An earthquake wave is a multidirectional random load, which is commonly converted to an equivalent cyclic load with uniform amplitude for laboratory tests. Dynamic responses of sand subjected to multidirectional earthquake loading are simulated using a FEM code. An elastoplastic boundary surface constitutive model is introduced. The method for determining material parameters is discussed. 155 groups of ground motions with multi-components from far to near field of moderate or strong earthquake events at different site conditions are used as input motions for unidirectional and multidirectional loading. Based on hybrid-effect regression analysis methods, a computation model for equivalent number of uniform strain cycles under the condition of multidirectional earthquake loading is proposed. Capability of the proposed model is clearly shown. Based on the ratio of equivalent cyclic number of strain, a method for computing the equivalent cyclic number of multidirectional earthquake loading is proposed. The results show that the proposed model can well predict the variation trend of the equivalent cyclic number of uniform strain cycles. The ratio of the equivalent cyclic number is trivially affected by the earthquake magnitude and site-to-source distance, though it is significantly influenced by the properties of sand. The ratio of equivalent number of strain cycles increases with the relative density of sand within different scopes of earthquake magnitude. For the sands of relative densities 45%, 60%, 80% and 100%, the mean ratio is about 1.60, 1.85, 1.90 and 2.05, respectively.

Constitutive models for rock under cyclic loading and unloading, which are rarely reported in literatures, are critical to predict the long-term stability of CAES caverns. A constitutive model for rock subjected to cyclic loading and unloading is proposed. The model for rock softening and damage, which is based on Weibull random distribution, is expanded. The fatigue constitutive model with internal variables is employed to describe the variations of initial modulus and unloading modulus during every cycle. Then, a constitutive model for rock under cyclic loading and unloading is obtained. The results from proposed constitutive model is subsequently compared with the existing test results. The physical meaning of this model is explicit. The parameters involved in the model are less and can be easily fitted. The proposed model can represent the relationship of the stress and strain of every cycle and shows a good agreement with the results of laboratory tests. The successful establishment of the proposed model can provide a new idea to the researches on constitutive models for rocks under cyclic loading and unloading.

The safety of earth-rock dam relies on whether hydraulic fracturing will happen or not in the core wall. One of the key issues is the mechanism and conditions of hydraulic fracturing. By using the self-made test apparatus, specimens without initial cracks and with 5 different depths of initial cracks are prepared for hydraulic fracturing laboratory tests under 2 different loading rates. Combined with numerical analysis and CT tests, the mechanism of hydraulic fracturing is confirmed as wedge splitting effect. When water pressure is applied onto the “cutting back” formed by initial cracks and the induced force on the “cutting blade” exceeds the critical value, it possibly leads to hydraulic fracturing. Test and analysis results show that the deeper the initial crack on the surface of specimen, and the higher loading rate, the easier hydraulic fracturing occurs. In order to prevent from hydraulic fracturing on earth-rock dams, attentions must be paid on the construction quality and smoothness of upper-surface of the core wall, and the water level of reservoir is recommended for slowly raising.

Hydraulic characteristics of coarse-grained soil for high-speed railway subgrade profoundly influence internal moisture migration and long-term accumulative deformation of the subgrade. Conventional test methods have many disadvantages such as small size of sample and difficulties involved in sample preparation in determining hydraulic characteristics of such coarse-grained soil with high compactness, and thus can hardly be applied. A test device for determining hydraulic parameters of coarse-grained soil is presented thoroughly in this paper. Tensiometers and time domain reflectometers (TDR) are installed in the test device, allowing the measurement of matric suction and dielectric constant of coarse-grained soil at different altitudes during wet and dry stage; and consequently the soil-water characteristic curve (SWCC) of coarse-grained soil of high-speed railway subgrade with high compactness can be obtained. Also, the relationship bewteen unsaturated hydraulic conductivity and matrix suction of such soil can be obtained by transient profile method. The test result indicates that this device can be applied to the coarse-grained soil whose maximum particle size is 20 mm and whose degree of compaction may be up to 0.95. By analysing a group of experiment data and refering to data from Ekblad’s experiments, it is found that ? ( a parameter related to air entry value )decreases and air entry value increases with the increase of fine particle content in such soil, and that the largeness of particle size and low concent of fine particle suggest a low water storage capacity and high value of n. This article will provide a method for measuring hydraulic parameters of coarse-grained soils of subgrade.

The water in grout will permeate toward surrounding rock due to the osmotic pressure, so that the grout itself will consolidate gradually during shield backfilled grouting; and the grouting pressure will dissipates slowly. The variation of grout viscosity will lead to a change in the permeability of soil layers during the grouting process. Based on this fact, the grout consolidation and pressure dissipation equations have been deduced; and the distribution regularities of grouting pressure acting on segments have been analyzed, which provide a guideline for fine analysis of segment mechanics during construction. The results show that: the increase of grout viscosity will result in decreases in the grout liquidity, the extent of grouting pressure dissipation and duration time of grout dissipation. The variation of grout mixing proportion and permeability coefficient of surrounding rock can also influence the extent of grouting pressure dissipation and duration time of grout dissipation.. The calculated results are consistent with the field measured results. It is suggested that the grout dissipation effect due to time-varying should be taken into account in backfilled grouting.

