International Journal of Geomechanics

To get an accurate bearing capacity of a postgrouting pile, the range of grout diffusion should be considered in practice. Considering the time-dependent behavior of power-law cement grout viscosity, calculation methods are proposed to determine the diffusion radius and the climbing height of the grout. Moreover, an iterative calculation method is established to compute the climbing height of the grout along a single pile embedded in layered soils. Four cases reported in the literature are used to demonstrate the effectiveness and accuracy of the proposed calculation methods. The calculation results show that the computed grout diffusion radius and climbing height of the grout are in good agreement with the measured value. For practical purposes, to get an accurate prediction on the bearing capacity of postgrouting pile, the time-dependent behavior of grout viscosity should be considered.

The excavation of multiple tunnels at shallow depths has become increasingly common. The tunnel spacings, arrangements, buried depths, and excavation sequences significantly affect the ground responses. In addition, rock rheology makes the mechanical response of the ground a complex function of time. This study provides a generalized time-dependent analytical model by which the ground responses induced by the sequential excavation of multiple tunnels in a rheological rock can be addressed rapidly and precisely. The key factors, i.e., any viscoelastic characteristics of the surrounding rock, the real interactions between tunnels, and the tunnel sizes, arrangements, excavation times, and sequences, are fully taken into account. Using Schwartz's alternating method combined with complex variable theory, the elastic solutions of stress and displacement are first addressed for n tunnel excavations at shallow depths. Then, based on the elastic solutions and the corresponding extended principle for the viscoelastic problem, the general time-dependent analytical solutions in all the excavation stages are obtained for the ground assuming any viscoelastic model. The analytical solutions exhibit close agreement with the numerical results for models that are consistent, and they are qualitatively consistent with the numerical results of a real case. Then, parametric analyses are conducted for the sequential excavation of three tunnels to investigate the influences of tunnel arrangements, excavation sequences, and excavation times on displacements and stresses. The proposed analytical model can help to reveal the particular mechanical mechanisms of time-dependent ground responses due to sequential excavations combined with rock rheology. Moreover, an alternative approach is provided for the preliminary designs of future shallow tunnels in the rock.

Stability analyses are crucial for identifying soil slope failure susceptibility. Currently, several analytical methods are available to perform such analyses. However, the degree of agreement of the analytical factors of safety from the different analytical methods with the field condition is an ongoing discussion in the geotechnical field. This paper presents the use of Bayesian inference to assess the accuracy of slope failure diagnostics from analytical methods based on limit-equilibrium (LE) and finite-element (FE) analysis in two- and three-dimensional spaces. In addition, a comprehensive statistical assessment is conducted by performing a randomized complete block design (RCBD) that provides the relationship of the factor of safety (FS) among the studied methods. From the analyses, a threshold FS of 1.20 is needed to achieve accuracy and an area under the receiver operating characteristic curve (AUC-ROC) larger than 90% for all current methods when compared to field conditions. The proposed method was able to identify the most vulnerable analytical condition for accurate diagnosis of slope failures. All the analytical methods under this study have a relatively low accuracy when a threshold value FS of 1 is used to indicate stability. Considering the findings, the reliability of back-calculated parameters should be carefully studied.

Buildings have different seismic responses in the topographic-soil–structural interaction (TSSI) conditions from those in the soil–structural interaction (SSI). This study utilizes 3D numerical analyses to investigate the seismic responses of three midrise buildings with 5, 10, and 15 stories in the vicinity of the slope crest. Nonlinear behavior for the soil and building components was considered. Seven earthquake records perpendicular to the slope were applied to the models, and the results were provided based on the average records. Results indicated that slope topography doubled the acceleration amplification at distances of two to three times the slope height (H) from the slope crest. Also, the midrise buildings exhibited different seismic responses in the two directions; this difference was smaller for the 5-story building than those of the 10- and 15-story ones. Slope topography enhanced the seismic responses of the 10- and 15-story buildings along the slope as compared with those in the direction perpendicular to the slope. According to the TSSI results, the seismic responses of the 10- and 15-story buildings, including lateral displacements and base shear forces, suggested a threefold rise as compared with the SSI results. In addition, the TSSI analyses of these buildings increased the peak horizontal acceleration of the stories along the slope by 1.2 times as compared with that in the direction perpendicular to the slope.

