Based on the equivalent viscoelasticity between the fractional Zener model and the time-varying viscosity Zener model, the significance of the relaxation time in the evolution of rock rheological viscoelasticity is highlighted. As the relaxation time approaches infinity, the evolution of viscosity during creep is equivalent to that during relaxation. Accordingly, the damage factor related to relaxation time is established to explain the physical significance of damage factor in rock rheological deformation. In specific, the function of variable order is constructed by using relaxation time and the variable-order fractional damage creep model is introduced. Furthermore, the variable-order fractional damage creep model is extended to the triaxial status. Based on the triaxial sandstone creep experimental data, the applicability and rationality of the variable-order fractional damage creep model in the triaxial state are verified. The results show that the developed variable-order fractional damage creep model and the creep experimental data are in good agreement, indicating that the damage creep model can be used to describe the nonlinear mechanical behavior of complete creep process. The effectiveness of the model fitting parameters is analyzed and verified, which encourages the applicability of the introduced model in other complex stress issues.

In order to explore the seepage characteristics of fractured rock mass in the shallow silty mudstone slope under different environmental conditions, a self-developed fractured rock mass seepage apparatus was used to conduct seepage tests on fractured silty mudstone samples with six different fracture surface roughnesses (JRC). The seepage characteristics of fractured silty mudstone under different confining pressures and overlying water depths were studied. The results show that the permeability coefficient of silty mudstone is inversely correlated with the confining pressure under different overlying water depths and JRCs, which can be characterized by a power function. The reduction of permeability coefficient can be divided into two stages: a rapid reduction (0? 30 kPa) and a slow reduction (30?50 kPa). CT scanning results confirm the main reason for the decrease of permeability coefficient is that the increase of confining pressure causes the decrease of fracture aperture of silty mudstone. With the increase of confining pressure or the decrease of overlying water depth, the discreteness of fracture permeability coefficient of different JRC silty mudstone decreases gradually. When the confining pressure increases to the maximum and the overlying water depth is the minimum, the effect of JRC on permeability coefficient would be eliminated. It is also found the permeability coefficients of the samples are positively correlated with the overlying water depth under different confining pressures, which can be characterized by an exponential function. Moreover, the nonlinear Izabsh model of seepage flow in fractured silty mudstone is derived, which can better reflect the nonlinear relationship between seepage flow and pressure gradient under low stress and low velocity. However, the correlation of the model decreases with the increase of confining pressure.

Dam foundation is subjected to a larger impact force when debris flow runs up, causing stress concentration and local impact failure. To address this problem, in this study the vertical structures are optimized into arc-shaped dams. Based on the principle of momentum and energy conservation, the theoretical calculations of the impact process of debris flow and arc-shaped dam are carried out, and the formulas of impact force and maximum run-up height of debris flow are deduced. The theoretical formulas are verified through a series of physical model tests of debris flow impact arc-shaped dam. The results show that the results of the physical model are highly consistent with those of the theoretical calculations, indicating that the proposed theoretical formulas are applicable in the calculation of the impact of debris flow on arc-shaped dam. The debris velocity, impact force and the maximum run-up height are proportional to the flume slope of debris flow. The impact force and the maximum run-up height are mainly controlled by Froude number(Fr), flume slope(?), and arc-shaped radius(R). Both the impact force and the maximum run-up height have quadratic relationships with the Froude number, and are inversely proportional to the cosine of the flume slope. Compared with the rigid vertical structures, the arc-shaped dams have no signicicant influence on the maximum run-up height, but it can reduce the normal impact force on the dam considerably, and the structure strength can also be enhanced by the strengthening of local structure. This study provides a theoretical and technical support for the dam structure design.

In order to study the influence of the cross joints on the fracture mechanism of rock mass, a joint model that can simulate the cross structural plane of rock mass was prepared by the 3D printing technology. By pouring similar materials, the specimen with prefabricated cross joints was formed. Based on the digital image correlation technology (DIC), the crack initiation, propagation and failure mode of specimen under uniaxial compression were analyzed. The results show that the closed joint model made by 3D printing technology can effectively replace the open joint fissures formed by traditional cutting or slotting methods. The experimental results show that the cross joints can significantly reduce the rock strength. With the increase of the cross joint angle, the strength of specimen increases firstly and then decreases. It reaches the maximum value when the cross joint angle is between 45o and 60o. The peak strain presents an opposite variation rule with that of the rock strength. The process of crack growth can be divided into four stages: the microcrack closure stage, the microcrack development stage, the initiation of main joints and the rapid extension of secondary joints, which correspond to each stage of stress-strain curve. It is also found that the influence of secondary joints on the failure of rock with cross joints is mainly reflected in the post peak stage. Combined with the maximum distortion energy theory, it has little influence on the stress distribution at the tip of the main joints, which play an absolute role in controlling the rock failure. This has a certain guidance for rock engineering.

