It has been gradually recognised in oil and gas exploration that it is not adequate to study only the current sealing properties of cap rocks. The geological history and the relationship between the stress state and the brittleness-ductility of the cap rock should also be understood for proper assessment of the sealing properties. A uniaxial strain test was carried out for argillaceous rocks at different diagenesis states from the western Hubei—eastern Chongqing area，using a thick-walled steel drum as a lateral restrainer. The relationship between lateral stress and axial stress was established based on the theory of thick-walled cylinders，and the apparent preconsolidation stress was calculated. Subsequently，the relationships between the apparent preconsolidation stress and the uniaxial compressive strength，the ultrasonic velocity，the porosity，the clay mineral content，and the changes in lateral stress coefficients were investigated. Preliminary assessments of the characteristics of the brittleness to ductility transfer of argillaceous rocks are given with the corresponding onset threshold conditions，as well as the sealing capacity under various geological conditions. This work lays the foundation for subsequent work in establishing the dynamic-static sealing model for argillaceous cap rocks.

In order to understand the progressive failure process of marble after thermal treatment at different temperatures，uniaxial compression tests were conducted on marble specimens after they were treated at temperatures of 25 ℃，200 ℃，400 ℃ and 600 ℃ respectively. Comprehensive studies were carried out on the characteristics of the detected acoustic emission(AE)，the failure mode of the specimens，the crack initiation stress and the damage stress level，the damage evolution and the stress-strain constitutive model. The results showed that as the treatment temperature increases，the peak strength of the rock decreases with increased corresponding peak strain，indicating that the rock becomes more ductile. It was also seen that the AE characteristics of the specimens treated at high temperatures show clear differences to those of the specimens treated at room temperature. Because of the thermal damage，the AE of the high temperature treated specimens was more active during the initial loading stage compared with specimens treated at room temperature. However，the AE in the elastic stage was less active compared with that of undamaged specimens. The ranges of the normalized crack initiation stresses and damage stresses determined using the AE method were 0.33–0.46 and 0.71–0.82 respectively，and both tend to increase as the treatment temperature increases. The failure mode changed from a single splitting crack to multiple splitting cracks，and finally to shear failure，which was in good agreement with the results derived based on AE locations. A variable describing the degree of damage was then established based on the accumulated AE count. For specimens treated at 25 ℃，the damage process can be divided into four stages，and for specimens treated at high temperatures，the initial damage level is high but the variation of the damage variable becomes gentle as the strain changes. Finally，a constitutive model based on the axial crack strain，the axial stress，and the damage variable determined from the AE count was established. Simulation results using the proposed constitutive model agreed well with the test results，and the higher the treatment temperature，the better the agreement.

Infiltration effects exist widely in the process of turbid fluid seepage in porous media，and directly influence the diffusion and migration of the turbid fluid particles. In this paper，the movement of cement grout in porous media was studied based on the theoretical filtration effect model. Equations of grout movement incorporating the infiltration effects were established which are applicable for both constant rate and constant pressure grouting. A one-dimensional numerical model for the infiltration diffusion of grout was established. Compared to Darcy?s law，the results show that the influence of infiltration effects on grout diffusion is significant. The influence of infiltration effects on the porosity of porous media，the grout concentration，and the grouting pressure distribution was further investigated to understand the interaction of infiltration effects with the grout diffusion and the effective range of grout reinforcement.

The study of the transportation and deposition characteristics of suspended particles in porous media is of great significance to engineering problems such as oil exploration，groundwater recharge and pollutant transportation. The advances in this area are presented in this paper with particular reference to mathematical models and experimental studies. A new transportation and deposition model was proposed based on data from field monitoring and a large number of laboratory tests. The transportation and deposition characteristics of suspended particles were studied under different conditions. The new mathematical model taking into account the velocity correction parameter，the porosity correction parameter，the particle capture efficiency and the variation of porosity was then established. Deficiencies of current experimental studies and mathematical models include the failure to accurately describe the pore structure of porous media，the neglecting of multi-factor coupling effects on the transportation and deposition characteristics，and the failure to properly integrate the macro-scale filtration phenomenon and the meso-scale particle motion. Future studies are expected to follow these four major directions：(1) Development of a dynamic three-dimensional experimental facility；(2) Establishment of a more accurate spatial model for porous media；(3) Development of mathematical models for particle transportation and deposition under the coupling effects of multiple factors；(4) Development of the theory and analytical methods for particle transportation and deposition across micro-meso-macro scales.

