Soils and Foundations最新文献

This is a review of the papers written by the author with co-researchers, which have been published in Soils & Foundations and related publications. The contents of the papers are related to experimental and theoretical aspects of geomechanics, namely, the constitutive modeling of cohesive and sandy soils, the governing equations of three-phase materials, and analyses of the behavior of geomaterials and grounds. The following topics are included in the papers: effective stress, skeleton stress, constitutive models of clayey and sandy soils and soft rocks, material instability, strain localization, consolidation, bearing capacity, excavation problems, governing equations of multi-phase geomaterials, liquefaction, unsaturated soil, seepage-deformation coupled analysis, gas hydrate-contained soil, internal erosion, the material point method (MPM), and X-ray CT for geomaterials.

Although the stability of tunnel face in the dry and saturated sandy ground is widely studied, the unsaturated sandy ground which possesses apparent cohesion is more common in engineering. For remedying this deficiency, the theoretical association between apparent cohesion and the saturation degree is firstly established in microscopic prospective. Then, the formation mechanism of the self-stabilized arch and the limit support pressure (LSP) of the tunnel face are derived by incorporating apparent cohesion into the macroscopic limit equilibrium analysis of the multi-arches model. Subsequently, the validities of the proposed approach in estimating apparent cohesion, loosening zone height and LSP are well confirmed (the average error rates of LSP are within 12 %) via comparisons with direct shear tests, model tests and other existing methods. Finally, as revealed by the parametric discussion, under the effect of apparent cohesion, LSP is negatively correlated with compactness, internal friction angle, and contact angle while decreases firstly (to a minimum value of 0.09γD ∼ 0.15γD) and then increase with the rise of saturation degree. Besides, the LSP has a parabolic distribution along the depth with its peak value emerges between 0.3D and 0.45D.

Enzyme induced carbonate precipitation (EICP) which applied to improve the quality of recycled aggregates (RA) is a novel technology in the field of civil engineering. The urease was extracted from soybean, and the factors including soybean powder concentration, temperature and pH value on urease activity were investigated. Then the EICP reaction kinetics was carried out to obtain the most suitable reaction environment. A spraying method instead of soaking method for modifying RA was proposed, and the physical and mechanical properties of RA were evaluated by water absorption, hardness, apparent density and crushing index. The results show that the optimum pH value of soybean urease is 8.0, the concentration of soybean power is 40 g/L, and the urease activity increases with temperature in the range of 10–50 °C. Spraying method was better than soaking method in water absorption reduction rate of RA with different particle sizes. When the concentration of the chemical solution is 0.5 mol/L, the improvement in the water absorption characteristics of the RA is most significant. And the modified RA have also undergone substantial improvements in terms of hardness and apparent density. On the 7-day of modification, the crushing index of the RA reaches the peak. Through microscopic observation, the pore volume of the modified RA is significantly reduced, and the content of CaCO₃ is significantly increased, and the main crystalline form of CaCO₃ are calcite and vaterite.

Piles driven in Intermediate GeoMaterials (IGM) pose multiple design and construction challenges because of the high uncertainty in IGM properties, lacking knowledge pertaining to pile responses in IGM, and absence of classification, static analysis (SA) methods, and design recommendations. A classification criterion is established for coarse grained soil based intermediate geomaterials (CG-IGM) using test pile data from bridge projects completed in four U.S. states. This study improves our understanding of pile resistance responses in CG-IGM and results in pile design recommendations. Unit shaft resistance (q_s) of CG-IGM increases with the ratio of effective vertical stress (${\sigma }_v^{\prime }$) to the ratio of corrected N-value, (N₁)₆₀. Unit end bearing (q_b) increases with the ratio of. corrected N-value, (N₁)₆₀ to the effective vertical stress (${\sigma }_v^{\prime }$). New SA methods are developed for predicting q_s and q_b. The proposed SA methods are compared against existing β-method developed for coarse grained soil and validated using an independent pile load test dataset. Pile setup is observed in q_s of piles driven in CG-IGMs, and pile relaxation is mostly observed in q_b. Statistical assessment concludes that the proposed SA methods provide more accurate and consistent q_s and q_b predictions than that by the β-method.

To make up for the shortcomings of single-pile composite foundations, combined composite foundations are increasingly used in engineering. However, studies for the consolidation theory of composite foundations reinforced by high replacement ratio gravel piles and vertical drains, in which the radial flow within gravel piles is considered, have been rarely reported in the literature. The establishment of a comprehensive composite foundation consolidation model is of significance for more reasonable design for stone columns and vertical drains, such as penetration depth, replacement ratio, distribution pattern and so on. Therefore, to solve such consolidation issues, a gravel pile-soil unit with several vertical drains around the perimeter is regarded as a calculation model. Then, the related analytical solution to the total average express pore water pressure (EPWP) is derived by considering the radial flow within gravel piles, and the reliability is verified by comparison with existing solutions. Moreover, extensive calculations are made to investigate the consolidation behaviors, and the results show that vertical flow in soils has little effect on the consolidation of this composite foundation; the effect of radial flow within high replacement ratio gravel piles is nonnegligible; installing vertical drains between piles can enhance the consolidation rate. Finally, the model is applied to the settlement calculation of an embankment in Malaysia, and the results by proposed solutions are in good agreement with the measured data, further indicating the applicability of the calculated model.

