Identification of the best-fit joint probability distribution for a small set of samples is a challenging problem. Based on the Bootstrap method, an optimum marginal distribution function and an optimum Copula function for identifying the geotechnical parameters with a small sample size are proposed. The Copula method for constructing the joint probability distribution function (PDF) for correlated geotechnical parameters is briefly introduced, and then the Akaike Information Criterion (AIC) is adopted to identify the optimum marginal distribution function and Copula function. The identification results are represented by a collection of the weight factors such that each candidate marginal distribution function and copula function become the optimum (best-fit). Four measured datasets of the hyperbolic load-settlement curve-fitting parameters of piles are used to demonstrate the validity of the proposed method. The results indicate that the sample mean, sample standard deviation and sample correlation coefficient derived from the geotechnical parameters with a small sample size are relatively scattering, leading to a higher variation in the AIC values associated with the fitted marginal distributions and Copulas. The proposed bootstrap method can effectively consider the variation of the AIC values of the fitted marginal distributions function and Copulas function. It can also account for the possibilities that each candidate marginal distribution function and Copula function become the optimum. The bootstrap method provides a general and practical tool for identifying the best-fit marginal distribution function and Copula function with a small sample size.

Long-term experience of practical applications and lab tests implies that the engineering characteristics of tailings is related to some factors such as mineral composition, damming layout, sedimentary characteristics of the ore pulp, and more closely to the particle size distribution of tailings. In order to analyze the upriver-type tailings variations of the particle composition and its influence on the tailings engineering properties after discharging, depositing, sorting, a series of tests is performed to determine the particle-size distribution, mechanical properties and permeability of tailings at different positions on depositional beach face, and the influence of the fine particles (particle diameter less than 0.075 mm) content on the engineering properties of tailing is analyzed. It is found that as the distance from the tailings beach crest increases, the composition of fine particle gradually increases, grain size distribution situation changes from normally to well-graded, then again normally-graded; void ratio initially decreases and then increases; the tailings cohesion grows gradually as the content of fine particles increases, whereas internal friction angle changes within a relatively small range; the permeability coefficient is significantly influenced by the fine particle content, and decreases rapidly with the increase of the content.

The content of cementation in structured soil and hydrate in the methane hydrate-bearing sediments can influence the mechanical behaviors of the materials. Microscopically, this can be attributed to the different contents of cementation between the particles in the materials of concern. To investigate the mechanical properties of bonded particles with different contents of cementation, a series of experiments on bonded granules with different bond widths is carried out. The results show that: (1) The peak compression force decreases nonlinearly with the bond width, and is significantly affected by the aspect ratio; (2) The peak tension force decreases nearly linearly with the bond width, and trivially affected by aspect ratio; (3) The peak shear force and torsion are composed of two parts, namely bond part and frictional part, which vary in a similar way. The peak force increases first with the normal force; once after a critical stress ratio, it starts to decrease, and when the stress ratio equals 1.0, i.e., the bond material fails, the cementation no longer contributes to the peak force and the friction becomes dominant; (4) In the normal-shear-torsion tests under different bias-centroid distances, the peak force on the shear-torsion space has a ellipsoid shape.

Proper selection of grouting pressure is required to ensure the good performance of back-fill grouting. It is suggested that that the back-fill grouting compacts the surrounding soil first, and then fracture the soil when the grouting pressure exceeds a certain value. To determine the optimal grouting pressure, a formulation for calculating the upper critical value of the grouting pressure is developed based on the elastio-plastic theory with considering the unlimited expansion of the grouts. By combining the shear resistance of bolts and the grouting pressure acting on the segments, the upper critical value of the grouting pressure is determined with considering the shear failure of the bolts. Based on active and passive earth pressures, the formulations of upper and lower critical value for the grouting pressure, which meet the requirement for soil strata stability, are developed. The calculating method of the optimal grouting pressure is also presented. A practical engineering case is analyzed, illustrating the effects of elastic modulus, cohesion, internal friction angle of soil, initial underground water pressure, and tunnel depth buried on the critical grouting pressure. It is found that the critical value of grouting pressure is influenced by many factors such as the elastic modulus, cohesion, internal friction angle of soil, initial pressure of ground water, segmental structure performance, and tunnel depth. The upper pressure limit increases with the increase of the elastic modulus, cohesion, internal friction angle of soil, initial pressure of ground water, and tunnel depth, while the lower pressure limit increases with the increase of tunnel depth as well.

The longitudinal deformation profile (LDP) can reflect the spatial effect of excavation face in tunneling. Most of the previous studies on LDP, however, ignore the influence of surrounding rock quality and stress level. Based on the Hoek-Brown failure criterion and the finite difference method, functions of LDP which can quantify the difference of spatial excavation effect are given. LDP with various surrounding rock qualities and stress levels can be calculated by using these functions. By means of an error analysis, and by comparing with other equations, the rationality and universality of the proposed method are shown. The results indicate that, when basic quality indices (BQ) of rock masses have the same value, LDP tends to become flatten as the tunnel depth increases, implying that the relaxation process of stress and displacement is slowing down. When tunnel depths are the same, LDP also tends to become flatten as the BQ decrease. These features of LDP behind the excavation face are even more salient compared to that at the front of the excavation surface. The longitudinal deformation at the excavation face depends also upon the surrounding rock quality and the stress level, and its maximum value is not more than 30% of the final longitudinal deformation.

