In the future, the extraterrestrial human activities, such as resources exploitation and base construction beyond earth need the aid of geotechnical engineering technology. Currently, there are only two approaches for humans to obtain the rock samples beyond earth: sample-return activities by spacecraft and meteorite survey. Meteorites are rare, expensive, small in size and arbitrary in shape, so it is difficult to process them into standard rock samples required by mechanical testing & simulation (MTS) and other traditional macroscopic rock mechanical tests. In this paper, a novel technique for measuring mechanical property of small-size meteorites is developed based on microscopic rock mechanics experiments (micro-RME) and statistical probability models. Firstly, the composition, content and distribution of NWA13618 meteorite rock-forming minerals were obtained by TESCAN integrated mineral analyzer(TIMA). Then, the nanoindentation technology was used to carry out a large number of indentation tests to obtain the multi-point elastic modulus. After that, the mechanical parameters of four main minerals in meteorite NWA13618 were derived by using Gaussian mixture model, and the elastic moduli of olivine, pyroxene, Fe-Ni and feldspar were 116.73, 101.77, 87.24 GPa and 70.74 GPa, respectively. Finally, the macroscopic cm-scale elastic modulus of NWA13618 meteorite determined by the homogenization method Mori-Tanaka model was 90.48 GPa according to the mineral content and mechanical properties. The novel micro-rock mechanical experiment technique and scale upgrading method proposed in this paper provide theoretical basis and technical means for predicting the mechanical properties of L4 parent asteroid.

The loess was stabilized using geopolymer (GP). Triaxial compression tests were conducted on stabilized loess with varied GP contents subjected to wet-dry cycles. The degradation law of the shear strength of the stabilized loess after varied wet-dry cycles was evaluated and an empirical model for predicting the shear strength was proposed. The chemical composition of the hydration products, the microstructure and pore size distribution of stabilized loess were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and mercury intrusion porosimetry (MIP) tests. The degradation mechanisms of GP stabilized loess under wet-dry cycles were discussed based on the experimental results. The experimental results show that compared with untreated soil, the shear strength of stabilized soils is significantly improved with the increasing GP content, i.e. the cohesion and internal friction angle increase by 260% and 43%, respectively. The shear strength of stabilized loess decreases with the increasing ratio of porosity to GP volumetric fraction ( ) in a power function. It indicates that GP stabilization can remarkably improve the durability of loess under wet-dry cycles. The stabilized loess with 10% and 15% GP can maintain over 75% of their original shear strength, but those with 5% GP shows evident deterioration in shear strength after nine wet-dry cycles. The wet-dry cycling has greater impact on the degradation of peak deviatoric stress and cohesion than that of internal friction angle. An empirical model was proposed and validated for predicting the degradation in shear strength of the GP stabilized loess under wet-dry cycles, considering influence of the GP content, confining pressure and the number of wet-dry cycle. The experimental results of XRD, SEM and MIP show that the main hydration products of GP are calcium silicate hydrate (CSH) and calcium aluminosilicate hydrate (CASH), which fill the soil pores and enhance the bonding between soil particles. Due to this reason, a denser microstructure develops and the cohesion of the stabilized loess increases, which consequently improves the shear strength of the GP stabilized loesses. Moreover, the wet-dry cycle results in the expansion of soil pores and the formation of new fissures, which destructs the bonding between soil particles and reduces the shear strength of the stabilized loess.

To study the active earth pressure of finite soil behind the retaining wall, the cohesionless soil behind the wall is taken as the research object. The fracture surface is assumed as the plane passing through the heel of the wall, and in the translational mode of the retaining wall, the soil behind the retaining wall forms an arc-shaped small principal stress arch. The soil behind the retaining wall is divided into several curve thin-layer elements by the stratification method along the small principal stress. Considering the inhomogeneity of stress distribution on the upper and lower surface of the element, a calculation method is proposed for the active earth pressure of finite soil retaining wall. The expressions of active earth pressure resultant force and the height of its action point are given, and the correctness of this method is verified. The results show that the curve thin-layer element method can accurately consider the complex stress condition of the element, and can better reflect the variation law of the active earth pressure of finite soil behind the retaining wall. The active earth pressure shows a nonlinear distribution along the wall height H, it firstly increases with the soil depth increasing, then decreases monotonically near the bottom of the wall. In parameter sensitivity analysis, the distribution of active earth pressure of retaining wall and the height of combined force applied point are analyzed with different width-height ratios of soil and wall back roughness. The results show that with the increase of width-height ratio n, the active earth pressure gradually increases, the curve of earth pressure distribution becomes more and more nonlinear, the height of resultant force application point gradually decreases, and it is always greater than . It tends to be stable when n is greater than 0.71, so 0.71 can be assumed as the critical width-height ratio of finite soil and semi-infinite soil. The active earth pressure decreases gradually with the increase of the frictional angle ; the curve of earth pressure distribution becomes more and more nonlinear, the height of resultant force application point increases gradually and is always greater than .

