An Experimental Study On Strength Evolution Of Net-like Red Soil Polluted By Acid

With the development of urban construction,the net-like red soil polluted by acid,distributed widely in the middle and lower reaches of the Yangtze River in southern China,brings an increasing challenge to the safety of engineering.However,the researches on the strength of net-like red soil polluted by acid is rare.Consequently,the corresponding experiment researches is necessary to carry out to reveal the evolutionary mechanism of the strength of acid polluted net-like red soil.Here,based on one-dimensional unsaturated direct shear experiment and the triaxial shear experiment and SEM test were carried out on specimens under different acid solution and testing concentrations,and the corresponding microstructure characteristics were also further discussed.The main conclusions are drawn as follows:The results of one-dimensional unsaturated direct shear test indicated that in the same condition of net normal stress and soaking time,when hydrochloric acid concentration is lower than 6%,the strength of polluted net-like red soil decreased with the increment of acid concentration;while hydrochloric acid concentration is higher than 9%,the corresponding strength increased with the increment of acid concentration.With the same variable of hydrochloric acid concentration and soaking time,the strength of soil increased with the increased of net normal stress.The hydrochloric acid concentration and net normal stress were determined as the identical,when soaking time is less than 14 d,the strength decreased with the extension of soaking time;when soaking time is larger than 21 d,the strength increased with the extension of soaking time.The results of triaxial shear test of net-like red soil in the condition of 7d soaking with confining pressure 300 kPa and different acid concentrat ion of 3%,6% and 9% indicated that the stress-strain cure of three different acid concentration show strain hardening characteristic,the peak shear strength increased with the increment of acid concentration.Simultaneously,the effective stress path curve of soil has correlation with polluted degree by acid.The effective stress path cure will shift to the left with the increment of hydrochloric acid concentration.The microstructure research results demonstrated that the particles arrangement of unpolluted net-like red soil is dominant in face–face characteristic,And the microstructures of net-like red soil polluted by acid is damaged,with acid concentrations increase,the average diameter of particles and pores was decreased first and then increase,the average diameter of the particle is greater pores' diameter,besides,the degree of orientation of particles remain unchanged,but that pores was reduced.The fractal dimension of particles and pore was almost 1.25 different concentrations acid polluted soil,acid pollution has a slight influence on fractal characteristics of particles and pores.The azimuthal angle of particles and pores mainly focus on 90°,compared with the pores,azimuthal distribution of particles is more uniform.