Parametric Study in the Soil Structure Interaction of a Diaphragm Wall Type Berthing Structure

Abstract

Berthing structure is one of the most essential facility required in ports and harbours. Diaphragm wall provides structural support and water tightness to the berthing structure by retaining the back fill soil. Large earth pressure and water loads result massive and costly construction. It is required to examine an innovative wall system that is more cost effective than traditional wall systems. The study of soil-structure interaction is essential to understand the behaviour of wall under static and dynamic loading conditions. The performance of the anchored diaphragm wall depends on the wall stiffness, embedded depth of wall, type of anchor and its location and the type of loads acting on the wall. Study of the effect of construction stages on the performance of wall is important for the safer wall installation. The difference in stiffness of the wall causes redistribution of stresses and consequent reduction in displacement and bending moment. The present study analyses the diaphragm wall without anchor, and with anchor at varying locations for static and dynamic loading conditions. The study is also extended for a diaphragm wall with varying stiffness. To study such behavior, finite element based software Plaxis 2D and 3D are adopted in the present study. In Plaxis 2D static and dynamic analysis are carried out to obtain the maximum displacement, shear force and bending moment of a diaphragm wall with and without anchor. Similarly, in Plaxis 3D, static analysis are carried to find maximum displacement, shear force and bending moment for the diaphragm wall with and without anchor. Analysis is undertaken to study the effects of construction sequences and effect of stiffness by varying the stiffness of the wall within the sections. To study the effect of stiffness on the behavior of diaphragm wall, static analysis is carried on uniform and non-uniform sections. Seven different diaphragm wall sections, section1 and sections 2, 3, 4, 5, 6 & 7, having uniform and non-uniform configurations respectively, are modelled and the results are compared with the actual section. In Plaxis 2D static analysis, the maximum displacement, shear force and bending moment are reduced by 91.79%, 11.69% & 57% respectively, when anchor is introduced in the diaphragm wall. In Plaxis 2D dynamic analysis for the case with anchor, the maximum value of displacement, shear force and bending moment are increased by 7.2%, 10% & 13.5%) with respect to static analysis. The maximum values of displacement, shear force & bending moment obtained in Plaxis 2D are higher by 22.82%, 15.43% & 17.98% when compared with Plaxis 3D results. The maximum bending moment obtained in Plaxis 3D analysis for anchored diaphragm wall for the case without considering the construction stage is reduced by 59.6% and in Plaxis 2D, it is 54.41%, when compared to the maximum bending moment obtained by considering the construction stage for the anchor location at +4.5 m. Even though the stiffness of section 1 is 83.77% less than that of actual section, displacement for section 1 is increased by 70.2%, and bending moment is reduced by 46.44% when compared with the actual section. Maximum displacement and bending moment are found corresponding to anchor location +4.5 m. Both displacement and bending moment are found minimum at anchor location -6 m. The displacement of the T section is reduced by 47.9%, 43.5% & 38.4% for anchor location +4.5m, +2.5m and 0 m respectively when compared to actual section. Similarly, the bending moment for T section is reduced by 82.6%, 80.14% & 81.6% respectively, for the same anchor locations. The analysis of section 4 & 5 shows that rigid concrete panel is susceptible to higher bending moment when flexible pile is introduced in between rigid RCC wall. When the two sections of different stiffness are coupled to form a single section, the stiffer member is taking higher bending moment. In the present investigation validation of analysis, results are carried by comparing the results obtained by empirical models, case studies having analytical and numerical results and field measured data of similar case studies.