Predictive permeability model of faults in crystalline rocks; verification by grouting in Seyahoo dam

Amidreza Rostami Barani

doi:10.17485/ijst/2012/v5i6.11

Amidreza Rostami Barani

Open Access

https://doi.org/10.17485/ijst/2012/v5i6.11

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Abstract

This paper deals with quantitative fault zone descriptions, qualitative fracture and fault rock properties, and engineering data in the study of the permeability structure of fault zones. Datasets include scan-lines, drill cores and cement grouting from Seyahoo dam in andesite and basalt rocks, from which systematic grouting volumes can be used to analyze the in-site relative permeability both in host rocks and fault zones. Dam-scale injection of cement reveals patterns that can be ascribed to the impact of faulting; there is an increase in cement injection in fault zones compared to areas with background fracturing away from faults. In detail, there is an innate division of the rock volume into sub- zones characterized by distinct structural style and permeability, with a background level and three fault related sub- zones (fault core, inner damage zone, and outer damage zone). Injection data shows that the background sub-zone commonly can be injected with less than 0.05 m 3 cement per meter dam (commonly not injected), whereas the fault

Highlights

Faults represent a challenge in all type of engineering projects, especially in tunnels and quarries, because of increased fracture density, weak rocks, poor rock stability, and enhanced fluid flow (Hoek & Bray, 1981; Hoek, 2000; Nilsen & Palmstrom, 2000; Blindheim &Ovstedal, 2002)
All faults intersected by the tunnels show a fault zone of [60,61,62,63,64,65,66,67,68,69,70,71,72,73,74,75,76,77,78,79,80] m width, where the fracture frequency commonly increases towards the core of the fault (Fig. 3)
A polyphase history characterized the studied faults, with fault products including impermeable mylonites and cataclasites, which are reworked in porous breccias and gouge

Summary

Introduction

Faults represent a challenge in all type of engineering projects, especially in tunnels and quarries, because of. These subjects have promoted significant attention around faults, spanning from fault arrays and displacement fields (Walsh et al, 2003a, b), to intrinsic fault geometry and fault architecture (Chester et al, 1993; Caine et al, 1996; Braathen et al, 2004; Collettini & Holdsworth, 2004), and into the realm of frictional behaviour, linked to mechanical and chemical processes (Sibson, 1986, 2000; Stewart et al, 1999; Braathen et al, 2004). The uniqueness in the work relates to the connection between structural observations that can be linked with pre-grouting cement volumes in Seyahoo dam. This opens for in situ considerations of the permeability structure of fault zones.

GROUTING CURTAIN BOUNDARY

Fault zone characteristics

Rati o

Injected series E