International Journal of Geomechanics

A data-driven approach is used to show the significant discrepancy between the coefficients of permeability that are estimated through packer field tests and those back-calculated from the actual discharge pumped out of randomly fractured rock masses (i.e., masses that do not have predominate oriented fracture sets) using either dewatering or pumping well systems. The presented data, some of the richest of its kind, are used to develop a novel correlation between the estimated and back-calculated coefficients of permeability. A procedure is proposed to evaluate the permeability of the rock masses that considers two different but frequently encountered scenarios: (1) lack of any field permeability test data; or (2) only packer test results are available. Numerical examples are presented to illustrate how the suggested procedure could be used. It constitutes an advance in the state of practice because the commonly used procedures to estimate the permeability of randomly fractured rock masses employ the direct use of packer field test results, which, as the data shows, could be orders of magnitudes out. The proposed procedure could be particularly useful for practitioners when faced with cases where field pumping tests are not feasible due to budget, time constraints, or both. It gives them a simple and reliable approach (based on case histories) to produce preliminary designs of dewatering systems in randomly fractured rocks.

The strength behavior of rocks is a question of complex determination. The Hoek–Brown failure criterion for rock masses is the currently accepted solution to this problem and has been applied to a large number of projects worldwide. However, the estimation of Hoek–Brown parameters is directly dependent on complex and time-consuming tests (e.g., triaxial tests), demanding excessive investments, and complicated analysis. This paper proposes a method to calculate the Hoek–Brown parameters and derive the nonlinear failure envelope of distinct types of artificially cemented materials (where the integrity of the samples is ensured), comparing these results with real laboratory data. The method utilizes basic tests, such as unconfined compression tests and Brazilian tests, to estimate the maximum shear strength of materials in triaxial tests with effective confining pressures up to 400 kPa. The proposed methodology presents an accurate and conservative fit for the experimental strength results, indicating the applicability of the approach to a wide range of artificially cemented materials without the need to perform triaxial tests or any other elaborate and time-consuming procedures.

Waste tires, which are a serious environmental threat due to the ever-increasing number of on-road vehicles, must inevitably be effectively recycled. Many researchers have posited that granular soil and crumbed waste tire mixtures can be used to reduce seismic forces in so-called geotechnical seismic isolation (GSI) systems because of the high-energy absorption capacity of sand and rubber (SR) mixtures. However, there are concerns about the stability of superstructures due to the high compressibility of SR mixtures. Asphalt mixtures have also gained new application areas outside of transportation engineering, such as in hydraulic structures and seismic isolation, due to their ductile, cohesive and viscoelastoplastic properties in recent years. In this study, sand–rubber–bitumen (SRB) mixtures were produced by adding bitumen as a binder to SR mixtures containing crumbed rubber (CR) at different ratios (1%, 2%, 3%, and 4% of the sand weight). The dynamic properties of the SRB mixtures were determined by cyclic simple shear tests, depending on vertical and cyclic stresses. We found that the SRB mixture containing 3% CR had the maximum damping ratio (D) and that an increase in the rubber content of SRB mixtures causes a decrease in the secant shear modulus (G_sec). In addition, it was observed that the G_sec increased with the vertical stress and decreased with the cyclic stress ratio. In comparing the D and G_sec values of the SRB mixtures with those of SR mixtures under similar loading conditions, it was found that the SRB mixtures had both higher D and stiffness. As a result, SRB mixtures are more suitable than SR mixtures in terms of damping, and SRB mixtures can be an alternative material for use in GSI systems.

In the present study, a number of triaxial tests were conducted to examine the shear behavior of rubber–sand mixtures, with an emphasis placed on the critical-state line and energy performance. The experimental results indicated that under otherwise similar conditions, the deviatoric stress reduces with increasing rubber content but increases with increasing confining pressure. The promotion of confining pressure and rubber content contributed to increased contractiveness of rubber–sand mixtures (RSM) in shear. The position of the critical-state line (CSL) in the e–lnp′ plane depended on both rubber content and confining pressure, and it shifted toward the right (or upward) direction with an increase of confining pressure and rotated in a clockwise direction with an increase of rubber content. The slope of the critical-state line (M) in the q−p′ plane decreased as the rubber content increased. In addition, the energy analysis indicated that most work input is dissipated, with the stored elastic potential energy taking a minor proportion. The energy dissipation decreased with increasing rubber content and increased with increasing consolidation pressure. Macroscopically, this was associated with the stress level within a specimen and microscopically linked with the contact force level and related energy dissipation through the interparticle friction behaviors.

