Maosong Huang

Bio: Maosong Huang is an academic researcher from Tongji University. The author has contributed to research in topics: Pile & Geotechnical engineering. The author has an hindex of 26, co-authored 143 publications receiving 2120 citations. Previous affiliations of Maosong Huang include Chinese Ministry of Education & Jingdezhen Ceramic Institute.

Strength reduction FEM in stability analysis of soil slopes subjected to transient unsaturated seepage

Abstract: The instability of soil slopes induced by the fluctuation of water level or rainfall has received much attention in the literature recently and the failure mechanism is closely related to the change of matric suction of unsaturated soils. Such a change is basically induced by unsaturated transient seepage. The traditional approach for estimating the stability of slopes subjected to unsaturated transient seepage is based on the limit equilibrium method (LEM). The limit equilibrium approach is limited by assumptions about analysis method and failure mechanism. In order to overcome those limitations, a finite element method with shear strength reduction technique (SSRFEM) has been successfully applied to the slope stability analysis in absence of seepage. The main objective of this paper is to extend the use of the strength reduction FEM to include the effects of unsaturated transient seepage and some primary numerical results concerning the stability of an earth dam under rapid drawdown are presented. Emphasis has been given to comparison of the safety factors obtained by LEM and SSRFEM. Topics for the further research in this area are also suggested.

Geotechnical influence on existing subway tunnels induced by multiline tunneling in Shanghai soft soil

Abstract: Multiline tunneling construction in soft soil significantly impedes risk control and environmental protection. Current research has investigated on the effect of single-line shield excavation on surrounding environments and tunneling for parallel-crossing or perpendicular down-crossing underground structures. However, minimal attention has been given to soil disturbances induced by multiline tunneling and complex overlapped interaction mechanics for adjacent structures, such as existing above-crossing and down-crossing subway tunnels. Few studies focus on oblique crossing construction and setting rules for the operation parameters of shield machines. Based on the Shanghai Railway transportation project and in situ monitoring data, the deformation analyses of existing subway tunnels induced by an earth pressure balance (EPB) shield during the process of above-overlapped and down-overlapped crossing tunnels with oblique angles are presented. The deformation analyses employ the three-dimensional finite element (3D FE) numerical simulation method, and the simplified analytical method. The analysis results from the theoretical methods are consistent with the monitoring data. The setting rules of multiline propulsion main parameters, including the earth pressure for cutting open, and the synchronized grouting, are also established. This study may provide a theoretical basis for the development of properly overlapped crossing schemes and geotechnical protective measures during multiline tunneling construction in soft soil.

Evaluation of deformation response for adjacent tunnels due to soil unloading in excavation engineering

Abstract: A major challenge in the design and construction of soil excavation and foundation pit engineering in urban areas is the protection of adjacent underground structures, such as existing tunnels. Excavation-induced soil unloading can adversely affect and even damage the tunnels in the vicinity. A simplified analytical approach is presented to analyze the deformation response for adjacent tunnels due to excavation-induced soil unloading in excavation engineering. Firstly, the green soil unloading stress due to adjacent excavation is estimated at the existing tunnel location. Secondly, the deformation response of the tunnel subjected to green soil unloading stress is calculated by the Galerkin’s method, which can be used to obtain the finite element equation converted from the differential equation. The accuracy of the proposed method is verified by comparisons with 3D finite element numerical simulation, centrifuge model tests provide by Kusakabe et al. (1985) and measured data in situ. Finally, the parametric analysis for deformation influence factors of the existing tunnel, including the tunnel buried depth, the distance from the excavation site, the soil geo-characters and the outer diameter of the tunnel, is presented to demonstrate the performance of the proposed method. This proposed method may provide certain basis to make protective measures of existing tunnels influenced by excavation engineering and enables a quick estimate of the deformation behavior of excavation-induced adjacent tunnels, resulting in savings in time and costs.

