Water vapor supply can induce frost heave of sand filler. Based on the self-developed moisture migration and frost heaving tester, the variations of sand moisture content, temperature and frost heave with freezing time under gaseous water recharge were studied. The change characteristics of sand microstructure during freezing were examined by stereomicroscope. By combining with the grey correlation theory, the correlation between the macroscopic index, i.e., frost heave and the microscopic parameters was analyzed. Notable frost heaving was observed under water vapor supply, and the frost heave reached 3.45 mm after 7 days of freezing. After sandy soil frost heaving, the proportion of large pore area increased and the proportions of small and medium micropore area decreased, and the change trend of pore number proportion was opposite to that of area proportion, while pore abundance value changed little, pore orientation angle distribution in each interval tended to be more uniform, the probability entropy of pore orientation present an overall upward trend of oscillation, and the pore fractal dimension showed a trend of decrease. In addition, the grey correlation theory is used to establish the correlation between the frost heave and the average pore size and other microscopic parameters, which provides an insight into the microscopic mechanism of sand frost heaving under water vapor supply.

In order to explore the influence of the relative positional relationship between the dynamic load and the long axis of the elliptical  cavern on the characteristics of impact rockburst, a cuboid sample with an elliptical hole is prepared. With two positional relationships of disturbance direction parallel or perpendicular to the long axis of the elliptical cavern, the elliptical cavern impact rockburst experiments are carried out. With the aid of video recording device, the characteristics of the impact rockburst of the elliptical cavern are discussed in terms of damage process of rockburst ejection, ejection speed, failure mode and fragment size. The experimental results show that the rockburst processes of the two samples with different positional relationships are the same, and the rockburst pits are all V-shaped. The initial failure stress, rockburst stress, rockburst ejection velocity, rockburst pit size, fragment mass and proportion of coarse-grained fragments of the samples whose disturbance direction is perpendicular to the long axis of the ellipse are smaller than those of the samples whose disturbance direction is parallel to the long axis. The fragment characteristics of the samples whose disturbance direction is perpendicular to the long axis of the ellipse are mainly presented as thin stripes. The samples whose disturbance direction is parallel to the long axis of the ellipse can significantly improve the bearing capacity of the cavern structure. However, the rockburst phenomenon is more severe and its debris characteristics are mainly of thick plate.

Natural gas hydrate in deep sea exists in a certain temperature and pressure condition. The depressurization rate during hydrate dissociation by depressurization has a great impact on the gas production rate and hydrate-bearing sediment deformation characteristics. In order to investigate the influence of depressurization rate on temperature field, pore pressure field, deformation characteristics, and gas production rate of hydrate-bearing sediment, a group of depressurization tests with different depressurization rates was carried out on the apparatus independently developed by Zhejiang University that can perform linear gradient servo depressurization for simulating the hydrate decomposition process. The results show that the temperature decreases first from the perimeter of the shaft where the decomposition region starts, and then gradually spreads to the surrounding sediment at the initial stage of depressurization. Increasing the depressurization rate appropriately can improve the production efficiency of the reservoir, but the higher depressurization rate may cause the hydrate regeneration, which is not conducive to gas production. Optimal gas production efficiency can be obtained by selecting a specific depressurization rate. In the process of hydrate exploitation, the pore shape of the hydrate-bearing sediment can be divided into three types, according to the connection degree between pores and the surrounding area: completely sealed, partially sealed, and open. After hydrate exploitation, the shallow surface soil of reservoir can be divided into three areas based on the deformation characteristics: Zone I is the soil layer around the shaft, showing a funnel-shaped subsidence structure; the soil layer in Zone II is flat with no obvious disturbance; Zone III is the boundary soil layer, where the upward migration of water and gas production is blocked, leading to a mound like uplift zone. These deformation characteristics are related to the migration paths and modes of gas production in hydrate-bearing sediment. Through similarity analysis, the corresponding relationships between the decomposition time and gas production of the model and prototype are given.