Fiber reinforced polymer (FRP) has good performance such as corrosive resistance, water resistance, high temperature resistance, high strength, high elastic modulus, light weight and so on. FRP materials can be used to enhance reinforcement effects significantly and improve durability of traditional reinforcements. A series of tests was conducted on pure sand and five types of horizontal reinforcement. Settlement, FRP strain and earth pressure were measured under different load levels, and the mechanism of FRP reinforcement was discussed. The testing results show that reinforcement can significantly improve the bearing capacity of the ground and reduce the settlement of foundation. In particular, the effect of double-layered horizontal reinforcement is pronounced, while the influence of anchor installation on the reinforcement is insignificant, and the horizontal FRP reinforcement mainly contributes to distributing the earth pressure.

Natural sedimentary clay can be disturbed in sampling and construction processes, resulting in the evolution of soil behavior. Although the disturbance degree and damage variable have been attracting many researchers’ attentions, but the relationship between them is still not clear. Here, the relationship between damage variable described by stress state and the disturbance degree represented by strength or deformation is discussed based on the experimental results. A marine clay, a typical quaternary sediments widely deposited in the Lianyungang coastal area, was selected and sampled with thin-walled tube method. The soil samples, trimmed into an appropriate size of 100 mm in length and 100 mm in diameter, were loaded quickly under different stress paths using GDS triaxial apparatus to simulate the damage process, and the consolidation and unconfined compression tests were conducted to investigate the disturbance degrees defined by the deformation and strength respectively. The relationships between damage variables controlled by the different stress paths and the disturbance degrees are developed. It is found that effect of the damage process on the compression curve is insignificant, and the unconfined compression strength decreases practically linearly with damage variables. These results imply that as stress path approaches to the failure line, the disturbance degree increases and the strength of soil decreases.

Five groups of impact load-driven fracturing experiments were performed on the granite specimens with different pre-existing crack lengths. The dynamic load was generated by a self-developed impact equipment with an adjustable dropping velocity hammer. The fracturing process of the sample was monitored by using high speed cameras with digital acquisition and the digital speckle correlation method. The characteristics of the dynamic fractures of Type I in the rock specimens under impact loading are quantitatively analyzed, including the development of displacement, the opening displacement of crack tip, expansion history of crack tip and stress intensity factor of dynamic fracturing. Experimental results show that from the moment that the hammer dropped down to the moment when the cracking process began, the crack tip stress intensity factor KI for an individual specimen constantly increase, and the magnitude of KI is greater than that of KII by 1-2 orders. For different specimens with pre-cracks under impact loading, stress intensity factor increases with the pre-cracking length.

The magnitude of initial geostress is one of the key parameters for designing underground structures and can directly influence the mechanical behavior of engineered rock masses. Although attention has been paid to the engineering problems related to high geostresses since 1980s, no clear definition is ever made thus far. In China, several rating schemes have been proposed for defining initial geostresses, but the rockmass behaviors inferred from such schemes differ more or less from the real ones. For example, no obvious high geostress characteristics were ever witnessed in some predicted high-geostress engineering sites (e.g. Guandi underground powerhouse), whereas heavy rockbursts could happen in the sites supposed to have low geostress (say, Ertan underground powerhouse site). To resolve this issue, the rating schemes for initial geostress commonly practiced in China is briefly introduced first; then the major factors affecting the geostress rating are discussed; finally high geostress is classified into two categories, i.e. the initial high geostress and the induced high geostress. The induced high geostress is a combined result of the high secondary stress concentration due to cavern groups and the dynamic disturbance due to blasting excavations. The criterion defining high geostress is clearly specified, which is the threshold of geostress that can induce failure of the embedded structure or the rockmass, and a qualitative criterion is also summarized based on the previous research results. The ratio of strength to stress is redefined as the uniaxial compressive strength of dry intact rock to the measured maximum principal stress, and a new initial geostress rating scheme (quantitative criterion) is suggested. The suggested scheme is validated using the monitoring data of 25 engineering cases, showing that the accuracy of the suggested scheme is much better than the commonly used rating schemes in China. The suggested scheme is similar to that proposed by CD Martin et al. in 1999.

Dilatancy angle is commonly used to describe the expansion behaviours of rock. Continuum theory generally assumes that the value of dilatancy angle is 0° for the materials obeying the non-associated flow rule, but for those materials obeying the associated flow rule the dilatancy angle is a constant value equal to internal friction angle. The full volumetric curves of triaxial compression show that volumetric dilatancy is highly dependent on the confining pressure and plastic parameters. In a full failure process, not only the characteristic strength but also characteristics of dilatancy properties behave in a nonlinear manner with change of confining pressure and plastic parameters,. Employing plasticity theory and the nonlinear fitting method, a double parameters’ dilatancy angle model is developed, based on damage control triaxial loading and unloading cycle test data of Jinping marble, to take into account the effects of the confining pressure and plastic parameters. The model reveals that the dilatancy behaviors of marble as well as similar hard rocks are mainly governed by the confining pressure and plastic parameters during a failure process, which shows significant nonlinearity, and the dilatancy angle rapidly increases to the peak and then decreases gradually with increasing plastic deformation. The proposed double-parameters nonlinear dilatancy angle model can be used to describe the volumetric dilatancy properties, helping understand the mechanism of surrounding rock failure around underground openings and predict the range of expansion volume. In addition, the proposed model has theoretical and practical bearings on the design of supporting structures in underground rock engineering.

