Influencing parameters of the grout mix on the properties of annular gap grouts in mechanized tunneling

Abstract

In mechanized tunneling with segment lining the annular gap between segment lining and soil, caused by tunnel driving, must be backfilled instantaneously with an adequate grouting mortar, to avoid bulking of the surrounding soil, to embed the tunnel lining and to minimize settlements of the ground surface. The decisive requirements for such annular gap grouts are on the one hand optimal flow properties lasting for several hours and sufficient stability against segregation at same time, on the other hand a fast development in shear strength immediately after grouting within a few minutes. Latter is usually achieved by dewatering of the mortar into the surrounding soil. Thus, two contradictory requirements are demanded on annular gap grouts.The main objective of this research study was to investigate the dewatering behavior of grouting mortars, which can be influenced by the constituents and the composition significantly. In systematic and extensive investigations the correlation of these properties has been studied fundamentally as well as the consistency.For this purpose, a test setup was developed, simulating the conditions within annular gaps up to 20cm in width. The amount of filterable water, including temporal effects, has been determined. Additionally, the development of shear strength, influenced by the dewatering effect, has been examined. In comparison, shear strengths were also determined at non-dewatered specimens, reflecting the worst case of non-dewatering. The investigations were based on grout compositions, which were primarily used in major traffic tunnels. These mixes have been modified by parameters such as fineness of the binder (cement, fly ash, inert additions) and types of aggregates.From the experimental results, the main influencing parameters on the dewatering behavior and on the development of the required shear strength could be defined.