At present, the calculation methods of active earth pressure are mostly only for the soil in a saturated or dry state, ignoring the gradual process of soil from unsaturated to partially saturated, or from saturated to unsaturated, which leads to distortion of the calculation results. In this study, a series of model tests on the active earth pressure of unsaturated sand behind retaining wall is carried out to reveal the failure law of soil behind the wall. Observations show that, 1) there is an approximately vertical crack on the top of the soil behind the wall, and its development depth increases with the increase of wall surface roughness and water content;  2) the wall-soil interface friction has almost no effect on the plastic zone of the soil behind the wall, and the shape of the plastic zone  remains approximately flat during the movement of the retaining wall. On the basis of tests, the generalized effective stress principle is introduced, an analytical method for calculating active earth pressure of unsaturated soil considering the effect of suction stress is developed based on limit equilibrium analysis. The theoretical and experimental results show that the proposed method is closer to the experimental values than other methods. Finally, the main factors influencing the active earth pressure of unsaturated soil are analyzed, and it is found that the active earth pressure decreases with the increase of soil friction angle, but the interface friction angle has little influence on the distribution of active earth pressure; compared with no suction case, the active earth pressure is smaller when considering suction; with the increase of air-entry value, the contribution of the suction stress to the active earth pressure decreases and eventually tends to be constant.

To solve the technical issues in vacuum preloading method, including the sediment clogging of drains and the limitation of drainage conditions, this study investigated vacuum preloading combined with flocculation and electro-osmosis consolidation for marine soft soil. A series of column settling tests was conducted to determine the optimal organic flocculant for the combined method. With the selected organic flocculant, laboratory tests were performed on the soil samples using the combined consolidation method, in which the electro-osmosis was added at different time moments. The tests considered three representative cases at different time moments: (i) at 48 h, i.e., the initial stage of vacuum preloading with the consolidation degree of 0; (ii) at 60 h, i.e., the obvious reduction in the dewatering speed with the consolidation degree of 60%; and (iii) at 84 h, i.e., the dewatering speed of 0 with the consolidation degree of 80%. The effectiveness of the combined method was evaluated using the tested results, including water discharge, soil vane shear strength, water content, and pore water pressure, along with the determination of the best time for adding the electro-osmosis. The results indicated that the combined method effectively delayed the decrease of dewatering efficiency and significantly increased dewatering duration. Also, the shear strength and load-bearing capacity of the consolidated soil were clearly improved, with the evenly dissipated pore water pressure. In addition, the cationic polyamide was the optimal flocculant for the combined method, which enhanced the initial dewatering speed and improved the permeability of the soft soil to solve the sediment clogging in the plastic board during the vacuum preloading. This research demonstrated the effectiveness of vacuum preloading combined with flocculation and electroosmosis consolidation for soil improvement.

The water softening of argillaceous sandstone in complex stress state will seriously reduce the bearing capacity of surrounding rock, resulting in the increase of failure range and deformation pressure of surrounding rock, and finally seriously threaten the safety of water tunnel during operation. To solve this problem, triaxial tests under different immersion time are carried out to investigate by using argillaceous sandstone from water delivery tunnel of Lanzhou water source project. The results are as follows. As the immersion time prolongs, the sensitivity of peak strength and residual strength to confining pressure decreases gradually. This may be attributed to the fact that the water reduces the sensitivity of peak strength and residual strength to confining pressure to a certain extent. In the early stage of immersion, the decreasing rate of residual strength with immersion time is significantly less than that of peak strength with immersion time, and the softening effect of water on the peak strength of argillaceous sandstone is more remarkable. The peak strength, residual strength and elastic modulus of argillaceous sandstone samples decrease with the increase of immersion time in a negative exponential relationship. With the increase of confining pressure, the influence of immersion time on elastic modulus gradually weakens, and the increase of confining pressure reduces the softening effect of water on the elastic modulus of argillaceous sandstone to a certain extent.

To investigate the proper value of unloading in the unloading collapse process of loess between piles, a correlation between pile-soil interface shear strength, shear displacement, and pile-soil interface normal force under collapse was studied by interface shear test. In the range of neutral points, the results indicate that the shear strength of the pile-soil interface under different vertical stresses and water contents can represent the pile side negative friction resistance. Using the mechanical principle of the mutual action and reaction force between the unloading amount and the negative frictional resistance, we proposed a method to calculate the unloading amount based on the unloading variation laws during loess collapse. The rationality of proposed method is verified via the comparison between the calculated unloading values and the field measured results of pile side negative friction resistance in different loess areas. This method provides a quantitative means of unloading effect to promote loess unloading collapse evaluation and optimize the relevant loess engineering design theory.

