Study On The Influence Of Large Gap Gravel Layer On The Swelling Shrinkage Characteristics And Bearing Ratio Of Expansive Soil

At present,due to the mixing of cohesive soil and sand,the construction site mixing is difficult to achieve the effect of uniform mixing in the laboratory,which not only seriously affects the construction progress,but also easily leads to the unstable treatment effect of subgrade.In this paper,using gravel interlayer as reference to treat clay subgrade,it is proposed to lay large gap gravel layer to treat expansive soil as subgrade filler.Taking the expansive soil in Baidong New District of Guangxi as the research object,this paper carries out the expansion and contraction characteristics test and CBR bearing ratio test on the expansive soil with gravel layer,studies the influence of the changes of particle size,porosity,layer thickness and gradation of the paved gravel layer on the expansion and contraction characteristics and bearing capacity of the expansive soil with gravel layer,and optimizes the gravel gradation design.The main conclusions are as follows:1.For compacted pure expansive soil,in the process of water absorption and expansion,the allowable micro deformation is called release expansion.With the increase of expansion release rate,the expansion force decreases exponentially;When there is overlying load,the softened compacted expansive soil can squeeze into the gap between the gravel particles.2.For expansive soil with single particle size interval gravel layer,when the porosity of gravel layer is 37%,the inhibition of expansion and contraction is the best;With the increase of porosity and thickness of gravel layer,the expansibility of expansive soil with gravel layer decreases,but the change of contractibility is very small.When the gravel with single particle size interval is laid to treat expansive soil,the particle size of gravel is more than 11 mm,and the laying thickness needs to be more than 4cm,and the total expansion and contraction rate of expansive soil with gravel layer is less than 0.7%.3.For the expansive soil with single particle size interval gravel layer,with the increase of gravel particle size,CBR first increases and then decreases;With the increase of void fraction of gravel layer,CBR decreases gradually;With the increase of the thickness of gravel layer;CBR bearing ratio increases gradually;The CBR value of expansive soil with gravel layer more than 3cm thick is more than 8%,which can meet the requirements of subgrade filling.When the thickness of gravel layer is more than 2 times of the maximum particle size,the CBR value is higher.4.For the expansive soil with graded gravel layer,the larger the content of coarse gravel in the gravel layer,the larger the CBR of the sample;When the thickness of the gravel layer is determined,the expansibility decreases with the increase of the porosity of the gravel layer.5.For the expansive soil laid with graded crushed stone layer,when the gradation of crushed stone is broken,i.e.the fine-grained crushed stone below4.75 mm is screened out on the basis of OGFC open graded crushed stone,which is the best gradation scheme for the treatment of expansive soil with 3 cm crushed stone layer.The CBR of the treated expansive soil reaches 19%,and the total expansion shrinkage ratio reaches 0.3%,which meets the requirements of highgrade highway for the treatment of expansive soil filler.