Compensation control and design methods for excavations in deep soft rocks

During the excavation and support process in deep soft rocks, complex conditions such as high stress and strong disturbance can be encountered. The complex conditions can cause failure of the support system. Aiming at stability control in deep soft rocks, we proposed the excavation compensation theory. A new high strength and high toughness material was developed. The breaking load and elongation of the new material are 1.59 and 1.78 times that of common bolt materials. To overcome the problem that the CABLE element in FLAC 3D cannot simulate failure of support structures, the numerical model for the whole process of force-breaking-anchorage failure simulation (FBAS) for bolts (cables) was established. The numerical experiments on the excavation compensation control of deep soft rock were carried out. The excavation compensation control mechanism of high strength and high toughness material was clarified. Compared with the common support scheme, the highly prestressed support has a maximum increase of 90.24% in radial stress compensation rate and a maximum increase of 67.85% in deformation control rate. The results illustrate the rationality of the excavation compensation theory. The compensation design method of excavations in deep soft rocks was proposed and applied in a deep soft rock chamber. The monitoring indicated that the maximum surrounding rock deformation is 180 mm, reduced by 64% compared to the common support. The deformation of the chamber was controlled and the surrounding rock was stable.