With the application of electronic detonators, delayed blasting is considered a very effective method to improve rock fragmentation, and this technique is widely used in practical engineering. Therefore, it is necessary to study the rock-breaking mechanism of double-hole delayed blasting. In this paper, based on the finite difference method, the influence of double-hole delayed blasting on the reservoir permeability was quantitatively analyzed by adopting the adjacent hole spacing, delay time, and decoupling coefficient (K) as variables and the permeability increment as an evaluation index. Based on the parameters studied in this paper, it was found that the effect of the delay time on the reservoir permeability depends on the hole spacing. When the hole spacing is less than 20r_a (r_a is the borehole radius), a reasonable delay time could significantly increase the reservoir permeability, but when the hole spacing is greater than 20r_a, the delay time does not affect reservoir permeability enhancement. The decoupling coefficient could control the attenuation speed of shock wave energy. For K = 2, energy attenuation occurred the slowest, and the reservoir permeability increase effect was the best. Based on site-scale numerical simulations, the mechanism of stress superposition between boreholes was revealed, and the position of stress superposition was controlled by adjusting the delay time to break hard reservoir rock so that the cracks between two holes were connected, i.e., accurate reservoir reconstruction was achieved. This work provides a certain guiding basis for actual engineering applications.

In deep underground mine, besides the high static in situ stress, openings such as stopes, drifts, and shafts in underground mine are also frequently subjected to dynamic waves coming from blasting and earthquake. The interactions of these waves with the opening boundaries can be under arbitrary incident angles and thus would induce different damages. In order to investigate the dynamic response of openings under the oblique incidence of blasting load, numerical modeling of wave incidence to a rectangular opening at different incident angles and the associated dynamic failure was carried out under various in situ stress states. The numerical model established by the discrete element code PFC2D was first validated against theoretical results for reflection of oblique wave incidence at the free surface at various incident angles. The simulation results showed that the reflected P wave causes spalling around the opening, and the subsequent reflected SV wave further promotes the propagation of tensile cracks. Among them, the opening with vertical wave incidence is the most seriously damaged, while wave incidence at 15° and 30° angles results in similar damage degree on the incident side of the opening. The damage of the opening at a 45° incident angle is light. With the increase of burial depth, the position of spalling at the incident side gets closer to the sidewall of the opening. When the buried depth is 1,200 m, the largest number of cracks around the opening is achieved for wave incidence at a 45° angle. This research can improve the understanding of the resulting failures from stress-wave incidence to the openings at arbitrary angles and contribute to the design of the opening in the deep underground.

Even though the energy pile is known as an efficient dual-purpose system nowadays, the interactive response under simultaneous mechanical and thermal loads requires further investigation. An attempt has been made to evaluate the effect of different factors on load-displacement response and bearing capacity, including different loading conditions, pile geometry, and ground conditions using a three-dimensional (3D) numerical model. The energy pile model was validated and then subjected to thermal loadings of +10°C, +20°C, and −10°C in saturated and dry sandy soil with different relative densities and coefficients of thermal expansion. In addition, analyses were carried out in conditions from the tip of the pile being embedded in very loose sand to being embedded in a rock-hard layer to provide a comprehensive coverage of all the scenarios in engineering practice. Results indicate that the ultimate bearing capacity of the energy pile can increase by 25.5% or decrease by 13% depending on the applied temperature and geotechnical conditions. When the pile is heated and cooled, the bearing capacity increases and decreases, respectively, while for the piles placed in dense and saturated sand, sand with a larger thermal expansion coefficient, or socketed into a very hard layer with 60 to 100 times higher elastic modulus compared with the upper layer, the effect of thermal loads on the pile bearing capacity are more noticeable. Results show that in piles with a smaller diameter, the temperature variation effects are slightly higher. The findings of the study are useful for engineers in design practice to optimize the performance of energy piles under different conditions.

In this study, a combined finite–discrete-element method (FDEM)-based grouting simulator, in which the effect of time-dependent rheological characteristic caused by grout hydration on grouting penetration is adequately considered, was developed for more accurately modeling the grouting penetration process in the fractured rock mass, especially for quick-setting grout. To implement the grouting penetration process, the time-dependent Bingham model for characterizing the time-dependent rheological characteristic of grout, the flow network searching algorithm combining with the grout flow solver for solving the grout flow, and the hydromechanical (HM) coupling algorithm for characterizing the grout–rock interaction were systematically integrated into the FDEM framework. After that, to validate the developed simulator for modeling the grouting penetration of time-dependent Bingham grout and the grout–rock interaction, two benchmark tests were conducted. Finally, to further demonstrate the capability of the developed simulator, the rheological model for characterizing the cement and sodium silicate (C–S) grout, a quick-setting grout, was embedded in the simulator to simulate the grouting penetration process in the discrete fracture network. The results indicated that the developed simulator can accurately capture the effect of time-dependent rheological characteristic caused by grout hydration on the grouting penetration process. As the water–cement ratio (W/C) increased or the cement–sodium silicate (C/S) ratio decreased, both the penetration rate and grouting ratio increased significantly. Increasing the W/C ratio was more effective than decreasing the C/S ratio to increase the penetration range. Decreasing the C/S ratio can increase the grouting penetration range more significantly than increasing the grouting pressure.

