Performance of Reinforced Load Transfer Platforms for Embankments Supported by Deep Cement Mixing Piles

Abstract

A 6 m high reinforced embankment was supported by Deep Cement Jet Mixed Piles on Soft Bangkok clay. Each clay-cement pile (or soil-cement column) had diameter of 0.50 m and length of 9.0 m and were installed at 1.5 m center to center spacing in square pattern. The performance of the full scale test embankment was observed for a period of one year until 90% consolidation was achieved. Subsequently, analytical analyses were performed and the results were compared with the measured data. Consequently, the relevant geotechnical parameters were back-calculated including the permeability ratio, compressibility ratio, and the coefficients of consolidation of the pile and surrounding clay. Since the actual load transfer mechanism is neither equal strain nor equal stress, weighting factors were utilized to obtain the average degree of consolidation. The results demonstrated that at any time, the overall load transfer mechanism can be taken as 80% equal strain condition plus 20% equal stress condition. Furthermore, the deep mixing piles has resulted in 70% settlement reduction in the improved foundation. 1. INTRODUCTION Ground improvement by cement stabilization can be broadly divided into shallow stabilization and deep stabilization. Shallow stabilization, which includes stabilization of subgrade for roadways and airfields and other similar structures, normally employs low water mixing. The deep stabilization, on the other hand, includes deep mixing method (DMM) using either slurries or powder of cement to form columns of improved soil in the ground. The improved column of soil is considered to act as reinforcement or as a pile, transferring the load to the skin and to the bottom-end of the improved column of soil. The methods of mixing are broadly divided in to two: either mechanical mixing or high pressure jet mixing (Kamon and Bergado, 1991; Porbaha, 1998). In the mechanical mixing the chemical admixtures are mixed into the soil by mixing blades, while in the jet mixing the same are mixed into the soil through jet of water or slurries of admixtures. The slurry deep mixing and jet mixing methods would normally produce high water content cement- admixed clay; besides, the soft clay deposit normally has high water content. The technique of reinforcing earth has been extensively used for construction of earth retaining wall and embankment slopes, and in stabilization of embankments placed on soft ground. The reinforced soil mass is generally called Mechanically Stabilized Earth (MSE). MSE structures can be divided into three main parts: