Research On Distribution Law And Engineering Properties In Sand And Gravel Strata Of Chengdu Metro Line 4

With the rapid development of Chengdu Metro, owing to the distribution law and engineering properties of Chengdu sand and gravel strata is not clear lead to some engineering geological problems in the subway construction process, then affect the construction schedule or cause safety accident. Therefore, the thesis regard west line engineering in second phase of Chengdu metro line 4 as a research objective, as built metro line land metro line 2 for reference, in-depth research on structural constituent, distribution law, Stratification and engineering geological property of sand and gravel strata of west line engineering in second phase of Chengdu metro line 4, analyze the adaptability between this type of sand and gravel strata and metro shield structure construction, and puts forward some suggestions on the selection of shield construction form in this sand and gravel strata, analyze the engineering geological problems that may be encountered in shield construction in this type of sand and gravel strata and propose the solution proposal. The main research contents and results are as follows:1. By counting and analyzing the content of gravel and boulder, length of particle size and the distribution, the overall performance of this type of sand and gravel strata from the west to the east boulder content is more and more low, the boulder size is more and more small, the boulder size from shallow to deep more and more big.2. Because of the depositional bedding of this sand and gravel strata is obvious; roundness is well; poor sorting; poor grain composition; contain large boulders etc, and it also has the both characteristics of the alluvial genetic type of sand and gravel strata and the pluvial genetic type of sand and gravel strata, Without the obvious characteristics of the glacial deposits genetic type of sand and gravel strata, combining the river inherent flow direction as a judgment obtain that the sand and gravel strata of west line engineering in second phase of Chengdu metro line 4 is a alluvial and pluvial genetic type of sand and gravel strata formed by Minjiang River.3. The main component of sand lens in this area is quartz, mica and debris, containing a small amount of flint, without clay mineral. The biggest influencing factors of stability in sand lens is water, the formation of tension on the surface between water and mineral particles is the main force to maintain the sand lens stable.4.The grain composition of west line engineering in second phase of Chengdu metro line 4 is poor, the natural compressive strength of sandy gravel is 41.8-170Mpa, the uniaxial compressive strength of pebble soil is 60.9-132.9Mpa, it has heavily influence on shield construction. Compactness is one of the important factors that control the deformation modulus of pebble soil; there is a closly relationship between mineral particle size and permeability coefficient, this relationship can be expressed by formula and model. So mineral particle size is one of the important factors which influence the important macroeconomic indicators of permeability coefficient of sand pebble soil.5. Shield type of this strata is composite mudding type EPB shield machine determined by the combination of theory and practice. Some engineering problems may appear in the shield construction process in this strata, such as cutter and tool wear, crushing problems of the large boulders and so on, in order to solve these problem the thesis proposed some solution for reference as soil improvement, select the appropriate cutter, adjust the boring parameter timely and so on.