Behavior of smear zone and performance of PVD under vacuum preloading with and without heat | |
| Author | Jaturonk Saowapakpiboon |
| Call Number | AIT Diss. no.GE-09-01 |
| Subject(s) | Vertical drains--Thailand--Bangkok Clay soils--Thailand--Bangkok |
| Note | A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Engineering in Geotechnical and Geoenvironmental Engineering, School of Engineering and Technology |
| Publisher | Asian Institute of Technology |
| Series Statement | Dissertation ; no. GE-09-01 |
| Abstract | The disadvantage of prefabricated vertical drains (PVDs) with surcharge preloading are the longer preloading period due to smear effect and the instability problem due to surcharge load that limited the height of the surcharge embankment. PVDs with embankment preloading combined with vacuum pressure has been utilized to reduce the instability problem and to accelerate the rate of consolidation. Vacuum consolidation can reduce the pore pressure and maintain constant total stress instead of increasing the total stress. The effective stress is increased due to the reduced (less than atmospheric) pressure in the soil mass. On the other hand, Thermo-PVD is the combination of heat with PVD which the horizontal hydraulic conductivity in smear zone, ks, around the PVD increased with heat application up to 90°C and minimized the retardation of the smear zone. This study consisted of laboratory investigations using small and large scale consolidometer tests and Scanning Electron Microscope (SEM) tests, numerical simulation. The laboratory tests consist of surcharge preloading combined with PVD (PVD), vacuum and surcharge combined with PVD (Vacuum-PVD), heat and surcharge combined with PVD (Thermo-PVD), heat, vacuum pressure and surcharge combined with PVD (Thermo-Vacuum-PVD). The field investigations consist of conventional PVDs and conventional PVDs combined with vacuum preloading (Vacuum-PVDs) using back calculation and numerical simulation. Laboratory model tests were performed on small and large scale consolidometers with undisturbed and reconstituted specimens. The method of Hansbo (1979) was applied in the back calculation. For small scale consolidometers, the increased hydraulic conductivity of the smear zone of undisturbed specimens using Vacuum-PVD and Thermo-PVD resulted in the decrease in kh/ks of 9.80% and 11.76%, and the increase in Ch by 1.25% and 12.50%, respectively. The increased hydraulic conductivity of the smear zone of reconstituted specimens using Vacuum-PVD and Thermo-PVD resulted in the decrease in kh/ks of 16.67% and 22.22%, and the increase in Ch by 51.03% and 53.79%, respectively. On the other hand, in the large scale consolidometer, the increased in Ch of reconstituted specimens using Vacuum-PVD, Thermo-PVD and Thermo-Vacuum PVD of 15.54%, 116.06% and 126.42%, and the increase in kh/ks by 10.00%, 53.33% and 63.33%, respectively. Vacuum pressure can increase the horizontal coefficient of consolidation, Ch. While, heat can increase the coefficient of horizontal consolidation, Ch with the reduction of Kh/Ks by reducing the drainage retardation effects in the smear zone around the PVD that resulted in faster rates of consolidation due to the increase in hydraulic conductivity with decreasing pore water viscosity at high temperatures. In addition, Vacuum-PVD images have not much difference compared to conventional PVD but have lower orientations of particles and higher percent of porosity than Thermo-PVD and Thermo-Vacuum PVD, respectively, and also the better orientation was found at locations adjacent to the PVD from the SEM results. The field data analysis based on the back-calculated results showed that the average kh/ks were 9.4 and 7.1 for the conventional PVDs and the Vacuum-PVDs, respectively. The average Ch values increased slightly from 2.49 m²/yr for the conventional PVDs to 4.43 m²/yr for the Vacuum-PVDs. The results of 2D finite element simulation in the field data show that the simulated settlement yielded quite good simulations of settlement both at the early stage and final loading stage. The Vacuum-PVDs improvement is faster than the conventional PVDs due to the reduced effect of smeared zone and increased coefficient of consolidation during vacuum preloading |
| Year | 2010 |
| Corresponding Series Added Entry | Asian Institute of Technology. Dissertation ; no. GE-09-01 |
| Type | Dissertation |
| School | School of Engineering and Technology (SET) |
| Department | Department of Civil and Infrastucture Engineering (DCIE) |
| Academic Program/FoS | Geotechnical Engineering (GE) |
| Chairperson(s) | Bergado, Dennes T.; |
| Examination Committee(s) | Noppadol Phien-wej ;Pham Huy Giao ;Kunnawee Kanitpong; |
| Scholarship Donor(s) | The Royal Thai Government ;Thailand Department of Highways; |
| Degree | Thesis (Ph.D.) - Asian Institute of Technology, 2009 |