Mechanical properties of rocks are significantly affected by various initial unloading levels, which are caused by deep rock excavation. In this study, conventional triaxial compression tests and triaxial unloading tests at different initial unloading levels were carried out on sandstone. The strength, deformation and dilatancy characteristics of rock were studied under loading and unloading of high stress. The testing results showed that with the same initial confining pressure, the higher the initial unloading level was, the lower the confining pressure was reduced, and the shorter the process of unloading confining pressure was. Under different initial unloading levels, the uniform decreasing increment of confining pressure increased with the increase of initial confining pressure. It indicates that under high-stress state, rock specimens can only be damaged when much greater unloading confining pressure was applied. With the increase of initial unloading levels, the cohesion c increased exponentially, whereas internal friction angle decreased in a polynomial relationship. The lateral strain increment was higher than that of axial strain increment in both two stages of unloading confining pressure, which exhibits an obvious lateral expansion. It was found that when the initial unloading level was lower, the maximum dilatancy angle was larger and the dilatancy effect was more apparent. The dilatancy index showed a power function relationship with the confining pressure, whereas it showed a quadratic function relationship with the initial unloading level. Moreover, the expression of Mohr-Coulomb yielding criterion for sandstone was modified under different initial unloading levels, based on the obtained experimental results.

Mechanism of Stress relaxation differs from creep in their mechanism, and they can not be simply exchanged. Consolidated undrained triaxial shear test(CU) can simulate many operating conditions containing a certain degree of stress relaxation. Engineering accidents caused by stress relaxation sometimes occur. Tianjin Binhai soft dredger fill has significant rheological properties. In this study, soft dredger fill was tested by triaxial-shear tests to examine the stress relaxation behavior of the soil samples under consolidated and undrained conditions. The results show that the stress relaxation process can be divided into rapid stage, slow stage and stable stage. Within a certain range, the stress relaxation rate increases with the increasing of initial deviator strain relaxation. there exists an approximate linear relationship between deviatoric stress and logarithmic time. Stress relaxation has little effect on the total shear strength index while decreases the effective cohesion and increases the effective angle of internal friction . Finally, a model for stress-strain-time relationship reflecting the stress relaxation characteristics of dredger soft fill is deduced and validated through fitting and normalizing the test data. This research has supplemented the rheological properties of Tianjin Binhai dredger soft fill, and can provide a theoretical reference for the prevention of related engineering accidents.

Recently, much attention has been made on the whole process of dynamic fracture, including crack initiation, propagation and arrest. This study mainly aims to investigate the propagation and arrest of rock under dynamic loading. Experiments were conducted on pre-cracked chevron notched Brazilian disc (P-CCNBD) specimens with a large diameter ( 160 mm) by using split Hopkinson pressure bar (SHPB). Then we determined mode-I dynamic initiation toughness and propagation toughness of marble. Since the employed large-size specimens did not satisfy the stress equilibrium condition in the dynamic test, the papular quasi-static method could not be applied in this study. Hence, an experimental-numerical-analytical method was adopted. The crack initiation time and the crack propagation velocity were monitored by using strain gauges and crack propagation gauges. The recorded experimental data, including dynamic loads applied to the specimens by SHPB, were simulated by 3D finite element analysis program. Then the time history of dynamic stress intensity factor of P-CCNBD was obtained by using the semi-analytical modification with an universal function. The results show that the dynamic initiation toughness of P-CCNBD marble specimen increases with the increase of loading rate. Dynamic propagation toughness of P-CCNBD marble specimen is slightly lower than dynamic initiation toughness. Moreover, dynamic propagation toughness increases with crack propagation velocity. In addition, the oscillation of crack propagation velocity and propagation path deflection were analyzed, and the possibility of achieving crack dynamic arrest in P-CCNBD was discussed as well.

This study aims to determine the reasonable anchorage length of the bolt in the roadway. Based on the slip-debonding failure mode of the interface between anchoring agent and surrounding rock, this paper deduced formulas of ultimate bearing capacity and interface shear stress distribution along the length of the bolt in the elastic stage. The safety and economy principle was also proposed for determining the reasonable anchorage length of anchors, according to the analysis of conditions of slipping and debonding at the interface between the anchors and the surrounding rock. The influencing factors on reasonable anchorage length and the design process were analysed as well. The results showed that the ultimate bearing capacity of bolts was mainly affected by the interface shear strength . Besides, the interface shear stiffness in the elastic deformation stage was the key control factor of the critical anchorage length. For different kinds of surrounding rock, the interface parameters and can be obtained through short anchor drawing test, which can provide guidance for the design of bearing capacity and reasonable anchorage length. A specific example was calculated and the obtained results agreed well with the results from practical engineering projects in coal roadway. Hence, it is proven that both the calculation method and the design process are feasible to determine reasonable anchorage length.

Particle shapes have great influence on strength and deformation of rockfill material. Particles with same volume and different shapes are made by cement paste pouring to simulate the rockfill material. The effect of particle shape on strength and deformation of artificial rockfill materials are investigated under different confining pressures in a series of triaxial shear tests. Test results show that the particle shape influences strength and dilatation of artificial rockfill material. As the particle roundness increases, the peak strength of artificial rockfill material increases. The rockfill material presents high dilatancy under a low confining pressure. As the particle roundness increases, ultimate stress ratio decreases, and initial tangent modulus and tangent bulk modulus increase. Initial internal friction angle is trivially affected by the particle roundness, and increment of internal friction angle is influenced by the particle sphericity. Larger particle sphericity leads to a less increment in internal friction angle.