Natural joints play an important role in the stability performance of rock engineering. To deeply understand the shear mechanism of natural joints (i.e., tensile fracture or shear fracture), direct shear experiments and acoustic emission (AE) monitoring were carried out for different kinds of joints under five levels of normal stress. By disposing the AE signals during a joint's shear process as AE samples databases, an optimal criterion to identify the tensile fracture and shear fracture modes was established based on the AE parameters, and this method was applied to reveal the shear damage of natural joints under the shear process. The results showed that the shear failure regions of natural joints were localized and inhomogeneous on a joint's surface, and the mesoscopic shear fracture and tensile fracture appeared along all the shearing process of the joint. The moment and the type of failure mode changed with the increase of the normal stress, but the main type of fracture did not change in each period during the whole shearing process, which provided a new way for disaster warning of shear damage.

This paper focuses on the effectiveness in the improvement of clay soils of using geopolymers of fly ash (FA), metakaolin (MK), or blast furnace slag, activated by an alkaline solution of sodium hydroxide (NaOH), sodium silicate (Na₂SiO₃), or a mixture of both. The unconfined compressive strength (UCS) of samples cured for 1, 7, and 28 days was determined, and X-ray fluorescence (XRF), X-ray diffraction (XRD), and Fourier-transform infrared (FTIR) spectroscopy were performed to record the mechanical, chemical, and mineralogical behaviors of the stabilized soils. The results showed an increase from 149.72 kPa (untreated clay) to 460.06 kPa for the clay soil treated with NaOH after 1 day of hardening. The highest UCS was obtained using a MK-based geopolymer (MKG) at 28 days. Oedometric testing showed a reduction in the swelling potential of the clay soil and a decrease in the swelling pressure from 600 to 300 kPa. It was found that all the tested treatments significantly improved the geotechnical properties of the clay soil. However, the MKG treatment was most effective in terms of increased resistance, while the FA-based geopolymer (FAG) provided better results in terms of reducing swelling.

The present study proposes a new approach to solve passive earth pressure problems using the method of slices, coupled with the limit equilibrium (LE) technique. Unlike existing LE studies that adopted failure surfaces of predetermined shapes, here, the backfill was discretized into thin vertical slices, and the Mohr–Coulomb failure criterion was enforced at each slice. The failure surface was then derived by joining the failure plane of the slices starting from the wall base. Consequently, the failure planes became the base of the respective slices. The outline of the failure surface is governed by the soil, wall, and interslice friction angles. The variation of the interslice friction angle was assumed to follow a power function, and the exponents were achieved by satisfying the static equilibrium of the slices and a boundary condition. The proposed results were verified with the available numerical and experimental results, and they show excellent agreement. Also, the results illustrate that the shape of the failure surface is majorly governed by the wall roughness and interslice friction function. For rough walls, failure surfaces are composite curved planar, and the degree of curvature increases with increasing wall roughness.

The complex response of underground geomaterials subjected to dynamic disturbance arises from the microstructure redistribution under high in- situ stress and the resulting fracture behaviors at multiaxial stress states. Inclined specimens were employed in an axially constrained split Hopkinson pressure bar (SHPB) system to achieve a combination of compression-shear stress states and static-dynamic loads. The loading rate under investigation ranged from 500 to 4,000 GPa/s, along with the axial prestress of 7, 21, 35, 49, and 63 MPa on specimens with an inclination of 0°, 3°, 5°, and 7°. The modified SHPB experimentation and discrete-element method modeling were implemented to unravel the combined effects of the loading rate, preload, and stress path on the failure mechanism of sandstone specimens involving the failure strength and envelope, fracturing pattern, fragmentation, and microcracking process. The positive rate dependence of the failure strength and Drucker–Prager envelope was observed. The preload showed double effects on the failure strength, indicated by an upper bound of the failure envelope as it expanded with the increasing preload. The microdamage accumulated during preloading and the global stress field collectively influenced the failure pattern of the inclined specimen, altering from a shear fracturing mode under dynamic loading or high-preload static-dynamic loading to an axial splitting mode near the specimen surface under low-preload static-dynamic loading.