The active earth pressure depends largely upon the inclining angle and the displacement of a retaining wall backfilled, for either sandy or clayey soil. Thus, it is necessary to address these factors in calculating the active earth pressure of the retaining wall backfilled by the nonlimit-state soil. Based on stress state analysis, the coefficient of lateral earth pressure is determined by considering the soil arching effect and the nonlimit soil state, and a closed form solution is given for the inclined retaining wall using the horizontal element method. The proposed method is validated by comparing the calculated results with model testing results. The key parameters, such as displacement ratio ?, the ratio of soil-wall friction angle and internal friction angle ? /?, inclining angel ?, and cohesion c, are analyzed, which have great influences on the distribution of the active earth pressure and the height of the acting point of the sum of the total earth pressure. It is shown that as the soil state transits from static to actively pushing the wall, the soil arching effect becomes stronger. Also, as ? /? increases, the distribution of the active earth pressure becomes more and more nonlinear and the height of the acting point of total earth pressure increases, while the effect of ? /? on the earth pressure increases as ? increases. In addition, as ? increase, the soil arching effect diminishes. For the cohesive soil, the cohesion has influence on the active earth pressure, and the height of the acting point of total earth pressure decreases as the cohesion increases. The proposed method may help improve the calculation of active earth pressure behind the retaining wall.

Rainfall-induced shallow landslide is a type of commonly occurring geohazards. To explore the evolution of the slope stability during a rainfall event, a conceptual model of rainfall-induced shallow landslide with considering the effect of transient pore water pressure is developed based on the Green-Ampt infiltration model, and the relationship between the factor of safety and precipitation duration for the slope with or without ground water is developed. The results show that for the slope with underground water, the pore water pressure in the slip zone drastically increases once after the wetting front touches the groundwater table; for the slope without ground water, the slip zone become inundated in the water and the soil strength decrease quickly. Based on these results, and according to whether the shallow landslide is completely saturated or not during rainfall, a concept of critical saturating time is proposed, with considering the case that the initial rainfall intensity is less than the soil’s infiltration ability. This critical time can be used as a parameter for early warning the shallow landslide.

It is still a common practice to calculate the foundation settlement through the layer-wise summation method using the e-p curve obtained with a compression test. In recent years the secant modulus method (SMM) is increasingly used to calculate the foundation settlement, which is not affected by the initial void ratio of the soil and convenient for computer. The compression stress-strain relationship of soil is expressed as a form of hyperbola in the traditional SMM. The compression stress-strain relationship of loess is discussed and the differences between the secant modulus and compression modulus are analyzed. It is found that the main reason for the discrepancy of calculated results between the SMM and the e-p curve-based method is related to a hyperbolic hypothesis, which assumes that the stress-strain relationship of compacted soils follows hyperbola. To fix the problem, we define the stress-strain relationship of compacted loess using a power function, which can match the actual situation correctly. The settlement formulation using the compression stress-strain relationship with a power function is developed. The proposed method is applied to a practical engineering problem, indicating that the calculated results agree well with measurements.

Although fractal method performs well in calculating the swelling deformation of bentonite, it does not provide an effective method to calculate coefficient K, which limits the application of the fractal theory. Because both the DDL theory and the fractal theory are applicable in analyzing the behavior of compacted bentonite, a method is proposed to determine coefficient K in the fractal theory based on the DDL theory, by which a value of 9.15 is determined for coefficient K of commercial bentonite. N2 adsorption tests are the performed on the commercial bentonite, and the measured isotherm data are used to determine a surface fractal number of 2.65. Then, the so-determined K and the surface fractal number are used to calculate the maximum swelling deformation through the fractal method, and the calculations are compared to the experimental measurements. It is shown that the results of the fractal method agree well with the experimental data, especially when the applied loading is large and the swelling deformation is small. It is also shown that the fractal theory yields better results than the DDL theory.

Composite bucket foundation is a new kind of wide-shallow foundation for offshore wind turbines. Compared to the local scour around a deep foundation such as pile foundation, scouring around composite bucket foundation can significantly influence the safety of wind turbine. According to an engineering instance, a test site for scour experiment is built and the monitoring points are displayed. A series of scale model tests is performed on the local scour around a composite bucket foundation model, and the scales of 1:20, 1:40 and 1:70 are adopted in the experiments. The morphology of the scour hole around the foundation, equilibrium scour time and maximum scour depth are investigated, and the maximum scour depth of the seabed around composite bucket foundations is determined according to the results of the scale model tests. The characteristics of local scour around composite bucket foundation are clearly captured in the experiments, providing some theoretical guidance for the application of composite bucket foundations.

The freezing-thawing experiments were performed to investigate the effect of pre-freezing moisture content and dry density on the compression and water migration in Qinghai-Tibet silty clay under double-direction freezing and one-direction thawing. The results show that (1) under large thermal gradients, the compressibility of the soil decreases at low initial densities and increases at high initial densities after freeze-thaw cycles, whereas under small thermal gradients, the soil compressibility constantly decreases; (2) As the pre-freezing moisture content increases, the soil compressibility under larger thermal gradients increases and approaches to a stable value, whereas it remains practically unchanged under small thermal gradients; (3) As the thermal gradient increases, all the compressibility coefficients of melted soils at different densities decrease first, and then increase, and the compressibility coefficients of melted soils under different pre-freezing water contents increase; (4) The water contents in the frozen specimen first increase, then decrease and finally increase from the top to the bottom. As the thermal gradient descends, the water content in the middle part of the specimen increases first and then decreases.