This study is to investigate the effect of the interlayer on mechanical properties and failure mechanisms of salt rock containing interlayers. To overcome the difficulties of field sampling, salt rock samples were prepared in the laboratory for uniaxial and triaxial compression experiments. The experimental results showed that the deformation difference between salt rock and interlayer had a great effect on the mechanical properties of interlayer-bearing salt rock, such as strength and elastic modulus. Under uniaxial compression condition, the fracture failure of salt rock initiated from the interlayer, and then developed into the salt rock layer. It was found that the compressive strength decreased with increasing the interlayer thicknesses. The compressive strength of salt rock samples containing a single interlayer was higher than that of salt rock containing two interlayers. The compressive strength and elastic modulus of salt rock were weakened by the inclined angles of the interlayer. Furthermore, the types of damage in bedded salt rock can be divided into fracture and slippage along the interface between interlayer and salt rock. Under triaxial compression condition, all the compressive strength, elastic modulus and deformation at peak load of bedded salt rock were lower than those of pure salt rock. The pure salt rock demonstrated lateral expansion and failure, and no obvious rupture surface was found. While the mudstone interlayer in the sandwich salt rock showed the characteristics of shear failure, and part of the salt interlayer was lateral expansion. Therefore, this paper can provide helpful guidance to the construction and operation of gas storage caverns in bedded salt rock.

The silty calcareous soil subgrade in the South China Sea contains fine particle calcareous silt interlayers with a particle size less than 0.075 mm. The permeability of these calcareous silt layers has an important effect on the development of underground fresh water in the islands. This study investigated correlations among the permeability coefficient, dry density and initial water content of calcareous silt through variable-head permeability tests in laboratory. The results demonstrate the reliability of Samarasinghe and Mesri formulas in calculating the permeability coefficient of calcareous silt. The variation of pore size of calcareous silty soil before and after infiltration test was analyzed by static nitrogen adsorption test. The results show that the permeability coefficient of calcareous silt decreases with the increase of the dry density, and increases with the increase of the initial water content. When the dry density is the same, and the permeability coefficient reaches the maximum at saturation. The Samarasinghe and Mesri formulae have high accuracy in calculating the permeability coefficient of calcareous silt. Seepage generates more micropores and transforms mesopores into macropores. The soil mainly shows pores with a uniform cylindrical hole with an opening at one end. This study provides a scientific reference for the calculation and analysis of groundwater seepage field in artificial reclamation island.

Finite element models for suction bucket foundations with and without cruciform inner clapboards and solid embedded circular foundation in soft soil were established in order to investigate effects of cruciform inner clapboards on uniaxial bearing capacities and failure modes of suction bucket foundation. A large number of finite element calculations and analyses have been carried out to obtain uniaxial bearing capacities of the above-mentioned 3 foundations with different embedment ratios and soil shear strengths by using displacement load method. The results show that the uniaxial bearing capacities of suction bucket foundation are nearly not affected by inner clapboards in uniform soft soil, and the failure modes of the above-mentioned foundations are similar. When the shear strength of soft soil is heterogeneous, uniaxial capacities except vertical capacities of suction bucket foundations with cruciform inner clapboards and low embedment ratios, especially for moment capacities, increase obviously due to cruciform inner clapboards. Meanwhile, the uniaxial horizontal and moment capacities of suction bucket foundation with cruciform inner clapboards increase with the increment of the unevenness index of soil shear strength and are nearly equal to those of solid embedded circular foundation. Failure mechanisms of suction bucket foundation without inner clapboards and with low embedment ratios built in heterogeneous soft soil are obviously different from the other two foundations. Simplified calculating formulas were proposed to predict uniaxial capacities of suction bucket foundation with cruciform inner clapboards.

Soils around structures such as shafts, tunnels, and chambers are usually under a non-limit state in deep underground engineering. The earth pressure on structure in the non-limit state cannot be predicted accurately by existing theories. In this paper, a model for earth pressure between slip surfaces in non-limit state is established considering soil arching effect. According to the principal stress rotation theory and the simplified parabolic slip surface, the lateral earth pressure coefficient on the slip surface is deduced. Based on the assumption of major principal stress arch, the analytical solution is obtained from the differential equation of average vertical stress in the soil using the limit equilibrium method. The accuracy of this analytical solution is validated by comparing the predicted earth pressures with those values observed from physical modelling under the limit equilibrium state, and calculated from other classical theories. An example of earth pressure analysis between non-limit state of slip surfaces suggested that the presented theory is applicatable to evaluate earth pressures both on the structure and inside soil between slip surfaces under the non-limit state.

Pile foundation is installed on the roof of karst cave under certain conditions. It is great significance to investigate the stability and the safety thickness of karst cave roof, when it is subjected to the coupling effect of the earthquake and pile-tip load. Based on the similarity theory and the separation similarity design method, dynamic failure characteristics of the cavern roof were studied by varying the roof thickness and cave diameter using the shaking table. Results show that the failure modes of the top of the cave roof are closely related to the thickness of the roof and the size of the cave in the earthquake. With a certain thickness of roof, when the cave-diameter was smaller than 2d (where d is the pile diameter), shear failure happened in the roof. On the contrary, when the cave diameter was larger than 4d, punching-shear failure occurred. This indicates that the larger the diameter is, the greater the proportion of punching volume is. According to failure characteristics of the karst roof obtained by shaking table tests, the theoretical calculation model was proposed for minimum roof safety thickness, combining with the quasi-static method. Besides, the proposed model considered characteristics of rock mass, seismic intensity and pile diameter. It was shown by numerical studies that the minimum safety thickness was larger than that under static condition, and it increased with the increase of seismic intensity. Under the same condition, the calculated values of punching and shearing were larger than those of shear failure, which indicates that in the earthquake environment, the greater the cave size is, the higher the thickness of the required roof is. Therefore, this study can provide a valuable reference for developing the design approaches for the karst-pile in the earthquake region.

