Performance Evaluation of Deep Excavation with Diaphragm Wall in Congested Urban Landscape-Paper

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The paper describes the design and construction of a 17 m-deep excavation for a six-level basement at an office development in downtown Chennai. The site was constrained by nearby high-rise buildings, Anna Salai’s heavy traffic, and a metro tunnel approximately 7 m from the boundary. Subsurface conditions included fill, soft to very soft clay, fine sand, and hard clay or weathered shale; the design conservatively assumed groundwater at ground level.<br /><br />To support the excavation and avoid costly ground anchors, the project used a 1,000 mm-thick diaphragm wall, designed to a depth of 23 m, with four levels of steel struts and waler beams. The system was analysed using WALLAP and PLAXIS, with structural support components designed in STAAD Pro. BIM modelling helped visualise the temporary works and check for clashes with the permanent structure. Uplift anchor piles were installed beneath the raft to resist groundwater pressure.<br /><br />Construction involved demolishing the existing basement, installing diaphragm-wall panels using polymer-supported trench excavation, and excavating in stages while installing the struts and walers. Inclinometers, settlement markers, and strain gauges were used to monitor performance and compare field behaviour with design predictions. Restricted site access and limited space for storing materials and removing excavated soil added to the challenges.<br /><br />Despite the congested setting and construction constraints, the final excavation was completed safely and on schedule. The authors report that the strut-and-waler system provided a more economical alternative to anchoring, while enabling deeper basement construction and avoiding additional piling and repeated excavation and backfilling.

Keywords

deep excavation

diaphragm wall

basement construction

strut and waler system

groundwater pressure

PLAXIS analysis

WALLAP design

BIM modelling

instrumentation monitoring

Chennai office development