The hybrid buffer block as a buffer barrier requires good thermal conductivity for geological storage of high-level waste (HLW). In this study, Gaomiaozi (GMZ) bentonite was mixed with standard quartz sand, and the sand mixing rate Rs was controlled at 30% according to the orthogonal test principle. The moisture contents were set at 7.0%, 11.0%, and 15.0%, and dry densities were set at 1.60, 1.70 and 1.80 g/cm3, respectively. A large buffer block was pressed with a semi-automatic hydraulic press. The heat transfer test was conducted on the cut and decomposed block. The relationship among the moisture content, dry density and thermal conductivity was established, and the spatial distribution characteristics of thermal conductivity were analyzed. Test results show that the thermal conductivity of buffer blocks increase linearly with the increases in water contents and dry densities. The mean value of thermal conductivity more than 0.8 W/m ? K satisfies the requirement recommended by International Atomic Energy Agency(IAEA). The thermal diffusion coefficient slightly decreases first and then increases, and the overall trend also increases. The spatial distribution and uniformity of the thermal conductivity of the hybrid buffer block were also analyzed. It is found that the thermal conductivity of the block edge fluctuates larger than that of the middle part, but the overall difference and non-uniformity are not obvious. The t-test method was used to test the uniformity of thermal conductivity of the hybrid buffer block. The test results show the block satisfies the uniformity test condition and the sample is uniform. Data analysis shows that the thermal conductivity of the hybrid buffer block can be predicted from the physical index using the Johansen model with a deviation of ±10%.

The construction of the underground continuous wall through the water-rich soft stratum is easy to induce the local instability of the weak stratum. In order to study its local instability mechanism theoretically, the local instability stress model is set up and various influence factors such as the cover load, soil strength and groundwater seepage are taken into account. The limit equilibrium of the theoretical model is analyzed to obtain the ultimate support pressure and the minimum height of the mud level of the local instability of the groove wall. Through the parameter sensitivity analysis, the influences of trench length, soil strength, thickness and permeability on the stability of the water-rich soft layer are studied. The results show that the ultimate support pressure is mainly affected by trench length, weak stratum strength and covering thickness, while the confined water seepage in weak stratum has only a slight influence on the support pressure. The theoretical model is applied in the ulta-deep wall of Suzhou and it is found that a good agreement is found between the field monitoring and the study results, which indicates the applicability of the current solution on the local failure evaluation.

The very weakly cemented rock has the characteristics of late diagenesis time, poor cementation, low intensity, easy weathering and disintegration. The special diagenetic environment and deposition process lead to its unique physical and mechanical properties. The X-ray diffraction test shows that the clay mineral composition of very weakly cemented rock is mainly kaolinite with the contents as high as 54%-69%. The microstructure of very weakly cemented rocks is honeycomb, porous and well-connected, with a poor overall structure. Hydration is easy to occur when encountering water, which results in an increase in porosity and a decrease in strength. It is easily weathered and cracks after a short period of exposure. Uniaxial and triaxial compression test of very weakly cemented rock are tested with the rock mechanical system MTS 815 and the complete stress-strain curves are obtained, revealing the post-peak strain softening and expansion deformation characteristics. The experimental results show that the rock sample has obvious volume expansion characteristics before and after the failure. With the increase of the confining pressure, the post-peak volume expansion characteristics are gradually weakened. Based on the crack volumetric strain model, the large dilation deformation failure mechanism of the very weakly cemented rock is analyzed, and the evolution law of rock mass strength and dilatancy parameters with equivalent plastic strain is revealed. At the same time, the pre-peak damage dilatancy and post-peak fracture dilatancy yield criteria are established, and the dilatancy and large-deformation constitutive model of the very weakly cemented rock is constructed.

The surface morphology of rock mass cracks is constantly changing under complex stress and long-term seepage erosion, which leads to more complicated evolution mechanism of seepage characteristics of rock mass fissures. The fluid flow experiments in different roughness limestone fractures were conducted. The effect of coupled stress-fluid flow erosion on the surface morphologies of rough fractures was analyzed according to the experimental results and the comparison of fractures surface morphology characteristics before and after fluid flow experiments, and permeability evolution of rough rock fractures was studied. The results show that the seepage discharge of different roughness fractures decreased rapidly in the initial stage of the experiment and then tended to stable with time under the action of stress. The equivalent hydraulic aperture and permeability of different roughness fractures were approximately equal in the initial stage of the experiment, and then continue to decrease. But under the coupling of stress and seepage erosion, the fractures surface was rougher, the decrease amplitude of equivalent hydraulic aperture and permeability was greater, the stable value was smaller at the end of the experiment. The fracture with small roughness had uniform seepage path and straight streamline, while the fracture with large roughness appeared groove flow and its seepage path was more tortuous and extended. The more the number of convex bodies on the fractures surface was, the greater the area for fluid flow was, and the stronger the erosion modification effect of stress and seepage erosion on the fractures surface morphology was. The above change of surface morphology aggravated the groove flow of the fracture surface and affected the permeability evolution of fractures in turn.

In this paper, more than ten kinds of common inrush water disaster prevention methods are classified and summarised by comprehensively considering the geological conditions and theoretical analysis models. These prevention methods are further unified with two types of inrush water disasters for water-damage rock mass failure and filling structure instability. For the water-breaking rock mass destruction type water inrush, the calculation formulas are classified according to the mechanical model and its applicable objects, and the minimum safe thickness calculation formula of the single crack extended three-zone model is improved. By comparing the calculation results of each formula under different working conditions, the results show that the three-dimensional (3D) rock-column shear model applicable to the intact rock and the single crack extended three-zone model applicable to the fractured rock mass are consistent with the empirical formula, which proves high accuracy and applicability. In terms of the unstable water inrush type of filling structure, it should be pointed out that the start-up force analysis of particles is suitable for judging the beginning of the seepage instability of the filling media and the fluid flow transition can be used as the critical criterion for the occurrence of seepage failure. Finally, this paper systematically evaluates the applicable conditions, judgment criteria, advantages and disadvantages of theoretical analysis, numerical simulations, model tests and engineering analogy. The results provide guidance and reference for the selection of monitoring objects, identification of disaster status and disaster warning in engineering projects.

