Interactions and performances of geogrid reinforced tire chips-sand lightweight embankment on soft ground | |
| Author | Tawatchai Tanchaisawat |
| Call Number | AIT Diss. no.GE-07-01 |
| Subject(s) | Rubber--Reinforcement Fillers (Materials)--Testing Tires--Performance Geogrids |
| 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-07-01 |
| Abstract | Scrap tires are undesired urban waste, the volume of which is increasing every year. One of the possible use of this waste is to use shredded tires alone or mixed with soil as a lightweight backfill. This study is aimed at studying the interactions between geogrid and tire chips-sand mixture, performances of full scale geogrid reinforced test embankment and numerical simulation of this full scale test embankment. Numerous experiments are performed to investigate the interactions between the geogrid and the tire chips-sand mixture including the determination of the index properties of the backfill materials, the shear strength parameters, the interaction coefficients, and the efficiency of geogrid reinforcements in tire chips-sand backfills. Laboratory testing program such as index tests, compaction tests, pullout tests, and large-scale direct shear tests were conducted. Saint-Gobain (geogrid A) and Polyfelt (geogrid B) were selected as reinforcing materials. Tire chip-sand mixtures with mixing ratios of 0:100, 30:70, 40:60, and 50:50 by weight were used as fill materials. The test results revealed that the unit weight of tire chip-sand mixtures depended more on the sand content, and less on the water content. The mixture at the mixing ratio of 30:70 by weight or 50:50 by volume was found to be the most suitable fill material. The pullout resistance and the pullout interaction coefficients of geogrid A were slightly higher than those of geogrid B. Moreover, the ultimate tensile strength of geogrid B was slightly lower than that of geogrid A. In contrast, in the direct shear resistance, the direct shear interaction coefficients, and the efficiency values of geogrid B were slightly higher than those of geogrid A. Since the interaction coefficient between geogrid and tire chip-sand mixtures has exhibited more of direct shear mechanism than pullout mechanism, the geogrid B was utilized in this study. The interaction coefficients between the tire chips-sand backfill with 30:70 mixing ratio by weight were found to be 0.71 in pullout mode and 0.92 in direct shear mode. The practical implication revealed that the use of geogrid B reinforcements in tire chips-sand mixture is beneficial in terms of vertical spacing, factor of safety, embedment length and tension in reinforcement compared to inextensible hexagonal wire reinforcement with conventional backfill. The full scale field test embankment was constructed at the campus of Asian Institute of Technology (AIT) in Bangkok, Thailand. The geogrid reinforced embankment system was extensively instrumented in the subsoil and within the embankment itself in order to observe its behavior during construction and post construction phases, and thereby evaluate its performance. The unit weight of rubber tire chip-sand mixtures with 30:70 % by weight is 13.6 kN/m3 compared to conventional sand backfill of 18.0 kN/m3. The former is lighter by about 75 % than the latter. The total settlement magnitude of 122 mm at ground surface is 67.5% less when compared to the corresponding value of 400 mm for conventional backfill without foundation treatments. The maximum pore water pressure of 57 kN/m2 was measured at 3 m depth at the period of full height of embankment construction. After the fifteenth day, there was rapid dissipation of excess pore water pressures for around 35 days followed by a period of low rate of dissipation until the pore pressures became constant. The maximum lateral wall movement at top of wall is 125 mm compare to 350 mm of hexagonal mesh reinforced sand backfill. This resulting in 65% less in lateral wall movement when using tire chips-sand backfill reinforced with geogrid. This lightweight geomaterials can be used for embankment construction on soft ground area to reduce total settlement and lateral movement of structure. Numerical simulation of the full scale test embankment was conducted by PLAXIS finite element 2D program and FLAC3D finite difference 3D program. The finite element program is used to simulate the behavior by means of undrained analysis in the construction stage and thereafter consolidation analysis was performed during the service stage. The settlement predictions of the soft clay foundation mostly depended on the assumed thickness of the weathered crust and the OCR values of the soft clay layer. The predicted excess pore water pressures were sensitive to the OCR values of the soft clay layer. The lateral wall movements were overpredicted by the analysis due to the partially drained consolidation process at the early stage of the construction. The FEM computed geogrid movements were smaller than the observed field data due to the use of lightweight tire chips-sand backfill. The maximum tension line agreed reasonably well with the coherent gravity bilinear failure plane. The sensitivity analyses of settlements, excess pore water pressures, lateral wall movements, geogrid movements and tensions in geogrid were performed by varying the weathered crust thickness, the OCR values of soft clay, the permeability values of the soft clay and the interface coefficient of the geogrid. The settlements and the excess pore water pressures changed significantly when the OCR and the permeability values of soft clay were varied. The interface coefficient of the geogrid reinforcements affected the lateral wall movements, geogrid movements and tensions in the geogrids. The higher interface coefficient yielded less wall/geogrid movement and resulted in higher tensions in geogrids as expected. The 2D and 3D condition simulation by FLAC3Dprogram revealed that the resulted from 3D condition are underestimated compare to 2D condition and observed data in view of settlements and excess pore water pressure. The predicted lateral wall movement and tension in geogrid by 2D condition method agreed reasonably well compare to 3D condition. The results of analyses show that the numerical analysis using 2D plane strain conditions provided satisfactory predictions for the field performance. |
| Year | 2008 |
| Corresponding Series Added Entry | Asian Institute of Technology. Dissertation ; no. GE-07-01 |
| 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;Panich Voottipruex; |
| Scholarship Donor(s) | Kasetsart University, Chalermprakiat Sakonnakhon Province Campus, Sakonnakhon, Thailand; |
| Degree | Thesis (Ph.D.) - Asian Institute of Technology, 2008 |