A lower shear strength and higher compressibility impose major challenges for construction on organic soils. Cementitious materials have been effectively used in the improvement of the engineering properties of mineral soils with low organic contents. However, limited studies have been devoted to the stabilization of the organic soils commonly encountered in forested regions in Canada. The present study investigated the effects of pulp mill fly ash (PFA) on the compressibility of a natural soil consisting of 26% organic matter. Fall-cone and oedometer tests were conducted on organic soil mixed with different PFA dosages (5%, 10%, 20%, 30%, 40%, and 50%), as well as on untreated soil samples. The mineralogical and microstructural aspects of PFA-treated organic soil were examined using scanning electron microscope and energy-dispersive X-ray spectroscopy techniques. The results suggest that when the organic soil was treated with PFA, its undrained shear strength and compressibility behavior were improved. Moreover, the potentially large settlement of organic soil can be reduced by the addition of PFA. The primary and secondary compression index (C_c and C_α, respectively) values decreased significantly when compared with the untreated organic soil, indicating that PFA stabilizers can effectively improve the creep behavior of organic soils. These findings indicate that the beneficial utilization of PFA for the stabilization of organic soils could be a practical step toward the environmentally sound management of this waste byproduct.

The kinematical approach of limit analysis has been historically employed to assess slope stability in the geotechnical community, for which most three-dimensional (3D) failure mechanisms are generally based on a composite of multiple common geometrical bodies. Although these failure mechanisms are straightforward, they may not perform well for slopes that involve multilayered soils with heterogeneous shear strength parameters. This paper aims at proposing a new 3D failure mechanism for steep slopes using a spatial discretization technique. The proposed failure mechanism is composed of a large number of elemental blocks that are generated point by point obeying the kinematically admissible velocity field and the normality condition. The discretization scheme makes it possible to simplify the calculations of internal energy dissipations and external work rates on the failure mechanism when both the soil properties and external loadings are spatially changing. The performance of the proposed method is illustrated to examine the stability of steep slopes in homogeneous soils, multilayer soils, and spatially variable soils, showing good agreements with previously published results and numerical modelings.

Rock bursts are disastrous when occurring during the construction of tunnels in a deep underground rock mass, and they occur under two key conditions: energy release from surrounding rocks; and fracture propagation. Based on the construction process of the excavated segment of the marble around a deeply buried tunnel at the Jinping-II hydropower station (Sichuan Province, China), an analysis was conducted on the whole initiation and propagation processes of 40 rock bursts of different intensities. The analysis was carried out by combining numerical calculation with field microseismic (MS) monitoring. During the analysis, the local energy release rate (LERR) and fractal theory-based calculations were introduced. Furthermore, the dynamic warning index for rock burst risk of deeply buried tunnels in hard rock was established. When the peak LERR reached 2.51 × 10⁵ J/m³ and the energy fractal dimension of MS events was greater than 0.32, there was a high rock burst risk. When the logarithm of the LERR was between 1.25 × 10⁵ and 3.16 × 10⁵ J/m³ and the logarithm of the energy released during MS was increased to 0.25–0.32, a slight rock burst risk arose. When the LERR was less than 10⁵ J/m³, no rock burst risk arose. By applying the aforementioned warning indices to engineering practice, the probability of occurrence and potential risk of a rock burst during subsequent construction operations were decreased. The aforementioned results provide an important theoretical basis for smart and green excavation and safety life cycle solutions under high geostress conditions.

The analysis of the wave propagation phenomenon on magnetoelastic fiber-reinforced (MEFR) composites has not yet been much explored. The present paper investigates the dispersive behavior of SH waves in a MEFR crustal layer lying over an inhomogeneous viscoelastic half-space under the action of corrugated boundary surfaces. The MEFR material is polarized in the x₁-axis direction. The exponential variation of the space variable, which is pointing positively downward, causes inhomogeneity in the inhomogeneous viscoelastic half-space. The frequency relation of SH-wave propagation on the considered composite structure is obtained by employing a variable-separable technique, Whittaker’s equation, and nontraditional boundary conditions. The profound effect of material parameters, corrugation, undulatory, inhomogeneity, and viscoelasticity on the phase velocity of SH waves is discussed with the help of numerical calculations and shown by graphical illustrations. The obtained result is well-matched with the classical case of a Love wave for validation, and is discussed as one of the problem’s special cases. The findings of this research may be useful in interpreting geomechanical, geological, and geodynamical applications within the Earth’s crust, which contains natural resources.