The acoustic emission experiments on marble under the uniaxial compression are carried out. The fast Fourier transform is applied to obtain the two-dimensional spectrum of the acoustic emission signal, and the spectrum parameters such as dominant-frequency, secondary dominant-frequency are extracted. Then,??-value, i.e., the ratio of the dominant-frequency to secondary dominant-frequency, and ?-value, i.e., the ratio of the dominant-frequency amplitude to secondary dominant-frequency amplitude, are adopted to characterize the spectrum characteristics of acoustic emission signal. The fractal theory is also used to study the characteristics of acoustic emission spectrum during the rupture process of marble. The results show that (1) the secondary dominant-frequency characteristics of acoustic emission in marble fracture process are not the common phenomenon of all waveforms, but are unique to some signals. The acoustic emission signals can be classified into two types: class A signals have only dominant-frequency characteristics, class B signals have both dominant-frequency and secondary dominant-frequency characteristics. (2) From the rock crack growth to failure stage, the low value event rates of two types of signals (i.e., class A and class B) decrease and gradually disappear the increase rate of the cumulative number of events presents a significant increase. (3) Both the dominant-frequency band and the secondary dominant-frequency band of the acoustic emission signal have the similar distribution characteristics, showing a continuous and dense strip-like evolution feature. (4) Both the ??and ? have fractal characteristics. With the increase of rock damage, their correlation dimension declines to some extent.

The stress state analysis of the pillar in inclined bedded ore-body mining is a key issue to ensure the safe mining. Based on the theory of rock mechanics, a mechanical model of inclined pillars under compression and shear loads is established, and the generalized Mohr circle equations describing the stress state of the pillars under compression-shear loading is derived. The position and radius of the generalized Mohr’s circle center are affected by the dip of the ore body and the loading on pillar, which reveal three types of stress evolution paths of the inclined pillar. These three stress paths are found to satisfy the line, circle and plane equation, respectively. Moreover, three types of control modes on the stress path evolution are presented. Based on the Mohr strength theory, the influences of stress path on pillar stability under three main control modes are analyzed. The inclined pillar is more easily unstable than vertical pillar and details are explained in this paper. Finally, the stress state of pillar obtained by numerical simulation is consistent with that of the general Mohr’s method, demonstrating that the failure mode of pillar is asymmetric hourglass shape. The results provide a new idea for the stability analysis of inclined pillars.

The surface trace length or the calculated value is often used to represent the ductility of the structural surface in the analysis of rock mass structure. However, the problems such as excessive cutting of structural surfaces or incomplete identification of structures may exist. In this paper, based on the measured trace length l, the probability of discontinuity persistence is analyzed. The probabilistic calculation formula for the formation of discontinuity is derived, and the classification of combination of structural body under different persistence is set up. According to the underground mining project of the zinc polymetallic ore body at the Tongkeng mine, the 3# ore block in the middle section of +255 m is selected as the test area, and the combination relationships of structural body with various possibilities in the mining and pillar area are studied. The results show that the calculated maximum probabilistic interval of the persistence is in the range of 0.5l and 0.8l. The structure combinations can be divided into three types, i.e., minimum, maximum, and variable combinations. There are different structure combinations in the mining and the pillar areas. It is suggested that the area of D6 structural body should be supported after excavation in time. In order to derive the true value of the combinations of structural body more accurately, various monitoring methods of rock mass structure should be supplemented in the project as far as possible. The study results can provide a reference for the analysis of the combination relationship of rock mass structures.

The temperature of cooling medium has a significant influence on the mechanical properties of granite under the thermal shock, which is mainly determined by the number and density of internal cracks that are determined by the thermal shock velocity and thermal shock factor, but have no direct correlation with the temperature difference of thermal shock. In this paper, the self-developed rock thermal shock cracking test apparatus is used to study the evolution of macroscopic mechanical properties (e.g., the uniaxial compressive strength, tensile strength, cohesion and internal friction angle) granites, taken from Gonghe basin, Qinghai province, under thermal shock tests in water with different cooling temperature. The results show that, with the same heating temperature, the uniaxial compressive strength, tensile strength and cohesion of granite decrease with the increase of the cooling temperature, and the internal friction angle increase with the increase of the cooling temperature in water. The compressive strength and tensile strength of granite under thermal shock show a regular deterioration trend with the degree of thermal shock cracking. The compressive strength and tensile strength of granite heated up to 600 ℃ and rapidly cooled in 100 ℃ water, is only 30% of the granite heated up to 250 ℃ and rapidly cooled in 20 ℃ water. The cohesion of granite under thermal shock decreases with the increase of thermal shock cracking, while the internal friction angle increases obviously. The unsteady heat transfer caused by thermal shock has a degrading effect on the mechanical properties of granite. Therefore, the design and construction of drilling engineering and artificial reservoir in hot dry rocks, all requires to consider the influence of thermal shock on the strength.

Uniaxial compression tests were carried out on sandstone specimens with different fracture angles by means of digital image correlation method and infrared thermal imaging technology, the differentiation degree and rate of strain field and infrared radiation temperature field were quantitatively described by using the standard deviation and approximate derivative. The evolution law, variation mechanism and precursory anomaly characteristics of these two fields during the deformation and rupture processes of the fractured sandstones were analyzed, and their correlations were also discussed. The results show that the evolution process of standard deviation for strain fields can be divided into four stages: initial differentiation, initial acceleration differentiation, intermediate acceleration differentiation and accelerated acceleration differentiation. The evolution process of standard deviation for infrared radiation temperature field can be divided into three stages: initial differentiation, stable differentiation and accelerated differentiation. The standard deviations of strain fields and infrared radiation temperature fields have similar variation trend during the deformation and fracturing process of flawed sandstone specimens. The Pearson correlation coefficients between these two fields are in the range of 0.50 to 0.91, presenting a significant or high positive correlation. There are two peaks in the variation curve of differentiation rate for strain field before failure, corresponding to the initiation points of tensile crack and shear crack, respectively, which could be regarded as two precursor points. The differentiation rate of infrared radiation temperature field increases continuously before the initiation of shear cracks, which could also be regarded as a precursor point. Research results can provide a new method and theoretical basis for monitoring and forecasting the stability of fractured rock masses.

