Study On The Mechanism Of Ionic Soil Stabilizer Reinforcement Based On Sand-mixed Bentonite

Due to the complexity composition of natural expansive soil,the wide range of swelling clay mineral content,and the diversity of mineral species,explain the role of main compositions in studying the characteristics of its expansion,water holding,and mechanical properties is difficult,which also greatly increases the difficulty for clearly understanding the mechanisms of expansion and moisture migration.Therefore,in this paper,different proportions of sand-bearing bentonite are selected as the research object to study the swelling deformation law of soil under different bentonite content.It also determines the sand content of sand-bearing bentonite,soil and water characteristics,moisture migration mechanism,attenuation of mechanical strength with sand content,etc.Thus it simplifies the theoretical model for expansive soil,which clearly explains the expansion mechanism.Ionic Soil Stabilizer(ISS)is a kind of chemical agent which improves the compaction,density,bearing capacity,cohesion of soil,and reduces the water sensitivity of soil.Curing agent is an ionic curing agent,and it is a highly concentrated organic solution.It has strong oxidation and dissolving power and contains a variety of natural dispersant compounds.The minerals in the soil can be decomposed and recrystallized to form metal salts,creating new chemical bonds and keeping the soil stable.The strong ion exchange promotes the activity of the soil,which destroys the double layer structure on the surface of the soil particles and weakens the chemical interaction between the surface of the soil and water.It also destroys the capillary structure of the soil,and irreversibly releases water from the surface of the soil particles.By rolling out the water molecules,the soil becomes hydrophilic and water repellent.The interaction of the soil particles is enhanced,cracks are not easily generated,the moisture content is decreased,and the density is improved,thereby increasing the strength and stability of the soil.Therefore,the ISS can be mixed in sand-bentonite to change the double-layer structure of the soil surface by changing the ion type of the clay mineral in the bentonite,the hydrophilicity of the soil and the type of the combined water.By this way,the bentonite and the sand particles are better connected,and the hydrophilicity and swelling characteristics of the sand-bentonite are improved as well as the strength and stability of the soil.In this paper,the basic physical and mechanical properties of bentonite with different sand content were experimentally studied.It was found that the sand content had a significant impact on the swelling-shrinkage characteristics and the mechanical strength of bentonite,and there is a boundary of sand content.The sand-mixed bentonite was then reinforced by ISS.According to a series of experimental studies,the effects of ISS on the swelling-shrinkage characteristics,mechanical strength,soil-water characteristics,and moisture migration process of the sand-mixed bentonite were studied,and the mechanism of ISS to reinforce sand-bentonite was further elaborated.The main research work of this paper is as follows:(1)Understand the influence of different sand content on the physical and mechanical properties of bentonite.The compaction test,liquid-plastic limit test,expansion rate test,swelling force test and uniaxial unconfined compression test were used to understand the relationship between the maximum dry density and the optimal moisture content of bentonite with different sand content.It also helps to understand liquid limit moisture content and plastic limit moisture content,soil swelling potential and mechanical strength properties.The experiment results show that the sand content has an effect on the physical and mechanical properties of the soil and the sand-mixed bentonite has a boundary for sand content.With the change of sand content,the maximum dry density and the optimal moisture content of the soil also changed,and the dry density of the soil reached the maximum when the sand content was 80%.The sand content has a great influence on the liquid limit water content and the plastic limit water content of the soil.With the decrease of sand content,the bentonite content increases.At this time,the liquid limit water content and the plastic limit water content of the soil increase,especially the liquid limit moisture content increased nearly exponentially.The sand content has a significant effect on the swelling characteristics of bentonite.When the sand content is higher than 80%,the soil swelling is weak,while the expansion rate is lower than 80%,the soil swelling is remarkable.So 80% is defined as the boundary of sand content.In addition,with the change of sand content,the strength of the soil has changed,and the soil strength is relatively higher when the sand content is 80%-70%.(2)Understand the electrochemical properties of the experimental curing agent and its best concentration for bentonite reinforcement.In this paper,a portable 290 A PH meter and a conductivity meter were used to measure the pH and the conductivity of the ISS at different concentrations.The cation exchange capacity experiment and the liquid plastic limit experiment were carried out using the method of forced ion exchange to determine a concentration,under which the effect of ion exchange between the curing agent solution and the expansive clay mineral is the best and the plasticity index of the soil is the lowest.Experiments showed that when the concentration of curing agent to water was 1:150,the cation exchange capacity of the soil is the lowest,and the plasticity index is the lowest.Therefore,under this concentration,the ISS has the best reinforcing effect on bentonite,and this concentration of ISS is used in this paper.(3)Understand the swelling characteristics of sand-mixed bentonite reinforced by ISS.It can be known from the results of the one-dimensional swelling test and the swelling force test that the ISS has a good inhibitory effect on the swelling of the sand-mixed bentonite.With the decreasing of the sand content and the increasing of bentonite content,the swelling characteristics of the soil changes more greatly and the inhibitory effect is more and more obvious.However,when the sand content reduced to a certain level,the curative effect of the ISS on expansive soil is reduced.This is because the ISS and the expansive clay mineral in the sand-mixed bentonite undergo full ion exchange,and the colloidal molecules in the expansive clay mineral in the sand-mixed bentonite changed from the hydrophilic to the drainage after the ion curative solution reacts.Then its water-absorption capacity decreases,and thus the expansibility decreases.With the increase of clay mineral content,although the ISS has a significant effect on reducing the swelling of the expansive soil,the increase of the clay mineral content causes the ISS to perform insufficient ion exchange with it.Therefore,the ability to suppress the shallow potential of soil expansion is reduced.It shows that the swelling of the soil is enhanced with the increase of the content of clay mineral,and the expansion of the expansive soil is inhibited by the ISS.However,when the content of the bentonite in the soil is too much,the water absorption activity of the soil increases.The content and concentration of the required ion curative agent also need to be changed correspondingly.Therefore,a corresponding concentration of the ISS needs to be prepared according to actual needs in engineering projects.