and the main sliding direction is 45°. (2)The landslide belongs to the phased landslide, which had been sliding for four times. The area of deposits is about 6.2×104 m2 and the total volume is about 50×104 m3. The average deposit thickness is about 10 m. (3)The main triggering factor of the landslide is continued irrigation, but the surface visible cracks and deep cracks plays an important role in the advantage infiltration, which leads to the continuous uplift of the groundwater level. And the width and sliding direction of the landslide are controlled by the joints of the edge scarp. Finally, based on the certain relevance between the frequency of the landslide and rainfall, the influence of rainfall on the landslide event and the possibility of landslide recurrence are discussed.
Loess landslides occurred frequently due to continued diversion irrigation in South Jingyang Platform, Shanxi Province. A loess landslide occurred near Miaodian Village on May 26, 2015, which destroyed several acres of farmland. In this paper, we regarded "5.26" landslide as a typical case study. Through detailed field investigation, mapping, investigation and so on, analysing its triggering factors, motion and accumulation characteristics. The results showed that:(1)The sliding distance was 278 m, the width of scarp is 222 m with a difference of 40 m in elevation, and the main sliding direction is 45°. (2)The landslide belongs to the phased landslide, which had been sliding for four times. The area of deposits is about 6.2×104 m2 and the total volume is about 50×104 m3. The average deposit thickness is about 10 m. (3)The main triggering factor of the landslide is continued irrigation, but the surface visible cracks and deep cracks plays an important role in the advantage infiltration, which leads to the continuous uplift of the groundwater level. And the width and sliding direction of the landslide are controlled by the joints of the edge scarp. Finally, based on the certain relevance between the frequency of the landslide and rainfall, the influence of rainfall on the landslide event and the possibility of landslide recurrence are discussed.
2018, 26(4): 939-950.
The Zemuhe fault zone has large sinistral strike slip faults, which locates at the southeastern margin of the Tibetan Plateau and the eastern boundary of Sichuan-Yunnan rhombic block projections. It has the characteristics of complex terrain and strong tectonic earthquake, active and serious secondary geological disasters due to its special tectonic position, crustal deformation and faulting. The Daqing fault is located in the faulted valley basin. The Daqing Liangzi uplift area is the largest in the secondary fault of the Zemuhe fault zone. The Daqing Liangzi is the earthquake center of the magnitude 7.5 earthquake in 1850. The river valley retains the remains of glacier activities, geological disaster development. So the Daqing fault as a research object has a good typical and representative. According to the geological background condition of the disaster, the response characteristics of the slope under the action of the earthquake power and the mechanism of the slope instability, the fault disaster pattern are divided into 3 categories, 7 sub-categories and 15 types. The division of the categories is mainly based on the types of geological disasters, sub-categories to consider the disaster dynamic response process and slope instability evolution model, which is the most significant difference in the failure of the slope instability. The sub-class division is mainly based on the slope of the geological structure and stability of the form of the difference. This paper systematically reveals the genesis mechanism and the disaster model of the geological fault of Daqing fault.
The Zemuhe fault zone has large sinistral strike slip faults, which locates at the southeastern margin of the Tibetan Plateau and the eastern boundary of Sichuan-Yunnan rhombic block projections. It has the characteristics of complex terrain and strong tectonic earthquake, active and serious secondary geological disasters due to its special tectonic position, crustal deformation and faulting. The Daqing fault is located in the faulted valley basin. The Daqing Liangzi uplift area is the largest in the secondary fault of the Zemuhe fault zone. The Daqing Liangzi is the earthquake center of the magnitude 7.5 earthquake in 1850. The river valley retains the remains of glacier activities, geological disaster development. So the Daqing fault as a research object has a good typical and representative. According to the geological background condition of the disaster, the response characteristics of the slope under the action of the earthquake power and the mechanism of the slope instability, the fault disaster pattern are divided into 3 categories, 7 sub-categories and 15 types. The division of the categories is mainly based on the types of geological disasters, sub-categories to consider the disaster dynamic response process and slope instability evolution model, which is the most significant difference in the failure of the slope instability. The sub-class division is mainly based on the slope of the geological structure and stability of the form of the difference. This paper systematically reveals the genesis mechanism and the disaster model of the geological fault of Daqing fault.
2018, 26(4): 951-958.
In order to study the formation mechanism of ground fissures in southern Jiangsu, a large-scale physical model is established under the buried-hill condition. The settlement process with water-drawing variability can also be simulated. Fiber optic sensing technology is used for revealing the development and evolution of ground fissures. The distribution and the genetic evolution of ground fissures are summarized. The test results are below:(1)The results of model test are basically consistent with the law of ground fissure disaster in the study area, which provides new methods and means for ground fissure research. (2)The tensile stress concentration of the rock mass is basically the same as the development stage of the ground fissure. Therefore, the stress concentration of the rock mass is an important omen to determine the development stage of the ground fissure. (3)According to rose diagrams analysis, in the flat region, ground fissures are radially distributed and its distribution center is near the drain holes. At the buried hill area, it shows that the shape and location of the buried hill, the settlement curve, and the most serious land area are consistent with the distribution area of ground fissures. (4)Excessive groundwater extraction as well as the location of buried-hill formation have a great influence on the distribution of ground fissures.
