Field Monitoring And Numerical Analysis Of Ground Movements Due To Diaphragm Wall Installation

With the development of the urban public facilities, a large number of high-rise buildings and underground buildings were being built. The depth, scale, difficulty of the foundation pit rapidly increased, bringing new challenges to the design and construction. In addition, recently, foundation pit damages emerged frequently. Foundation pit engineering need more detailed and comprehensive studies in terms of the whole process of construction.The diaphragm wall with strong stiffness and good integrity are usually used as retaining structures where the displacements caused by the deep foundation construction need to be strictly confined. Generally, the displacements of the soil caused by the retaining structures construction are extraordinarily small, and therefore, are not calculated during the design. However, in many projects, the measured data showed that the impact induced by construction of foundation pit is very significant and can not be neglected.This paper presents a project of diaphragm wall installation. The monitoring lasted nearly 10 months. In the south of deep foundation, there are four monitoring sections and each section has a set of observing points such as inclinometers, pore pressure gauges, etc.The field data showed that diaphragm wall installation had a significant impact on the ground movements and pore pressure. After the completion of the diaphragm wall, a horizontal deformation away from the trench was observed, this is primarily because the soil lateral pressure coefficient of Tianjin is small(less than 1). During the excavation of the diaphragm wall, the pore pressure of the soil near the trench decreased as a result of unloading. When the concreting process completed, the pore water pressure rose rapidly due to the loading effect.A three-dimensional finite element model was estabilished to simulate the diaphragm wall installation and to verify the field data obtained during the construction of the diaphgram wall. A series of analyses on the ground movements were carried out in view of different contruction conditions, such as the existence of the deep cement mixing piles(different depth), the existence of the ground buildings(different heights and distances from the wall).Based on Mindlin solution, the elasticity solution of horizontal displacements of the soil caused by the diaphragm wall construction was proposed. The variable parameters are the Poisson's ratio, elastic modulus of the soil and depth of the diaphragm wall. The calculation formula is well simplified and is expected to be used in the future projects.