The Mohr-Coulomb yield criterion takes on the simplest form in the Mohr stress space, which has thus been most extensively applied in limit analysis and limit equilibrium methods because of its accuracy. However, the Mohr-Coulomb yield surface in the stress space is non-smooth, causing huge troubles to the constitutive integration in the deformation based finite element plasticity analysis. In addressing strength problems, meanwhile, solvers based on the load controlled method (LCM) are hard to bring the finite element model to the limit equilibrium state. Aiming at these issues, the solution schemes are proposed as follows. First, an algorithm named GSPC is designed for the constitutive integration for plasticity with non-smooth yield surfaces. GSPC is always convergent for arbitrary large strain increments, with far more excellent numerical properties than the return-mapping methods available. A solver based on the displacement controlled method (DCM) is developed for the finite element plasticity analysis. The DCM solver is able to bring easily the finite element model into the limit equilibrium state, with no convergence issue, and far more efficient and robust than any LCM solvers. At last, combined with the strength reduction method, the secant method for the factor of safety of slopes is developed, and the location and depth of tension cracks at the slope top are proposed. Keywords: constitutive integration for plasticity; Mohr-Coulomb yield surface; displacement controlled method; slope stability; tension cracks

In order to explore the impact of moisture on the mechanical properties of coal, the triaxial compression tests of raw coal with different moisture contents are carried out by using the triaxial servo-controlled seepage equipment for thermal-hydro- mechanical coupling in coal containing methane. Based on elastic damage mechanics, the damage variables of coal with different moisture contents are deduced, and the damage constitutive model of coal under hydro-mechanical coupling is established, the deformation characteristics of coal with different moisture contents are obtained. The results show that: (1) the deformation and failure process of coal under different moisture contents are similar, which can be divided into pre-peak stress stage, post-peak stress stage and residual stress stage; (2) as the moisture content increases, the peak stress, elastic modulus and brittleness of coal decrease, but the Poisson's ratio increases; (3) the damage constitutive model of coal can better represent the deformation characteristics of coal in the complete stress-strain process under different moisture contents, which is suitable for the analysis of the triaxial compressive stress-strain of coal under different moisture contents; (4) both the damage correction coefficient q and the damage constitutive coefficient n determine the curve shape of the damage constitutive model. The damage correction coefficient reflects the characteristics of residual deformation of coal, and the damage constitutive coefficient reflects different degrees of post-peak strain softening of the stress-strain curve.

Setting a flexible cushion behind the rigid retaining wall can increase the actual lateral displacement of the backfill and effectively reduce the earth pressure acting on the wall. A self-made model box was used to conduct laboratory tests to simulate the working conditions of the retaining wall with EPS cushion behind the wall in the static state and the translation mode, and to explore the distribution of the static earth pressure and active earth pressure of the retaining wall under different backfill widths, and to study the influence of EPS cushion parameters on its decompression performance. By defining the decompression efficiency of the EPS cushion, the decompression performance of the EPS cushion behind the retaining wall was quantitatively analyzed. The results show that under limited backfill conditions, there is a gap between the maximum decompression efficiency of the EPS cushion and the equivalent decompression efficiency of the active earth pressure. However, under this circumstance, parameters of the EPS cushion have little effect on the decompression efficiency. As the backfill width gradually increases to the semi-infinite soil range, the maximum decompression efficiency of the EPS cushion gradually increases and then keeps stable at the equivalent decompression efficiency of active earth pressure.

Enzyme induced calcite precipitation (EICP) technology is applied to mineralize dispersed soil and improve dispersion resistance. The dispersed soil was sampled from a dam filler of reservoir in Hulunbuir, Inner Mongolia, and acted as parent soil during mineralization process. The dispersion of the soil sample before and after bio-mineralization was identified and evaluated by pinhole test, double hydrometer test and broken soil test. The results showed that the anti-dispersion ability of soil improved by bio-mineralization was significantly enhanced, especially by the microbial modifier prepared by urease solution. When the improved soil samples experienced 50, 180, 380 mm and 1 020 mm water heads in the pinhole test, the outflow water always remained clear and transparent, the water outlet was flat, and the size of the pinhole remained unchanged. The soil samples after the pinhole test were collected for broken soil test, and there was no colloidal particle dispersion during the test. During the double hydrometer test, it was found that the dispersity of soil samples improved by urease solution was less than 30%, which was reduced by about 50% compared to that of the unimproved dispersed soil, and the properties of soil sample changed from dispersive to non-dispersive. But for soil samples improved by microbial solution, the dispersity was 41.1%, which was 22% lower than that of the unimproved dispersed soil, the properties of soil sample changed from dispersive to transitional. The microbial modifier prepared by urease solution played a more adequate role in the mineralization process for fine-grained soil, and it was superior to the microbial modifier prepared by microbial solution in terms of the improvement of dispersed soil modification and the anti-dispersion ability improvement. In this paper, it is the first time that the bio-mineralization base on EICP technology was applied to the improvement of dispersed soil. This is an innovation combining green bio-mineralization technology with dispersed soil improvement in water conservancy damming engineering. It has a good application prospect in improving the dispersed soil of damming filler.