The roughness coefficient is an important influencing factor of the joint shear strength. However, the research of size effect on joint roughness coefficient has not gained great progress due to surface morphology complexity of rock joint. This paper summarizes three methods to obtain joint roughness coefficient, i.e. standard profile comparison method, theoretical equation method and inverse analysis method, and then analyzes some existing problems and difficulties on studying size effect on joint roughness coefficient. In order to achieve the relationship between joint roughness coefficient and sample size, the ratios of raw materials such as medium sand, silica fume, cement, non-air entraining naphthalene super-plasticizer, are firstly investigated. Then rock materials for simulation are obtained, in which physico-mechanical properties are similar to calcareous slate. Finally, eight groups of rock joints with 176 pairs of different sizes and roughness are made through molds in preparation process. In addition, the roughness coefficients of rock joints are tested by homemade push-pull shear apparatus and experimental data are further analyzed. The results show that statistical mean values of joint roughness coefficient generally decrease with the increase of sample size. However, the size effect tests on the specific rock joints need to be performed through push-pull shear strength testing method. It is found that size effect variations calculated by Barton formula are in good agreement with experimental results, whereas the theoretical and experimental values are different. In particular, when the size of sample is smaller, the differences are greater. Furthermore, rock roughness coefficients even with specific joint surfaces are various and the roughness coefficients of large size rock joint should be comprehensively judged according to the surface morphology and distribution.

Gravel cushion is often used as the foundation of immerse tunnel; but the experience of using gravel cushion as the force transmission between pile and immersed tube tunnel structure has been lacking. Physical model tests have been carried out to reveal the deformation characteristics of gravel cushion and to examine the effects of ditch dimension, horizontal displacement of structure, sediment, ditch diverge, top incline and so on, upon the deformation characteristics of gravel cushion. The experimental results show that 1) small particle size gradation is not suitable for the foundation gravel cushion, and in selecting gravel gradation the compression modulus, porosity, particle size and other factors must be taken into account; 2) the existence of the groove can reduce compression modulus of gravel cushion greatly, and the main reason for this is that the joint effect of compaction and groove causes lateral extrusion of gravels; 3) at piled foundation sections, the ultimate bearing capacity of gravel cushion is about 480 kPa. As the force transmission structure between pile and immersed tube tunnel structure, the force mechanism of the gravel cushion is complicated, and several factors may come into play in influencing the behaviors of the gravel cushion. Hence, some measures need to be adopted to control the stress of the pile top within the ultimate bearing capacity of gravel cushion

With considering the vertical heterogeneity of soil layers and the feature of torsional vibration, the dynamic motion equations of a generalized Gibson saturated soil are developed. Then the proposed equations are solved by using the integral transformation. Given the stress-free boundary condition at the top surface of the saturated half-space, the mixed boundary condition in the plane where the rigid circular plate is laid, and the wave radiation condition at the infinite depth, the dual integral equations are developed to depict the torsional vibration of a rigid circular plate embedded in a generalized Gibson saturated soil. By appropriate transformation, a Fredholm integral equation of the second kind is obtained; and the dynamic response of the soil is determined. The dynamic compliance coefficient and the torsional angular amplitude is formulated by comparing the relation between a static torque and angular displacement. The problem can be degenerated into a simple case, which is consistent with previous research results. Numerical studies indicate that there exists a boundary-layer phenomenon in the torsional vibration of a rigid circular plate in a generalized Gibson soil when the embedment depth is five-times smaller than the radius of the circular plate; in addition, the smaller embedment depth, the more pronounced the boundary-layer phenomenon is.

A solution to dynamic response of cylindrical lined cavity under internal transient load is one of the classical soil dynamics problems. Most previous literatures about the problem assumed that soil surrounding with cavity is an elastic medium or full-saturated poroelastic medium. In fact, perfectly elastic and completely saturated soil does not exist in practical engineering. The lining structure and its surrounding soil are treated as an ideal elastic medium and a nearly saturated poroelastic medium, respectively. On the basis of Newton’s second law, Darcy’s law and Biot’s theory, the governing equation of nearly saturated soil is derived. According to boundary conditions, solutions for the radial displacement, hoop stress and pore stress of the lining and saturated soil are obtained in Laplace transform space; and then they are transformed to solutions in time domain using inverse Laplace transforms numerical method. Also, the influence of the saturation degree ( ) on the dynamic response of the lining and soil is investigated. It is indicated that the saturation degree has a less effect on the radial displacement and hoop stress when 95% 99% and has a significant influence on them when 99% 100%. But the saturation degree has much more effect on the pore stress than on the former two. The same conclusion can be drawn that the influence of saturation degree on the attenuation of dynamics response along radial direction. The saturation degree has a less effect on the radial displacement and hoop stress when 95% 99% and has a significant influence on them when 99% 100%. It also indicates that the saturation degree on the attenuation has more effect on pore stress than that of raidial displacement and hoop stress.

A coupled model including the combination of pressure solution model and stress corrosion model is proposed to simulate the observed strength recovery of limestone fracture. Thus, the coupled model can consider both pressure solution and stress corrosion in modification of the fracture contact area, which is used to predict the frictional healing of the fracture. The simulation results show that the pressure solution model underestimates frictional healing during short hold times, and with extending the hold times, the simulated results of the pressure solution model obviously increase with the growth of temperature, whereas the results are slightly influenced by the effective confining stress. Generally, the stress corrosion model reflects the growth of fracture contact area caused by compaction. Therefore, the coupled model can simulate the frictional healing well observed from Slide-Hold-Slide (SHS) tests. In conclusion, the stress corrosion model should be considered, when the pressure solution model is employed to simulate the frictional healing, especially under short hold times and at low temperatures when the domain effects are mechanical.