K0 compression tests and constant stress ratio path tests were performed on three kinds of coarse-grained soils in conventional consolidated-drained (CD) triaxial tests. Parameters of unified hardening (UH) model were calibrated according to the triaxial test data, and then stress-strain relationships under the other two paths were simulated. The simulation results were compared with those obtained from Duncan’s E-B model. It is shown that UH model can reasonably describe the mechanical behaviors of coarse-grained soil under different stress paths, while Duncan’s E-B model behaves poorly in predicting the results. The applicability of UH model to coarse-grained soil has been verified. Finally, three-dimensional finite element analysis of stress and deformation for a core rockfill dam was performed by using UH model. The calculation results were compared with those of Duncan’s E-B model and the field monitoring data. It is shown that from a qualitative perspective of the distribution of dam deformation and stress, the results obtained from UH model are similar to those from Duncan’s E-B model. However, from a quantitative perspective, the deformation calculated from UH model is overall closer to the field monitoring data. The applicability and rationality of UH model in the field of earth rockfill dam have also been verified.

The coefficient of earth pressure at rest K0 is particularly important in the calculation of earth pressure of retaining wall. In this paper, the K0 value of sand with different particle sizes and compactions was studied by centrifugal model tests. Firstly, soil samples were prepared by sand pluviation method, and the designed compactions of sand samples under different types of sand outlets and drop distances were measured by self-made sanding device. Then, through reasonable design of earth pressure measurement model structure, the centrifugal model test was used to simultaneously measure the soil compression and the horizontal earth pressure on the aluminum alloy plate. The variation of the K0 value of sand with different particle sizes and compactions was finally obtained by calculation. The test results showed that, when using the sand pluviation method to prepare the samples, different types of sand outlets and drop distances should be adopted for different soil samples. In the centrifugal model test on the K0 value of sand, the order of soil settlement was #1 sand > #3 sand > #2 sand, and the settlement of #1 sand and #3 sand was close to each other. For sand with the same particle sizes, the K0 value increased gradually with the increase of the relative compaction of soil sample. For sand with different particle sizes, under the same compaction, the larger the sand particle size is, the smaller the K0 value is.

A simplified analytical method is proposed for the geotechnical analysis of energy pile groups under thermo-mechanical loads. The relationship between the shear stress and the relative displacement at the pile-soil interface is modeled by a hyperbolic function. The elastic shear displacement method is used to determine the deformation of the surrounding soil. Assuming the settlements induced by the adjacent piles are elastic, the shaft and base interactions among piles are considered separately. The effects of the nonlinear behavior at the pile-soil interface, the pile head restraint condition, and the location of energy piles in the pile group can be predicted reasonably. The computed interaction factor between two energy piles by the proposed method are better than those from the elastic approach. The reliability of the present method is also validated with the experimental data collected from literatures. Both the computed and the measured results show that if part of the piles are subjected to the temperature change, the foundation tilting and the redistribution of the axial load among the piles will be induced. The present method can capture the main characteristics of energy pile groups efficiently and be used as a useful analysis tool for the engineering design.

The geometrical damage model of rocks is an important basis for the establishment of statistical damage constitutive model. Based on the mechanical properties of rock deformation, the existing geometrical damage models of rock are reviewed and these models have difficulties in considering the initial damage and post peak deformation failure characteristics. The rock mass is composed of the undamaged part, the initial damage part and the subsequent damage part, and a geometrical damage model of rocks considering the initial damage is proposed in this paper. The parametric geometric damage model of rocks is established by studying the influence of Weibull distribution parameters m and F0 on the variation of damage variable. Furthermore, a statistical damage constitutive model of rocks characterized by strain softening is established and modified, and the determination method of model parameters is given. The model verification and parameter analysis show that the modified model can better simulate the whole process of rock deformation and failure. The influences of parameters l and h on damage variable are equivalent to m and F0, which solves the common problems of current rock geometric damage models. It demonstrates that the model and method in this paper are reasonable and feasible.

To study the dynamic response characteristics of host rockmass and supporting bolt under blasting load, a three-dimensional dynamic loading physical model test was performed using an underground engineering model test system. The propagation law of blasting seismic wave and the dynamic response characteristics of supporting bolt were tested using electric spark source instead of traditional explosives. Experimental research results show that the electric spark source has the characteristic of the impact loading, which can well replace traditional high explosives. The radial acceleration peak values and the axial and hoop strain peak values of blasting seismic wave within host rock do not decrease gradually as the increasing of the radial distance along the excavation, but show a wave-like attenuation pattern of positive and negative alternating. In addition, the acceleration peak values show a nonlinear and decrease gradually along the excavation axial direction. The peak acceleration values are affected largely by the seismic load amplitude, that is, the higher the source load, the higher the peak acceleration value at the same measurement point. In addition, the vibration characteristics of the supporting bolt were measured under blasting load. It is found that the extension anchor bolt, the free section of the anchor bolt is mainly in tension state, but the anchor section of the bolt is in the state of both tension and compression. The maximum tensile strain of the anchor and free section is approximately the same, while the maximum compressive strain of the anchor section is much larger than that of the free section. The vibration duration of anchor section and free section is also approximately similar. As for the full-anchored bolt, the bolt has subjected both a tensile state and a compressive state, and the tensile strain is greater than the compressive strain. As for the end-anchored bolt, the stress state is mainly in the tension state, and the tensile strain is much greater than the compressive strain. The research conclusion not only has important theoretical significance, but also can provide predictable guidance for the ground support design of underground excavation.