The rock mass in the hydro-fluctuation belt of the reservoir bank slope is subjected to long-term water-rock interaction and frequent moderate-low intensity reservoir earthquake. The deterioration of the mechanical properties of the rock mass caused by this directly affects the dynamic response and seismic capacity of the reservoir bank slope. Based on this, the settings of the fluctuating zone of the bank slope of the reservoir are simulated, and the water-rock interaction test to simulate the periodic rise and fall of the reservoir water level is designed and carried out. In the course of the test, the cyclic loading and unloading method is used to simulate the influence of seismic action, and the sequential action of water-rock interaction and cyclic loading and unloading is mainly considered. According to the test results, the following conclusions are obtained. (1) The dynamic parameters of the rock sample generally change exponentially from steep to gentle under the water-rock interaction. After considering the sequential action of water-rock interaction and cyclic loading and unloading, the deterioration rate and trend of dynamic parameters of rock samples increase obviously, indicating that frequent moderate-low intensity reservoir earthquakes can obviously promote the damage development of bank slope rock mass in the environment of water-rock interaction for a long time. (2) Under the action of water-rock interaction and cyclic loading and unloading, the microstructure of rock samples gradually loosens from the compacted state, and the corresponding integrity degradation coefficient and the secondary porosity also show a trend of steepness and then slowness. Among them, the microstructure changes of rock samples under the sequential action of periodic water-rock interaction and cyclic loading and unloading are the most significant, followed by the rock samples with initial cyclic loading and unloading damage, and the change of rock samples under the water-rock interaction alone is the smallest. The changes and differences of the microscopic structure of the rock sample under different schemes also govern the degradation law of its dynamic characteristics. (3) Under the long-term water-rock interaction and frequent moderate-low intensity reservoir earthquakes, the internal damage of the reservoir bank slope will gradually accumulate and develop, which will directly affect the dynamic response characteristics and seismic capacity of the reservoir bank slope. Therefore, the degradation law of the dynamic characteristics of the bank slope rock mass should be systematically considered in the analysis and evaluation of long-term seismic performance of reservoir bank slope.

The physical and mechanical properties of coral sand particles determine the macro mechanical behaviors of coral sand, which is closely related to several geotechnical engineering problems, especially those related to particle breakage. The apparent and internal structure characteristics of coral sand particles were studied by SEM and X-CT tests. It was found that the coral sand particles were porous. The porosity of coral sand particles with biological skeleton components was as high as 41%, while the porosity of coral sand particles formed by weathering and depositing was less than 20%. Most of the pores on the surface of the particles can be connected with the interior so that the gas can flow through the particles. The failure type of coral sand particles was closely related to the porosity. The coral sand particles with low porosity were broken into fragmentations step by step, similar to silica sand particles. The coral sand particles with high porosity were gradually compressed with the failure of skeleton. The failure of the skeleton was accompanied by the formation of fine detritus which did not detach from the skeleton until the particles were compressed into powder. The elastic modulus, yielding strength and crushing strength of circular, branched and flaky coral sand particles were determined by compression tests and statistical analysis. The correlations between particle strength and particle size was clarified, which provided parameter basis for studying the mechanical properties of coral sand. Furthermore, the stress-strain curves of yielding and crushing were exponentially distributed, which laid a foundation for further exploration of particle crushing characteristics in the future.

Laterite is prone to aggregate and difficult to disperse. When treated with lime, it actually adheres to the surface of aggregates in fact, resulting in inhomogeneous distribution inside and outside. In this study, two groups of laterite were selected with different aggregate sizes ( 5.0 mm and 0.5 mm). A series of mechanical and hydraulic properties tests, such as shrinkage test, compression test and direct shear test, were conducted, and the effects of hardening and intergranular cementation on the surface of treated laterite aggregates were evaluated. The results showed that aggregate size, initial water content, and treated method significantly affected the treating effect. Compared with the treatment with lime alone, the metakaolin-lime cooperation method was better, with reduced compressibility, increased cohesion and reduced shrinkage. However, the treatment effect was influenced by the aggregate sizes of laterite, and the improvement of mechanical and hydraulic properties of laterite declined with the increasement of aggregate size. Based on this, it can be inferred that after treatment, “hard shell” was formed on the surface of laterite aggregates, which improved the compressive resistance and surface roughness of the aggregate. Cementations were formed between aggregates, inhibiting the shrinkage behavior and improving the cohesion, but after aggregate size increased, the influence scope of metakaolin-lime was limited to the surface of aggregates, and the aggregate size effect counterbalanced the treatment effect of metakaolin-lime.

