Experimental Study Of Vibrating Characterisies Of Prestrengthening And Foststrengthoning Liquefying Silt Deposit

During earthquakes, liquefaction would take place in saturated silt deposits, which is of crucial importance of upstnieture. In view of this, vibration characteristics of prestrengthening and poststrengthenmg saturated silt deposits were studied in this paper.First of all, a series of shaking tests were conducted on the above-mentioned deposits. Among vibrating characteristics of three model deposits with three different amounts of clay particles, the pore-water pressure, the acceleration of shallow soil layer and the shear strains were analyzed. Three model deposits consist of the prestrengthening silt deposits, the poststrengthening deposits respectively by cast-in-place cement-stabilized soil pile and by compaction sand pile. After being put horizontal sine wave in three model deposits, some vibration characteristics were showed, as follows: A) on prestrengthening deposits: (1) After about 6~7s, vibrating gives rise to pore-water pressure in soil, then increases till the peak, and maintains that to cease-vibration. On vibration ceasing, pore-water pressure began to dissipate. And pore-water ceiling is the effective up-covered pressure. (2) The dissipation form of pore-water pressure is from high-pressure region to low-pressure region. Finally in the whole soil pore-water pressure came to equally dissipate. (3) The critical pore-water pressure ratio of silt is about 0.6-0.7. As pore-water pressure arrived at 0.5-0.6, the acceleration begins to decrease from the peak. (4) Before liquefaction, soil would amplify the function of vibration. On liquefying, vibration would be restrained. (5) As for silt deposits, liquefaction region is from soil surface down to 10m. (6) In original stage about 0-12s, soil was compressed and pore-water pressure slowly increased. During 12s~20s, soil became expanded while pore-water pressure acutely increased. For 20s~40s,circular shear strain had got been very large and pore-water pressure came to the peak, soil liquefied and collapsed. B) "on poststrengthening model deposits: As for shallow soil layer, the pore-water pressure ratio decreased to 30%-35% of that prestrengthening model deposits, and the acceleration always increased during vibration, which -showed that the liquefaction-resistant abilities of silt deposits were strengtheried.Besides. SEM was carried on all model deposits. Along with the macro-phenomena and analysis, micro-structures were compared, the conclusions that at Pc=9% the liquefaction-resistant abilities: were the lowest, and the measures "being taken to strengthen silt were effective.