International Journal of Geomechanics

Stiffened deep-mixed columns (SDM columns) have increasingly been used to reinforce soft soils. When an embankment is constructed on a thick saturated soft clay, partially penetrated SDM columns are usually adopted. However, limited studies have been carried out to investigate the consolidation characteristics of thick soft soil with partially penetrated SDM columns. This paper conducted a theoretical analysis of the consolidation problem in soft soil with partially penetrated SDM columns under an embankment load. Two types of SDM columns were considered. The length of the outer deep-mixed (DM) column is equal to the length of the core pile or longer than the core pile length. After the load share effect of the core pile was considered under one-dimensional (1D) consolidation, the complex two-dimensional (2D) consolidation problem was transformed into a simplified layered consolidation problem, where equivalent consolidation coefficients were utilized. The effectiveness of the developed solution was confirmed by comparing it with the outcomes from a three-dimensional (3D) finite-element analysis. A systematic investigation was conducted to analyze the consolidation properties of this composite ground, which led to practical recommendations for its application. To validate the proposed solution further, it was implemented in a centrifugal model test that involved an embankment that was supported by partially penetrated SDM columns. The predictions made by the solution aligned well with the actual measurements, which indicated a high level of agreement.

This paper focuses on the horizontal bearing behaviors of an innovative type of foundation, the monopile–friction wheel hybrid foundation, for offshore wind turbines (OWTs). First, the scouring morphology of a monopile–friction wheel composite foundation under unidirectional flow is obtained by means of laboratory flume model tests. Then, the effects of key scouring parameters and the height of the loading point are further investigated through numerical simulations in terms of deformations, soil resistance distributions, and bearing ratios. The results indicate that for composite foundations, the effects of scouring parameters and the height of the loading point on the lateral bearing behaviors are not negligible, with the scouring depth having the most significant effect, followed by the scouring angle, and finally the scouring extent. Between them, the friction wheel contributes more than 40% to the bearing capacity while about 50% is borne by the pile side. In addition, the prediction formulas for the bearing ratios are obtained taking into account the scouring pits. The results provide valuable insights into understanding the load-bearing behaviors of composite foundations and their engineering applications.

The interaction mechanism between matric suction and osmotic suction was clarified through the analysis of certain physicochemical effects on unsaturated saline clay. The Young–Laplace equation for unsaturated saline clay was then derived by considering the contribution of the chemical potential to the Gibbs free energy at the air–solution interface. An effective stress equation for unsaturated saline clay considering the capillary and osmotic effects was obtained by utilizing a soil skeleton stress equilibrium analysis method. The definition and calculation formula for the osmotic efficiency parameter was determined by analyzing the chemical osmotic effect. Finally, the volume deformation and shear strength of unsaturated saline silty clay were tested under different salt content and matric suction conditions, and the validity of the effective stress equation was verified through tests on expansive clay saturated with salt solution. The results indicated that the effective stress–based generalized effective stress equation for unsaturated saline clay, taking into account the effect of the salt solution on the pore liquid pressure, u_sw, was related to osmotic suction and the osmotic efficiency parameter. The osmotic efficiency parameter is the ratio of change in the surface tension at the air–solution interface to the change in the corresponding osmotic suction, which reflects the strength of the chemomechanical coupling in the micropore space and its smooth transition to the macroscopic scale. In addition, the validation demonstrated that the proposed effective stress equation was able to uniformly describe the mechanical phenomena of unsaturated saline clay. Our findings provide a convenient way to simulate the mechanical behavior of unsaturated clay in saline environments.

Calcareous sand, which is characterized by irregular morphologies and abundant intraparticle pores, poses difficulties for ocean construction. This study investigated the effects of microbially induced carbonate precipitation (MICP) treatment methods and grain size on the biocementation of calcareous sand. Calcareous sand specimens with a wide range of grain sizes were first treated by MICP with immersion and mix methods. Scanning electron microscopy analysis revealed the presence of air bubbles inside the specimens treated by the mix method, which hindered biocement production, further promoting the emergence of a gradual failure pattern and reducing the strength and stiffness of the sand specimens. A series of unconfined compressive strength tests indicated that the strength and stiffness of the calcareous sand specimens treated by the immersion method were considerably greater than those of the specimens treated by the mix method in the suitable grain size range. In addition, the immersion method was not suitable for sand specimens with a median grain size of <0.5 mm. By contrast, the mix method was suitable for sand specimens of various sizes. As with the immersion-treated specimens, the specimens treated by the mix method displayed better mechanical properties at the early treatment stages, although the mix method-treated specimens exhibited much lower increase rates of strength and stiffness; moreover, the mix method-treated specimens exhibited lower strength and stiffness after long-term treatment than the immersion-treated specimens.

