Research On Development And Performance Of Modified Msb Vertical Cutoff Walls Materials

The paper relies on the national key research and development plan "Key technology research and integrated demonstration of the remediation and safe use of pesticide contaminated sites in the Yangtze River Delta"(2018YFC1803101),the national key research and development plan "Solid waste landfill soil pollution risk management and control and purification technology"(2018YFC1802304),the state Natural Science Foundation "Research on the Mechanism and Performance of Polyphosphorus-based Dispersant Modified Bentonite Vertical Engineering Barrier to Block High-risk Heavy Metal Pollutants"(41877248),through indoor and on-site tests for polyanionic cellulose(PAC)modified bentonite and The modified magnesia activated granulated blast furnace slag-bentonite vertical barrier material(modified MSB material)has carried out systematic research,and the main research results include:(1)The basic physical properties of polyanionic cellulose modified bentonite and the workability of mud construction were studied.The results showed that the liquid limit and swelling index of modified bentonite with a polyanionic cellulose content of 2% increased by18.8% and 28%,respectively,compared with unmodified bentonite,and increased with the increase of the polyanionic cellulose content.Increase;when the content of bentonite is 10%and the content of polyanionic cellulose is 2%,it can meet the workability of slurry construction.(2)Through free swelling test and modified fluid loss experiment,the chemical compatibility of polyanionic cellulose modified bentonite under the action of heavy metal cadmium nitrate polluted liquid and p-xylene polluted liquid was studied.The results showed that the swelling index decreased as the concentration of cadmium nitrate and p-xylene increased,but the swelling index of polyanionic cellulose-modified bentonite decreased less than that of unmodified bentonite;The average void ratio of the unmodified bentonite filter cake decreases with the increase of the test stress;the permeability coefficient of the modified bentonite filter cake is 50-89% lower than that of the unmodified bentonite filter cake.(3)Based on the optimal design,an modified magnesia activated granulated blast furnace slag-bentonite vertical barrier material has been developed through laboratory tests.The results show that the optimal moisture content of the modified MSB material is 5～16% higher than that of the MSB material;the permeability coefficient of tap water after 28 days of standard curing for the modified MSB material is 8.4×10-10～3.6×10-10m/s,which satisfies Less than10-8m/s requirements;the unconfined compressive strength of the modified MSB material standard curing for 28 days is 107～250k Pa,which meets the requirement of more than 100 k Pa;the modified MSB material standard curing 28 days water retention rate is compared with The MSB material has increased by 11-22%;the modified MSB material has a smaller increase in permeability coefficient under long-term immersion stress of high-risk pollutants than the MSB material,and the strength remains unchanged;the modified MSB material has strong high temperature resistance and high temperature resistance The strength meets the requirement of higher than 100 k Pa.(4)The actual application evaluation of MSB and modified MSB vertical barrier materials under different construction techniques was carried out on a typical pesticide-contaminated site in Yangzhou,Jiangsu.The results show that the barrier integrity of the three-axis mixing pile,two-axis mixing pile,canal-cut cement-soil continuous wall(TRD)and high-pressure jet grouting pile construction technology is good;the modified MSB material and MSB material meet the requirements of natural curing after 28 days.The confined compressive strength is higher than 100 k Pa and the permeability coefficient is less than 10-8m/s;the TRD construction method has better construction quality;the modified MSB material has a lower lateral displacement and deformation of 56 days compared with MSB material.～97%,the maximum lateral displacement deformation is basically located near the center point of the barrier;the layered settlement of the modified MSB side soil is basically smaller than that of the MSB side soil of the same age.