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Volume 11, Number 1, July 2016

The finite element method (FEM), discrete element method (DEM), and Discontinuous deformation analysis (DDA) are among the standard numerical techniques applied in computational geo-mechanics. However, in some cases there no possibility for modelling by traditional finite analytical techniques or other mesh-based techniques. The solution presented in the current study as a completely Lagrangian and mesh-free technique is smoothed particle hydrodynamics (SPH). This method was basically applied for simulation of fluid flow by dividing the fluid into several particles. However, several researchers attempted to simulate soil-water interaction, landslides, and failure of soil by SPH method. In fact, this method is able to deal with behavior and interaction of different states of materials (liquid and solid) and multiphase soil models and their large deformations. Soil indicates different behaviors when interacting with water, structure, instrumentations, or different layers. Thus, study into these interactions using the mesh based grids has been facilitated by mesh-less SPH technique in this work. It has been revealed that the fast development, computational sophistication, and emerge of mesh-less particle modeling techniques offer solutions for problems which are not modeled by the traditional mesh-based techniques. Also it has been found that the smoothed particle hydrodynamic provides advanced techniques for simulation of soil materials as compared to the current traditional numerical methods. Besides, findings indicate that the advantages of applying this method are its high power, simplicity of concept, relative simplicity in combination of modern physics, and particularly its potential in study of large deformations and failures.

Key Words
SPH (smoothed particle hydrodynamics); mesh-free methods; numerical modelling; soil; interaction; large deformation; failure

(1) Hamed Niroumand:
Department of Civil Engineering, Buein Zahra Technical University, Buein Zahra, Qazvin, Iran;
(2) Mohammad Emad Mahmoudi Mehrizi:
Department of Civil Engineering, Islamic Azad University of Central Tehran Branch, Tehran, Iran;
(3) Maryam Saaly:
Department of Civil Engineering, Faculty of Civil Engineering Amirkabir University of Technology, Tehran, Iran.

This paper focuses on the deformation behavior of tunnels crossing a weak zone in conventional tunneling. A three-dimensional finite element model was adopted that allows realistic modeling of the tunnel excavation and the support installation. Using the 3D FE model, a parametric study was conducted on a number of tunneling cases with emphasis on the spatial characteristics of the weak zone such as the strike and dip angle, and on the initial stress state. The results of the analyses were thoroughly examined so that the three-dimensional tunnel displacements at the tunnel crown and the sidewalls can be related to the spatial characteristic of the weak zone as well as the initial stress state. The results indicate that the effectiveness of the absolute displacement monitoring data as early warning indicators depends strongly on the spatial characteristics of the weak zone. It is also shown that proper interpretation of the absolute monitoring data can provide not only early warning for a weak zone outside the excavation area but also information on the orientation and the extent of the weak zone. Practical implications of the findings are discussed.

Key Words
conventional tunneling; finite element analysis; absolute displacement monitoring; weak zone; deflection line; displacement ratio

School of Civil, Architectural Engineering and Landscape Architecture, Sungkyunkwan University, 2066 Seboo-ro, Jangan-gu, Suwon, Kyounggi-do 16419, Republic of Korea.

Penetration problems in geomechanics are common. Usually the soil is heavily disturbed around the penetrating bodies and large deformations and distortions can occur. The simulation of the installation of displacement piles is a good example of the interest of these types of problems for geomechanics. In this paper the Material Point Method is used to overcome the difficulties associated with the simulations of problems involving large deformation and full displacement type penetration. Recent modifications of the Material Point Method known as Generalized Interpolation Material Point and the Convected Particle Domain Interpolation are also used and evaluated in some of the examples. Herein a footing submitted to large settlements is presented and simulated, together with the processes associated to a driven pile under undrained conditions. The displacements of the soil surrounding the pile are compared with those obtained by the Small Strain Path Method. In addition, the Modified Cam Clay model is implemented in a code of MPM and used to simulate the process of driving a pile in dry sand. Good and rather encouraging agreement is found between compared data.