The stress path and strain-softening effect have a great influence on the strength and deformation of soils. Former test results show that the strength and deformation behaviors under lateral unloading conditions are quite different from those under axial loading conditions, especially for the structured soils. Based on the deformation mechanism of structured soils and incremental linear elasticity theory, a four-parameter stress–strain curve model is proposed by analyzing the stress–strain curves of axial loading and lateral unloading consolidated undrained shear tests. The model contains four important parameters: ultimate residual strength, curve shape factor, initial tangent modulus parameter, and peak strength parameter. All the parameters can be determined easily by conventional triaxial tests. Besides, comparisons of predicted and measured results of shear tests of different sands and soft soils indicate that the newly built model can describe the stress–strain curves with extensive adaptability and high accuracy, and it provides a unified nonlinear elastic model for both strain-hardening and strain-softening soils.

A hand-calculation method for estimation of nonlinear load–settlement response of piled raft foundations (PRFs) embedded in sandy soils is developed using three-dimensional finite-element (FE) analysis in which the elastoplastic constitutive behavior of the soil is modeled using the unified Clay And Sand Model (CASM). Three types of PRFs with rectangular, strip, and circular rafts and with a variety of pile dimensions and arrangements are considered in the study. The PRFs are assumed to be embedded in five different sands (Ottawa sand, Erksak sand, Sacramento sand, Portaway sand, and Decomposed Granite sand) with different elastic properties, critical state parameters, and relative densities. Systematic parametric studies are performed to develop equations for the estimation of the average nonlinear settlement of PRFs. The maximum and differential settlements are also estimated from the average settlement. The proposed equations require the relative density, elastic constants, and critical state friction angle of sand, and the piled raft geometry and properties as inputs. The settlement equations are applicable to PRFs of sizes similar to those considered in the study and can be used by practitioners for quick, initial estimation of PRF settlement as part of design calculations.

Rutting is the main distress of the semirigid base asphalt pavement (SBAP). The rutting prediction model embedded in the Chinese specification was based on the rutting test results of laboratory specimens that show an unstable prediction accuracy when used in different areas. To get more accurate rutting prediction results for SBAP, the Hamburg wheel tracking (HWT) test using field core specimens was adopted and a new rutting prediction model for SBAP was developed in this paper through a case study. First, field rutting data and core specimens of SBAP in Jiangsu Province were collected. Second, the HWT test was conducted, based on which an M–E prediction model was proposed. Finally, the model was validated through field data, and a comparison between the proposed model and the original model in Chinese specification was also made to evaluate the model effectiveness. The results show that the prediction results of the proposed model have a close correlation with the field rutting values, and the prediction error rate is significantly lower than that of the Chinese specification model. The model developing process could also be used for the rutting prediction model development in other areas.

Soft sensitive clays around a pile shaft experience destructuration during pile installation, excess pore pressure (u) dissipation, and creep after pile installation, but their influence on pile shaft resistance is difficult to assess quantitatively. This paper will present a semianalytical approach to evaluate the shaft resistance setup by considering soil destructuration, consolidation, and creep. Pile installation effects will be captured using the cavity expansion method. The dissipation of u will be modeled using linear radial consolidation theory, and the corresponding radial effective stress increase will be estimated by considering the stress relaxation effects. The changes in soil state after installation will be obtained by solving a system of ordinary differential equations with the initial conditions representing the pile installation effects. The limiting skin friction (τ_f,i) will be calculated by applying an interface reduction factor to the ultimate shear stress under simple shear conditions. Analysis of the results shows that the shaft resistance increases rapidly during the first few days after installation and continues to increase approximately linearly with the logarithm of time (t) after pore pressure equalization. The initial bonding (χ₀) and overconsolidation ratio (OCR) have a marked influence on the time-dependent shaft resistance.

