Performance and behavior of full scale reinforced soil embankment/wall on DMM improved foundation | |
| Author | Poon, Lai Yip |
| Call Number | AIT Diss. no.GE-08-02 |
| Subject(s) | Soil cement Soil-cement construction--Simulation methods |
| Note | A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Engineering in Geotechnical Engineering, School of Engineering and Technology |
| Publisher | Asian Institute of Technology |
| Series Statement | Dissertation ; no. GE-08-02 |
| Abstract | An engineered composite material consists of backfill soil and tensile reinforcement materials commonly known as reinforced soil/earth or Mechanically Stabilized Earth (MSE) has been used extensively for construction of embankments and retaining walls worldwide. Over the years, MSE walls were formed by different combination of tensile reinforcements and facing elements. The most commonly and aesthetically pleasing facing element used in the MSE wall construction is the precast concrete facing panel besides other alternatives such as geotextile wrap-around facing, steel plate facing, gabion facing, cast-in-situ concrete facing, welded wire facing, segmental block facing and etc. Various types of reinforcements commonly used are geotextile, geogrid, steel strip, steel rod, welded wire grid, hexagonal wire mesh, etc. All these components influence the load distribution along the reinforcement in reinforced wall due to different stiffness modulus. Determination of quantity of reinforcement used in MSE wall is closely related to the actual tensile load needs to be stabilized. Therefore, prediction using an accurate method to obtain an optimum quantity of reinforcement is essential. Numerous experiments are performed to investigate the interactions between the hexagonal wire mesh and the silty sand backfill including the determination of the index properties of the backfill materials, the shear strength parameters, the interaction coefficients. Laboratory testing program such as index tests, compaction tests, and pullout tests were conducted. The full scale field test embankment was constructed at the Wangnoi Power Plant located 35 km north of campus of Asian Institute of Technology (AIT) in Bangkok, Thailand. The soft foundation soil was improved with DMM cement-clay piles using jet grouting pressure of 20 MPa. The hexagonal wire mesh reinforced embankment system was extensively instrumented in the DMM improved foundation and within the embankment itself in order to observe its behavior during construction and post construction phases, and further evaluate its performance. The DMM improvement has effectively reduced the settlement of reinforced test embankment by 70%. The average excess pore water pressure just after the installation of DNlM cement-clay pile using jet grouting pressure of 20 MPa were 9.2 kPa and 27 kPa at 3 and 6 m depth within the improvement zone, respectively. These excess pore pressures were dissipated to 1.6 and 8.3 kPa after 70 days. The jet mixing method has created cement-clay piles with higher after-curing void ratio and hence, higher coefficients of permeability and consolidation. The analytical back-analysis obtained the compressibility ratio (mmv,p/mv,c) of 0.10; coefficient of consolidation of the deep mixing }pile (cv,p) and of the surrounding clay (cv,c) of 800 and 2.0 m²/yr, respectively. Numerical simulation of the full scale test embankment was conducted by PLAXIS finite element 2D and 3D program. The finite element program was 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 DMM improved foundation and the surrounding soft clay mostly depended on the assumed cement-clay pile modulus and permeability values. The lateral wall movements were well-predicted after about 400 days of construction. The maximum tension line agreed reasonably well with the coherent gravity bilinear failure plane. The sensitivity analyses of settlements, excess pore water pressures and lateral wall movements were performed by varying the cement-clay pile modulus and permeability, interaction coefficient, and stiffness of reinforcement. The settlements and the excess pore water pressures changed significantly when the cement-clay pile modulus permeability were varied. Morever, the interface coefficient of the hexagonal wire mesh affected the lateral wall movements. Furthermore, the higher interface coefficient yielded less wall/wire mesh movement as expected. Numerical simulation in 2D and 3D conditions revealed that the clay-cement modulus; E, and the interaction coefficient of hexagoanal wire mesh with backfill soil; R, were 50 MPa and 0.67, respectively; agreed well with observed data. However, the permeability ratio of cement-clay pile; kpile/ksoil, were 10 and 18.8, in 2D and 3D conditions agreed well with observed data; respectively. Coherent gravity method was found to overestimate the hexagonal wire mesh reinforcement load in reinforced wall on DMM improved foundation. Subsequently, the K-stiffness method based on the new load distribution factor envelope was proposed to improve the accuracy of predicting the maximum tensile load along the reinforcements |
| Year | 2009 |
| Corresponding Series Added Entry | Asian Institute of Technology. Dissertation ; no. GE-08-02 |
| 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) | Pham Huy Giao ;Hadikusumo, B. H. W. ;Panich Voottipruex; |
| Degree | Thesis (Ph.D.) - Asian Institute of Technology, 2008 |