The desiccation cracking of expansive soil plays a crucial role in the structural integrity and long-term stability of infrastructure foundations. While the occurrence of surface cracks and shrinkage deformation in expansive soil has been widely acknowledged, limited research has been conducted on the development pattern of internal cracks and their correlation with hydraulic properties. In this study, undisturbed samples of expansive soil were subjected to high-precision X-ray computed tomography scanning, and three-dimensional visualization and quantitative characterization of the cracks within the samples were conducted using the Avizo (version 2022.1) software analysis platform. Additionally, seepage simulations were employed to study the relationship between crack structure and the hydraulic properties of expansive soil. The results indicate that the desiccation process led to a significant increase in the volume content and connectivity of cracks in the expansive soil. Based on their connecting states, the cracks were classified into interconnected and isolated categories. Regression analysis suggests that the degree of cracking in expansive soil is predominantly determined by the interconnected cracks. The initiation, propagation, and coalescence of desiccation cracks substantially augmented the number of flow paths and enhanced the hydraulic conductivity of the soil. This study elucidates the microscopic evolution of desiccation cracking in expansive soil, offering a better understanding of the relationship between the three-dimensional characteristics of crack structure and their hydraulic properties.

The behavior of an existing shield tunnel is significantly affected by undercrossing shield tunneling. In previous theoretical analyses, however, the effect of the interaction angle between the new and existing shield tunnels on the settlement of the existing tunnel is missing. Furthermore, in conventional methods of calculating tunnel settlement, mechanical parameters of soils, such as the shear modulus of shear layer g_s and the coefficient of subgrade modulus k, are mainly determined by engineers' experience, which may lead to subjective or even biased calculation results. This paper proposes an analytical method to predict the settlement of an existing tunnel subjected to the undercrossing excavation of a new tunnel with different intersection angles. The method implements an iterative process to find reliable foundation parameters and the dimensionless parameter γ (iteration factor) in the modified Vlasov model. The robustness of the proposed method is validated by comparing the calculation results with the field measurement of two practical projects, and good agreements are obtained. The influences of the intersecting angle, the clearance distance, and the ground volume loss on the settlement and bending moment of the existing tunnel are discussed in detail. Results indicate that the intersection angle of the new and existing tunnels plays a significant role in settlement of the existing tunnel. The proposed analytical method enables engineers to predict the settlement of the existing tunnel subjected to undercrossing tunneling with different interaction angles.

Helical piles are commonly used as foundations under electrical transmission towers, bridge abutments, highway signs, and light poles. The present experimental investigation focused on the lateral resistance of vertical and battered single-helix piles installed on the crest of Slopes 1V:2H and 1V:3H. The helix was placed at various positions below the ground surface, such as 0.25 L_p, 0.35 L_p, and 0.45 L_p (“L_p” refers to the embedment length of the pile), to analyze the influence of helix position on the lateral capacity of single-helix piles. The negative batter angle was varied as 7.5°, 15°, and 22.5° for all single-helix piles with different helix positions. The lateral capacity of the battered helical pile was compared with that of the vertical helical pile and the vertical regular pile (without helix) to assess the batter efficiency and net efficiency, respectively. A linear regression model was proposed to depict the variation of batter efficiency with several significant response variables like slope angle (α), batter angle (β), pitch (p), helix diameter (D_h), and shaft diameter (D_p). It was found that the battered single-helix pile with a helix at an embedment depth of 0.35 L_p is beneficial in improving the allowable lateral capacity for batter angles up to 15° on Slope 1V:2H. The helix position closer to the ground level (h = 0.25 L_p) was relatively efficient on Slope 1V:3H because higher lateral resistance mobilization occurs at a relatively shallow depth on the gentle slope. The allowable lateral capacity of the single-helix pile battered at 22.5° showed a remarkable improvement by 50%–53% on Slope 1V:2H and 22%–32% on Slope 1V:3H. The effect of helix was significant at smaller batter angles of 7.5° and 15° but turned marginalized at a higher batter angle of 22.5°.

In this paper, an analytical approach is proposed to investigate the topographic amplification effects of slopes under seismic loads. The method of region decomposition and matching was adopted to decompose the whole research region into two subregions. Wave function series solutions that satisfied the boundary conditions of stress and displacement of the subregion under the excitation of plane SH waves were constructed. Wave function analytical solutions for slope models under the excitation of plane SH waves were derived. The appropriate number of truncated terms were determined by convergence tests to ensure the accuracy and validity of the wavefield displacement function. The analytical solutions obtained from the proposed method agreed with the numerical solutions. In addition, based on the proposed method, the effects of slope angle, slope height, dimensionless frequency, and the incidence angle of seismic waves on the peak displacement amplification factor were quantitatively studied.