Consolidation drained triaxial compressive tests and unconfined compression strength tests were carried out on cement-mixed pile core samples to study the strength and deformation properties of the cemented soil on-site construction process. The effects of confining pressure and cement content on strength and properties of cement-mixed pile core samples are investigated. It is observed that with increasing the cement content, the strength, deformation modulus and the fragility of the cemented soil core samples obviously increase, but the failure strain decreases; when the cement ratio is more than 18%，the stress-strain relationships of the samples show softening; and with increasing cell pressure, the strength and destruction strain increase, the friability decreases, and the stress-strain curves may transform in the form. The behaviors of the samples all firstly exhibit a volumetric shrinkage and then a dilatancy under different confining pressures. in the consolidation drained triaxial compressive tests. And the dilatation-induced strain is slightly smaller than the failure strain. The dilatancy is caused by moving of particles. Only the particles moving reach a certain extent，the shear strength can develop up to a peak. Because the cemented soil has larger structural yielding stress, its cementation structure is not damaged under confining pressures, and its strength envelope meets Mohr-Coulomb linear rule. According to the strength and deformation properties of cemented soil, its complete stress-strain curve can be divided into three stages of elastic, plastic, softening. Popovics model is used to simulate the stress-strain relationship of cemented soil core sample, which shows that the calculated results agree well with the experimental results.

The damage degree can be characterized by the acoustic wave velocity of rock masses effectively. The rock samples are pre-damaged by the artificial cyclic loading, and the damage degree is determined by acoustic determining method. Then the mechanical properties of rock samples under different damage degrees are studied through triaxial compression test. The relationship between the decrease of acoustic wave velocity and the variation of the mechanical parameters of rock masses is established. The results show that, when the acoustic wave velocity of rock samples decreases by 5%-8%, the value of the cohesive of rock samples will reduce by 15%-25%, and the internal friction angle will increase by 14%-32%. It is shown that using the reduction of the acoustic wave velocity to describe the change of the rock mass parameters is feasible, because the rock is hardly damaged in the case of acoustic wave testing. So according to the field measurement data of the variation of the acoustic wave velocity, the change of rock mass parameters can be estimated to a certain extent, the bearing capacity of rock mass in damage zone can be further illustrated.

The shear strength of rock joint is the basis information to assess the response and safety of rock engineering in practice. Using the rock shear machine CSS – 342, a series of tests has been made on artificially cemented rock joint samples with varied morphology to investigate the influence of surface morphology on its shear strength. It can be easily found that the peak shear strength increases with increasing the normal stress and roughness. However, in the case of same surface morphology, the ratio of shear stress to normal stress decreases with increasing normal stress, indicating that the dilatancy angle caused by the morphology decreases with increasing normal stress. A hyperbolic function is proposed to describe the evolution of dilatancy angle under varied normal stress on the basis of a detailed boundary condition of dilatancy angle. In the current research, the tensile strength is used to capture the effect of intact rock. Then, a new empirical formulation is suggested to evaluate the peak shear strength of rock joint by using the slope root mean square. A comparison between the proposed empirical criterion and the famous Barton formula is also made. The results indicate that the calculated values by the proposed criterion are in good agreement with the measured ones.

Coal deformation induced by gas migration is significant to investigate coal bed methane recovery and geological sequestration of greenhouse gas. Generally, the variations of effective stress result in the shrinkage of geo-materials. However, the relationship between coal permeability and effective stress or pore pressure is nonlinear from extensive experimental results. Therefore, experiments are performed to study coal deformation caused by the flow of injected pure helium gas under hydrostatic pressure and triaxial stress conditions, respectively. Experimental results show that the coal sample undergoes a transition from shrinkage to recovery under hydrostatic pressure. Although both the coal shrinkage and recovery are proportional to the pressure of injected gas, the magnitude of shrinkage is greater than that of recovery. Under triaxial stress conditions, the coal sample rapidly expands at the beginning of helium injection. As the gas injection approaches equilibrium, the coal deformation is significantly controlled by the boundary condition. The coal expansion rate changes slowly under stress controlled condition, while the coal transits from expansion to shrinkage under displacement controlled condition. The above results indicate that the gas pressure difference between coal matrices and cleats is able to compress the matrix volume, and such compressed coal also could recover due to gas diffusion. In addition, the coal deformation is controlled by the interaction between cleats and matrix. It can be explained that coal matrices and cleats expand freely under the stress controlled boundary, while the coal matrix expansion induced by gas diffusion only narrow the aperture of cleats under displacement controlled condition. In conclusion, this study demonstrates the deformation evolution of coal induced by gas injection based on experimental results, which is particularly significant for deeply understanding the coal permeability.

