近松散层采煤覆岩采动裂缝水砂突涌临界水力坡度试验

以带不同尺寸裂缝的混凝土块模拟采动裂缝岩体,以黏土、粉土、粗砂和砾砂配制不同颗粒组成的7种土样,采用改装的渗透仪,对松散层经过采煤上覆垮落带和裂缝带发生渗透变形破坏的类型和机制进行研究,得出采煤垮落带和裂缝带上覆松散土层发生从上往下渗透变形破坏的临界水力坡度与土层粒度成分、物理力学性质和裂缝尺寸的关系.试验结果表明,黏粒含量较少的粉土、粗砂、砾砂比较容易发生水砂突涌,土的d50小于裂隙宽度的1/10时,容易出现潜蚀甚至涌(突)砂现象;当临界水力坡度大于1时,同一种颗粒组成的土样重度越大,液性指数越小,土的黏聚力越大,则临界水力坡度越大;同一种土样发生通过裂缝的渗透变形破坏时,裂隙宽度越大,临界水力坡度越小,发生破坏的临界水力坡度随裂缝宽度的增大呈指数下降.试验还获得溃砂时水砂涌出量与裂缝的宽度和初始水头高度的关系,在相同初始水头条件下,随着突砂口尺寸的加大,突砂量基本呈线性增加;在相同突砂口张开的情况下,涌砂量随着初始水头增大而增大.发生水砂突涌的涌出物中含砂量随时间延续逐渐减少.由此可见,含水层的初始水头和突砂口张开程度是控制矿井工作面突砂量的关键因素.

EXPERIMENTAL RESEARCH ON CRITICAL PERCOLATION GRADIENT OF QUICKSAND ACROSS OVERBURDEN FISSURES DUE TO COAL MINING NEAR UNCONSOLIDATED SOIL LAYERS

Concrete blocks with fissures of different sizes are adopted to simulate mining fractured rock mass,and the clay,silt,coarse sand and gravel are used to compose 7 kinds of soil samples with different particle size distributions.Then,the types and mechanisms of the seepage deformation and failure of the unconsolidated soil layers across the caving zone and water flowing fractured zone within overburden,and the relationship among the critical percolation gradient of unconsolidated soil layers while seepage failure across mining-induced fissures from above to bellow vertically,soil particle size distributions,physico-mechanical properties and the widths of fissures are studied in laboratory tests by reequipped seepage meters.The results show that the silt,coarse sand and gravel with small amount of clay are easier to quicksand,and pipe and quicksand occurs frequently while d50 is less than 1/10 of the width of fissure.When the critical percolation gradient is larger than 1,the critical percolation gradient of soils with same particle size distributions is in direct proportion to the unit weight and cohesion,in inverse to the liquid index.The wider the fissures are,the smaller the critical percolation gradient for the same soil sample is when seepage failure deformation occurs across fissures,and the critical percolation gradient decreases exponentially with the extension of the width of fissures.Moreover,the relationship among the volume of quicksand and the width of fissure,and the initial water level are also studied in tests,and the results indicate that the volume of quicksand increases linearly with the width of sand inrush mouth in the same initial water head,and increases with the initial water head in the same size of sand inrush mouth,but the sand content in the quicksand decreases with time.So it can be deduced that the initial water level and width of fissures are the key factors controlling the amount of the quicksand in mine working face.