Steep fill–bedrock interfaces usually appear in many filling soil infrastructures, such as airports, houses, and road embankments in mountainous areas, when the excavation of rock slopes is constrained. These interfaces are prone to be tensioned up to failure, which easily triggers landslides of fill slopes. The anchor system buried in the fill soil, named radial cable system, was proposed for effectively enhancing the stability of steep fill–bedrock interfaces. At the interface, the steel ropes of the anchor section cable were equally divided into three subcables with a radial distribution. The pullout performance, failure evolution, and branching effect of the radial cable coupled with anchor plates were studied by a pullout test (in a laboratory setup) and a numerical simulation. The results showed that (1) the ultimate pullout capacities (P_u) of the radial cables were 193.53%–312.94% (for the 7 mm diameter of the anchor plate) and 141.25%–247.50% (for the 10 mm diameter of the anchor plate) greater than those of the single cables; (2) the pullout performance of the radial cable was significantly improved with an increase in the diameter of the anchor plate, and the optimal radial inclined angle of subcables coupled with anchor plates was 15°; (3) the soil surrounding the radial cable showed a progressive failure pattern, and its failure area was basically a symmetric conical; and (4) the radial cable can better reinforce the steep fill–rock interface than the conventional cable, as verified by a hill-fill project. The results of this study provide some new and important guidelines for the design and application of the radial cable system.

This paper presents a numerical study to model the thermal-induced pipeline buckling–soil interaction as a demonstration of the feasibility of modeling global buckling using an effective stress remeshing and interpolation technique with a small strain (RITSS) approach in 3D. The numerical results are compared with a previously published large-scale laboratory test, centrifuge, and numerical models. The influence of embedment depth, pipe weight, and pipe–soil interface roughness on the global pipe–soil response is investigated. The current study unveiled some of the key behaviors of partially embedded and buried pipes during thermal expansion. First, the expansion-induced displacements comprise vertical and lateral displacements. Heavy pipes dive deeper into the soil, whereas lightweight pipes rise above their initial position as they move laterally for partially embedded and buried pipes. Furthermore, expansion-induced displacements become insignificant as the burial depth increases. The soil in front of the buried pipe flows up and above to its rear end as the expansion-induced displacements increase. Moreover, lateral buckling occurs in buried pipes even though the lateral out-of-straightness of the pipe is within the recommended limit set by the Det Norske Veritas (DNV) guideline. Finally, the pipe–soil interface roughness significantly influences the undrained lateral resistance for partially embedded pipes.

A comprehensive experimental program was performed in order to understand the mechanical behavior of model piles associated with water infiltration in collapsible loess. Real-time measurements were recorded for pile head settlement, pile shaft friction, and pile base resistance, as well as for the soil behavior, including soil settlement, volumetric water content, and soil suction. The experimental results suggest that both the pile head settlement and pile base resistance increased with water infiltration. The linear pile axial force distribution gradually changed to a “D” shape, with the maximum pile axial force occurring in the middle instead of the end stage of water infiltration. Such behavior can be attributed to a reduction in the contribution of soil suction, degradation of the pile–soil interface shear strength, and settlement of the collapsible soil. In addition, a softening model was proposed by modifying the traditional shear displacement method for interpretation of the mechanical behavior of piles in collapsible loess. There was good agreement between our experimental results and those from the literature and the results predicted using the proposed model, suggesting that the model can be used as a tool in the rational design of pile foundations in collapsible soils.

Laboratory one-dimensional consolidation tests were conducted to measure the variation trend of the soil pore pressure at the drainage boundary with time under different magnitudes of loads. Based on the test data, continuous drainage boundary interface parameters under arbitrary loads were inversely derived, the reasonableness of which was verified by comparing the theoretical values of the boundary pore pressure with the experimental results. Moreover, the one-dimensional consolidation model of the layered foundation was established with a continuous drainage boundary. The semianalytical solution of the corresponding model under an arbitrary load was given by using the boundary transformation method. A comparison with degraded results and the finite-element calculation results verified the correctness of the present solutions. Finally, the influences of the interface parameters and loading rate on the soil consolidation behavior were studied, where three different types of loads (i.e., linear, exponential, and simple harmonic) were considered. The results revealed that the consolidation rate reaches the peak value for the linear loading pattern when the loading is completed. Moreover, the exponential load used to describe the surcharge preloading method also positively influenced the theoretical analysis due to its concise expression form. When the simple harmonic load was applied, the excess pore-water pressure in the soil element presented stable periodic vibration after the first cyclic load. In addition, the loading rate and interface parameters exhibited different influences on the consolidation behaviors. The research results of this paper can provide a theoretical reference for the settlement calculation of subgrades during the construction and operation phases.