Based on the axisymmetric consolidation model with the inward radial flow in the soil around a vertical drain, the consolidation equations of the composite ground with long vertical drains and short impervious columns under time-dependent loading were presented. The analytical solutions for consolidation of this combined composite foundation were derived under the single-sided drainage condition, including the solutions for the excess pore water pressures within the vertical drain and the surrounding soil, and for the overall average consolidation degree of the composite foundation. The rationalities of the proposed solutions were verified by 3D FEM simulations. The main influencing factors were analyzed using the proposed solutions, and the consolidation characteristics of the combined composite ground were also investigated. The results show that the consolidation rate of the combined composite foundation increases gradually with the increasing penetration ratio of the short impervious columns and decreases with the increases in the well resistance and the thickness of the smear zone. The variations in the stiffness and replacement ratio of the short impervious columns have less effect on the consolidation rate of the composite foundation.

In order to study the localized failure characteristics of sandstone deformation under the coupling of seepage and stress, the three-dimensional digital image correlation (3D-DIC) technology was applied to the visualized three-axis servo control test system, and the triaxial compression tests under different seepage pressures were carried out on the sandstone. The results show that, under the coupling of seepage and stress, the cloud image of the sandstone surface deformation field has undergone an evolutional process from uniform to non-uniform. The deformation before the peak is relatively uniform, the strain concentration appears at the peak, and a deformation localized zone is formed rapidly in a short time after the peak. With the increase of seepage pressure, the peak strength and elastic modulus of the rock exhibit exponential nonlinear attenuation, the peak strength weakening coefficient and elastic modulus weakening coefficient both increase, the permeability gradually increases, and the earlier the maximum permeability appears. With the seepage pressure increases, the deformation localization zone of sandstone transits from shearing to tension-shearing, the internal and external strains of the axial and radial deformation localized zone show large differences within a short time after the peak, and the in-band strain is much larger than the out-of-band strain. With the increase of seepage pressure, the higher the starting stress level of deformation localization, the earlier the starting time point. The seepage pressure is linearly associated with the stress level of the sandstone deformation localization start-up stress. The axial deformation localization start-up level is more significantly affected by the seepage pressure than the radial direction.

Geogrid reinforcements can effectively improve the pullout capacity of anchor plates, but the failure mechanism and influencing factors during the uplift process need to be further investigated. In this paper, a series of uplift tests was carried out on horizontal anchor plates in sand to investigate their pullout characteristics, and the influence of various factors was analyzed, including sand density, anchor embedment depth, and number of geogrids and their locations. The particle image velocimetry (PIV) technology was used to explore the deformation and failure mechanism of the sand around anchor plates. The results show that for the pullout capacity of an anchor plate is significantly enhanced by one layer of contact-type geogrid, and the reinforcing effect is better than that with non-contact geogrid. This phenomenon is associated with mobilized friction of the geogrid and the increased weight of sand within the failure surface. When two layers of geogrids are installed, the lower geogrid plays a dominant role in restricting the lateral soil deformation and homogenizing the stress distribution, and the contribution of the upper geogrid is relatively low. Whether geogrids are applied or not will alter the deformation mechanism at the anchor-sand interface. With geogrid reinforcement, the failure surface converges inward, and the shear strain distribution is more uniform.