Adequate quantification of dynamic impact risk is important to rockburst prevention on working faces. In this paper，an impact risk appraisal methodology was proposed based on the superimposition of stress increments caused by various impact risk factors on top of gravitational stresses. Such a technique allows a better quantitative assessment of the impact risk on working faces. The detailed procedure for applying the methodology was demonstrated by applying the method to stope working face 3-04，which is overlaid by buildings，water bodies and railways. The results from the example demonstrated that the method can quantify the variation of impact risk with the length of the stope working face. The assessment indicated that there were 3 severe，9 moderate，and 14 slight hazardous zones in the area，which is in line with actual observed rockburst situations. The case study clearly showed that the proposed approach is an effective impact risk appraisal method，as it is capable of providing a more quantitative assessment of the degree of impact risk on working faces compared with other existing techniques，such as the synthetic index method or the probability index method.

A new multi-functional true triaxial fluid-solid coupling experiment system was designed，fabricated， calibrated，and successfully tested to better simulate in-situ triaxial stress conditions and reveal geomechanical properties and seepage laws for rocks and coals subjected to these conditions. The experiment system comprises a load frame，a true triaxial pressure vessel，a high pressure loading system，an internally sealed seepage system，a control and data acquisition system and an acoustic emission monitoring system. The advantages and innovations of the experiment system include：(1) Geomechanical and seepage experiments can be performed for different stress-strain paths under uniaxial，biaxial or true triaxial stress conditions. (2) Three new stress and strain control modes(Trace-F，Trace-D and Trace-Df) are implemented to ensure that the center point of the specimen stays in the same position during experiments. (3) The internally sealed seepage system is designed to accomplish the independent control and monitoring of fluid flow in the specimen under true triaxial stress conditions. (4) To reduce the specimen end friction effect，stiff loading mode is applied in two directions and either flexible or stiff loading mode is applied in the third direction. In addition，high frequency dynamic control is implemented for the load system，therefore experiments with complex stress-strain paths can be performed. (5) New multi-functional loading platens are designed to accommodate hydraulic fracturing experiments. (6) The experiment system can apply a force of up to 6 000 kN in each of two directions and 4 000 kN in the remaining direction. The applied fluid pressure can be up to 60 MPa based on a servo-controlled supercharger. A series of testing methods and experiments were performed to verify the accuracy and reliability of the experiment system. This system will provide a comprehensive new tool to study geomechanical properties and seepage laws for rock and coal under true triaxial stress conditions，which can be further applied to research in areas such as geological storage of CO2，efficient oil-gas exploitation and deep underground rock engineering applications.

A function describing the performance of tunnel lining with the protection of rock bolts and shotcrete was derived based on the theory of build-up arches and the failure model of shear slip. Because of the high nonlinear and implicit characteristics of the function and the correlation between the basic parameters，the reliability was difficult to be obtained. In order to eliminate the influence of the correlation between the basic parameters，the semi analytical Nataf transform was introduced，and thus the original random variables were converted into the standard normal space. According to the point estimate method，the moment estimation formula of the performance function was established on the statistical characteristics of basic random variables. According to the relationship between the statistical moment and variables，the probability density function was derived based on the maximum entropy principle with the constraint of the first four moments of the performance function. A one-dimensional numerical integral method of reliability analysis was then developed for structural stability of tunnel lining consisting of rock bolts and shotcrete based on build-up arch theory. The accuracy of the proposed approach was verified using a numerical example，and the reliability analysis for Jingzhushan highway tunnel was conducted.