To take the advantages of both the FEM and the particle DEM methods, a procedure is proposed to transit the FEM into the DEM. In this procedure, the domain of concern is first discretized into a certain number of coarse FEM elements, and the behavior of each element is characterized by using a continuum constitutive model. During simulation, the stress state of each element is tracked for each time step. Once if the stress state of an element satisfies either the Mohr-Coulomb criteria or the maximum tensile stress criteria, the element is deleted and immediately replaced by a cluster of particles, which are randomly distributed and slightly interpenetrated. As such, the response of the deleted element is fully described by this cluster of particles. The particle properties of the cluster, including mass, material properties, velocity, displacement and contact force, are all inherited from the deleted element by using an interpolation method. To realize the simulation coupling FEM and particle DEM, the point-edge (2D) and point-face (3D) contact models are introduced, and the contact forces are calculated using normal and tangent numerical springs. Numerical examples such as the impact of a particle ball onto a slab, the uniaxial compression and rock cutting, are provided to illustrate the capability of the proposed method.

Soft interlayer is a widely existing geological body in rock and soil mass. Due to its weak mechanical properties, it usually brings potential safety hazard to engineering construction. Based on the plastic limit equilibrium method, an ultimate-load formulation of soft interlayer is derived by using the modified Prandtl squeezing theory and assuming that the upper and lower layers close to the soft interlayer to be quasi-rigid. In the analysis, we suggests that under the limit state the soft interlayer between quasi-rigid layers displays plastically squeezing failure behaviors. Due to the inaccuracy of Prandtl’s shear stress solution in the x direction, new solutions of stress components and ultimate load of soft interlayer are determined with considering various boundary stress conditions. A simple formulation of the ultimate load on the soft interlayer is derived, which could reflect the comprehensive effects of dead weight, boundary stress conditions, as well as friction condition of boundaries on the ultimate load of soft interlayer. Meanwhile, by comparing results from proposed method to other methods, it is shown that, if the dead weight of interlayer is ignored, the variation of ultimate load with thickness of soft interlayer in this text generally agree with what the Prandtl method predicts; when the dead weight is taken into account, the solutions of the proposed method yields results similar to the method in the construction code. For thick interlayer, however, the proposed method can more properly reflect the influence of width on the ultimate load. In addition, the effect of the boundary friction on the ultimate load varies with width-thickness ratio of soft interlayer, and a critical width is found to exist for the interlayer, which is hardly affected by the friction condition for the interlayer with a certain thickness.

Fault-crossing tunnel structures were severely damaged by fault movement during Wenchuan Earthquake. This phenomenon demonstrates that traditional aseismic technologies cannot guarantee the security of tunnel and underground structures. Therefore, new types of deformable aseismic and damping measures have to be developed for tunnel and underground structures. Shaking table tests are conducted to investigate seismic response characteristics and post-seismic destructive patterns of tunnel structures with these measures. The results show that the absorbing joint can reduce the internal forces and the strains of fault-crossing tunnel structures. The casing-shape damping measure can effectively protect both the inner casing and most parts of outer casing structures except for the arch springing and tunnel invert of the outer casing. The casing-shape damping measure performs better than the absorbing joint, since the former can improve the waterproofing quality and recoverability of tunnel structures besides the aseismic capacity. It is necessary to enhance the intensity of secondary lining concrete when using deformable aseismic and damping measures. No matter what kind of aseismic measures are employed, the arch springing and tunnel invert parts are needed to be reinforced. The above research results can provide references for seismic fortification of tunnel and underground structures across geological hazards zones.

To characterize the failure mechanism of anti-slide micropiles and the failure mode of slope, three sets of large-scale physical model tests were carried out on the soil slopes reinforced by anti-slide micropiles in a single row and three rows. The displacements and the strain of piles during the loading process were measured and the failure pattern through excavating was observed. It is found that the triple-row micropiles behave better in anti-sliding, whose capacity is 51.5% higher than that of the single-row piles, and the sliding body can deform significantly before it completely collapses or fails, implying that the triple-row micropiles are suited to be used for the expedient treatment. Secondary sliding surface which is arch-shaped can be generated in front area of the piles and links to main sliding surface preset; for the three-row piles, pumping area between pile and soil would appear in front of the third row and longitudinal cracks come into being in the slope surface. The pile deformation displays S-shaped. The bending deformation of piles leads to tension-compression and shear failure instead of the fracture failure as at the sliding surface of rock slope. The maximum of bending moment of the pile is located above the sliding surface. For the triple-row micropiles, the bending moment of the first row piles is the largest, then the third row and that of the second row is smallest.