The confined water inrush is typically caused by fault activation under high ground pressure due to coal mining. It is one of the main forms of water disaster in deep mining in North China. Based on the equipment of similar simulation tests, we designed the testing device and proposed the testing method. Fault F13 in Wugou mine was chosen as a geological background in this study. Then the overburden movement, the expansion characteristics of the bottom plate, the stress and structure evolutions of the fault zone and the whole process of the aquifer were investigated. Taken the mining distance as a time reference, the water inrush consists of four obvious stages: the yield of fault zone caused by over-stress, cracking and extending of the fault zone, diastrophism and slip of fault zone, rising of confined water. Based on the height of the pressurised water along the fault zone, its correlation factors were analysed. It was found that the relationship between the mining distance and confined water rise was an approximately negative liner. Moreover, the pressure of confined water showed positive correlations with the width of the fault zone and the height of confined water. In particular, the correlation between the pressure of confined water and the height of confined water exhibited a strong-weak-strong law during the whole experiments. According to the obtained experimental result, the waterproof coal pillar was designed as 40 m in the fault F13, and the no water leakage and inrush were found. This indicates that the designed height is reasonable. Therefore, this study can provide a useful reference to understand and prevent mining water disasters.

Microbial-induced calcite precipitation (MICP) is an emerging ground treatment technique in geotechnical engineering. This technique is performed through injecting bacteria into the soil and then hydrolyzing urea into carbanion to induce the calcite crystals at the presence of calcium ions. Accordingly, the precipitated calcite crystals are used to bond loose soil particles together. Distribution uniformity of calcite crystals is a key point for this technique. In this study, calcium chloride solution with a concentration of 0.05 mol/L is introduced into the pure bacteria solution to intervene in the distribution of bacteria, the effects of biological injection methods, i.e. the pure/mixed bacteria solution, the mixed bacteria solution and the traditional pure bacteria solution on the dynamic behavior of bio-cemented sand are analyzed by dynamic triaxial test and scanning electron microscope (SEM) test. The test results indicate that the pure/mixed bacteria solution can effectively improve the distribution uniformity of calcite crystals in bio-cemented sand, obtaining bio-cemented sand with higher content of calcite, greater dynamic modulus and energy-dissipating capacity.

Mudstone, as a host rock medium widely distributed in oil and gas reservoirs, exhibits unusually complicated creep behaviour under conditions of high temperature and high pressure. Moreover, this creep behaviour is an important factor causing the failure of casing. In this study, gypsum mudstone from a deep oil and gas reservoir was chosen to investigate the creep characteristic. Triaxial compression tests and triaxial creep tests were conducted to characterise the instantaneous mechanical behaviours of mudstone at 130℃ temperature and with 30 MPa confining pressure. It was found that the mudstone presented characteristics of soft rock, such as no obvious heterogeneity, great plastic compression and ductility dilation strain, and low peak strength. Both axial and lateral peak strains reached more than 1.5%, with a corresponding peak strength of 74 MPa. The mudstone showed obvious time-dependent behaviour in mechanical properties, and had a low creep stress threshold. Stress and duration had significant effects on creep characteristics. Under a long-term low stress, the mudstone also exhibited clearly a steady-state creep and accelerated creep failure, furthermore, the start time of acceleration creep decreased exponentially with the increase of stress. The damage and accelerating creep characteristics of mudstone were discussed as well. It is suggested that the creep damage variable in mudstone can be represented as an exponential function, and the creep deformation is the binary exponential function of stress and time. Therefore, the results provide a valuable reference for the establishment of rock creep model and the analysis of long-term stability in deep oil and gas reservoir engineering.

Soil-cement pile is a common cost-effective reinforced structure used in soft soil slope. However, its deformation, failure, and mechanism of anti-sliding to improve the slope still remain unclear. Currently, relevant researches on stability analysis are relatively limited. A slope model was established by finite element method to analyze the deformation and failure characteristics of reinforced discrete cement-soil pile. The results show that, when failure occurs, the deformation incompatibility between the pile and soil would cause plastic sliding. The soil-cement pile with large stiffness and strength deflects into S-shape, leading to a bending failure of soil-cement pile. It indicates that the soil-cement pile fails to develop the slide-resistant ability as design required. Finally, a shear slip band, instead of a slip surface, passed through the stabilized slope. A concept about soil-cement shear wall has been proposed. By the finite element simulation, the sliding force was found between the shear wall and slide mass due to the effect of interface friction when the soil-cement shear wall was used to stabilize the slope. The general shear failure would occur in the stabilized slope, meaning that the shear wall has effectively mobilized its slide-resistant capacity. At last, a lateral shear model test on the pile-soil composite structure has been carried out to verify the results of the numerical simulation.

To investigate the coupling effect among coal seam temperature, gas seepage field and stress field, a temperature field controlling equation was reestablished by employing binary-energy-state theory in coal gas flow. Then, the theoretical solution of desorption differential heat term in the equation was derived as well. Finally, a fully coupled thermal-hydrological-mechanical (THM) model was improved. Based on the improved THM model, this study discussed complex interactions among adsorption, desorption, stress field, temperature field and seepage field in coal gas flow. Moreover, the THM model was used to investigate the changes of temperature, gas pressure and permeability of coal seam during gas drainage. The model results showed good agreement with the results from previous experimental studies. The results indicated that the drop-down rate of coal seam temperature was controlled by the combined effect of the original gas content, pore pressure and permeability of coal seam during gas drainage. It means that the greater the permeability of the coal seam is, the faster the dropdown rate of the temperature is. The greater the coal seam gas content and gas pressure are, the faster the temperature drops. Meanwhile, the permeability of coal seam increased with the elapsed time of drainage and the amplitude of the increase declined with the increase of the distance from borehole axis along the radial direction.