In this paper, we study the seismic behavior of pile group bridges in inclined liquefiable soil and reveal the failure mechanism by conducting large-scale shaking table tests. Two bridge models were supported by two foundations: a group pile in an inclined liquefiable site and a rigid foundation. Typical results of the model test under a strong event (Tabas 0.3 g) are illustrated, and the effects of soil–group pile–bridge interaction are explored. The inertial and kinematic effects of the pile–pier curvature are evaluated, and the seismic failure mechanisms of the pile–bridge system are revealed. The results demonstrated that the near-pile shallow soil exhibited significant shear dilation response during the occurrence of strong earthquakes, which induced acceleration spikes for both soil and structure. The interaction state was soil pushing the pile and pile pushing the soil during the first and the subsequent strong earthquake, respectively, due to the bridge P−Δ effect. The liquefaction-induced lateral spreading increased the kinematic effect and reduced the inertial effect on the pile head curvature. In addition, the inertial effect on the pile curvature decreased gradually from the shallow layer to the middle of liquefiable soil, while the kinematic effect increased gradually. The results also demonstrated that the rigid foundation assumption overestimated the acceleration demand of the bridge during strong earthquakes; however, it seriously underestimated the lateral displacement. Finally, the lateral spreading shifted the vulnerable position of the pile group–pier system from the pier bottom to the pile head and bottom, and the leading piles sustained more damage than the trailing piles.

Field compaction control is arguably the most common yet critical quality control procedure in geotechnical engineering. Since the early 1930s, the systematic process for performing quality control of compacted soils has often been implemented by measuring the in-place dry unit weight (or density) and as-compacted soil moisture content after placement in a fill. However, the current practice overlooks several facts resulting from comparing soil prepared and compacted in the laboratory to soils placed and compacted in the field. These issues include comparing the compaction energy in the lab versus what is applied in the field, and the behavior of saturated soils in the laboratory to the performance of unsaturated soils in the field. To address some of these gaps, this study presents a new saturation-based framework for compaction quality control. The aim of this new framework is to reduce the uncertainties and assumptions of the compaction control process and provide practicing engineers with further insight into the key engineering attributes of compacted soils. The proposed saturation-based approach compares a degree of saturation difference with a normalized dry unit weight ratio, making saturation upon compaction the controlling diagnostic variable and the focus of the monitoring effort. In essence, the optimal compaction conditions will be referenced to a characteristic saturation state near 80%. Compared with the conventional quality control system for field compaction, the saturation-based approach is developed with the same field and reference data collected for most earth fill projects. The results of this approach enhance the engineering judgment required to match the laboratory reference values to the field conditions. For the purposes of illustration, the proposed saturation-based framework is applied to compaction control data of a large earth dam and compared against the conventional method side by side.

In loess slopes, landslides are easily caused by rainfall and can be prevented by using retaining structures of stabilizing piles. This paper investigated the deformation and mechanical behaviors of the cantilever and fully buried stabilizing piles under complex pile–soil interactions. The deformation and mechanical behaviors, failure modes, and soil pressure distributions of two types of stabilizing piles were analyzed based on field model tests. Further, a calculation method for stabilizing piles considering nonlinear pile–soil interactions was proposed. Also, the numerical solution of the pile deformation and force was obtained by using the finite difference method and Newton's iterative method. The results showed that the deformation and mechanical behaviors of fully buried piles are superior to those of cantilever piles. Fully buried piles and cantilever piles have plastic double-hinged and single-hinged failure modes and undergo bending damage and shear damage, respectively. Besides, the landslide thrusts and soil resistances acting on the pile showed a parabolic distribution pattern. Compared to the model test results, the traditional calculation method overestimated the deformation and internal force of the stabilizing pile by 37.32%, and the newly proposed calculation model considering nonlinear pile–soil interactions was more consistent with the measured values. The study results help to guide the design and calculation of stabilizing piles under complex pile–soil interactions.