In order to study the evolution characteristics of the fracture plane of the anti-dip rock slope with the steep and gently dipping structural plane under the condition of its own weight. Taking the toppling deformation form of right abutment of Miaowei Hydropower Station as the geological prototype, the centrifugal model test was carried out by presetting non-penetrating cracks of the rock strata in different parts of the slope body to simulate the evolution characteristics of the fracture surface of the anti-dip rock slope under the condition of its own weight. The researches have demonstrated that: (1) The failure of anti-dip rock slopes with steep and gently dipping structural planes are marked by the formation of fracture surfaces, which are divided into three stages: in the initial period (0–40g, g is the acceleration of gravity), it refers to the stage of partial fracturation which takes partial fracturation and stratum forwarding on the trailing edge as the major failure characteristics with less position changes in slope plane. In the middle period (40g–80g), it refers to the formation stage of major fracture plane which can be formed in the deep structural plane of slope through expansion and connection in a top-down approach. Position changes in slope nearly account for 3/4 of total position changes. In the later period (80g–120g), it refers to the formation stage of multi-stage fracture plane whose main formation feature is the stress redistribution of fracture strata within the slope. Position changes in slope basically remain unchanged. (2) The fracture of rock bridge between structural planes is transient, but the formation of fracture plane is a gradual development process which is mainly controlled by steep-inclined structural planes. The strain at the crevice of the main fracture plane is the greatest and the stress mode is the most complex. And the fracture strain at the secondary fracture plane takes the second place. Based on fracture mechanics, the fracture criteria of the rock compression-shear and unbalanced force formula for rock stratum have been simplified. It is revealed that the unbalanced force of the rock stratum at the main fracture surface decreases from 1/3 of the slope height to the bottom and top of the slope. The formation of fracture surface is mainly affected by the ratio of the intensity factor of shear stress to normal stress, the length of rock structure plane and the crack rate.

In order to understand the significance of stratum stratification characteristics during the formation of underground freshwater lens in the coral reef islands, the particle size distribution of the samples drilled at various depths of a coral reef island in the South China Sea is analyzed. The zone and stratification of the island are determined according to the particle size characteristics in the horizontal and vertical directions, respectively. The area of each zone is determined based on the range covered by each drilling, and the thickness of each stratum is determined by the thickness of the samples with similar particle size in each drill hole. The permeability of the strata is controlled by the particle size distribution of different zones and strata of the loose layer above the reef limestone, while the vertical and horizontal permeabilities control the difficulty of the underground freshwater lens formation, the total thickness of the freshwater lens, and the thickness of the transition zone. The numerical model is established by considering the total area of the island and the number of strata. Finally, the numerical results of groundwater concentration characteristics at different times, horizontal positions and depths are obtained.

Flexible debris flow barriers are important engineering measures to prevent debris flow disasters. The existing prevention structures are mainly in the form of closed barriers, which are prone to blockage with poor regulation abilities. Therefore, we proposed open flexible debris flow barriers to overcome the above shortcomings. Based on theoretical analyses and physical model tests, the research on the regulation performance of the open flexible debris flow barriers was carried out, and the theoretical formulas for the velocity attenuation rate, run-up height, and blocking rate of debris flows were deduced. The results show that compared with the closed flexible debris flow barriers, the improved structure has a good self-cleaning effect and can effectively control the peak velocity of debris flows. The calculation results through the derived non-dimensional theoretical formulas are in good agreement with the physical test results. The velocity attenuation rate, run-up height, and blocking rate of debris flows are mainly controlled by the relative open height, dimensionless flow depth, relative density of debris flows, and the Froude number. The velocity attenuation rate and blocking rate are negatively correlated with the relative open height, and positively correlated with the relative density of debris flows. The run-up height is negatively correlated with both the relative open height and the relative density. The above research can provide theoretical and technical support for the application of open flexible barriers in debris flow prevention and control projects.

Based on visualized pull-out system and digital photogrammetry measurement technology, pull-out tests were carried out for five kinds of coarse-grained soils with different coarse-grained contents (mass percentage of particles with particle size>5 mm). The effects of coarse-grained content on the interface strength index, particle displacement evolution and geogrid strain were discussed. The test results show that the interface cohesion c and the interface friction angle increase with increasing in different degrees. When increases from 20% to 35%, the pull-out displacements of geogrid corresponding to the peak value of strain and pull-out force at the end of geogrid decrease, but the geogrid strain increases at each section; with the increase of , the displacement vector direction of coarse-grained soil particles tends to be horizontal, and the displacement decreases significantly. At the same time, the void of the interface between reinforcement and soil decreases obviously. The increase of reduces the displacement of coarse-grained soil particles at the interface of reinforcement and soil, while the range of indirect influence zone expands, which indirectly drives coarse-grained soil particles within a certain height range, and increases the cohesive force of the interface at macroscopic scale. With the increase of , the maximum displacement velocity of soil particles at the V3 interface decreases. The maximum displacement velocities of soil particles at V1 and V2 in the indirect influence area increase slightly due to the expansion of the indirect influence area and the strengthening of particle disturbance.

