Engineering Geological Properties And Mining Deformation Characteristics Of Paleo-Weathering Crust On The Top Of Jurassic In Ordos Basin

In the Ordos Basin,there is a relatively thick paleoweathering crust in the unconformity contact zone between the thick Cretaceous and the Lower Jurassic.Affected by the difference in engineering geology of the contact zone between the bottom of the Cretaceous and the top of the Jurassic,the contact zone will be affected by mining Large-scale separation of layers occurs.After the weathering crust is poured into the overlying Cretaceous water,the rocks disintegrate and become muddy,and there is a danger of the separation of water carrying mud and sand.The basic engineering geological properties of the weathering crust become the basis for the study of the formation of the separation layer and the water(sand)outburst.In this paper,theoretical analysis,field survey sampling,indoor test,in-situ test and other methods are used to study the basic engineering geological properties of the ancient weathering crust at the representative point of the Jurassic in the Ordos Basin.Simulation,on-site monitoring and other means analyzed the deformation and failure characteristics of weathering crust mining and the danger of carrying mud and sand.The results are as follows:(1)The Cretaceous in the Ordos Basin is in unconformity contact with the Lower Jurassic,and a paleoweathering crust 20-30 m thick is developed on the top of the Jurassic.According to the characteristics of the outcrop: its weathering is strong,the joints and fissures are developed,the rock mass is broken,and the quality of the rock mass is obviously different from that of adjacent rock layers.(2)The properties of paleoweathering crusts vary greatly in different locations.The minerals are mainly quartz,calcite,mica,and dolomite,and the clay minerals are mainly chlorite;the rock disintegration resistance ranges from weak to strong;point load uniaxial compressive strength estimation Its strength ranges from weaker to harder;the particle composition is dominated by particles smaller than 0.075 mm except for individual rock samples.(3)The in-situ direct shear test was used to obtain the shear strength parameters of the ancient weathered crust at the representative point.Under the same normal load level,the test results of each group show that the shear strength is small.The upper part of the weathered crust is dark red and the rock mass is harder and the shear strength is the largest,while the lower brown and dark brown specimens have the shear strength parameters Lower and similar.(4)Taking a coal mine with a huge thickness of Cretaceous as an example,the conditions for the development of mining-induced separation of the ancient weathering crust in the upper part of the Jurassic were analyzed,and the development characteristics of the weathering-induced deformation of the weathering crust were analyzed by theoretical analysis,numerical simulation,and on-site monitoring.Combined with the mine hydrological monitoring data and the water inrush coefficient method to analyze the risk of mud and sand collapse after the layer separated water.