Rock-like specimens were made in the laboratory to have two pre-existing transfixion cracks of designated size and inclination. The failure characteristics of the specimens were studied using conventional triaxial compression tests. The macroscopic fracture trace of the samples shows the characteristics of coplanar cracks，anti-wing cracks and wing cracks. The two pre-existing cracks may be linked by stretching coalescence or shear coalescence，or one crack may propagate to link with the other via an anti-wing crack，or the two pre-existing cracks may not be linked. Under triaxial loading conditions，the anti-wing crack is the major propagation crack，which affects the final failure mode of the samples. The arrangement of the two pre-existing cracks and the confining pressure are the two main factors that dictate the final failure mechanism of the specimens. The axial stress-strain curves of the samples show multi-peak characteristics under triaxial loading conditions and the deformation characteristics change from brittle behaviour under low confining pressure to more ductile under high confining pressure conditions. Under high confining pressure，the dilation is insignificant or almost nonexistent. The axial stress-strain curves are closely related to the processes of fracture initiation，fracture propagation and fracture coalescence.

The numerical manifold method(NMM) has succeeded in providing a unified solution to continuum and discontinuum problems and therefore it is highly suitable for solving fracture mechanics problems. However，the conventional high-order NMM using the first order polynomial as the local displacement function has the problem of linear dependence，which restricts to a certain degree its further development and application. A new NMM framework was established in this research by introducing a new localized displacement function，as well as a special displacement function for modeling the stress singularity around crack tips. A new paradigm that eliminates the problem of linear dependence is then derived to solve linear elastic fracture mechanics problems. The numerical examples show that：(1) The proposed method successfully eliminates the problem of linear dependence；(2) For classic linear elastic fracture problems，the stress intensity factors at the crack tip can be calculated accurately even if the mesh is relatively sparse；(3) The stress function at interpolation points inside the physical domain is continuous；(4) All the degrees of freedom defined on non-singular physical patches are physically meaningful，with the third to the fifth being the strain components at the interpolation point of the patch. As a result，the stress components at the interpolation point can be directly obtained. Finally，the proposed approach can be easily extended to other methods based on the theory of the partition of unity.

In order to investigate the problem of rock fracture propagation and arrest under mixed-mode I and II dynamic loading，single cleavage semi-circle compression(SCSCC) plate specimens of sandstone were subjected to dynamic impact by a split Hopkinson pressure bar(SHPB). Numerical simulations were used to study the fracture propagation path under mixed mode dynamic loading. In order to verify the reliability of the numerical simulation，dynamic finite difference analysis was applied to a finite plate with a central crack subjected to impact tension at the boundary. For the SHPB tests，the measured strain at the incident bar was compared with the strain obtained from the numerical simulation. The results show that：(1) The numerical model produced outcomes that are consistent with published results. The strain values at the incident bar from numerical simulations and experiments agree extremely well with each other，suggesting the feasibility of using numerical methods to model SHPB tests. (2) The crack propagation path from the numerical simulation agrees reasonably well with the SHPB test results. (3) During the fracture propagation in SCSCC specimens，the crack tip suffers some instantaneous arrests but eventually will propagate towards the central axis(maximum stress zone) of the specimen. (4) SCSCC specimens provide a suitable geometry to study dynamic rock fracture problems. They can be easily used for mixed-mode I and II loading conditions and will provide an effective tool for subsequent research on crack propagation arrest.

