Study On Unconfined Compressive Strength And Indoor Improvement Technology Of Collapsing Gully Rock Soil

Collapsing gully is a particular type of soil and water loss in hilly areas of tropical and subtropical granites in southern China.The occurrence and development of crustal erosion is closely related to the physical and mechanical properties of rock and soil.As the loosing granite weathering crust and weak structure surface which accompanied by plenty of primary joint and structural fissures,the soil characteristics of the collapse rock are significantly different.Therefore,the mechanical properties of rock and soil are unstable.The limit strength of shear failure is defined as unconfined compressive strength under the condition of no lateral restraint,which is a significant index to reflect the stability of soil.Thus,it is necessary to carry out a systematic study on the unconfined compressive strength of the collapsed rock soil,which is of profound significance for enriching and improving the mechanical properties of the soil.Currently,combined method of engineering measures and biological measures is commonly used,while new technology and process are less applied.Meanwhile,due to the collapse of rock soil adhesion is poor,and there is severe wet and dry change,it possibly leads to collapse wall failure.Therefore,it is necessary to properly improve the soil of the fallen soil and improve the soil strength.In this paper,the typical collapsing gully of Tongcheng county in Xianning city of Hubei province is taken as the object of study.Field investigation and indoor experiment were carried out.study revealed the material basis of the cause of the collapse,tested the unconfined compressive strength of different types of rock and soil by on remodeled soil samples,discussed the effects of dry density and moisture content on the unconfined compressive strength,and investigated the effects of jute fiber and lime on the rock mass at different levels by using jute fiber and lime.The results are as follows:(1)The variation law of the bulk density of the soil in the collapsing soil is detritus layer > speckle layer > the red soil layer> surface soil layer;the change of total porosity is detritus layer > surface soil layer > the red soil layer> speckle layer.The change of mechanical composition is from the beginning of the red soil layer with the increase of the sampling depth.The content of the grit is increasing and the clay content is decreasing.The plastic limit moisture content of the red soil layer is the highest,and the liquid limit water content of detritus layer is the smallest.With the increase of soil depth,soil organic matter content decreased significantly,in which the organic matter content of the detritus layer is particularly low.The pH value of the soil is depleted,and the ion exchange capacity of the detritus is the smallest.There is significant difference in free iron oxide content.(2)The unconfined compressive strength of the collapsing soil is increases first and then decreases with the increase of the water content,and the water content at the maximum is about 15% or 20%.The increase of dry density and the unconfined compressive strength increase slowly and then decrease slightly,and the maximum density is about 1.30g/cm3.The dry density and water content have significant obvious interaction effect on the unconfined compressive strength of rock and soil.It can be divided into three regions in the contour map: dry effect main effect area,water content main effect area,dry density and water content interaction effect area,In the three-dimensional surface map there are "valley","mountain","ridge" and other curves.(3)The unconfined compressive strength of collapse soil is gradually attenuated with the increase of the number of wet and dry cycles,and the change rule is roughly divided into three stages: rapid decay,deceleration decay.The attenuation was stable,that is the maximum attenuation after the first wet and dry cycle,respectively 26%,15%,40% and 49%,in the second to four times the wet and dry cycle after the attenuation gradually reduced,The results showed that the unconfined compressive strength of the collapsing pile was as follows: surface soil layer > the red soil layer > speckle layer > detritus layer.There is a good exponential function relationship between the unconfined compressive strength and the number of wet and dry cycles The model of unconfined compressive strength was established by considering the soil depth ratio at different levels and the number of wet and dry cycles.(4)The optimal reinforcement condition of jute fiber was optimized by orthogonal design of collapsing gully soil.Surface soil layer: reinforcement length was 15 mm,reinforcement rate was 0.35%,and the overall reinforcement.The red soil layer: reinforcement length was 15 mm,reinforcement rate was 0.25%,and the upper reinforcement.Speckle layer: reinforcement length was 15 mm,reinforcement rate was 0.35%,and the overall reinforcement.Detritus layer: reinforcement length was 15 mm,reinforcement rate was 0.30%,and the lower reinforcement.The change rule of the stress-strain curve can consist of three stages: the rapid decay stage,the deceleration stage and the decay stabilization stage.The unconfined compressive strength of the collapsing gully soil was improved by 27.81%,29.73%,23.26% and 39.58% respectively under the condition of optimal reinforcement.(5)The optimal ratio of lime ratio,age and water content was optimized by response surface design.The surface layer: lime ratio of 8.99%,age: 28 days,moisture content of 25%;the red soil layer: lime ratio of 8.98%,age: 28 days,moisture content of 25%;speckle layer: lime ratio of 5.84%,age 18 days,moisture content of 20%;detritus layer: lime ratio of 6.58%,age 28 days,water content of 23%.(6)In the future,we should consider the combination of improved materials to improve the mechanical properties of the soil in the governance work of collapsing gully,jute fiber is a low-cost and environmentally friendly improved material that can be used in the surface soil layer and the red soil layer management work to improve soil strength;and lime is a significant effect and easy to improve the construction materials,In the collapse of the speckle layer and detritus layer to work to be used.