In order to study the characteristics of overburden movement, breaking and evolution of rock pressure in fully mechanized caving face, according to the 302 working face in Cuimu coal mine, the similar material model experiment is performed. The breakage characteristics and rock pressure evolution of roof are observed during the coal mining. Based on the test results, a mechanical analytical model of the fracture at the coal wall is established, and the formula for calculating the critical support strength is deduced. The effects of the tensile strength, load and the thickness of the basic roof on the critical support strength are investigated. The mechanical criterion of the breakage at coal wall in fully mechanized caving face is formed, and the supporting effect of hydraulic support in the 302 fully mechanized caving face in Cuimu coal mine is analyzed. The result shows that the cantilever length of basic roof gradually increases during the advancing process of fully mechanized caving face. Together with rear fractured roof, the structure of "cantilever and articulated rock beam" is formed. The hydraulic support is under the protection of the structure, making a small working resistance. If the basic roof fractures and becomes unstable at the coal wall, the support resistance rises rapidly with the safety valve opening. Even the support crushing accidents easily occur. With the increase of the load on the basic roof, the critical support strength of tensile fracture linearly increases. However the tensile strength of the basic roof has little influence on the critical support strength of tensile fracture. The study in this paper provides a method for the prediction of the breakage at coal wall of basic roof and the support crushing in the fully mechanized caving face.

Constant seepage conditions are one of the main hydrodynamic conditions for triggering the debris flow. However, few scholars have studied the triggering discriminant model and the variation of hydraulic parameters in the slope. In this paper, a simple geological structure consisting of the debris is selected for theoretical analysis, and the triggering discriminant model of debris flow is established. The variation of hydraulic parameters in the slope is studied by means of the model test. The discriminant model is verified and compared with other models. The results show that both the seepage force and the seepage scouring force play an important role in controlling the movement of debris during the constant seepage process. The seepage velocity increases with the increase of bed slope and inlet water flow rate, but the variation degree is smaller for the latter case. The total water head loss parallel to the water flow direction decreases at first and then increases with the increase of the bed slope, and it has a positive correlation with inlet water flow rate. The stability coefficient and the bed slope show a power function relationship. The correlation coefficient differs depending on different discriminant models. Compared with other models, the discrimination model presented in this paper is strictly deduced to meet the requirements of dimensional analysis and experimental verification, and it has a much higher accuracy.

The construction of a geological repository for high radioactive waste requires a large amount of concrete. A large amount of heat will be released because of the decay of radionuclide, which will accelerate the aging of cement, releasing a plenty of alkaline pore water which has a negative impact on the buffer performance of bentonite. The Gaomiaozi (GMZ) Ca-bentonite is used as the experimental material and NaOH solution is selected to simulate the alkaline pore water. Swelling pressure experiments of bentonite with different dry density saturated in NaOH solution with different concentration are carried out by self-developed corrosion resistant consolidometer. The results show that the final swelling pressure of bentonite which is saturated in the same solution increases with the initial dry density of bentonite. Under the same initial dry density of bentonite, ,the low concentration of NaOH solution can strengthen the swelling pressure of bentonite, while high concentration of NaOH solution can weaken the swelling pressure of bentonite. The bentonite samples saturated in three kinds of NaOH solution (i.e., 0.3, 0.5 and 1.0 mol/L s), the evolution curves of swelling pressure decrease after to a maximum value. The decrease degree of the swelling pressure relates with the solution concentration but not with the initial dry density of bentonite. The XRD analysis on the mineral composition and interlayer spacing show that the content of montmorillonite and cristobalite decrease with the increase of alkaline solution concentration, while the content of feldspar increases with the increase of alkaline solution concentration. The exchange of Na will occur in the Ca-bentonite soaked in NaOH solution and the degree of Na-modification is related to the alkaline solution concentration. Finally, the relationship between the montmorillonite void ratio and the final swelling pressure of the bentonite sample is linearly fitted in a double logarithmic coordinate system, and the expression for predicting the swelling pressure of Ca-bentonite saturated in alkaline solution is given.

Mud film forming support is an important protection method in the construction process of shield belt pressing and opening, etc. The supporting effect mainly depends on slurry materials. In order to effectively utilize the natural red layer weathered soil as raw material for mud film formation, and reduce the cost of artificial materials and reduce its negative impact on the environment, we independently developed a fully transparent and high-pressure filter cake airtightness test device by taking the natural red layer weathered soil as materials and drawing lessons from the process of mud film formation. The Orthogonal tests of mud film formation and airtightness of weathered soil are carried out.without adding any other materials. The mud film forming mode, impact factors, evaluation on application effect, formation time and damage criterion of red layer weathered soil are studied. The results show that the airtight properties of filter cake made from the weathered soil of red-bed are similar to that of common artificial bentonite slurry materials. The application feasibility and reliability of mud film formation using red layer weathered soil are preliminarily verified. It is helpful to promote the development of low-cost, green film-forming technology to provide new support for film formation construction technology.

The uniaxial compression process of granite is monitored by acoustic emission and thermal infrared technology, and the variations of acoustic emission and infrared radiation during rock fracture are analyzed. On this basis, the analytical expressions of rock damage variables are derived from the perspectives of internal damage and surface damage. According to the complementarity of these two at different stages, a piecewise curve damage model based on sound-heat is established to study the damage evolution characteristics of rock under uniaxial compression. The results show that: (1) The damage evolution process of rock can be divided into three stages: initial damage stage, stable damage stage and accelerated damage stage. In the initial damage stage, neither internal damage nor surface damage develops. In the stable damage stage, the micro-damage in rock accumulates continuously, but there is no development on the surface damage. In the accelerated damage stage, both the internal damage and the surface damage increase rapidly. Compared with the increase in internal damage, the abnormal increase in surface damage occurs earlier. (2) By comparing the stress-strain curves calculated from the comprehensive damage variables with the experimental curves, it is found that the trend of the two curves is approximately the same. The comprehensive damage variables defined are reasonable and can better reflect the progressive evolution of crack defects in rock from generation, development to failure.

The microbial decomposition can reduce the organic content of peat soil and change its composition, thus affecting the engineering properties of soil. To explore this phenomenon, a model test device was developed to decompose the peat soil with enriched bacteria solution for 90 days. Then the physical and mechanical properties of the peat soil were analyzed and tested during the decomposition process. The results showed that the organic matter content of peat soil decreased from 67% to 61.5% within 90 days. As the decomposition time increased, the relative density Gs and saturation γsat of peat soil increased, the liquid limit wL decreased significantly, and the plastic limit wP almost maintains constant. The compression coefficient a1-2 of the decomposed peat soil decreased, while the compression modulus Es increased. The fast shear strength of the consolidated peat soil generally increased by 15%-25% after decomposition. The cohesion ccq decreased from the initial 18.3 to 15.6 kPa, while the internal friction angle φcq increased from 13.9oto 18.8o. The decomposition time increased, and the permeability coefficient of the pre-compressed peat soil sample decreased. The mechanism analysis shows that the change of engineering properties of peat soil is not only related to the decrease of organic matter content, but also related to the change of composition.

