Study And Numerical Simulation On The Dilatancy Properties Of Hard-clay In Hefei Area

The dilatancy of soil is an important factor in the design and construction of highrise and super high-rise buildings.The surface uplift,the inclination and collapse of adjacent piles caused by pile foundation construction are closely related to the dilatancy of soil.In order to provide a reasonable basis for the design and construction of pile foundation,this paper takes Hefei old clay as the research object.Firstly,through the determination of the basic physical property indexes of old clay and the collection of relevant data in Hefei area,the paper expounds the engineering geological conditions and basic characteristics of old clay,and analyzes the factors affecting the shear dilatancy of old clay in Hefei area,and then adopts the indoor test and theory The triaxial test was carried out to analyze the change rule of dilatancy under different conditions.The triaxial test is simulated by using the subloading Cam-clay model,and the test results are compared with the theoretical design,and the soil squeezing effect and the dilatancy of the soil mass during the construction of the prefabricated pile and the bored pile are simulated.Through the triaxial test,it is found that the larger the overconsolidation ratio is,the greater the dilatancy is,and there is a strong linear relationship.On the other hand,the smaller the overconsolidation ratio is,the larger the axial strain will be when the soil reaches the maximum dilatancy rate,otherwise it will be reversed.Through the study of remolded soil with different overconsolidation ratio,it is found that the dilatancy of remolded old clay decreases by about 15%.When overconsolidation ratio of remolded old clay is less than 2,the phenomenon of shear shrinkage will appear.With the increase of overconsolidation ratio,the phenomenon of shear shrinkage will disappear gradually,and the phenomenon of shear expansion will become more and more obvious.The overconsolidation ratio of 2 may be the boundary point between the phenomenon of shear shrinkage and shear expansion of old clay.When the overconsolidation ratio is less than 2,the soil shows strain hardening.With the increase of overconsolidation ratio,strain softening gradually occurs.The overconsolidation ratio of 2 may be the boundary point of strain hardening to strain softening of old clay.Through numerical analysis,it is found that the subloading Cam-clay model can reasonably reflect the stress-strain characteristics of old clay in Hefei area.It is found that the soil squeezing effect and the soil dilatancy are obvious in the process of pile penetration.The soil dilatancy in the range of 3 times of pile diameter is between 3.5% and 1%.The soil squeezing effect and the soil dilatancy in the range of 0.5 times of pile diameter are obvious in the bottom of the pile and 0.5 times of pile diameter It is found that the dilatancy in the range of 1.5 to 0.5 times of pile diameter is between 4.5% and 1%.