Efficient tunneling solutions using hydraulic fracturing in hard rock cutting

Conventional mechanical cutting methods in hard rock tunneling encounter accelerated cutter wear and suboptimal breaking efficiency. In contrast, hydraulic fracturing offers a viable alternative to improve rock cuttability, featuring lower energy requirements and the ability to generate extensive fractures. In this study, the theory of hydraulic fracturing-assisted cutting was proposed, the cuttability characteristics of fractured rocks through cutting experiments were revealed, and the effectiveness of this technique was further confirmed through on-site applications. The results of the study indicate the following: Firstly, hydraulic fracturing induces shear slip to generate dilatant weak layers on the tunneling face. These layers intensify the stress at cutting-induced fracture tips, thereby reducing cutting forces and deflecting fracture propagation. Consequently, the spalling block volume increases while the specific energy consumption decreases. Secondly, experimental results confirm that hydraulically fractured rock samples exhibit lower peak cutting force and specific energy consumption compared to intact samples. Hydraulic fractures has been observed to induce alterations in the morphology of spalling blocks, transitioning from a wedge-like configuration to a quasi-cylindrical form. Thirdly, specific energy consumption in fractured rock displays a power-law correlation with a strain-based brittleness index. This index demonstrates a strong positive exponential correlation with cuttability enhancement ratios. Fourthly, field trials confirm that by applying the hydraulic fracturing-assisted cutting technique has led to a substantial enhancement in tunneling efficiency, with an increase of 53.8%. Concurrently, there has been a notable reduction in the number of worn cutting picks by 55.6%, and the particle size of the cutting spalling blocks has increased severalfold. This research offers a theoretical framework and technical guidance for achieving continuous, environmentally sustainable, and highly efficient tunneling operations in hard rock conditions.