In order to investigate the shear characteristics of remolded loess under suction-controlled true triaxial condition, firstly, soil-water characteristic curve of remolded loess was tested by using the unsaturated soil oedometer, so the relationship between moisture content and matrix suction of remolded loess was obtained. Then, true triaxial shear tests under consolidated drained conditions of remolded unsaturated loess were carried out with matrix suction of 50, 100 and 200 kPa. In the true triaxial shear tests, the net mean stress was kept at 300 kPa and the intermediate principal stress parameters(b-values) were respectively 0, 0.25, 0.50, 0.75 and 1.00. The relationship curves of major principal strain, intermediate principal strain and minor principal strain versus deviatoric stress from true triaxial test results were given. The effects of matrix suction and intermediate principal stress parameter on the stress-strain response of remolded loess were studied. It could be concluded that the shear strength of remolded loess increased with the increase of matrix suction. And it could be summarized that the shear strength of remolded loess decreased with the increase of intermediate principal stress parameter(b-value). The stress-strain curves gradually transformed from strain-hardening type to ideal elastic-plastic type with the increase of intermediate principal stress parameter(b-value). The strength failure line of the remolded loess on π-plane was given. The failure line expanded outward with the increase of matrix suction. Matrix suction might affect the position, size and shape of the failure line. Besides, the test results of different matrix suction were more similar to those predicted by Lade-Duncan criterion.

The modification and utilization of dispersed soil are critical issues in geotechnical engineering. The traditional modification with lime has a high cost and environmental damage and other adverse effects, so it is urgent to explore new treatment materials and technologies. Based on this, aluminum compounds and traditional special soil modifier(lime) were used to treat the typical dispersive clay in a homogeneous dam in northeastern China. The effects of different types and contents of modifiers on the physicochemical properties, dispersibility and mechanical properties of dispersive clay were investigated. The microscopic mechanism and modification mechanism of modified dispersive clay of aluminum compounds were studied by microscopic experiments such as scanning electron microscopy. The results show that when the lime content reaches 1%-3% or the aluminum compounds content reaches (2～4)×10?4 mol/g, both of the two modifiers show good modification effect and can improve the shear strength of the dispersive clay. Lime has no obvious effect on the particle composition of the soil. With the increase of lime content, the pH value of the dispersed soil increases and the dispersibility is effectively suppressed. The aluminum compounds can change the particle composition of the soil by agglomeration and cementation with the soil. Meanwhile, it can effectively reduce the pH value of the soil, which can achieve excellent improvement effects. Compared with lime-modified dispersive clay, aluminum compounds-treated soil has high application value in practical engineering with the advantages of environmental friendliness, convenient construction and in-situ treatment.

To solve the partial danger release of rock burst, a partial risk reduction method that creates cracks in the foundation of the pressure relief hole was proposed. A double-axis compression test of the specimen with the tendency of rock burst was carried out in combination with strain gauge and acoustic emission(AE) monitoring techniques. The results show that compared with the simple pressure relief hole, the control of the process of local de-danger evolution of surrounding rock containing 0° and 45° split cracks is changed from two sides of decompression holes to the end of the split fracture, which expands the decompression area, and the decompression hole work together with the split cracks. The nonlinear characteristics of the relation curve between the stress and vertical strain before the peak are enhanced. The energy dissipation prior to the peak is enhanced, but the integrity of the surrounding rock is reduced to a greater extent, which means the effect of decompression is obvious. The process of local de-danger evolution of surrounding rock containing 90° split cracks is still controlled by the two sides of decompression holes. The local de-danger effect of 0° split crack is demonstrated as the best one with the pre-peak energy release of 85.70%, followed by those with 45° and 90° split cracks. The results provide valuable guidance and reference for rock burst prevention and control.

Geosynthetics reinforced soil flexible abutment composite structure, as a new technology, can realise the integrated design and construction for bridges. However, the literature on the seismic performance of this structure is very limited. This paper is to study the seismic performance of a scaled model of geosynthetic reinforced soil abutment structure by the shaking table test. Experimental results showed that the geosynthetic reinforced soil abutment structure had excellent seismic performance, which could maintain great global stability under strong earthquakes until the peak ground acceleration reached 1.0g. There was only a small camber deformation found at the top of the abutment, and the maximum deformation was around 2% of the abutment height. The slight differential settlement was also observed at the bridgehead. Due to the directionality and asymmetry of the seismic excitation, the inertial forces pointing to the free surface of the abutments on both sides were different. The bridge beam could transfer and coordinate the inertial forces of the nearby reinforced soil and made it approximately equal. In addition, reducing the reinforcement spacing was beneficial to improving the seismic performance of the geosynthetic reinforced soil abutment, which was mainly manifested in minimising the structural deformation and distributing the axial forces of reinforcements.

The vibrations induced by high speed train(HST) may cause negative impacts on the surrounding environment, instrument operation, and even the safety of buildings, thus it should be paid more attention by the researchers and governments. In-situ measurements at the transition section to measure the ground vibrations caused by the operation of HST were conducted on the Beijing-Shanghai high-speed railway in China. The ground vibration accelerations were recorded during the tests in three directions (i.e., vertical, horizontal and longitudinal directions) when train speeds are between 250 and 350 km/h. The characteristics of vibrations in the time domain, the frequency domain and the amplitude under different distance and speeds are analyzed. Furthermore, based on the levels of acceleration, the extents of site vibration caused by the operation of the high-speed rail at the transition section are evaluated. The analysis results show that the vertical vibrations are usually dominated in the near-field region and are comparable in the mid- and far-field and horizontal-direction vibrations. An obvious vibration amplification zone is found in the region within a distance of 20 m to the railway The dominant vibration frequencies of the ground are typically n times than the characteristic frequencies related to the train’s geometry dimension and unevenness of the railway. The test results are of great significance for the verification of numerical values about the vibration in high-speed railway environment.