To study the effect of the loading rate change on the deformation and strength properties and creep behavior of mudstone, a series of uniaxial compression tests and graded loading creep tests was conducted on mudstone specimens at four loading rates (0.005, 0.05, 0.5, and 3 mm/min). The test results find that the mudstone exhibits an obvious loading rate change effect, which is represented by an isotach viscosity behavior. When loading at a constant rate, different stress-strain relationships are observed and corresponded to different constant loading rates. When loading at variable rates, as the loading rate changes, the stress-strain relationships also change. In addition, the loading rate of mudstone prior to creep has a large impact on the creep deformation and creep rate. As the loading rate of mudstone increases before creep, the amount of creep deformation and creep rate show a gradually increasing trend. The mudstone creep rate shows a gradual decay trend over time, and the decay process can be divided into three phases: linear decay, logarithmic decay and stable decay. Furthermore, based on the three-component model and loading rate variation effect, an elasto- viscoplastic constitutive model was established. The developed constitutive model was used for the numerical modeling of mudstone laboratory tests. Compared the modeling results to the laboratory test results, it is found that the elasto-viscoplastic constitutive model can properly simulate the loading rate change effects on the mechanical properties of mudstone under uniaxial compression conditions.

The jointed rock mass exhibits an obviously instantaneous plastic strain under fatigue loading, and thus it is imperative to establish a fatigue constitutive model of jointed rock considering instantaneous plasticity. Based on the assumption that the relationship between the plastic stress of the joint and stress follows a power function, and the accelerated fatigue strain is a second-order nonlinear viscous strain, a joint plastic fatigue component and a double-triggered nonlinear viscous fatigue composite component are proposed. Then a new elastic-plastic viscous fatigue model of jointed rock is established. The results reveal that the proposed model can accurately simulate the fatigue strain of intact rock and jointed rock. Moreover, the proposed model can simulate the stationary fatigue curve of jointed rock mass under fatigue loading, and it can also be applied in the simulation of instantaneous elastic-plastic fatigue, decelerated fatigue, constant speed fatigue and accelerated fatigue of jointed rock under non-stationary fatigue. The model fitting results show that the instantaneous fatigue plastic strain of jointed rock accounts for a large proportion of the instantaneous fatigue strain which should not be ignored. The results of this study are of great reference value in the prediction of fatigue strain and fatigue stability of jointed rock in rock engineering.

In general, the steel anchor cable can effectively reduce the deformation of the slope body, and is useful for slope reinforcement when the seismic intensity is low. However, the anchored rock mass deforms excessively under strong earthquake conditions, and conventional prestressed anchor cable cannot sustain the large deformation, which leads to the catastrophic slope instability and failure. Additionally, the corrosion of steel anchor cable often occurs under the groundwater containing corrosive substances. In view of this, the dynamic response of the slope reinforced using the new basalt fiber reinforced plastics (BFRP) and the unsupported slope was compared through the large-scale shaking table tests, aiming to provide a scientific basis for the dynamic rational design of BFRP anchor cables for reinforcement of high slopes. The result shows that: compared with the slope supported by BFRP, the unsupported slope has obvious deformation stages during seismic loading, which can be divided into elastic stage, plastic stage, plastic reinforcement stage, and failure stage. When the peak value of input wave is less than 0.2g, both the slope supported by BFRP anchor cable and the unsupported slope are in elastic state. In addition, the peak acceleration value of the slope supported by BFRP anchor cable is greater than that of the unsupported slope, which indicates that the BFRP anchor cable can effectively improve the rigidity of the slope. Under the action of seismic wave in the same condition, the displacement spectrum value of each measured point in the unsupported slope is greater than that of the corresponding measured point in the slope supported by BFRP anchor cable, which indicates that the BFRP anchor cable can reduce the deformation and improve the seismic performance of the slope in the slope supporting engineering.

As a flexible structure, reinforced earth retaining walls have been widely used in the field of civil engineering. However, excessive horizontal displacement of reinforced earth retaining wall due to earthquake could affect its service performance. Therefore, it is very important to develop an effective analytical method to calculate the horizontal displacement of reinforced earth retaining wall under earthquake. The reinforced earth retaining wall was divided into two regions for calculation based on the different movement characteristics of the backfill behind the wall. The key factors affecting the horizontal displacement of the reinforced earth retaining wall in different regions were discussed. Based on Mindlin displacement theory and pseudo-dynamic method, the calculation method of horizonal displacement in different regions under the earthquake, under the assumption of no soil-reinforcement relative slippage, was proposed and the influence of soil-reinforcement relative slippage on calculated results was studied. This method is further verified by centrifuge model test and can be used in the seismic dynamic analysis of general reinforced earth retaining walls. This provides basis for the dynamic design and stability analysis of reinforced earth retaining walls.