In order to study the formation mechanism of ground fissures in southern Jiangsu, a large-scale physical model is established under the buried-hill condition. The settlement process with water-drawing variability can also be simulated. Fiber optic sensing technology is used for revealing the development and evolution of ground fissures. The distribution and the genetic evolution of ground fissures are summarized. The test results are below:(1)The results of model test are basically consistent with the law of ground fissure disaster in the study area, which provides new methods and means for ground fissure research. (2)The tensile stress concentration of the rock mass is basically the same as the development stage of the ground fissure. Therefore, the stress concentration of the rock mass is an important omen to determine the development stage of the ground fissure. (3)According to rose diagrams analysis, in the flat region, ground fissures are radially distributed and its distribution center is near the drain holes. At the buried hill area, it shows that the shape and location of the buried hill, the settlement curve, and the most serious land area are consistent with the distribution area of ground fissures. (4)Excessive groundwater extraction as well as the location of buried-hill formation have a great influence on the distribution of ground fissures.
2018, 26(4): 959-968.
The building structure in the southwest of China crosses into the mountain areas. Many pile foundations are located in slope terrain grounds that the overburden is gravel soil. The pile-soil interaction caused by pile deformation can generate soil horizontal resistance. If the soil resistance is too small to prevent slope deformation, the slope can be unstable and destroyed. However, the existing codes do not provide the methods to calculate the soil resistance on slope ground. This paper presents four piles that are in gravel soil under in-situ lateral loading tests on terrain with 30°slope angle. Based on the measured data, the relationship between deflection and soil resistance for the four piles is compared. The results of the above analyses are used to establish the mode of horizontal resistance distribution for gravel soil slope ground in elastic and plastic phases.
The building structure in the southwest of China crosses into the mountain areas. Many pile foundations are located in slope terrain grounds that the overburden is gravel soil. The pile-soil interaction caused by pile deformation can generate soil horizontal resistance. If the soil resistance is too small to prevent slope deformation, the slope can be unstable and destroyed. However, the existing codes do not provide the methods to calculate the soil resistance on slope ground. This paper presents four piles that are in gravel soil under in-situ lateral loading tests on terrain with 30°slope angle. Based on the measured data, the relationship between deflection and soil resistance for the four piles is compared. The results of the above analyses are used to establish the mode of horizontal resistance distribution for gravel soil slope ground in elastic and plastic phases.
2018, 26(4): 969-977.
In order to solve the theoretical research on the reinforcement of landslide by short anti-sliding piles which does not match the needs of engineering application. Use FLAC3D based on fast Lagrange algorithm to simulate the whole process of the reinforced gravel soil landslide with short anti-sliding piles with varying length. By analyzing the laws of displacement and stress of the sliding body, displacement and the bending moment of short anti-sliding piles, the mechanical deformation characteristics and pile-soil interaction mechanism of anti-sliding short piles are studied. The results show that reinforced by the short anti-sliding pile, the stability of the slope is increased obviously. The maximum displacement of slope is decreasing with the increasing length of short pile, but the range of decreasing is reducing. With the increase of pile length, the more uniform the stress distribution after pile, the better the integrity of short anti-sliding pile and soil around pile is, and the maximum displacement of sliding body decreases gradually, effectively inhibiting the displacement of sliding body. When the pile length is less than 60cm, "over the top" phenomenon occurs in the sliding body, and a penetrating sliding surface is formed at the top of the wedge's leading edge, and a small range of instability failure occurs. When the length of free segment of pile is 0.52~0.59 times of the sliding body thickness, the reinforcement effect is the best. The results of the study complement the anti-sliding mechanism of short anti-skid pile.
In order to solve the theoretical research on the reinforcement of landslide by short anti-sliding piles which does not match the needs of engineering application. Use FLAC3D based on fast Lagrange algorithm to simulate the whole process of the reinforced gravel soil landslide with short anti-sliding piles with varying length. By analyzing the laws of displacement and stress of the sliding body, displacement and the bending moment of short anti-sliding piles, the mechanical deformation characteristics and pile-soil interaction mechanism of anti-sliding short piles are studied. The results show that reinforced by the short anti-sliding pile, the stability of the slope is increased obviously. The maximum displacement of slope is decreasing with the increasing length of short pile, but the range of decreasing is reducing. With the increase of pile length, the more uniform the stress distribution after pile, the better the integrity of short anti-sliding pile and soil around pile is, and the maximum displacement of sliding body decreases gradually, effectively inhibiting the displacement of sliding body. When the pile length is less than 60cm, "over the top" phenomenon occurs in the sliding body, and a penetrating sliding surface is formed at the top of the wedge's leading edge, and a small range of instability failure occurs. When the length of free segment of pile is 0.52~0.59 times of the sliding body thickness, the reinforcement effect is the best. The results of the study complement the anti-sliding mechanism of short anti-skid pile.
2018, 26(4): 978-988.
The cities of Suzhou, Wuxi and Changzhou(the Su-Xi-Chang Cities) have ground fissures in some regions due to the long-term over exploitation of groundwater. Although groundwater extraction in this area has been prohibited for more than ten years, some ground fissures are still active. The development of ground fissures is affected by many factors and the mechanism is still not clear. In order to find out the influence factors of ground fissures, and then to determine the influence of each factor, the potential risk of ground fissures in the Su-Xi-Chang area is predicted based on multi-factor overlay method. This prediction is on the basis of the current status of ground fissures in the Su-Xi-Chang cities. Eight influencing factors are considered. They are bedrock depth, bedrock slope, cumulative land subsidence, subsidence slope, the second confined aquifer thickness, the second confined aquifer thickness gradient, hydraulic head reduction at the second confined aquifer, and quaternary sedimentary facies. The prediction results show that the ground fissures are prone to occur in the northern part of the Su-Xi-Chang cities, and the potential of ground fissures occurring in the southeast is relatively small. The results are primarily coincident with field investigations on ground fissures at the study area, which verifies the validity of the method. The predicted results of ground fissure risk are helpful for the planning of groundwater exploitation and urban construction.