Concrete diaphragm walls (CDWs) are widely used as support for deep excavations in saturated soft soils with sensitive construction environments. The lateral deformation of the CDWs is typically measured by inclinometers cast in the wall. This paper discusses the evolution of the lateral deformation of the CDWs during deep excavation and the main sources of errors in inclinometer measurements. Furthermore, a correction method for the most influential errors is proposed. It is found that the multilevel supported CDWs generally experience three types of deformations during the excavation: cantilever, transition, and bulging. Accordingly, the joint error correction method for inclinometer readings can be operated efficiently to reprocess the monitored data, using total station measurement as a cross-reference. Based on the case studies of deep excavation projects located in Suzhou, China, the proposed error correction method has been demonstrated to perform satisfactorily and can assist in guiding key safety control decisions on construction sites.

Magnesium oxychloride cement (MOC) is an environment-friendly cement often used for stabilizing soft soils because of its exceptional mechanical properties. In this study, the influence of curing temperature on the strength development of MOC-solidified clay is explored, considering different MgO/MgCl₂ molar ratios. Different tests were carried out to study the corresponding effects. The results show that the effect of curing temperature on the strength of MOC-solidified clay differs greatly from that of cement-solidified soil. Increasing the curing temperature leads to strength reduction, whereas decreasing the curing temperature increases the corresponding strength. Scanning electron microscope (SEM) and X-ray diffraction (XRD) analyses indicate that the variation in type and amount of hydration products of the solidified soil account for the strength development difference between MOC-solidified and cement-solidified soils. A model based on the experimental results is proposed to characterize the relationship between strength development and curing time. The strength influence factor (η_T) and the strength expedite factor (K) were introduced to demonstrate the relationship between strength development at a specific curing temperature as well as at room temperature.

Tunneling efforts that use shield machines often encounter weak and fractured rock formations, where the stability of the tunnel face is the principle safety control factor during tunnel construction operations. Within the framework of the limit analysis method, an improved model was proposed. The model consists of two failure modes, effectively addressing the shortcomings that arise from the incomplete contact interface between the traditional model and the tunnel face. Furthermore, the proposed model introduces the nonlinear Hoek–Brown criterion and improves the shape of the sliding failure surface within the cover layer to account for the arching effect. Subsequently, the proposed model was validated by comparison with numerical simulations and results in the literature. Further parameter analysis was conducted to investigate the influence that the Hoek–Brown parameters and tunnel depth have upon the critical support pressure and effectively identify the characteristics of failure mechanisms. The resulting data show that a reduction in the geological strength index (GSI), Hoek–Brown parameter (m_i), or uniaxial compressive strength (σ_ci) or an increase in the disturbance coefficient (D) leads to a nonlinear increase in the critical support pressure and an expansion of the failure zone of the tunnel face. Conversely, as the tunnel depth increases, the extent of the failure zone gradually expands, and the stability of the tunnel face exhibits a trend of initially decreasing and then increasing.

In this study, the behavior of soft clay improved with a conductive jute geotextile-encased stone column was investigated, considering the effects of electrokinetic coupling. The study findings suggest that electrokinetic-coupled encased stone columns (e-ESCs) improve the dewatering efficiency, consolidation settlement rate, and shear strength of the soft clay compared to nonelectrokinetic encased columns. After the inclusion of e-ESCs, the time required to remove 50% of the total discharge was decreased by 92% compared to encased stone columns (ESCs). A significant decrease in the volumetric shrinkage and surface cracks was observed for e-ESC-improved soft clay. Further, due to anode corrosion during the process, brass electrodes experienced a 4.25% loss in weight at the end. The consumed power per unit weight of treated soil (Wh/kg) at the end of the test period was 24.03, 19.70, 20.10, and 23.38 Wh/kg for the e-ESC with mild steel, copper, brass, and aluminum anodes, respectively. The findings showed that the choice of anode material affects the characteristics of soft clay, such as undrained shear strength, pore water discharge, flow pattern, and moisture content. Further, a noteworthy modification in the physicochemical properties of clay was observed.

The bearing capacity of large rectangular foundations on soil subjected to combined loading [simultaneously subjected to vertical load (V), overturning moment (M), and horizontal or lateral load (H)] is one of the central topics of interest to geotechnical engineers as it relates to the design of foundations such as ground anchorages of bridges, offshore structures, and gravity dams. To solve this problem, a combination of numerical simulation and theoretical research was used, and a stability evaluation model of large rectangular foundations on soil subjected to combined loading was established. First, an empirical equation for the failure envelope in the V‒M‒H loading space of rectangular foundations was developed. Second, the safety factor for load-path dependency (LPD) was established by considering the combined effects of V, M, and H, the stability evaluation model for large rectangular foundations on soil subjected to combined loading was constructed by proposing a method for calculating the LPD safety factor based on the V‒M‒H failure envelope. Last, the accuracy and effectiveness of the stability evaluation model proposed was verified. The proposed model provides a convenient means of calculating the stability of large rectangular foundations on soil under combined loading. The model was applied to the optimal design of a gravity anchorage project of a suspension bridge, which proves that the proposed model is rational and efficient.

