Estimating strut forces for excavation support systems

• Main Author: Bernard, Hendrie.
• Other Authors: Goh Teck Chee, Anthony
• Format: Final Year Project
• Language: English
• Published: 2013
• Subjects: DRNTU::Engineering::Civil engineering::Geotechnical
• Online Access: http://hdl.handle.net/10356/53854
• Institution: Nanyang Technological University

Braced excavation has been widely used for basement and other infrastructure projects in Singapore. The supporting system is carried out using struts which are preloaded after the connection to the waler takes place. The struts are monitored regularly to check the deformation of the steel in order to prevent any failure in the supporting system. Several studies have been proposed in measuring the strut loads where the Peck's Apparent Pressure Diagram or APD is commonly used in design. In this study, the strut forces are estimated using the finite element software called PLAXIS 2D. The study is conducted under various cases which are expected to govern the pressure distribution. A comparison against the APD is done in order to check the consistency of the semi - empirical method. The aspects that are examined are the wall stiffness, the depth to the hard stratum, embedment length of the wall, and the soil strength. In addition, a phi-c reduction is carried out to calculate their safety factor. The results show that the pressure distribution is influenced by the wall stiffness where stiffer wall will yield a larger pressure distribution which may cause an under estimation of the strut force using the APD. The thickness of the soft clay below the excavation also affects the profile of the strut forces. Since the stiff clay layer below the soft clay helps to restrain wall deformation, the strut forces exerted on the wall are smaller. The pressure distribution is reduced when the soft clay layer thickness is reduced. Furthermore, the embedment length is found to have no influence on the pressure distribution. Wall analyses also show a significant influence of the soil strength whereby lower strength will result in higher strut forces.