In this study, we instrument the foundations and towers for two onshore shallow wind turbine generators (WTGs) to evaluate foundation response, quantify in-service loads, and assess the assumptions behind WTG foundation design calculations. Measurements of pressure at the soil–foundation interface, soil strain just below foundation level, and tower moments over long periods provide insights into the operational moments experienced by the tower and the load transfer mechanisms to the foundation system. The results of this study have implications for design practices in three distinct ways: (1) the assessment of rotational stiffness calculation assumptions, (2) the evaluation of pressure distribution used in the bearing capacity formulation, and (3) the estimation of tower loads used in the tower and anchor bolt design. Our observations show that the induced overturning moments correlate well with incipient wind speeds and directions and the associated soil pressure and strain responses. The overturning moments and the response parameters relate linearly within the spectrum of measured magnitudes. However, the pressure distribution across the foundation footprint does not monotonically increase or decrease with distance from the neutral axis of the foundation base (e.g., the pressure sensed at the foundation's center close to the foundation is between 1.5 and 2 times greater than the pressures sensed at the edges). In addition, the measured soil strain as a function of cyclic moments shows that the in-service cyclic shear strains are less than 1.4 × 10⁻⁵ (i.e., two orders of magnitude smaller than the assumed design strain level). Finally, the spectrum of cyclic moments follows a semilog trend, thus indicating that operational and nonoperational loads dominate the fatigue load spectrum. Our study suggests that adequately designed WTG foundations on competent fine-grained soil result in very low operational soil shear stresses and strains, which might indicate that the current design practices are too conservative in nature. Field measurements establish load spectrums for cyclic fatigue loads for the long-term operational conditions of WTGs.

The effect of saline on the shear strength of compacted bentonite is important to investigate the safety assessment of engineering barriers of deep geological repositories. Different methods used for saturating compacted specimens yield inconsistent relationships between shear strength and salt solution concentration. In this study, we performed direct shear tests on compacted Na–bentonite saturated with distilled water and Na solutions using the constant-vertical stress (CP) method and the constant-volume (CV) method. Scanning electron microscopy (SEM) and nuclear magnetic resonance (NMR) measurements were conducted to investigate the microstructural characteristics of compacted bentonite. The results show that the measured shear strength increases with increasing vertical stress or solution concentration. Furthermore, the shear strength of specimens prepared through the CV method is larger when distilled water is used for saturation; at the same time, when salt solutions are used for saturation, CP samples show greater shear strength. On the microscale, both SEM images and NMR results show that specimens become increasingly aggregated with increasing pore-water salinity and that saline solution has a greater effect on the microstructure of the compacted bentonite when using the CP method for saturation because of the change in volume during saturation. The intergranular stress equation, which considers physicochemical effects, is introduced to theoretically characterize the mechanical behavior of compacted bentonite. It is found that the relationship between intergranular stress and shear strength is unique, independent of the saturation method. In other words, the salt solution concentration affects the microstructure, thereby affecting the interparticle stress of compacted bentonite.

Rock abrasivity is an important parameter that influences tool design and wear, the efficiency of tools, and cost during rock excavation. Generally, the abrasiveness of rocks is measured with the Cerchar abrasivity index (CAI). In this research, several Cerchar abrasivity parameters such as penetration of stylus (P_s), the volume of material scratched in the groove (V_m), scratching force (SF), scratching energy (SE), and Cerchar scratching specific energy (CSSE) were determined using an Cerchar device. For evaluating Cerchar abrasivity parameters, 24 rock samples were used comprising igneous, metamorphic, and sedimentary rocks. The new classification was presented based on the Cerchar abrasivity index and Cerchar abrasivity parameters. In this research, the specific energy of the Sievers J miniature drill test (SJ) was calculated for comparison with the specific energy of the Cerchar abrasivity test. Then, the relationship between Cerchar abrasivity parameters with SJ was investigated, new relationships between Cerchar abrasivity parameters and SJ with accurately acceptable presented. The results indicated that the Cerchar abrasion ratio (CAR) is a good parameter for measuring rock abrasivity and cutting. The SJ exhibited a good relation (R² = 0.78) with CAR. In addition, CAR showed a good correlation (R² = 0.97) with the specific energy of the rock cutting test (SE_cut). The CAR can be used to evaluate abrasivity laboratory tools and the specific energy of a rock cutting test.

Excavation often results in a decrease in the stability level of natural and manmade slopes. To address this issue, a new reinforcement method––structuralized cementation––has recently been introduced to reinforce coarse-grained soil slopes. However, previous studies have not adequately considered the interaction between excavation and structuralized cementation. Consequently, in this study, a series of centrifuge model tests were conducted to investigate the deformation and failure characteristics of structuralized cemented slopes under excavation conditions. It was found that structuralized cemented slopes exhibit significant progressive failure from bottom to top when subjected to excavation. The depth of the slip surface and the safety limit of the structuralized cemented slope increases with an increase in the extent of the solidification zone. During the failure process, slope deformation occurs inside a limited region that expands toward the interior of the slope. Structuralized cementation induces a nonuniform distribution of displacement direction and increases the dilatancy extent of the potential slip surface. The failure mechanism of structuralized cemented slopes can be explained by the significant coupling processes of deformation localization and local failure, which may also elucidate the variation in the position and shape of the slip surface of the slope from using different cement contents. Structuralized cementation reinforces slopes by weakening and delaying the deformation localization of the slope under excavation conditions.