In ground control theory，the supporting action of a coal seam under a tight roof has often been simplified to that of an elastic foundation，which ignores the influence of the decreasing bearing capacity in the plastic zone of the coal seam near the working face. In order to solve this problem，in this research，the coal seam was divided into two regions：a plastic zone near and an elastic zone ahead of the working face. A nonlinear expression for calculating the supporting force in the plastic zone of the coal seam was proposed based on the fact that the variation of the coal seam supporting force is continuous and the maximum supporting force occurs at the boundary between the plastic and the elastic zones. The calculation method to determine the maximum supporting force and two methods to assess the accuracy of this value are presented. The supporting mechanism of the elastic and plastic zones and the hard roof mechanical behaviour were analyzed by extending the traditional assumption that the roof is fully supported by an elastic foundation. An equation for roof deflection above the plastic zone of the coal seam was derived and constants were obtained for all five parts of the equation. A numerical example has demonstrated that with increasing step size of gob area，the deflection of the roof，the maximum supporting force in the plastic zone，and the bending moment of the roof between the working face and the middle of the gob area all increase，while the supporting force near the working face decreases slightly. However，the maximum bending moment ahead of the working face is always greater than that in the middle of the gob area. Therefore if failure occurs because of too large a bending moment，the fracture lines will be in the plastic zone of the coal seam ahead of the working face. Compared with the traditional approach of assuming a fully elastic foundation，our analysis has led to the following new conclusions. The roof and the coal seam work together to support the weight of overlying rocks. The supporting force of the coal seam at the working face assuming a fully elastic foundation is several times greater than that obtained when the plastic zone of the coal seam is considered. Consequently，when fully elastic foundation is assumed，the roof deflection is small due to small bending moments in the roof，and the range of significant deflection in the roof is also small. However，when the plastic zone is considered，the supporting force of the coal seam near the working face reduces significantly and therefore the roof will take more of the weight of the overlying rock，resulting in much greater deflection in more areas of the roof. This leads to significant increases in both the maximum bending moment and the distance from where it occurs to the working face，which is directly related to the fracture failure in the roof ahead of the working face. The predicted distance based on the plastic zone approach in this case is greater than 4 m，which agrees well with in-situ observations of the fracture failure in the roof ahead of the working face，suggesting the bending force and deflection of the roof calculated based on the proposed approach are much closer to reality.

Triaxial loading and unloading tests were carried out on prefabricated cylindrical rock samples with non- interpenetrated joints at three different joint connectivities. The stress-strain curves，the failure mechanism and the strength characteristics of the specimens during loading and unloading under the three test conditions were compared. The relationships between the characteristics of deformation and strength and the joint connectivity were also analyzed. The results show：(1) The rock samples with non-interpenetrated joints exhibit anisotropic mechanical properties during loading or unloading conditions. An increase in joint connectivity leads to an increase in the degree of anisotropy；(2) The unloading process produces more cracks and hence greater extent of damage in the specimen；(3) The joint connectivity has significant influence on the deformation behaviour of the specimens at the unloading stage. The deformation modulus decreases gradually as the joint connectivity increases；(4) For different joint orientations，the decrease in deformation modulus of rocks with non-penetrated joints at the unloading stage has a linear relationship with the joint connectivity；(5) As the joint connectivity increases，the peak strength of the specimen at the loading stage decreases and，at the unloading stage，its cohesion and internal friction angle also decrease.

The control of soil deformation and the rectification of shield machine tilting are the major technical difficulties in double-O-tube(DOT) tunnel constructions. In this paper，the tilting characteristics of a DOT shield machine during construction were analyzed. Based on the theory of stochastic medium，the relationship between tilt angle and surface subsidence and horizontal deformation was derived by transformation of the coordinate system and integration over several partitioned areas. The relationship was then applied in the analysis of two case studies：anticlockwise and clockwise tilting. As demonstrated，the tilting of the DOT shield causes additional surface deformation and results in asymmetric surface deformation curves compared with symmetric profiles when there is no tilting. There are three focal points(V1，V2 and V3) on the surface subsidence curve and four focal points(H1，H2，H3 and H4) on the horizontal surface deformation curve，where surface deformation increments of soils occur in opposite directions on either side of any focal point. For anticlockwise tilting of the DOT shield，the additional vertical deformation of soils on the left side of V1 and between V2 and V3 is upward while that on the right side of V3 and between V1 and V2 is downward. The additional horizontal deformation of soils between H1 and H2 and between H3 and H4 is positive while that between H2 and H3，on the left side of H1 and on the right side of H4 is negative. The maximum surface settlement increases nonlinearly as the tilting angle increases and its position moves left. The maximum horizontal surface deformation to the right increases linearly while the maximum horizontal surface deformation to the left decreases slightly first and then increases，while the point with no horizontal deformation gradually moves left. For clockwise tilting，additional surface deformation of soils on both sides of any focal point is in the opposite direction to that of the anticlockwise case. The maximum horizontal surface deformation to the right decreases as the tilt angle increases and both the position of the maximum surface settlement and the point with no horizontal deformation gradually move right.

