Soils and Foundations最新文献

Up to this day, there are great uncertainties in the design procedures of monopiles, especially concerning the soil state condition and penetration response during their installation. A numerical model, based on the Coupled Eulerian method and using the hypoplastic law with intergranular strain, is proposed and validated in this paper, after which a series of open-ended pile installation tests have been carried out numerically, to investigate the influence of the jacked installation on the initial conditions for three types of silica sand. A range of soil densities and pile diameters is considered in this analysis. A full investigation of the installation forces, stress level, changes in volume-stress level and voids ratio is conducted. The numerical solution provided a correlation between the penetration resistance and the granulometric properties of the studied sands. Subsequently, the radial stresses in the surrounding soil mass are correlated with the type of sand and its relative density. The stress-volume state of a set of points in the soil domain during installation is presented and discussed from the critical state framework, revealing the contribution of the in-situ state in the pile installation. Finally, the lateral earth pressure resulting after installation is presented.

This paper presents a novel analytical formulation to study the impact of shear deformations on beam-columns and piles by means of the Timoshenko-Engesser’s and Timoshenko-Haringx’s theories. The proposed solution enables the analysis of lateral deformation or buckling, while considering the effect of shear deformations. It offers the flexibility to i) incorporate different boundary conditions at the ends of the element (e.g., semi-rigid connections and lateral transverse springs) and ii) consider an inhomogeneous elastic foundation. When certain variables are disregarded, the proposed GDE can capture particular cases of GDEs found in the literature for beam-columns and piles. Examples are provided to demonstrate the simplicity and practicality of the proposed method, and its accuracy is validated against available analytical or numerical methods. The influence of the shear effects, as computed from Engesser’s and Haringx’s methods, on the lateral and buckling responses of beam-column and pile elements is discussed.

Excavated rock produced during tunnel construction projects in volcanic areas and sedimentary rock of marine origin pose the potential hazard of introducing naturally occurring arsenic (As) into the surrounding soils and groundwater. Thus, appropriate management and/or countermeasures against As mobility is required by comprehending the leaching characteristics of the As in excavated and sedimentary rock. This study focused on the Neogene Miocene sedimentary rock of marine origin that is widely distributed between Shin-Hakodate-Hokuto and Oshamambe Stations along the Hokkaido Shinkansen in Hokkaido, Japan. The probability distribution of the leaching concentration of As from the rock excavated from the tunnels between the above stations was evaluated via batch leaching tests using crushed rock as a countermeasure against the rock containing naturally occurring toxic elements. A statistical evaluation of this probability distribution was conducted using a vast amount of test results. The results showed that the As leaching concentration followed a logarithmic normal distribution depending on the geological formation. The concentration was influenced by various factors, including the As content, key chemical composition in the rock, such as calcium (Ca), iron (Fe), and sulfur (S), as well as the pH and electrical conductivity (EC) in the leachate. In addition, the thickness of the overburden was found to impact the As leaching concentration. These results suggest that reasonable countermeasures against the risks of As leaching into the surrounding environment can be devised by considering the probability distribution of the As leaching concentration.

In undrained cyclic triaxial tests on crushed gravel, it is difficult to maintain undrained conditions because of the penetration of the rubber membrane (MP: membrane penetration) into the rough surface of the test specimens. A method has been developed in the present research to physically mitigate the MP-effect wherein the rough surface of each specimen is coated and smoothed by a prefabricated fines-soil sheet. This mitigation measure has been found very effective in minimizing the C_R (compliance ratio for an undrained system) to achieve more strict undrained conditions. It has been further clarified that this method prevents not only the overestimation of the strength of loose specimens, as has already been recognized, but also the underestimation of the strength of dense specimens with highly positive dilatancy. The undrained cyclic strength of dense crushed gravel, comprised of various grain sizes and gradations, has been summarized in a series of undrained cyclic triaxial tests by employing the MP-mitigation method to find that, in place of the relative density governing the liquefaction resistance of loose soils, the void ratio or absolute density is a key parameter for uniquely estimating the strength with a simple empirical formula.

A novel less-destructive field impression method that overcomes the uncertainties in stability assessments of rock joints in historical monuments, due to material sampling or existing destructive test limitations, has been developed. A thermoplastic resin with low fluidity and a short curing time is used to obtain the surface morphology of rock joints owing to its less destructive nature and wide applicability to the walls and ceilings of historical monuments. However, the insufficient filling of this thermoplastic resin can decrease the geometric accuracy of the impressions. Thus, the geometric accuracy of resin impressions and mortar replicas has been examined through laboratory experiments, and the results have been compared with those obtained using existing silicone-based methods, based on the statistical indicators associated with mechanical replicability. The indicator values of the method developed in this study were comparable to those of the replicas in previous studies that have sufficient geometric accuracy to satisfy mechanical replicability requirements. Furthermore, although roughness-coefficient-based methods underestimate the shear strength because of the insufficient filling of thermoplastic resins, they provide an acceptable safety margin in stability assessments of rock joints. The proposed method is suitable for conducting accurate stability assessments of historical monuments and ensuring their conservation.