The cities of Suzhou, Wuxi and Changzhou(the Su-Xi-Chang Cities) have ground fissures in some regions due to the long-term over exploitation of groundwater. Although groundwater extraction in this area has been prohibited for more than ten years, some ground fissures are still active. The development of ground fissures is affected by many factors and the mechanism is still not clear. In order to find out the influence factors of ground fissures, and then to determine the influence of each factor, the potential risk of ground fissures in the Su-Xi-Chang area is predicted based on multi-factor overlay method. This prediction is on the basis of the current status of ground fissures in the Su-Xi-Chang cities. Eight influencing factors are considered. They are bedrock depth, bedrock slope, cumulative land subsidence, subsidence slope, the second confined aquifer thickness, the second confined aquifer thickness gradient, hydraulic head reduction at the second confined aquifer, and quaternary sedimentary facies. The prediction results show that the ground fissures are prone to occur in the northern part of the Su-Xi-Chang cities, and the potential of ground fissures occurring in the southeast is relatively small. The results are primarily coincident with field investigations on ground fissures at the study area, which verifies the validity of the method. The predicted results of ground fissure risk are helpful for the planning of groundwater exploitation and urban construction.
2018, 26(4): 989-998.
Concrete production system of Gushan hydropower station is located in an old landslide. Excavation induced serious deformation in the old landslide, which severely damaged the engineering construction. Through the systematic research on engineering geological conditions and deformation characteristics of engineering site, the deformation was mainly caused by improper construction excavation, rainfall and groundwater activity. Other factors also played a certain role in triggering. The excavation had dismembered landslide into three parts:the east, the middle and the west. The landslide deformation has a great influence on the overall stability to the west, but little to the east and middle areas. Emergency engineering measure has been adopted to deal with the landslide deformation characteristics. According to excavation status and stability condition, this paper assesses the stability of the landslide under different situations. The results show that in the natural state, besides the east ② regional landslide deformation in an unstable state, the west in a less state, the other parts are in the basic stability to the steady state. Under the condition of continuous heavy rainfall, the whole landslide is in a less stable or unstable state and needs to be governed.
Concrete production system of Gushan hydropower station is located in an old landslide. Excavation induced serious deformation in the old landslide, which severely damaged the engineering construction. Through the systematic research on engineering geological conditions and deformation characteristics of engineering site, the deformation was mainly caused by improper construction excavation, rainfall and groundwater activity. Other factors also played a certain role in triggering. The excavation had dismembered landslide into three parts:the east, the middle and the west. The landslide deformation has a great influence on the overall stability to the west, but little to the east and middle areas. Emergency engineering measure has been adopted to deal with the landslide deformation characteristics. According to excavation status and stability condition, this paper assesses the stability of the landslide under different situations. The results show that in the natural state, besides the east ② regional landslide deformation in an unstable state, the west in a less state, the other parts are in the basic stability to the steady state. Under the condition of continuous heavy rainfall, the whole landslide is in a less stable or unstable state and needs to be governed.
2018, 26(4): 999-1007.
Recently, the land subsidence problem in Panjin region begins to be concerned. In order to find out the current situation of land subsidence in Panjin region, we select 19 Radasat-2 SAR data of C band covering the study area during 2013-2016. We extract the land subsidence rate and cumulative amount of land subsidence in Panjin region using SBAS-InSAR method. The results show that there are two land subsidence centers in the study area. One center is Shusilian subsidence area. Its area is about 43.6 km2 and its highest subsidence rate is -151.49 mm·a-1. The other is Longwang village subsidence area. Its area is about 33.28 km2 and its highest subsidence rate is -119.55 mm·a-1. Through time series analysis of accumulative displacement, the land subsidence area expands with time, and the cumulative settlement increases. Compared with the leveling monitoring data, it is found that the settlement range and cumulative amount of land subsidence are generally consiste, but there is still difference between the two monitoring methods. The distribution of oilfield site, the drawdown funnel of groundwater level and the distribution of subsidence area in the study area are compared and analyzed. The results show that the land subsidence is closely related to the exploitation of groundwater, the exploitation of oil and gas resources, the new structure movement and so on. This study can provide the basis for the geological environmental management, the prevention and control of land subsidence and the development and utilization of resources.
Recently, the land subsidence problem in Panjin region begins to be concerned. In order to find out the current situation of land subsidence in Panjin region, we select 19 Radasat-2 SAR data of C band covering the study area during 2013-2016. We extract the land subsidence rate and cumulative amount of land subsidence in Panjin region using SBAS-InSAR method. The results show that there are two land subsidence centers in the study area. One center is Shusilian subsidence area. Its area is about 43.6 km2 and its highest subsidence rate is -151.49 mm·a-1. The other is Longwang village subsidence area. Its area is about 33.28 km2 and its highest subsidence rate is -119.55 mm·a-1. Through time series analysis of accumulative displacement, the land subsidence area expands with time, and the cumulative settlement increases. Compared with the leveling monitoring data, it is found that the settlement range and cumulative amount of land subsidence are generally consiste, but there is still difference between the two monitoring methods. The distribution of oilfield site, the drawdown funnel of groundwater level and the distribution of subsidence area in the study area are compared and analyzed. The results show that the land subsidence is closely related to the exploitation of groundwater, the exploitation of oil and gas resources, the new structure movement and so on. This study can provide the basis for the geological environmental management, the prevention and control of land subsidence and the development and utilization of resources.