We conducted an experimental study on the swelling–shrinking characteristic of expansive soil treated with enzyme-induced carbonate precipitation (EICP) using yellow soybean. A series of tests including the free swell test, swelling rate test, swelling pressure test, and shrinking test were conducted on expansive soil specimens with various water contents and equimolar concentrations. The test results showed that EICP-treated expansive soil samples exhibited an obvious reduction in the magnitude of free swelling rate, swelling rate, swelling pressure, and shirking rate compared with the untreated one. This indicates that EICP using yellow soybean can effectively reduce the swell and shrink potential of expansive soil. The free swelling rate consistently decreases with the increasing equimolar concentration. A more remarkable reduction in swelling rate can be observed at a concentration of 1 mol/L compared with a less significant decrease at a higher concentration. The free swelling rate shows an ascending trend first and then a declining tendency with the increase of water content at higher equimolar concentrations. The influences of equimolar concentration and water content on the change of swelling rate for treated samples with applied loading pressures are insignificant. The swelling pressure reduces remarkably with increasing equimolar concentration and then tends to level off. The swelling pressure exhibits an ascending tendency with the increase of water content. The shrinking rate reduces more remarkably with equimolar concentration at first and then increases less remarkably, with an equimolar concentration of 2 mol/L exhibiting the lowest shrinking rate. The soil specimen with higher water content shows a higher value of shrinking rate than that with a lower one.

In this study, the fractal characteristics and energy dissipation behavior of gas-bearing coal are explored under both dynamic and static loads. Multifactor coupling mechanical tests are conducted using visualized static and dynamic loading experiment systems. The effects of impact velocity, axial compressive stress ratio, and initial gas pressure on energy dissipation and fragmentation characteristics of gas-bearing coal are analyzed. An internal correlation between the debris fractal and the energy dissipation density is clarified considering the fact that debris distribution has prominent fractal characteristics in the log–logarithmic coordinates. It is discovered that the fractal dimension experiences exponential growth with the strain rate in the impact velocity group, while showing that it rises linearly in the gas pressure group. There exists a critical axial compressive stress ratio that causes the formation of the debris fractal segment in the axial compressive stress ratio group. The debris fractal dimension change with the energy dissipation density is divided into two stages, and it is found that the dissipated energy value and its ratio decrease with the rise of initial gas pressure; debris fractal exhibits a quadratic decreasing relationship to the density of energy dissipation. Furthermore, by considering the dimension of the strain rate, the relationship of the aforementioned three indicators are uniformly quantified and compared. The research results reinforce the fundamentals of gas-bearing coal dynamics and provide a theoretical reference for further research on gas composite dynamic disasters in mines.

Variables that can be considered in experimental investigations of internal instability of earth dam materials are often bounded by practicality and feasibility constraints. To overcome these shortcomings, a total of 164 previous published experimental results were compiled to study statistically the relative significance of vertical effective stress, grain size ratio (D15/d85), fines content, coefficient of uniformity (C_u), and specimen length in the mechanism of internal instability. The present statistical results agreed with previous experimental findings on the combined dominant roles played by fines content and stress in the internal instability. However, the stress reduction factor was found to be inversely correlated with the vertical effective stress, which was not reported previously. The scale effect of specimen size has significant positive correlations with both the stress reduction factor and critical hydraulic gradient, whereas the influences of C_u and D15/d85 were minimal, in contrast to previous experimental findings. An improved theoretical hydromechanical envelope for predicting internal instability of cohesionless soil in the space of stress-gradient–stress reduction factor was proposed in this study. The unstable envelope moved with increasing applied hydraulic gradient until the state of material touching the envelope.

Pond ash is a byproduct obtained from the combustion of coal in thermal power plants. It can be used as an alternative to conventional granular materials in compacted subgrade or subbase layers in pavements. The properties can be further enhanced by the addition of small doses of cement. Typically, the modulus parameters required for the design of pavements are based on resilient modulus models. Such models presume that the material attains a shakedown response in every loading sequence and the resilient modulus (M_R) can be defined. However, it is not very clear whether a nonconventional material such as pond ash or cemented pond ash attains shakedown within 100 cycles of each sequence as stipulated in the resilient modulus test protocol. The number of loading cycles required to reach the shakedown limit is explored in this study. There are two sets of experiments conducted: the conventional resilient modulus tests with 100 cycles in each sequence and repeated load triaxial tests with 10,000 cycles for three confining pressures (41.4, 27.6, and 13.8 kPa) at a deviator stress of 69 kPa. The effect of cement dosage (2% and 3%), compaction condition (standard and modified Proctor compaction), and water content (optimum moisture content (OMC), OMC−2%, and OMC+2%) were studied. The shakedown theory is explained in terms of permanent deformation increment per cycle, dissipated energy, and tangent modulus. The resilient modulus is defined as the tangent modulus of the material which has attained shakedown. The cemented pond ash did not strongly correlate to confining pressure and hence, a constant value of the resilient modulus may be used.

