厚表土薄基岩煤层开采覆岩运动规律

 厚表土薄基岩煤层采用综放开采后基本顶将难于形成稳定结构，发生滑落失稳导致工作面“压架”，在对薄基岩定义的基础上，综合采用实验室试验、理论分析、数值模拟和现场实测的方法对薄基岩煤层开采上覆岩层运动规律进行了研究。研究结果表明，若其他条件不变，“砌体梁”结构的稳定主要取决于基岩厚度和上覆表土层的力学性质及厚度，具有较大承载力的厚黏土层能与薄基岩组合形成稳定的结构，降低稳定结构所需最小基岩厚度。由此建立薄基岩工作面结构力学模型，并针对司马矿具体条件分析认为当表土为松散砂土，最小基岩厚度40 m；当黏土厚度40 m，最小基岩厚度20 m；黏土厚度30 m，最小基岩厚度30 m。据此提出首采面可安全开采，在现场工业性试验中得到成功验证。

MOVEMENT RULES OF OVERLYING STRATA AROUND LONGWALL MINING IN THIN BEDROCK WITH THICK SURFACE SOIL

Stable structure of main roof couldn¢t be formed because of sliding instability and crushed support during fully-mechanized mining with top coal caving in thin bedrock and thick surface soil. By defining thin bedrock through “three belts” which are decided by strata control，it is found that “three belts” are closely related to mining height and rock mechanical properties. The overlying strata movement rules are studied by laboratory experiment，theoretical analysis，numerical simulation and in-situ measurement. The result indicates that bedrock thickness and mechanical properties and thickness of surface soil are the key influential elements for the stable structure of “stacked layer of blocks”，while the other conditions remain the same. The thick clay in surface soil that owns large permissible bearing capacity can form steady structure with the composition of thin bedrock，so it reduces minimal thickness of bedrock to ensure structure stability. According to the practical condition of the first face in Sima coal mine，the mechanical model of structure which is combined by thick clay and thin bedrock is built. It shows that the immediate roof and top coal can be regarded as “similar zero rigid body” by using plastic and elastic combination body. Through designing the mechanical features of surface soil and change of thickness in bedrock，the rules of the vertical stress，bearing pressure and top coal convergence are simulated and studied，and the minimal bedrock thickness is ensured. The minimal bedrock thickness is about 40 m in loose surface soil condition；when the clay thickness is 40 m，the minimal bedrock thickness is 20 m；and when the clay thickness is 30 m，the minimal bedrock thickness is 30 m. Through the study，it can be deduced that safety mining is feasible at the first face，and it has been proven successfully in mining experiment.