2018, 26(4): 1008-1016.
This paper aims to achieve the automation monitoring of landslide surface deformation with a low-cost system. It proposes and adopts a high accurate real-time landslide monitoring system based on Beidou cloud. This system consists of Beidou monitoring receivers with the functions of wireless transmission, cloud storage and Ntrip protocol, the softwares of the efficient real-time data flow management, high-precision landslide deformation monitoring and positioning, and optimized design of the field operation solution. The results of practical application show that the real-time monitoring accuracy of Beidou short baseline is better than 2 mm, 3 mm and 3 mm for east, north, up compositions, respectively. It can meet the high precision requirements of real-time monitoring of landslide. This paper compares the long-term continuous monitoring results of the test landslide using the method mentioned above with the precision measurement results obtained by the automatic total station. The results show that the two methods are in good agreement with each other in the horizontal and elevation directions with better than 3 mm for difference, respectively.
This paper aims to achieve the automation monitoring of landslide surface deformation with a low-cost system. It proposes and adopts a high accurate real-time landslide monitoring system based on Beidou cloud. This system consists of Beidou monitoring receivers with the functions of wireless transmission, cloud storage and Ntrip protocol, the softwares of the efficient real-time data flow management, high-precision landslide deformation monitoring and positioning, and optimized design of the field operation solution. The results of practical application show that the real-time monitoring accuracy of Beidou short baseline is better than 2 mm, 3 mm and 3 mm for east, north, up compositions, respectively. It can meet the high precision requirements of real-time monitoring of landslide. This paper compares the long-term continuous monitoring results of the test landslide using the method mentioned above with the precision measurement results obtained by the automatic total station. The results show that the two methods are in good agreement with each other in the horizontal and elevation directions with better than 3 mm for difference, respectively.
2018, 26(4): 1017-1024.
The geological hazards investigation is carried out, with the application of the single channel seismic detection technology, to evaluate the stability of the Qiongzhou strait cross-sea corridor engineering. Two paleochannels are found between the seismic reflection layers I and Ⅲ. They are along the both bank slopes of the present trough. The northern one lies on the bank slopes from the Dengloujiao Cape to the Haian Port. It has an arc-shaped geometry around the southwest basalt platform of the Leizhou Peninsula. The other is from the Lingao Cape to the Dongshui Port. According to the regional geological data, they both have a relatively late chronological characteristic. The northern one is at least later than the Middle Pleistocene, and the other may be Holocene. The geometric characteristic analysis shows their asymmetric "U" geometric feature. They are steep in the south side and gentle in the north. According to the drilling data, their filling has the deposition characteristics of mutual layer of soft soil and sand. Therefore, it is easy to trigger geological disasters including bedding collapse, sand liquefaction and soft soil seismic subsidence, due to the combined action of external forces such as earthquakes, waves and tidal currents and major engineering construction. Their geological conditions and stability can be one of the geological problems unable to evade and must be solved in the Qiongzhou strait cross-sea corridor engineering.
The geological hazards investigation is carried out, with the application of the single channel seismic detection technology, to evaluate the stability of the Qiongzhou strait cross-sea corridor engineering. Two paleochannels are found between the seismic reflection layers I and Ⅲ. They are along the both bank slopes of the present trough. The northern one lies on the bank slopes from the Dengloujiao Cape to the Haian Port. It has an arc-shaped geometry around the southwest basalt platform of the Leizhou Peninsula. The other is from the Lingao Cape to the Dongshui Port. According to the regional geological data, they both have a relatively late chronological characteristic. The northern one is at least later than the Middle Pleistocene, and the other may be Holocene. The geometric characteristic analysis shows their asymmetric "U" geometric feature. They are steep in the south side and gentle in the north. According to the drilling data, their filling has the deposition characteristics of mutual layer of soft soil and sand. Therefore, it is easy to trigger geological disasters including bedding collapse, sand liquefaction and soft soil seismic subsidence, due to the combined action of external forces such as earthquakes, waves and tidal currents and major engineering construction. Their geological conditions and stability can be one of the geological problems unable to evade and must be solved in the Qiongzhou strait cross-sea corridor engineering.
2018, 26(4): 1025-1034.
The geological structure environment of the Sichuan-Tibet railway study area is relatively fragile. There are especially 5 main plate collision zones including Jinshajiang combination zone, Lancangjiang combination zone, Nujiang combination zone, Jiali faults and Yarlung Zangbo River combination zone. They show different tectonic activities. Theirs tectonic activity seriously restricts the construction of Sichuan-Tibet railway. Based on the deep study of geologic characteristics, seismic, deep structure and activity characteristics, this paper uses the method of micro-dose radon measurement to characterize the geochemical characteristics of the collision zone, and obtains the background value through the conventional statistical method. We define the anomalous coefficient(peak value mmax/background value m0). We then study the relationship between the coefficient and other factors including geological structure, deep features, earthquake and tectonic activity. The results show that there is a "special point" in each profile of radon measurement. The difference among 5 min, 10 min and 15 min radon measurement data is very small. The radon background value is significantly related to the crustal rock construction. The peak value is related to the geotectonic position of the collision zone. The anomalous coefficient of radon decreases from southwest to northeast, which is remarkably related to tectonic activity. The anomalous coefficient has a positive correlation with horizontal displacement velocity, sliding velocity and ground stress. The results are as follows:y=0.869x+0.1278, y=0.7318x+15.1052, y=4.2196x+7.52639. The research results have a great significance to the study of tectonic activity of Sichuan-Tibet railway plate collision zone and the construction of Sichuan-Tibet railway.