Post-grouting technique has been applied to the infrastructure construction of coral reefs, but there has been little research about the horizontal bearing behavior of post-grouted piles in calcareous sand. Based on the case of post-grouted piles in calcareous sand under horizontal load, the horizontal bearing rule of ungrouted and post-grouted piles in calcareous sand was studied comprehensively by laboratory model tests, and the influence of post-grouting on the horizontal bearing behavior of pile in calcareous sand was investigated. The infiltration and diffusion of injected cement grout in calcareous sand were analyzed through soil excavation of post-grouted piles. The results show that the lateral critical load and the lateral ultimate load of post-grouted piles in calcareous sand are significantly improved compared with those of ungrouted piles under the same condition. Besides, the ability to control lateral deformation under grouting is better than that of piles without grouting. The proportional coefficient m of the lateral soil resistance coefficient of ungrouted and post-grouted piles gradually tends to be consistent with the increase of the lateral displacement of the pile head, and the bending moment of pile shaft and the soil pressure around piles are mainly concentrated in the upper part of the pile and soil. The lateral bearing capacity of piles is greatly affected by the upper level of soil, and grouting at the pile side can effectively increase lateral bearing capacity by improving the upper soil physico-mechanical properties. In addition, according to the soil excavation analysis, the cement grout injected at the pile side is mixed with calcareous sand to form a stable structure of cement stabilized soil. This provides the improved lateral bearing capacity of the pile in calcareous sand.

The drilling with pre-stressed concrete pipe cased pile (referred to as DPC pile) is a new type of large-diameter (800?1 400 mm) non soil-squeezing PHC pipe pile with drilling hole, sinking pile and discharging soil occurring simultaneously. DPC pile is energy-saving and environmental-friendly. In this paper, in-situ tests, theoretical calculation analysis and physical simulation tests are carried out to compare and analyze the better vertical load-bearing capacity of this new type of pile, the skin friction distribution characteristics and the load transfer characteristics. Based on the aforementioned tests, the following conclusions are obtained. 1) In the in-situ tests, DPC pile is a type of end bearing friction pile, whose vertical bearing capacity is mainly dominated by skin friction with a proportion variation ranging from 67.84% to 72.85%. The bearing capacity of DPC pile is closely related to the grouting effect and it has been increased by 33.42% and 23.16% compared to the large diameter drill hole pile and hammered pipe pile, respectively. When the sediment thickness at the bottom of the DPC pile is small, the load-displacement curve belongs to slow deformation type (pile No. 1), otherwise it belongs to a steep drop type (pile No. 2). 2) Indoor physical model tests in sand show that the load-displacement curves of DPC pile, large diameter drill hole pile and hammered pipe pile belong to the steep drop curves under the condition that all the three types of pile mentioned above are not rock-socketed. The load-bearing capacity of DPC pile has been improved by 18.60% compared with large diameter drill hole pile. 3) The skin friction of piles with different manufacturing processes are quite different, i.e. the skin friction of DPC pile is the largest, followed by the large diameter drill hole pile, and finally the hammered pipe pile, which is related to the physical test of the simulating mud on the side of large diameter drill hole pile. The distribution rule of the skin friction of all pile types along the depth of the pile body shows a rule “a large portion in the middle and a small portion at both ends”. As the load increases, the position of the maximum skin friction gradually moves downward from the top of the pile to its deepest position until the pile foundation is damaged. 4) Under the ultimate bearing capacity, the skin friction of DPC pile is 6 061.65 N, which accounts for 74.40% of its ultimate bearing capacity (8 147.62 N). It can be implied that the DPC pile is a type of end bearing friction pile and is mainly dominated by skin friction.

A large number of particle crushing test results show that there is a noticeable size effect on the particle crushing strength. The particle crushing strength decreases with the increase of particle size. However, the influence of particle shape on the size effect of particle crushing strength is still unclear. In this paper, particle scanning, particle shape analysis, and single particle compression test of sand-gravel and limestone mixture of Dashixia rockfill dam are carried out. The sphericity and convexity of sand-gravel are larger than those of the limestone mixture. The particles of sand-gravel tend to be round, while the particles of limestone mixture are angular. The test results show that the crushing strength of both kinds of rockfill particles exists noticeable size effect. The applicability of different strength size effect models is then evaluated. Comprehensive analysis of the test results together with the data collected from literature shows that the particle shape has a significant influence on the size effect of the particle crushing strength. The more irregular the particle shape is, the smaller the Weibull modulus of the particle crushing strength is, and the more obvious the size effect of the particle crushing strength is.

