NameӤ LE ANH TUAN
Thesis titleӤMeasurement of elastic shear modulus of sand under low confining stress
Supervisor: Toyota Hirofumi
””Conventionally, in model experiments about soil dynamic problem, the soil shear modulus has been considered to have a square root (to the power of 0.5) relationship with soil confining pressure (overburden pressure). That can be shown in the following experiential formula G = Ap'0.5 (referred to as the square root rule). This formula has been confirmed by triaxial tests at confining stress over 50 kPa (about 5m soil depth). However, in the lower stress condition, only limited data are available because of the difficulty of the triaxial tests.
To confirm the formula of the square root rule, we will measure the shear wave velocity Vs in 3 methods (plate hitting, triaxial BE (bender element), soil container BE) to determine the shear modulus G (G=¦ŃVs2) under low confining stress conditions. Then we confirm the reliability of the square root rule between shear modulus G and effective confining stress p' under low confining stress conditions. Finally, transmitting distance in BE method was changed from tip-to-tip method to bas-to-base method.
The results obtained from the study are summarized as follows:
1. In soil container BE experiment, the data were obtained only the conditions of BE distance of less than 5cm and soil depth of over 10 cm.
2. In plate hitting mehotd, the result was larger than the square root rule comparing with the other methosds. The estimation of transmiting distance might be a problem.
3. The results of triaxial BE and soil container BE nearly obey the square root rule. However, the result of soil container BE is smaller than taht of triaxial BE.
4. When the wave transmitting distance was set to the base-to-base distance in BE method from the tip-to-tip distance, the results of triaxial BE and soil container BE became closer and connectable through confining stress.
According to the results, the square root rule can be complated even in low confining stress conditions.
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