Red mudstone compacted at optimal water content has been verified to be appropriate as fill material of high-speed railway subgrade. But the accumulative deformation behaviour of compacted red mudstone at saturated condition has not been investigated very well. In this study, a series of cyclic triaxial tests was carried out to study the effect of confining pressure and dynamic load on the accumulative deformation of saturated red mudstone fill (SRMF) material. Results indicate that the equivalent Young’s modulus decreases rapidly to a stable state with increasing the cyclic number. The stable is strongly correlated to the stress state, and it increases with increasing the confining pressure and decreases exponentially with increasing the cyclic stress ratio. Based on shakedown theory, three types of accumulative deformation modes, namely, plastic shakedown, plastic creep, and incremental collapse, were identified. The stress state causing the unstable deformation was named as the plastic shakedown limit. The stress state that causes a sudden increase in strain rate was defined as the plastic creep limit. The cyclic stress ratios corresponding to the plastic shakedown and plastic creep limit were smaller than the shear strength at static state, and decreased exponentially as the confining pressure increases. With particular emphasis on the effects of rainfall, the drainage facilities and improved red mudstone fill material were suggested in the design of surface layer of subgrade to enhance their stability.

In this study, one-dimensional consolidation creep test was conducted to study the consolidation creep characteristics of the sandy grain muddy soil of Dongting Lake, and an empirical creep model suitable for describing the stress-strain-time relationship of the sandy grain muddy soil of Dongting Lake was established based on the test results. The results show that there is a good linear increasing relationship between axial strain ε and time t in double logarithmic coordinate system. In addition, with the increase of consolidation stress, the slope of - relationship curve decreases significantly, and the distance between - relationship curves becomes shorter under the action of two adjacent loads. Under high stress levels, the - relationship curve tends to be horizontal, and the decrease rate of the slope of the curve is significantly reduced. Moreover, hyperbolic function is more suitable than exponential function to describe the stress-strain relationship of the sandy grain muddy soil of Dongting Lake, and it is more in line with engineering practice to modify the strain-stress relationship in Singh-Mitchell model to hyperbolic relationship. It is found that the slope of the - relationship curve has a hyperbolic function relationship with the consolidation stress. On this basis, a modified Singh-Mitchell model with five parameters reflecting the influence of stress level and suitable for describing the creep characteristics of the sandy grain muddy soil of Dongting Lake is established.

A shaking table experiment was conducted on a shield-enlarge-dig type subway station structure in sandy ground subjected to the near field earthquake and the far field earthquake. The horizontal displacement, surface deformation, acceleration, earth pressure response of the model ground and the acceleration and strain of the model structure of sandy soil are analyzed. The measured data substantiate that, the seismic response of soil-structure interaction system is more intense to the ground motion with low-and medium frequency. The subway station structure subjected to strong earthquake motions has obvious spatial effect, and the existence of underground structure will result in a change in the deformation distribution mode of ground surface. The acceleration response of columns of the model structure increases gradually from bottom to top as result of a low-intensity earthquake, while for the high- intensity earthquake, the acceleration response presents a law of increasing first and then decreasing. The acceleration response of the top plate is the biggest, followed by middle plate and bottom plate is the smallest under seismic action. And in addition to this, the acceleration response of the model structure is roughly equal to that of the model soil, and the dynamic earth pressure of the side wall increases gradually from bottom to top as result of the low-intensity earthquake; while for the high-intensity earthquake, the acceleration response of the model structure significantly surpasses that of the model soil, and the maximum value of earth pressure occurs at the arch shoulder and the middle part of the expanded tunnel. The earthquake damage mechanism of the shield-enlarge-dig type subway station structure is given based on the macroscopic phenomena of model structure after shock and the stretching strain amplitude under different ground motions.

To investigate the dynamic response characteristics of pile groups in liquefaction sites under strong earthquakes as well as the laws between soil resistance and pile-soil relative displacement (p-y), a shaking table model test associated with the project of Haiwen Bridge was conducted. The dynamic responses of sand pore pressure ratio, pile bending moment and p-y curve under different embedded depths of saturated silty sand encountered by 0.15g-0.35g seismic action were studied. The results show that when the seismic intensity reaches 0.25g, the pore pressure ratio of saturated silty sand under different embedded depths is larger than 0.8 and the liquefaction phenomenon occurs. As the embedded depth increases, the increased time of the pore pressure ratio is obviously delayed. At different embedded depths, the maximum bending moment of the pile appears at the interface between liquefied soil layer and the non-liquefied soil layer. At the same embedded depth, the area surrounded by the p-y curve increases gradually with seismic intensity, and its overall slope decreases, indicating that the dynamic energy dissipation of pile-soil interaction increases gradually and that the stiffness of soil around the pile decreases gradually. As the embedded depth increases, the area enclosed by the p-y curve gradually decreases and its overall slope gradually increases, indicating that the dynamic energy dissipation of pile-soil interaction gradually decreases and the soil stiffness around the pile gradually increases. Therefore, when performing the seismic design of bridge pile groups at liquefied sites, the relationship between liquefied soil layer and pile foundation should be considered comprehensively to ensure the bending bearing capacity of the pile foundations at the boundary between liquefied and non-liquefied soil layers.