According to various human needs, such as mineral supply, transportation, and underground storage, tunnel excavation has become commonplace today. However, one of the undesirable phenomena encountered during tunnel excavating, particularly when employing drilling and blasting techniques, is the overbreak phenomenon (OBP). This phenomenon not only compromises the safety of the work environment but also leads to increased operating costs. Therefore, accurately predicting the occurrence of OBP in tunnel excavation is of utmost importance. Due to the numerous uncertainties and complexities associated with rock formations, traditional methods have limited accuracy in predicting OBP. Consequently, this research used the rock engineering system (RES) method to comprehensively understand the physical and mechanical characteristics of the rock mass at any given point. By employing the RES method, accurate modeling of the OBP can be achieved in a time- and cost-efficient manner without requiring extensive and complicated coding. To construct the model using the RES method, 217 data points from three case studies were utilized: the Tarzeh underground coal mine in Iran, the Azad tunnel on the Tehran-North road in Alborz, Iran, and an Indian mine. The parameters considered in this study that affect the OBP (%) included perimeter hole powder factor (PPF, kg/m³), spacing-to-burden ratio of contour holes (S/B, kg), tunnel section area (A, m²), specific drilling (SD, m/m³), and rock mass rating (RMR, %). To compare and evaluate the RES method, various regression methods were also employed. Statistical criteria revealed that the RES method (RMSE = 0.0046, MSE = 0.068, R² = 0.945) demonstrated high accuracy compared to other regression methods. Consequently, it can be concluded that the RES is a highly valuable and essential tool for rock engineers.

In this study, enzyme-induced carbonate precipitation (EICP) combined with chitosan curing technology was used to improve the mechanical properties of standard sand, and the curing effect of EICP combined with different chitosan contents was studied by macroscopic tests, such as the unconfined compressive strength test, direct shear test, and calcium carbonate content test, and microscopic tests, such as scanning electron microscope (SEM) and nuclear magnetic resonance (NMR). The results show that compared with the pure EICP treatment, the unconfined compressive strength, shear strength, and calcium carbonate content of the sand treated by EICP combined with chitosan were significantly improved, and increased first and then decreased with the increase of chitosan content, reaching the maximum value when the content is 1.5%. The calcium carbonate content is positively correlated with the strength, indicating that calcium carbonate crystals can effectively play a role in filling and cementation. After the incorporation of chitosan, the shape of calcium carbonate crystals is still mainly spherical, but the number and volume become larger. At the same time, the incorporation of chitosan can greatly reduce the proportion of large pores and medium pores, significantly increasing the proportion of small pores, which greatly improves the pore structure.

Analytical approaches to determine the long-term settlement of shallow foundations subjected to dynamic cyclic loading with a large number of cycles (millions) are presented. The approaches use the high-cycle accumulation (HCA) model to calculate the permanent strain caused by the cyclic loading and are conceptionally similar to conventional settlement analyses. The incorporation of a threshold strain amplitude, below which no accumulation of deformations occurs, in the HCA model is discussed. It is demonstrated that the simple analytical approach, which does not require numerical calculations, gives results very similar to more complex finite-element simulations.

Underground mine structures like mine seals or built-in-place (BIP) refuge alternatives (RA) are exposed to specific loadings like explosions because of overlying and underlying strata conditions. Previous studies worked on the vertical loading response of structures like abutments from panel extraction but not the explosion resistance upon being subjected to these vertical strata loads. In this study, two steel-reinforced concrete wall designs as seal and RA applications are simulated to examine the performance and failure analysis under abutment-loading conditions during an explosion for a coal mine model using dynamic analysis by a distinct element code (3DEC). The available abutment monitoring data by longwall stoppings was used to estimate the abutment-loading conditions. The model setup was calibrated through two validation stages: (1) the concrete wall simulation with the explosion test of steel-reinforced concrete mine seal conducted by previous researchers; and (2) the stress change at the strata by the tailgate convergence-abutment-load multiplier curve. The calibrated models are subjected to various dynamic loadings to simulate explosions. The findings demonstrate that, in addition to magnitude, the pressure versus time mode of loading significantly influences the wall response. Instantaneous loading criteria can provide more cautious measurements to assess how well such walls operate in similar situations. Except for a few cases, the deformations after a single explosion are more pronounced for the effects of subsequent second and third explosions. As a result, the changes in deformation during subsequent explosions are relatively minor compared with the initial permanent deflections.

