The new clay mud and its improvement effects of tunnels

•A new clay mud was developed for the earth pressure balance shield.•Mud prescription was obtained and optimized through the orthogonal experiment method.•Verification tests were conducted, and the test instruments were developed.•Indoor comparative experiments were conducted to verify the improvement effects.•Field tests were carried out to further verify the improvement effects.

During tunneling process by earth pressure balance (EPB) shield, the strata containing large amounts of sand and gravel are often encountered. The excavated soil in the shield chamber has poor plastic flow and larger permeability, so it leads to the difficult construction of the EPB tunnel. In order to ensure tunneling advance successfully, the excavated soil must be improved by adding modified materials to change its physical and mechanical properties, and make it to have a good plastic flow state, low friction angle and low permeability. Soil improvement techniques can guarantee the stability of excavation face, achieve the balance advance of shield tunnel, reduce machinery load and the ground settlement, and improve the excavation speed. The existing mud used in engineering practice is the dispersing mud and water system whose compositions are bentonite and water. Both the composition and function are simple. The existing mud has various problems, such as large amounts of waste mud emission, difficulties in controlling mud indicators, large areas for mud treatment and large uses of new mud materials and environmental pollution. In this paper, a kind of environmentally friendly clay mud was developed, and the laboratory and field tests were conducted to verify its adaptability and superiority.