Rough cross joints widely exist in actual rock mass. The laboratory study on the mechanical fracture evolution of specimens with rough cross joints at different angles can provide important guidance for rock mass engineering. Based on Barton joint profile, we use 3D printing to generate rough cross joint models with different angles. Then we carry out uniaxial compressive tests after pouring the specimens. The deformation characteristics of the surface are processed and analyzed by the digital image correlation (DIC) technology. The results show that the uniaxial strength of specimens with larger dips of primary joint is less than that of specimens with smaller dips. The influence on the uniaxial compressive strength and elastic modulus of the specimen is most significant when the angle γ between the primary and secondary joints is between 45° and 60°. We analyze the obtained strain contour figures by DIC, as well as the whole range of strain of joint tips and strain rate surge points. The observations are listed as follows. The fracture initiation mainly occurs at the upper and lower ends of primary joint and the upper end of secondary joint, and the initiation stress is between 90% of the peak stress and the peak. The fracture propagation rate is slow in the yield stage, and the rapid expansion mainly occurs in the post-peak stage. The fracture initiation direction of the rough cross joint specimen is different from that of the smooth joint specimen. The fracture at the tips of joints is mostly in the form of shear, and evolves into tensile fracture under the action of maximum principal stress. The stress intensity factor at the lower end of the primary joint is larger than that at the upper end of the secondary joint, which indicates that the primary joint plays the main role in the fracture of the specimen. KII at the joint tipis is greater than KI, which indicates that the shear effect is greater than the tensile effect on the initiation and propagation of fracture.

Moment tensor inversion theory is an effective method to study the rock failure mechanism. However, the inversion results are prone to large errors, which can mislead the understanding of fracture mechanism. In order to achieve a better understanding of the generation process and the mechanism of the rock macro-fracture surface, we perform a location analysis of source events based on the uniaxial compression test of a granite sample, with the help of ultrasonic testing and acoustic emission monitoring. The events near the macro-fracture with small location errors are selected for moment tensor inversion. Then, we use the network calibration method to calibrate the sensors so that more accurate moment tensors can be obtained. The results show that the source event locations are in good agreement with the locations of the specimen's macro-fracture. After the sensors having been calibrated, there are a few noticeable observations. The inversion root-mean-square (RMS) errors of moment tensors reduce significantly. The distributions of events on the T-k plot and P/T axis plot become more concentrated. The shear component and the proportion of different types of events change accordingly. The distributions of strike, dip and rake angles of the events become more concentrated, which are in general consistent with the macro-fracture of the specimen. The tensile angles of some events change from negative to positive. The above results reasonably explain the failure process and mechanism of the specimen and highlight the importance of sensor calibration for the moment tensor inversion, which can be a useful tool to provide guidance and reference for a deeper understanding of rock failure mechanism.

For quasi-static pushover test of soil-underground structure system, the optimization of model box type and the influence of lateral boundary displacement distribution in the test are studied by the numerical method in this paper. Firstly, a quasi-static pushover test scheme of soil-underground structure system is introduced, and then the free-field finite element model and the soil-structure finite element model of the quasi-static pushover test are established and analyzed. It compares the distributions of the equivalent seismic load, the soil-structure interaction forces, the seismic capacity of the structure and the equivalent plastic strain nephogram of concrete structures under different lateral boundary displacement distributions. The results show that the distribution of the lateral boundary displacement has influences on the distribution of the equivalent seismic load and the soil-structure interaction forces and the structural inner forces. In particular, the lateral boundary displacement distribution has a significant impact on the test results of the multi-story model structure, and may even affect the failure process and weak components of the multi-story model structure. Due to the randomness of seismic load and the diversity of model structure, it is reasonable to use laminar shear box with adjustable lateral displacement distribution in the quasi-static pushover test of soil-underground structure system.

The revival of ancient bank landslide is a serious geological hazard in reservoir operation. In order to study the deformation characteristics and instability mechanism of ancient bank landslide, a large-scale physical test model was designed based on Outang landslide which is a typical multi-phase ancient bank landslide. By simulating the fluctuation of reservoir water, rainfall and their combination, the curves of pore water pressure and earth pressure with time and digital image data of landslide evolution were obtained. Results indicate that the three-phase sliding masses that compose the landslides have different deformation characteristics under the reservoir water level fluctuation and rainfall. The deformation due to the fluctuation of reservoir water is mainly concentrated in the first phase sliding mass. The rapid rise of the water level has no obvious effect on the first phase sliding mass. But the rapid decrease of water level induces a local retrogressive sliding at the toe of first phase sliding mass. Heavy rainfall causes a local retrogressive sliding at the toe of the first phase sliding mass, and the stability of the second and third phase landslides decrease obviously. The failure mode under the rapid decline of water level and heavy rainfall is local retrogressive sliding at the toe of the first phase sliding mass or/and sliding of the third phase sliding mass. The experimental phenomena coincide with the deformation characteristics and the developing tendency of actual reservoir landslide. This study provides the deformation characteristics and instability mechanism of the ancient landslide in reservoir bank under the condition of reservoir water level fluctuation and rainfall, which is helpful for the research and prevention of similar landslides.