A shield tunnel is an assembled structure that is composed of segments and connecting bolts, and its longitudinal seismic response needs to be investigated. Bolt prestress is a common measure for shield tunnels, and longitudinal bolts with different prestress can affect the longitudinal deformation stiffness of shield tunnels; therefore, they affect the longitudinal seismic response characteristics of the shield tunnel. Based on this, this paper establishes a longitudinal analysis model of a shield tunnel that considers longitudinal bolt prestress and uses an iterative algorithm to study the effect of longitudinal bolt prestress on the longitudinal force and opening of shield tunnels under transverse seismic excitation. Further, the detailed seismic response characteristics of the circumferential joint are studied. The results are as follows: (1) the internal force between the segmental rings under transverse excitation of the seismic load is dominated by the vertical bending moment; (2) under the bolt prestress, the bending moment between the rings and bending stiffness reduction coefficient are nonlinearly related. When the bending moment is less than the critical value, the bending stiffness reduction coefficient is assigned to one, which means that the circumferential joint interface does not open under the collective effect of the bolt prestress and bending moment; (3) the application of the bolt prestress increases the opening of the circumferential joints in the stiffness changed area, and decreases the opening in the position far from the stiffness changed area; and (4) the segment maximum principal stress and the largest stress of the bolt increase nonlinearly and monotonically with the increase in the prestress, which is not consistent with the changing law of the largest joint opening. The research results could provide some reference for the selection of the bolt prestress in a shield tunnel in an earthquake area.

In this paper, the three-dimensional time-domain inversion of ground motions and its application are performed. The relationship between the incident wave time series and design ground motions is established, and the oblique incident wave time history is inverted. Subsequently, the free field is constructed based on the three-dimensional inversion of ground motions as an accurate solution. The errors based on the one- and two-dimensional inversions relative to the three-dimensional inversion are analyzed, and the errors with the incident angles, site sizes, and material parameters are revealed. Finally, the seismic responses of a canyon and an embankment dam with asphalt–concrete core are studied. The results show that the three-dimensional inversion of ground motions considers the oblique incidence angles, and the constructed three-dimensional nonuniform ground motions are more comprehensive. With regard to the core wall, the acceleration amplification effect obtained based on the three-dimensional inversion is the most significant, and the tensile failure area is the largest. Compared with the three-dimensional inversion, the tensile stress based on the two- and one-dimensional inversions is reduced by 57.1% and 20%, respectively. Therefore, the influence of the three-dimensional inversion on the seismic responses should be considered during the seismic designing of dams near faults.

A stepped cyclic loading test was designed to investigate the stress memory and acoustic emission characteristics of siltstone under different previous stress levels. This study aims to improve the applicability of the acoustic emission in situ stress measurement method in porous weak cementation strata. The stress memory failure range for siltstone and the memory stress correction formula were determined based on characteristic stress value. The analysis of acoustic emission characteristics revealed the failure mechanism of the Kaiser effect of siltstone, and the following conclusions were obtained. Crack initiation stress can serve as the failure criterion for the stress memory effect in siltstone. Therefore, the failure range for the stress memory effect in siltstone can be defined as a previous stress of less than 15.3 MPa and a memory stress of less than 13.7 MPa. The pore compaction process in siltstone and the friction-generated acoustic emission signal during this process negatively affect stress memory. The primary cause of the stress memory effect in rocks is the irreversible development of new internal cracks. The compression rebound effect of primary soft pores in siltstone mainly causes the Kaiser effect to fail. The compression rebound effect of primary soft pores in siltstone is the main reason for the failure of the Kaiser effect.

The nonuniform stress distribution caused by soil arching can affect suffusion in soil under seepage. To investigate the development of suffusion in soil with arching and the evolution of soil arching during suffusion, coupled computational fluid dynamics (CFD) and discrete-element method (DEM) simulation of trapdoor tests under horizontal seepage flow was performed. A soil sample susceptible to suffusion was prepared by mixing particles in two sizes with a size ratio of 5.0. Soil arching consisting of stress reduction and concentration areas was formed by lowering the trapdoor at the bottom of the model and then a horizontal seepage flow was introduced to trigger soil suffusion. It was discovered that, due to the existence of soil arching, the fine particles within the stress reduction area were more prone to migrate, while the fine particles within the stress concentration areas were hindered by strong force chains. Soil arching degrading with the suffusion process was characterized as the decrease of critical soil arching height and soil arching ratio, the breakage of horizontal force chains, and the reconnection of vertical force chains. The degradation of soil arching during suffusion led to additional surface settlement during the postsuffusion stage.