The characteristics of particle breakage and shear strength of soil-rock aggregate with six rock contents under six normal pressures were studied from macro and mecro perspectives by large-scale direct shear test, particle observation test and particle sieving test. The relationship between macroscopic shear strength properties and mecroscopic particle breakage characteristics was established, thus further revealing the influence mechanism of rock content and particle breakage on the shear strength characteristics of soil-rock aggregate. The results showed that particle breakage mainly occurred near the shear plane. The breakage morphology can be divided into surface grinding, local fracture, complete fracture and complete breakage, resulting from the stress concentration caused by uneven contact forces between particles. Due to particle breakage, the content of fine particles increased, coarse grains decreased, and intermediate grains fluctuated. The relative particle breakage Br increased with the increase of normal pressure ?n or rock content P5, which accorded with the function of two variables. With the increase of normal pressure ?n, the shear strength τ increased nonlinearly and met the modified M-C strength criterion. When the rock content P5 increased, the cohesive force c0 of soil-rock aggregate decreased, the internal friction angle ?0 of soil-rock aggregate increased, and the non-linear parameter Δ? increased. Particle breakage was the direct cause of non-linear strength characteristics of soil-rock aggregate.

The combined technology of chemical flocculation and vacuum preloading was proposed to achieve efficient and rapid dewatering of dredged sludge. Five representative flocculants were selected to facilitate the dewatering process using a self-made vacuum preloading filter device. The sedimentation and deep dewatering process of dredged sludge were comprehensively evaluated using a set of designed parameters, including supernatant height, mud-water interface height, settling rate and water content of bottom sludge. The experimental results indicate that the optimal amount of flocculants is 1 500 mg/L for Ca(OH)2, 200 mg/L for PAFSI, 200 mg/L for PAC, 50 mg/L for HCA and 500 mg/L for APAM, respectively. Compared with natural sedimentation process (17.14 cm in height and 96.8% of water content of bottom sludge), the effect of vacuum preloading can accelerate the consolidation and reduce effectively the sludge volume, i.e. the water content of bottom sludge decreases from 96.8% to 53.5% and the volume is compressed further by 20.48%?36.99%. The settling rate of sludge after vacuum preloading reaches its peak within 50 min, and the effect of flocculants associated with the mud-water separation degree plays a dominated role within 120 min. Compared with the original sludge subjected to vacuum preloading, the combination of flocculation-vacuum preloading significantly improves the settling rate of sludge and effectively shortens the required time to reach the peak settling rate. For the optimal flocculant (APAM), the time needed to reach the peak settling rate of bottom sludge and the peak settling rate calculated from total height of sludge are shortened by 87.5% and 83.33%, and the peak settling rate is increased by 3.56 and 5.18 times, respectively. The combined technology of chemical flocculation and vacuum preloading can effectively improve the dewatering performance of flocculated sludge, increase the particle size to prevent blockage, accelerate drainage, promote the sludge sedimentation and improve the mud-water separation efficiency. The combined technique of flocculation-vacuum preloading, contributing to decrease sludge volume, shorten construction period, speed up construction progress and reduce the floor area, can play an important role if it is applied to engineering practice.

To study the frictional resistance characteristics of geogrids and construction residue interface, a series of direct shear tests were conducted on the interface between four different gradations of construction residue and three types of geogrids. The results showed that the relationship between the unit shear displacement and the frictional resistance of the interface between geogrid and construction residue could be expressed by hyperbolic model. The strength of the frictional resistance at the interface increased linearly with the vertical pressure. The structure characteristics of geogrid and the gradation of construction residue determined the frictional resistance characteristics of the grid-residue interface, among which the influence of the tensile modulus of geogrid was the most obvious. The higher the tensile modulus of geogrid was, the greater the quasi friction coefficient and the quasi cohesive strength of the interface were. The quasi friction coefficient was not affected by the gradation of construction residue, but determined by the structure characteristic of geogrid. The quasi cohesive strength was not only affected by the gradation of construction residue, but also related to the structure characteristic of geogrid. For the interface between triax-geogrid and residue, the graded construction residue dominated by medium and fine gravel had the greatest quasi cohesive strength but for the interface between biaxial-geogrid and residue, the graded construction residue dominated by coarse gravel had the greatest quasi cohesive strength. Before and after shearing, the change of the particle gradation of construction residue was a little, so its influence could be ignored.