Foundation pit unloading will create additional loads on the underlying existing tunnel. Based on the engineering practice, a semi-analytical solution considering the effect of foundation depth and tunnel shear effect is proposed to predict the longitudinal response of tunnel caused by the above excavation. A modified subgrade reaction coefficient considering different buried depth of tunnel is introduced, additional pressure induced by excavation is given based on the Mindin solution. By regarding the tunnel as a Timoshenko beam resting on the Pasternak foundation, the longitudinal deformations of the tunnel are analyzed. Compared with the three-dimensional finite element method and the measurements of the Jiusha river foundation pit crossing the No. 1 metro line in Hangzhou, the accuracy of the proposed method is verified. The effects of bending stiffness and shear stiffness on the response of the tunnel are systematically analyzed. The results suggest that the mechanical response of tunnels could be better analyzed with the Timoshenko beam model. Increasing bending stiffness can effectively reduce the displacement, moment and shear of the tunnel, but increase the distribution range of them. At the same time, the increase of bending stiffness will not affect the location of maximum positive bending moment and the location of maximum shear force but will make the location of the maximum negative bending moment move toward both ends of the tunnel. When the shear stiffness exceeds 20% of the bending stiffness, the displacement and the bending moment, as well as the shear force of the tunnel, is hardly affected by the shear stiffness. The conclusions can provide some theoretical support for similar projects.

The water and sand gushing accidents occur frequently in shield tunnels located at confined aquifer of soft soil areas in China, resulting in huge economic losses and adverse effects. However, due to the high water pressure in the confined aquifer, it is difficult for the traditional methods(e.g., grouting technique) quickly playing an effective role. According to the settlement-time curve after the seepage disaster, the development process of the disaster is put forward. Based on the rapid construction of wells in 6-8 hours, which is proved in field tests, an emergency plan of rapid decompression and recharge of confined aquifer is suggested during the slow development period of seepage disaster in the shield tunnel. The feasibility of applying this technology in tunnel emergency rescue is analyzed by using the precipitation theory considering the water level in the well. The results show that this technology can reduce the water level at leakage point in a short time and thus can control the surrounding water level at the same time. The shorter time to deal with the tunnel disaster requires, the higher amounts of pumping and recharging water require. When the ratio of distance between pumping well and recharging well to the leakage point is fixed, the smaller the distance value is, the fewer pumping and recharging water amount require. The circumferential buildings can be protected by arranging the recharge wells along the ring using the decompression center as the center of a circle. Finally, the design steps and well layout principles of emergency rescue (i.e., decreasing the pore pressure in the confined aquifers) are put forward.

 In order to study the stress state of shaft lining affected by seasonal temperature variation during shaft operation, the elastic mechanics and heat conduction principles are applied in the analysis of shaft lining and surrounding rocks. The contact surface problems are considered to establish the mechanical model by analyzing the temperature and stress fields of shaft lining and the surrounding rocks. The derived formula shows that the temperature fields of the shaft lining and surrounding rocks changes periodically with the temperature of the airflow in the shaft during the operation of the shaft. The temperature field of the shaft lining and surrounding rocks always presents uneven distribution. With the increase of radial distance in the surrounding rocks, the influence of temperature gradually disappears. The total tangential and circumferential stresses of shaft lining change periodically with the air flow temperature during the operation of shaft. The maximum circumferential stress occurs at the inner edge of the shaft lining, and the total radial stress is minimized. The horizontal stress at the far field has a great influence on the total stress of shaft lining during its operation. The temperature change of surrounding rocks is an important factor affecting the stress state of shaft lining. The shaft lining is usually in a compressive stress state during the ventilation period. In the design of shaft lining, the stress differencewith the maximum temperature of the inner edge of shaft lining changes, considering the early and medium-term stresses of shaft lining temperature stress, should be taken as the reference minimum value for selecting the strength of shaft lining concrete. 

When shaft boring machine is tunnelling in strata, the inadequate bearing capacity of the surrounding soil underlying gripper can lead to insufficient propulsion, inability of excavation direction control and even shaft instability, therefore, it is necessary to study the ultimate bearing capacity of the surrounding soil underlying gripper. Based on the first mine-type shaft boring machine developed in China, the interaction between the gripper and soil is herein investigated by numerical simulation and the failure mode of the soil underlying gripper is determined to be shear-slip failure. Based on the failure mode simulated and the assumption made to treat the fracture face of surrounding soil under gripper as a combination of logarithmic helix and linear rotating surface, the stress distribution on the fracture face is analysed. Then, the formula of ultimate bearing capacity of surrounding soil underlying gripper is derived using the plastic limit equilibrium theory. Finally, the formula of ultimate bearing capacity is compared and analysed with the numerical simulation results to show its rationality. The results of this investigation can provide important guidance to the gripper design of shaft boring machines and stability evaluation of surrounding soil underlying shaft boring machine’s gripper in different conditions.

The soft rock mass of deep-buried tunnel often has obvious rheological characteristics and time-weakening effect. After excavation, the parameters of surrounding rock gradually decrease with time, resulting in the increase of rheological deformation of surrounding rock, which easily leads to the cracking of first lining and secondary lining of tunnel, and seriously affects the safety of tunnel construction and operation period. In order to ensure safety of the tunnel, a buffer layer is set between secondary lining and surrounding rock, which can absorb rheological deformation of surrounding rock. The buffer layer has ideal elastic-plastic characteristics. Its special mechanical characteristics make it compatible with deformation of surrounding rock, absorbing long-term deformation energy of surrounding rock, and realizing the long-term stability of soft tunnel surrounding rock. Therefore, in recent years, the design of buffer layer yielding support has gradually been recognized by many scholars and engineering construction units, but at present, buffer layer yielding support has not been widely used, because the design of yielding deformation and yielding stress of buffer layer support has always been a difficulty in engineering construction. Based on elastic-plastic theory, the design method of buffer layer yielding support for tunnel engineering is proposed considering the time-effect weakening of surrounding rock parameters and the resistance of buffer layer support. The rationality of the buffer layer yielding support is verified by the support design of V-grade soft rock tunnel.