Key Words
MPM; penetration problems; pile installation effects; large deformation; MCC; SSPM

(1) R. Lorenzo:
Department of Civil Engineering, Federal University of Tocantins, Av NS 15 Bala I, Palmas, Tocantins, Brazil;
(2) Renato P. da Cunha, Manoel P. Cordão Neto:
Department of Civil and Environmental Engineering, University of Brasilia, Campus Darcy Ribeiro, Asa Norte, Brasilia, Brazil;
(3) John A. Nairn:
Wood Science and Engineering, Oregon State University, Corvallis, OR 97331, USA.

A forked tunnel, as a special complicated underground structure, is composed of big-arch tunnel, multi-arch tunnel, neighborhood tunnels and separate tunnels according to the different distances between two separate tunnels. Due to the complicated process of design and construction, surrounding jointed rock mass stability of the big-arch tunnel which belongs to the forked tunnel during excavation is a hot issue that needs special attentions. In this paper, an elasto-plastic damage constitutive model for jointed rock mass is proposed based on the coupling method considering elasto-plastic and damage theories, and the irreversible thermodynamics theory. Based on this elasto-plastic damage constitutive model, a three dimensional elasto-plastic damage finite element code (D-FEM) is implemented using Visual Fortran language, which can numerically simulate the whole excavation process of underground project and perform the structural stability of the surrounding rock mass. Comparing with a popular commercial computer code, three dimensional fast Lagrangian analysis of continua (FLAC3D), this D-FEM has advantages in terms of rapid computing process, element grouping function and providing more material models. After that, FLAC3D and D-FEM are simultaneously used to perform the structural stability analysis of the surrounding rock mass in the forked tunnel considering three different computing schemes. The final numerical results behave almost consistent using both FLAC3D and D-FEM. But from the point of numerically obtained damage softening areas, the numerical results obtained by D-FEM more closely approach the practical behaviors of in-situ surrounding rock mass.

Key Words
jointed rock mass; forked tunnel; stability analysis; D-FEM; FLAC3D

(1) Hanpeng Wang, Yong Li, Shucai Li, Qingsong Zhang:
Geotechnical & Structural Engineering Research Center, Shandong University, No. 17923 Jingshi Rd., Jinan, Shandong Province, P.R. China 250061;
(2) Yong Li, Jian Liu:
School of Civil Engineering, Shandong University, No. 17922 Jingshi Rd., Jinan, Shandong Province, P.R. China 250061.

A novel higher order shear-deformable beam model, which provides linear variation of transversal normal strain and quadratic variation of shearing strain, is proposed to describe the beam resting on foundation. Then, the traditional two-parameter Pasternak foundation model is modified to capture the effects of the axial deformation of beam. The Masing.s friction law is incorporated to deal with nonlinear interaction between the foundation and the beam bottom, and the nonlinear properties of the beam material are also considered. To solve the mathematical problem, a displacement-based finite element is formulated, and the reliability of the proposed model is verified. Finally, numerical examples are presented to study the effects of the interfacial friction between the beam and foundation, and the mechanical behavior due to the tensionless characteristics of the foundation is also examined. Numerical results indicate that the effects of tensionless characteristics of foundation and the interfacial friction have significant influences on the mechanical behavior of the beam-foundation system.

Key Words
nonlinear quasi-static analysis; Pasternak foundation; Masing.s friction law; higher order beam model; finite element method

(1) Guanghui He, Rong Lou:
School of Maritime and Civil Engineering, Zhejiang Ocean University, Zhoushan, China;
(2) Xiaowei Li:
Songjiang Campus of Shanghai Open University, Shanghai, China.