The geological structure environment of the Sichuan-Tibet railway study area is relatively fragile. There are especially 5 main plate collision zones including Jinshajiang combination zone, Lancangjiang combination zone, Nujiang combination zone, Jiali faults and Yarlung Zangbo River combination zone. They show different tectonic activities. Theirs tectonic activity seriously restricts the construction of Sichuan-Tibet railway. Based on the deep study of geologic characteristics, seismic, deep structure and activity characteristics, this paper uses the method of micro-dose radon measurement to characterize the geochemical characteristics of the collision zone, and obtains the background value through the conventional statistical method. We define the anomalous coefficient(peak value mmax/background value m0). We then study the relationship between the coefficient and other factors including geological structure, deep features, earthquake and tectonic activity. The results show that there is a "special point" in each profile of radon measurement. The difference among 5 min, 10 min and 15 min radon measurement data is very small. The radon background value is significantly related to the crustal rock construction. The peak value is related to the geotectonic position of the collision zone. The anomalous coefficient of radon decreases from southwest to northeast, which is remarkably related to tectonic activity. The anomalous coefficient has a positive correlation with horizontal displacement velocity, sliding velocity and ground stress. The results are as follows:y=0.869x+0.1278, y=0.7318x+15.1052, y=4.2196x+7.52639. The research results have a great significance to the study of tectonic activity of Sichuan-Tibet railway plate collision zone and the construction of Sichuan-Tibet railway.
2018, 26(4): 1035-1042.
Pipeline is one of the most commonly used methods in petroleum transportation. There are different engineering problems when pipelines go across different geological conditions. In order to solve the diseases like thawing collapse of pipelines and frost heaving of engineering structures, an investigation of gas pipeline was undertaken in a certain permafrost region in Qinghai Province. We selected typical sections and buried temperature sensors and magnetic settlement rings to monitor the temperature and displacement of the soil around pipelines during cold and warm seasons. We studied the law of ground temperature variation around the pipelines and the law of frost-heaving and thawing-settlement, which provides reference for the design, construction, operation and disease treatment of gas pipelines in permafrost region. The studies show that ground temperature changes greatly with the temperature during cold and warm seasons in this area, and the closer to the pipelines, the greater the annual amplitude of ground temperature. The ground temperature of frozen soil in this area is -2℃~1℃, which means that the temperate zone belongs to basically stable zone. Heat disturbance of the gas transmission in positive temperature causes the thawing settlement of soil. Due to the heat release of pipelines, ground temperature of the soil above the pipeline turns positive, and the impact range is about 1.5m. Ground temperature from 1m to 4m under the ground surface is influenced by multiple factors. The annual ground temperature range is relatively small under the depth of 4m, all of which are negative temperature. Frost-heaving occurs from the depths upwards. There is a hysteresis in time. The freezing-thawing cycle is very severe in October and November and should be monitored in time.
Pipeline is one of the most commonly used methods in petroleum transportation. There are different engineering problems when pipelines go across different geological conditions. In order to solve the diseases like thawing collapse of pipelines and frost heaving of engineering structures, an investigation of gas pipeline was undertaken in a certain permafrost region in Qinghai Province. We selected typical sections and buried temperature sensors and magnetic settlement rings to monitor the temperature and displacement of the soil around pipelines during cold and warm seasons. We studied the law of ground temperature variation around the pipelines and the law of frost-heaving and thawing-settlement, which provides reference for the design, construction, operation and disease treatment of gas pipelines in permafrost region. The studies show that ground temperature changes greatly with the temperature during cold and warm seasons in this area, and the closer to the pipelines, the greater the annual amplitude of ground temperature. The ground temperature of frozen soil in this area is -2℃~1℃, which means that the temperate zone belongs to basically stable zone. Heat disturbance of the gas transmission in positive temperature causes the thawing settlement of soil. Due to the heat release of pipelines, ground temperature of the soil above the pipeline turns positive, and the impact range is about 1.5m. Ground temperature from 1m to 4m under the ground surface is influenced by multiple factors. The annual ground temperature range is relatively small under the depth of 4m, all of which are negative temperature. Frost-heaving occurs from the depths upwards. There is a hysteresis in time. The freezing-thawing cycle is very severe in October and November and should be monitored in time.
2018, 26(4): 1043-1053.
Three-dimensional finite element models with consideration of soil small strain stiffness characteristics and the thickness variation of soil layers were developed to investigate the effect of excavation of urban square of metro line 1 to adjacent pipelines in Xiamen city. The models were applied to investigate the safety of deep metro excavation. Protection measures based on the result of models were proposed. Then the computation results were compared with the real-time monitoring data to verify the model accuracy. Based on the models, the effect of pipeline material and diameter on deformation and endogenous force was analyzed. Different protection schemes for unsafe pipelines were proposed. The best alternatives were proposed by numerical simulation. It was shown that the influence of three-dimensional space-time effect on deformations and axial force of pipelines was significant. Taking safety threshold of relative angle and tensile stress as standards, the DN1000 was under unsafe condition. The protection measures of 2m×2m grouting reinforcement and two rows of prefabricated pipe pile near pipelines settlement were adopted.