The evolution of the temperature field in the nuclear waste repository is an essential basis for the design and safety assessment of the repository. The layered heat transfer model of a single nuclear waste container was established, according to the conceptual design of the disposal repository. The Laplace transform was applied upon the equations of heat conduction in the bentonite and surrounding regions, and the semi-analytical solutions of the temperature field were derived in the Laplace domain under different combinations of internal and external boundary conditions. The temperature distribution in the near-field time-space domain of the waste container was obtained by numerical inversion of the semi-analytical solution using the Crump’s method. Finally, the evolution of the surface temperature of single waste container under different parameter conditions was analyzed. The results show that the higher the burn-up value of nuclear waste is and the shorter the cooling time of nuclear waste is, the higher the surface temperature of the waste container is. The surface temperature of the waste container calculated by the finite external boundary condition was higher than that calculated by the infinite external boundary condition, the higher the thermal conductivity of bentonite is, the lower the surface temperature of the waste container is. The thicker the bentonite soil layer is, the worse the internal temperature diffusion is. The results provide references for evaluating the evolution of the near-field temperature of waste container under different conditions.

slide slope; three-dimensional arbitrary slip surface; minimum potential energy method; genetic search; software development

Energy pile is a new type of pile foundation technology that bears the load of the upper building and transmits the shallow geothermal energy. Heat transfer efficiency and thermal induced stress are two key problems must be solved before energy pile can be widely applied. Present studies mainly focus on the thermo-mechanical coupling characteristics of single pile, while the researches on the thermo-mechanical characteristics of pile-raft foundation are relatively limited. Based on the pile-raft foundation, field tests on heat transfer efficiency and thermo-mechanical characteristics under different velocities were carried out. The temperature and stress changes of both energy pile and raft under cooling condition were measured and analysed. The influence caused by different velocities was also discussed. The results show that when the energy pile is running at the velocities of 0.8, 0.4, 0.2 m/s, the corresponding heat transfer efficiency are around 75.0, 82.5, 63.8 W/m. Under the influence of raft restraint, the maximum constrained tensile stress of pile is about 38.9 kPa, which is generated in the top of the pile; and the maximum constrained tensile stress of raft is about 47.2 kPa, which is in the bottom side of the raft. As the velocity of flow decreases, the temperature of pile rises slightly is increased and the value of tensile stress decreases. The influence of short-term cooling condition on the temperature of the raft is negligible.

The deformation modulus of rock mass is often estimated by empirical formulas in rock mass engineering. There are many empirical formulas in rock mass classification system, but few studies are found on the statistical characteristics of the results using different empirical estimation formulas and the weight analysis of independent variables. In this paper, the Monte Carlo method is used to analyze the statistical distribution of the deformation modulus estimated by different emperical formula and the weight of the independent variables based on GSI system. Besides, impacts of different disturbance factors are discussed. The results show that the disturbance factors play different roles in the statistical distribution modes of rock mass deformation modulus. The disturbance factor has the greatest impact on the statistical models of rock mass deformation modulus obtained by Hoek formula and the high quality rock mass is less affected compared with that of poor quality rock mass.

The field survey, numerical simulation and geomechanical analysis methods are applied in studying the fault effect on the deformation and failure of surrounding rock in the laneway, such as the ?340 m and ?410 m stages of the transportation lanes that are located at the eastern part of the Jinshandian iron mine. The results show that the deformation and damage of roadway near the fault fracture zone affected by mining is serious. The failure modes of surrounding rock include roof collapse, asymmetric subsidence and deformation of the roof, spalling induced by the deformation of surrounding rock in tunnel, horizontal tensile cracks of roadslides, etc. The fault-fracture zone F4, where the transportation lane at ?340 m level, is located at the deformation zone of the ore body induced by mining. The horizontal stress release caused by the movement and deformation of rock body leads to a dislocation stair at the interface between the fault-fracture zone F4 and the hornfels A2 near the ore body. The deformation and failure mechanism of ?340 m level haulage roadway includes the surrounding rocks in tunnel move and deform towards the worked-out area induced by the mining and the slippage and activation of the fault-fracture zone caused by mining result in the collapse of the roof along the steep structure plane. The deformation and failure mechanism of the transport lane at the ?410 m stage is controlled by the squeezing deformation caused by the slip activation of the rock mass at the fault-fracture zone at the ?340 m level and above depth.

The morphological features and mechanical properties of rock structural surfaces are important scientific issues in the field of rock mechanics and engineering geology at home and abroad. The borehole images can accurately record the hole-wall information of borehole and the morphological feature of in-situ rock structural surfaces in the borehole. In this paper, a method for analyzing and extracting the outline of rock structural surfaces based on borehole images is proposed, which is used to study the three-dimensional morphological features and mechanical properties of rock structural surfaces. In view of the uniqueness of the contour line of the rock structural surfaces in the image, the three-dimensional morphological features of borehole rock structural surface are accurately restored by the following steps: information extraction, coordinate transformation, ring information analysis and contour line’s sampling processing. Then, the roughness and anisotropy of rock structural surfaces are described by fractal dimension of each section of the contour. Finally, the dominant sliding direction of rock structural surfaces can be determined according to the fractal dimension and then the shearing strength of the structural surface can be evaluated for further explanations. Results show that the transformed contour line of the structural surfaces based on borehole images can well reflect the three-dimensional morphological features of rock structural plane in the borehole, which can be used to determine the dominant anti-slip direction and to estimate the shear strength of rock structure plane in practical engineering application.

The risk management of the construction on foundation pit of the metro in the soft clay area is challenging, not only affected by the complex geological conditions and construction environment, but also disturbed by engineering construction and external factors, making it difficult to obtain the actual data for predicting the deformation of foundation pit, thus resulting in the risk in construction and its surrounding environment. Based on the data analysis and the dynamic prediction theory of the wavelet transform and Elman neural network, a new time series wavelet Elman prediction model (WEPM) of the foundation pit deformation was proposed and was applied in the foundation pit engineering of the Wuhan metro. The actual deformation data was obtained based on the wavelet decomposition de-noising process of the previous measured data. Then the wavelet intelligence model was used to realize a rolling prediction on the deformation of foundation pit. The analysis results show that the WEPM has a high prediction accuracy and a high generalization performance, which was suitable for the time series prediction on the deformation of foundation pit under different conditions. The proposed model provides basis for deformation prediction, construction safety and accidents prevention of foundation pit construction in Wuhan.