The time variation characteristic of impact parameters in the contact process between rockfall and slope or protective structure is an important index to describe the process of rockfall collision. It is significant to reveal the interaction mechanism between rockfall and slope and to take reasonable protective measures. In the existing relevant design specifications, there are no calculation methods for the time history relationship of rockfall impact, and only a maximum value of rockfall impact force is determined by referring to relevant specifications or empirical methods. Therefore, based on the linear viscoelastic contact theory, a mechanical model of rockfall impact on the ground is established firstly; according to the different combined initial conditions, two theoretical analytical solutions of the characteristic parameters of rockfall impact are derived respectively. Then, based on the ANSYS/LS-DYNA nonlinear dynamics software, a three-dimensional numerical model is established, and the mechanical characteristics of the rockfalls impacting the ground at different speeds are studied. Finally, the theoretical results of this paper are compared with the indoor test and existing research results, and the following conclusions are drawn: 1) According to the Hertz elastic contact theory, the changes of various parameters show a symmetrical trend during the loading stage and the recovery stage. The characteristic parameters of rockfall impact under the initial condition combination of velocity-acceleration in this paper are very close to the dynamic finite element method, and the initial condition combination of displacement-velocity is not suitable for research on dynamic characteristics under the impact of rockfall. 2) At different speeds and falling heights, the maximum impact force value of the rockfall increases with the increase of the falling height and impact velocity of the rockfall, while the impact time of the rockfall decreases with the increase of the falling height and impact velocity. 3) The maximum impact force and impact time of the rockfall obtained by the calculation in this paper are close to the indoor test and the existing results. Compared with the oscillation of the indoor test and the finite element results, the results of this paper can better reflect the change law of the impact force of the rockfall.          4) Comparing the maximum impact force of rockfall obtained by different methods under a variety of impact speeds, the calculation results in this paper are all within the range of various impact force calculation results, and have good reliability. The results of this paper enrich the rockfall collision theory, which can guide the protection design of engineering related to rockfall disasters.

Silicate cement as a conventional soil curing agent has problems of high energy consumption and high emissions, and researchers have been seeking a more economical and environmentally friendly alternative to cement. In this study, geopolymers based on ground granulated blast-furnace slag (GGBS) and fly ash (FA) were used to reinforce sandy soils, and the effects of different factors on the mechanical properties of geopolymer stabilized sandy soils were investigated by adjusting the type and ratio of exciter, slag-fly ash ratio, water-cement ratio, and curing conditions. The specimens were studied in depth by unconfined compressive strength (UCS) test, electron computed tomography (CT) analysis, and scanning electron microscopy (SEM). The results show that the GGBS-FA-based geopolymer can effectively improve the mechanical properties of the sandy soil; the reinforcement effect of the composite exciter is better than that of the single-component exciter; the low temperature does not significantly reduce the final mechanical properties of the geopolymer stabilized sandy soil, but only delays the polymerization reaction and structure formation; the alkaline environment promotes the strength of the geopolymer stabilized sandy soil; the acidic environment and prolonged exposure to air reduce the strength of geopolymer stabilized sandy soils.

To study the effect of both low temperature and loading on the deformation and failure characteristics of water-rich Cretaceous sandstone in Longdong area, the uniaxial and triaxial compression tests and microstructure test on different sandstones (medium and coarse-grained sandstones) under different temperatures (−30, −20, −10, −5 and 25℃) and confining pressures (0, 4, 6 and 8 MPa) were conducted using MTS-815 servo rock mechanics testing machine and scanning electron microscope (SEM). Then the freezing-loading deformation, the failure characteristics and the internal mechanism of saturated Cretaceous sandstone were systematically analyzed. The results show that the pre-peak pore compaction deformation of sandstone samples is significant, and that of medium-grained sandstone is more notable. The decrease in test temperature and the increase in confining pressure can weaken the compaction deformation of samples and increase the rigidity and strength. And the post-peak deformation of samples is accompanied by a significant increase in volume. As the test temperature increases, the elastic modulus E, shear modulus G, and volume modulus K_v of the samples show a nonlinear attenuation trend of first fast and then slow, and these parameters of the medium-grained sandstone are always lower than those of coarse-grained sandstone under the same conditions. But the change laws of Poisson’s ratio m and Lame constant l are opposite. In addition, the relationships between these deformation parameters and test temperature can be well characterized by a unified exponential model. Under the negative temperature condition, the frost heave failure of the medium-grained sandstone is more serious than that of coarse-grained one, mainly in the form of transverse cracking and point-like bulge failure. Moreover, the loading failure mode of frozen sandstone samples is significantly affected by the factors such as lithology, temperature and confining pressure. The internal mechanism of the difference in deformation and failure of the two types of frozen sandstones is determined by their macro- and micro-structure characteristics such as grains and pores. The results obtained in this study are helpful for the development of the soft rock mechanics and the frozen shaft design of the coal mines in western China.

