Preliminary Study On Influencing Factors Of Calcareous Sand Foundation Bearing Capacity And Foundation Pit Stability

Calcareous sand is widely distributed around the world,and the construction of islands in the South China Sea is a national strategic requirement and an important part of the development of the "Belt and Road".According to the site data of hydraulic filling,calcareous sand has a wide range of particle size distribution,and some data show that the particles of hydraulic filling can even reach the standards of gravel and crushed stone.In the process of dredging and filling,the effect of throwing and water conservancy sorting make the thickness and fineness of calcareous sand particles separate significantly,which further aggravates the unevenness of calcareous sand gradation.In view of the fact that calcareous sand is a wide-graded soil,the current research results mainly focus on fine sand.The existing research results may be quite different from the actual situation.At the same time,the calcareous sand area has sufficient rainfall and the engineering construction areas are mostly sea-side.The tidal action makes the sea level rise and fall significantly and the calcareous sand pores are relatively high.Effect of these factors will cause significant changes in the water content of calcareous sand.In this paper,calcareous sand in a certain area of the South China Sea is the research object,and the basic physical properties of calcareous sand are tested.Triaxial shear and compression tests with different average particle size,water content,and density were carried out.Preliminary analysis of the influence of the test parameters on the calculation results of the ultimate bearing capacity of the classic foundation and the stability of the excavation of the foundation pit.The main work content of this paper are as follows:(1)The physical properties of calcareous sand were tested,and the basic physical parameters were obtained.Calcareous sand is mostly irregular in shape,with obvious pores in the grains,and its specific gravity is larger than that of quartz sand.(2)Carry out indoor triaxial shear test,and analyze the primary and secondary relationship of the influence of various factors on the shear strength of calcareous sand.The test results show that calcareous sand exhibits stress softening under low pressure conditions.The larger average particle size,the higher shear strength of calcareous sand,and the greater the axial strain corresponding to the peak strength.Water can increase the shear strength of calcareous sand to a certain extent.With the increase of water content,the friction angle in the soil decreases while the cohesive force first increases and then decreases.Average particle size and relative density have no significant effect on cohesion,average particle size has a greater influence on internal friction angle than relative density.(3)The confined compression test of calcareous sand was carried out with a triple consolidation instrument.The Hardin crushing model is used to quantitatively analyze the particle crushing laws under different influencing factors.The results show that calcareous sand behaves as a low compressibility soil under conventional engineering stress,with good engineering properties,and it mainly produce plastic deformation.The larger the average particle size,the higher the crushing rate of the particles and the greater the compression deformation.Improving the compactness can effectively reduce the compression deformation of the sample under the action of external force,and the influence of the initial void ratio state on the compression characteristics gradually decreases with the increase of pressure.(4)The classic foundation ultimate bearing capacity calculation formula was compared and analyzed,combined with the triaxial shear test results,the ultimate bearing capacity of calcareous sand foundation was calculated,and the influence of average particle size and water content on ultimate bearing capacity was explored.The Lizheng software was used to calculate the calcareous sand foundation pit,and the influence of water content on the stability of the foundation pit was analyzed.