This paper aims to investigate the influence of transversely isotropic property on the splitting strength and failure modes of shale. Brazilian tests and acoustic emission tests were conducted upon the shale specimens with seven bedding orientations. It is revealed that the bedding orientation plays an important role in the splitting strength and the final failure modes. With the increase of inclination angle ?, the splitting strength decreases gradually. Three failure modes can be identified under different inclination angles from the tests: straight-like crack ( 0°, 90°), crescent-like crack ( 15°) and arc-like crack ( 30°, 45°, 60°, 75°). By analyzing the the normal and shear stress components decomposed along the bedding plane, the failure mode of specimen for 0°is the tensile failure of matrix；the failure mode of specimen for 90°is the tensile failure of bedding plane and the composed failure mode occurres when 15° 75°. The spatial evolution and distribution of the acoustic emission(AE) points we have observed is similar to its macroscopic failure modes. The AE points of straight-like crack is evenly distributed at both sides of the specimen axis; the AE points of arc-like crack is dense on the one side and sparse on the other side of Brazilian disk; the AE points of crescent-like crack are distributed at the middle and one end of the specimen. The fractal dimension can reflect the failure modes of the specimen very well. From the inverted V shaped trend of the fractal dimension, the value D of the straight-like failure mode is close to 2; while D of the crescent-like and arc-like failure modes is between 2.2 and 2.7.It can be drawn from the fact that the larger of the value D is, the larger of the crack’s radius curvature is. The smaller of the value D is, the crack is more close to a straight line and failure mode is simpler.

Since the concept of representative elementary volume (REV) of fractured rock masses is fundamental and significant in rock mechanics, it is worth studying by researchers. This paper critically reviews the latest research achievements in the field of REV of fractured rock masses. Three main aspects are discussed, which are research viewpoints and its relevant parameters, research approaches and quantitative methods. Firstly, from the point view of studying REV, the geometrical parameters of discontinuities and rock blocks, the mechanical and hydraulic parameters of rock masses are investigated in detail. Secondly, the applied conditions, merits and drawbacks of research approaches are briefly introduced, including statistical, analytical and numerical methods. Finally, the quantitative methods for determination of REV, i.e., intuitive judgment, error and coefficient of variation prediction, hypothesis tests, curve fitting and grey correlation analysis, are summarized. This paper provides reference and guidance for relevant studies.

Dynamic response of a deposit slope under seismic excitations are very complex, and it is insufficient to evaluate the seismic stability of slope just by using the single seismic safety factor. Through the large-scale shaking table tests, the influences of the input seismic wave are investigated on the permanent displacements of slope surface under multiple sequential ground motions, and the failure mechanisms of deposit slope are analysed. The experimental results show that the vibration type of seismic wave can result in more permanent displacement than the impact type of one at the same peak acceleration. It is also found that the predominant frequency of seismic wave has significant effect on permanent displacement. When the peak acceleration of seismic wave reaches 0.2g, the large gravel particles on the deposit slope surface begin to roll. The corresponding permanent displacement of slope surface begins to accrue, and it increases significantly when the peak acceleration increases from 0.2g to 0.3g. An improved Newmark approach is used to estimate the permanent displacement of the crest, with assuming that the formulation of the yield acceleration is geomertric-dependent. It is shown that the permanent displacements of slope surface can be used to evaluate the deposit slope dynamic stability.

The settlement of high backfill foundation in deep ravine of Q2 and Q3 loess under natural moisture content and saturated conditions was investigated based on the centrifuge testing. A large-scale centrifugal model test was carried out to simulate the behaviors of the high backfill foundation in its construction and post-construction periods. In this test, the intact loess and disturbed loess were selected as testing materials. It is shown that the settlement deformation of the high backfill foundation mainly occurs in the construction period, and the settlement rate increases with the filling height. After the test, the settlement trough can be clearly seen on the top of the foundation. The maximum settlement occurs in the middle of the filling body. The deformation on the gentle slope with the joint of the filling body and the original foundation is smaller than that on the steep slope. Under the natural moisture content, the total settlement is small, whereas the differential settlement is large. In contrast, the deformation under the saturated condition shows different characteristics, and the foundation is less stable. Differential settlements can yield a rupture between the original foundation and the filling body, so that the joint zone needs special treatments during construction period to improve the constraint of the filling body. It is suggested here that a certain reserved height of the filling body should be determined by the end of the filling process, and then measures must be taken to avoid the post-construction cracking owing to large differential settlement deformation.

After mining, the goaf unloads and the floor below lateral wall is subject to abutment pressure, which results in the stress redistribution. Therefore, it is necessary to establish a new mechanical model for the mining floor strata regarding to the feature of the final stress field of surrounding rock, which is a superposition of in situ stress field and excavating stress field after the exploitation of coal seam. Then the analytical expressions of stress and displacement of mining floor are deduced, in which the Fourier integral transform is used to solve the biharmonic equation and the form function method is employed to solve dual integral equation. Furthermore, the Mohr-Coulomb criterion is applied to determine the plastic failure depth of floor strata as well. The results of the example show that principal stresses in goaf floor increase up to in-situ stress with increasing the depth, but the maximum principal stress in the floor below lateral wall decreases up to in-situ stress with decreasing the depth. When the depth is lower than 10 m, the minimum principal stress, , changes to be the intermediate principal stress due to the rotation of the principal stresses and further decreases with the increase of depth, while turns to increase with the continually increased depth, until up to in-situ stress. It is also found that the maximum upheaval of the floor in the central region of goaf can reach 0.236 m, while lateral wall floor moves downward due to the effect of abutment pressure on the lateral wall floor. The plastic failure region is shown to be greater in the middle than two edges and the greatest failure depth reaches 31.2 m, which is 1.04 times the half width of excavation. At last, the FLAC3D software is employed to simulate the excavation of coal seam. The tendency of simulation results compared with theoretical results is consistent except a certain departure. The proposed methods is proved to solve stress and displacement of floor accurately, which can provide significant guidance in practical engineering.

