International Journal of Mining Science and Technology
Influence of dynamic pressure on deep underground soft rock roadway support and its application
Introduction
Due to the high speed development of national economy and the growing demand for coal resources, shallow coal resources gradually decrease and the mining depth increases year by year. Recently, most of the eastern mining areas have entered into a state of deep mining in our country [1], [2], [3]. With the increase of mining depth, the rock characteristics of deformation, failure and its mechanism between shallow and deep roadway have obvious differences. Besides, tectonic activity remarkably influences on the stability of surrounding rock of roadway, which reduces the stability of surrounding rock in roadway and increases the difficulty of controlling surrounding rock [4], [5], [6], [7], [8]. With the increase of mining depth, the ratio of soft rock roadways increases year by year [9], [10], [11]. When the soft rock roadway is excavated, plastic deformation energy stored in the surrounding rock will be released, and plastic state surrounding rock still has a certain bearing capacity [12]. Due to failure to take reasonable supporting technology in deep soft rock roadway excavation, a lot of excavated soft rock roadways need repaired due to serious deformation.
Stability of deep soft rock roadway is conditioned by many factors. Surrounding rock stability often causes excessive deformation which begins with surrounding rock stress concentration areas, and eventually leads to the instability and failure of roadway surrounding rock and supporting structure [13], [14]. When distance between working face and roadway is close, mining disturbance exerts great impact on the deformation of roadway surrounding rock and supporting structure. When working face is mining, large changes of surrounding rock have taken place, and surrounding rock stress readjusts, but the load of roadway increases dramatically, so the supporting structure under mining disturbance whether to meet the requirements of roadway stability is an urgent study [15], [16], [17]. Under the influence of superimposed stress, including high geo-stress and mining disturbance, deep soft rock roadways have difficulty in maintaining stability and availability. Therefore, it needs to carry out technology research of deep soft rock roadway supporting under the influence of dynamic pressure, in order to satisfy the stability of deep soft rock roadway excavation and available requirements.
Section snippets
Profile of engineering geology
The bottom extraction tunnel, located in the fifth mining area below 25 m, belongs to 11501 working face in Zhujixi Coal Mine of Wanbei Coal and Electricity Company, and its buried depth is −987 m. Main roof of the bottom extraction roadway is composed of thick mudstone and siltstone. The siltstone is gray, and its main composition is quartz. The horizontal beddings and fissures develop in the siltstone. Direct roof of roadway is mainly gray fine sandstone, and thin layer of carbonaceous mudstone
Impact of mining pressure on the bottom extraction roadway
The overlying strata above goaf produces bend, subsidence, fracture and caving during mining coal. Generally, caving zone strata is in falling and loose stage condition, whose weight is transferred to the both sides of the coal (Fig. 3). In Fig. 3, A is the original stress zone, B is the increased stress area, C is the reduced stress area, and D is the recovery stress area. I is the stress change area in front of the working face, II is the working face roof control area, III is the caving
Similar simulation of deep soft rock roadway support technology influenced by dynamic pressure
At present, the filed measurement technique is the most popular method to study the mine pressure. But the cost of actual measurement is expensive, and the observation data of mine pressure have some limitations because of long time and complex production conditions. However, similar simulation test can help to obtain mine pressure rule by carrying out strict similar conditions [21], [22].
Application effect evaluation
To verify the feasibility of combined supporting technology that uses anchor net-spraying-anchor cable-grouting-U-shaped steel, the underground industrial test is carried out. The deformation of roadway surrounding rock is displayed in Fig. 16.
In Fig. 16, the convergence amount between roadway roof and floor is 29.18 mm, and displacement of two sides is 25.33 mm. Thus, it indicates that the combined support technology solution can control deformation of soft rock roadways and floor heave
Conclusions
- (1)
Based on the theoretical study, it analyzes the influence of mining disturbance on bottom extraction roadway, reveals the change law of floor stress in mining area, and gets the stress change of surrounding rock in floor caused by mining.
- (2)
According to the change of stress field around the bottom extraction roadway, the displacement, plastic zone and the difference distribution of principal stress in surrounding rock under different support schemes are simulated by means of FALC3D. The reinforced
Acknowledgments
The authors are grateful for financial assistance provided by the National Natural Science Foundation of China (Nos. 51322401, 51404262, 51579239, 51574223), Shandong Provincial Key Laboratory of Depositional Mineralization & Sedimentary Minerals (Shandong University of Science and Technology) of China (No. CDPM2014KF03), China Postdoctoral Science Foundation (Nos. 2015M580493, 2014M551700, 2013M531424), and the Natural Science Foundation of Jiangsu Province of China (No. BK20140213).
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