The temperature field can significantly influence the performance of the liner system, the gas migration process and the mechanical behavior of the municipal solid waste (MSW) in a landfill. The thermal conductivity coefficient is the important parameter for determining the temperature field in the landfill site. Using DRCD - 3030 type intelligent thermal conductivity tester, the thermal conductivity coefficients of the MSW sampled from Taizhou Luaoli landfill are determined at different water contents and porosities. In the experiment, the water contents of the samples are targeted to 0%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45% and 50%, respectively, and the porosities are targeted to 77.8%, 75.0%, 71.4% and 66.7%, respectively. The experimental results show that the thermal conductivity coefficient of the dry MSW is generally small, about 2.5-3.5 times that of the air in standard state, and it decreases as the porosity increase. The thermal conductivity coefficient of the unsaturated MSW increases with the increase of water content. At the same water content, the smaller the porosity of MSW, the greater thermal conductivity coefficient. Based on the experimental data, a formulation is developed, using the weighted geometric mean method and the linear curve-fitting method, to calculate the thermal conductivity coefficient, which can provide an important tool for determining the temperature field in a landfill.

A large number of landslides were triggered by the 5.12 Wenchuan earthquake and the 4.20 Lushan earthquake. The statistical results of field surveys indicate that the overall distribution pattern of the scale of earthquake-induced rockmass collapse and landslide changes with the earthquake intensity. This statistics-based result needs to be confirmed by performing laboratory physical experiments. Based on the framework of self-organized criticality (SOC) theory, shaking table tests of sandpile model under seismic excitations was conducted. The results show that for peak ground acceleration (PGA) in the range of 0.075g-0.125g, the relation between the amount and cumulative frequency of sand follows a negative power law; for PGA between 0.15g and 0.25g, the relation obeys a lognormal distribution; for PGA between 0.35g and 0.45g, the relation turns to obey a normal distribution. Data from the cellular automata numerical simulation demonstrate that, as the earthquake intensity increases, the dynamic behaviors of sandpile model exhibit a strong power-law first, then a weak power-law, and finally a normal distribution. It is suggested here that the above-revealed distribution laws may also apply to other areas. The new recognition will provide a scientific basis for the prediction of landslides triggered by earthquake.

This paper reviews the insufficiency of anticorrosion performance of the bolts used in underground engineering and introduces both the structure and the anticorrosive mechanism of the multiple anticorrosive bolts. The experiments on corrosion resistance of both the dual and multiple anticorrosive bolts have been conducted under different corrosive environments, and the apparent change of bolts has been observed and the pullout capacity has been tested. The relationships of bond strength and sliding displacement between two types of anchor bar and cement mortar are also analyzed and compared. The analytical results indicate that because multiple anticorrosive bolts are enwrapped by casing in cement mortar, their pullout capacities in different corrosion environments are always greater than that of dual anticorrosive bolts, and the capacities grow more significantly with time. Sulfate crystallization and the drag effect between corrosion factors can cause a transient increase in pull-out capacity of the anticorrosive bolts, so that the bond strength of multiple anticorrosive bolts corresponding to same sliding displacement is higher, and the residual strength posterior to peak value is also greater than that of dual anticorrosive bolts. The above results can be used in the design of anticorrosive bolts in underground structures as well as the durability analysis during the later service period and also can provide valuable basic data for the study of corrosion resistance of anticorrosive bolts in practical engineering.

The hollow pipe-piles can effectively reduce soil squeezing effect during static pile driving, and accelerate the dissipation of excess pore water pressure, decreasing its maximum value. With accelerating the dissipation of excess pore water pressure, unfavorable situation including pile floating and skewing can be effectively avoided, while the bearing capacity of pile foundation as a whole and the stability of foundation pit can be raised. But the openings in the shaft of pipe-pile can certainly generate stress concentration and weaken the bearing capacity of the pipe-pile. Thus, a series of model tests on stress concentration and ultimate bearing capacity of the hollow pipe-pile is carried out. The stress concentration and the reduction of ultimate bearing capacity are analyzed. The testing results show that the performance of the piles with symmetrical opening holes is better than that with the asymmetric opening holes with regard to the bearing capacity, and the bearing capacity of the pipe-pile with hole opened in a radial direction is the highest among all types of piles. The above results can provide guidance for designing the hollow pipe-pile foundation and help promote their application.

Under a large temperature gradient, the freezing front moves fast in a freeing soil and pore water transits into ice, resulting in local volumetric expansion. However, because the temperature gradient is generally small in a natural environment, water migrates from unfrozen areas to the freezing area, and crystalizes in some position, where pore ice accumulates and ice segregation occurs. Because the frost heave induced by ice segregation is much more significant than that induced by local volumetric expansion, it is very important to establish a model to simulate the moisture migration and ice segregation formation process. Based on the secondary heave theory, a frost heave model of freezing saturated soil is developed. The proposed model assumes that the flow rate in freezing fringe is constant for each time step. Thus, the water pressure is firstly calculated in freezing fringe, and then ice pressure is obtained based on the Clapeyron equation. The magnitude of the ice pressure is used as a criterion of ice segregation formation, with assuming that when new ice segregation occurs, old ice segregation stops growing. This model also considers the velocity of moisture migration and heave rate as basic unknown quantities, and simulates the heave under similar natural conditions where soil has overburden pressure at the top boundary and nonpressure water supply at the bottom. By comparing the numerical simulations to experimental results, the validity of the model is validated.