A brittle material such as rock deteriorates when subjected to freezing and thawing, it is generally observed that water phase transition due to temperature changing is the main reason of rock deterioration. Hydraulic pressure is generated by 9% volume increase of freezing water in closed crack. The pressure makes the crack expand and when the temperature rises, water moves to new cracks. The repeated cycles create new damage of rock. The freezing and thawing process of rock is also affected by a number of factors such as length of cracks, permeability, and heaving stress. The relationship between frost heave stress and crack extension length of a single fracture is established based on elastoplastic mechanics and fracture mechanics. Combined the equation of relationship between ice pressure and microcrack propagation length, the initial damage compliance tensor of the rock under the different freezing-thawing cycles can be calculated. According to the distribution of microcracks, the strain of rock induced by freezing-thawing can be decomposed into the initial damage strain, additional damage strain and plastic damage strain; and an elastoplastic damage model for rock under different number of freezing-thawing cycles is developed based on frictional sliding of pre-existing microcracks in this work. In the damage model, the plastic yield criterion of Drucker–Prager yield criterion is used simultaneously with the micromechanics damage model to simulate the inelastic deformation of rocks and Voyiadjis’ strain hardening function under compression; and it is used to define plastic behaviors of such materials. The calculated results show, the crack propagation length increases nonlinearly with increasing the crack and the compressive strength under different cycles of freezing and thawing. Finally, the applicability of the model is validated by freezing-thawing experiment, it is shown that the developed model can simulate the stress-strain curves under different of freeze-thaw cycles better.

The unconsolidated undrained triaxial shear tests are carried out to explore the stress-strain relationship behaviors of unfrozen silty sand under different freeze-thaw cycles. Based on the test results, when the confining pressure is low, both the unfrozen silty sand or the silty sand experiencing fewer freeze-thaw cycles exhibits weak strain softening phenomenon; And stain of silty sand will change from weak stain softening to stain hardening after experiencing a certain number of freeze-thaw cycles. No matter the unfrozen silty or the frozen silty shows strain hardening under a higher confining pressure level, their stress-strain curves are both the typical hyperbola. and the normalization of the stress-strain relationship is vital to study the stress-strain properties. In this paper, four kinds of common normalization factors, which are widely adopted for unfrozen soil to study stress-strain characteristics as well as the corresponding normalized conditions, are introduced. Based on the normalization factors above, a new normalized factor is proposed to analyze the stress-strain relation of soils under freeze-thaw cycles and the normalized conditions are defined. A new normalized stress-strain equation is established to predict the stress-strain curve of silty sand under freeze-thaw cycles and confining pressures. Comparison of the prediction and test results shows that the established predict model can consider the influences of freeze-thaw cycles and has better fitting and prediction accuracy.

In this paper, the FLAC3D software is applied firstly to simulate the deformation and stress distribution of the winch room at level of -648 m, considering the serious floor heave and characteristics of tensile-shear damage in Gubei Coal Mine of Huainan. From simulation results, obvious stress concentration is found at variable cross-sections and corners. The results also demonstrate that the fundamental reason of floor heave is caused by base shear slip and floor fracture uplift under high in-situ stress. Based on the theory of stepwise supporting, the supporting method for winch room floor is optimized. Moreover, the surface and deep displacement, anchor cable tensile force and the internal stress of concrete foundation are monitored. From the monitoring results, we can see that roadway floor heave occurs and the cross section of roadway tends to roundness with the original support method; the grouting tube and the base beam can well resist base shear slip; floor deformation is influenced greatly by in-situ stress orientation, and the newly combined supporting method can not only control floor deformation, but also effectively enhance the stabilities of roadway walls and concrete foundation of winch room.

A method for predicting ground surface settlement in artificial thawing period of tunnel horizontal frozen wall is presented based on the stochastic medium theory. In this method, the artificial thawing process of frozen wall is taken into account, and the temperature field of frozen wall under artificial thawing conditions is approximately derived using the single-pipe thawing theory. Based on the calculation formulation for thawing settlement in the one-dimensional case proposed by ЦЫТОВНИЧ, the methods of calculating the thawing soil column radius and the inner radius of thawing contractive region are derived. The proposed methods are applied to predict the ground surface settlement during the artificial thawing process of a full-section horizontally frozen circular tunnel. It is found that ground surface settlement distribution in the artificial thawing period is similar to that in a natural thawing period, though the temporal variation of the ground surface settlement exhibits a linear growth trend, which is different from that of the natural thawing period.

