Experimental Study On Two-dimensional Expansion Characteristics Of Expansive Soil

At present,it is common to study the expansion characteristics of expansive soil under one-dimensional and three-dimensional axisymmetric stress state,but less to study the two-dimensional expansion characteristics under plane strain state.Many expansion problems in subgrade,retaining wall and other engineering construction belong to plane strain problem.In this paper,a series of confined swelling tests,two-dimensional swelling force and swelling deformation tests and swelling deformation tests considering the influence of stress history are carried out by using a self-developed two-dimensional swelling instrument,and the effects of overlying load,water content,dry density and stress history on two-dimensional swelling characteristics are discussed.The research contents of this paper are as follows:1.Two different instruments,one-dimensional consolidation instrument and two- dimensional swelling instrument of expansive soil under confined conditions,are used to compare and study the swelling characteristics of expansive soil under confined conditions.The test results show that the swelling law of expansive soil obtained by the two instruments is consistent.With the increase of the overlying load,the vertical swelling ratio and swelling limit decrease exponentially,and the greater the load,the more obvious the restraining effect is.With the increase of overburden load,the lateral swelling force also increases.2.Two-dimensional swelling force characteristics of expansive soil are studied.The test results show that the change rule between swelling force and water content is not obvious,dry density is the main factor affecting swelling force,and the change trend of biaxial swelling force is consistent.When the water content is constant,there is a positive correlation between swelling force and dry density.When the initial water content is 35%and the dry density is1.0g/cm~3,the vertical swelling force is slightly greater than the lateral swelling force,and under other initial conditions,the lateral swelling force is always greater than the vertical swelling force.3.Two-dimensional swelling deformation characteristics of expansive soil are studied. The test results show that under the action of variable unidirectional load,the swelling ratio decreases exponentially with the increase of load.For constant pressure direction,when the load in this direction is small,the swelling deformation increases with the increase of variable directional load,and when the load in this direction is large,the swelling deformation is basically unaffected by variable directional load.When bi-directional isobaric,the lateral swelling ratio is always greater than that of vertical,and the swelling ratio decreases exponentially with the increase of load.In the two-dimensional swelling deformation test,the volume strain of the specimen decreases with the increase of the average stress,and there is a linear negative correlation between them The load determines the swelling limit,which decreases with the increase of load in any direction;Swelling limit is positively correlated with swelling ratio.4.The relationship between stress history and expansion characteristics is studied.The test results show that the stress history has little influence on the swelling property of expansive soil,and the void ratio has little change under the load of more than 10k Pa.Under initial loading,the void ratio decreases exponentially with the increase of overlying load.When unloading,the increase of void ratio is very small,the complete unloading does not return to the original point,and some deformation can not be recovered;When loading again,the void ratio on the curve is larger than that on the initial loading curve.The expansion and deformation curves of unloading and reloading form a closed hysteresis loop.