Locating boulders in metro shield zones is a complex three dimensional detection problem that has not been resolved. In order to improve the detection accuracy，3D resistivity cross-hole tomography was introduced into boulder detection in subway construction. Based on the typical detection arrangement of cross-hole resistivity prospecting using four parallel boreholes，the inverse imaging equation and the suitable corresponding equipment were investigated. It was found from numerical simulations that using potential gradient data gathered by an array of AM-BN electrodes will produce the best quality image of the detected boulders. On this basis，further numerical simulation studies were carried out on the influence of borehole distance and electrode spacing on the final the detection result. Consequently，the rational parameters for the 3D resistivity cross-hole tomography detection method were determined. The method was then tested on the detection of small boulders and densely populated boulder swarms. Finally，physical model experiments were carried out to verify the study. The detection result indicated the actual distribution of high resistivity bodies with a high level of accuracy，suggesting the feasibility of using the 3D resistivity cross-hole tomography method in metro shield zone boulder detection.

The groundwater level around the front section of the Kuyu water conveyance tunnel is far above the ceiling of the tunnel，causing groundwater infiltration to be so severe that it ‘rains’ constantly in the tunnel. During construction，accidental collapse occurred often and many collapse galleries were formed above the tunnel，which brought serious problems and delays to the construction. Based on investigation and analysis of some of the collapse incidents，the failure mechanism was studied systematically using the finite difference software FLAC3D，and the effectiveness of ground reinforcement on a typical collapse section was assessed. The study showed that the formation lithology was the internal cause of the collapses，and that the groundwater further exacerbated the instability potential，with the deformation almost triple that under anhydrous conditions. Lack of timely initial support and too large an advance per excavation cycle were two direct causes of tunnel collapses，as these practices caused additional deformation of 80% and 20% respectively. The rationality of the ground reinforcement schemes and the quality of construction of the ground support system are crucial to the long-term stability of the tunnel.

At present，there is no comprehensive theoretical framework that not only can describe reasonably the behaviour of normal cyclic deformation of soil，but is also suitable for its calculation and prediction at high-cyclic conditions，i.e.，at large numbers of load cycles. In this paper，an elastoplastic accumulation model was developed which incorporates the characteristics of high-cyclic loading and allows a free selection of the integration step size. This model adopts the theoretical framework of Perzyna viscoplasticity and uses an accumulated plastic strain increment over a number of load cycles as a response envelope. Based on the general principles of critical state soil mechanics，the accumulated plastic volumetric strain was used as the hardening parameter to describe the size of the plastic strain accumulation using a power law. A factor representing the influence of average stress was introduced to describe the strain hardening process. In addition，the principles of the modified Cam-clay model at the average stress state were used to describe the direction of the plastic strain accumulation. The developed model was calibrated with data from cyclic triaxial tests. It was found that the model can describe with a sufficient level of accuracy the plastic strain accumulation at low stress levels. However，there were some discrepancies between the model predictions and experimental results at high stress levels，especially when the average stress level was close to or higher than the critical state values.