Since the conventional deformation and failure measurement of surrounding rockmass in coal-bearing strata are conducted behind the heading face, it is difficult to obtain the deformation of surrounding rockmass, and thus it is challenging to further analyzes the characteristics of deformation and failure in whole excavating process of deep coal roadway. In this study, advance monitoring measurements are performed on deep coal mine roadway in Jining Coal Mine Ⅲ that are arranged at the first time and then the deformation and failure of surrounding rockmass in whole excavating process are characterized. An improved anisotropic stain-soften model with considering volumetric stress is adopted to analyze the characteristics of deformation and failure of surrounding rockmass during excavating. It is shown that both the cumulative deformation and its rate of superficial part are higher than the deep part under the geological condition of 7th mining area in Jining Coal Mine Ⅲ. It is also found that the deformation in the whole process of excavating goes through 3 stages, including slow growth, rapid growth and stable deformation. Moreover, the loosened zone is about 1.0 m when the deformation tends to be stable. After excavation, both the displacement and failure depth of roadway sides are in the controlled range. However, the failure of surrounding rockmass at the roof and floor are relative severe and the corresponding treatment measures are given. Therefore, this paper provides an important basis for revealing the deformation and failure characteristics and the rational determination of supporting scheme and parameters.

The foundation pit of Longcao Road Station of Shanghai Metro Line 12 passes through beneath the viaduct of operating Metro Line 3, so that the pier located in the middle of foundation pit needs protection to ensure the safety of Metro Line 3. Based on the project above, the piers response of viaducts due to unloading is analyzed with combination of 3D numerical method, laboratory test and field test. It is shown that the piers in soft soil rises due to unloading, which agrees well with numerical estimation. The horizontal displacement of piers develops toward the unloading side with significant fluctuations during the process, and the final deformation is consistent with numerical simulation. Unloading leads to a slight loss of ultimate bearing capacity of piles, but it does not threaten the safety of viaduct. Upheaval of piers recovers partly under semi-surrounding unloading condition, and it does not recover under surrounding unloading condition.

The seismic response of high-arch dam in meizoseismal area is of great importance. Analysis of static stability and ultimate seismic resistance is one of the crucial issues to ensure the reservoir safety during earthquakes. By using the verified parameters after the Wenchuan Earthquake and considering the influence of strength reduction, the static and dynamic analysis for Shapai roller-compacted concrete arch dam are performed based on physical model tests and numerical calculation. Through the 3D static geomechanical model destruction test by comprehensive method, the stability of arch dam abutment under the normal load is studied. The comprehensive stability safety coefficient is determined as 3.76, and the areas destroyed seriously are suggested to be reinforced. Based on this, the 3D dynamic finite element analysis is conducted based on the method of superposition response spectrum. The calculated stresses are used to analyze the dynamic response of Shapai arch dam after reinforcement, based on the Drucker-Prager criterion and Mohr-Coulomb criterion. The fracture situation of dam and ultimate seismic resistance are discussed. The calculation results show that the seismic resistance of Shapai arch dam is good, only the instability of shallow surface will occur under the condition of earthquake in ten thousand years. The results also show that the abutment stability and reinforcement effect of Shapai arch dam is favorable. Thus Shapai arch dam performed very well with regard to overall stability and seismic resistance in "5.12" Wenchuan Earthquake. The comprehensive researches and these engineering treatment measures can provide valuable reference for other similar projects in meizoseismal area.

This paper proposes a fundamental framework for assessing the exceedance probability of liquefaction-induced lateral displacement within an exposure time period considering seismic randomness and uncertainty of soil properties by combining an empirical regression model of lateral spread and the joint probability model of seismicity. The effectiveness of the proposed model is demonstrated through a case study. The prediction provided by the proposed model is compared with the results generated by several available empirical regression models. Results show that the standard deviation has insignificant effect on the results if the conditional probability of lateral spread is normal distributed and the standard deviation ranges from 5% to 20% of the mean value, while it affects results to a certain extent if the conditional probability is lognormally distributed. The empirical regression models can only predict the magnitude of lateral spread for a given seismic level; while the proposed model is able to simultaneously predict the value and the likelihood of lateral spread due to considering uncertainty of all possible seismic levels in a certain exposure time period. Thus the proposed model is more appropriate for the aim of regional assessment of liquefaction hazard.

Predicting the ultimate bearing capacity of anchor bolt is the most important part in the bearing capacity prediction of the anchor bolt. In traditional methods, the elastoplastic stage experimental data are usually from pull-out tests on anchor bolts used to predict bearing capacity. However, in practice, it is not easy to discriminate the elastic stage from elastoplastic stage, and additionally the actual P-S curves usually have various shapes. Thus, the single model is difficult to accurately predict all kinds of anchor bolts ultimate bearing capacity. Since the prediction of ultimate bearing capacity belongs to an uncertain problem, a combined forecasting model is developed with the Dempster-Shafer(D-S) evidence theory fusion algorithm that is widely used in the multi-sensor information fusion. The D-S theory is an efficient method to process uncertain incomplete and vague information in data fusion. The aim of the management of uncertainty in a system is to reach the best approximation. The D-S algorithm firstly employs a complete set consisting incompatible basic hypothesis to represent all possibilities, and assigns the basic possibility of confidence. Then, the D-S combination rules is applied to calculate the confidence of the new evidence body reflecting the combination of information produced by the same proposition with various evidence. Finally, the best approximation of the "uncertainty" will be determined by analyzing the confidence of new evidence body generated by each proposition. This paper, by reducing the elastic phase data, enables each prediction model participating in combination generate many predicted values, and then supposes each predicted value as an evidence, with the same identification framework. Moreover, it combines the evidence with the same type but different characteristics into a new evidence accordance with the D-S combination rules, and obtains the final prediction results according to the decision rules. Comparing the D-S method with traditional arithmetic mean method, the results show that the prediction accuracy using the D-S method is more accurate. As the prediction values are easily influenced by the given initial value, the modified prediction method in this paper shows that the modified method has higher precision. The results can be used for mine construction, underground construction, subsequent quality testing, stability evaluation and rock strength prediction.

