Pseudo-elastic shear modulus of Bangkok clay using bender elements | |
| Author | Lohani, Tara Nidhi |
| Call Number | AIT Thesis no.GE-96-17 |
| Subject(s) | Strains and stresses Clay--Thailand--Bangkok--Testing |
| Note | A thesis submitted in partial fulfillment of the requirements for the degree of Master of Engineering, School of Civil Engineering |
| Publisher | Asian Institute of Technology |
| Series Statement | Thesis ; no. GE-96-17 |
| Abstract | The stiffness profile of the Bangkok clay at very small strain, 10-3 % and less is examined using relatively new laboratory technique, called bender element test. The measured experimental results were plugged into suitable correlations of initial shear modulus (Gmax) with easily available borehole data. In total, thirteen tests were used for the interpretation. The reliability of the test in interpreting the site values are also checked. As the in-situ measurements of shear wave velocity (V5) involves very small disturbance of the original ground, Gmax value from V5 is taken as correct representative values. The data from the seismic cone penetration test is used for the comparison with Gmax measured in the laboratory. Previous downhole survey performed by Ashford et al. (1996) was also compared. With only one exception out of three test results at ,9-10 m at Nong Ngoo Hao (NNH) site, all the laboratory test results for the soft clay is iµ close agreement with field values. It can thus be concluded that this test can very well represent the site characteristics. For NNH site which has relatively uniform deposit of clay extending to deep depths, the results match closely. For the AIT test site, the clay portion of the profile was represented well, but in weathered clay and stiffer clay, scatter with laboratory test has increased. In those layers, even results from seismic tests differ very much. This may be due to the non-uniform profile of Gmax with depth at AIT location. Some of the relations compnsmg different void ratio functions were observed in formulating the proposed new relation. With many trials made, by taking some of the existing formulae, the type ( 1 +e r2 .4 was found applicable and adopted for all the interpretations. The value of the exponent n ·to the effective vertical stress, ranged from 0.4 and 0.75 but most of them fall in the range of 0.6. The void ratio relations e-1.s and e-1.3 are pretty similar and seems to represent well in the tested range. Sample disturbance effect is also examined for the results of bender element tests. The comparison of results between fixed piston sampler equipped with mechanical pushing (FP) and floating piston sampler by · manual pushing (ST) gives the idea that at and below preconsolidation pressure, the results from the latter type could underestimate the actual value. After the clay reaches normally consolidated stage or with one unload-reload cycle, the values from both methods are comparative. Reconstituted samples from NNH site are prepared and tested to see the effect of soil structure on·.Gmax· The effect is higher for higher OCR depth of 9-10 m than 12-13 m. The friction of the consolidometer cylinder is found affecting the result quite a lot, so triaxial type of testing should be preferred. |
| Year | 1997 |
| Corresponding Series Added Entry | Asian Institute of Technology. Thesis ; no. GE-96-17 |
| Type | Thesis |
| School | School of Civil Engineering |
| Department | Department of Civil and Infrastucture Engineering (DCIE) |
| Academic Program/FoS | Geotechnical Engineering (GE) |
| Chairperson(s) | Shibuya, Satoru; |
| Examination Committee(s) | Balasubramaniam, A. S. ;Tian Ho Seah; |
| Scholarship Donor(s) | DAAD, Germany; |
| Degree | Thesis (M. Eng.) - Asian Institute of Technology |