The effect of principal stress ratio on creep behaviour of over-consolidated soil was studied through tests on undisturbed soft clay samples under plane strain conditions. The over-consolidation shear stress ratio (OCRq)，defined with the generalized shear stress，was found to be a function of the principal stress ratio and the pre-consolidation pressure. OCRq can provide a better and more direct description of the creep behaviour of over-consolidated soft clay under plane strain conditions compared with the over-consolidation spherical stress ratio(OCRp). There is a one-to-one relationship between the creep coefficient and the OCRq：as the OCRq increases，the corresponding creep coefficient decreases. For the same OCRq，over-consolidated soils with smaller principal stress ratios will have larger creep coefficients. For different principal stress ratios，the over-consolidated soft clays will have smaller generalized shear stress than normally consolidated ones. Under certain conditions，the generalized shear stress increases with decreasing principal stress ratio and the corresponding over-consolidated soil will have greater long-term creep deformation.

Common shapes of excavations include strip，rectangle，circle and pistol. When other conditions are the same，excavations with different shapes have different safety coefficients of heave-resistant stability. However，all recommended methods from existing guidelines for heave-resistant stability analysis ignore the influence of excavation shape on the safety coefficient. In this paper，based on an unloading model of excavation，a new safety coefficient has been defined which takes into account the plane shape，dimensions and embedment ratio. The safety coefficients for various excavation shapes，such as strip，rectangular and pistol，can be calculated analytically based on the definition. For circular excavations，the coefficient can be calculated by numerical integration，so the challenging problem of analyzing the stability of circular excavations is solved. When the diameter of circular excavations is large enough，the safety coefficient will be identical to that of extra wide strip excavations，indicating the wide applicability of the proposed safety coefficient. For excavations with a small embedment ratio of retaining wall in clay stratum，the proposed safety coefficient converges to the result from the Terzaghi method. The variation of the bearing capacity coefficient of foundation soil calculated using the proposed method is consistent with that of recommended values，and its rationality can be validated by field data and results from the strength reduction method. Field statistics indicate that there is a definite relationship between the safety coefficient and the deformation of circular excavations and the relationship can be used to determine the acceptable safety coefficient of excavations.

Shaking table test on the interaction between the pile group and super highrise building system on liquefiable foundation was conducted to reproduce the liquefaction-induced large deformation of the system in saturated sandy ground. The excess pore water pressure(EPWP) of ground，the natural frequency，the damping ratio，the strain of pile group，the contact pressure at the bottom of pile and the displacement at pile top was calculated and analyzed before and after large deformation. It was shown that the EPWP response in and out of pile group was different. The sand layer liquefied，the natural frequency of pile group decreased and the damping ratio of pile group increased with the raise of peak acceleration. The dynamic response of piles was relevant to both the peak acceleration and the spectral characteristic of earthquake wave. Besides，the peak strain of pile increased upward along pile body so that there were more cracks on the top of pile. The displacement of pile head varied with the seismic behavior. The primary cause of the large deformation of the system was revealed through the phenomenon which two corner piles were pulled up and pressed down alternately under excitation. Consequently，it is effective to improve the anti-seismic capacity of super highrise building-pile group system by strengthening compressive and tensile resistant property of pile and improving the liquefaction conditions of ground.

As a new type of bridge foundation，the lattice shaped diaphragm wall(LSDW) provides a potential new solution to the problem of bridge foundation in soft soil for the construction of high-speed railways. In this paper，three LSDW foundation models with one，two and four chambers respectively were studied using an indoor test model having a similarity ratio of 1∶30. It was found that the Q-s curves of all three LSDWs show the characteristics of gentle variation in settlement，and the ultimate bearing capacity of LSDWs increases non-linearly with the growth of material consumption and the number of chambers. The outer skin friction is related to soil properties and the relative displacement between the wall and the soil. The inner skin friction arises from the bottom of the wall，extending up to 1/4 of its depth and showing an“L”shaped distribution. Its influence on the bearing capacity becomes more significant as the lattice size increases. The direct soil resistance to the LSDW foundation is relatively small and its contribution to the ultimate bearing capacity of the foundation can be ignored. During the loading process，all three LSDW foundations show the change from an end-surface bearing to a friction bearing dominant wall. At the same depth and wall thickness，adopting fewer chambers in the LSDW foundation，compared with using a larger chamber size，is more effective at weakening the combined effect of wall groups and achieving a better bearing performance of the foundation.