This paper reports a field case of the excavation of a large-scale basement parallel to twin existing shield-driven tunnels in soft soils. A comprehensive field monitoring program was conducted to measure the performances of the shield tunnels during excavation. The trapezoid-shaped basement with an excavation area of 26,982 m² was excavated at the side of twin existing shield tunnels using a bottom-up excavation sequence. The tunnel horizontal and vertical displacements, and the tunnel convergence, were extensively measured. Based on field observations, the existing shield tunnels developed horizontal movements toward the excavation side, and settlements in the shield tunnels were observed due to the stress relief of the excavation of the large basement. The tunnel rings within the excavation width generally experienced horizontal elongation as a result of the reduction in the lateral earth pressure because of excavation. During the excavation of the elevator shaft, soil flow occurred, which resulted in a sudden and continuous increase in the tunnel horizontal displacements, tunnel settlements, and tunnel convergences. The down track suffered more serious adverse impacts than the up track, with eight leakages and 61 cracks observed in the down track. The newly induced cracks mainly occurred in a range within the excavation width, and were generally consistent with the distributions of the tunnel horizontal displacement and tunnel convergence. The measured data for the normalized tunnel horizontal and vertical displacements mainly fell between δ_h/|δ_hm| = δ_v/|δ_vm| − 0.5 and δ_h/|δ_hm| = δ_v/|δ_vm| + 0.4, and it was difficult to establish a direct linear relationship between them. However, a fairly good relationship between the tunnel convergence and horizontal displacement can be observed, the measured data mainly falling along δ_c/|δ_cm| = δ_h/|δ_hm|. An approximately linear relationship can be roughly found between the normalized tunnel vertical displacement and the tunnel convergence. The data mainly fell between δ_c/|δ_cm| = δ_v/|δ_vm| + 0.2 and δ_c/|δ_cm| = δ_v/|δ_vm| − 0.3.

Blasting presplitting is an effective method for preventing rock bursts in thick hard roofs. In this study, two adjacent working faces in the No. 10 mining area of the Jining No. 2 coal mine were considered as case studies, and the conditions of the working face and the construction parameters for roof blasting presplitting were introduced. The microseismic characteristics of the 2 working faces during the mining period were analyzed, and 10 indices for evaluating the microseismic characteristics of the working faces were proposed. Accordingly, the influence of blasting presplitting on the microseismic characteristics of the surrounding rock was evaluated. The results showed that the frequency of microseismic events changed with the mining stage of the working face. After the roof of the 103_down03 working face was presplit, the average energy of microseismic events, maximum energy of microseismic events, and proportion of high-energy events all decreased significantly. The average height of the source decreased from 31.08 m above the coal seam to 8.78 m, and the average strike location of the source decreased from 102 to 32 m in front of the working face. After presplitting, the roof gradually changed from large-scale and high-energy fractures to small-scale and low-energy fractures. After blasting presplitting, the energy accumulated in the roof was released through the collapse of the roof in the goaf, which improved the burst risk in the coal and roadway in front of the working face, thus ensuring the safety of underground construction personnel and equipment.

Improved depth is of fundamental importance for earth-filled foundations with dynamic compaction (DC) and is closely relevant to the mechanical characteristics of earth fillers under impact load. This study carried out numerical DC tests on fine-grained soil to estimate the improved depth more easily and accurately. The filler’s multiscale responses, including crater depth and porosity, were evaluated. Results showed that a heavier tamper weight with a lower drop distance was relatively more efficient in densifying soil fillers, although the tamping energy (MH^1.0) and tamping momentum (MH^0.5) were the same; however, contrary results were observed under the same value of MH^0.2. In addition, three different combinations of M and H led to similar soil responses under the same value of MH^0.3, which is thus recommended as the new index to estimate the improved depth and densification efficiency of DC. A mechanistic analysis found that M contributes more than H to compact soil fillers, which can be quantified by contribution ratio α. Moreover, large-scale field DC tests confirmed the findings.

This article presents a critical discussion of the repercussion of overshooting effects on element tests and finite-element simulations. For exemplification purposes, three advanced constitutive models for sands that had already achieved a certain level of accuracy in the simulation of monotonic and cyclic loading were carefully selected; namely, a bounding surface plasticity model, a hypoplastic model with intergranular strain, and a hypoplastic model with elastoplastic anisotropic intergranular strain. Cyclic loading laboratory data and scale tests on Karlsruhe fine sand were considered to support the analyses. The obtained results suggest that the overshooting issue is one of the most serious limitations of the selected models and has a major impact on elemental and finite-element simulations. Therefore, models’ end-users should be aware of this drawback when performing simulations under certain conditions involving unloading–reloading episodes with different strain amplitudes.