Six scaling methods are adopted to create six grading curves for numerical simulation based on one in-situ grading curve. The rate of number of particles in an interval to total number of particles is regarded as the number of measuring fractal, and thus a fractal model is developed. Fractal characteristic of particle size distribution is analysed. Using the particle flow cod, six sets of numerical samples corresponding to six grading curves are generated and used to carry out biaxial compression tests. In this test, the effect of scale method on the macroscopic and mecroscopic mechanical properties of numerical samples is observed, and the relationship between the fractal feature of particle size distribution and the mechanical properties of numerical sample is determined. The results show that the particle size distribution of numerical samples has a fractal feature, its fractal dimension D is from 1.463 to 1.783. With the increase of similar scale M based on the different scale methods, fine particle number in numerical samples increases and the filling rate between coarse and fine particles becomes better reasonable. As a result, the mechanical property of numerical sample is gradually ameliorated. Fractal dimensions D of particle size distribution linearly agrees with the mechanical properties of numerical samples.

The successful cases about soil liquefaction mitigation are reviewed, in the sites of the 1989 Loma Prieta, USA earthquake, the 1993 Kushiro-Oki, Japan earthquake, the 1994 Hokkaido Toho-Oki, Japan earthquake, the 1995 Hanshin, Japan earthquake, the 1999 Chi-Chi, Taiwan earthquake, the 1999 Kocaeli, Turkey earthquake ,the 2001 Nisqually, USA earthquake and the 2011 great east Japan earthquake, and the applicability and performance of various mitigation measures are analyzed. The lessons we have learned from these successful cases of soil treatment include: (1) for bay areas or reclaimed lands, the ground treatments against soil liquefaction are indispensable; (2) the choice of soil liquefaction countermeasures should be based on the consideration of site conditions, economic conditions and the environmental conditions; (3) compacted sand piles and stone columns are widely used, which have become mature and economical technics, and they are suitable for improving liquefaction-prone soils in the seismic intensity VIII zone and below; (4) the dynamic compaction method is simple and less expansive, and this method is especially suitable for large fields in the seismic intensity VIII zone and below; (5) grouting, deep soil mixing and jet grouting methods are effective in mitigating the earthquake-induced liquefaction damages in the seismic intensity IX zone and below; 6) the combination of various liquefaction countermeasures is more effective than an individual measure. If possible, multiple methods should be used in combination to achieve better effects.

The large rheological deformation of surrounding rock caused by the high ground stress is an important factor that affects the safety and stability of deep soft roadways. Deformation and failure mechanism of weak surrounding rock at the west roadway of Coal Mine of Yangquan Coal Mining Group No.1 are analysed. A finite element model is developed which can address the local geological conditions and the initial design scheme. Based on the field monitoring deformation data and rock borehole results, the mechanical parameters and creep parameters of the surrounding rock are obtained through a back analysis. A new support scheme, which consists of double cacheable and gradually variable supporting shells, is proposed for deep soft-rock tunnelling. The scheme is implemented through hierarchically grouting reinforcement according to the damage condition of the surrounding rock and setting up a U-steel support in the external area to form deformable buffer layer. Finite element method for simulating the new support scheme is developed. Using the parameters obtained from the back analysis, deformation of surrounding rock is predicted. By comparing the numerical results with the field monitoring data, the effectiveness of the new support scheme is verified.

The waveforms of microseismic events recorded during rockburst contain abundant precursor information of the rockburst. Based on the attenuation characteristics of microseimic wave in the deep tunnel, the maximum effective amplitude is modified, and the relative effective amplitude and maximum effective frequency are used as analysis parameters of frequency spectrum. Case studies reveal that the evolution characteristics of frequency spectrum during instant rockburst induced by the tunnel boring machine (TBM) and the drilling and blasting (D&B) are similar. As there no rockburst occurs, the magnitude of relative effective amplitude corresponding to the largest radiated microseismic energy for daily event is often at a level of 10-6 m/s or even less; and most of the maximum effective frequencies are greater than 300 Hz. Before the medium intensity rockburst happens, the magnitude of relative effective amplitude maintains at a level of 10-5 m/s, and the maximum effective frequencies are between 200 Hz and 300 Hz. (3) Before the intense rockbust occurs, the magnitude of relative effective amplitude increases and reaches 10-4 m/s; and the maximum effective frequencies are almost below 200 Hz. For a whole process rockburst, the relative effective amplitude reach its maximum value and the maximum effective frequency become minimum on the occurrence of rockburst. The evolution of frequency spectrum of microseismic signals can provide reference for early warning the occurrence time and degree of instant rockburst.

The percolation and fractal theory are employed for analyzing evolution of the crack networks in the coal and rock masses at the site of the coal mining face No. 15-22060 at Mine No.8 of Pingdingshan Coal Mining Group. The evolving characteristics and corresponding relationship of percolation probability and fractal dimensions with advancement of the coal mining face are determined. The results show that, being controlled by initiation and propagation of transverse delamination fractures and vertical broken fractures, the permeability probability linearly increases in a stage-wise way with advancement of the coal mining face and the magnitude of amplification is increasing. The crack network propagates into the coal body ahead of mining face and the overburden strata with advancement of the coal mining face. The length, width, quantity and distribution of cracks play dominant roles in fractal dimensions, and evolution of fractal dimensions falls into 3 stages. Relationships between percolation probability and fractal dimensions of crack network in coal and rock masses can be fitted using a power function for the first stage and two linear functions for the second and the third stage. These results lay a foundation for determining the equivalent permeability of the crack networks in coal and rock masses.