 Ground collapse accidents pose a large threat to the safety of cities due to their suddenness. It is very important to understand the development process of internal deformation of collapsed soil for prediction of ground collapse. In this study, based on the optical frequency domain reflectometry (OFDR) and particle image velocimetry (PIV) technologies, ground collapse model test was performed, and the tempo-spatial distributions of ground settlement in the collapsed area were investigated. The influence of anchoring methods of distributed strain sensing cables on the fiber optic monitoring results was explored. The results show that the fiber optic strain measurements reflect the deformation state of the overlying soil in different collapse stages and reveal the internal strain evolution mechanism of the ground soil. The coupling effect of the cable-soil interface is effectively enhanced by adding circular micro-anchor plates and is better with the increase of the diameter of the anchoring circulars at a certain burial depth. The research results show that the distributed strain sensing technology has good applicability in monitoring ground collapse and can provide a powerful tool for mitigating such geohazards.

 Statistical analysis and clustering of discontinuities existing in rock mass are the basis of rock mass engineering stability analysis. Considering that the mechanical and hydraulic properties of discontinuities are affected by many factors such as occurrence, trace length, opening, roughness, and filling state. A multi-parameter dominant grouping method of rock mass discontinuities based on principal component analysis is proposed. Firstly, the principal component analysis method is used to select the criterion of the dominant grouping and calculate the weight value of its participation in similarity measurement. Secondly, the global optimal initial clustering center of the fuzzy C-means clustering algorithm is searched using the annealing genetic algorithm. Lastly, the objective function is established by minimizing the weighted sum of the distance between the discontinuities to be grouped and the clustering center, achieving the dominant grouping of multi-parameter rock mass discontinuity. The 200 discontinuities simulated by the computer are divided into dominant groups using the multi-parameter method and compared with other methods. The results show that this method has higher grouping accuracy. The method is applied to the multi-parameter dominant grouping of the measured discontinuities of Huayang Tunnel of Chongqing Third Ring Expressway. The grouping results are reasonable and reliable, which further verify that the method has significant engineering application value.

Hydrates are often filled in the pores of sediment soil particles or bonded between grain contacts, which have filling or bonding effects on sediments. These formation patterns of hydrate change the original void ratio and density of soil, which significantly affect the physical and mechanical properties of sediments, so it is necessary to consider the effects of hydrate filling and bonding to describe the mechanical properties of hydrate-bearing sediments. In this paper, the equivalent hydrate ratio was proposed to reflect the filling effect of hydrate based on the unified critical state constitutive model for both clay and sand (clay and sand model, referred to as CASM) and combined with the densification characteristics of hydrate intrusion pores. The cohesive strength was introduced to reflect the cementation of hydrates on sediments. Furthermore, an elastoplastic constitutive model for hydrate-bearing sediments was established to describe the hydrate filling and bonding effect by using the state parameters to reflect the stress state and the dilatancy of the soil and adopting the non-associated flow rule. The comparison between laboratory test results and presented constitutive models shows that this model can effectively simulate the stress-strain relationship of hydrate-bearing sediments, and reasonably describe the influence of hydrate content and effective confining pressure on the mechanical properties of sediments, such as strength, stiffness, dilatancy, and so on.

The seismic responses of soil-pile-isolation pedestal-nuclear island structure and soil-pile-nuclear island structure were studied by large-scale simulated shaking table test. In the test, rubber lead-zinc bearing was used as foundation isolation and placed between pile foundation cap and upper nuclear island structure. The foundation soil was uniform silty clay from an engineering site. The ground motion time history was fitted by RG1.60 response spectrum designed by Nuclear Power Corporation of the United States. The test results show that the isolation bearings can not only change the frequency of the superstructure, reduce the acceleration and the magnitude of the response spectrum, but also dwindle the bending moment of the lower pile, which can reduce the reaction isolation of the superstructure. However, the use of isolation bearings will change the bending moment distribution of pile foundation, thus special seismic design should be made for pile foundation stress and deformation in nuclear power engineering to ensure the seismic stability of the whole soil-pile-superstructure system