Large slip often occurs in deep soft soil during large area filling or excavation, which brings great difficulty to the analysis of anti-sliding pile considering pile-soil interaction. For this purpose, a modified cantilever pile method was proposed to overcome the problem in the calculation of the existing cantilever pile method considering the sliding behavior of deep soft soil layer. The soil pressure of the pile passive loading segment adopts an isosceles triangle distribution, and the maximum value is identical to the ultimate lateral soil pressure. The soft soil around the pile anchorage segment is assumed as ideal elastic-plastic to consider the large displacement of the soft soil. In addition, the displacement superposition principle is applied to deal with the discontinuous displacements around the sliding surface existed in previous methods. The displacement and bending moment results obtained by the proposed method are verified by in-situ pile side loading test. The displacement error of pile top is less than 3%, the maximum bending moment error of pile is less than 10%. The proposed method is helpful for the design and calculation of anti-sliding piles in deep soft soil layer.

Tens of thousands of ancient landslides and potential landslides are distributed along the Three-rivers basin in the southeast of Qinghai-Tibet Plateau, posing a severe threat to the Sichuan-Tibet railway under construction. A shaking table model test was performed to study the dynamic response of bedding rock slope with weak interlayer under strong earthquake. The influences of different ground motion parameters, input wave types, and weak interlayer on slope dynamic response were analysed. The test results show that the natural frequency of the slope decreases gradually with the increase of the number of input seismic waves, and the vibration intensities of 0.3g and 0.6g are the critical dynamic conditions for crack initiation and instability of the slope. There is an obvious elevation effect on the slope, and the acceleration amplification factor increases first, then decreases, finally increases along the slope surface, and is larger at 1/4 of the slope height and the top of the slope. The vertical acceleration amplification factor inside the slope increases linearly with elevation. The frequency has a great impact on the dynamic amplification response of the slope. The slope does not significantly amplify low-frequency seismic waves, and even inhibit them. With the increase of frequency, the dynamic amplification effect of slope becomes more and more prominent. As the amplitude increases, the acceleration amplification factor firstly increases and then decreases, finally reaches the maximum value at the vibration intensities of 0.3g–0.4g. Under the excitation of different types of seismic waves, the amplifying effect of slope on natural waves is higher than that on synthetic waves. The existence of a weak interlayer amplifies the input seismic wave markedly, and the fast Fourier transform (FFT) shows that the sensitivity of positions of the weak interlayer to frequency bands of input seismic waves differs. This experiment reveals the dynamic response law of bedding rock slope with weak interlayer under strong earthquake action and provides a basis for further study on the failure mechanism and prevention of slope.

Model tests were conducted to investigate the installation behavior of modified suction caisson (MSC) and regular suction caisson (RSC) in layered soil (sand, clay, sand over clay and clay over sand). It was found that the MSC can penetrate the layered soil to the desired depth. The final penetration depths for MSC in sand, clay, sand over clay and clay over sand increase approximately 10.0%, 2.3%, 3.0% and 9.6%, compared with the RSC. In addition, the maximum required suctions for MSC in sand, clay, sand over clay and clay over sand increase approximately 0.9%, 14.4%, 66.2% and 92.2%, compared with the RSC. It was found that the installation behavior of MSC in layered soil is strongly influenced by the position and the thickness of the clay layer. When the MSC penetrates clay over sand, the maximum value of suction is achieved when the suction caisson tip contacts the interface between sand and clay. The maximum applied suction increases with increasing the soil distribution coefficient t (ratio of upper soil thickness to the total soil thickness). However, the final penetration depth was found to decrease with increasing the t value. When the MSC penetrates sand over clay, the maximum applied suction was obtained at the final penetration depth. The maximum applied suction decreases with increasing the t value. The soil distribution coefficient has little effect on the final penetration depth for MSC in sand over clay. In addition, the installation way effectively influences the final penetration depth. The final penetration depths for MSC in sand, clay, clay over sand ( 0.4) and sand over clay ( 0.4) under the installation way of simultaneously pumping out water in the internal compartment and external structure increase about 13.8%, 3.4%, 16.4% and 4.6%, compared with those under the installation way of only pumping out water in the internal compartment. This study results can guide the design and construction of the suction caisson in layered soil.

