Design challenges associated with deep retaining walls in weathered / faulted Silurian Age siltstone

This paper addresses key geotechnical challenges inherent to the design of deep cut and cover/retaining structures, and associated excavations, in weathered faulted Silurian age siltstone. It also presents recommendations on how to apply innovative geotechnical design approaches to deal with this unique geological setting.

The paper briefly explains some the features encountered within this geological setting and the intrinsic challenges and risks they pose to design and construction. The former include high-stress rock masses either with fractured/faulted zones or with bedding planes with an unfavourable orientation and dip angle relative to the excavation. From a design perspective, approaches on how to incorporate the impact of these geological features in a soil-structure interaction (SSI) analysis are discussed in detail, which cover not only the shortcomings of two-dimensional analytical assessments but also the need for a critical calibration between 2D and 3D analyses to derive design efficiency.

The impact of bedding planes is explored as part of the design process, as well as performance during construction of a deep, multi-anchored soldier pile wall. This segment offers an insightful overview on the influence of bedding planes on the stability and serviceability performance of the wall, illustrating the intricate interplay between geological features and engineering design principles.

A separate section of the paper focuses on the repercussions of highly fractured/faulted bands of rock on the design of diaphragm wall structures. The design approaches adopted to capture the effect of such features via an efficient SSI approach are discussed, along with the key findings of targeted additional investigations that may assist in de-escalating the risk profile of a project during successive stages of design.