To study the fracture dynamic evolution process of grouting specimens under loading conditions, the graded gravel grouting specimen was periodically scanned during the uniaxial compression damage process using a CT scanning system. Based on the image reconstruction technique, the spatial visualization of the fracture structure inside the test grouting specimen block is achieved, and the structural characteristic parameters are characterized quantitatively such as the number and volume of fractures. The gray value and fractal dimension of the CT slices are calculated using Python programming to analyze the mesoscale damage extent at different loading stages of the grouting specimen. It is shown that the specimen’s internal fracture volume shows a trend of slow rise, slow fall, slow rise, and rapid rise. The fracture number shows a trend of increasing firstly and then decreasing during the whole compression stage. When the fracture expansion paths encounter gravel, most of the fractures expand around the gravel location and few fractures expand through the gravel. In addition, the fracture bifurcation expansion mostly appears at the interface between the cement matrix and gravel. The specimen damage process could be divided into four stages in terms of the fracture evolution process inside the specimen: initial defect expansion stage, internal crack compacting stage, fracture expansion stage, and fracture penetration stage. For the slice at the same loading stage of the test specimen, it is found that the value of the damage variable and fractal dimension shows a certain positive correlation, which is similar to the trends of the fracture volume evolution. The research results can provide a reference for the study of the failure process and fracture evolution law of the grouting body.

The pollutants produced by in-situ leaching of uranium ore pose a hazard to groundwater resources through osmotic migration, which has significantly restricted the development of this leaching method. Microbial cementation can effectively reduce the permeability of sandstone uranium ore and prevent the pollutants migrating into the groundwater in the vicinity of the mining area. Therefore, in this study, sporosarcina pasteurii was chosen and tested for acid resistance. The permeability coefficients of the uranium ore sand cemented in condition of different concentrations of cementing solution, volume ratio of bacterial solution and cementing solution as well as grouting rounds were measured using a self-made experimental setup, then, the best value of these parameters was determined. In addition, the microstructure and mineral composition of uranium ore sand before and after bio-cementation were observed using scanning electron microscope (SEM) and X-ray diffraction spectroscopy (XRD) in order to explore the mechanism of the impermeability by bio-cementation. The results show that sporosarcina pasteurii still grows and reproduces well with high urease activity at pH value of 4, indicating that it can adapt to the acidic uranium ore sand. The formation of calcium carbonate can be promoted by increasing the concentration of cementing solution and the volume ratio of bacterial solution and cementing solution within a certain range, and the best cementing solution concentration and volume ratio are 1 mol/L and 1:3, respectively. The permeability reduction ratio of uranium ore sand reaches 95.33% after 7 rounds of bio-grouting. The permeability coefficient of uranium ore sand decreases with increasing the grouting round. The permeability coefficient of uranium ore sand is reduced by up to 99.75% after 11 rounds of bio-grouting, with a value of 2.8×10−5 cm/s. Calcite is the main crystal form of deposited calcium carbonate. It blocks the intergranular pore and cements the sand particles together, which is the main reason for the reduced permeability coefficient of uranium ore sand. The impermeability mechanism of uranium ore sand cemented by microbial induced calcium carbonate precipitation provides important theoretical guidance for the control and reduction of groundwater pollution.

 In order to explore the evolution law of the shear-seepage characteristics of the rock mass in the high pressure hydraulic infiltration zone and fluctuation zone under the coupling action of pressure shear load and fluid infiltration, a new shear-seepage coupling test and shear creep-seepage coupling test were performed on saturated argillaceous shale under different injection water pressures using a new rock shear-seepage coupling test system. The test results show that: 1) With the increase of injection water pressure, the peak shear strength, peak normal deformation and shear creep failure strength of saturated argillaceous shale decrease, which indicates that injection water pressure has a degradation effect on the mechanical strength of rock samples. 2) During the shear-seepage coupling test, the shear stress and normal deformation of the rock sample have obvious up and down fluctuations at the end of the linear elastic change, accompanied by the outflow of water. The sudden changes of shear stress and normal deformation have time-dependent consistency. 3) During the shear creep-seepage coupling test, the seepage rate of water is positively correlated with the injection water pressure. With the increase of the applied level of shear load, the creep deformation of the rock sample is larger and the cumulative amount of seepage water per unit time also increases.

