NUMERICAL ANALYSIS OF COMPOSITE SOIL NAILING RETAINING WALL UNDER EARTHQUAKE Tianzhong MA 1,2, Yanpeng ZHU 1,2 and Deju Meng 1,2

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1 Applied Mechanics and Materials Online: ISSN: , Vols , pp doi: / Trans Tech Publications, Switzerland NUMERICAL ANALYSIS OF COMPOSITE SOIL NAILING RETAINING WALL UNDER EARTHQUAKE Tianzhong MA 1,2, Yanpeng ZHU 1,2 and Deju Meng 1,2 1 Key Laboratory of Disaster Prevention and Mitigation in Civil Engineering of Gansu Province,Lanzhou University of Technology, Lanzhou , China; 2 Western Engineering Research Center of Disaster Mitigation in Civil Engineering of Ministry of Education, Lanzhou, PR China Keywords: Composite soil nailing; slope; earthquake action; dynamical response; Abstract:The seismic response of slope supported by composite soil nailing is analyzed by using finite element software ADNIA, in which the EL-Centro wave is selected as input earthquake wave.the analytical contents include the displacement and acceleration of supporting slope, as well as the time history responses of the axial forces of anchors. In the establishment of finite element model, the interaction between soil body and supporting structure is considered. The elastic-plastic M-C model with nonlinear static and dynamic behavior is used to simulate the soil body, and the dual linear strengthen model is adopted to simulate the supporting structure, then the interaction between soil body and supporting structure is simulated with contact element. The results show that the composite soil nailing slope supporting structure has better seismic performance than the general soil nailing slope supporting structure. The maximum horizontal displacement of the latter occurs at the slope top, but that of the former occurs at the slope upper. Especially after the imposition of the prestress, the slope displacement under earthquake reduces significantly, and the axial forces of anchors under earthquake enlarge significantly. Moreover, the axial forces of anchors reach maximum values near the slipping surface. The displacement and the acceleration of slope increase along the slope height. The conclusions obtained provide basis for the seismic design of permanent supporting slope and reference for similar projects. Introduction At present, for the dynamic analysis of pure slope under earthquake effect relatively large, but considering the dynamical study of supporting and retaining structures and slope collaborative working is very little. In recent years, some scholars began to do the theoretical research into this area, and obtained a great breakthrough.in 1997 Alampalli [1],and 1998 Koseki [2], Ramakrishnan [3],for the dynamic stability of retaining wall structure and the reinforced earth retaining wall structure make a large number of experimental research. In 2007,Dongjianhua and Zhuyanpeng [4, 8] established slope stability model of soil nailing under earthquake effect with the pseudo-static method, and analysis method of seismic stability of soil nailing slope has been improved by the combined with the vertical slice and horizontal slice method. With more and more high slope supporting applied to composite soil nailing with this flexible support structure.carry out the dynamic analysis and research of composite soil nailing structure under earthquake in loess areas, to ensure service safety of highway, railway and building,reducing landslide harms for highway, railway and building has great realistic meaning. The article adopts large nonlinear finite element analysis software ADINA to a slope deformation,acceleration and axial force of anchor boltof under earthquake action was calculation and parametric analysis. Considering soil structure interaction and support their work together, to create three-dimensional finite element model. Application of the nonlinear static and dynamic performance of elastoplastic model to simulate soil ;Adopting double linear elastoplastic model simulation supporting structure; Soil and supporting structure interaction simulation by contact element. Major analyzes the seismic response of slope displacement peak, peak acceleration and bolt after the input seismic wave,can be used as a reference for engineering design in future. All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of Trans Tech Publications, (ID: , Pennsylvania State University, University Park, USA-08/04/16,19:54:19)

2 1354 Applied Mechanics and Materials I Constitutive model of soil The soil generally is not a simple linear elastic material, the stress-strain relationship is much more complex than the linear elastic relationship. To truthfully express engineering problems, you have to use some non-linear form. About three categories defined soil constitutive relation [9,10,11].:(1)Curve fitting, interpolation or mathematical functions have been given the stress-strain curve;(2)nonlinear elastic model;(3)elastoplastic model. In this paper, the process of analysis and calculation is using elastic-plastic model. The input of the seismic wave In the finite element analysis, it is input different seismic waves, the derived seismic response may be a far cry from. Calculate the difference between the results due to the randomness of the ground motion and different seismic waves, during the power analysis to choose a reasonable seismic waves became an important guarantee for the reliability of calculated results. Select input earthquake accelerograms usually have proportion method and numerical method. Numerical method is divided into three: trigonometric series method, randomly pulse method and autoregressive method. The most common is trigonometric series method. In this paper, using the proportion method input seismic wave. Fig 1 and Fig 2 is used EL-Centro seismic waves, it through the proportion method obtaining horizontal and vertical acceleration time history. Fig 1 EL-Centro wave level of the waveform Fig 2 EL-Centro wave vertical waveforms Engineering examples The project is a slope supporting design of student dormitory about a University in Lanzhou City, The slope height as 10.0m, The slope importance coefficient as 1.0,the Soil nailing load partial coefficient as 1.25, The soil nailing tensile resistance partial coefficient as1.30, the Slope angle as The slope designs four-layer soil nailing and two-layer anchor, anchor designs in the second layer and the fourth layer, anchor added to prestress as100kn, detailed parameters is shown in Fig 3. Soil parameters is shown in table1 and table 2. geotechnical name Tab.1 Soil Parameters of Slope 3 severe kn/m cohesion c kpa miscellaneous fill silt silty clay gravel internal friction 0 angle