By using triaxial apparatus, 36 consolidated drained tests were conducted on the unsaturated soil to determine the parameters and the model of the high-fill soil-rock mixture project. The effects of compaction degree, matric suction and mixing ratio on the strength and deformation characteristics of the unsaturated remoulded mixture were quantitatively examined by controlling net confining pressure. Modified expressions for shear strength, tangent deformation modulus and tangent volume modulus of unsaturated compacted soil were also developed. The experimental results showed that the failure stress and cohesion increased linearly with the increase of suction, whereas the changes of suction had little influence on the effective internal friction angle. It was found that failure stress and strength parameters increased with the increase of compaction coefficient. The failure stress and strength parameters of soil samples with the ratio of 4: 6 were slightly higher than those of soil samples with the ratio of 2: 8. Moreover, the effective cohesion increased with the increase of silty clay content. For the same mixing proportion and compacting coefficient of soil samples, the intensity of sample grew with the increase of net confining pressure and suction. Correspondingly, its volume gradually changed from shrinkage to dilatancy. For the same net confining pressure, the suction and the mixture ratio of soil samples, the strain curve progressively turned from the strain hardening type to the ideal elastoplastic type with the increase of compaction coefficient. However, partial soil samples tended to strain softening type under the low net confining pressure. It is verified that the revised incremental nonlinear constitutive relationship of unsaturated soil is consistent with the practical project of large area fill. Thus, this study can be used for calculating the deformation of high-fill foundation and analysing the stability of the high embankment slope.

In this study, analytical viscoelastic solutions were derived for the lined circular tunnels by the correspondence principle and complex variable method under full contact and smooth contact conditions between liner and ground in non-hydrostatic stress field. In the solutions, all kinds of viscoelastic tunnels with an elastic liner was considered and the delayed installation of the liner was also taken into account. Therefore, the obtained analytical solutions can be applied to all linear viscoelastic models. The analytical solutions were verified by the solutions of references and numerical results. According to the solution, the surrounding rock was assumed to conform to the generalized Kelvin (H-K) viscoelastic body. The results showed that the radial, tangential stress, the circumferential displacement of the lining and the bending moment of the lining increased with time until converged to the fixed value. Under two kinds of contact conditions, there were quite differences on the displacement of the surrounding rock, the stress distribution of the lining, the distribution of the displacement and the internal force. Furthermore, the above differences between these two conditions increased with the time. Compared with the existing solutions, the solutions derived in this paper are more suitable and reasonable for practical deep buried tunnels especially for the full contact condition. The comparison between the two solutions can provide a useful reference for selecting liner and construction reasonably.

Sand solidification is to increase the strength of sands and decrease infiltration. Culture medium was used to cultivate bacteria, and growth properties were obtained in various conditions. The relationship between pH and Ca2+ concentration of effluent was analyzed to reveal the evolution of permeability and unconfined compressive strength. Effect of solidification was investigated through microstructure. The relationship between Ca2+ concentration and strength of samples was studied. 2 mL of the bacterial mother liquor was added to 100 mL of the culture medium. The results show that the sporosarcina pasteurii possess optimal growth conditions under a pH of 6 and vibration velocity of 150 rpm with 30oC incubation. pH decreases during curing, and Ca2+ concentration increases. The 0.5 mol/L gel solution shows good curing effect and requires short time of the curing cycle. The gaps between sand particles are filled by calcium carbonate after curing, reducing sample permeability up to 3-4 order of magnitudes. The lower the rate of injection produces longer the curing time and the better the effect of solidification. The failure mode of all specimens is the brittle fracture mode. When the gelling solution is a mixture of urea and calcium acetate, the utilization ratio of Ca2+ is dramatically increased.

Disintegration of soft rock within water is considered as a fatal factor causing the engineering disasters. It is widely accepted that the disintegration results of soft rock from the variation of the microstructure of soft rock within the water. However, only a few studies were carried out to quantitatively describe soft rock disintegration, based on its meso-mechanism. We conducted experiments on the static disintegration of soft rock and immersion tests of soft rock debris in the laboratory. Besides, the compositions of soft rock at different soaking stages were analyzed by scanning electron microscopic as well. Finally, this study revealed the microscopic evolution of the interface between water and soft rock, according to the obtained results. The disintegration mechanism of the red-layer soft rock was generally caused by the hydration, diffusion and loss of clay particles in the water-rock interface in the mud-filled area of the soft rock fragments. Then the related shale cementation was reduced, resulting in the decrease of cohesion between debris. The cohesion between fragments of soft rock decreased exponentially with time under hydrostatic action. On the basis of the above analysis, the loss of hydrated clay particles in soft rock and the cracking type of model Ⅱ between soft rock fragments were quantitatively identified by using the interface and colloid chemistry and fracture mechanics theory. The interfacial model of soft rock with water disintegration was established, and the disintegration process of soft rock was further demonstrated quantitatively. By comparing the obtained results, the flaking time of soft rock fragments calculated by the above model was similar to that observed in the experiment, which verified the rationality of the model.