Gas hydrate bearing sediments can be regarded as a composite material composed of matrix phase (soil particles, pore water and gas) and inclusion phase (pure hydrate crystals). In this paper, the multi-scale method that is commonly used in the field of composite materials research was adopted to study the mechanical properties of gas hydrate bearing sediments. The constitutive relationship between the matrix and hydrate phases was characterized by the critical state elastoplastic-constitutive model related to the sand state and the elastic-brittle model, respectively. Meanwhile, the factor of hydrate activity was introduced to represent the slip and fracture of hydrate crystals during the triaxial shearing process the proportion of hydrate crystals which can bear the load effectively in the deformation process. Based on Eshelby’s equivalent inclusion theory and Mori-Tanaka method in the meso-mechanics theory, the equivalent elastoplastic stiffness matrix of gas hydrate bearing sediments was derived. And then, an elastoplastic constitutive model of gas hydrate bearing sediments was established considering the occurrence mode, strength, strain softening and dilatancy of gas hydrate bearing sediments under different confining pressures, different gas hydrate bearing sediments contents and different hydrate occurrence modes. The physical meaning of the proposed model was clear, the form was simple, and all the parameters included in the proposed model were easy to be obtained through simple laboratory tests. Finally, the model was verified by the existing experiments data. The results show that the proposed model can well describe the mechanical properties of gas hydrate bearing sediments under different test conditions.

The analysis of joint surface damage of rock mass under dynamic loading is helpful to grasp the essential characteristics of jointed rock mass failure. In view of the current situation that few studies have been conducted on the impact of joint morphology on dynamic compression failure of jointed rock mass, we use the modified split Hopkinson pressure bar (SHPB) device to operate impact loading test on the artificial rough joint sample. Using the 3D scanner and other equipment, the damage characteristics of joint surface under multiple low-amplitude impact loads have been observed and studied quantitatively. The results show that under multiple impact loading, the amplitude of the transmitted wave is reducing, and the transmission ability of the stress wave at the joints is severely weakened. The wave velocity detection technique has been used to verify the fact that the damage of rock under multiple impact loads is reduced, whereas the damage of joint surface is more obvious. The overall undulation of rough joint surface decreases and the joint roughness increases. The morphology of joint surface including the joint matching coefficient (JMC), the joint distribution and the joint undulation are confirmed to have different influences on the joint dynamic damage effect. At the same time, we calculate the dissipated energy of joint samples using the experimental data to define the damage variables. We find that the reduction of joint matching coefficient (JMC) aggravates the damage degree of joint surface. However, by comparing the change of damage variables, the results show that there are still limitations in using the damage variables to fully describe the damage of jointed rock mass.

Based on the application and promotion of polypropylene (PP) fiber-reinforced loess in loess slope protection, the anti-erosion performance and slope protection effect of polypropylene fiber-reinforced loess were discussed. A series of laboratory experiments was conducted to study the effects of fiber length and fiber content on the shear strength, disintegration resistance, and permeability coefficient of reinforced loess. Based on the optimum mixture ratio of fiber-reinforced loess obtained by the test, the rainfall scouring model test was carried out. The results showed that the PP fiber could effectively improve the shear strength and disintegration resistance of loess. With the increase of fiber content and fiber length, the cohesion and disintegration rate of fiber-reinforced loess decreased first and then increased. When the fiber length was 15 mm and the fiber content was 0.5%, the shear strength and disintegration resistance of the fiber-reinforced loess were optimized. Compared with plain loess, the cohesion of fiber-reinforced loess increased by 135.3% and the disintegration rate decreased by 91.7%. The permeability coefficient of loess was improved by adding polypropylene fiber. The saturated permeability coefficient of PP fiber-reinforced loess increased with the increase of fiber content, but decreased with the increase of fiber length. The slope protection effect of PP fiber-reinforced loess was obvious. When the slope ratio was 1:1.5, 1:1 and 1:0.75, compared with the unprotected slope, the scour rate of protected slope was reduced by 90%, 90.4% and 87.3%, respectively, and the cumulative scour amount of protected slope was reduced by 85%, 85.5% and 83.6%, respectively.

The aim of this study is to investigate the variation of sandstone mechanical properties under the condition of spilt after high temperature treatment. We heat-treat the sandstone sample at 400–1 000 ℃ and measure its physical properties. Based on that, we use digital image correlation (DIC) to record and analyze the evolution of strain field, crack generation, propagation and penetration process of sandstone that treated by different temperatures under Brazilian test. The results show that: With the increase of temperature, the mass of sandstone decreases, the volume increases, and the P-wave velocity decreases rapidly. When the temperature is lower than 800 ℃, the tensile strength of heated sandstone shows a downward trend, but the overall decrease is not significant, approximately 10%. The influence of high temperature on the tensile strength of sandstone is much greater than that of the compressive strength. When the temperature exceeds 800 ℃, the tensile strength decreases rapidly because of the increase of cracks inside the sandstone. Therefore, 800 ℃ can be regarded as the temperature threshold for the tensile deterioration of sandstone. As the heating temperature increases, the pores and fractures of sandstone keep developing, which reduces the difference of strains between the edge and the center of the Brazilian disk.