Abstract

The limiting stability of finite rock slopes is assessed in this paper by implementing the stress characteristics method (SCM) alongside the generalized Hoek‒Brown (GHB) yield criterion. By employing the SCM, a set of differential equations governing the equilibrium stress field is derived and later combined with the rock mass failure envelope characterized by the GHB criterion. Subsequently, the limiting slope face (LSF) with a global factor of safety (FS) as unity is obtained to preserve the state of plastic equilibrium. The current approach overcomes the necessity of a preconceived slip surface in the analysis. The resulting curvilinear LSFs exhibit more excellent compatibility with the shape of the naturally occurring slope profiles. The LSFs evolved from this investigation are generally found to be steeper than the traditionally encountered planar slopes without negotiating the mechanical stability. Numerical validation of the current approach using the finite-element limit analysis (FELA) is also established to authenticate the reliability of the present outcomes. The current results are suitably compared with the solutions available in the literature. Design charts are provided in the form of curvilinear slope faces for the ease of practicing rock engineers. Finally, the proposed LSF-based stability concept is applied to two selected case studies reported in the literature.

Practical Applications

Using the nonlinear generalized Hoek‒Brown strength criterion, this study directly determines the rock slope profile required to maintain limiting stability (factor of safety = 1.0). The profile thus derived is referred to as the LSF. The LSF serves as the basis for two potential field applications: designing the optimal rock slope profile and conducting routine stability checks on existing rock slopes. Taking the derived curvilinear LSF as a reference, optimal linear, bilinear, or multilinear/stepped slopes can be designed with a sufficient safety margin. Additionally, the LSF operates as an interface between the zone of stability and instability. Therefore, a simple profile-matching scheme between any existing rock slope and the corresponding LSF can provide the safety status of that existing slope. Therefore, the present design charts containing LSFs contribute to a readymade solution for a rapid and reliable rock slope stability assessment.

In-depth investigations into the effect of water saturation on the damage and failure mechanisms of rock have significance for analyzing the stability of the surrounding rock in water-rich rock masses. Uniaxial compression tests were carried out on two types of sandstone to explore the influence and mechanism of water saturation on their strength and deformation, stress thresholds, energy evolution, and acoustic emission (AE) characteristics. The deduced the following after water saturation: (1) water saturation had an obvious softening effect on both types of sandstone, manifested by a reduction in uniaxial compressive strength and elastic modulus, and an increase in the Poisson’s ratio; (2) the normalized crack initiation stress (σ_ci/σ_f) increased and the normalized crack damage stress (σ_cd/σ_f) decreased; (3) the total energy (U), elastic energy (U_e), and dissipated energy (U_d) at the peak strength decreased and the ratio of elastic energy to total energy (U_e/U) decreased; and (4) the peak values of AE count and AE cumulative count decreased in both types of sandstone. Based on our analysis of the AE b-values, the proportion of small-scale ruptures increased. An analysis based on the AE ratio of the rise time to amplitude (RA) value and average frequency (AF) value showed that the proportion of shear fracture increased after water saturation. Our findings provide an indication of the significance of determining the failure mechanism of water-saturated rocks.

Numerous studies have been carried out to characterize uncertainties of soil properties, and lots of multivariate databases have been compiled to make the characterization of uncertainties more realistic. However, when it comes to complex situations, that is, for complex critical state constitutive models and soil–structure interface properties, the uncertainty quantification becomes a challenge. This paper aims to quantify the uncertainties of the soil–structure interface properties from laboratory tests. A framework of uncertainty quantification based on a simplified two-dimensional Monte Carlo simulation is first proposed. To validate the performance of the framework, an enhanced hypoplastic interface model considering particle breakage is then proposed and employed in the uncertainty quantification framework. The CMA-ES algorithm is then used to calibrate the uncertainties based on the framework and the hypoplastic soil–structure interface model. The results showed the proposed framework with the enhanced model can capture the uncertainties of the soil–structure interface properties. In the studied experiments, 30 out of 42 experimental curves were found to be well calibrated based on the Kolmogorov–Smirnov normality test. Furthermore, to obtain acceptable results, based on the calibration-validation process, the effect of the selection of experiments on the calibration performance is discussed. Some suggestions on how to choose experiments to calibrate the soil–structure interface properties are summarized, which should be helpful in practice.