Theory of fractional calculus is introduced to Kelvin-Voigt constitutive model to describe the mechanical behavior of viscoelastic saturated soil. Applying Laplace transforms upon the one-dimensional consolidation equation of saturated soil and the fractional order derivative Kelvin-Voigt constitutive equation, we derived analytical solutions of the effective stress and the settlement in transformed domains. Then the semi-analytical solution of one-dimensional consolidation problem in physical space was obtained after implementing Laplace numerical inversion by using Crump method. As for two classical cases of elasticity and viscoelasticity, the simplified semi-analytical solutions in this study are the same as those of the two classical cases. It indicates that the analytical solutions of two classical cases can be considered as the special cases of the solutions presented in this paper. Last, parameter studies were conducted to analyze the effects of the various parameters on the consolidation settlement. The results show that, in the case of instantaneous loading, the final settlement is independent on the viscosity coefficient and the fractional order, while the consolidation time is influenced greatly by the viscosity coefficient and the fractional order. The present study contributes to further understand the mechanical behavior of the consolidation of viscoelastic saturated soil.

Rock is usually corroded by chemicals in groundwater. Meanwhile, deformation and failure of rock occur frequently due to the dynamic load in underground engineering. Hence, this study aims to investigate dynamic mechanical properties of limestone corroded in an acid environment. Limestone samples were firstly soaked at pH=3 of KHSO4 solution and NaCl solution for different days, respectively. Then, the porosity, pore size distribution and magnetic resonance image of some samples were obtained by using the nuclear magnetic resonance (NMR) test. Finally, uniaxial dynamic compressive tests were conducted at five strain rates by using the split Hopkinson pressure bar (SHPB) system. The experimental results showed that the porosity of limestone increased sharply with increasing the corrosion time. After 28 d corrosion, the porosity increased from 0.26% in the natural state to 3.20%. Besides, the micro-pores in limestone samples expanded obviously with the corrosion time. It is found that the dynamic compressive strength was significantly reduced (30.3%) and can be divided into two stages according to the descent rate. Moreover, the dynamic elastic modulus and specific energy-absorption decayed exponentially with time. Under natural state and post-corrosion state, limestone samples both exhibited similar responses to the strain rate. Specifically, the failure mode changed from the typical splitting failure to the tensile-shear failure, shear failure, even powders with increasing strain rate. Moreover, the dynamic compressive strength and elastic modulus increased linearly. However, these two mechanical parameters of limestone were both more sensitive to the strain rate in a natural state than post-corrosion. It is proven that the effect of acid corrosion on the dynamic carrying capacity and anti-deformation capacity of limestone is significant, which should be taken into account in practical engineering.

The composite foundation with permeable and impermeable piles can promote the consolidation process of soft soil, and enhance the strength of foundation, implying practical applications for the soft ground treatment. Based on the axisymmetric consolidation model, a differential equation governing the consolidation of combined composite foundation subjected to an instant loading is established, considering the volume compression of the permeable pile. The analytical solution is derived for given initial and boundary conditions. Then, the solution is verified through the comparison with the existing solution. The main influencing factors such as disturbance effect, well resistance effect and compression modulus are analyzed to explore the consolidation behavior of composite foundation. The results show that the consolidation rate of the combined composite foundation will be overrated without considering the volume change of the permeable columns. The consolidation rate can be accelerated by reducing the effects of well resistance and the disturbance effect of permeable column or increasing the replacement ratio and the compression modulus, reducing the post-construction settlement in practical applications.

This study aims to study the deformation laws of soil under cyclic loading. Based on the existing fractional dashpot, a new fractional-order Nakahara Model (FNM) was established to replace the constant dashpot in the viscoplastic body of Nishihara model under cyclic loading. This model can be used to describe various types of deformation law of soil under cyclic loading. When the stress amplitude of cyclic loading is larger than the critical stress amplitude of soil, the model is regarded as a FNM which can reflect the deformation law of soil failure. On the contrary, it is considered as a generalized Kelvin model which can reflect the law of soil stability and critical deformation. In this study, the cyclic loading was firstly decomposed into a static load and a cyclic load with zero average stress by using the stress decomposition method. Based on the established FNM, a rheology constitutive equation of soil was put forward under the static load, according to the theory of rheological mechanics. Meanwhile, a dynamic constitutive equation of soil was deduced under the alternating stress, by considering the theory of viscoelastic mechanics. Finally, a new constitutive equation of the model was obtained by superimposing the constitutive equations of soil under two different stress conditions. Compared with existing experimental results of soil, the obtained constitutive equation of soil can well describe various types of deformation law of soil under cyclic loading. Moreover, the fitting results of various types of deformation curve of soil showed good performance and the fitted correlation coefficients were above 0.90. Meanwhile, the values of model parameters decreased in power function law with the increase of the dynamic stress amplitude of cyclic loading.

The stability of tunnel is gradually undermined by the effects of unsaturated seepage and soil expansion under the condition of continuous rainfall infiltration. Hence, it is important to investigate their effects on the deformation of surrounding rock mass and stress in the supporting system. This study simulated the processes of unsaturated seepage and soil expansion with the rainfall infiltration by using the seepage module and thermal module in the finite difference software FLAC3D, respectively. FISH language was also adopted to investigate the impacts of changes in matrix suction, soil softening and soil expansion during the unsaturated seepage process. A shallow expansive soil tunnel was simulated as a case study. Then the effects of rainfall duration, permeability coefficient and expansion coefficient on the deformation of surrounding rock mass and stress in the supporting system were analyzed. The results showed that during the rainfall infiltration process, the horizontal stress of surrounding rock mass increased remarkably, whereas the vertical stress changed within a small range. Moreover, the supporting system transformed from initial vertical extrusion deformation to horizontal extrusion deformation. It was found that the permeability coefficient and expansion coefficient exerted great actions on the stress in the supporting system. When the permeability coefficient and expansion coefficient reached a particular value, the bending moment of the supporting system substantially increased, which greatly reduced the tunnel stability and safety.