Based on the theory of three-dimensional wave propagation, this paper proposed a method to evaluate the amplified seismic responses of two adjacent structures in horizontally stratified ground owing to seismic structure–soil–structure interaction (SSSI) and backfill soils. A guided flowchart was used to simplify the analysis for the propagation of seismic waves between adjacent substructures and their interference in the soil layers. Using the proposed method, a parametric study was performed to examine the influence of three parameters (namely, the slope of the excavation boundary, the distance between structures, and material properties of the backfill) on the amplification of seismic earth pressure on the substructures. An optimal distance between adjacent substructures was determined that conform to the minimum SSSI.

Clay with free gas bubbles can be frequently encountered in the seabed. Gassy clay is an unsaturated soil, but its mechanical behavior cannot be described using conventional unsaturated soil mechanics because it has a composite internal structure with a saturated soil matrix and gas bubbles. The gas bubbles can have either a detrimental or beneficial effect on the undrained shear strength of clay. New lower and upper bounds for the undrained shear strength of gassy clay are derived by considering the effect of total stress path and plastic hardening of the saturated soil matrix. For the upper bound, it is assumed that there is only bubble flooding, and the shear strength of an unsaturated soil sample is the same as that of the saturated soil matrix. Bubble flooding makes the saturated soil matrix partially drained and increases the undrained shear strength. The amount of bubble flooding is calculated using the modified Cam-Clay model and Boyle's law for ideal gas. The lower bound is derived based on the assumption that the entire soil fails without bubble flooding and the gas cavity size evolves due to plastic hardening of the saturated soil matrix. Compared with Wheeler's upper and lower bounds that do not consider plastic hardening of the saturated soil matrix, the new theoretical results give a better prediction of the undrained shear strength of gassy clays, especially for the upper bound. Implications for constitutive modeling of gassy clay are discussed based on the new research outcomes.

Talus deposits naturally form to a certain height in the toes of slopes because of the accumulation of collapsed material and small landslides. However, the stability of concealed cataclinal slopes with talus deposits accumulated at their toes (referred to as TDAT-CC slopes) with respect to biplanar failure is rarely studied. In this work, the typical geological profiles associated with TDAT-CC slopes are summarized and generalized and their failure modes are classified. A qualitative analysis of their stability is also carried out. The biplanar failure process is investigated by analyzing the development of plastic failure and displacement deformation using Universal Distinct Element Code. The analysis reveals the penetration process occurring in the biplanar sliding planes and clarifies the compression–shear failure processes taking place in such slopes. A new method for determining the stability of TDAT-CC slopes and predicting the failure surface formed is proposed based on limit-equilibrium theory and a model consisting of sliding mass blocks. Finally, the proposed method is used to calculate the stability of TDAT-CC slopes with deposits of different shapes and strengths and the results compared with the results of numerical simulations. The results obtained using the two methods are generally consistent. The talus deposits at the toe of the slope play the role of a toe buttress and help improve the slope’s stability. The safety factor of the slope increases as the inclination of the toe deposits becomes gentler; it also increases as the height of the toe deposits increases. The method proposed offers a sound basis for investigating biplanar failure in TDAT-CC slopes.

With the development of urbanization, numerous underground structures were constructed in composite soil. It is common that the aseismic capacity of the underground structure is influenced by the soil. Hence, during the seismic design, the underground structure located at the composite soil should be noticed. In this study, the seismic response of a frame-type subway station located in composite soil was explored by shaking table tests. The acceleration response, the strain distribution, and the earth-pressure distribution of the model system under the motion of the Kobe wave and the Chongqing artificial wave were obtained and interpreted. The test results demonstrated that the peak acceleration response of the model soil and the model structure increases with the input acceleration and the distance to the shaking table. The acceleration response of the model soil is influenced by the location of the model structure, and the model soil can determine the seismic response of the model structure. The strong strain response of the model structure occurred when the peak accelerations of both input waves were greater than 0.4g. Under the action of major earthquakes (e.g., PGA = 0.4g, 0.8g, and 1.0g), the strain at the top of the upper intermediate column and the bottom of the lower intermediate column is significantly greater than that of other components. It is suggested that the ductility of the intermediate columns ought to focus on the seismic design of the frame-type station located in composite soil. The maximum earth-pressure occurs in the middle of the external side wall. The earth-pressure pattern demonstrates a U-type distribution in the X-direction, and the distribution characteristics are more significant as the input peak acceleration increases.

