International Research Journal of Engineering and Technology (IRJET)
e-ISSN: 2395-0056
Volume: 09 Issue: 05 | May 2022
p-ISSN: 2395-0072
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Analysis of Design Parameters Affecting Deformation Behaviour of a Braced Excavation in Soft Clay: Numerical Study Saptarshi Roy1, D. Basu2, K. Dan3, R.B. Sahu4 1Research
Scholar, Department of Civil Engineering, Jadavpur University, West Bengal, Kolkata 700 032, India, Professor, Department of Civil and Environmental Engineering, University of Waterloo, 200 University Avenue West, Waterloo, ON N2L 3G1, Canada, 3Assistant Professor, Department of Civil Engineering, Cooch Behar Government Engineering College, West Bengal 736170 4Professor, Department of Civil Engineering, Jadavpur University, West Bengal, Kolkata 700 032, India. 2Associate
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Abstract - Adequate prediction of ground movement during braced excavation is critically important as excessive soil
displacement damage adjacent properties. Various factors like diaphragm wall thickness, wall embedment depth, strut locations influence the magnitudes and patterns of ground movement and wall deflection. In present paper an analysis of design parameters affecting deformation characteristics of braced excavation has been performed using finite element analysis. The importance of correct estimation of soil parameters for braced excavation design is also documented. The finite element analysis of typical braced excavations is implemented in soft clayey deposits using the software package Plaxis 2D, employing the soft soil creep constitutive model. On the basis of parametric investigation a design guideline is recommended which may be handy for design engineers.. Key Words: Finite element analysis, ground movement, soft soil creep model, excavation, wall deflection.
1.INTRODUCTION In the recent years, rapid infrastructure development and scarcity of space for new constructions in urban India have resulted in constructions such as underground commuter (metro) railway, tall buildings with multiple basement floors, tunnels, and similar other structures that require excavations to significant depths. These excavations require vertical sides with bracings (instead of sloped sides) for lack of space, and continuously braced wall structures are often used to ensure the stability of the excavations and to reduce the detrimental construction effects on the neighboring structures and underground utilities. Vertical cuts with bracings, if not properly designed, may lead to excessive ground movement and wall deflections, which may cause distress to neighboring structures. Therefore, ground movement and wall displacements should be estimated carefully and accurately while designing the braced excavation systems. Early studies on braced excavations were based on field observations, and those studies focused on excavation-base instability caused by bottom heave, lateral movement of support systems, ground settlement adjacent to excavations, effects of soil type and excavation geometry on the performance of the excavation system, and earth pressure on braced walls (Terzaghi 1943, Bjerrum and Eide 1956, Peck 1969, Lambe 1970, Goldberg et al. 1976). Lambe (1970) concluded that the state of the art for design and analysis of braced excavations was far from satisfactory, and suggested the use of finite element method in conjunction with field studies as the way forward for gaining proper understanding of deep excavation performance. Palmer et al (1972) evaluated influences of different variables on braced excavations where interaction and behaviour of soil and supporting materials were taken into consideration. From their observation it was found that soil deformation modulus, wall stiffness and strut stiffness have influence most on the behaviour of excavation. Other parameters like soil shear strength, initial in-situ stress, soil to wall adhesion have lesser impact. O’Rourke (1981) pointed out the importance of site preparation in ground excavation work and related the lateral movement of excavations to ground settlements, based on field observations. Clough and O’Rourke (1990) categorized movements in a braced cut into two types: movement related to excavation and support process, and movement related to auxiliary construction activities. Finno and Harahap (1991) simulated the construction of a 40-ft-deep braced excavation in saturated clays in Chicago by using a coupled finite element (FE) analysis. Tefera et al. (2006) studied the ground settlement and wall deformation of a sheet pile wall during different stages of excavation using a large-scale model test in dry sand bed and compared the results with those of FE analysis. Finno et al. (2007) used the FE software PLAXIS for conducting a parametric study to show the effects of excavation geometry on the deformation behaviour of soil around braced excavations. They observed that when the ratio of the excavated length to excavated depth of a wall is greater than 6, plane strain simulations yield the same displacements in the centre of the wall as those obtained from three-dimensional FE analysis. Hsiung (2009) investigated the deformation characteristics of several excavations in Kaohsiung, Taiwan, and found that the maximum lateral wall displacement (δhm) is approximately 0.03-0.3% of
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