In order to ascertain the difference of dynamic time-history response between large-diameter, deep-long single pile and pile group foundation under strong earthquake, a large shaking table test was carried out based on the physical project of Haiwen Bridge. The various rules and differences of pile top acceleration, pile top relative displacement, and pile bending moment between the single pile and pile group foundation under four types of seismic waves were studied. The results show that the time-history response of pile top acceleration is double-sided due to the pile group effect. The peak acceleration of pile group is larger than that of single pile, but the peak time lags behind that of single pile by 0.29–1.06 s. The pile top maximum relative displacement of the group pile is significantly smaller than that of the single pile, and there is an obvious lag in the time. Excited by the Kobe wave, the lag time is as long as 3.82 s. The maximum bending moment of the pile group is 7.54%–9.22% less than that of the single pile. Because the single pile is greatly affected by seismic waves, its amplitude of bending moment time-history response is obviously larger than that of the pile group. In the seismic design of pile foundation, the lag characteristic of dynamic time-history response of the pile group foundation can be fully used to design and select the optimal pile type reasonably.

Thermal property is one of the basic physical properties of rock and soil, and it is widely used to evaluate the retention, conduction and distribution of the heat. Thermal conductivity, specific heat capacity and thermal conductivity are the most common parameters, and they are also used in geothermal energy management and development, engineering freezing excavation and construction design in cold areas. The existing studies have shown that soil thermal parameters are associate to some factors such as the soil types, source, water content, density. In this study, the thermal parameters of silty clay and clay at a construction site in Zhanjiang, Guangdong province were tested. The results show that with increasing water contents, the thermal conductivity and thermal diffusivity of silty clay increase to a maximum value and then decrease, while the specific heat capacity increases linearly. The effect of dry density on thermal conductivity of silty clay depends on the moisture. When the water content is less than 20.0%, the thermal conductivity increases with the increase of dry density, while the water content is over 27.5%, it decreases with the increase of dry density. At the water content of about 24.5% (liquid limit), there is no law to follow. The effect of dry density on thermal diffusivity of silty clay is not obvious. Both the thermal conductivity and specific heat capacity of clay increase with the increase of water content and dry density. As the water content increases, the thermal diffusivity increases nonlinearly until it is stable. Under a low water content, the dry density does not significantly affect the thermal diffusivity; however the thermal diffusivity increases firstly and then decreases with increasing dry densities under the high water content. In addition, it is also found that the existence of large particles can cause the thermal conductivity of silty clay to be more complicated than that of clay.

The overall failure mode of a tower-shaped unstable rock mass associated with bottom compression-induced fracturing frequently occurs on the steep-high slope with a gentle dip angle in the karst regions, and its damage-catastrophe mechanism belongs to a key issue in the mountainous disaster discipline. Taking a collapse case of Zengziyan unstable rock mass #W12 in Nanchuan District of Chongqing, China, for example, a damage-catastrophe geomechanical model considering the load and the water-weakening effect was built. A damage constitutive equation and a total damage degree evolution equation were derived based on the strain equivalence principle, and the water-weakening function was developed into a cubic function in one unknown for the softening coefficient. Then, the geomechanical model was simplified into an equivalent spring model and the damage-fold catastrophe model was established by the energy balance theory. Finally, the failure criterion and eigenvalue expression of critical displacement mutation for the tower-shaped unstable rock mass were obtained. The results show that when the unstable rock mass #W12 fails, the control variant determining the stability of a fold catastrophe model is –0.003 251, which is less than zero, demonstrating that the system turns into an unstable state. The initial calculated value of the theoretical displacement mutation of 148.70 mm is smaller than the first inflection point of the measured value of 154.34 mm, and the relative error is about 3.65% which tends to be safer. The theoretical damage constitutive curve and evolution curve are consistent with the numerical results obtained in the literature, suggesting that the theoretical model has a good applicability. The research outcome can be applied to predicting the damage evolution process and the eigenvalue of critical displacement mutation for the compression-induced fracturing and failure of a tower-shaped unstable rock mass. It also provides a theoretical basis for monitoring and early-warning of the steep-high unstable rock mass collapse and disaster prevention and mitigation in limestone area.