Anti-seepage is of great significance on hydraulic engineering such as dikes, underground engineering and pollutant migration. Based on the formation of impermeable soil layers due to the complexation between metal ions and organic matter during the formation of natural podzolic soil layer, a novel approach was proposed to reduce soil permeability by Al-OM flocs formed by the interaction between aluminum chloride (AlCl3·6H2O) and organic matter (OM). Extensive laboratory tests were conducted to investigate the effects of slurry concentration, injection rate and the particle size distribution of sand on the reduction of hydraulic conductivity and the distance of flow barrier. The results showed that the Al-OM flocs could significantly reduce the soil permeability. As the concentration of Al-OM flocs in the slurry increased, the decreasing rate of hydraulic conductivity also increased. This is because due to the increase in the concentration of Al-OM flocs, the rate of pore clogging increased, which prevented it from diffusing further, thus reduced the length of flow barrier. The size of Al-OM flocs decreased with the increasing injection rate. When the injection rate was larger, the size of Al-OM flocs was small, so the reduction of hydraulic conductivity was slower and the diffusion distance of Al-OM flocs was longer. The particle size distribution of sand had a significant impact on the reduction of hydraulic conductivity. The higher the coarse particle content was, the slower the reduction of hydraulic conductivity was.

The strength and deformation behavior of granular soil have an important influence on the safety and stability of earth-rock dams, slopes and subgrade. For the strength and deformation behavior of granular soil under complex stress state, a state-dependent bounding surface plasticity model was established for granular soil by incorporating the state parameter and dynamic critical state line in the framework of the bounding surface plasticity theory and the critical state theory. The established model can not only predict the strain hardening and volumetric contraction, but also well describe the strain softening and volumetric expansion behaviors. Based on the secondary development platform of ABAQUS, the UMAT subroutine of the bounding surface plasticity model was developed by using the modified Euler integration algorithm with error control. The accuracy and convergence of the modified Euler integration algorithm were analyzed with different strain increments and integration error tolerance values. Finally, the rationality of the modified Euler integration algorithm with error control applied to the bounding surface plasticity model was verified by simulating the triaxial drained shear tests of granular soil under different densities and pressures, which laid a foundation for further engineering application.

Cantilever collapse is a common type of collapse disaster, which is usually found in river valley and rock slope with soft and hard slope structure. Under the action of differential weathering, rock cavity often forms at the foot of slope, and finally develops into cantilever collapse. Cantilevered collapse is a common geological disaster and characterized by toppling deformation. As the shape and size of this type of collapse are quite different, their failure modes are quite different, it is thus not able to describe its failure process quantitatively at present. Therefore, according to the deformation and failure characteristics of cantilever collapse, the judgment formula of tension failure and shear failure of cantilever collapse based on the quadratic parabola-typed Mohr criterion is established by using the mechanical analysis method. The calculation results of the judgment formula is compared with the results of the physical simulation test, and the analysis result shows that the tensile safety factor of the cantilever collapse is far less than the shear safety factor. With the crack growth, the tensile failure occurs first, and then the shear failure occurs when the crack continues to expand to a certain depth. The judgment formula can describe the deformation and failure process of cantilever collapse quantitatively and accurately, and reveal the deformation and failure mechanism of cantilever collapse quantitatively and accurately.

To investigate the force and stability of surrounding rock in recovering standing pillars with aeolian in fully-mechanized solid backfilling mining working face, the similar physical simulation method was used to compare and analyze the deformation of the surrounding rock and the stress characteristics of the coal pillar when the caving method and the backfilling method were used. Firstly, based on the similarity principle, the methods to simulate process and time control room mining stage, caving to recover pillars stage and backfilling to recover pillars stage were given, while the precompression of paper, plastic foam and sponge combination were chosen to simulate the stress-strain characteristics of aeolian backfilling material. The results showed that: 1) Comparing with caving method, backfilling with aeolian could reduce activity of overlying strata movement, delay and extend period of overlying strata movement, also could avoid failure of pillars and room roof caused by periodic weighting of main roof and hard formation in caving mining working face; 2) The maximum load were both found at the first rank pillars in front of working face whether caving method or backfilling was used to recover standing pillars, backfilling method could effectively reduce the overall load and the stress of standing pillars, and eliminate the phenomenon of dynamic load damage on these standing pillars.

