Fixed-length roof cutting with vertical hydraulic fracture based on the stress shadow effect: A case study

Pre-driven longwall retracement roadway (PLRR) is commonly used in large mine shaft. The support crushing disasters occur frequently during the retracement, and roof management is necessary. Taking the 31107 panel as research background, the roof breaking structure of PLRR is analyzed. It is concluded that the roof cutting with vertical hydraulic fracture (HF) at a specified position, that is, fixed-length roof cutting, can reduce support load and keep immediate roof intact. The extended finite element method (XFEM) is applied to simulate hydraulic fracturing. The results show that both the axial and transverse hydraulic fracturing cannot effectively create vertical HFs. Therefore, a novel construction method of vertical HF based on the stress shadow effect (SSE) is proposed. The stress reversal region and HF orientation caused by the prefabricated hydraulic fracture (PF) are verified in simulation. The sub-vertical HFs are obtained between two PFs, the vertical extension range of which is much larger than that of directional hydraulic fracturing. The new construction method was used to determine the field plan for fixed-length roof cutting. The roof formed a stable suspended structure and deformation of the main PLRR was improved after hydraulic fracturing.(c) 2022 Published by Elsevier B.V. on behalf of China University of Mining & Technology. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Automated summary

Pre-driven longwall retracement roadway (PLRR) is commonly used in large mine shaft. The study concludes that the cutting of roof with vertical hydraulic fracture (HF) at a specified position, known as fixed-length roof cutting, can reduce support load and maintain the integrity of immediate roof. An innovative construction method, based on the stress shadow effect (SSE), is proposed to create vertical HF that surpasses the limitations of axial and transverse hydraulic fracturing. The method improves the stability and deformation of the main PLRR after hydraulic fracturing.