| Author | Singh, Narayan |
| Call Number | AIT Thesis no.GT-85-29 |
| Subject(s) | Soil consolidation
|
| Note | A thesis submitted in partial fulfillment of the requirements for the degree of Master of Engineering. School of Engineering and Technology |
| Publisher | Asian Institute of Technology |
| Abstract | To study the effectiveness of prefabricated plastic band drains in soil improvement of Bangkok clay, Membra drains, a type of pl astic band drain, were installed in triangular patterns at 1.5 m spacing t o a depth of 8 m in a test site inside the AIT Campus. Field and laboratory tests were carried out to determine the compressibi1ity and strength characteristics of the subsoil. The coefficient of horizontal consolidation, Ch, was determined from oedometer tests with horizontal oriented samples. A 4 m high we ll- instrume nted test embankme nt was constructed. Both vertica l and lateral displacements and pore pressure dissipation were observed during and after the construction. Until the time of thesis submission, the tota l monitoring period was 110 days since the beginning of the embankment construction. The results within this period are pr esented herein. The maximum recorded surface settlement on llOth day i s 19.79 cm. The predicted t ime for 90% consolidation is 340 days. The consolidation settlements were recorded at 2.5 m, 5.5 m and 7 m depths. At 110 days 44% and 36% consolidation has occurred at 3 m and 6 m depths, respective ly.The maximum subsurface later a 1 displacements occurred between 2.5 to 4.5m depth in soft clay zone. But minimum surface lateral movement was observed at the weathered clay near the surface. Observations and f ield measurements indicated that excess pore presure dissipated at faster rate than predicted; the rate of dissipation was faster at 3 m depth than at 6 m. In the analysis, the one-dimensional method unde rpred i cted the settlements while the Skempton-Bjerrum method overpredicted the settlement in most of the methods o f stress distribution. The settlement predicted from Elastic method was lower than the observed. In pore pressure predicti on, Henkel 's method gave a fair agreement between observed a nd predicted pore pressure at 6 m depth. Perloff's method was fo und to predict a better approximation of stress distribution in soil. It was found that in the case of prefabricated drains, Hansbo's theory was found to predic t better rate of consol idat ion than Barron's t heor y. Back analysis of Ch from fie l d pe r formance of d r ains gave about 1.5 to 4 times higher values than that determined fr om consolidation tests. The shear s trength of the clay was cons iderably reduced dur ing the installation of drains because of disturbance caused by penetrat ion of mandrel. However, a set of f i e l d vane shear tests carried out on 57th day after constructi on indicated some increase in shear strength t han at the begining of drains insta ll a tion. Bjerrum's method gave drain effi ciency of 64.4%. But it was found that the drai n e fficiency wi 1 1 reduce to 14.6% during t he rainy season which i ndicated the effect of subsidence on the performance of drains. An additional load of 17.5 kN/sqm wi 11 be needed to overcome this defficiency and this together with t he existing pre load can maintain an overall effi ciency of 77%. The installation of pr efabricated drai ns did not clearly indicated any recharge of pore water pressure at deeper depths. The presence of discontinuous sand and silt seams in AIT clay can significantly contribute to the rate of consolidation settlements if vertical drains are installed with preloading above the maximum past pressure. |
| Year | 1986 |
| Type | Thesis |
| School | School of Engineering and Technology (SET) |
| Department | Other Field of Studies (No Department) |
| Academic Program/FoS | Geotechnical and Transportation Engineering (GT) |
| Chairperson(s) | Bergado, Dennes T. |
| Examination Committee(s) | Balasubramaniam, A.S. ;Whitney, Joseph B. R. |
| Scholarship Donor(s) | Government of Denmark |
| Degree | Thesis (M.Eng.) - Asian Institute of Technology, 1986 |