The indies currently used for evaluating the compaction quality of railway subgrade are not sufficient for evaluation. Based on the fundamental theory of continuous compaction control, a kinetic analysis of the interaction between the roller’s vibrating wheel and the subgrade structures is performed, and the acceleration signals of the vibrating wheel, which was collected by collecting vibration frequency sensor, are analyzed by magnifying, filtering and other treatment; through analogue-digital conversion, the analogue signals are converted to digital ones. The treated acceleration signal of the vibrating wheel is used as the measuring index for continuous compaction–vibrating compaction value (VCV), to evaluate the real-time compaction quality of the subgrade. By comparing and analyzing the VCV and regular indexes of K30, Evd, Ev1 and Ev2 under category of plate loadings, which were obtained from two testing sections of high speed railway, it is revealed that, the continuous compaction index has a linear relationship with the regular index under category of plate loadings. Therefore, the control standard for vibrating compaction value can be determined with the compaction standard of the regular index, providing a basis for the inspection and control of the continuous compaction of subgrade.

In practical tunnel construction, the stress redistribution of underground rocks caused by tunneling usually leads to microcrack-expansion damage in the surrounding rock, with accompanied plastic flow deformation. The high pore water pressure is generated in the pores of rock and microcracks under stressed conditions in groundwater environment, which in turn influences the mechanical properties and the changes of the failure modes of the surrounding rock. To investigate the coupling effect of two types of failure mechanisms which are the damage-induced stiffness degradation and the plasticity-driven flow. based on the elastoplastic and damage theories, the modified effective stress principle is adopted to consider the effects of pore water pressure, and then an elastoplastic damage constitutive model is developed adopting the Drucker-Prager yield criterion. To implement this model, a numerical integration algorithm-implicit return mapping algorithm is developed with considering the effect of pore water pressure, and the detail descriptions of the implicit return mapping algorithm about the trial stress returning to the smooth cone surface or sharp point singularity on the yield surface are given. The implicit return mapping algorithm has good performance with regard to stability and accuracy. The set of parameters related to elastoplastic damage models is large and not easily determined. To resolve this issue, a back analysis method is introduced. The elastoplastic damage constitutive model is implemented by adopting the method of object-oriented programming using C++ language. The proposed model and the computational procedure are validated by comparing the numerical simulations to the experimental measurements. The proposed procedure is applied to Jilin Fusong tunnel project to analyze the development of the plastic zone and the damage zone. The results show that the proposed elastoplastic damage constitutive model can well describe the mechanical behavior of the rock, and the computational procedure can simulate the practical engineering problems, giving certain guidance for site construction.

A 3D elastoplastic numerical model is developed for the structure-soil layers-pipeline system in the Gongyixiqiao metro station project of Beijing metro line 4, and used to analyze the deformation of pipeline and its surrounding soil, based on the measured displacement data. By combing the field monitoring data, numerical simulations and empirical formulations, the effects of pipeline stiffness on ground deformation are analyzed. It is shown that as the soil-pipe stiffness k is less than 0.18, the differential soil-pipe settlement is less than 5%, and the empirical formulation can be used to calculate the soil settlement at the level of pipeline axis. With the increase of pipeline stiffness, the pipeline can constrain the ground movement more significantly, resulting in a reduction of the growth rate of ground settlement or even a negative growth so that the surface settlement can even exceed the ground settlement. By a fitting analysis of the numerical results, a method is proposed for estimating the maximum pipeline settlement for rigidly jointed pipelines, which is based on the soil-pipe stiffness and tunnel-induced ground surface settlement. The method has been used to calculate an actual project settlement, and the difference between the calculated and measured values is found to be less than 4%, showing the applicability of the proposed method.

Based on the unique feature of the combined soil-rock geological conditions in Qingdao, Shandong province, the deformation and dynamic responses of the end-suspended piles for foundation pits in the combined soil-rock foundation pits under gantry crane moving loads are studied by using the finite element code, Plaxis, and field monitoring. The results indicate that the numerical predictions agree well with the measured deformations of the pre-bored pile shaft, and the major deformation of foundation pit occurs in the soft soil strata in rocky area, whereas the stress concentration occurs at the rock-socketed part of the end-suspended piles. In addition, under the gantry crane moving loads, the horizontal displacement of the pile head is larger, and its dynamic response is the least pronounced, whereas the horizontal displacement of the rock-socketed part is smaller and its dynamic response is the most significant. At the rock-socketed part, maximum positive bending moment part and maximum hogging moment part, the dynamic responses of earth pressure are the most pronounced, and the largest response occurs as a moving load passes by. The results can provide reference for the deep foundation pit supporting design in similar geological conditions.

To release once for all the pressure in the coal seam with high rockburst risk before driving or mining, and to achieve the goal of regional rockburst prevention, the fixed-point hydraulic fracturing technique for coal seam is developed. To explore theoreticallythe feasibility and effectiveness of the fixed-point hydraulic fracturing method for coal seam rockburst prevention, a mechanical model is first developed for the coal seam, and then used to analyze, both qualitatively and quantitatively, the mechanism of the fixed-point hydraulic fracturingfor rockburst prevention. It is shown that hydraulic fracturing can prevent rockburst by increasing the resistance and releasing the energy of the coal seam.By introducing the efficiency index In, a procedure is proposed for evaluating the efficiency of the proposed rockburst prevention method, and a formulation is developed for calculating the critical volume of the bursting rockmass, providing a reference for the selection of hydraulic fracturing parameters. Finally, the proposed hydraulic fracturing method is applied to No.1412 working face of Huafeng Coal Mine, and its feasibility and effectiveness of rockburst prevention is illustrated with field observation, pipeline pressure, microseismic events and stress variation.

