A new monitoring method for overlying strata failure height in Neogene laterite caused by underground coal mining

Abstract

Determination of the overlying strata failure height, that is, water flowing fractured zone height (WFFZH), is critical to underwater coal mining, especially in the fragile geo-environment areas. Due to the property discrepancy of rock and soil, WFFZH penetrating the clay layer in the Jurassic coalfield cannot be accurately determined by conventional measurement method, a new formation micro-scanner image (FMI) method was presented and verified in the paper. Taking the N1208 coalface in the Shennan mining area, Shaanxi, China, as a case study, FMI based field test for monitoring WFFZH was carried out firstly. The scanning results show that subtle changes of drilling sidewall cracks could be presented intuitively in FMI scanning image, and the WFFZH was be determined as 145.15 m. Secondly, the whole evolutionary process of WFFZH is simulated using UDEC, whose maximum height of WFFZ is calculated as 147.0 m. Comparison results between on-site measurement and numerical simulation suggest that FMI technology is applicable to monitor the WFFZH in laterite layer. Thirdly, in order to illustrate the discrepancies in WFFZH developed in laterite and bedrock, a comparative numerical simulation tests results show that laterite layer has an inhibitory effect on WFFZH.