Three-dimensional finite element models with consideration of soil small strain stiffness characteristics and the thickness variation of soil layers were developed to investigate the effect of excavation of urban square of metro line 1 to adjacent pipelines in Xiamen city. The models were applied to investigate the safety of deep metro excavation. Protection measures based on the result of models were proposed. Then the computation results were compared with the real-time monitoring data to verify the model accuracy. Based on the models, the effect of pipeline material and diameter on deformation and endogenous force was analyzed. Different protection schemes for unsafe pipelines were proposed. The best alternatives were proposed by numerical simulation. It was shown that the influence of three-dimensional space-time effect on deformations and axial force of pipelines was significant. Taking safety threshold of relative angle and tensile stress as standards, the DN1000 was under unsafe condition. The protection measures of 2m×2m grouting reinforcement and two rows of prefabricated pipe pile near pipelines settlement were adopted.
2018, 26(4): 1064-1077.
With the acceleration of the urbanization process and the rapid development of industrial production, soil heavy metal pollution is increasing seriously, which is causing serious harm to the ecological environment. Biochar is a solid material containing high fractions of aromatic functional groups and carbon. It is produced through thermal degradation under anoxic or oxygen-limited conditions. It attracts extensive attention because of significant effect in the remediation of soil contaminated with heavy metals. Based on the recent research achievements on biochar remediate heavy metals contaminated soil at home and abroad, the advances of some important aspects on, the research current situation and progress are summarized from several important aspects. They include production and properties of biochar, remediation effect and influencing factors and adsorption mechanism. The follows are shown. (1)Biochar has the advantages of low prices, high efficiency, soil improvement and friendly environment. (2)The physicochemical properties of biochar are affected by biomass materials and pyrolysis temperatures. Activation, magnetization, oxidation and digestion can improve the properties of biochar and efficiency of remediation. (3)The effect of biochar on heavy metal mobility and bioavailability includes two aspects:immobilizing heavy metals to reduce bioavailability or mobilizing heavy metals to increase bioavailability. The latter can be modified to reduce the mobility and bioavailability of heavy metals. (4)The effect of biochar on soil solidification is general, combining with other solidifying materials to improve the mechanical properties of solidified soil. (5)The effect remediation mechanism of biochar immobilized heavy metals is ranked as follows:precipitation > complexation > electrostatic interaction and ion exchange > physical adsorption. Finally, on account of research status in this field, some important research emphases and directions in the future are proposed. They mainly include establishing a uniform classification criterion of biochar, exploring the efficiency of biochar on multi-heavy metals pollution, illustrating the mechanism and contribution rate of adsorbing heavy metals by biochar, expanding the research scale, and carrying out solidification experiment and mechanical property research based on biochar.
With the acceleration of the urbanization process and the rapid development of industrial production, soil heavy metal pollution is increasing seriously, which is causing serious harm to the ecological environment. Biochar is a solid material containing high fractions of aromatic functional groups and carbon. It is produced through thermal degradation under anoxic or oxygen-limited conditions. It attracts extensive attention because of significant effect in the remediation of soil contaminated with heavy metals. Based on the recent research achievements on biochar remediate heavy metals contaminated soil at home and abroad, the advances of some important aspects on, the research current situation and progress are summarized from several important aspects. They include production and properties of biochar, remediation effect and influencing factors and adsorption mechanism. The follows are shown. (1)Biochar has the advantages of low prices, high efficiency, soil improvement and friendly environment. (2)The physicochemical properties of biochar are affected by biomass materials and pyrolysis temperatures. Activation, magnetization, oxidation and digestion can improve the properties of biochar and efficiency of remediation. (3)The effect of biochar on heavy metal mobility and bioavailability includes two aspects:immobilizing heavy metals to reduce bioavailability or mobilizing heavy metals to increase bioavailability. The latter can be modified to reduce the mobility and bioavailability of heavy metals. (4)The effect of biochar on soil solidification is general, combining with other solidifying materials to improve the mechanical properties of solidified soil. (5)The effect remediation mechanism of biochar immobilized heavy metals is ranked as follows:precipitation > complexation > electrostatic interaction and ion exchange > physical adsorption. Finally, on account of research status in this field, some important research emphases and directions in the future are proposed. They mainly include establishing a uniform classification criterion of biochar, exploring the efficiency of biochar on multi-heavy metals pollution, illustrating the mechanism and contribution rate of adsorbing heavy metals by biochar, expanding the research scale, and carrying out solidification experiment and mechanical property research based on biochar.
2018, 26(4): 1078-1085.
Under the influence of climate warming, sea plane rising and human activities, the problem of seawater intrusion is becoming more and more serious. The change of salinity is an important basis for judging the severity of seawater intrusion. Therefore, it is very important to monitor the seawater intrusion in situ. At present, the traditional monitoring method of seawater salinity lacks in situ, real-time, long-distance function. In recent years, the study of liquid refractive index based on Long-Period Grating(LPG)technology has provided a new perspective for salinity monitoring during seawater intrusion. Based on the monitoring of salinity change during seawater intrusion, the authors design the feasibility test of LPG technology applicable to salinity measurement of seawater, and compare the measured result with the theoretical value. The experimental results show that there is a good linear relationship between the resonant center wavelength and the salinity of LPG, and the linear correlation between the measured value and the theoretical value is high. Then the salinity can be measured with calibration. LPG technique is feasible for salinity measurement. The research results lay the foundation for the development of the next generation LPG in situ real-time monitoring technology of seawater intrusion.
Under the influence of climate warming, sea plane rising and human activities, the problem of seawater intrusion is becoming more and more serious. The change of salinity is an important basis for judging the severity of seawater intrusion. Therefore, it is very important to monitor the seawater intrusion in situ. At present, the traditional monitoring method of seawater salinity lacks in situ, real-time, long-distance function. In recent years, the study of liquid refractive index based on Long-Period Grating(LPG)technology has provided a new perspective for salinity monitoring during seawater intrusion. Based on the monitoring of salinity change during seawater intrusion, the authors design the feasibility test of LPG technology applicable to salinity measurement of seawater, and compare the measured result with the theoretical value. The experimental results show that there is a good linear relationship between the resonant center wavelength and the salinity of LPG, and the linear correlation between the measured value and the theoretical value is high. Then the salinity can be measured with calibration. LPG technique is feasible for salinity measurement. The research results lay the foundation for the development of the next generation LPG in situ real-time monitoring technology of seawater intrusion.
2018, 26(4): 1086-1094.
Many engineering cases show that the risks of the circumstances around the metro station caused by the excavation of these accessory structures including shaft, cross channel, and metro station pilot tunnel are the major component of the metro construction risk. This paper aims to comprehend the response of surrounding area during the construction of subway shaft. It is based on a subway shaft engineering project of the Changchun subway line 1. The shaft is located at the crossings of Ziyou Road and Renmin Street of Changchun city. Settlements of the surface and adjacent buildings around shaft are studied using finite element software and field monitoring data. The ground surface deformation characteristics and deformation mechanism are discussed. The effect of row piles beside the buildings is also analyzed. The results show that the horizontal deformation of the lining and the land upheaval at the shaft bottom are the important reasons to cause the stratum deformation in the surrounding area. The row piles can interrupt the deformation of foundation and reduce the cumulative settlement and the differential settlement. Finally, the length of the row piles is also discussed. These conclusions are useful for similar project construction.
Many engineering cases show that the risks of the circumstances around the metro station caused by the excavation of these accessory structures including shaft, cross channel, and metro station pilot tunnel are the major component of the metro construction risk. This paper aims to comprehend the response of surrounding area during the construction of subway shaft. It is based on a subway shaft engineering project of the Changchun subway line 1. The shaft is located at the crossings of Ziyou Road and Renmin Street of Changchun city. Settlements of the surface and adjacent buildings around shaft are studied using finite element software and field monitoring data. The ground surface deformation characteristics and deformation mechanism are discussed. The effect of row piles beside the buildings is also analyzed. The results show that the horizontal deformation of the lining and the land upheaval at the shaft bottom are the important reasons to cause the stratum deformation in the surrounding area. The row piles can interrupt the deformation of foundation and reduce the cumulative settlement and the differential settlement. Finally, the length of the row piles is also discussed. These conclusions are useful for similar project construction.
COMBINED SLOPE AND TUNNEL DEFORMATION ANALYSIS FOR NO. 1 SPILLWAY TUNNEL OUTLET OF CENTIANHE PROJECT
2018, 26(4): 1095-1104.
The No.1 spillway tunnel outlet of Centianhe project has large excavation section, steep slope, strongly weathered surrounding rocks and high unsymmetrical rock stresses. After the excavation of the upper part of the tunnel, the construction had to be stopped since the heavy rainfall induced cracks were found in the tunnel sidewall and the outlet slope. More reinforcement and monitoring measures were designed to help restarting the construction quickly, and then to insure that the reservoir could store water on time. A three dimensional calculation mesh was built to accurately reflect construction progress. The monitoring results of initial stage were adopted to estimate the mechanical parameters of the surrounding rocks, which were then used to predict the subsequent deformation and stability of the slope and tunnel. The results showed that the deformation induced by later excavation could be controlled under the enhanced reinforcement measures and the subsequent construction could be safe. The measured deformation increment induced by the subsequent excavation of the lower half of the tunnel and the open channel foundation was used to conduct the back analysis. The calculated results agreed very well with the monitoring data. Then the stress of the lining was predicted. This study helped restarting the construction of the tunnel, and also benefited the water storage and flood discharge of the reservoir.
The No.1 spillway tunnel outlet of Centianhe project has large excavation section, steep slope, strongly weathered surrounding rocks and high unsymmetrical rock stresses. After the excavation of the upper part of the tunnel, the construction had to be stopped since the heavy rainfall induced cracks were found in the tunnel sidewall and the outlet slope. More reinforcement and monitoring measures were designed to help restarting the construction quickly, and then to insure that the reservoir could store water on time. A three dimensional calculation mesh was built to accurately reflect construction progress. The monitoring results of initial stage were adopted to estimate the mechanical parameters of the surrounding rocks, which were then used to predict the subsequent deformation and stability of the slope and tunnel. The results showed that the deformation induced by later excavation could be controlled under the enhanced reinforcement measures and the subsequent construction could be safe. The measured deformation increment induced by the subsequent excavation of the lower half of the tunnel and the open channel foundation was used to conduct the back analysis. The calculated results agreed very well with the monitoring data. Then the stress of the lining was predicted. This study helped restarting the construction of the tunnel, and also benefited the water storage and flood discharge of the reservoir.
2018, 26(4): 1105-1112.
We used the tectonic evolution background, geothermal reservoir characteristics and geothermal resources formation conditions, and made comprehensive analysis of the geothermal resources of Jiyang depression. We consider its geothermal resources are conducted by rock strata and controlled by regional tectonic background. The thermal reservoir is Cambrian and Ordovician limestone of bedrock uplift area covered by Neogene System. Ground water is mainly sedimentary burial nonrenewable water and has a strong scaling and corrosion. The geothermal resource quantity is 10.75×109 GJ, and the geothermal recoverable resource quantity is 1.61×109 GJ.
