REVIEW OF LITERATURE AND SCOPE OF PRESENT STUDY
2.4 GEOSYNTHETIC REINFORCED SOIL MATTRESS OVERLYING STONE COLUMN/ PILE REINFORCED CLAY STONE COLUMN/ PILE REINFORCED CLAY
Gupta and Somnath (1994) used the concept of geocell in the construction of box culverts over marine clay deposits in New Bombay area. Since the depth of marine clay was more than 6 meters, first tubular gabions were constructed in the soft soil with ends resting on hard moorum layer underlying the soft clay. Next the geocell mattress was constructed on the clay surface. In this arrangement the gabions serve as granular piles and the geocell mattress as flexible pile cap. The performance of the geocell mattress has been reported to be satisfactory.
Han and Gabr (2002) carried out a numerical study to investigate pile-soil- geosynthetics interactions by considering three major influence factors: the height of the fill, the tensile stiffness of geosynthetic, and the elastic modulus of pile material.
The obtained results have shown that inclusion of geosynthetics in the earth platform can reduce the settlements above the pile head. The stress concentration ratio and the
maximum tension in geosynthetic increase with the height of the embankment fill, the tensile stiffness of geosynthetic, and the elastic modulus of the pile material. The distribution of tension force in the geosynthetic reinforcement indicated that the maximum tension occurs near the edge of the pile.
Deb et. al. (2007) have developed a mechanical model to predict the behavior of a geosynthetic-reinforced granular fill over soft soil improved with stone columns. The saturated soft soils were idealized by Kelvin–Voight model to represent its consolidation behavior. The stone columns were idealized by stiffer springs.
Pasternak shear layer and rough elastic membrane represented the granular fill and geosynthetic reinforcement layer, respectively. The nonlinear behavior of the granular fill and the soft soil was considered. Effect of consolidation of the soft soil due to inclusion of the stone columns had also been included in the model. An iterative finite difference scheme was applied for obtaining the solution. The results indicate that inclusion of the geosynthetic layer effectively reduces the settlement. Nonlinearity in the behavior of the soft soil and the granular fill is reduced due to the use of geosynthetic reinforcement layer.
Abdullah and Edil (2007) carried out a series of tests on embankment constructed over soft ground to evaluate the performance of different types of load transfer platform (LTP) placed at interface of embankment and clay bed reinforced with rammed aggregate piers (called ‘geopiers’). Three types of LTP were constructed in accordance with the recommended design for each: a geosynthetic-reinforced LTP with two layers of geogrid (catanary LTP), a geosynthetic reinforced LTP with three or more layers of geogrid (beam LTP), and a reinforced concrete LTP. The results indicate that the differential settlement between the geopiers and the matrix soil is relatively small in all LTP sections, with the smallest in the beam LTP. The tensile
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strain in the geogrid was approximately 60% of the allowable design strain of 5% in the beam LTP. In the central LTP, the tensile strain in the geogrid was approximately 20% of the allowable design strain of 6%, although the differential settlement was larger than the beam LTP. The total and differential settlements observed indicate that the use of low stiff geopier column together with LTPs provide an attractive option for supporting low embankments on soft ground with tolerable total and differential settlements. The presence of LTPs and the supporting columns also tend to reduce the lateral movement of the foundation soil. The cost analysis of the different LTPs indicates that construction cost for geosynthetic-reinforced LTPs are likely to vary with locality, however, it appears that beam LTPs offer a less costly approach, with enhanced performance.
Madhav et. al. (2009) studied the interaction between granular pile and the overlying raft using continuum approach. Results show that consideration of radial displacement compatibility does not influence the settlement response or sharing of the applied load between the granular pile and the raft. The percentage of load carried by the granular pile increases with the increase in its stiffness and decreases with the increase of relative size of the raft. The normal stresses at the raft soil interface decreases with the increase of stiffness of granular pile and/or relative length of granular pile. The influences of granular pile stiffness and relative length of the granular pile are found to be more for relatively large size of raft. The percentage of load transferred to the base of granular pile increases with increase in size of raft.
Arulrajah et. al. (2009) reported that the construction of a high speed railway project for trains of speed of upto 160km/hr, between Rawang and Bidor (110km long) in Peninsular Malaysia. The ground improvement methods adopted in the project were vibro-replacement with stone column, dry deep soil mixing (cement columns),
geogrid reinforced pile embankments with individual pile caps. It was observed that where a geogrid layer was laid over the pile caps its tension provides additional support and prevents lateral spreading of the embankment.