Soil classification is one of the key issues in geotechnical investigation and design. And soil classification based on cone penetration test with pore water pressure measurement (CPTU) is an efficient and pragmatic method. The classification standards of existing methods are not consistent with Chinese code for geotechnical investigation on port and waterway engineering (JTS133-2013). Therefore, developing a CPTU-based soil classification method for port and waterway engineering is an urgent and meaningful task. This objective is achieved in this study by collecting database from a large number of worldwide water transportation projects including 616 CPTU and corresponding sampling boreholes, with spacing less than 5 m between them, and comparing and analyzing data and corresponding laboratory test results. Seven existing CPTU-based soil classification charts are selected for performance evaluation using the compiled CPTU and soil type database. It is shown that the stress normalization methods employed in existing soil classification charts may have limitation in shallow soils. A more adequate CPTU-based soil classification method is developed by introduction of new stress normalization method and modification of zone boundaries. It is implied that the proposed method can properly describe the general variation of soil types from CPTU data, particularly for soft soils, silty or fine sands and medium to coarse sands. And the developed CPTU-based soil classification method will provide a more accurate result as compared other existing methods in Chinese port and waterway engineering.

In previous studies on the mechanisms of deformation and failure of tunnels across active faults, the two effects of quasi-static faulting and seismic excitation were often studied separately, ignoring the possibility that the two effects are often threatening to the tunnel at the same time in the high seismic risk zone. In this study, sophisticated numerical methods and constitutive models were used to study the effect of combined fault rupture deformation and subsequent seismic excitation upon a tunnel. The weakening of the rock-tunnel interface under relative dislocation and degradation of the concrete material in the tunnel liner were considered. The deformation response and failure mechanism of the tunnel subjected to combined fault rupture deformation and subsequent seismic excitation were investigated. Relative deformation time histories, plastic strain, tensile strain of the tunnel were studied. And the performance of “joint” design was numerically verified, followed by a detailed parameter study that aimed to provide deep insight into the design factors of the technique of “flexible jointing”. The influences of some important factors were investigated, such as the range of the joints, length of the segments, and infill material properties. The results indicated that: (1) When solely affected by the faulting, the influence and damage to the tunnel are limited within the fault zone, while the other parts of the tunnel remain relatively intact. (2) Under the combined fault rupture deformation and subsequent seismic excitation, notable ovaling deformation and roof settlement would occur in the tunnel liner, also the tunnel spring line would suffer significate damage. Tunnels with initial faulting induced damage would suffer more damage under the action of earthquakes, and the damage degree increases with the increasing initial faulting distance. (3) The flexible joint design could decrease the tunnel’s relative deformation under the combined effect and enhance the stability of the tunnel. However, it should be noted that this benefit would be limited within the fortification range. (4) The suggested range of the fortification would be slightly larger than the width of the fault. A smaller segment length is preferred to improve the tunnel’s stability. And it seems that the width of the joint is irrelevant with the performance of the tunnel under the combined effect. As a preliminary exploration, current research results provide a certain reference for further improving the seismic resistance and fault resistance of underground engineering in strong earthquake areas in western China.

To evaluate the effect of the strain-softening of structured clays on the vertical bearing capacity of the spudcan foundations, firstly, the VUSDFLD subroutine was used to define the relationship between the undrained shear strength and accumulated absolute plastic shear strain , so that the coupled Eulerian-Lagrangian (CEL) numerical analysis method can simulate the strain-softening effect of structured clays. Then, based on the improved CEL numerical analysis method, the effects of soil sensitivity , soil strain-softening parameter , and soil brittleness parameter on the soil backflow above the spudcan as well as on the vertical bearing characteristics of spudcan foundations were analyzed. The results show that soil sensitivity , soil strain-softening parameter and soil brittleness parameter all have impacts on the soil backflow and on the vertical bearing capacity of spudcans, in which the effect of the brittleness parameter is most significant. Also, compared with the situation without considering the strain-softening effect, the bearing capacity factor of spudcan foundations and limiting cavity depth considering the strain-softening effect of structured clay are dramatically lower. Finally, the prediction expressions of the normalized limiting cavity height and vertical bearing capacity of spudcan foundations in structured marine clay were established, and the prediction results are reasonable. The research results of this paper can be used to assess the bearing capacity and penetration depth of spudcan foundations in practical engineering.