When constructing tunnels in landslide areas, the stability of landslide is severely affected by the crossing position of tunnel. At present, the problems of tunnel excavation and the stability of landslide were separately investigated by many researchers. However, very little attention has been made on these two kinds of engineering problems together. In this study, a formula was deduced to calculate the disturbance range of surrounding soil and rock mass induced by tunnel excavation, according to the slip line theory. Combined with the analysis of loosened rock over the tunnel opening, an analytical expression was developed for the minimum safety distance of the tunnel orthogonally crossing the landslide. Moreover, its influencing factors were discussed. Besides, the stability of landslide body above the tunnel was analyzed using Sarma method, and the corresponding safety factor was also obtained. At last, a series of numerical simulations was carried out to investigate multiple examples of tunnel orthogonally crossing landslide. The accuracy of the deduced formula was verified by the analysis of rock plastic zones. Therefore, the results can provide a theoretical basis for the accurate selection of tunnel position in the landslide area.

The sealing ability of cap rock has a critical influence on the storage capacity, economy, and security in CO2 geological storage project. Due to the obvious characteristic of layered heterogeneity of the cap rock, it directly affects the migration and leakage process of CO2 in the cap rock. As a result, the cap rock sealing ability is also affected. Currently, the effect of isotropic heterogeneity on the sealing ability of cap rock was studied in the literature. However, the effect of layered heterogeneity has not been investigated yet. In this study, the homogeneous, non-layered heterogeneous and layered heterogeneous models were separately established by considering the different spatial distribution of porosity, permeability and capillary pressure of cap rock. Under consistent CO2 injection conditions, numerical simulations were conducted using these three models to comparatively study the whole leaking process of CO2 entering, migrating and breakthrough all over the cap rock by using TOUGH2. Results revealed that the distributions of free CO2 saturation in the cap rock agreed with the spatial distributions of porosity and permeability among the models. In contrast with the homogeneous model, non-layered heterogeneity accelerated the CO2 migration, whereas layered heterogeneity slowed down CO2 migration in the cap rock, and increased the period of CO2 breaking through the cap rock. Compared with the homogeneous and non-layered heterogeneous models, layered heterogeneous model greatly decreased the leakage rate and total leakage amount of CO2 after the breakthrough of CO2. At last, limitations on the geological modelling were addressed. Hence, the research results provide helpful guidance for more objective and quantificational evaluation on CO2 migration and leakage through the cap rock.

Strata in Tianjin area are featured as an alternated multi-aquifer aquitard system. Based on this strata condition, lots of numerical calculations investigate the effect of deep foundation pre-dewatering on lateral displacement of support wall in soft ground under different construction conditions, including dewatering time (t), dewatering depth ( ), pit length (L) and pit width (b). The calculation results were compared with relevant field data, and nonlinear regression analysis was then conducted based on the calculation and observation results. The results indicate that the maximal lateral displacement of support wall ( ) increases nonlinearly with t, and the growth rate decreases continuously. In the first few days of the dewatering, lateral displacement of support wall development can occupy large proportion of its stable value during pre-dewatering. Moreover, has a great influence on the development and the depth of wall with cantilever-type deflection ( ). In general, and will be larger with the increase of . Specifically, before reaches the second permeable stratum of the field, increases linearly with by a small scale. Otherwise, the growth proportion of with increases greatly. Before reaches the center location of the thick aquitard, increases synchronously with increased, and otherwise, the increment is apparently greater than the increment. Furthermore, as to the same pit width (b), when the pit length (L) reaches a specific value, the corner effect induced by dewatering always appears at a specific distance from the pit corner along the pit length direction. In practical pre-dewatering, cross wall can be used to partition the pit into some parts, and let the ratio of cross wall spacing ( ) to b be less than 4, or let / be less than 3.7, using the corner effect to effectively reduce the maximal lateral displacement of support wall induced by pre-dewatering.

U-shaped crushed-rock embankment (UCRE) is a combination of the crushed-rock sloped embankment and the crushed rock basement embankment applied to the Qinghai-Tibet railway construction. Under a warming climate on the plateau, the effect of long-term cooling in warm permafrost regions needs to be concerned. Based on in-situ measurements for 10 years from the warm permafrost Chuma’er High Plain, the cooling process, cooling mechanism and deformation characteristics of a UCRE were analyzed. Results indicate that the UCRE showed a continual cooling process. Permafrost table beneath the UCRE was elevated significantly and quickly, then maintained in a stable state. Temperatures near artificial permafrost tables decreased significantly, resulting in a great cold energy accumulation. Temperature differences between top and bottom boundaries of crushed rock layers differed with cold and warm seasons, indicating natural convection occurred within the layer for the shady side during January to the early March. while for the sunny side, the convection period was shortened for nearly half a month, due to the high surface temperature of this side. A weak warming for 2 to 3 years caused by thermal disturbances from the initial stage of embankment construction occurred in deep permafrost. However, it was replaced quickly by the subsequent significant cooling process. The small settlement of the UCRE mainly comes from the compression deformation of warm permafrost under the embankment during initial stage after construction. In general, the UCRE shows the long-term effect of decreasing ground temperature, and the relatively weak embankment settlement ensures its stability.