The relationship between stress and strength in granular soil differs under low confining pressure as compared to high confining pressure, which is of great importance for the geotechnical engineering. Numerical simulations using discrete element method (DEM) are conducted to model consolidated-drained triaxial compression tests, with the confining pressure σ_c ranging from 1 to1000 kPa. From the analysis of the shear strength of granular soils under various confining pressures and void ratios, it is found that the peak stress ratio η_p under a low σ_c is significantly lower than that under the high σ_c, particularly for samples with the same initial void ratio. As the confining pressure increases, η_p for samples with the same initial void ratio increases up to 29 % under the low σ_c while stabilizing under the high σ_c. Conversely, η_p for samples with the same void ratio after the consolidation can increase up to 13.5 % under the low σ_c while declining under the high σ_c. In addition, the critical confining pressure distinguishing the low and high confining pressures is about 200 kPa for dense samples with initial void ratio of 0.605 used in the study, and it increases as the sample void ratio increases. From the microscopic analysis, the variation of η_p under the low ${\sigma }_c$ can be attributed to the enhanced anisotropy of normal contact force and contact normal under the low confining pressure. Finally, a modified Mohr-Coulomb failure criterion is proposed, which can determine the strength of granular soils under the low confining pressure with different void ratios.

This contribution investigates the characteristics of elastic wave velocities (V_p and V_s) during triaxial shearing tests under dry and drained conditions. Samples of tested materials with different particle morphologies (i.e., particle shape and surface roughness) were prepared under three strategies, namely, similar initial void ratios (e₀), relative densities (D_r0), and side tapping numbers (N_t). Regarding the elastic wave velocities as functions of e₀ and confinement ${\sigma }^{\prime }$ at very small strain ranges, i.e., $V=a(B-e_0){\left(\frac{{\sigma }^{\prime }}{1kPa}\right)}^b$, a was seen to increase for more angular materials or smoother surfaces, while b and B were seen to decrease as the particles became more angular or the surfaces became smoother. During triaxial shearing, V_p increased initially and then tended to decrease more gently, whereas V_s increased initially and then showed a marked decrease before convergence upon shearing regardless of the e₀ for the given material. The influence of particle morphology on the absolute values for V_p and V_s was found to be complex during shearing, whereas the wave ratio (V_p/V_s) was consistently greater under rougher conditions for the same shape. Importantly, the wave ratio (V_p/V_s) was found to correlate well with the particle morphology: more angular materials and rougher surfaces exhibited a greater V_p/V_s ratio normalized by the stress and density conditions for each material, which further indicates a higher degree of fabric anisotropy with reference to the microscopic evidence in the literature.

Case histories from at least 28 earthquakes worldwide have indicated that liquefaction can occur in gravelly soils (both in natural deposits and manmade reclamations), inducing large ground deformation and causing severe damage to civil infrastructures. However, the evaluation of the liquefaction potential and cyclic strain accumulation characteristics of gravelly soils remains a major challenge in geotechnical earthquake engineering. To provide new and useful insights into this crucial topic, stress-controlled undrained cyclic triaxial tests were conducted on sand-gravel mixtures (SGM) having sand-dominated microstructure but different packing states (i.e., soil grain arrangement), which were obtained by varying the gravel content (G_C) and relative density (D_r). The experimental results confirmed that both the G_C and D_r have marginal (at low G_C and D_r) to significant (at high G_C and D_r) effects on the cyclic resistance ratio (CRR) of SGM, but highlighted the need to consider G_C and D_r effects together. In this regard, the use of state parameters, such as the equivalent void ratio ($e_{f\left(eq\right)}$) and equivalent relative density (D_{r f(eq)}), were found to be suitable approaches to describe the combined effect of G_C and D_r on CRR as they provide unique correlations for sand-dominated SGM irrespective of their packing states.

Soil water conditions should be adequately evaluated because they influence the occurrence of surface failures. Digital twin systems, connecting field measurement data with numerical simulations, must be created to enable early warnings to be issued before a surface failure occurs. This study discusses the applicability of the merging particle filter (MPF) method for estimating the posterior distribution of seepage analysis models based on the volumetric water content field measurement data from two case studies. The first case study estimated the posterior distribution of parameters for unsaturated soil hydraulic properties based on data obtained from three slopes of different soil types (decomposed granite, weathered mudstone, and pyroclastic flow deposits). The simulation results agreed well with the raw data, where only precipitation data were input into the estimated seepage analysis model. The second case study estimated and discussed the applicability of a seepage analysis model using parameters for the unsaturated soil hydraulic properties and drainage boundary conditions. The simulated results reproduced the field measurement data with sufficient accuracy to attain the groundwater behavior. Therefore, based on field measurement data, the MPF can estimate the posterior distribution of parameters for the seepage analysis model, considering the inhomogeneity and uncertainty of in-situ soil.

Earthquakes generally consist of one mainshock and subsequent aftershocks. Although effects of aftershocks following the mainshock on surface structures has been studied extensively, similar studies on underground structures are rarely reported in the literature. With the fast advances in underground space development, robustness of remediation measures against underground structures uplift induced by soil liquefaction shall be examined to ensure their functioning subject to not only the mainshock but also the subsequent aftershocks. This paper studies the uplift behaviour of a conventional manhole subjected to the mainshock-aftershock sequence. It was found that, in the ground that becomes liquefied during the mainshock, manholes become more vulnerable when faced with aftershocks. Due to this reason, some of the previously proposed remediation measures, such as increasing the manholes’ self-weight, roughening the sidewalls, were examined using centrifuge modeling in this study. It was found that such measures had little effect in the aftershocks despite their effectiveness in the precedent mainshock. In contrast, the methods that mitigates manhole uplift by enhancing the manhole’s base permeability, demonstrated better performance in the aftershock than in the mainshock, indicating its promising application potential in future mitigation design.