High seepage pressure has a great significance on creep behaviors of brittle rocks under deep underground engineering. However, the macro-mecro relationship between mecrocrack growth and macroscopic deformation under high seepage pressure during the decelerated, steady-state, accelerated creep has been rarely studied. In this study, based on the stress intensity model of crack tips with the influence of initial cracks and new wing cracks, the mechanical relationship between seepage pressure and initial cracks and new wing cracks is introduced, and the stress intensity model model of crack tips considering seepage pressure is established. Then combined with the subcritical crack law and crack-strain damage model, a macro-mecro mechanical model is proposed to explain the relationship between creep crack growth and macroscopic deformation of brittle rock considering the influence of seepage pressure. The rock behaves elasticity when the applied axial stress is smaller than the crack initiation stress, while behaves plasticity when the axial stress exceeds the crack initiation stress but is less than the rock peak strength. The theoretical creep curves subjected to step axial loading are studied under different seepage pressures, and the rationality of the proposed model is verified by experimental results. Furthermore, the creep evolution of crack length, crack growth velocity, axial strain, and axial strain rate under constant or step loading seepage pressure are discussed. The new model provides a significant theoretical basis for the evaluation of the stability of surrounding rocks in deep underground engineering under high seepage pressure.

Glutenite formations usually characterized by their dense and heterogeneity, thus the fracturing effect of conventional fracturing methods is not ideal. Liquid CO2 (L-CO2) fracturing is a fracturing stimulation method proposed in recent years, and the fracturing effect has obvious advantages. Water and L-CO2 fracturing tests are conducted on downhole cores, ?CT scanning and NMR tests are used to compare the difference of breakdown pressure, fracture characteristic and crack distribution and the L-CO2 fracturing mechanism in glutenite is deeply analyzed. It is found that under the same confining pressure, L-CO2 can greatly reduce the breakdown pressure, and the difference between the breakdown pressure of L-CO2 fracturing and water fracturing increases with increasing confining pressure. ?CT scanning shows that the fractures induced by L-CO2 fracturing are irregular fractures, which are more likely to deflect between gravel particles in glutenite, causing a branch fractures and complex fractures networks. The fracture volume of L-CO2 fracturing is much larger than that of hydraulic fracturing. Nuclear magnetic resonance (NMR) results show that L-CO2 fracturing mainly breaks through the micro-cracks at the interface of gravel particles, and the shear activation mechanism has a significant effect, while hydraulic fracturing mainly takes the form of a single tensile fracture rupture. The better fracture network obtained by L-CO2 fracturing is mainly related to the strong heterogeneity caused by gravel particles in glutenite, which affects the complexity of induced fractures. Relevant research results can provide guidance for glutenite reservoir fracturing and process optimization for increasing production and efficiency.

Temperature has a significant effect on the deformation monitoring of fiber Bragg grating (FBG), which leads to great limitations of FBG technology in the monitoring of seasonal frozen soil subgrade. The temperature compensation method to solve the cross-sensitivity problem of FBG sensors is presented in this paper, and the deformation law of FBG-based monitoring beam under different loads and negative temperatures is analyzed. A subgrade model for laboratory tests is proposed, and the applicability of FBG in the monitoring of permanent deformation for seasonal frozen soil is verified. The results show that the wavelength of FBG is linearly correlated with temperature. The lower the temperature, the smaller the wavelength, and the greater the influence on the monitored deformation. The wavelength of the FBG monitoring beam is calculated using the temperature compensation method, so that the wavelength error caused by low temperature can be eliminated. Based on the deformation testing results of the subgrade model, the deformation measured using the FBG is similar to that measured using the cable displacement meter when the influence of temperature is eliminated. This means that the FBG monitoring beam can deform synchronously with soil and the soil deformation monitoring under low temperature can be achieved. Under the influence of freeze-thaw cycle, the FBG testing result is close to the actual deformation, and the error is within 5%. After 4 to 5 freeze-thaw cycles, the permanent deformation of the subgrade model tends to be stable.

On the basis of triaxial and direct shear tests, modified Mohr-Coulomb strength criterion and the modified Lade-Duncan strength criterion in which the effect of methane hydrate saturation is considered are used to describe the strength of micro-elements for methane hydrate-bearing sediments. Based on the results, statistic damage constitutive models for methane hydrate-bearing sediments are put forward using the theory of continuous damage mechanics together with statistical theory. Then, by comparing the results obtained from theoretical models to those from laboratory tests, the validity of statistical damage models based on different strength criteria are verified. The results show that the damage constitutive model based on the modified Lade-Duncan strength criterion can accurately simulate the stress-strain curves of hydrate-bearing sediments before reaching the peak stress, while the damage constitutive model based on the modified Mohr-Coulomb strength criterion can capture the strain-softening characteristics after the peak stress observed in the experiments. For the experiments with different hydrate saturations and lower effective confining pressure, the simulation accuracy of the damage constitutive model based on the modified Mohr-Coulomb strength criterion is better than that based on the modified Lade-Duncan criterion. On the contrary, under the same hydrate saturation and different effective confining pressures, the simulation results of the damage constitutive model based on the modified Lade-Duncan strength criterion are better than those based on the modified Mohr-Coulomb strength criterion.