Previous studies for soil movements induced by tunneling have primarily focused on the free soil displacements. However, the stiffness of existing structures is expected to alter tunneling-induced ground movements, the sheltering influences for underground structures should be included. Furthermore, minimal attention has been given to the settings for the shield machine's operation parameters during the process of tunnels crossing above and below existing tunnels. Based on the Shanghai railway project, the soil movements induced by an earth pressure balance (EPB) shield considering the sheltering effects of existing tunnels are presented by the simplified theoretical method, the three-dimensional finite element (3D FE) simulation method, and the in-situ monitoring method. The deformation prediction of existing tunnels during complex traversing process is also presented. In addition, the deformation controlling safety measurements are carried out simultaneously to obtain the settings for the shield propulsion parameters, including earth pressure for cutting open, synchronized grouting, propulsion speed, and cutter head torque. It appears that the sheltering effects of underground structures have a great influence on ground movements caused by tunneling. The error obtained by the previous simplified methods based on the free soil displacements cannot be dismissed when encountering many existing structures.

Key Words
shield tunneling; stiffness influence; shield propulsion parameters; simplified theoretical method; 3D FE numerical simulation; case study

(1) Zhi-guo Zhang:
School of Environment and Architecture, University of Shanghai for Science and Technology, 516 Jungong Road, Shanghai 200093, China;
(2) Zhi-guo Zhang, Qi-hua Zhao:
State Key Laboratory of Geohazard Prevention and Geoenvironment Protection, Chengdu University of Technology, Chengdu 610059, China;
(3) Zhi-guo Zhang:
Key Laboratory of Geohazard Prevention of Hilly Mountains, Ministry of Land and Resources, Fuzhou 350002, China;
(4) Meng-xi Zhang:
Department of Civil Engineering, Shanghai University, Shanghai 200072, China.

This study elucidates the uplift behaviors of the straight-sided and belled shafts. The field uplift load tests were carried out on 18 straight-sided and 15 belled shafts at the three collapsible loess sites under an arid environment on the Loess Plateau in Northwest China. Both the site conditions and the load tests were documented comprehensively. In general, the uplift load.displacement curves of the straight-sided and belled shafts approximately exhibited an initial linear, a curvilinear transition, and a final linear region, but did not provide a well defined peak or asymptotic value of the load, and therefore their uplift resistances should be interpreted from the load test results using an appropriate criterion. Nine representative uplift resistance interpretation criteria were used to define the "interpreted failure load" for each of the load tests, and all of these interpreted uplift resistances were normalized by the failure threshold, TL2, obtained using the L1-L2 method. These load test data were compared statistically and graphically. For the straight-sided and belled shafts, the normalized uplift load.displacement curves were respectively established by the plots that related the mean interpreted uplift resistance ratio against the mean displacement at the corresponding interpreted criteria, and the comparisons of the normalized load.displacement curves were made. Specific recommendations for the designs of uplift belled and straight-sided shafts in the loess were given, in terms of both capacity and displacement.

Key Words
loess; pullout testing; straight-sided shafts; belled shafts; transmission tower; load test; ultimate load

(1) Zeng-zhen Qian:
School of Engineering and Technology, China University of Geosciences, No. 29 Xueyuan Road, Haidian District, Beijing, 100083, China;
(2) Xian-long Lu, Wen-zhi Yang, Qiang Cui:
China Electric Power Research Institute, No. 15, Xiaoying East Road, Haidian District, Beijing, 100192, China.

A series of experimental studies are conducted on the deformation and shear strength property of compacted loess. The results reveal that the relationships of both the initial moisture content (w) and the initial degree of compaction (K) of compacted loess with cohesion (w) and the angle of internal friction (φ) are linear. The relationship between the secant modulus (Esoi) and K is also linear. The relationship between Esoi and w can be fitted well by a second-order polynomial. Further, when the influences of w and K are ignored, the relationship between the confined compression strain (ε) and vertical pressure (p) can be expressed by a formula. A correction formula for the deformation of compacted loess caused by a change in w and K is derived on the basis of the study results.

Key Words
compacted loess; shear strength; deformation property; deformation correction formula

(1) Yuan Mei, Chang-Ming Hu, Yi-Li Yuan, Xue-Yan Wang, Nan Zhao:
College of Civil Engineering, Xi'an University of Architecture and Technology, Xi'an, China;
(2) Xue-Yan Wang:
College of Environmental and Chemical Engineering, Xi'an Polytechnic University, Xi'an, China.

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