Abstract

Cavities are common subsurface anomalies that have a significant impact on the bearing capacity of footings. While cavities behave three-dimensionally, in previous studies, the analysis of cavities has been limited to two-dimensional plane-strain analysis because of the time-consuming nature and complexity of three-dimensional modeling. However, this study demonstrates that the bearing capacity factor derived from three-dimensional modeling can be up to 10 times higher than that obtained from plane-strain analysis, highlighting the importance of considering three-dimensional effects. The present paper conducted three-dimensional simulations to investigate the impact of spherical cavity on the failure mechanisms and bearing capacity of footings under undrained conditions. An extensive parametric study was performed to investigate the influential parameters, including footing width to cavity dimension ratio (B/D), cover depth ratio (C/D), overburden factor (γD/S_u), and void eccentricity ratio (S/D) for both circular or square footings. The results indicate that increasing the overburden factor and void eccentricity ratio leads to a decrease and increase in the bearing capacity of the footing, respectively. Furthermore, changes in other parameters can either increase or decrease the bearing capacity depending on the characteristics of the cavity (size and location) and footing (size and shape). General solutions for the bearing capacity factor are provided for different variations of the dimensionless parameters. This study also examined various failure mechanisms, including both cavity-independent and cavity-dependent failure mechanisms, associated with circular and square footings and influential parameters. These mechanisms are categorized into three zones for cavity-independent failures and four zones for cavity-dependent failures. The changes in the influential parameters including B/D, S/D, γD/S_u, and C/D lead to changes in the type of failure mechanism and the size of the failure zones, while the foundation shape does not have a significant effect on the failure mechanism.

Practical Applications

Sinkholes and underground cavities annually contribute to infrastructure damage and financial losses. The 1981 incident in Winter Park, Florida, exemplifies the real-world consequences. Previous investigations have been limited to two-dimensional models due to the time-consuming nature and complexity of three-dimensional modeling, but the real-world nature of cavities in three dimensions requires a more comprehensive understanding. This study directly addresses this need by investigating the impact of three-dimensional cavities on the bearing capacity of circular and square building foundations, also known as footings. This study thoroughly investigated the factors influencing the results, encompassing cavity size, depth, soil weight, and off-center position. It extensively explored potential footing failures, providing detailed discussions. Our findings are presented as easy-to-understand maps and charts covering a broad range of potential scenarios. These visual tools can help engineers and researchers accurately estimate the stability of a building's foundation when a cavity is present underneath. In simpler terms, this research has created a handy tool for professionals to predict the potential danger posed by hidden cavities to buildings and infrastructure. This knowledge can then be applied to ensure safer building practices, potentially saving a significant amount of money and preventing accidents in the future.

Abstract

A method to assess the influence of tension cracks on the seismic external stability analysis of geosynthetic-reinforced soil slopes is carried out in the present study. In addition to being subjected to uniform surcharge loading, hydrostatic and hydrodynamic pressures with water on both sides of the c-ϕ soil slope and seismic inertia forces are considered, and the reinforcement length for both sliding and overturning conditions is evaluated by using a two-part wedge mechanism. The analysis is implemented separately by considering and neglecting the effect of the formation of tension cracks, and reinforcement lengths are evaluated for both the slope angles 60° and 70°. It is seen that when the horizontal seismic acceleration coefficient increases from 0 to 0.2 for a 60° slope angle under the direct sliding mode of failure for a particular set of input parameters as shown in Table 3, the required minimum length of the geosynthetic reinforcement increases from 0.59H to 1.30H, and in the overturning mode, it increases from 0.46H to 0.60H, when the analysis is implemented without considering similar tension cracks when tension cracks are considered in the study, for the increases in k_h, as mentioned previously, required minimum length of the geosynthetic reinforcement against direct sliding mode of failure increases from 0.80H to 1.67H, and increases from 0.55H to 0.64H for overturning mode of failure. In addition to k_h, the influence of the height of water on the downstream side, pore pressure ratio, soil friction angle, cohesion, and surcharge on the length of reinforcement against sliding and overturning modes of failure are presented in this paper in the form of design charts. The results obtained from the present study are compared with the previous literatures and usefulness of the present method in analysis of reinforced soil slopes against direct sliding and overturning modes of failure has been proposed.

Practical Applications

The present research work delves into the external stability analysis of reinforced soil slopes. This analysis evaluates the optimal length of reinforcement necessary to maintain long-term safety and stability against potential failures, such as direct sliding and overturning. While direct sliding is influenced by forces pushing the slope forward, overturning is concerned with rotational risks. Geosynthetic reinforcement for soil slope stability plays a crucial role in stabilizing slopes across various infrastructures: highways, railways, airports, landfills, mining operations such as tailings dams and heap leach pads, urban developments, and erosion control measures along riverbanks and shorelines. Adopting the insights and methodologies of this research can amplify the safety benefits by reducing landslide risks and facilitating the customization of designs according to specific site conditions. This approach paves the way for a more efficient use of resources, ultimately slashing costs and bolstering the long-term reliability of slope performance. Furthermore, the study presents a clear analysis of geosynthetic-reinforced soil slopes, considering soil properties, failure risks, seismic forces, and water effects. This framework, suitable for both experts and novices, bridges academic research with practical engineering, making the latest insights usable and valuable for the engineering community.