Element tests, such as water retention tests and triaxial tests, are efficient and widely used methods for investigating the elementary hydro-mechanical behavior of unsaturated soil. In recent research, discrepancies observed in unsaturated test results using axis-translation techniques (ATTs) with ceramic disks and microporous membrane filters (MM filters) have indicated that misunderstandings might be hiding behind the perceived elementary behavior seen in element tests. In this study, triaxial tests with ceramic disks and MM filters were firstly conducted on specimens of unsaturated completely decomposed granite sand, referred to as Masado in Japan, to compare the influence of different techniques on the test results. Then a soil–water-air coupled finite element-finite difference (FE-FD) method, based on a newly proposed unsaturated/saturated constitutive model coupled with a deformation-dependent water retention curve (WRC), was utilized to simulate triaxial tests as boundary value problems (BVPs) because of the non-uniform deformation of the specimens. Drained/vented triaxial tests showed that the stress–strain relation of Masado is basically the same regardless of the applied technique, while the amount of drainage discharge and degree of saturation during the shearing stage are quite different. The calculated average stress–strain relation basically reproduced a tendency similar to that of the tests. It was also shown from the calculation that the ATT with ceramic disks or MM filters significantly influences the distributions of saturation and stress within the specimens during shearing. It should be emphasized that unsaturated triaxial tests with the ATT are basically BVPs instead of so-called element tests.

Granular flow is affected by multiple parameters, which makes its study challenging. The discrete element method (DEM) is widely employed to simulate granular flow in consideration of particle motion, particularly when the effects of related parameters and particle shape on flow characteristics are being studied. In this study, different combinations of four input parameters (spring coefficient, friction angle between elements, coefficient of restitution, and bottom friction) were first obtained with the help of the Latin hypercube sampling method. Then, a series of simulations were performed using DEM with different sets of input parameters in consideration of different particle shapes and contact models. Radial basis function (RBF) interpolation was then employed to construct a response surface of run-out distance. Monte Carlo simulations were also conducted to obtain the contribution ratio of each input parameter. The result revealed that the bottom friction has a significant influence on the run-out distance, while friction angle between elements and spring coefficient account for a small proportion in the contribution ratio. Moreover, it was confirmed that the coefficient of restitution has a considerable contribution ratio in the front part of elements. The results also revealed that the influence of the particle shape and contact model on the contribution ratio was not as important in comparison.

The paper presents an iterative approach based on stochastic simulations and adaptive Kriging metamodels to perform reliability and safety assessments of soil slopes. Two new rules for adaptively selecting support points are proposed, considering an entropy learning function and the closeness to the failure domain defined by a limit state function. In addition, a stopping criterion is proposed based on root-mean-square and mean absolute percentage errors computed with cross-validation at the local level, focusing on regions where the uncertainties are relevant. Finally, the selection rules for support points and the error metrics are implemented in two benchmark problems with a low, moderate, and high probability of failure. Ultimately, the work leads to an adaptive Kriging strategy for slope stability assessment, offering: (1) a fair comparison with other strategies based on a significant number of realizations, (2) a stopping criteria based on a new local error metric, (3) an insight of the behavior across different magnitudes of the probability of failure, and (4) a new selection rule that reduces the total number of support points significantly. The proposed scheme is easily paired with commercial software to compute support points, resulting in an attractive tool for practitioners.

Surface settlement due to tunnel excavation is affected by several factors. However, no explicit mapping correlation exists between surface settlement and the main influencing factors. In this study, three tree-based methodologies, including classification and regression tree (CART), random forest (RF), and gradient boosting decision tree (GBRT), were implemented to predict the tunneling-induced surface settlement of the South Hong-Mei Road tunnel in Shanghai, where a large mix-shield was used. Thirteen influencing factors within three categories (tunnel geometry, geological conditions, and shield operation factors) were employed as input variables. Results show that the ensemble methods (RF and GBDT) provide superior performance over the single-tree model (CART). Moreover, GBDT has the highest level of prediction accuracy among the three statistical learning methods. The importance of influencing factors on the tunneling-induced surface settlement was probed. The tunnel geometry had the greatest effect on surface settlement. It is followed by the influencing factors in shield operation factors. Moreover, geological conditions were not as influential as the other influencing factors. The outcomes of this study may provide a reference for evaluating tunneling-induced surface settlement in other similar tunnel projects.

Based on previous studies on the seismic monitoring of isolated (IS) and non-isolated (NI) buildings supported by piled rafts with a DMW (deep mixing wall) grid, under similar soft-soil conditions during the 2011 Tohoku earthquake, the effects of kinematic and inertial forces on the piled rafts, for which the natural periods of the superstructures were significantly different, were investigated. To evaluate the degree of contribution of the kinematic and inertial forces on the maximum bending moments and incremental axial forces near the pile heads, the coefficients related to the kinematic and inertial forces were presented. The coefficients of inertial force were separated into those of the superstructure and raft inertias to consider the embedment effects. Furthermore, the mechanisms of the inelastic behavior of the settlement and the load transfer in the piled raft systems, observed during the principal motion, were discussed. Consequently, it was found that the ratio of the natural period of the soil-pile-structure system to the predominant period of the ground, T_s/T_g, plays an important role in the contribution of the kinematic and inertial forces to the maximum bending moments near the pile head. Moreover, the T_s/T_g values were seen to be closely related to the differences in the inelastic settlement and load transfer mechanisms of the piled raft systems.