3 Applied Mechanics and Materials Vols Fig 3 Sectional view supporting structure with composite siol nailing Tab.2 Design Results of Composite Siol Nailing Retaining Wall for Static Support Soil nail / anchor Layer number horizontal interval/(m) altitude separation/ (m) The soil nail anchor and horizontal angle( ) anchorage body diameter /(mm) reinforcement diameter /(mm) Soil nail / bolt length/(m) Finite Element model Slope dynamic analysis, the object of study is a semi-infinite space. Finite element calculation object can only be a bounded domain, so you want to calculate the boundary approximation. Theorily, Farther away from the structure, the less side boundary wave reflection, the smaller the artificial boundary slope seismic dynamic response. Therefore, the position of the lateral boundary selection principle is to minimize the influence of the reflected wave on the boundary. Practices based on experience, is usually taken the slope depth range of 4 to 10 times the calculated area. Computing model herein taken to a height of 4-fold range of slope. Soil used a three-dimensional solid eight-node element. Its constitutive relation is elastic-plastic model, as Mohr - Coulomb yield criterion. Soil nail and anchor adopted rebar unit. The corresponding stress strain relation used elastic-plastic bilinear. Retaining plate used a three-dimensional solid eight-node unit. The retaining plate material is assumed to be linear elastic. Between the soil and retaining plate uses contact element. The bottom of the finite element model is assumed to be a fixed boundary. The seismic waves input from the bottom of the fixed boundary. The before and after borders of the finite element model assumes a slip boundary. Such reflection by the boundary vibration may affect the composite soil nailing slope dynamic response. The results show that this effect is small due to the large finite element analysis model of the grid and the damping effect of the soil in the earthquake. Model size of 40 m 1.5 m 20m, to establish the finite element model is shown in Fig 4 and Fig 5.

4 1356 Applied Mechanics and Materials I Fig 4 Dynamic analysis model Fig 5 Nail, bolt layout diagram Analysis of Results Anchor axial force change analysis Seen from Figures 6 and 7, the anchor axial force in the longitudinal direction is the middle is larger than at both ends, rendering zaohe shaped; significantly larger than the tail of the axial force of the anchor front portion, and generally appear in the middle (4.2m near). This is consistent with the theoretical analysis, indicating that the maximum axial force of the anchor occurs in the vicinity of the soil sliding rupture can be found at the same time, the anchor axial force significantly larger after the seismic waves, the first row of anchor axial force maximum value from the original 148kN increases to 179kN, an increase of 20%; second row anchor axial force maximum value from the original176kn increases to 204kN, an increase of 15%; maximum axial force is higher than the first row of the second row of anchor. Fig 6 Seismic waves before and after comparison in the Fig7 Seismic waves before and after first row of anchor axial force comparisonin the second row of anchor axial force Anchoring structure acceleration response As can be seen from Fig 8, along the slope each point in the height direction of the horizontal peak acceleration, positive and negative to peak acceleration value substantially symmetrical. The slope of the airport side of the peak displacement is greater than the peak displacement of the side of the slope. Along the slope in the slope after the amplitude of the respective positions from top to bottom are not equal, The difference between them so that the relative displacement between the soil, such a displacement of the anchoring structure of generating a large shearing deformation and destruction. In the slope height range, peak acceleration of the top of the slope, that is the seismic response of the ground soil near the most intense, so exciting force to bear in these parts is also the largest, and most prone to destruction.

5 Applied Mechanics and Materials Vols Fig8 Peak acceleration response Fig9 Shows the peak horizontal Anchor displacement response of the structure Seen from Fig 9,displacement of the seismic process slope along the depth direction of each node., the slope displacements peak is not at the top of the slope in the Earthquake process, but at a distance of the top of the slope 2.3m-4.6m between. This is consistent with the results obtained by theoretical analysis, is also set in the composite soil nailing will anchor the second floor to the fourth floor of reasons. Peak displacement of the engineering examples is at the height of 7.2m, displacement peak 11.5cm. Conclusions The results showed that the composite soil nailing slope supporting structure dynamic finite element analysis of composite soil nailing anchor structure better seismic performance than pure soil nail slope supporting structure, the ordinary soil nailing largest horizontal displacement occurred in the side-slope at the top, while the composite soil nailing retaining occurred in the upper part of the slope, applied prestressed-slope under earthquake displacement significantly reduced anchor axial force in the earthquake enlarge significantly, slip plane near the axial force, displacement and acceleration along the slope height is gradually increasing. This conclusion is to provide the basis for the permanent support of slope seismic design, and design reference for similar projects. Acknowledgements The authors would like to thanks the financial support by the National Science foundation of china ( ); the National Science foundation of Gansu Province(1112R2A009); the National key technology support program(2011bak12b07).

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