DEM investigation on the evolution of microstructure in granular soils under shearing

Abstract: The mechanical behaviors of granular soils at different initial densities and confining pressures in the drained and undrained triaxial tests are investigated micromechanically by three-dimensional discrete element method (DEM). The evolutions of the microstructure in the numerical specimen, including coordination number, contact force and anisotropies of contact normal and contact force, are monitored during the shearing. The typical shear behaviors of granular soils (e.g. strain softening, phase transformation, static liquefaction and critical state behavior) are successfully captured in the DEM simulation. It is found that the anisotropies of contact normal, normal and tangential contact forces comprise the shear resistance and show different evolution features during shearing. After large strain shearing, the microstructure of the soil will finally reach a critical state, although the evolution path depends on the soil density and loading mode. Similar to the macroscopic void ratio $$e$$ and deviatoric stress $$q$$ , the coordination number and anisotropies of contact normal and contact force at the critical state also depend on the mean normal effective stress $$P^{\prime }$$ at the critical state.

Simplified analytical method for evaluating the effects of adjacent excavation on shield tunnel considering the shearing effect

Abstract: Adjacent excavations may have adverse impacts on the existing tunnels. Due to the increasing demand for building excavations in close proximity to existing metro tunnels, ensuring the safety and integrity of tunnel structures is a major challenge for city designers and geotechnical engineers. Urban metro tunnels in soft areas of Chinese cities are often constructed using shield tunnelling technology, and the installed precast reinforcement concrete segmental lining are generally connected together by various steel bolts. Due to the presence of joints, the overall tunnel stiffness, including the bending stiffness and shearing stiffness, are significantly reduced. Due to the reduction in shearing stiffness, the tunnel longitudinal deformation can be decomposed into two distinct modes: a bending mode and a shearing dislocation mode. However, current methods for predicting tunnel longitudinal responses to adjacent excavations generally simplify a tunnel as an Euler-Bernoulli beam, which only considers the bending effect and ignores the shearing deformation of jointed tunnels. Moreover, tunnel-ground interactions are commonly considered through the Winkler foundation model, which is unable to account for the interactions of adjacent springs and leads to overestimations of shear forces and bending moments in shield tunnels. In this paper, a new analytical method is proposed that uses a Timoshenko beam to simulate jointed shield tunnel responses when subjected to an adjacent excavation, which can consider both the bending and shearing effects of a shield tunnel. The tunnel-ground interaction is considered by introducing Pasternak two-parameter foundation, which is able to further take account for the interaction between adjacent springs. The tunnel-excavation interaction is analyzed using a two-stage analysis method. First, the excavation-induced unloading stress on the existing tunnel is computed using Mindlin’s solution. Second, the tunnel longitudinal deformation due to the corresponding stress is calculated using finite difference method. The effectiveness of the proposed approach is validated by two well-document case histories, including finite element analysis and field measurement. The predicted results are also compared with those obtained using the traditional methods. Based on the verified analytical solution, a parametric analysis is also conducted to investigate the effects of key factors on the responses of existing tunnels, including excavation-tunnel relative position, ground Young’s modulus and equivalent shearing stiffness.

Discrete element models for non-spherical particle systems: From theoretical developments to applications

Abstract: A fundamental understanding of the underlying physics of granular (particulate) systems is not only of academic interest, but is also highly relevant for industrial applications Nowadays computational techniques, eg the discrete element method (DEM), are frequently applied as a tool to probe the behaviour of granular systems The DEM is a particularly attractive modelling technique since it can provide both macroscopic and microscopic ‘measurements’ in granular systems and allows particles of non-spherical shape to be modelled This ability is important since there is a common understanding that particle shape has a strong influence on the dynamics of these systems Here, we critically review recent developments in DEM to model particles of non-spherical shape The first section of the review is concerned with advances in the formulation and implementation of non-spherical particle models, including shape representation, algorithms for the efficient detection of contacts and the determination of contact parameters In the second part, we review the main findings obtained from numerical ‘measurements’ in granular systems containing non-spherical particles using the DEM The systems covered in this review include the packing of particles, particle flow (eg plane shear flow, the discharge of particles from hoppers and particle motion in vibrated beds and rotating cylinders) and two-phase particle flows such as gas–solid fluidized beds and pneumatic conveying We conclude with an outlook highlighting the future research needed to further advance this promising modelling technique

