The HTHP (high temperature and high confining-pressure) triaxial compression test has been conducted on dolomite at 8000m deep in the Tarim Basin, China. We first study the characteristics of rock deformation based on the experimental results. An improved damage constitutive model is introduced to overcome the limitations inherent in the existing models which cannot accurately characterize rock residual strength after failure. The Drucker-Prager model serves the failure criterion of the ultradeep rock. The model is used to fit the experimental data and the results show a good agreement, which indicates that the improved model can be used to predict the mechanical behavior during the whole loading process. The model provides a theoretical knowledge of the mechanical characteristics of ultra-deep rocks in Tarim oil field.
The deformation and failure of rock has always been a critical issue in the field of rock mechanics (Zhang et al.2013 and Wang et al.2018). As a heterogeneous and anisotropic material, rock contains a large number of pores and microcracks. The complexity of crack propagation evolution in rock deformation complicates the simulation of stress-strain relationship. The statistical damage function based on the Weibull distribution was first proposed by Krajcinovic & Silva (1982) and then improved by Lemaitre (1984). The correction of the model includes the following two parts. The first part is the strength criterion. Cao et al. (2005, 2008, 2012) established a constitutive model with Mohr-Coulomb criterion. The criterion is a linear failure criterion. The Drucker-Prager criterion considers the intermediate principal stress and hydrostatic pressure, which matches the failure characteristics of deep rocks (Cao et al. 1998 and Chen et al. 2021). The second part is the correction of the post-peak deformation. Cao et al. (2013) introduced a residual strength correction, but its physical significance is unclear. Cao et al. (2012) established a new damage model that can reflect the residual strength characteristics of rocks after failure. A large number of tests and constitutive models were carried out in granite (Cao et al. 2013), marble (Zhang et al. 2022), sandstone (Xu et al.2007 and Cao et al. 2012). Those rocks were all taken from shallow layers and were tested at low temperature and low confining-pressure condition. He et al. (2005) summarized the main differences between deep and shallow mining engineering, manifested in the harsh environment of "three-high-one-destabilization" (high temperature, high pressure, high karst water pressure, mining disturbances). However, there are relatively few tests carried out on limestone and dolomite at HTHP condition.
