Tunnel in situ stress measurement by hydraulic fracturing based on the iS3 platform

Abstract

In situ stress is an important fundamental design and construction parameter in tunnel engineering as the external load of tunnels, especially in case of deep tunnels in which potential geological hazards caused by high in situ stress can be often observed. This paper describes the integration of the acquisition technique and analysis method of tunnel in situ stress measurement via hydraulic fracturing into the infrastructure smart service system (iS3) platform. The hydraulic fracturing method, which is recognized as the most reliable and effective means to measure in situ stress deep in the crust, is applied in iS3 to acquire the stress information of the rock. The transient pressure analysis (PTA) method is integrated as the analysis module of iS3 because of its advantage of accurately capturing the hydraulic fracture closure event and determining the shut-in pressure (equal to the minimum horizontal principal stress) through flow regime analysis of the fracturing fluid. The hydraulic fracturing measurement based on iS3 has been applied to a deep rock highway tunnel in south-western China (maximum depth: 1259 m). The iS3 integrated system provides a valuable reference for tunnel in situ stress measurement.