Based on the theory of plates and shells, a mechanical model is established for high-located main key strata with two clamped edges and two simply supported edges. With Rayleigh-Ritz method, an analytical expression of flexural function and an expression of stress distribution are derived for high-located main key strata. Thus, the formulation of fracture span for high-located main key strata is solved and then the fracture laws under the same condition are further analyzed. According to microseism monitoring, the dependence of the fracture at high-located main key strata on microseism activities is investigated. It is shown that the point of maximum deflection before the key strata fractured is located near two simply supported edges. During the destabilized fracture process of high-located main key strata, fracture initially occurs along the dip clamped edge when the spanning coefficient prior to fracture is higher than 1, whereas fracture firstly happens along the strike clamped edge when the coefficient is lower than 1. Moreover, the relation curve of fracture span a and dip suspension length b fits in W-shape. Finally, it is found that microseism activities with high energy result from the fractures and movement of high-located main key strata. Furthermore, the predicted fractured step and format are in good agreement with the monitored microseismic activities.

This paper investigates the formation mechanism and deformation law of earthquake-induced shattering-sliding collapses induced by studying the collapse at K70+340-K70+388 of S303 highway from Wolong to Balangshan in Sichuan province, using the combination of geomechanical method and the simulation of discrete element method UDEC. It is shown that: these collapses mainly occur in bedding slopes with steep joints; the seismic wave leads to a tensile-shear failure to the slope; and the tensile stress at dome of the slope is greater than that inside the slope; deformation induced by seismic force is found to be faster and greater at the upper and dome of the slope than that at the lower and interior of slope; the higher amplitude of seismic acceleration is, the greater slope dynamic response is, and the larger displacement of collapse mass. The failure process of shattering-sliding collapse can be divided into six stages, 1) rock mass damage and tensile fractures formatting under earthquake; 2) tensile fractures expansion and coalescence of weak slip plane; 3) the whole slump-mass scattered and local rocks slip; 4) local rocks fall, ejection, mass ejection and tumble; 5) rock mass fall, ejection, mass ejection and tumble; 6) slump-mass tends to be stability. Therefore, this research provides not only a new method for geological hazard analysis, but also a significant guide to disaster prevention and mitigation in earthquake region.

The Pastor-Zienkiewicz-Mark III (PZIII) constitutive model, which can be used to describe the nonlinear behavior of sandy seabed soil, is implemented into a well-validated computer code, FSSI-CAS 2D, for analyzing the wave-seabed-structure interaction. The characteristics of wave-induced liquefaction in offshore loosely-deposited sandy seabed is quantitatively investigated. The analysis results indicate that the developed coupled numerical model FSSI-CAS 2D is capable of capturing a series of the properties of wave-induced cumulative liquefaction in loose seabed, as well as its wave-induced dynamics. The results also show that the wave-induced liquefaction in seabed is progressive. That is, wave-induced liquefaction initiates at the surface of seabed, and propagates downward under long-term wave loading.

Lower bound finite element method converts the mathematical variation problem of lower bound theorem into an mathematical programming one, which can overcome the difficulty of artificially constructing a statically admissible stress field; thus, it has a broad prospect in engineering practice. The lower bound programming model arising from finite element discretization of stress field contains a large number of optimization variables and constraints; therefore, it is hard to be solved by traditional optimization methods. By analyzing characteristics of the nonlinear lower bound programming model, feasible arc technique and Wolfe’s inaccurate search technique are introduced to enhance the optimization efficiency of this model. Example analysis shows that, based on feasible arc technique and Wolfe’s inaccurate search technique, the convergent speed and step-length searching efficiency of optimization procedure of lower bound finite element method are evidently improved; and numerical stability and good accuracy are acquired. As a result, the new method is more adaptable to engineering practice.

An in-depth research is carried out on damage modes and energy characteristics of rock-like materials, with the whole impact process of spit Hopkinson pressure bar (SHPB) being simulated by ANSYS/LS-DYNA. A comparison between the experimental stress-strain curve and the curve derived from numeral simulation is made, the model’s efficacy is proved; and the transmitting process of effective stress within the specimen is duly analyzed, three modes of damage are identified: tearing strain damage, axial splitting tensile damage and crushing damage. By analysing the history curve of specimen internal energy obtained via numerical simulation, it is found that the internal energy has an evident strain rate effect: at lower strain rate, the time history of the internal energy can be divided into two stages, and at high strain rate it can be categorize into four stages.

Because the surrounding rock mass of a subsea tunnel or an offshore water tunnel chronically resides in the groundwater environment, its stability is significantly influenced by seepage field, which can in turn induce stress variation and even damage in the rock mass. Conversely, the stress variation and rock damage can exert influence on the seepage field. In this study, inversion analysis is carried out to determine the material parameters for the coupling model. A computer program is developed using C++ language to describe the elastoplastic stress-seepage-damage coupling of the rock mass, and the intelligent back analysis is performed to examine the stability of the surrounding rock along the Dalian Maritime University subway test line under construction. The parameter inversion is performed based on the displacement data from field monitoring, and in calculation, the indirect iteration coupling method of stress field and seepage field is used. The stress distribution and seepage field of the supporting structure are analyzed using the inversion damage parameters of the surrounding rock. The results show that the mechanical parameters of the surrounding rock obtained from the displacement back analysis can be used in the numerical analysis of the surrounding rock of similar geological conditions. Based on this, the deformation of surrounding rock can be determined, and the stability of surrounding rock can be evaluated. It is also shown that the groundwater seepage has influence on the deformation of surrounding rock of an offshore tunnel, which can induce increase in the stress and displacement of the surrounding rock. The results can provide some guideline for the tunnel waterproof design and construction.

