Journal Published Online: 02 June 2023
Volume 51, Issue 6

Effects of Basement Excavation and Raft Loading on Urban Tunnel in Sand: Model Testing and Analysis

CODEN: JTEVAB

Abstract

This paper describes an experimental investigation carried out in the laboratory to examine the effects of basement raft excavation and loading on an existing tunnel in Yamuna sand. A small-scale testing facility was designed to simulate the process of basement excavation and installation of basement raft with retaining wall in close vicinity to an existing tunnel. A simplified tunnel excavation system was also designed to simulate tunnel-excavation–induced stresses. Dimensions of model tunnel, sheet pile wall, basement raft, and retaining wall were arrived at after applying the physical scaling laws on prototype dimension using a scale factor of 40. The dimensions of the tunnel and raft foundation were decided based on the stressed zone of soil mass from the edge of the foundation and tunnel periphery. Experiments were performed for different geometrical configurations of raft and tunnel. Results indicate that the circumferential and longitudinal strains at different locations of tunnel lining are significantly affected by various stages of construction/excavation and raft loading. This effect is seen more at crown level when the distance between tunnel and raft is short. The critical zone of influence is found in the region enclosed such that the raft loading is at a clear distance equal to diameter of the tunnel on either side of tunnel axis and strains in tunnel lining are measured up to three times the tunnel diameter on either side from the center line of raft loading. Results further indicate that the magnitude of circumferential strain induced at different cross sections of the lining is larger than the magnitude of longitudinal strain. A numerical analysis was conducted to simulate the experiments using PLAXIS 3D, which fairly predicted the measured phenomena. Thus, it is recommended that the site-specific quantification of the influence of new construction on tunnel lining is very much essential.

Author Information

Mahajan, Sumeet
RITES Ltd., Gurgaon, India
Sharma, Krishan Gopal
Department of Civil Engineering, Indian Institute of Technology Delhi, Hauz Khas, New Delhi, India
Ayothiraman, Ramanathan
Department of Civil Engineering, Indian Institute of Technology Delhi, Hauz Khas, New Delhi, India
Pages: 26
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Stock #: JTE20220660
ISSN: 0090-3973
DOI: 10.1520/JTE20220660