When groundwater leaks into the tunnel from damaged joints or cracks of the linings, fine particles could be pulled off by seepage force and transported throughout the soil matrix into the tunnel. Currently, very limited attention has been paid to the effect of the loss of fine particles induced by the water leakage, namely the internal erosion. In this study, the evolution of soil porosity, gradation, seepage flow, the induced ground movement and lining stress change due to tunnel leakage has been numerically investigated using a novel coupled hydro-mechanical approach formulated within the continuous porous medium framework. A critical state based constitutive model considering the influence of the fines content has been implemented for modelling the mechanical consequences of internal erosion. The numerical results show the spatial and temporal evolution of the eroded zone and the hydro-mechanical response of the tunnel and its surroundings. The results indicate that the commonly used pore pressure reduction-based method without considering internal erosion will under-estimate the leakage induced lining stress change and ground movement. Moreover, the influences of three-dimensional condition are highlighted.

To solve the problem of safe fully-mechanized mining in steeply dipped thick soft coal seam, physical modelling integrated with digital image correlation (DIC), acoustic emission (AE) and distributed optical fiber sensing (DOFS) technology, and the numerical simulations were conducted in this study. Based on the geological and engineering conditions of the 1212 (3) working face of Panbei Mine in Huainan mining area, the evolution of the fracture tendency zone of the regenerated roof during the lower slice mining was studied. The acoustic emission characteristics and the fiber strain responses of the regenerated rock mass were deeply investigated. The results show that the caving of regenerated roof consists of rock slippage, fracture of the low and mid-level cantilever beams and high-level articulated rock beams. Furthermore, the fracture of the double-beams is the key to the instability of the support in lower slice. The acoustic emission energies from the upper and middle parts of the lower slice are highly concentrated with short durations. Moreover, the fiber strain results indicate that the breakage occurs in the low cantilever beam and the high strain peak appears in the upper and middle parts. The middle and upper parts of the lower slice are the key areas for the stability control of the support and the regenerated roof. The lower part of the regenerated roof is densely filled with fragmented rock with much smaller grain size, where the rock leakage between and in front of the shelf is commonly encountered. A high-stress arch is formed in the regenerated roof of the lower slice, which is approximately 30 m in height from the goaf. The fracture of the double-beams mainly occurs in the arch, and the rock breakage in the arch has a certain collapse effect on the support.

During tunnel construction, blasting excavation and shotcrete are usually carried out alternately. Under blasting vibration, the bond between shotcrete and tunnel rock may be lost, resulting in local cavities at the interface. In this study, the influence of the cavity on blasting vibration characteristics and safety assessments of the tunnel shotcrete are investigated by using a theoretical model of thin-plate vibration, 3DEC modeling and field monitoring. The results show that when cavities exist at the interface between shotcrete and surrounding rock, the vibration velocity is amplified, the vibration duration becomes longer and the vibration frequency decreases for the shotcrete at the cavity location. Furthermore, the amplitude-frequency spectrum of the vibration has only one prominent peak. In addition, the peak particle velocity (PPV) decays faster with distance based on the regression analysis. For the safety assessments of the shotcrete layer, the extent of the dangerous zone is increased accordingly because the vibration on the shotcrete at the cavity location is amplified. As a result, the support time of shotcrete needs to be delayed and the maximum charge weight per delay needs to be reduced so as to ensure the safety of shotcrete under blasting vibration. This will lead to a decrease in the tunnel excavation efficiency and an increase in the construction cost.

Aiming at the limitation of stress relief method in vertical deep hole, an in-situ stress measurement technology suitable for vertical deep hole is proposed. A contact type aperture deformation measurement device based on the principle of micro optical imaging is developed, and a rapid in-situ stress measurement technology suitable for vertical deep holes is formed through the optimal connection of single acting double pipe drilling tools. The aperture deformation measuring device adopts key technologies such as aperture deformation perception, micro-imaging and directional measurement. This technology could simplify the test process, shorten the test time, realize multi-directional aperture deformation measurement under high temperature and high water pressure environment in vertical deep hole. A single acting double pipe drilling tool is introduced to optimize its drilling, coring and overflow, and an in-situ stress auxiliary testing device is formed. In-situ stress measurements are carried out at –410 m and –500 m levels in Jinshandian iron mine. The obtained annular core has stable inner diameter and high integrity, which verifies that the auxiliary test device has the technical advantages of accurate hole forming and complete coring, and provides a guarantee for the accurate measurement of borehole diameter deformation. The in-situ stress data at 4 points are obtained through measurement. The principal stress basically increases with the increase of depth, and the direction of the maximum horizontal principal stress is about NNW-NNE. The research shows that the in-situ stress measurement technology based on stress relief method proposed in this paper can realize in-situ stress measurement quickly and reliably in vertical deep holes.