Abstract
In a high geo-temperature environment, it is rarely reported that geo-temperature has been considered during a back analysis. This may cause the initial geo-stress field that is obtained by a back analysis to be wrong. In this study, according to the theory of elasticity, the theoretical solution of the hydraulic fracturing equation is obtained in a high geo-temperature environment. Since the vertical stress that is obtained by the hydraulic fracturing method is calculated using the density of overlying strata, this vertical stress lacks the thermal stress that is caused by geothermal gradients. Therefore, in a high geo-temperature environment, inverting the initial geo-stress field of rock masses directly using the stress that is measured by the hydraulic fracturing method can cause serious errors. We propose that the regression coefficient of a gravitational stress field should be set to one during a back analysis if stresses are measured by the hydraulic fracturing method, and this regression coefficient should not be equal to one if stresses are measured by overcoring methods. We also propose a workflow for the back analysis of the initial geo-stress field of rock masses that considers geo-temperature, and this workflow is applied to the Sangzhuling tunnel in China.
Highlights
With the gradual implementation of underground engineering projects in western China, such as the Sichuan–Tibet Railway and the Sichuan–Tibet Highway, deep, long, and high geo-stress tunnels have emerged in Tibetan areas [1,2,3]
As can be seen from Equation (20), in a high geo-temperature environment, since the vertical stress that is measured by the hydraulic fracturing method contains only gravitational information, inverting the initial geo-stress field of rock masses directly using the stress measured by the hydraulic
In a high geo-temperature environment, the stress measured by overcoring methods contains gravitational information, and the information of stresses caused by geo-temperature, weathering, deposition, erosion, or tectonism
Summary
With the gradual implementation of underground engineering projects in western China, such as the Sichuan–Tibet Railway and the Sichuan–Tibet Highway, deep, long, and high geo-stress tunnels have emerged in Tibetan areas [1,2,3]. In order to obtain the initial geo-stress field with macroscopic distribution, it is of great theoretical significance to invert the initial geo-stress field of rock masses [15,16,17]. Current studies rarely report that geo-temperature has been considered during a back analysis of the initial geo-stress field of rock masses [12,15,18,19,20,21,22,23,24,25,26,27,28,29,30,31]. In order to make the initial geo-stress field that is obtained by a back analysis more compatible with the actual state of rock masses, we propose a workflow for a back analysis that considers geo-temperature and is based on current studies. Taking as an example the Sangzhuling tunnel, in which high geo-temperature and high geo-stress occur, we carry out a back analysis of the initial geo-stress field of rock masses
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