As a bearing structure, the reinforced soil abutment has attracted much attention for its bearing capacity and its influencing factors. Taking the Bowman bridge as the engineering prototype, this paper studies the bearing capacity of the reinforced soil flexible abutment by the scale model test. In the experimental study, three groups of load tests of the reinforced soil flexible abutment were set up, which uses the geotextile as the reinforcement material. This paper mainly studies the influence of bridge base position on the bearing capacity of the abutment. Test results show that the setback is an important factor affecting the bearing capacity of the reinforced abutment, and that the bearing capacity increases with the setback, but the amount of increase is rapidly diminishing. The horizontal and vertical settlements at the top of the abutment decrease with the increase of the setback, and the decreasing trend shows convergence. With the increase of setback, the maximum strain of reinforcement decreases, and the overall stability of abutment is enhanced, showing better complex characteristics. In addition, the results of this experimental study also prove that the calculation method of bearing capacity of reinforced abutments in the current US regulations may be limited to specific packing and reinforcement arrangement. Therefore, it should be combined with actual conditions in engineering practice.

To study the deformation and failure characteristics of the slope of gently inclined accumulation layer caused by intermittent rainfall, taking the Yingtaogou landslide as an example, a physical simulation study on the slope deformation and failure under the action of rainfall was carried out. The results showed that under the action of early rainfall, the deformation characteristics of the slope body showed the sliding and subsidence at the leading edge, the sliding in the middle part, the subsidence at the rear edge, and the formation of slope cracks and the obvious expansion of leading-edge cracks. Under the action of late rainfall, the slope foot area was the first to slide, and then the sliding was transferred to the trailing edge resulting in progressive sliding failure. Rainfall infiltration was easy to store on the bedrock surface, forming transient groundwater level, high pore water pressure area and slope seepage field. The soil near the bedrock surface was saturated with water for a long time, so it had a high degree of softening, and a significant weakening in shear strength, causing the slope prone to landslide along the soil layer at the base interface. Slope sliding tended to occur during the rainfall intermittent period. The triggering characteristic of slope sliding were as follows: after rain, the continuous infiltration of the water in the transient saturated area of slope body and the accumulated water on the slope surface led to the rise of the groundwater level lagging behind the rainfall, causing the increase of buoyancy in the slope, permeability and pore water pressure, so that the effective stress in the slope body decreased, which induced the landslide.

The constant resistance yielding support is the ideal form of support for squeezing tunnel. Current technology is difficult to satisfy the safety requirements of high bearing capacity, large deformation and load stability at the same time. In response to this problem, the conversion constant resistance yielding device (CCYD) was developed inspired by the metal drawing process in combination with the characteristics of steel arch support. In this paper, the working principle of the CCYD was discussed, and its mechanical response law and characteristics were analyzed. Through the indoor test and numerical simulation, the influence of the design parameters was analyzed, and the performance measurement index of the conversion constant resistance yielding device was determined. The analysis shows that: 1) The conversion constant resistance yielding device can constantly resist deformation under pressure; when installed in the steel arch joint allowing it to be part of the steel arch, the device can ensure the stability of the arch, improve its large deformation adaptability while providing constant support for the surrounding rock. 2) Based on the four design parameters: the cone angle, the friction coefficient, the cross-section shrinkage rate and the diameter of the pressure bar, the device can realize pressure resistance and pressure control with satisfactory load stability, which can provide important technical support for soft-rock tunnel large deformation and the stability control of support.

Slurry performance is one of the key factors to maintain the stability of excavation face when slurry balance shield is tunneling in complex strata. Based on the engineering background of slurry shield tunneling in mudstone and gravel composite stratum of Nanning Metro Line 5, the control variable method and the self-made slurry shield tunneling system are adopted to compare and select the mud admixture and to analyze the influence of the admixture amount and the formation composite ratio on the slurry relative density. Then, the mud permeability law and the dynamic and static mud film forming law under different formation composite ratios, swelling water ratios and slag dosages are analyzed comprehensively by factorial design. The results show that different admixtures have significant influence on the properties of bentonite slurry. Specifically, potassium methyl silicate and potassium chloride can effectively reduce the relative density of slurry, while sodium chloride and sodium silicate can promote the disintegration of mudstone in water. In addition, the slag admixture can effectively reduce the water filtration, improving the film quality and reducing the consumption of bentonite. When the cutter head speed is less than or equal to 2.5 r/min, the formation rate of mud film is greater than or equal to the failure rate so as to ensure the stability of driving face. The mud swelling water ratio suitable for mudstone and gravel composite stratum (composite ratio: 0?1) is 0.1?0.20, the residue content is 100?200 g/kg, and the potassium methyl silicate is 3.75%?7.50%.