Pile foundations are widely used in geotechnical engineering. Meanwhile, the calculation method and reliability of the pile vertical bearing capacity attract more attention from geotechnical engineers. The pile capacity is affected by the uncertainty of properties of the layered soil. To solve this problem, we present herein a robust geotechnical design (RGD) as a new geotechnical design concept based on the reliability design (RBD). The mean and standard deviation of the soil properties are considered as the uncertainty of soil parameters in RGD method. and the scope of the RGD method is expanded in the pile vertical bearing capacity from sand to clay by introducing more soil properties. The pile side friction(Qside), calculated layer by layer by RGD method, is used as one of the uncertain parameters in the change of applicability of the pile vertical bearing capacity by layered soil. Both of ultimate limit state (ULS) and serviceability limit state (SLS) are used as performance function in pile design. In this paper, as a safety evaluation standard, robustness is used to evaluate the feasibility of the design scheme in pile design with the RGD method. With the RGD approach, the focus is to satisfy two design objectives, namely cost-efficiency and robustness. As with multi-objective engineering optimization, it is possible to provide a best solution set to accomplish the goal both in cost-efficiency and robustness. Meanwhile, the pile vertical bearing capacity of the design is guaranteed.

Heterogeneous settlement is a common engineering problem in the soft soil foundation or at the juncture between new and old subgrade induced by consolidation settlement, rainfall or earthquake. The reinforced soil structure is commonly applied to reduce the unequal settlement in practices. However, less attention goes to theoretical research on the deformation of reinforcing material under differential settlement condition at present. To improve and simplify the design theory of reinforced earth structure, the deformation of reinforcement in reinforced soil structure is investigated based on the theory of parabolic cable. A method is developed to calculate reinforcement material deformation under differential settlement condition. The feasibility and accuracy of the proposed method are verified by laboratory experiment and theoretical analysis. The method does not require repeated numerical simulation. The calculation results can satisfy the needs of the actual project.

Umbrella suction anchor foundation (USAF) shows great potential in marine geotechnical applications for its unique structure improved by traditional suction anchors. The control standard of displacement for horizontal load bearing capacity of USAF has been determined by small-scale model tests. The bearing capacity of USAF and deformation characteristics of the soil around USAF at different loading heights in soft clay were evaluated by the finite element analysis method. Meanwhile, stress reduction effects of seabed under cyclic wave loading were described. The results show that the rotation center of USAF moves up, and the stress diffusion depth of seabed goes deeper, with the increase of horizontal loading height. The soil resistance around the sidewall of master cylinder leads to stress redistribution for the “anchor branch” and “skirt” structure. The core control area of the bearing capacity for USAF is the soil around the upper front and the bottom back part of anchor. In addition, accumulation of excess pore water pressure in the clay seabed around USAF exerts influence on soil resistance significantly. Thereby the horizontal bearing capacity of the entire structure reduces. The above research results are necessary and significant for the improvement of USAF in marine geotechnical engineering.

A mathematical model based on the discrete fracture network model is developed for the problem of unsaturated seepage flow in fractured rock. The saturated-unsaturated flow behavior is governed by Darcy’s law, Richards’ equation, the constitutive relationships and the complementary condition of Signorini’s type on the potential seepage surface. The finite element method is used to establish a numerical solution scheme and a corresponding iterative algorithm for the unsaturated seepage flow model of the fracture network. The effectiveness of the proposed algorithm is verified by comparing with the rectangular seepage, the one-dimensional vertical fracture unsaturated infiltration and the indoor two-dimensional transient drainage seepage test, numerical and theoretical results. According to the principle of flow equivalence, the effectiveness of the fracture network model in solving the problem of unsaturated seepage in continuous media is highlighted. It proves that the algorithm is effective to solve the problem of rainfall infiltration in the fissure slope. The nonuniformity of the flow distribution of the fracture network and the occurrence of the fractures show important control on the rainfall infiltration flow.

A multivariate distribution model that describes the relevance of variables has a wide range of engineering applications. Based on the multiple linear autoregressive model and the sorting algorithm, a generation algorithm of multidimensional random variable with the specified edge distribution and the specified structure is studied. The algorithm was implemented using MATLAB. The proposed approach, a direct sampling Monte Carlo simulation method, is applied to determine the structural reliability and slope reliability. The problem related to correlative variables, difficult to solve by traditional Carlo Monte simulation, is solved by the proposed method. The numerical analysis shows that this method is reliable in calculation. The method can loosen the idealized restrains of theory model, and realistically reflect the practical problem. Compared the results from first-order second-moment method, it is found that the first-order second-moment method usually gives a high estimation in reliability. Failure probability is sensitive to the distribution type of the variable. Same safety factor maybe correspond to different failure probabilities. The proposed approach can be applied to calculation of complex structural system reliability and to simulation with dependent random variables in other fields.

Ground motion plays an important role in the estimation of dynamic loading for ground support design in burst-prone underground mines. A semi-empirical scaling law is often used for peak particle velocity (PPV) estimation; however, this method does not account the influence of geology and excavation effect on the ground motion in the dynamic support design. For better understanding the excavation effect of boundary distribution in the underground on the ground, the author puts forward a coupled numerical simulation method for non-linear velocity model and FLAC/ SPECFEM2D. Aiming at the high quality and fair quality rock masses, the numerical analysis of the ground motion distribution of an underground stope is carried out. It is found that different velocity models influence ground motion distributions near excavation boundaries greatly. Considering the effects of confining pressure and excavation on the nonuniform velocity model can better simulate the distribution of ground motion near the underground excavation boundary, amplification effect at excavation surface is captured, which agrees well with underground field observation results. Compared with the high quality surrounding rock mass, when the simulated excavation rock is fair quality rock mass, the excavation boundary of the stope has stronger ground motion and wider seismic response.

