Behavior of Stabilized Peat Soils in Unconfined Compression Tests

Wong Leong Sing,Faisal Haji Ali,Roslan Hashim

doi:10.3844/ajeassp.2008.274.279

Abstract

Problem statement: Deep stabilized peat columns were known to be economical at forming foundations to support highway embankments constructed on deep peat land. However, failure in the formation of the columns with adequate strength was often attributed to unsuitable type and insufficient dosage of binder added to the soil. Organic matter in peat was known to impede the cementing process in the soil, thus retarding the early strength gain of stabilized peat. Approach: To evaluate the strength characteristics of stabilized peat, laboratory investigation on early strength gain of the stabilized soil was conducted to formulate a suitable and economical mix design that could be effectively used for the soil stabilization. To achieve such purpose, the study examined the effect of binder, sodium chloride as cement accelerator and siliceous sand as filler on the unconfined compressive strength of stabilized peat soils after 7 days of curing. Binders used to stabilize the peat were Ordinary Portland cement, ground granulated blast furnace slag, sodium bentonite, kaolinite, lime and bentonite. All the stabilized peat specimens were tested using unconfined compression apparatus. Results: The test results revealed that the stabilized peat specimen (80% OPC: 10% GGBS: 10% SB) with addition of 4% sodium chloride by weight of binder and 50% well graded siliceous sand by volume of wet peat at 300 kg m-3 binder dosage yielded the highest unconfined compressive strength of 196 kPa. Such finding implied that the higher the dosage of siliceous sand in stabilized peat, the more solid particles were available for the binder to unite and form a load sustainable stabilized peat. Conclusions/Recommendations: It could be summarized that as the rate of hydration process of stabilized peat was accelerated by inclusion of sodium chloride, the solid particles contributed to the hardening of stabilized peat by providing the cementation bonds to form between contact points of the particles.

Highlights

Peat originates from plant and denotes the various stages in the humification process where the plant structure can be discerned[1]
It was evident from the result that the presence of lime in the binder composition of 10% L: 70% OPC: 10% GGBS: 10% SB with sodium chloride promoted the cement hydration and secondary pozzolanic reaction process
While addition of lime and cement into the wet peat basically produced more calcium hydroxide to react with slag and sodium bentonite in the stabilized soil admixture, inclusion of small amount of sodium chloride accelerated the rate of cement hydrolysis in saturated peat, thereby speeding up the setting time and increasing the early strength gain of the stabilized soil

Summary

Introduction

Peat originates from plant and denotes the various stages in the humification process where the plant structure can be discerned[1]. The decaying process of plant under acidic condition without microbial process results in the formation of organic matter in peat. This renders peat extremely soft and problematic type of soil. It is generally recognized that organic matter tends to retard the hydration and secondary pozzolanic reactions of peat stabilized with Ordinary Portland cement This is possible due to the fact that black humic acid (a component of organic matter) tends to react with calcium liberated from cement hydrolysis to form insoluble calcium humic acid making it difficult for calcium crystallization, which is responsible for the increase of cement soil strength to take place[2]. Secondary pozzolanic reaction of cement stabilized peat is retarded due to insufficient silica (SiO2) and alumina (Al2O3) that can react with calcium hydroxide [(Ca(OH)2] generated from cement hydration to form secondary calcium silicates and aluminates, which are responsible for the long term strength gain of stabilized peat[3]

Methods

Results

Discussion

Conclusion