Performance of embankment on bamboo-geotextile composite reinforced soft clay

Abstract

Road embankments and other constructions on deposits of natural soft clay are still a challenge in geotechnical engineering work. The used of various soil improvement methods to stabilise the soft clay need to be carried out in order to increase the bearing capacity and reduce the settlement. Most methods are costly while the time taken to complete the improvement works takes a long period. The Soft Soil Research Group of Universiti Teknologi Malaysia had proposed the combined used of bamboo as a green technology and a layer of low strength geotextile to become a reinforcement system called the “Bamboo-Geotextile Composite” (BGC). Full-scale embankments on BGC system reinforced soft clay (BGC embankment) together with an embankment on unreinforced soft clay (UR embankment) and also an embankment on high strength geotextile reinforced on soft clay (HSG embankment) had been constructed. Each embankment measured 10 m long, 16 m wide and about 3 m height. Semantan Bamboo of about 8 cm outer diameter with 48-94 MPa tensile strength and 43-49 MPa bending strength, and TS 40 Geotextile of 13.5 kN/m length tensile strength were selected as the materials for the system. In BGC system, the bamboo poles arranged in 1 m x 1 m square pattern were laid at the top of soft clay layer and the geotextile was then laid on top of bamboo. The objectives of this research are to determine the performance of BGC embankment and to develop a representative method of modelling the BGC embankment through the evaluation of field data using finite element (FE) model from PLAXIS 2D computer software. The embankments were monitored since the start of the construction until Day 418. Field monitoring data showed that the used of BGC system reduced more than 20% of immediate settlement and 57% of lateral movement during construction compared to UR embankment. The confinement of the soft clay in square pattern arrangement of bamboo increased the bamboo stiffness while the tensile resistance of horizontal ribs and compressive resistance of vertical ribs of bamboo prevented excessive settlement. The BGC system retained the surcharge load and distributed only small load to the underlain soft clay soil resulting in smaller consolidation settlement compared to UR and HSG embankments. The BGC system was best modelled as a geogrid element using PLAXIS 2D software. Although the drainage capability as well as the buoyancy effect of the BGC system could not be modelled, the settlement at the centre point of BGC embankment showed that the result from FE model differs only 1% from the field settlement at the end of construction while at Day 418, the model overestimated about 6%. For the lateral movement, the model predicted about 100% higher than the field value while the location of the maximum lateral movement was predicted to occur at a greater depth compared to the field performance. Hence, it can be deduced that the BGC embankment can be modelled using PLAXIS 2D software, in which the prediction for settlement can be better represented.