In this paper, vertical vibrations of a group of flexible strip foundations on multilayered transversely isotropic poroelastic soils are presented. The dynamic interaction problem is studied by employing a variational approach based on the discretization of the strip-soil contact region. Exact stiffness matrices for each layer and the half-plane are explicitly derived in the Fourier transform space for the first time to determine the influence functions required in the variational scheme. A set of numerical results for the vertical displacement and the bending moment of the foundations are presented to illustrate the influence of governing parameters such as anisotropic properties, foundation rigidity, and distance between strips on the dynamic interaction between foundations.

It is well known that there are multiple sliding surfaces behind inverted T-type retaining walls and that reflective sliding surfaces may develop in narrow backfill. Combined with numerical analysis, this paper establishes a mathematical model for the stress rotation trajectory considering multiple sliding surfaces. This paper proposes a theoretical solution for the active earth pressure in narrow backfill on inverted T-type retaining walls under translation mode using the horizontal layer differentiation method. The theoretical solution accurately considers the redistribution of stresses and is suitable for complex working conditions and various soil properties. Parametric analysis reveals the effects of backfill geometries, soil properties, and soil–wall interface friction angles on earth pressure. A quantitative equation was presented for the critical condition of narrow and semi-infinite backfills.

A two-dimensional finite-element analysis based on PLAXIS 2D was used to study the behavior of connected and unconnected back-to-back mechanically stabilized earth walls under earthquake loading. The numerical model was first validated with the results from the full-scale dynamic centrifuge tests on reinforced soil-retaining walls. The behavior of connected and closely spaced unconnected back-to-back mechanically stabilized earth walls (BBMSE) was compared in terms of tensile forces mobilized in geogrids, and the lateral earth pressures and maximum displacements of the wall. The total seismic earth thrusts at the end of the reinforced zone and at the facing of BBMSE walls and their points of application were presented. These results were compared with the widely used Mononobe–Okabe method. The connected walls were found to significantly reduce the dynamic loads on the walls compared with those on unconnected walls.

This paper deals with the behavior of piles subjected to inclined compressive loads. Some numerical results are first presented to document the influence of the load inclination on the pile response to high loads capable of determining an ultimate condition of the soil–pile system. On the basis of these results, a simple-to-use approach is proposed for a preliminary evaluation of the bearing capacity of piles embedded in cohesionless soils as well as in cohesive soils. Comparisons with numerical results and experimental data from model pile load tests are presented to assess the reliability of the proposed approach. A fairly good agreement is found in all considered case studies. In addition, it is shown that the predictive capability of the present approach is better than that of other simplified methods published in the literature.

A vertical cut reinforced with inclined nails subjected to seismic loading was analyzed using the modified pseudodynamic approach, assuming a log-spiral failure surface. A novel calculus-based methodology has been devised to obtain the maximum individual nail force demands and locus of maximum tension, which directly affect nail length in the passive and active zone. The influence of depth of cut to wavelength ratio, nail declination, surcharge, wave amplitudes, soil’s shear strength parameters, and damping ratio were reported. The maximum nail forces required to restrict the failure of a cut have been observed to increase nonlinearly with the depth of nails. The lower angle of shearing resistance, stronger horizontal base acceleration, and closeness of frequency level to fundamental shear wave frequency claimed additional nail lengths in both active and passive zones highlighting their significance in the stability of nailed cut. Practicing engineers can use proposed expressions by employing inexpensive spreadsheet software rather than costly finite element or slices-based commercial software.

The aim of this study is to propose an effective approach to evaluate the stability of a shield tunnel face with tensile strength cutoff by using the upper-bound limit analysis method. Based on the discretization and “point by point” techniques, two improved rotational failure mechanisms, namely the improved collapse failure mechanism and the improved blowout failure mechanism, are developed with the tensile cutoff for the first time. Based on these improved failure mechanisms, the critical collapse and blowout pressures of tunnel faces are then determined by using the upper-bound limit analysis method. The proposed method is then validated by comparisons with previous analytical solutions and numerical results, showing that the proposed method is an effective approach to evaluate the stability of shield tunnel faces. The influences of model parameters on the critical support pressures and the failure feature of the proposed mechanisms are finally presented.

