Hydraulic fracturing of rock-fill dam

Jun-Jie Wang,Jun-Gao Zhu,Mroueh Mroueh,Chiu Chiu

doi:10.1260/175095407781421595

Abstract

The condition in which hydraulic fracturing in core of earth-rock fill dam maybe induced, the mechanism by which the reason of hydraulic fracturing canbe explained, and the failure criterion by which the occurrence of hydraulicfracturing can be determined, were investigated. The condition dependson material properties such as, cracks in the core and low permeability ofcore soil, and “water wedging” action in cracks. An unsaturated core soiland fast impounding are the prerequisites for the formation of “waterwedging” action. The mechanism of hydraulic fracturing can be explainedby fracture mechanics. The crack propagation induced by water pressuremay follow any of mode I, mode II and mixed mode I-II. Based on testingresults of a core soil, a new criterion for hydraulic fracturing was suggested,from which mechanisms of hydraulic fracturing in the core of rock-fill damwere discussed. The results indicated that factors such as angle betweencrack surface and direction of principal stress, local stress state at thecrack, and fracture toughness KIC of core soil may largely affect theinduction of hydraulic fracturing and the mode of the propagation of thecrack.The condition in which hydraulic fracturing in core of earth-rock fill dam maybe induced, the mechanism by which the reason of hydraulic fracturing canbe explained, and the failure criterion by which the occurrence of hydraulicfracturing can be determined, were investigated. The condition dependson material properties such as, cracks in the core and low permeability ofcore soil, and “water wedging” action in cracks. An unsaturated core soiland fast impounding are the prerequisites for the formation of “waterwedging” action. The mechanism of hydraulic fracturing can be explainedby fracture mechanics. The crack propagation induced by water pressuremay follow any of mode I, mode II and mixed mode I-II. Based on testingresults of a core soil, a new criterion for hydraulic fracturing was suggested,from which mechanisms of hydraulic fracturing in the core of rock-fill damwere discussed. The results indicated that factors such as angle betweencrack surface and direction of principal stress, local stress state at thecrack, and fracture toughness KIC of core soil may largely affect theinduction of hydraulic fracturing and the mode of the propagation of thecrack.

Highlights

A great number of high earth-rock fill dams are being or to be constructed in Western China where water resources are very abundant, such as Nuozhadu dam (261.5 m in height) on Lancang River in Yunnan Province, ShuangJiangkou dam (322 m in height) and Changhe dam (240 m in height) on Dadu River in Sichuan Province
FAILURE CRITERION Since the mechanism of hydraulic fracturing can be explained in terms of fracture mechanics (FM), a reasonable failure criterion should be established based on the FM theory, because the singularity of stress state at crack tip is always ignored in those criteria based on tensile or shear strength
Hydraulic fracturing in the core of the earth-rock fill dam is a very complicated and unsolved problem

Summary

INTRODUCTION

A great number of high earth-rock fill dams are being or to be constructed in Western China where water resources are very abundant, such as Nuozhadu dam (261.5 m in height) on Lancang River in Yunnan Province, ShuangJiangkou dam (322 m in height) and Changhe dam (240 m in height) on Dadu River in Sichuan Province. The core soils of the earth-rock fill dams may subject to cracks, which are resulted from the arching action and/or hydraulic fracturing (Zhu and Wang [1]). Previous studies have suggested different methods to determine the water pressure required to induce hydraulic fracturing. These methods may be classified into three groups. Hydraulic fracturing in the core of the earth-rock fill dam is still an unsolved problem and its mechanism is not well established. The crack in the core which allows water to enter the core is prerequisite for hydraulic fracturing. Present paper comprehensively deals with the hydraulic fracturing in the core of earth-rock fill dam, i.e. the condition of its formation, mechanism and failure criterion. Proposed failure criterion for hydraulic fracturing is tested in the core of rock-fill dam

CONDITIONS

MECHANICAL MECHANISM

FAILURE CRITERION

DISCUSSION

CONCLUSIONS

Methods and observations