Study And Test On Engineering Properties Of Sand-gravel Cushion

Sand-gravel soils, distributing abroad in nature, belong to coarse-grained soil. As a sort of nicer natural building material, it has good compactibility, high permeability, great filling density, high shear strength, less settlement and deformation, and high bearing capacity etc. On the basis of plentiful practice engineering data about sand-gravel cushion finished by author and Northwest Electric Power Design Institute (NWEPDI) over the last 16 years, and data collected in the field test combined with some real projects, the systemic research on failure characteristic, bearing capacity, deformation, dynamic properties and the base friction for horizontally-loaded footings in sand-gravel cushion is done in theory and practice.In the testing phase, the importance of backfill material selection is introduced and emphasized in the paper. Especially, in the area where natural sand-gravel is absent, a detailed discussion on how to acquire reasonable grade by mixing crushed artificial gravel are presented.During the construction, the importance of reasonable workmanship is emphasized in this paper, detailed research and discussion from the thickness of single layer of lose material spread, water content, number of roller passes, and dry density testing and to quality control requirements are done.The test methods, as plate loading test, wave velocity test, test of mass foundation vibration, cyclic plate test, the base friction for horizontally-loaded footings in sand-gravel cushion, dynamic penetration test etc., are used to obtain detailed test data for some rules and conclusion, which obtains guidance and demonstration for the application of sand-gravel cushion, and moreover, it provides theory and technical gist for further popularization in geotechnical field.The building settlement on the sand-gravel foundation is discussed in the paper by illustrating the detailed engineering examples. Practices have proved that a majority of deformation of the sand-gravel itself would has completed during construction, and settlement is less, deformation is uniform, differential settlement is small too.