Study On Strength And Crack Development Of Improved Expansive Soil

Expansive soil is composed of strongly hydrophilic minerals such as montmorillonite and illite.It has obvious characteristics of expansibility,namely water absorption,expansion,water loss,shrinkage,overconsolidation and multi-fissure.This phenomenon is caused by the long-term natural climate.Under the action of long-term dry environment,the soil body shrinks and produces cracks.It is the cracks in the soil body that reduce the bearing capacity of the soil body,causing the collapse and damage of the slope,roadbed,dam and other structures,causing a large number of casualties and economic losses.In this paper,three characteristics of expansive soil are studied experimentally.The consolidation test,free expansion rate test,expansive force test and other laboratory tests were carried out on the improved expansive soil by adding different basalt fibers.Unconfined compressive strength test and undrained consolidation triaxial test were carried out on the improved expansive soil by adding phosphorus tailings and basalt fiber of different proportions.By means of MATLAB and IPP software,the quantitative and regular research on crack development in the process of improved expansive soil dehumidification was carried out,and the functional relationship between crack degree and initial moisture content and phosphorus tailings content was explored.The research conclusions are as follows:(1)Phosphorous tailings can inhibit the expansion of expansive soil to a certain extent,and promote the unconfined compressive strength and shear strength of the improved expansive soil,showing a trend of first increase and then decrease.When the content of phosphate tailings is 10%,the expansion inhibition and increase strength reach the optimal level?(2)Basalt fiber can effectively weaken the expansive force of expansive soil,and the best inhibiting effect is when the content is 0.3%.It has no obvious promoting effect on the unconfined compressive strength of improved expansive soil,and the shear strength is improved to a certain extent.(3)The sample fracture can be divided into three types: one through the middle fracture plus several side secondary fractures,wind turbine blade fracture,annular fracture.The samples mixed with phosphorous tailings are mostly annular fissure.(4)Under the same initial moisture content,the critical moisture content shows little difference.Under the action of phosphorus tailings content,it has a certain degree of influence,but does not show obvious regularity.However,after curing,the critical water content increases.And the initial water content is positively correlated.(5)The critical moisture content of the sample with phosphorous tailing mixed after curing is larger than that of the sample without curing.(6)The sample fracture degree increases with the increase of initial water content,but decreases with the increase of phosphorus tailings content.With the increase of temperature,the crack degree first increases and then decreases.Best temperature,dosage of phosphate tailings for optimal improved expansive soil fracture degree of inhibition,temperature is about 35 ?,the phosphorus content of tailings for between 10% and 15%.