Experimental Study On Effect Of Calcium Lignosulfonate On Engineering Properties Of Dispersive Clay

Dispersive clay,a special type of soil,has particles that are susceptible to erosion in running water.This is due to the fact that the repulsive force between the particles is greater than the attractive force,resulting in back-flocculation,which causes the soil particles to be suspended in the water.Dispersed soil in China’s western and northeastern regions are widely distributed,if it does not have a reasonable treatment measure,easy to lead to water conservancy projects in the first water storage when serious damage to th e pipe surge.The current treatment measures for such soils in water conservancy projects are mainly chemically improved with traditional modifiers such as quicklime,but the production and application of these traditional modifiers can lead to large amounts of CO2 emissions.Therefore,in this paper,based on the relevant research results of scholars at home and abroad on various methods of dispersive clay modification,an environ mentally friendly polymer material,calcium lignosulfonate,was selected as a dispersive clay modifier,and the natural dispersive clay from a mine site was purchased as the research object.The test soil samples with different calcium lignosulfonate doping(0%,1%,2%,3%,4%),different dry densities(1.61g/cm3,1.67g/cm3,1.73g/cm3)and different initial water contents(14.1%,16.1%,17.1%)were prepared by using the controlled variable method,and the effects of calcium lignosulfonate doping,initial water contents and dry densities on the engineering properties of dispersive clay were investigated through extensive indoor tests.The effect of calcium lignosulfonate modification and the mechanism of modification were also investigated.The main conclusions of the study are as follows:(1)Calcium lignosulfonate can significantly reduce soil dispersibility,and it is recommended to use ≥3%calcium lignosulfonate to improve soil dispersibility.The dry density of the specimen also has a significant effect on the dispersibility of the soil sample,and the lower the dry density,the stronger its dispersibility.Compared with lime modified dispersive soils,calcium lignosulfonate modified dispersive soils are more effective.(2)With the increase of calcium lignosulfonate,the liquid limit,plastic limit and plastic limit index of the soil samples decreased to some extent.The shear strength parameters(cohesion and internal friction angle)and unconfined compressive strength of the soil samples showed a trend of increasing and then decreasing when the amount of calcium lignosulfonate was increased from 0%to 4%,and the extreme value was reached near 2%of calcium lignosulfonate.The permeability coefficient of the specimens tended to decrease and then increase with the increase of calcium lignosulfonate,and the permeability coefficient of the specimens was the smallest at 2%.The addition of calcium lignosulfonate reduces the thermal conductivity of the soil samples.The dry density and initial moisture content of the specimen also affect the unconfined compressive strength,cohesion and internal friction angle,permeability and thermal conductivity,and the temperature of the specimen(negative temperature)also significantly affects the thermal conductivity.(3)From the crack scour test,it can be seen that the specimens with calcium lignosulfonate doping 2%-4%can make the prefabricated cracks heal themselves in a short time under the protection of the backfilter layer from the beginning of the test to the stage when there is seepage water flowing out of the downstream outlet(onset),thus causing a significant increase in the slope drop in the seam.The specimens with 0%and 1%modifier doping had little change in the inseam slope drop during the crack scour test.In the stage from the downstream outlet seepage outflow to the end of the test,as the doping of calcium lignosulfonate in the protected soil sample increased,the crack self-healing effect became worse.(4)When the soil sample was mixed with calcium lignosulfonate,the pores between soil particles were filled,the number of pores decreased,the bonding substance on the surface of soil particles increased,and the soil particles aggregated with calcium lignosulfonate to produce a block structure.However,excessive calcium lignosulfonate incorporation can lead to the formation of a large number of aggregates in the soil sample,and the large pores between these aggregates make the soil sample difficult to compact and prone to the formation of soft structural surfaces,thus reducing the soil strength.Calcium lignosulfonate can significantly reduce the alkalinity of naturally dispersed soils.(5)Modification mechanism of calcium lignosulfonate:When calcium lignosulfonate is added into the dispersive soil,it will adsorb on the surface of soil particles to bond between soil particles,neutralize the surface charge of soil particles,reduce the distance between soil particles,thus filling the soil pores and increasing the strength of soil.The pore salt solution of dispersive soil contains a large amount of sodium ions,which make the soil particles more easily dispersed.When calcium lignosulfonate is incorporated into the soil,the calcium ions it carries will displace the sodium ions out of the soil.Since calcium lignosulfonate itself is microscopically acidic,it reacts with soil alkalinity to produce water molecules,thus lowering soil pH and reducing soil dispersion.In addition,because calcium lignosulfonate has hydrophobic groups,it can interact with the surface of soil particles to improve soil impermeability.Therefore,calcium lignosulfonate modification of dispersive soils can be considered as a "physical+chemical"improvement method.The research results show that calcium lignosulfonate is suitable for modifying the engineering properties of dispersive soils.It is recommended that the amount of calcium lignosulfonate should be controlled between 2%and 3%for the treatment of dispersive clay in actual water conservancy projects.