In order to study the suitability of different types of piles for diatomite foundations, deformation characteristics and protective measures of diatomite slope under rainfall, deformation characteristics of pile-raft composite foundation and subgrade bed dynamic response in diatomite, field loading test on single pile, rainfall on diatomite slope, bearing capacity of composite foundation and in-situ dynamic excitation tests were conducted on the Hangzhou-Shaoxing-Taizhou high speed railway. The result shows that CFG pile, plain concrete pile, reinforced concrete pile can be applied to diatomite foundation, whereas the screw pile is inapplicable due to compaction effect and high pressure rotary jet pile due to poor quality effect. The natural diatomite slope has connecting cracks that form network within the slope under drying-wetting cycles, resulting in insufficient shallow stability. The arch-shaped skeleton revetment has a better protective effect on the diatomite slope, while drilling during the construction of anchor frame beam will lead to the softening of diatomite, which is not suitable for the protection of diatomite slope. The CFG and plain concrete pile-raft composite foundation can satisfy the requirement for deformation control, and the structural integrity of concrete pile raft is better between the two types of piles. The capillary drainage layer has a good drainage effect, which ensures that the water can be discharged in time to avoid the adverse impact on the diatomite foundation.

For inclined high-rise building with pile raft foundation, vertical hole digging is often used to relieve the ground stress to achieve the inclination correction. Due to the lack of theoretical guidance, the engineering design and construction have to rely to a large extent on experience. In this paper, the problem of stress redistribution around a vertical hole at a certain depth is simplified as a plane strain problem, and the analytical solution of the radius of plastic zone is derived by using the Mohr Coulomb strength theory. The analytical solution shows that the plastic radius increases with the decrease of shear parameters, the increase of digging hole radius and the increase of depth. By combining the site rectification phenomenon with the analytical solution formula, the influences of the groundwater, water injection, pumping, cyclic soil digging disturbance on the plastic radius are discussed. Finally, the numerical simulation is used to verify the analytical solution, which shows the validity and applicability of the formula. The research results will provide scientific insight for the design and smart construction of the rectification practice.

Aiming at large deformation of roadway on working face of deep island mining, the dynamic evolution law of the stress in roadway surrounding rock and goaf are studied by means of field measurement, and the evolution characteristics of deformation and failure of surrounding rock are analyzed. The results show that the stress evolution and deformation failure of surrounding rock on working face of deep island mining have obvious stage characteristics, when the distance from the working face is more than 250 m, the surrounding rock of the roadway is not affected by mining, so the stress of surrounding rock changes little, and the deformation is mainly concentrated in floor and coal pillar. The stress of the supporting structure is increased obviously in the range of 100?250 m in front of the working face, the shallow surrounding rock of the roadway is broken, and the coal pillar is squeezed and deformed, which causes the roadway to appear the obvious asymmetric deformation and failure. In the range of 100 m in front of the working face, the stage of strong mining influence occurs, especially in the range of 20?22 m in front of the working face, the vertical stress and space principal stress of the surrounding rock change more significantly, the roof and floor moving closer and the both sides of roadway deformation more prominent, which make the surrounding rock of the roadway shows obvious large deformation and failure characteristics. According to the characteristics of stress zoning in goaf, the dynamic evolution process of the covering rock structure is analyzed. Combined with the evolution characteristics of stress and deformation, the reform suggestions of roadway support are proposed to provide some guidance for the control technology of roadway surrounding rock in deep mine.

In view of the control of ground vibration isolation, a novel type of vibration isolation barrier, open trench-wave impedence block barrier, is proposed. The vibration isolation performance is analyzed by numerical simulation. Firstly, the governing equation of a non-splitting perfect matched layer (PML) absorbing boundary is established in the frequency domain by using complex coordinate stretching. Secondly, using Galerkin approximation technology, the frequency-domain finite element method formula of the second-order non-splitting PML with displacement as the basic unknown quantity is given. Finally, through numerical examples, the influence of physical parameters (modulus ratio of foundation to wave barrier), geometric parameters (trench depth, wave impedence block depth) and load parameters (frequency of vibration source) on the vibration isolation performance are investigated. The results show that the open trench-wave impedence block barrier can effectively control the ground vibration caused by different frequency vibration sources.

A new method is proposed for predicting the in situ stress of local surrounding rock of large underground cavern group in high stress, various stress-induced fracturing, such as spalling of caverns and borehole breakouts are considered as the inversion information. This method quantitatively describes the location, depth or width of stress-type failure such as sheet wall and hole spalling of underground caverns, represent by the range of constant deviatoric stress greater than crack initiation stress of rockmass according to the elastic model calculation. The value or direction of local in-situ stress could be constrained based on the law of the measured geo-stress data, and the other in situ stress component are predicted by simulation modeling intelligent inversion method. This method is applied to predict the natural stress of rockmass near chainage 0+76 of the right bank underground powerhouse of Baihetan hydropower station. The predicted maximum principal stress is about 34 MPa, and the prediction rationality of in situ stress is verified by fracturing characteristics in other position through comparison of numerical simulation and field observation.