Self-organizing criticality theory provides a new interpretation for the behaviour characteristics and evolution patterns of disordered and non-linear complex systems. Based on this theory, the law of fracture evolution with different rock types was discussed. Considering the influence of body shape on the failure characteristics, uniaxial compression test and acoustic emission (AE) test were carried out on two rock specimens, i.e. cube and cylinder. The acoustic emission information before and after the self-organized critical point during the evolution of rock fracture was analyzed. According to the distributed of the probability density of AE energy, the spatial positioning of AE event and the AE waiting time, and their critical exponent k, productivity exponent α  of after shock distribution, and waiting time distribution exponent δ were analyzed statistically. The results show that the failure processes of both cube and cylinder specimens are self-organization processes from disordered stable state of low energy value to ordered unstable state of high energy value. The body shape has little effect on the self-organization process of its destruction. Comparing with cylindrical specimens, the first phase of cubic specimens from compression to the first critical point of self-organization, volume expansion point, lasts relatively longer, and the self-organization evolution process from the first critical point to the second critical point of self-organization, speak strength point, is also faster. The failure of the cubic specimen is more regular, which is more conducive to failure prediction. Cubic specimen is isotropic in the process of compression, which restricts the development of cracks so the critical index of the whole process of fracture is larger. While the local yield weakening characteristic of cylindrical specimen is obvious, which makes the development of cracks under compression easier and its critical index is smaller. For the productivity exponent α of Omori law of rocks with different sizes, the value α of the second stage of the self-organization evolution of fracture of cubic specimens is greater than 1, while that of cylinderical specimens is less than 1, indicating that the cube specimens have entered the critical instability state before the second critical point. In the large waiting time range (>0.1 s), the critical exponent of the second stage of self-organization evolution of fracture of specimens with different body shapes is larger than that of the first stage, which is consistent with the fact that the frequency of new cracks increases with the self-organization evolution of fracture.

The subgrade mud pumping of heavy-haul railway is widespread and harmful, which seriously affects the stability of tracks and the safety of train operation. The properties of railway subgrade soil, such as the particle size distribution, the void ratio, have a significant impact on the characteristics of subgrade mud pumping under the train load. In this study, a series of remolded samples consisted of silty clay and different contents of kaolin was subjected to mud pumping tests with a self-developed test model, and the influences of different particle size distribution (kaolin content) and different initial dry densities (void ratios) on the characteristics of axial strain, excess pore water pressure and fine particles migration under dynamic load were analyzed. The results show that with the increase in kaolin content and initial dry density, the axial strain and the excess pore water pressure of the samples, the average migration height of fine particles, and the degree of subgrade mud pumping all decrease. We also find that the excess pore water pressure gradient is the leading factor driving the migration of fine particles in subgrade soil, and the interlayer has a promoting effect on the occurrence of subgrade mud pumping.

The use of high-quality materials and the strengthening of soil layers, especially in areas with poor bedding, are among the most important factors in stabilizing and achieving the useful life of building structure. An experimental study on a strip footing coated with unreinforced, geogrid-reinforced, and folded geogrid layers of fine sand is presented in this paper. Testing procedures evaluate variables such as the number of planar geogrid layers, the position of the folded geogrid within the soil, the thickness of the geogrid folded layer, the overlap lengths of a folded geogrid, the spacing within folded layers of geogrid, and several layers of geogrid. Compared to planar geogrid reinforced sand, folded geogrid reinforced sand performed better as a result of static loading. In addition, a critical region was found at a certain depth under the footing, where a geogrid folded results in increased footing settlement. This critical area affects the behaviour of sandy soils with low footing widths. Moreover, the results show that the embedment depth and thickness of the folded geogrid are 0.41 and 0.20 of the footing widths, respectively. By increasing the number of folded geogrid layers, the settlement rate is significantly reduced. It was determined that wrapping the reinforced cases around the surrounding frames significantly improved the bearing capacity, reduced settlement, and allowed them to be used in tight spaces.