We used the tectonic evolution background, geothermal reservoir characteristics and geothermal resources formation conditions, and made comprehensive analysis of the geothermal resources of Jiyang depression. We consider its geothermal resources are conducted by rock strata and controlled by regional tectonic background. The thermal reservoir is Cambrian and Ordovician limestone of bedrock uplift area covered by Neogene System. Ground water is mainly sedimentary burial nonrenewable water and has a strong scaling and corrosion. The geothermal resource quantity is 10.75×109 GJ, and the geothermal recoverable resource quantity is 1.61×109 GJ.
2018, 26(4): 825-834.
In the seasonal frozen soil area, periodic freeze-thaw action has continually changed micro-structure and physical-mechanical properties of shallow unsaturated soil, which has directly affected the interaction between soil and structure. The stress-strain relation and strength characteristics of the interface between soil and structure are the bases and keys to determine the bearing capacity and security of foundation engineering, and to analyze the interaction between structure and soil in seasonal frozen soil regions. In order to provide the practical engineering with better services, the stress-strain curve and the interface strength parameter changing with the number of freeze-thaw cycles under different experimental conditions are obtained from the direct shear test of unsaturated loess-concrete samples with different water contents and different freeze-thaw cycles. Correspondingly, the matrix suction of the loess under the same experimental conditions is tested using filter paper method. Moreover, the constitutive model of shear stress and displacement as well as freeze-thaw cycle in the loess-concrete interface is established with experimental data, which has a good description of the relationship between shear stress and displacement of the loess-concrete interface under different pressure after several freeze-thaw cycles. Also, the research results will provide reference for the numerical calculation of the foundation bearing capacity in the seasonal frozen soil area.
In the seasonal frozen soil area, periodic freeze-thaw action has continually changed micro-structure and physical-mechanical properties of shallow unsaturated soil, which has directly affected the interaction between soil and structure. The stress-strain relation and strength characteristics of the interface between soil and structure are the bases and keys to determine the bearing capacity and security of foundation engineering, and to analyze the interaction between structure and soil in seasonal frozen soil regions. In order to provide the practical engineering with better services, the stress-strain curve and the interface strength parameter changing with the number of freeze-thaw cycles under different experimental conditions are obtained from the direct shear test of unsaturated loess-concrete samples with different water contents and different freeze-thaw cycles. Correspondingly, the matrix suction of the loess under the same experimental conditions is tested using filter paper method. Moreover, the constitutive model of shear stress and displacement as well as freeze-thaw cycle in the loess-concrete interface is established with experimental data, which has a good description of the relationship between shear stress and displacement of the loess-concrete interface under different pressure after several freeze-thaw cycles. Also, the research results will provide reference for the numerical calculation of the foundation bearing capacity in the seasonal frozen soil area.
2018, 26(4): 1054-1063.
During the mining of ultra-thick coal seam(12~18m) in Cuimu site of Yonglong mine area, separation water inrush occurred in roof Cretaceous overburden, which and its prevention measures caused a bad influence on the water resources of overlying Luohe formation aquifer. Thus the study on dynamic recovery of Luohe formation water level can provide reference for the influence of water resources caused by the exploitation of coal resources. This paper analyzes the development position and the dynamic process of bed separation using the discriminant formula and discrete element software UDEC, respectively. Based on the water level monitoring, water inrush analysis and theoretical analysis, this paper firstly obtains the hydrogeological parameters of Luohe formation, then establishes the water dynamic recovery model using Theis's equation, finally obtains the time consuming of water recovery. The results show that the bed separation developed in the interface between the sandy conglomerate in the bottom of Luohe formation and the underlying sandy mudstone is relatively closed and largescale. The lowest water level of water inrush point can be regarded as the cone of depression caused by virtual pumping well with discharge Q during the period from 0 to tp. The water recovery process can be recognized as the superposition of pumping water with discharge Q and injecting water with discharge Q during the period from tp to t. Based on the Theis's equation, the time needed for Luohe formation to drop to the lowest point is 7.9459 days. The consuming time of water recovery is 35.6090 days. The results are similar to the actual data. The water recovery of Luohe formation is faster in the initial period but slower in the later period.
During the mining of ultra-thick coal seam(12~18m) in Cuimu site of Yonglong mine area, separation water inrush occurred in roof Cretaceous overburden, which and its prevention measures caused a bad influence on the water resources of overlying Luohe formation aquifer. Thus the study on dynamic recovery of Luohe formation water level can provide reference for the influence of water resources caused by the exploitation of coal resources. This paper analyzes the development position and the dynamic process of bed separation using the discriminant formula and discrete element software UDEC, respectively. Based on the water level monitoring, water inrush analysis and theoretical analysis, this paper firstly obtains the hydrogeological parameters of Luohe formation, then establishes the water dynamic recovery model using Theis's equation, finally obtains the time consuming of water recovery. The results show that the bed separation developed in the interface between the sandy conglomerate in the bottom of Luohe formation and the underlying sandy mudstone is relatively closed and largescale. The lowest water level of water inrush point can be regarded as the cone of depression caused by virtual pumping well with discharge Q during the period from 0 to tp. The water recovery process can be recognized as the superposition of pumping water with discharge Q and injecting water with discharge Q during the period from tp to t. Based on the Theis's equation, the time needed for Luohe formation to drop to the lowest point is 7.9459 days. The consuming time of water recovery is 35.6090 days. The results are similar to the actual data. The water recovery of Luohe formation is faster in the initial period but slower in the later period.
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