Using the Richards’ equation of saturated-unsaturated seepage, the commercial Multiphysics finite element software COMSOL is adopted to deduce the governing equations of two boundary conditions with the pore water pressure as the control variable for the infiltration and seepage (overflow) boundary conditions in the rainfall infiltration problem of slope. Based on the two-dimensional soil column model and the published models, the value of the boundary coupling length scale L in the governing equation is discussed, and L equal to 0.001 m is found reasonable. A simple two-dimensional slope model is then established, and the governing equations of the above boundary conditions are applied to analyze the infiltration and seepage law of rainfall with different intensities (long and weak, short and strong). The results show that when the rainfall intensity is 4 mm/h, the actual infiltration rate is always equal to the rainfall intensity, and the water content of the surface soil has increased from 0.29 to 0.35. When the surface seepage has occurred for 75 h at the foot of the slope, the total infiltration of the study area at 200 h is 39.068 m3; when the rainfall intensity is 40 mm/h, the actual infiltration rate first equals the rainfall intensity, and then gradually decreases, and the water content of the surface soil increases from 0.29 to 0.415 (saturated). When the surface seepage has occurred for 4 h at the foot of the slope, the total infiltration of study area at 20 h is 26.908 m3, which is far less than the former. This conclusion is consistent with the existing rainfall infiltration law in slope, which further proves the reliability of the above boundary condition governing equations that provides a feasible method for the boundary condition problem in finite element analysis of rainfall in slope.

On the eve of the landslide disaster, bursting, friction and fracture of rock and soil mass in the sliding body will cause low frequency infrasound signals to propagate outward. Advance positioning based on infrasound signals has become a key technology for landslide monitoring and early warning. In this paper, the wave equation was transformed into Helmholtz equation by Fourier transform, and the Kernel function of the wave equation was obtained by Hankel transform. Based on this, we established the normal wave geological sound field model, and simulated the reflection-refraction relationship between the air, soil and rock interface. By matching the measured infrasound signals of the vertical receiving array with the copied infrasound signals of the propagation model, we proposed the advanced matching field location algorithm for infrasound signals of landslide, which searches for the coordinates at the maximum correlation coefficient as the predicted sound source. We compared the performance of three matching field algorithms and found that the variable-coefficient-likelihood matching field algorithm can be applied to landslide positioning technology due to its small sidelobe and accurate positioning, and found that the 12-element vertical array in the soil layer could be accurately positioned, but the error in the air was large. Finally, we applied the algorithm to the advanced positioning of landslides, and obtained the local failure position and predicted the slip line of landslide. This algorithm provides a new idea for the landslide advanced prediction and positioning technology.

This study presents a self-developed device that can visually reflect the seepage characteristics of single fracture in rock. Taking the deformation modulus of simulated rock as the main technical index, the additive content of K39 transparent rock material is obtained: accelerator 0.8%, hardening agent 0.6%, defogging agent 0.6%. The roughness of the fracture surface of the original rock is obtained by the accurate re-engraving technique of the second mould turning, which provides technical supports for the study of microscopic seepage flow of fracture. Through the simulation test of the visualization device and the original rock device, the difference coefficient between them is yielded. Furthermore, the modified formula of the seepage flow in original rock is derived. The relevant parameters reflecting rock properties, such as the seepage flow rate and the seepage area, are obtained. The inherent mechanism of the influence of K39 transparent rock material on seepage flow is also clarified. Compared with the seepage test using ELE instrument as research platform, the relative variation coefficient of the difference between the two seepage devices is obtained, which suggests that the visualized seepage device developed in this study is capable in studying the seepage flow in rock fractures. The new device is applied to carry out space multi-angle experiments. Under the influence of multiple factors such as coupling roughness, osmotic pressure, confining pressure, space multi-angle and water self-weight effect, the digital self-identification technology of seepage area provides a foundation for accurately access the relevant parameters of rock seepage characteristics.

In recent years, the active heated fiber optic(AHFO) method has been widely applied in the in-situ soil water content due to its ability to be used in long distance, good durability and distributed monitoring. However, the soil temperature in some areas in China varies greatly with seasons. The soil temperature reaches dozens of degrees below zero in winter, causing the water to freeze. Therefore, it is of great significance to study the influence of different ambient temperatures on the in-situ monitoring results of soil water content using AHFO method. In this paper, the self-developed internally heating alundum tube FBG sensor was used to monitor three loess samples with different water contents at a temperature of ?20 to 40 ℃. The results show that when the water content of the loess is not higher than 8.8%, the maximum error of water content measured at different temperatures is less than 1.5% of the range. Since the measurement accuracy is high, the effect of ambient temperature on the monitoring results of water content of soils can be ignored in the actual measurement. When the water content of loess is higher than 8.8%, the maximum error of the measurement of the water content in the positive temperature zone accounts for about 1.34% of the range, and the measurement accuracy is still high. In the negative temperature zone, since free water and capillary water undergo phase transition when the temperature is lower than 0 ℃, the heat transfer mechanism and sample structure change. As a result, the original calibration formula is no longer applicable. Therefore, it is necessary to recalibrate the relevant parameters in water content measurement. The research results provide important reference value for further improvement and application of this technology.