Sivakanthan, Sivanathan; (2024) A study towards a single pass sprayed concrete lining. Doctoral thesis (Eng.D), UCL (University College London).

Text SIVANATHAN_SIVAKANTHAN_A Study Towards a Single Pass Sprayed Concrete Lining_Sivanathan Sivakanthan.pdf - Other Access restricted to UCL open access staff until 1 September 2024. Download (17MB)

Abstract

Over the past 30 years, the continuous development of sprayed concrete materials, equipment, testing, and quality assurance has advanced to the point where primary tunnel linings can be designed as permanent structures. This advancement makes the concept of one-pass lining highly desirable, primarily for its potential benefits in cost reduction, carbon footprint minimization, and enhanced sustainability compared to traditional multi-layered Sprayed Concrete Lining (SCL) systems that include a waterproof membrane. However, the implementation of one-pass lining systems is hindered by several challenges. Key among these is the issue of water ingress through construction joints, an area that has seen less research focus compared to studies on composite action of multiple layers, watertightness, or thickness reduction. While durability and permeability of tunnel linings have improved significantly with the development of new design mixes, construction joints remain a weak point for water ingress. This weakness is a critical obstacle that needs to be addressed to enable the widespread adoption of one pass tunnel lining systems. This research addresses these knowledge gaps via laboratory testing, a field trial and numerical modelling. The primary lining behaviour revealed that high cement content together with the use of accelerator increases the temperature of the lining during the hydration period, which expands and subsequently during cooling contracts the sprayed concrete lining against the substrate. Although the curing of SCL linings is complex to measure and to analyse, the field trial data and subsequent numerical analysis showed that the concrete around the joints expands during heating due to high temperature rise and high coefficient of thermal expansion of concrete during early age A high degree of restraint leads to multiple cracks forming during the cooling stage, typically within the first 8 days after spraying. Laboratory studies revealed that concrete mixes modified with Crystalline and Polymer Latex admixtures, meeting minimum performance standards for permanent sprayed concrete, demonstrate enhanced potential to control water ingress through joints. However, a large-scale field trial, planned but not conducted due to unforeseen spraying machine issues causing delays and sprayer unavailability, along with extended joint water penetration tests, is crucial to validate these mix designs' effectiveness.

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