In the geotechnical engineering reliability analysis and design, it is very difficult to accurately select the random field parameters and the correlation function, and to accurately describe the spatial variability of soil parameters. Based on Bayesian theory, this paper presents a method to quantify the spatial variability of effective internal friction angle of sand. A proper correlation function using prior knowledge and cone penetration test (CPT) data are used to determine the random field parameters and the correlation function of the effective internal friction angle of sand by the method. This method takes reasonable account of the uncertainty of the empirical regression equation between the effective internal friction angle and the cone resistance. Markov chain Monte Carlo simulation (MCMCS) method is applied in this paper to generate random samples following the posterior distribution. The MCMCS samples are used to calculate the posterior distribution by a Gaussian Copula-based method. Then, the plausibility of a candidate correlation function is obtained and the most probable correlation function is selected. Finally, the proposed approaches are illustrated and validated by using real-life CPT data obtained from NGES at Texas A&M University. It is shown that the proposed approaches can, correctly and reasonably, determine the random field parameters and correlation function of sand effective friction angle by using the indirect CPT data. It is possible to accurately describe the spatial variability of sand effective friction angle. The correlation function of effective friction angle at the sand site of NGES at Texas A&M University is second-order Markov correlation function.

Osmotic technique is an important method for measuring the matrix suction of unsaturated soil. It is very important to control the osmotic time, which is one of the key points to obtain the accurate measurement result. Based on the finite element numerical analysis software SEEP/W, we set up a numerical model of osmotic technique to analyze water movement during the osmotic process. Then, we analyzed the influences of the suction of solution, the hydraulic properties of soil sample, the initial gravity moisture content, the initial dry density and the size of soil sample on equilibrium time of the osmotic technique for unsaturated clay in the process of humidification. The results show that with the increase of osmotic time, the difference of suction between the solution and the soil sample will decrease and then the osmotic process will become slower. Soil samples should not be too large. For small samples, the equilibrium time for the osmotic technique is about 1.5-8.0 days in most cases. The equilibrium time increases greatly when the suction of solution is high or the saturated hydraulic conductivity of soil sample is low. The equilibrium time decreases with the increase of the fitting parameters (a, n) for soil-water characteristic curve, the saturated hydraulic conductivity, the initial moisture content and the initial dry density. On the contrary, the equilibrium time increases with the increase of saturated volumetric moisture content.

Based on the solid-fluid coupling theory and Bayesian theory, a coupled probabilistic back analysis model is developed for an unsaturated soil slope. A method of multi-objective probabilistic inverse analysis using time-varied data of displacement and pore water pressure is proposed based on Markov chain theory. The results of the multi-objective inverse analysis and single-objective inverse analysis found that the posterior standard deviations of the input parameters obtained by multi-objective inverse analysis are smaller than the single-objective cases. It is also found that the results obtained by single-objective agree with the measurement well but have an unsatisfied prediction on other objectives. Multi-objective inverse analysis could optimize all the objectives simultaneously and the results of inverse analysis can meet well with all the objectives. For the multi-objectives case, 95% uncertainty bounds are narrower than the single-objective cases, and the soil parameters obtained by the multi-objective probabilistic inverse analysis using different types of data are more reasonable, and the prediction using the results of the multi-objective probabilistic inverse analysis is more correct than the single-objective probabilistic inverse analysis results.

Desaturation is a new method to improve the liquefaction resistance of foundation by decreasing the saturation degree of saturated sand. Based on the coupling simulation method of water-gas two-phase flow reaction and soil skeleton deformation, a two dimensional numerical model is established to simulate the static liquefaction behavior under monotonic loading conditions. Also numerical simulation of undrained triaxial tests are carried out. By comparing the numerical results with the laboratory test results, it is found that the two-phase flow model shows great accuracy in describing the stress-strain relationship, stress path and pore water pressure growth in the static liquefaction process, which verifies the effectiveness of the two-phase flow simulation method. In addition, the saturation degree of desaturated loose sand during loading process increases until a stable value is reached. While the confining pressure is constant, the saturation degree at the end of loading linearly increases with the initial saturation. At the same time, the air in the sand is compressed under loading, which enables the desaturated sand to develop shear shrinkage with undrained condition. When the initial saturation degree of loose sand is reduced from 100% to 94.5%, pore water pressure coefficient B will decrease by 80%, the greatest pore pressure will decrease by 40%-50%, the undrained shear strength will increase by 2.0-2.5 times, and the residual strength can improve by more than 10 times. Therefore, this is the main mechanism of desaturation method to improve the liquefaction resistance, and the matric suction isn’t the main reason for desaturation method to improve the sand shear strength.

To better describe the coincidence degree of rock, the point cloud alignment algorithm was employed to calculate 3D joint matching coefficient (JMC3D) in this study. Firstly, 3D laser scanning technology was used to collect point clouds of rock discontinuities, including upper and lower joints. Then point clouds from both reference surface and testing surface of rock discontinuities were registered into the same global coordinate system, based on the iterative closest points (ICP) algorithm. Moreover, the corresponding Z-coordinate difference between the aligned testing surface and the reference surface was calculated. These point clouds, with Z differences in the range of alignment errors, were regarded as the matching portions. Finally, the percentage of matching portions was calculated to represent the parameter of JMC3D. The comparison of shear strength results obtained from direct shear tests in the laboratory and JRC-JMC model was conducted to clarify the reliability of the proposed method. The relative errors of four joint specimens were 7.38%, 3.21%, 9.03%, and 10.02% respectively, which indicated that the presented calculation of JMC3D was characterized by high feasibility and good performance. Meanwhile, this study revealed that there was a close relationship between the parameter of JMC3D and shear strength of rock discontinuities.