A lecture for a work shop

PRIMARY COMPRESSION AND SECONDARY COMPRESSION OF SAIGON SOFT CLAY BASED ON GIBSON’S MODEL OR TAYLOR-MERCHANT’S THEORY TRẦN QUANG HỘ tqho@hcmut.edu.vn Part I Review: Taylor and Merchant’s theory Taylor and Merchant’s theory During the process of consolidation void ratio of an element of soil is a fuction of effective vertical stress and time: (1) Taylor and Merchant’s theory The rate of compression in terms of rate of change of void is: (2) Taylor and Merchant’s theory Equation is integrated to obtain total compression in a peoriod of elapsed time t: (3) Taylor and Merchant’s theory Alternatively, Eq (3) can be written as: (4) Taylor and Merchant’s theory • A comparison of Eqs and idicates that beyond the time d’v /dt=0 • In other words represents the peoriods of consoliddation during which effective stress increase, called primary consolidation stage Taylor and Merchant’s theory • The total compression that takes place during primary consolidation stage is called primary compression • The endless period that follows primary consolidation stage is called secondary consolidation stage (or creep stage) Taylor and Merchant’s theory • The total compression that takes place during secondary consolidation stage is called secondary compression • The first integral on the right side of Eq.(4) is primary compression; the second integral on the right side of Eq.(4) is secondary compression Theory A The manifestations of the first integral of the right side of Eq (4) by Taylor and Merchant (1940) is called Theory A Table Test results for BH02-8m Table Test results for BH02-16m Table Test results for BH02-24m Primary compressibility a Secondary compressibility b Soil viscosity, 1/ Ratio /b Degree of settlement versus time factor curves for M=1,304 and different values of N Conclusion Based on Gibson-Lo’s model for soft clay along Sài gòn river, the final secondary compression is about 30,4% of the primarry compression (Tsytovich 36,4% for Saratop clay LL= 68%, PL = 32%.) Conclusion The deeper layers has deposited longer so they have smaller primary and secondary constants than the upper layers Conclusion On the contrary the deeper layers has deposited longer so they have higher viscosity than the upper layers Conclusion Because “Creep” does act insignificantly during primary consolidation stage the influence factor N does not affect the shapes of the curves relating Us(t) and time at the early stage of consolidation Conclusion The influence factor N which characterizes the rate of secondary compression affects the shapes of the curves relating Us(t) and time at the late stage of consolidation Conclusion Gibson-Lo’s (or Taylor-Merchant’s) model parameters can be used to predict the settlement versus time of embankments along Saigon river THANK YOU FOR LISTENING