To study the reinforcement mechanism of expansive slurry from a mesoscopic perspective, shear simulation tests were conducted on a slurry–fractured rock mass composite using PFC2D (version 5.00.35). The tests analyzed the distribution of cracks, the process of damage evolution, the distribution characteristics of intergranular contact forces, and the displacement of particles. The results indicate that (1) the volume expansion of the expansive slurry compressed the rock mass, causing the slurry particles to penetrate the pores of the rock particles. This process increased the contact area between the slurry and the rock mass, improved the friction, and intensified the degree of interlocking between the slurry and the rock mass, thus improving the bonding between them. (2) Both composite rock masses exhibited similar macroscopic damage patterns consistent with the laboratory tests. During shear tests, both composites experienced four stages of crack development: crack initiation, slow crack development, rapid crack development, and stable crack number. (3) The expansion stress, along with its reaction force and friction force, increased the integrity of the composite rock mass, reducing the differences in particle displacement direction and velocity. This led to improved internal deformation coordination within the composite rock mass, resulting in fewer cracks during shear tests.

To solve the problem where the prediction formula for vibration velocity by dynamic compaction cannot fully reflect the elevation amplification effect, the elevation amplification effect of vibration velocity by dynamic compaction was studied theoretically, and the factors that influence the elevation amplification effect of vibration velocity by dynamic compaction were systematically analyzed in this paper. The elevation amplification effect of a loess high slope under dynamic compaction is coformed by the refraction and reflection superposition effect of dynamic compaction vibration waves at the soil layer interface and the diffraction effect of dynamic compaction vibration waves. The propagation path of dynamic compaction vibration waves in soil was analyzed, and the elevation amplification effect was verified theoretically. The related physical quantities that affected the dynamic compaction vibration velocity of a loess high slope were analyzed based on the dimensional analysis method, and the calculation and improved calculation formulas that considered the elevation amplification effect of dynamic compaction vibration velocity were obtained. The multiple regression analysis of the calculation and improved calculation formula that considered the elevation amplification effect of the dynamic compaction vibration velocity was carried out using MATLAB with engineering examples. The results show that the relative error of the two formulas is small when the elevation difference is small; when the elevation difference is large, the calculation accuracy of the improved calculation formula that considered the elevation difference is higher, and it is more in line with the actual situation. Finally, according to the selected maximum allowable value of the slope particle velocity (e.g., 1.5, 2.0, and 2.5 cm/s), the allowable safe distance for dynamic compaction on a loess high slope is proposed area of northern Shaanxi Province, China. The results of this paper could provide a reliable basis for predicting vibration velocity by dynamic compaction in the Loess Plateau area of northern Shaanxi Province, China. They might have a reference value for dynamic compaction vibration control under similar terrain environments with large elevation differences and provide a safe guide for a dynamic compaction construction site in the Loess Plateau area of northern Shaanxi Province, China.

Abstract

This study focuses on the area of large deformation of soft rocks across the fault in Dongmachang China to investigate support methods for fractured surrounding rocks Negative Poisson's Ratio (NPR) anchor cable support. The research employs field monitoring, 3D physical model experiments, and numerical simulations. The results show that: (1) the maximum settlement displacement of the Dongmachang Tunnel section with original support can reach about 476 mm and has an upward trend, the limit of initial branch intrusion is 41.2 cm, and the width of invert joint is 5–50 mm; (2) the dynamic impact experiment of NPR anchor cable shows that the NPR anchor can withstand several impacts, the maximum cumulative impact deformation within the range of constant resistance is 500–1,000 mm, and the impact resistance is strong; and (3) NPR anchor cable can effectively control the large deformation disaster of surrounding rock in the fault fracture zone of Dongmachang Tunnel, basically ensuring that the deformation of the surrounding rock is below 300 mm, and the control effect is good. These findings suggest that NPR anchor cables are effective for controlling large deformations in tunnels constructed through soft rock across faults and provide a scientific basis for implementing new support systems for other similar tunnels.

Practical Applications

At present, the international support of deep-buried underground engineering still takes the new Austrian method as the mainstream, but the core idea of the new Austrian method is passive support, which often cannot effectively support the deep-buried soft rock with high stress and large deformation. This paper takes the anchor cable with high preload (350 kN) as the core and the excavation compensation method proposed by Academician He Manchao as the starting point, and innovatively supports the deep-buried soft rock large deformation tunnel, which provides a new idea for the support of other deep-buried underground projects. Although this paper studies the support effect of negative Poisson’s ratio (NPR) cable compensation mechanics from the perspectives of laboratory test, physical model experiment, and numerical simulation, because the tunnel has not yet been started, it has not been studied from the perspective of field application. The support effect of NPR anchor cables on surrounding rock in the fracture zone needs further study.