The scientific prediction of the TBM penetration rate is of great significance to the selection of hydraulic tunnel construction methods, construction schedule and cost estimation. In view of the high nonlinearity, fuzziness and complexity of TBM excavation process, and in order to improve the prediction accuracy and computational efficiency, the partial least squares regression (PLSR) has been applied to extract the principal components of the influencing parameters. Then the deep neural network (DNN) is employed to train and forecast the TBM penetration rate. A prediction model of TBM penetration rate based on the coupled method of PLSR and DNN is proposed. Based on the measured data of the double-shield TBM construction of a water conveyance tunnel in the Lanzhou water source construction project, six impact parameters including the rock uniaxial compressive strength, rock uniaxial tensile strength, cutter head thrust, cutter head speed, rock mass integrity coefficient and rock Cerchar abrasiveness index are selected to verify the prediction reasonability of the model. The fitting and prediction accuracy of the different prediction methods are compared and analyzed. The research results show that the PLSR can effectively overcome the problem of multiple collinearity between the independent variables. The extracted principal components are trained as the input layer of the DNN, which simplifies the structure of the neural network. The PLSR-DNN coupled model effectively avoids the over-fitting and inadequate fitting problems. It has the characteristics of fast convergence, stable solution and high fitting accuracy. The average relative fitting error of the PLSR-DNN prediction model is 2.96%, and the average relative prediction error is 3.27%. The fitting accuracy and prediction accuracy of the PLSR-DNN prediction model is significantly higher than those of PLSR model alone, BP neural network model and SVR model, respectively.

Energy pile is a new building energy-saving technology, which has both functions of the bearing performance and the ground source heat pump heat exchanger. Based on the pile foundation engineering project of Zhoukou Normal University gymnasium in Henan province, field tests on the thermo-mechanical response and bearing capacity of PHC energy pile under cooling-heating cyclic temperature are carried out. The temperature and the strain of PHC energy pile are measured. The temperature-induced stress, side resistance, and heat exchange performance are analyzed and discussed. Test results show that: the distribution of the temperature-induced stress along pile depth varies greatly under cooling-heating cyclic temperature in this study. There is some negative shaft friction resistance developed in the upper part of the pile. The multiple relationship between the maximum thermal stress and temperature difference is 212 or 115 under summer or winter mode. Finally, a calculation formula of pile-soil friction coefficient considering temperature effect is proposed. Using this formula, the calculation method of bearing capacity of PHC energy pile is modified. The calculation results are in good agreement with field test results.

The vibration induced by human activities such as rail traffic, power machine, blast construction and pile driving could seriously influence the normal use of adjacent buildings, the production and use of precision instruments, and the normal production and life of human beings. The control of environmental vibration has become a research focus of soil dynamics. In this paper, a newly designed combined vibration isolation barrier, i.e., wave impeding block (WIB) with incorporation of Duxseal (DXWIB), is proposed to reduce the ground vibrations, and the isolation performance is evaluated by field experiment under harmonic vertical excitation within 0–3 s. Through a set of tests, the amplitude and mean value of ground vibration acceleration and displacement with different embedded depths, DXWIB thicknesses, excitation forces and excitation frequencies are obtained and compared. The corresponding curves of amplitude attenuation ratio are drawn. The test results show that: compared with vibration in the horizontal direction, the isolation effect of DXWIB on ground vertical vibration is better. The vibration isolation efficiency of DXWIB barrier varies unevenly with the distance. When DXWIB is embedded in the foundation, the attenuation coefficient of surface displacement amplitude is less than 1. Compared with the influence factors such as DXWIB thickness, excitation force and excitation frequency, the embedment depth of DXWIB has the most significant influence on the vibration isolation effect, and there is a best buried depth and a critical thickness. DXWIB can improve the characteristics of WIB only for low-frequency vibration damping below 10 Hz, and increase the frequency bandwidth of vibration damping. From the experimental data, it has good vibration isolation effect at 5–70 Hz.

In the failure process of slopes, the contribution of different mechanical or material parameters to the stability is different and dynamic. In the context of shear strength reduction method (SRM) for stability analysis, it is of great significance to determine the factor of safety (FOS) by considering non-proportional reduction for these different mechanical or material parameters. This study firstly examines the mechanism of energy evolution in the process of slope failure. Then, the contribution of different mechanical parameters to dissipated energy evolution is weighted in conducting SRM, based on which we proposed a new method to calculate the FOS with multiparameter non-proportional reduction of shear strength parameters. This method can reflect the characteristic of FOS following the whole reduction path of different shear strength parameters. Subsequently, the proposed method is verified by examples. Finally, the influence of the reduction step and reduction path of the non-proportional reduction factors on the calculated FOS results is discussed.