The signature of shear-induced anisotropy in granular media

Abstract: This paper presents a micro-mechanical study on the characteristics of shear-induced anisotropy in granular media. Based on three-dimensional Discrete Element Method (DEM) simulations, the distinct features associated with the evolution of internal granular structure and different anisotropy sources during drained/undrained shearing of granular samples are carefully examined. The study finds that static liquefaction occurs when the geometrical anisotropy in a sample dominates the mechanical anisotropy in the overall shear strength, and the weak force network features an exceptionally high proportion of sliding contacts and develops certain degree of anisotropy. Phase transformation corresponds to a transitional, unstable state associated with a dramatic change in both coordination number and the proportion of sliding contacts in all contacts. The critical state in a granular material is always associated with a highly anisotropic fabric structure wherein both the critical void ratio and critical fabric anisotropy are uniquely related to the mean effective stress. The relations provide a more comprehensive definition for the critical state in granular media with proper reference to the critical fabric anisotropy.

Soil–environment interactions in geotechnical engineering

Abstract: The range of problems that geotechnical engineers must face is increasing in complexity and scope. Often, complexity arises from the interaction between the soil and the environment – the topic of this lecture. To deal with this type of problem, the classical soil mechanics formulation is progressively generalised in order to incorporate the effects of new phenomena and new variables on soil behaviour. Recent advances in unsaturated soil mechanics are presented first: it is shown that they provide a consistent framework for understanding the engineering behaviour of unsaturated soils, and the effects of suction and moisture changes. Building on those developments, soil behaviour is further explored by considering thermal effects for two opposite cases: high temperatures, associated with the problem of storage and disposal of high-level radioactive waste; and low temperatures in problems of freezing ground. Finally, the lecture examines some issues related to chemical effects on soils and rocks, focusing i...

Closure of "Static Instability and Liquefaction of Loose Fine Sandy Slopes"

Abstract: Soils that exhibit nonassociated flow may, according to stability postulates by Drucker and by Hill, become unstable when exposed to certain stress paths inside the failure surface. Series of conventional triaxial tests on fully saturated and on partly saturated specimens were performed under drained and undrained conditions to study the regions of stable and unstable behavior. For specimens that compress and have degrees of saturation higher than critical, undrained conditions lead to effective stress paths directed within the region of potential instability, and instability was observed provided the yield surface opens up in the outward direction of the hydrostatic axis. Thus, instability occurs inside the failure surface. Instability is not synonymous with failure, although both may lead to catastrophic events. The location of the instability line is discussed. Examples of a shallow submarine slope and a nearly fully saturated steeper slope representing a tailings dam, which both should remain stable a...

Prediction of seismic slope stability through combination of particle swarm optimization and neural network

Abstract: One of the main concerns in geotechnical engineering is slope stability prediction during the earthquake. In this study, two intelligent systems namely artificial neural network (ANN) and particle swarm optimization (PSO)---ANN models were developed to predict factor of safety (FOS) of homogeneous slopes. Geostudio program based on limit equilibrium method was utilized to obtain 699 FOS values with different conditions. The most influential factors on FOS such as slope height, gradient, cohesion, friction angle and peak ground acceleration were considered as model inputs in the present study. A series of sensitivity analyses were performed in modeling procedures of both intelligent systems. All 699 datasets were randomly selected to 5 different datasets based on training and testing. Considering some model performance indices, i.e., root mean square error, coefficient of determination (R2) and value account for (VAF) and using simple ranking method, the best ANN and PSO---ANN models were selected. It was found that the PSO---ANN technique can predict FOS with higher performance capacities compared to ANN. R2 values of testing datasets equal to 0.915 and 0.986 for ANN and PSO---ANN techniques, respectively, suggest the superiority of the PSO---ANN technique.