This technical note aims to investigate the effects of biotreatment on the response of a concrete model pile embedded in poorly graded sand through lateral loading tests. The bending moment profiles along pile length were obtained from strain gauges collected during the pile load tests. The pile deflection and soil resistance were derived from a bending moment profile based on beam theory. The ultimate lateral resistance of the pile with biotreatment was 2.6 times as large as that without biotreatment. The bending moment for the pile in biotreated soil is significantly smaller than that for the pile in untreated soil due to the reduction in curvature. The spatial distribution of calcium carbonate generated during the biotreatment was obtained from 1,800 sand samples, which was also validated by the scanning electron microscope images. Biotreatment of sand surrounding a pile is demonstrated to be a promising measure to effectively improve the lateral capacity of the pile.

A slip line solution is proposed to analyze the active earth pressure on cantilever retaining walls supporting a layered cohesionless backfill. The reduction in earth pressure in the presence of a dense sand layer resting on the top of a loose sand stratum is estimated under static and seismic conditions. Unlike the conventional limit-equilibrium or limit analysis approach, the present methodology can trace an adaptive failure surface by developing a network of slip lines based on the properties of each layer. The results are presented in terms of the active earth pressure coefficient, which includes the contribution from both the layers. Rapid mobilization of stresses at the layer interface and the wall backface is presented with normalized stress contour. Though the failure surfaces are nonlinear, the active earth pressure distribution behind the wall is observed to be almost linear. Under the static condition, the present results lie between the solutions obtained from the equivalent layer analysis and the layered calculation method.

To more accurately determine the stress distribution law of coal and rock masses containing faults, the fA42 reverse fault of the Shihao coal mine is taken as an example to carry out an in situ stress test near the fault, and multilinear regression analysis is used to invert the tectonic stress field of the fault. The results show that the magnitude of the in situ stress in the area near the reverse fault varies greatly, and the main influence area of the fault is within 100 m of the fault. Outside the fault-affected area, the maximum principal stress and maximum shear stress of each rock layer decrease with the rock strength. The maximum principal stress and the maximum shear stress magnitudes of the coal seam increase closer to the fault, whereas those of the sandy mudstone and limestone first decrease and then increase sharply. The maximum value of the maximum principal stress and maximum shear stress of each rock layer are obtained at the fault interface. The research method in this paper accurately inverts the fault tectonic stress field, which has a certain guiding significance for the safe mining of coal mines.

Drilling and blasting (D&B) technology is an appropriate method for rock excavation in underground mining and civil engineering projects. Specific charge as the amount of explosives used per cubic meters of extracted rock is the most important role in D&B operations. Therefore, different models have been proposed for the estimation of specific charge. The aim of this research is to develop a second-order quadratic model using response surface methodology (RSM) to estimate the specific charge in rock tunneling (V-cut D&B pattern). For this purpose, 31 data series related to geomechanic and D&B are used for modeling. In the suggested model, rock quality designation (RQD), P-wave velocity (Km/s), tunnel cross section area (m²), blast hole coupling ratio, and D&B pattern spacing/burden ratio are used as effective factors on specific charge as model response. The proposed RSM-based quadratic model consists of one quadratic, five linear, and five interaction terms. The statistical details of this model, conventional related graphs, and RSM specific analysis have satisfied the recommended model. For the specific charge, the spacing/burden ratio is more effective than the other factors and interactions.

The soil’s undrained shear strength is affected by the rate of shearing. This dependency can be inferred from mechanical laboratory testing at different operation rates or from using different in situ testing methods (associated with dissimilar shear-rate fields). However, all test results of a given soil can be correlated with a constant rate-independent shear strength by accounting the soil viscous behavior. This work investigates the viscosity model’s role in evaluating the reference strength of soft clays. Three viscosity models are examined by their influence on the reference undrained shear strength values. The clay is tested by vane shearing at different rotation rates, in which the viscosity parameters are calculated based on strength ratios between tests at different rotation rates. The experimental results are compared with two types of analytical solutions, rigorous and simple, to examine the effect of the solution order on the obtained reference strength values. Among the examined viscosity models, this work finds the power-law model as more appropriate and applicable for rate-effect analysis in soft clays.