Muzhailing Highway Extra‐long Tunnel in Lanzhou, Gansu Province, China, belongs to the soft rock tunnel in the extremely high geostress area. During the construction process, large deformation of the soft rock occurred frequently. Taking the no. 2 inclined shaft of Muzhailing tunnel as the research object, an NPR (negative Poisson’s ratio) constant resistance and large deformation anchor cable support system based on high prestress force, constant resistance, and releasing surrounding rock pressure was proposed. The characteristics of the surrounding rock under the steel arch support and NPR anchor cable support were compared and analyzed by using 3DEC software. A series of field tests were conducted in the no. 2 inclined shaft, and the rock strength, displacement of the surrounding rock, deep displacement of the surrounding rock, internal force of steel arch, and axial force of anchor cable were measured to study the application effect of the NPR anchor cable support system in tunnel engineering. Moreover, the 3DEC numerical simulation results were compared with the field test results. The research results show that the application of NPR constant resistance and large deformation anchor cable support system in tunnel engineering has achieved good results, and it plays a significant role in controlling the large deformation of the tunnel surrounding rock.

The deformation characteristics of the rock mass in the intersection between the Muzhailing highway tunnel and the inclined shaft is a complicated three‐dimensional problem. Under the influence of high geostress, large deformation hazards may occur in the surrounding rock. Taking this as the research background, this paper analyzes the deformation mechanism of surrounding rock before and after prestressed anchor cable support through numerical simulation. Then, through theoretical analysis, a new tunnel support method using high prestressed constant resistance and large deformation anchor cable was proposed. The field monitoring results show that the constant resistance and large deformation anchor cable support can well control the deformation of surrounding rock, and the maximum deformation is within 300 mm. At the same time, the constant resistance anchor cable can always maintain a high prestress, which makes the stress of the surrounding rock uniform, and reduces the risk of damage to the steel arch due to local pressure. Moreover, the support method limits the expansion of the plastic zone and improves the overall stability of the surrounding rock.

Rock-socketed pile is one of the important foundation forms for offshore wind turbines, however, the construction of rock-socketed piles is very difficult. In this work, we propose to use hydraulic fracturing to pre-crack the rock foundation seabed around the piles to assist the construction of rock-socketed piles. Understanding the propagation mechanism of hydraulic fractures is the theoretical basis for hydraulic fracturing of rock seabed. Using mortar specimens containing single internal cracks and corresponding numerical simulations, hydraulic fracturing tests were carried out to study the influences of pre-existing crack characteristics and in situ stress on hydraulic fracture propagation behavior. The mortar specimens showed a tensile-shear failure mode under confining stress in hydraulic fracturing tests, and a macro-fracture penetrated the upper and lower ends of the specimens. Quantitative analysis of hydraulic fracture propagation behavior shows that under the comprehensive influences of the pre-existing crack angle and the stress, it is relatively easy to obtain good engineering results by selecting the pre-existing crack dip angle of 45°∼60° for directional hydraulic fracturing, and the increase of in-situ stress will improve the stability and deflection capacity of the cracks in the seabed.

During the construction of the Muzhailing tunnel, the maximum deformation of the surrounding rock was more than 2500 mm. When the tunnel is in the breakthrough stage, more attention should be paid to the danger of large deformation in order to ensure the safety of construction. This paper comparatively analyzed the deformation characteristics and stress distribution of the Muzhailing tunnel surrounding rock under the bolt support and the prestressed anchor cable support by numerical simulation. Then through theoretical analysis, a new method of tunnel support using high prestressed constant resistance and large deformation anchor cable is proposed. The field test results showed that the combination support form of long and short anchor cables with constant resistance and large deformation can improve the stability of the stop working face, and the rock pillar between the working faces, and reduce the influence of excavation disturbance on the surrounding rock of the stop working side. When the tunnel breakthrough construction was completed, the displacement difference of surrounding rock on both sides of the breakthrough position was controlled within 100 mm, and the maximum displacement of surrounding rock was 223 mm. the support method can well control the large deformation of the surrounding rock and improve the stability of the surrounding rock.