In the Wuxia section of the Three Gorges Reservoir area, it is found that there are many deformation signs of sliding-bending along the bedding bank slope, and the cyclic fluctuation of reservoir water worsens the deterioration and instability of the bank leading edge. Taking Qingshi #6 slope in the Wuxia section as an example, an indoor generalized model is constructed to study the catastrophe mechanism of bedding limestone bank slope under the deterioration of rock mass in hydro-fluctuation belt. The research shows that: the bank slope is in a stable state as a whole for a long time before impoundment. After impoundment, with the deterioration aggravation of rock mass, the bank slope deformation intensifies until buckling failure. The deterioration of rock mass shortens the instability process of ‘deterioration-buckling’. Kinematic analysis shows that the peak velocity of the same rock stratum is similar during buckling failure. The movement characteristics of the rear part of the ‘buckling point’ of rock mass are relatively consistent, but the front part is relatively discrete. The buckling failure is the turning point and apex of bank slope energy release. Both displacement and stress show signs of premature failure after gradually increasing with deterioration evolution. The stress produces ‘concentration-release’ around the buckling failure. On the whole, the stress variation is earlier than the displacement variation, indicating that the stress monitoring is more effective. The core of stress monitoring is to determine the ‘key section’. For the ‘deterioration-buckling’ bank slope, the sharp increase of stress at the ‘deflection section’ of the front edge can be an important characterization of the critical instability of the bank slope. The trailing edge pushing always exists in the evolution process of ‘deterioration buckling’, which is the premise of bank slope catastrophe failure. However, the dominant factor of bank slope instability is the continuous deterioration of the rock mass in the hydro-fluctuation belt. The Qingshi #6 slope is currently in the process of evolution toward ‘strong bending uplift’, it may gradually evolve from a stable/basically stable state to an understable state, due to the continuous deterioration of the rock mass in the hydro-fluctuation belt.

As a direct retaining structure in the process of foundation pit excavation, the internal force and deformation of pile under horizontal load have great influence on the safety and economy of foundation pit engineering. In order to calculate the internal force and deformation of the supporting pile more accurately, the nonlinear foundation reaction modulus is obtained according to the nonlinear soil resistance-pile lateral displacement (p-y) curve of pile-soil interaction. At the same time, the Pasternak two-parameter foundation model is introduced to fully consider the continuity of pile side soil deformation. The differential equation of retaining pile deflection considering pile-anchor deformation coordination is derived, and the internal force and deformation of the retaining pile are obtained by the transfer matrix method. Then the calculation program is compiled based on the engineering example, and the calculation results of the program are compared with the monitoring values and the calculation results of the p-y curve method based on the traditional Winkler foundation model. It is found that the traditional Winkler foundation model will overestimate the horizontal deformation and internal force of the retaining pile. The displacement and bending moment calculated by the program can better meet the actual requirements of the project. Furthermore, the finite element software is used for numerical simulation analysis of the engineering example to verify the rationality and applicability of the calculation method of foundation pit supporting piles based on the nonlinear Pasternak two-parameter foundation model.

This paper aims to propose an analytical method for complex supporting problems of deep foundation pit using elastic resistance method and structure mechanical method, with considerations of compatibility of deformation and spatial effects for retaining pile, crown beam, and braces. Comparisons between calculation results and field data indicate the effectiveness of the proposed method, and further parametric study investigates the spatial and size effects of crown beam and braces on the deformation of retaining piles. Results show that the deformation of retaining structure is nonlinearly related to the dimensions and spatial distributions of crown beam and braces. For retaining structure without waist retaining, the maximum displacement of the crown beam increases exponentially with the brace spacing, and the maximum displacement of retaining pile occurs at a depth of about 1/3 of the pile length which gradually shifts to the pile top with the increase of brace spacing. The effect of increasing bracing stiffness to prevent the deformation of retaining structure is limited when the bracing stiffness is larger than a certain limit, and the displacement of crown beam in the side span is shown greater than that in the middle span. Increasing the sectional width of crown beam by certain significance could restrain the maximum displacement of the crown beam.

Based on one-dimensional consolidation-creep tests, comprehensively considering primary consolidation and creep effects, the one-dimensional Koppejan model was selected to characterize the time-dependent deformation of soft soils, and the model was extended to the three-dimensional stress space in incremental form, and the corresponding material subroutine was implemented in ABAQUS software. The subroutine was then applied to a numerical analysis considering pile-soil coupled interactions based on a field prototype test. The time-dependent variations of pile response, additional pressure acting on the pile shaft, and the soil-arching between piles under long-term surcharge loads were investigated, and the mechanism of time-dependent interaction between passive piles and soft soils was revealed. Results show that the additional load caused by the surcharge load is mainly distributed in the relatively soft-weak layer, and increases with increasing duration of loading, but its distribution range is unchanged. With increasing duration of loading, the soil plastic zone between the passive piles enlarges, the arch height of principal-stress decreases, and the soil-arching effect continues to weaken. The weakening law of the soil-arching effect changes with the change of surcharge conditions. The smaller the surcharge distance or the greater the surcharge load is, the longer the time for the pile response reach a steady growth stage, and the more significant the time-dependent influence of soft soil deformation on pile response is. For different thicknesses of soft soils, the distribution range of the additional load acting on the pile shaft is different, resulting in different influences of the surcharge load or the loading duration on the pile response distribution. The deduced extended Koppejan model well reflects the process of time-dependent interaction between the pile foundation and soft soils and provides reference for the prediction of the long-term lateral deformation of pile foundations.