Energy tunnel, which is based on ground source heat pump system, is one of the green, economical and efficient geothermal heat exchange techniques. It can integrate both the anti-freezing and heat preservation for tunnel. Based on the Yinchuan-to-Xi′an high-speed railway tunnel located in loess region, the heat exchange tubes are placed in series in the tunnel invert, and the ground source heat pump system has been built. The heating system is operated under different input powers as well as the inlet and outlet temperature, and the temperature and stresses of the inverted arch are measured. The thermal response characteristics of the tunnel under difference input powers are discussed and analyzed, including heat transfer capacity and thermal induced stresses, etc. Under this field test condition, the results show that the temperature of the inverted arch of tunnel has increased by 4.2℃ and 7.1℃ under 0.5 kW and 1.0 kW input power, respectively. With the increase of water temperature, the invert temperature increases slightly in a short period of time. When the heat propagation path has stabilized, the invert temperature finally presents a linear relationship. The increment of axial stress of the inverted arch of tunnel is larger than that of the longitudinal stress. The axial stresses are 1.15 and 1.29 times of longitudinal stresses under 0.5 kW and 1.0 kW input power, respectively.

The deep excavation of foundation pit in soft soil layer will cause serious disturbance to the soil at the bottom of the pit. Affected by excavation disturbance, the mechanical properties and stress state of the soil at the bottom of the pit will change. Hence, it is important to accurately evaluate the degree of soil disturbance caused by excavation and the influence of disturbance on soil mechanical properties. Based on the summary of the existing evaluation methods of soil disturbance, taking the foundation pit excavation of Taihu tunnel as an example, the distribution of disturbance degree and the depth of strong disturbed zone of soil under the center of the pit bottom under different excavation depths were studied by using the finite element simulation method. Then, taking the undrained shear strength as an evaluation index, a method for evaluating excavation disturbance of clayey soil based on the cone tip resistance in the piezocone penetration test (CPTU) was established. The soil disturbance calculated through cone tip resistance was agreeable with that determined by numerical calculation. Finally, combined with the soil disturbance determined by the finite element method, the settlement of disturbed soil at the bottom of the pit under different base additional stresses was calculated considering the settlement of soil disturbance. The results showed that the soil disturbance would cause a significant increase in the base settlement. When the base additional stress increased from 100 kPa to 150 kPa, the ratio of base settlement with soil disturbance to that without soil disturbance would increase from 1.43 to 2.24.

The calculation of total water inflow of foundation pit is the key of a foundation pit dewatering scheme. In this scheme, influence radius is a parameter of great importance. At present, empirical formulas, empirical values and graphic methods are usually used to estimate the influence radius in the industry. The empirical formula takes the permeability coefficient and drawdown of dewatering well as the main factors to determine the influence radius, while it takes less consideration of other influencing factors into account. The measurement and drawing errors existing in graphic method have great influence on the results. In this paper, a finite element method is proposed to calculate the influence radius based on the principle of minimum total potential energy in the real domain. When the water level of well reaches the control level, taking the original stable water level of the groundwater as the upstream hydraulic head, the water level of the dewatering well as the downstream hydraulic head, the water leaping zone between the control water level and the water level of the well as the escape boundary, and the influence radius as the horizontal distance of seepage field, the calculation of the influence radius can be simplified to the calculation of the horizontal size of the model with the upstream boundary head, the downstream boundary head and the escape boundary known. Two engineering scenarios were calculated using this method. Results obtained were compared with the results of field pumping tests and empirical formula solutions. The results show that the algorithm in this paper can accurately calculate the influence radius. The outcome of this research can be used to improve the calculation accuracy of foundation pit water inflow, make the design of foundation pit dewatering more reasonable, and have potential engineering application value.

The inhomogeneity of layered rock mass is mainly contributed by the inhomogeneity of bedrock and the inhomogeneity of bedding plane joints. It is important to consider the different homogeneity of bedrock and bedding plane joints. Therefore, this paper combines the WLPB model and the WSJ model to characterize the inhomogeneity of bedrock and bedding plane joints, respectively. We put forward a new theory and calculation method of micro-inhomogeneous contact mechanics model of bedded rock mass, and analyze the deformation characteristics, failure modes and micro-evolution laws of bedded rock samples under uniaxial compression. The results show that the elastic modulus, peak strength and failure mode of layered rock samples present obvious anisotropic characteristics, which are in general consistent with the laws of laboratory tests. It demonstrates the rationality and adaptability of the developed inhomogeneous microcosmic contact model of layered rock mass. When the mechanical behavior of layered rock mass is controlled by the bedding plane, the inhomogeneity of bedding plane becomes an important factor affecting the macromechanical characteristics of layered rock mass. When the bedding plane plays a controlling role, the influence of bedding plane spacing is not obvious on the peak strength of layered rock samples, but it is obvious on the deformation characteristics of rock samples. The paper reveals the micro fracture mechanism and transformation law controlled by the inhomogeneity of bedding plane of layered rock mass with different inclination angles under uniaxial compression.