Suction bucket foundations are increasingly used in ocean engineering. The numerical analysis of the installation procedure is helpful in engineering practice. A two-dimensional axisymmetric model has been implemented into the finite element software ABAQUS based on the ALE (Arbitrary Lagrangian-Eulerian formulation) technique, which will be used to simulate the penetration process of the suction bucket foundation in clay. The undrained shear strength and elastic moduli of soil vary with the soil depth, which are considered through the subroutine VUFIELD. Centrifuge testing results and theoretical calculations are used to validate the proposed FEM model, and some key parameters including the penetration resistance, the height of soil plug under different suctions and the bucket wall friction are examined. The numerical results show that the ALE technique is capable of simulating the suction bucket penetration without mesh distortion problems. The installation method can significantly affect the penetration resistance, namely, the suction penetration can reduces the resistance significantly compared to the purely jacked penetration. In addition, it is found that as the final suction increases, the penetration resistance reduces and the soil plug height increases. It is also shown that the internal friction has a significant contribution to the penetration resistance and the properties of soil-bucket wall friction exert more significant impact on the purely jacketed penetration than on the suction penetration.

A simplified numerical testing method is developed to estimate the three-dimensional (3D) elastic compliance tensor and study the mechanical representative element volume (REV) of fractured rock mass, on the basis of the numerical test for two-dimensional (2D) elastic compliance tensor. Firstly, 3D stochastic discrete fracture networks are randomly generated using the Monte Carlo method, according to the statistical parameters and the probability distribution functions. Then rock samples are collected in varied directions and the 2D elastic compliance tensors of the examples are further calculated using the 2D numerical test. Thus the 3D elastic compliance tensors are obtained, regarding to the topological relationship between the 2D and 3D elastic compliance tensors. For rock samples with three sets of orthogonal and continuous fractures, it is found that the maximum relative error of the main diagonal components of the elastic compliance tensor is less than 5%, comparing the results of the numerical test with analytical solutions. Therefore, the reliability and effectiveness of the numerical tests are verified. Finally, this method is applied to determine mechanical properties of Xiaowan Hydropower Station and the REV is approximately estimated as REV≈11×11×11m3.

The 3D geological modeling is one of the key technologies in spatial analysis and visulization of geological data. To improve the speed, efficiency and accuracy of geological modeling, a fast progressive 3D geological modeling method (FPGM) from point to line to surface to body with borehole data has been proposed in this paper. Firstly, the geological profiles are constructed with strata data of boreholes by human-computer interaction, then the real positon of geological profile is restored in 3D space according to the coordinates of the boreholes. After that, using the same strata lines in sections, a series of strata surfaces model are constructed by Kriging interpolation. Based on the steps above, the frame model would be accomplished. Finally, the binary space partitioning (BSP) vector shear technology is adopted to cut the boundary of the model, thus a 3D geological model of study area is constructed. This method has been applied to the construction of 3D geological modeling in Shangjie Town, Fuzhou city, showing that this method can not only realize the fast construction of 3D geological model but also improve the accuracy of the model remarkably.

General fracturing techniques are extremely difficult to satisfy requirements of the development of shale gas, due to the highly low porosity and permeability and well developed natural fractures and horizontal beddings in shale reservoirs. Therefore, one of and key technologies is the multiple clusters staged hydraulic fracture of horizontal well, which can greatly increase the stimulation volume, the production rate of gas and final recovery efficiency. In order to locate the fracturing point and fracturing pressure of multiple clusters staged horizontal well of shale gas reservoir, a three-dimensional breaking model of multiple clusters staged horizontal well is established with finite element method, which considers cement mantle and casing. Comparing the simulation results with laboratory experiment of fracturing pressure, the good agreement indicates that the numerical model is reliable and validity. This paper further studies the effect of parameters on fracturing points and fracturing pressure of multiple perforation clusters within multi-stage hydraulic fracturing in shale gas horizontal well using the simulation model. The research results show that fracturing points are found near the roots of perforation clusters, when there is no influence of natural fractures and horizontal bedding plane around perforations. The smaller perforation cluster spacing is, the greater interference between perforation clusters is, which may induce that the perforations cluster in the middle is unable to fracture. Moreover, the fracturing pressure is reduced with the increase of perforation density and perforation length. The existence of natural fracture can reduce the fracturing pressure and change the fracturing initiation position under certain circumstance, mainly depending on the natural fracture distribution and orientation and horizontal principle stress difference. In addition, the bedding plane may reduce the fracturing pressure, but relating to the difference between vertical principal stress and minimum horizontal principal stress. The regularity of fracturing pressure can provide basis for further research on the fracture propagation in multiple clusters staged horizontal well of shale gas reservoir. This study also offer concrete advises on perforating parameters in hydraulic fracture design and hydraulic operation in shale gas reservoir.