Experimental Study On Crack Resistance Of Cement Improved Clay

Clay is often used as the filling material of earth-rock dam core wall,and its strength is low.Because of the different modulus of filling material between the core wall and the dam body,uneven settlement is generated,which is easy to make the core wall crack.However,the problem of clay core wall crack has not been well solved.In view of this,this paper uses cement to improve the clay material（cement soil for short）.Based on the research method combining experiment and theoretical analysis,the influences of cement content and curing age on the fracture parameters of cement soil-type I and I-II compound are found out,and the fracture failure mechanism of cement soil-type is revealed.The main work and results of this thesis are as follows:（1）The mix ratio of soil with different cement content（5%,10%,15%,20%and25%）is obtained through compaction test.Mode I fracture test is carried out to study the influence of fracture relative length a/R on mode I fracture toughness(K_IC).The results show that the mode I fracture toughness(K_IC)decreases with the increase of fracture length a/R.（2）Find out the cement content and curing age on the behavior of cement-soil mode Ⅰ fracture and the effect of including the mode I fracture toughness(K_IC),mode I fracture energy(G_IC)and tensile strength（σ_t）.Through empirical formula to calculate the crack tip micro fracture zone critical dimension（r_c）,analysis of the rock and soil materials K_ICandσ_tcorrelation and difference of r_c.The research results show that the K_IC,G_ICandσ_tand cement content and curing age is a logarithmic function relation,and set up in the cement content and curing age under the influence of cement-soil fracture characteristics of empirical formula;r_cis 4.03～6.7mm under different cement content and curing age.The reasons for the differences in the correlation coefficients of fracture toughness and tensile strength between rock and soil materials are expounded.（3）The effects of cement content and curing age on Ⅰ-Ⅱ composite fracture properties are studied.The test results show that the peak displacement and peak load increase with the increase of initial crack Angle,but the effect of cement content and curing age is not significant.The K_If～K_IIfenvelope range increases with the increase of cement content and curing age.Under the influence of cement content,the K_II/K_ICvalue ranges from 0.39 to 0.45,and under the influence of curing age,the K_II/K_ICvalue mainly ranges from 0.40 to 0.44.Different cement content and curing age of soil-initiation angle has little difference.（4）The mechanism of cement soil mode Ⅰ and Ⅰ-Ⅱ composite fracture are analyzed theoretically,and the classical fracture criterion is considered to be limited in describing the fracture failure of cement soil mode.Generalized circumferential stress criterion（GMTS criterion）is introduced to study the influence of T stress on initiation angle and envelope.The results show that when T<0,T stress can inhibit crack development and enhance material strength.When T>0,T stress is conducive to crack development.GMTS criterion can better describe fracture behavior of soil-cement.By comparing the theoretical curve with the experimental data,it is found that the theoretical predicted value of r_cis lower than that calculated by the empirical formula（4.03～6.7mm）.Finally,combined with the GMTS criterion,the range of r_cis calculated to be 0.3～1.9mm.