The change of landslide displacement in Zhongxian area of the Three Gorges reservoir area shows step deformation characteristics. Because rainfall as the main influencing factor, the high energy frequency point of amplitude is obtained by fast Fourier transform, and a Fourier series fitting function based on high energy frequency is proposed by using the fast Fourier transform method of signal processing. The monthly rainfall in the Zhongxian region of the Three Gorges Reservoir area is fitted, and the fitting model of high correlation and acceptable mean square error is obtained. In the research area with similar geological model and landslide mechanism, the influence of landslide inclination on horizontal displacement is greater. By defining the influence weight of landslide inclination angle, the total weight displacement in the study area is calculated, which can better reflect the effect of the dip angle. By setting the rainfall Fourier series fitting function as the rainfall factor term, and the step function as the step factor term, the least square method is used to fit the step process of the three-stage deformation in the study area, a mathematical statistical model consisting of a combination of rainfall impact control and rainfall items is obtained. The method is applied to the 11-month monthly monitoring data of 9 step deformation landslides in the Zhongxian area of the Three Gorges reservoir area, which shows that the fitting accuracy obtained by the method is better, the correlation is higher, the mean square error is smaller, and it can accurately reflect the step deformation characteristics of horizontal displacement in this region at different time and different deformation stages. This method can be used as a new idea for regional landslide spatial prediction.

In order to reasonably calculate the surrounding rock pressure of an ultra-shallow-buried passageway with rectangular section during construction, an available finite element method is suggested firstly to analyze the failure mode of the surrounding rock of the primary support structure under the limit state of bearing capacity. Based on the failure mode, the limit equilibrium equation of each surrounding rock slider is established, and the ultimate equilibrium solutions of the vertical and lateral surrounding rock pressures of the super shallow buried primary support structure in silty clay soil layer in Qingdao area are obtained. Finally, the calculation value and field test of surrounding rock pressure are compared, demonstrating a maximum deviation amplitude is less than 9.0%, and the feasibility of limit equilibrium method is verified.

The geostress field is the basic data for the excavation and support design of deep mine roadways. Aiming at the large random errors of geostress measurements in the deep strata of the coal mine, a geostress field inversion method based on support vector regression(SVR) optimization algorithm is proposed. The optimization algorithm takes the feature vector structure risk minimization as the principle, making the empirical risk and confidence range minimized to reduce the interference of random errors of measured geostress on parameter inversion. A three-dimensional finite element calculation model is established based on the geological and geostress data of Pingmei No.1 mine. The lateral pressure coefficient is introduced and the uniform design table test method is used to construct the stress boundary condition. The learning samples are created based on the calculation results. Then the support vector regression algorithm is used to optimize the boundary condition parameters, and the optimal stress boundary condition is determined. The optimal stress boundary condition is applied to the model to obtain the geostress field of the whole model. The comparisons between the inversion value and the geostress measurement point show that the errors are within a reasonable range, and the inversion values are less random than the measured values. The distribution of geostress field is consistent with that of inversion results in Pingdingshan mining area, revealing that the inversion results are accurate and reliable.

The separation between concrete face slab and rockfill due to uncoordinated deformation is a common phenomenon in the concrete-faced rockfill dam engineering. It may even cause cracking of concrete face slab and threaten the overall safety of the dam. Therefore, it is necessary to analyze whether the separation will occur and predict the separation magnitude. However, the previous calculation methods can hardly achieve a balance between intuition, accuracy, and ease of implementation. The paper attempts to treat the separation as relative displacements of discontinuous interface in an object and use the extended finite element method (XFEM) to simulate the movement. A hybrid XFEM contact constitutive model is extended to three-dimensional(3D) to describe the three dimensional opening and dislocation of discontinuous interfaces. Results are compared using the self-programming and the ABAQUS contact mechanics methods in a slider model example, and to validate the 3D interface contact algorithm. Taking the Tianshengqiao concrete face rockfill dam as an example, the separation of the face slab is calculated and compared with the measured values and simulated results by the dual mortar method, which verifies the ability of this method to calculate the large-scale practical engineering.

The full-section tunnel-boring machine(TBM) is widely used in the tunnel construction due to many advantages include high efficiency, safety and environmental protection etc. The rock breaking mechanism of the TBM cutter is the essence deciding the design and construction of TBM. The rock will break when it interacts with the TBM cutter. The discrete element method (DEM) has become an effective means to study the rock breaking mechanism of the cutter. However, the dimension of the numerical model generated by most discrete element softwares is relatively small and the simplified two-dimensional models are always applied, which has an obvious size effect. The MatDEM software based on discrete element method is used to construct a large-scale 3D model of rock breaking cutter, thus simulating the real rock breaking process of the cutter. The clustering unit is used to simulate the rigid cutter, which can realize the dynamic process of rock breaking under different conditions using the double cutters. The forces of cutters during the rock breaking process can be monitored, and the force model of cutters and variation of specific energy (SE) under different cutters spacing/penetration ratio (S/P) are calculated and analyzed. The simulation results show that the cutting force is a complex and irregular impact load during the rock breaking process. It is related with the cutting parameters, rock properties etc. The increase in the penetration depth and the cutters spacing requires a much higher force to break the rock. For a specific rock, there is an optimal ratio of the spacing/penetration degree, making the minimum SE for rock breaking. The MatDEM software can better simulate the rock breaking process of the cutter, which matches well with the indoor linear cutting test, thus it is beneficial to comprehensively explore the rock breaking mechanism.

To explore the evolution law of the spatial arching effect of pile-supported low embankment, three kinds of three- dimensional movable gate particle flow models with different heights and low embankments were established by PFC3D software. Comparing the test results with the existing analytical solutions, the distribution characteristics of vertical earth pressure inside the embankment, the development mode of soil arches, and the settlement and deformation law of soil are analyzed. The results show that the spherical arch structure, which forms the path of load transfer, is composed of force chains at the top of piles after the pile-soil load sharing ratio reaches a steady state. The height of stress-arch increases first and then stabilizes as the filling height increases. Stable soil arching rate ? is in the range of about 0.2-0.4 at various positions on the trapdoor, which reflects the uneven earth pressure distribution. The vertical stress at the center of four piles is higher than that between two piles, and also larger than that at adjoining two-pile-centers. From the perspective of deformation, it can be judged that the height of equal settlement plane is about 1.2B times the net spacing of piles(B represents pile clear spacing) from the pile top, based on the contour of vertical displacement at different filling heights. The differential settlement, between particles above the pile top with larger settlements and particles above subsoil, grows with the increase of buried depth and presents an overall convex shape. As the settlement deepens, two different patterns of the external slip surface are observed according to surface deformation: triangular expansion pattern and equal settlement pattern. Particularly, the internal slip is dome-shaped under equal settlement plane.

