Designing Cement-Based Grouting in a Rock Mass for Underground Impermeabilization

Iñigo Escobal-Marcos,María-Belén Prendes-Gero,Martina-Inmaculada Álvarez-Fernández,Celestino González-Nicieza

doi:10.3390/en14134062

Abstract

Fractured rock masses below the water table are a problem in underground excavations because of their low strength and high permeability. Nowadays, these negative connotations can be reduced with techniques such as injection of cement, microcement, or resins grouts. These materials increase the rock mass cohesion while reducing the flow of water through the discontinuities. This paper describes the work carried out to design a waterproofing screen for a three-storey underground basement located in a building near the Bilbao estuary (Northern Spain) and with problems of water seepage from the river. First, a survey of the rock mass is carried out. This survey shows the presence of highly fractured zones and the variability of the permeability as functions of the fractures. Subsequently, the effect on permeability caused by the injection of cement grouts and microcement is studied by means of two pilot injection boreholes and eight control boreholes. Finally, a behavioural model is proposed to explain the heterogeneity observed in the radius of influence of the injection. As a result, a waterproofing screen with three types of treatment is designed: An ordinary treatment with cement grouts, an intensive treatment with microcement grouts, and an isolation treatment with cement-bentonite grouts.

Highlights

Today, injections are becoming increasingly important in mining and civil works, both on the surface and under it
There is a large body of research worldwide, whose objective is to develop laboratory-scale tests to try to predict the injectability of a grout in grounds or fractures
The results indicate that grout penetration at openings of 125 μm and 200 μm is verified at up to 40% of the maximum theoretical penetration length

Summary

Introduction

Injections are becoming increasingly important in mining and civil works, both on the surface and under it. The injection of a ground involves the introduction of a fluid mixture into the ground, which subsequently sets and hardens. There are more and more works where the first objective of the injection treatment is waterproofing. In such cases, the identification of the need for treatment requires studies to clearly state the problem to be solved and determine its theoretical evolution in the event that no treatment is carried out. There is a large body of research worldwide, whose objective is to develop laboratory-scale tests to try to predict the injectability of a grout in grounds or fractures

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Discussion

Conclusion