Research On The Spatial Distribution Of Sand-Cobble Stratum In The Chengdu Central City

With the continuous acceleration of the process of large-scale urbanization in China and the constantly advancing of the development of high-rise buildings,underground space and stereoscopic traffic,the problems facing with the urban engineering geology are becoming more and more prominent.The article is based on the center of Chengdu City surrounded by the Line 7 of the Metro.And it is based on the data of a large number of engineering data collected in the Line 1,2,3,4 and 7 of the Metro.Combining with some construction engineering date and the hydrological survey data of the predecessors,the GOCAD 3D modeling software is used to construct an invisible three-dimensional visualization strata model in the downtown area of Chengdu.The 3-D visualization strata model is used to study the three dimensional distribution of sandy cobble stratum,the total volume of sandy cobble stratum,and the fluctuation of the bed rock.(1)Constructing the fourth-generation stratum 3-D geological model of Chengdu City by the Surfer based on the quaternary strata isopach maps of Chengdu City.Aiming to exploring the distribution of quaternary strata:The Cenozoic sediment thickness in the northwestern side is large,and the thickness of the southeastern gradually decreases.(2)Constructing the downtown area of Chengdu three-dimensional visualization geological model by GOCAD.Aiming to studing the three-dimensional distribution pattern of sandy cobble stratum;the total volume of sandy cobble stratum;the ups and downs of bedrock.The sandy cobble stratum are mainly distributed in three areas:the pebble area of the middle river zone,the zonal belt between the western rivers,and the pebbled soil on the edge of the eastern fan-fringe.From west to east,the thickness of sandy cobble stratum has a tendency to decrease,while the bedrock shows a significant upward tilt.The eastern turbulent pebble soil area is close to the outcrop area of the bedrock,and the mud content of the formation is significantly increased.Horizontally,the thickness of the sand and gravel stratum gradually decreases from northwest to southeast,and the clay content increases from small to large.The ratio of sandy cobble stratum increases from small to large.In the longitudinal direction,the sandy cobble stratum from old to new,and the degree of weathering is gradually weakened;From top to bottom,the stratum are slightly dense sandy cobble stratum,medium dense sandy cobble stratum,and dense sandy cobble stratum.the density and pressure of the sandy cobble stratum increase with depth.It is estimated that the total volume of sand sandy cobble stratum is approximately 1.7576×10~8 m3.(3)Constructing the sound wave;the bearing capacity and the compression modulus3-D geological model with GOCAD software,which is based on engineering parameters along the subway to explore the law of variation of engineering parameters in the study area.All the parameters are in direct proportion to the depth and density of the sandy cobble stratum.The stratum becomes denser and harder and the sound wave,bearing capacity and compression modulus become larger with the depth of the ground increasing.The parameters of the same stratum are basically kept within a certain range which determine the range of values of the mechanical parameters at each stratum.(4)The accuracy of the model was verified by comparison of the data obtained from the reserved borehole data and the model-derived data,the undulating surfaces of bedrock and the section with survey data from different sources.