Methods for analyzing micropile groups considering complex pile–soil interaction have received less attention. This paper proposes a calculation method to study the internal force of micropile groups considering shadow effects of pile groups and nonlinear soil pressure. The nonlinear load transfer mechanism of micropile groups based on the concept of p-multipliers is studied, and the relationship between the p-multipliers of nonlinear landslide thrust and soil resistance and the normalized pile spacing are established. The new governing equations and calculation models of the micropile groups considering the possible failure modes and the p-multiplier method are established. Finally, the proposed method is verified by two case studies. The study results show that the established p-multiplier model of landslide thrust and soil resistance is closely related to soil properties and normalized pile spacing. Comparing the measured results, it is noted that the newly proposed model improves accuracy by an average of 29% over the traditional method. The effect of bending stiffness on the internal forces of piles is more significant than the normalized pile spacing.

Surface settlement caused by shallow shield tunneling can occur frequently. Machine variables such as face pressure, tail-void grouting pressure, and grout volume play an essential role in the settlement control of earth pressure balance (EPB) tunnel boring machines (TBMs). Combined with literature review, theoretical derivation, case verification, and numerical simulation, methods were established for adjusting the key parameters, including the face pressure in the plenum chamber, the advance speed of the shield machine, and the rotational speed of the screw conveyor. The grouting volume required to backfill the tail void was calculated according to shield kinematics, a physical model test under high pressure and soil states during excavation,. From the mechanical properties of soil, the function between surface settlement and tail-void grouting pressure based on the Peck formula, stochastic medium theory, and Terzaghi soil arching theory was deduced for the first time. With the increase in grouting pressure, the soil was compressed after the formation of the soil arch, and the process from original settlement to upheaval was also expressed by numerical simulations. In addition, the proposed methods could control the surface settlement effectively and result in more accurate predictions. By comparing the predicted surface settlement to measured data from the Harbin Metro Line 2 project, the adaptability of the proposed methods for the face pressure, tail-void grouting pressure, and grout volume was verified.

This study was part of a preliminary safety assessment for a real project of existing bridge piles passing through beaded karst caves threatened by a nearby newly built embankment. To investigate the severity of the effect of the embankment on the performance of these piles, a series of reduced-scale model experiments of piles considering different cave numbers (n = 0, 1, 2, and 3) near surcharge loads were designed with a similarity ratio of 1:35. Two phases of loading, the vertical loading atop the pile and nearby surcharge loading, were imposed successively to explore the vertical bearing characteristic and lateral response characteristic of the piles passing through beaded karst caves. The effects of cave number, vertical load atop the pile, and nearby surcharge load on the responses of pile and soil were clarified and several fitting functions were presented to characterize the variations of responses with different cave numbers and nearby surcharge loads. The results and conclusions can provide a reference for the design and safety assessment of bridge piles in karst terrains.

The existing research on anchor foundations has predominantly focused on their axial load-carrying capacity, disregarding their resistance to the combined uplift and lateral forces during operation. To address this gap, the present study employs a three-dimensional finite-difference analysis to examine the behavior of horizontal anchor foundations buried in sand under the influence of uplift and lateral loads. The novelty of this work lies in the application of combined loading on the shaft head and the subsequent evaluation of both vertical and horizontal displacements of the foundation. The results reveal that the displacements are notably more significant in the horizontal direction. Furthermore, the paper presents a detailed analysis of the foundation’s failure mechanisms under various combinations of vertical and horizontal forces. It is observed that pure vertical forces induce an uplift shear failure, whereas pure horizontal forces lead to a rotational failure. Based on the results, a failure envelope in the V:H loading plane is proposed for the horizontal anchor foundation subjected to oblique loads.

This paper proposes a generalized framework to estimate the seismic active earth thrust on rigid retaining walls with unsaturated backfill. A novel suction stress-dependent approach was developed to compute the horizontal and vertical seismic acceleration profiles within the backfill. The framework applies the limit equilibrium method with a log-spiral failure surface and considers the influence of suction-stress through the effective stress approach. A detailed validation of the proposed framework is conducted by comparing it with well-established solutions reported in previous studies showing a satisfactory agreement. Validation was performed for the cases of static loading with suction and seismic loading without suction because of the unavailability of the data for the combined case. The influence of suction on the seismic active earth thrust for different soil types and environmental conditions is presented together with other parameters including wall height, soil friction angle, frequency of input excitation, and horizontal and vertical seismic acceleration coefficients.