The accurate input of bedrock ground motion has a significant impact on the rationality of the evaluation results of seismic effect characteristics in complex sites. The restart-iteration method is used to separate the incident wave from the downgoing wave contained in the bedrock observation record, and the incident wave is converted into the equivalent nodal force and viscoelastic boundary as the input form and the bedrock boundary condition. The seismic incident wave separation method is proposed which can be used in the site numerical simulation analysis. The IKRH01 array of KiK-NET strong earthquake observation network in Japan is used for numerical verification, and the method is compared with the existing direct nodal force input method and acceleration input method, and the site amplification effect is analyzed from the frequency domain by surface-to-borehole spectral ratio method. The results show that: 1) The incident wave separation method can separate the incident wave at the bedrock of the array and achieve accurate input of ground motion. 2) The spectral ratio obtained by the method of incident wave separation is in good agreement with the peaks of order 2−6 observed by the array, indicating that the method can effectively simulate the seismic site response. 3) By comparing the spectrum ratio of downgoing wave with or without consideration, it is found that the surface-to-borehole spectral ratio within 0−10 Hz is mainly affected by downgoing wave interference, and the site amplification effect caused by incident wave is not significant.

Liquid nitrogen freezing reduces the temperature of environmental soil layer by boiling heat absorption and convection heat transfer of liquid nitrogen in the freezing pipe, and quickly freezes the water in the soil to form a freezing curtain with supporting effect. Compared with the traditional brine freezing technology, the freezing temperature of liquid nitrogen is extremely low, the temperature field is not uniformly distributed, and there are more factors affecting the freezing effect, while the heat exchange of liquid nitrogen freezing process lacks of study. Based on the theory of convective heat transfer, the freezing energy exchange process in the pipe is analyzed, the convection heat transfer coefficient of liquid nitrogen heat absorption is calculated, and the characteristics of the freezing temperature field of liquid nitrogen is simulated. Combined with the field measured data, the reverse heat transfer analysis of the liquid nitrogen convective heat transfer coefficient is carried out, which reduces the calculation error of the convective heat transfer coefficient. The study results show that the liquid nitrogen absorbs heat mainly by boiling heat absorption of liquid nitrogen and convective heat transfer of low-temperature nitrogen. The simulation of the freezing temperature field of liquid nitrogen based on convective heat transfer theory and its heat transfer coefficient needs to consider the change of heat transfer coefficient with freezing time and freezing depth, and a constant heat transfer coefficient cannot accurately reflect the whole process of convective heat transfer, which will lead to the difference between the temperature decline trend and actual measurement during the active freezing period and maintenance freezing period, and between the simulated temperature and actual temperature, the temperature obtained by calculation is relatively low. The freezing time is divided into 16 time periods and the freezing space is divided into 4 areas. The non-uniformity correction of the heat transfer coefficient is carried out to make the heat transfer coefficient a variable that changes with the freezing time and space, which not only conforms to the reality but also reduces the error, and it is more consistent with the practical engineering measured data. The research results can provide theoretical basis and technical reference for similar liquid nitrogen freezing projects.

The failure mechanism of slope instability is complex, and the characteristics of sliding surface often show complex forms such as compression shear-tension failure. Based on the finite element strength reduction method, the limit stress field and strain field of slope are obtained. Starting from the limit stress field of three-dimensional slope, and considering tension-shear composite failure, the positioning problem of slope critical sliding surface is transformed into the initial value problem for solving the first-order quasilinear partial differential equation, namely, the Cauchy problem. The tensile failure mode is adopted in the equal tensile stress area at the scarp of the slope, and the shear failure mode of Mohr-Coulomb yield criterion is adopted in the passive sliding area. In this way, the critical slip surface is determined without assuming the geometry of the slip surface and specifying the slip mode automatically. The three-dimensional slope of gently inclined structural plane and steeply inclined structural plane are studied respectively. Not only the geometric characteristics and distribution of the two are described, but also compared with the jointed homogeneous slope. Finally, combined with the physical model test, the failure characteristics of homogeneous slope under uniformly distributed load in ultimate stress state are studied to verify the correctness and reliability of the method.