Abstract

Grouting has been used frequently as a countermeasure of seepage control for underground construction. Conventional grouting techniques including cement grouting and chemical grouting can be used for seepage control for underground construction in rock when relative large joints are present. However, the high viscosity and large particle size of grouting material makes the grouting materials difficult to permeate into fine cracks. A novel biogrouting technique which employs biocement as the basic grouting material is presented in this paper. Laboratory experiments for use of biogrout to seal the interfaces between 18 pieces of horizontally laid granite slabs were carried out. The results of hydraulic pumping tests show that the seepage rate through the interfaces of the 18 pieces of granite slabs reduced by 1000 folds. A numerical analysis of the biogrouting process were also conducted to simulate the biocementation process and its pattern on the granite sheets. A comparison of the experimental data and the simulation results were made. Factors controlling the biogrouting process are discussed.

1.
Introduction

Safety and stability are always important issues in underground constructions. However, due to the sophisticated geological conditions, underground construction such as tunnelling or cavern excavation can be risky and expensive. Especially when unforeseen discontinuities such as faults or fractures in sedimentary rock mass are encountered, excessive and uncontrolled seepage may occur and even result in devastated consequences. This has been one of the major factors for the failures of a number of underground constructions.

Conventional cement or chemical grouting have often been employed to cope with the risk of undesired seepage and increase work safety level in underground constructions. Successful history cases have shown their potential of dealing with excessive and uncontrolled seepage. However, shortcomings also have emerged. The cement grout suffers two big disadvantages: firstly the viscosity of the grouting material is high, and secondly the cement grouting cannot permeate into fine cracks due to the size of particle in suspension. In recent years, the availability of ultrafine cement has extended the performance of hydraulic base grout for crack filling. Unfortunately, the high cost of ultrafine cement makes its vast application impracticable. Furthermore, even ultrafine cement may not be fine enough to permeate some fine cracks. Chemical grouting is another alternative to regular cement grouting. However, suspended solids are often added to chemical grouts to modify the solution properties as additives (Karol, 2003). So its application is also restrained by the size of the additives not to mention its high cost and potential negative environmental impact.

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