A new model of dynamic resilient modulus was proposed to evaluate the subgrade soil by NCHRP 1-37A project in USA in 2004. The model is widely applied in engineering analysis since it considers the influence of volume stress and deviatoric stress. In the finite element analysis, however, the model is usually implemented using the equivalent tangent stiffness matrix determined from an equivalent dynamic triaxial test through local iteration at material points. In order to eliminate the error caused by the simplified method under complex stress state，the accurate consistent tangent stiffness matrix of dynamic resilient modulus is derived based on the general Hooke law. The model is implemented into ABAQUS by compiling the user material subroutine (UMAT); the finite element simulation is carried out for the cases of axial pressure and confining pressure; the simulated results demonstrate that the new method has a higher precision and efficiency compared to the existing simplified method based on an equivalent triaxial test. Finally, an analysis of typical asphalt pavement structure shows that, in order to improve the accuracy of the response of subgrade under complex stress state，it is necessary to use the consistent tangent stiffness matrix instead of the equivalent stress tangent stiffness matrix in pavement structure analysis.

Rockburst is a type of geologic hazards frequently occurring in the deep underground engineering construction. The prediction and classification of rockburst remains an unrsolved problem in underground rock engineering. To evaluate the rockburst intensity, a novel comprehensive evaluation model based on the normal cloud model and Delphi method is developed to overcome the issue of fuzziness and randomness in evaluating the rockburst intensity. Based on a comprehensive analysis of the controlling factors of rockburst, four factors are chosen as the indices for the intensity evaluation, including the ratio of uniaxial compressive strength and tensile strength, ?c / ?t, the ratio of tangential stress and uniaxial compressive strength, ?? /?c, the rock brittleness index, Is, and the elastic strain energy index, Wet. The Delphi method is adopted to determine the weighting coefficient for each evaluation index. The normal cloud model is used to calculate the cloud characteristics for each evaluation index in rockburst classification, which generates the normal cloud droplets, and the undetermined mapping between the rockburst intensity and the evaluation index are realized, keeping the randomness in the evaluation process. Finally, the proposed model is validated with a series of typical rock projects. The obtained results show a good agreement with practical rockburst classification, and the accuracy of cloud model is higher than that of the efficacy coefficient method and set pair analysis method. indicating that the normal cloud theory is applicable and effective for classifying the rockburst intensity.

Because conventional numerical methods fail to evaluate the effectiveness of grouted bolts in reinforcing the surrounding rockmass, a simple and effective equivalent numerical method, with combination of a formulation for the bolt supporting pressure induced by rockmass deformation, is proposed for this purpose. In this method, the maximum axial force of each bolt is first determined by numerically simulating the bolt-supporting tunnel excavation. The obtained maximum axial force is then used to calculate the equivalent force distributing along the rock bolt by using the formulation of the bolt supporting pressure. Finally, the excavation process without bolt supporting is simulated by applying the equivalent distributing force to the surrounding rockmass surface. This method is applied to calculate the excavation and support of the underground powerhouse at Jinping Ⅱ hydropower station and the diversion tunnel #4 (section 0+550 m) at Wudongde hydropower station. By comparing the calculation results with the field measured data, it is found that the proposed method can well address the effectiveness of grouted bolts in reinforcing the surrounding rock, and the simulation results can provide reference for tunnel construction and support design.

The precision of slope stability assessment is highly affected by the randomness of soil parameters. Massive groups of soil parameters and slope geometry parameters are randomly generated by Latin hypercube sampling method according to their common distribution characteristics. For each group of parameters, safety factor is calculated by the strength reduction finite element method (SRFEM); and failure probability with consideration of the spatial variation of soil properties is investigated by combining Monte Carlo simulation and SRFEM under the two-dimensional random field. The sample data and corresponding safety factors and failure probabilities are then implemented in the training and testing processes of radial basis function (RBF) neural network to establish forecast models for slope stability analysis. The simulation results of an example show that the two-dimensional random field model can reasonably well reflect the spatial variation of soil properties; and the created RBF neural network-based forecast models not only has high prediction precision on safety factor and failure probability, but also can effectively save the computational time.

Due to the limit of Surpac software, the method for 3D numerical grid generation based on the Surpac software generally suffers for some deficiencies such as time-consuming and cumbersome. By adopting the basic idea of octree subdivision, the batch and automatic meshing technology of multiple geological body is investigated. To resolve the confliction issue arising when both the precision and the model scale need to be considered in computation, the grid local encryption and multi-scale partitioning methods are introduced and discussed based on the concept of multiple grid method. An automation software platform is developed for 3D numerical grid generation by using VC++. The platform can be conveniently and effectively used to generate the numerical grids for the mining fields with complex geomorphology, providing a strong support for the automation of excavation numerical analysis. The new platform has been used in the in-situ stress inversion analysis of Linglong gold mine, showing its applicability and capability.