Considering the weakening effect of strength and stiffness of the shale layer, the two dimensional particle flow numerical models of shale specimens are established using the granular distinct element method. Based on the evolution law of the macroscopic mechanical parameters with the relative water absorption rate, which is obtained from the triaxial compression tests of shale specimens, the mesoscopic parameters of the numerical model under different water absorption time are calibrated, in order to study the unloading mechanical properties and failure characteristics of shale specimens under different water absorption time. The results show that the strength parameters under loading and unloading stress paths decrease with the increase of water absorption time. However, the cohesion is generally smaller in unloading condition compared with that of loading condition, while the internal friction angle presents an opposite law. Under different water absorption time, the rock samples mainly fail along or at a certain angle to the bedding plane. More fractures are found in the rock samples with the increase of water absorption time. Thus the failure modes of the samples, changing from single shear to double shear, are more easily controlled by the bedding planes. The development law on the number of microcracks in rock samples under different unloading stages is also different. The growth rate of tensile and shear cracks in the yield stage under unloading status is differentiated, showing that the growth rate of shear cracks gradually tends to be stable while that of tensile cracks continues to increase. When the stress residual point at the post-peak stage is reached, the growth rate of tensile cracks significantly decreases, and then basically tends to be stable.

The damage and broken of falling rocks due to collision and velocity of fragments are crucial to the accurate prediction of trajectory of falling rocks. In order to reveal the collision damage and fragment velocity, a three-dimensional discrete element modeling of crystallization method is used to simulate the collision damage of ball and gravel based on experimental tests. The simulated results show that the collision damage patterns of ball and gravel agree well with that of the laboratory results. Higher collision velocity causes the radial and secondary macro cracks, breaking the rock gravel into small pieces. The secondary macro cracks result from the compression of orange-slice-shaped fragments. The radial macro cracks leads to a significant increase in the number of micro cracks. The damage rate based on the number of cracks shows three different stages with increasing collision speed. The contact force is also strongly affected by the damage and fragmentation of rock spheres. The simulation results show that the fragmentation of rock gravel collision can lead to high-velocity fragments. The maximum fragment velocity can reach up to 3.2 times of the collision velocity. The equivalent size of the high-velocity fragments is generally less than 0.11. After the collision, the velocity direction of fragments changes significantly with the collision velocity, which corresponds to the crushing mode of ball and gravel collision.

The subway construction in sandy cobble and loess layers in Xi'an is selected as the background. Applying numerical methods, in-situ monitoring and other means,, in view of the excavation methods during the construction of cross passage by tunneling and back well method, the pre-reinforcement schemes of existing shield pipe segment is proposed, optimized analyzed and evaluated. The results show that the increase of excavation layers will result in the surface settlement and the shortage of construction work space. It is suggested to use the 4 steps, and the core soil method is reserved for excavation. The length of the upper and lower steps should not exceed 3 m. The grouting thickness of the gravel and loess stratum from outside of the cross passage is at least 2.0 m, and the elastic modulus of the stratum should be increased by more than 0.2 times after the reinforcement. The advanced support methods of small and large pipe sheds can be used to enhance the excavation stability of the stratum and the safety of the shield tunnel segments. Before the existing pipe shield segment is broken, the connecting bolts of 4 to 6 ring segments on both sides of the transverse channel should be loosened to reduce the effect of longitudinal compression stress concentration of the shield segment caused by the excavation of the transverse channel. When the horizontal cross passage passes through the existing shield segment, the static breaking method should be adopted to remove the segment vertically from top to bottom. Then the concrete pouring and reinforcement implantation should be carried out at the interface between the air shaft cross passage and the shield segment. The WSS grouting should be used to reinforce the soil stratum and implement the anti-seepage treatment at the joint.

The wave velocity of low liquid limit clay with different moisture contents is tested using a GDS bending-extension element system. The shear modulus, oedometric modulus and poisson's ratio of clay are measured based on wave theory. The effects of different moisture contents, effective confining pressure and signal input frequency on the test results are studied. The output waveform signals characteristics of S wave (shear wave) and P wave (compression wave) are analyzed. The results of different signal analysis methods are compared with that of the resonance column experimen. The experimental results show that (1) the Vs (shear wave velocity) and Vp (compression wave velocity) increase with the increase of input frequency, and the increase rate decreases with the increasing frequency. The near-field effect of S wave decreases with the increasing moisture content and stimulated frequency in clay materials. (2) the shear modulus G0 and oedometric modulus M0 increase with the increase of confining pressure, while G0 decreases with the increase of moisture content. (3) the Poisson's ratio increases with the increase of moisture contents and the impact of confining pressure on Poisson's ratio weakens with the increase of moisture contents.

Textile companies produce a large number of synthetic waste fabrics every year, and improper handling can cause serious environmental pollutions. The discarded fiber yarn is used to form a fiber yarn-reinforced loess sample by loosening, combing, and cutting into the plain loess at a certain ratio. Related tests were carried out on plain loess, monofilament fibre-reinforced loess and fiber yarn-reinforced loess samples by using pavement material strength tester, true triaxial apparatus, tensile strength tester and soil erosion equipment, respectively. The results showed that when the fiber yarn blending ratio increases, the unconfined compressive strength increases first and then decreases, which indicates the optimal fiber doping ratio is found. For the unconfined compressive strength, fiber yarn-reinforced loess and monofilament fibre-reinforced loess are larger than plain loess. Under the same fiber blending ratio, fineness and length, the unconfined compressive strength of fiber yarn-reinforced loess is more significant than that of monofilament fiber-reinforced loess. The cohesive strength of fiber yarn-reinforced loess is greater than those of monofilament fibre-reinforced loess and plain loess; while the internal friction angle of these three loesses is similar. Plain loess exhibits brittle failure characteristics in the tensile strength test. Tensile strength of fiber yarn-reinforced loess is higher than those of monofilament fiber-reinforced loess and plain loess. Tensile strain of fiber yarn-reinforced loess is larger than that of monofilament fiber-reinforced loess. At the same time point, the pores formed by the fiber yarn-reinforced loess are smaller than the plain loess, and the amount of erosion is less than that of plain loess.