A new approach for predicting bedding separation of roof strata in underground coalmines

In order to avoid the influence of monitoring location to measured vertical bedding separation, a new estimating approach for vertical bedding separation, which uses the ratio between current and average vertical bedding separation, λk, has been proposed. In-situ investigations showed, there exists a threshold value of λkT for any kind of roof stratum, and the sedimentation has a great influence on it. In the eastern deep coal mines, which are subjected to intense sedimentation in Shandong Province, China, λkT ranges from 1.48 to 1.73. In the western shallow coalmines, which are subjected to weak sedimentation, Inner Mongolia, China, λkT ranges from 1.32 to 1.37. λkT is related to σ′tσ′t, the lower layer thickness and separation position. When separation occurs in the anchored range, λkT increases with σ′tσ′t but in a downward gradient, and slightly decreases with the lower layer thickness. When separation occurs outside the anchored range, λkT increases with σ′tσ′t in an upward gradient, and increases with the lower layer thickness. To combine monitoring the technique for λk and the borehole camera scanning technique is a more reliable for estimating roof safety in a roadway.

► As a new approach, vertical bedding separation velocity ratio (VBSVR), λk, was firstly proposed, which avoids the difference of separation velocity, induced by different monitoring locations, along a roadway cross section. It is more reliable for early warning of roof cave-in in a roadway. ► The threshold of the VBSVR, λkT, was determined by using a bedding separation survey system. ► It was found that in the eastern deep coalmines, Shandong Province, China, λkT ranges from 1.48 to 1.73. In the western shallow Gaojialiang Coalmine, Inner Mongolia, China, λkT ranges from 1.32 to 1.37. Obviously, λkT in the eastern deep regions is larger than that in the western shallow region in China.