Vol.8 (2018) No. 3 ISSN: 2088-5334 Compression Behavior of Fibrous Peat Stabilized with Admixtures of Lime CaCO3+Rice Husk Ash and Lime CaCO3+Fly Ash Noor Endah Mochtar # , Faisal Estu Yulianto * # Civil Engineering, FTSP, Institut Teknologi Sepuluh Nopember, Surabaya, Indonesia E-mail: noormochtar@gmail.com * Civil Engineering, Engineering Faculty, Madura University, Pamekasan, Indonesia. E-mail: faisal_ey@yahoo.co.id Abstract— Compression behavior of stabilized fibrous peat has similar behavior with the initial one. Therefore, one step loading consolidation test is still applicable for the stabilized fibrous peat to predict its compression. The stabilized fibrous peat behavior, however, still depends on the type of the admixture used and stabilization age or curing period. Based on that reason, this study was carried out to study the change of compression behavior of the stabilized peat and to know whether the correction curves developed for laboratory compression parameters are still applicable to predict the settlement of the stabilized peat in the field. For this purpose, two types of stabilizing material adopted, admixtures lime CaCO3+Rice Husk Ash (admix-1) and lime CaCO3+Fly Ash (admix-2). The stabilized peats were cured and tested at different curing periods 20, 30, 45, 60 and 90 days to check their behavior changes. Besides, laboratory models of peat stabilized at different layer thicknesses 1/3H, 2/3H, and H (H=peat sample thickness) were carried out to monitor their settlement under 50kPa load at different curing periods. This settlement is then compared with the predicted settlement. The results show that the fibrous peat stabilized with admixture-2 gives better behavior improvement than the one stabilized with admix-1; it is, however, then slightly decreases after 60 days of curing periods due to the fiber decomposition. Peat stabilized with admix-2 also give first settlement prediction when it is compared to the settlement of stabilized peat in the laboratory model. Keywords— admixture; compression; fibrous peat; fly ash; laboratory model; lime CaCO3; rice husk ash; stabilization I. INTRODUCTION Peat is a soil which has very high organic content (≥75%) as a product of organic materials decomposition [1]. For fibrous peat which has a fiber content of more than 20% [2], the fibers dominantly influence its characteristics especially its compression behavior [3], [4]. The e vs. log σ curve of fibrous peat has two straight lines, and ΔH vs. log t curve has four components of compressions [4]. In this case, the Terzaghi consolidation method [5] is not applicable to fibrous peat soil. In 1979, Gibson Lo model was adopted to evaluate the compression behavior of the fibrous peat [7]. For this method, it is used one step loading consolidation test in the laboratory and the load applied is the same as the load in the field. Parameters obtained from the laboratory test are primary compression factor (a), secondary compression factor (b), and rate factor for secondary compression (λ/b). To predict the field settlement, the laboratory parameters are corrected using the correction curves [8]. This method had been successfully applied for Palangkaraya fibrous peat [9]. To improve the compression behavior of the fibrous peat, stabilization method using admixture materials was adopted [10]-[12]. They figured out what type of admixture used and its curing period affects the stabilization results. Their effect on the stabilized fibrous peat compression will be discussed in this paper. Besides, the prediction of stabilized peat settlement using the correction curve [8] is also be presented. II. MATERIAL AND METHOD The research reported herein was carried out in the Soil Mechanics laboratory. Materials used were fibrous peat, lime CaCo3, rice husk ash (RHA), and fly ash (FA). The fibrous peat was taken from Barengbengkel, Palangkaraya, Central Kalimantan. In Fig. 1, Scanning Electron Microscope (SEM) of the peat studied is presented, and its parameters are given in Table 1. Peat parameters were determined based on Peat Testing Manual [13]. From those parameter values, the peat studied was classified as “Hemic Peat soil with Medium Ash Content and Highly Acid” (Standard Classification of Peat Samples by Laboratory Testing ASTM D4427-92 [14]). There were two types of admixture used in this study; those were an admixture of 30% lime CaCO3+70% RHA (admix-1) and admixture of 30% lime CaCO3+70% FA 792