Bearing capacity of helix pile on tropical fibrous peat soil under compression loading

Abstract

Fibrous peat soil is a type of soil which comprises of fibrous organic materials, changed and fossilized to be a soil in wetland. This type of soil is generally deposited in the lowlands of East Sumatera, Central and South Borneo, and West Sulawesi Indonesia. However, due to poor characteristics associated with low shear strength, high compressibility and high-water content, the tropical fibrous peat soil has become problematic for sub-grade embankment of road constructions. The use of helix pile to reinforce the tropical fibrous peat soil for road embankment has been recently investigated. However, load-transfer mechanism of the helix pile in peat soil with more fiber content is not yet fully understood. Therefore, this paper presents laboratory scale experiment and numerical model of helix pile in fibrous peat soil under compression loadings. The effect of helix pile numbers and dimension of helices were investigated through laboratory model tests. In addition, numerical model with back-calculated input parameters from the experimental tests was also undertaken by using ABAQUS in order to examine load-displacement on the helix pile with various number of helices during loading. The results show that bearing capacity of the helix pile much influenced by the number of helices. This is due to the bearing capacity is more contributed from the bearing of helices, at about 60%-70% of the total capacity, while the shear resistance in between helices just contributes 23%-35%. The existence of fiber in the peat soil, could increase the shear resistance by factor of 1.30, while the increase of number of helices in the pile would increase the bearing by 5%. Hence, a new formula of predicting bearing capacity of the helix pile in the fibrous peat soil is proposed by modified Mitsch & Clemence Formula (1985) with modified Meyerhof & Adam’s (1968) Nq value to accommodate typical fibrous peat soil characteristics, with the accuracy of the prediction of 98% - 99% of the bearing capacity from the experimental tests.