(4)The long-term stability of sand-mixed bentonite reinforced by ISS was studied.By setting the experimental conditions,the uniaxial compressive strength of the soil was measured after repeated freezing and thawing of the sand-mixed bentonite before and after the reinforcement of the ISS.The experimental results are as follows(1)The sand content has a great influence on the mechanical strength of bentonite and the ISS has a certain influence on the sand concentration of the sand-mixed bentonite.The sand concentration of sand-mixed bentonite reinforced by ISS is about 80%.At this time,the compressive strength of the sand-mixed bentonite is 200 kPa,and the sand content of the soil after the consolidation by the ISS is significantly reduced which is between 70% and 60%.The uniaxial compressive strength of sand-mixed bentonite is increased to about 250 kPa.This shows that through a series of reinforcements,the ISS can effectively increase the soil compactness,reduce the porosity ratio of the soil,and make the bentonite and the quartz sand adhere to each other better.Then it effectively reduces the swelling potential of the soil,and improves the strength of sand-mixed bentonite.(2)The sand content has a significant effect on the freeze resistance of bentonite.Under the action of freeze-thaw cycles,the mechanical strength of sand-mixed bentonite decreases with the number of freeze-thaw cycles,and the attenuation rate of the soil after the first freeze-thaw cycle is the greatest.However,the strength of the soil is still attenuated to some extent,but the change is not significant.When the sand content is higher than 80%,the strength of the soil is relatively low,and the freeze resistance is also poor.The ISS has little effect on the strength and the stability of the soil.When the sand content is in the range between 70% and 50%,the strength of sand-mixed bentonite is improved.Under the effect of freeze-thaw,the strength has a certain degree of attenuation,but the overall stability is still good.When the sand content is less than 50%,the strength of the sand-mixed bentonite has a certain degree of attenuation,but the strength of the sand-mixed bentonite reinforced by the ISS is higher than that of the unreinforced soil,and the reinforcement effect of the ISS is obvious.(5)The HYPROP device was used to measure the soil-water characteristic curve of the sand-mixed bentonite before and after the ISS reinforcement.The experiment results shows that,after reinforcement by the ISS,the water content of the sand-mixed bentonite is lower than that of the soil unreinforced by the ISS under the same suction force.On the other hand,due to the ion exchange between the macromolecular organic colloid in the ISS and the clay minerals in the expansive soil,the hydrophilic groups in the soil are replaced by several large molecules of the drainage.The surface of the particle is combined with a thin water film,which reduces the water absorption of the soil.Sand content also affects the soil-water characteristics of bentonite.With decreasing of the sand content,the bentonite content of the soil,the matric suction,and the water absorption capacity all increased.(6)Experimental study on water migration process of sand-mixed bentonite reinforced with ISS in open system.This experiment was conducted by a self-improved and assembled moisture migration experiment device.The results show as follows:1 After multiple freeze-thaw cycles on the sand-mixed bentonite,the water content of the soil reinforced by the ISS at different heights is lower than that of the sand-mixed bentonite sample unreinforced.This is due to the ion exchange effect between the organic macromolecule colloid in the ISS and the original hydrophilic group of the clay mineral in the soil.The soil changes from the hydrophilicity to the water repellent,and the particles of the soil interact mutually.The connection becomes tighter,which to some extent hinders the migration of water molecules.Therefore,the water absorption capacity of the soil reinforced by the ISS decreases,and the moisture content is low.2 The effect of sand content on the moisture migration in soil.When the sand content in the sand-mixed bentonite is high,the swelling soil expands hardly after being reinforced by the ISS.The soil temperature decreases and then the soil freezes.Although a certain amount of free water at the bottom moves upwards and freezes at the frozen front,the water content of the soil increases to some extent,and the volume expands.However,when the temperature rises,the ice in the soil starts to melt.As the sand content in the soil is high and the pores of the soil particles are larger,so the capillary force is weak.After the soil thawed,the free water molecules flow back to the bottom from the pore channel between particles.The content of bentonite in the soil increases with the decreasing of the sand content.When the temperature decreases,the top of the soil freezes as well as the free water in the soil,then the capillary force increases,and the water molecules migrate upward along the pore channel.When the temperature rises,the ice melts.Because of the large clay content in the soil,the suction force of the soil matrix is large.Therefore,most of the free water molecules that rise along the capillary channel remain in the soil.3 When the sand-mixed bentonite was treated by the ISS,although the cracks in the soil will have a certain degree of growth during freezing,the growth rate of the cracks is slow,and the freeze-thaw effects little on the overall structure of the soil.The ISS effectively reduces the growth rate of cracks in expansive soils during freeze-thaw cycles.In this paper,by carrying out the above-mentioned experiments,the ISS was described in terms of the expansion characteristics of sand-mixed bentonite reinforced by ISS,the improvement of mechanical strength,the relationship between matrix suction and moisture content,and the change of temperature and moisture content during moisture migration.The reinforcement effect and reinforcement mechanism of sand-mixed bentonite are reinforced by the ISS,thus providing an important theoretical basis and reliable experimental data for the reinforcement and application of the sand-mixed bentonite.