Sina Kazemian

Settlement Problems in Peat Due to Their High Compressibility and Possible Solution Using Cement Columns

Tropical peat soils are considered as extremely soft, wet, unconsolidated deposits. These kinds of soils are geotechnically problematic due to their high compressibility or high settlement and low shear strength. Cement columns may be used to improve the settlement problem of these soils. This paper describes the results of the effects of cement columns on the compressibility of fibrous tropical peat soils. Coefficient of consolidation, compression index, coefficient of secondary compression, and coefficient of volume compressibility were obtained by a Rowe cell test for both, untreated peat soil and peat soil treated with cement column. The results indicate that installing cement columns and increasing cement ratio could reduce the compressibility of peat soils and decrease its settlement dramatically.

Stabilization of organic soil using sodium silicate system grout

Cation binding by organic matter content (OMC) in soils has consequences for the behaviour of the organic compounds themselves, influencing adsorption, aggregation, and solubility, and thereby soil structure, translocation of organic matter within soils, and transport to waters. The study reported here involved a number of experiments using composition of alkaline earth metals grout to treat organic soils, in order to provide a better understanding of the engineering behaviour of this soil after stabilization. Besides, it provides a series of the laboratory mix design and testing which in turn provide an essential guide regarding the choice, dosage and economical amount of chemical binders. We carried out a series of batch test using composition of sodium silicate system binders to find their effects on physic-chemical properties of the organic soil. The results show that in the batch tests unconfined compressive strength (UCS), increases of up to 220% of the soil’s baseline strength can be achieved by adding the 3 mol/L Na2Sio3, while UCS results enhanced to 270% having an activator CaCl2xa0and/or Al2(SO4)3xa0additives. Moreover, using higher molarities of CaCl2xa0(for example, 1mol/L) did not show any remarkable effect on the UCS results. n n xa0 n n Key words:xa0Organic soil, soil improvement, cationic stabilizer, cementation, unconfined compressive strength, sodium silicate grout system.

Effect of peat media on stabilization of peat by traditional binders

Peat normally has high organic matter content and is generally associated with high compressibility and high magnitude and rates of creep. It may also be associated with poor strength characteristics and a risk of large deformation. The main specifications in the peat nature are the presence of acidic or less commonly alkaline media, combined with axa0high level of ground water. One of the most common methods for improving peat is by cement columns by adopting the dry mixing method. This paper presents the results of the effects of peat nature on cementation and pozzolanic reactions over time by treating peats with ordinary Portland cement (cement) and blast furnace slag (slag). Samples of peat were prepared by mixing specific amounts of cement and also cement and slag (cement-slag). Unconfined compressive strength (UCS) of the stabilized samples was evaluated after curing for 15, 45 and 90 days in different pH media.xa0The results indicated that, acidic media (pH = 3 and 5) has negative effect on the cementation and pozzolanic reactions, whereas alkaline media (pH = 10 and 12) improves the strength of the mixtures. It showed that, the aggressive media has less negative effect on treated peat with cement-slag as slag decreases the permeability of the mixture. Furthermore,xa0the strength of treated peat in an acidic media was found to be less compared with others due to its physico-chemical characteristics. n n xa0 n n Key words:xa0Peat nature, cementation, pozzolanic reactions, dry mixing method.

Assessment of stabilization methods for soft soils by admixtures

Soil stabilization by admixture was developed in Japan during 1970s and 1980s. The treated soil has greater strength, reduced compressibility and lower hydraulic conductivity than the original soil. The original technique known internationally as the deep mixing method (DMM) was developed simultaneously in Sweden and Japan in the mid-1970s. It is an in-situ soil treatment technology whereby the soil is blended with cementitious and/or other materials. Jet Grouting is suitable to be used as the injection method for the DMM. It utilizes a fluid jet (air, water and/or grout) to erode and mix the in-situ soft or loose soils with grout. The grouting method is one of the ground improvement methods suitable for the soft soil. Chemical stabilization is the effective method to improve the soil properties by mixing additives to soils. Selecting the right method for soil stabilizing however, depends on several conditions like; soil type and layering, magnitude of the load, situation and type of the project, among others. In this paper, the authors have investigated and compared the different methods used according to their characteristics. By utilizing this information and their inter-relationship, it is expected that the geotechnical engineers will be in a better position to select a suitable method to improve the soft soils and overcome their difficulties.

The Effect of Cement-Sodium Silicate Grout Compounds on Void Ratio and the Coefficient of Secondary Compression of Treated Fibrous Peat

Peats have low shear strength and high deformation characteristics. Peat is a naturally occurring material that is extremely soft with a high moisture content and exists in an unconsolidated state. The conventional binders used are cementitious materials, and the introduction of a new binder, sodium silicate, with other additives gives a better output than the conventional peat treatment. This article describes a laboratory study on the effect of different compounds of cement–sodium silicate grout on void ratio and the coefficient of secondary compression of fibrous peat. It is shown that by increasing the amount of sodium silicate (within 2.5 %), cement, and kaolinite in treated peat, we were able to decrease the mentioned properties of treated peat.

The Rheology Properties of Peat Treated with Sodium Silicate System Grouts

In the present study, the effect of sodium silicate stabilizers on the flowability and soil volume reduction are investigated. Two secondary additives are also admixed in order to assess their effects. Accordingly, a series of viscosity, shrinkage limit, and pH tests were performed to assess the effects of the mentioned cationic reagents as a suitable grout. It is observed that the sodium silicate grout has a viscosity higher than water and causes a very high soil volume reduction during the air curing. The reduction in the soil’s volume was reduced significantly when secondary additives were used. The microstructure analysis performed to help understanding the reason of highly soil’s volume reduction due to presence of sodium silicate reagent.

Sensitivity analysis of slopes affected by possible earthquake loading and heavy rainfall: Case study

The effect of seismic loading on slope failure is studied both experimentally and analytically to establish the spatial and temporal process of failure initiation and propagation during possible earthquake loading or heavy rainfall. For such purpose different limit equilibrium modeling were carried out and factor of safeties against sliding caused by both excess earthquake loading and heavy rainfall were found. As for this study, two parameters normally taken into account which were soil properties changing as well as exerted seismic loading. Moreover to show the reality and importance of the main objective of this research, two of the constructed slopes in Malaysia were selected and modeled. The factor of safety against landslides in normal condition (without any extra seismic loading consideration) at Johor was 1.293, 1.425 and 1.301 using ordinary, bishop and Janbu methods, respectively. Also, factor of safety against slope failure at Besut was 1.508, 1.637 and 1.519 according to ordinary, bishop and Janbu methods, respectively. As a result, mentioned slopes will collapse applying even low seismic loading of 0.2 g. Internal friction angle reduction more than 25% also caused significant decrease in the slope’s factor of safety.

Effect of Cement on Compressibility and Microstructure of Tropical Peat

Peats are geotechnically problematic soil due to their high compressibility and low shear strength. Cement is widely used for the stabilization of peat by deep mixing method (DMM). This paper presents the results of the model study of compressibility property of peats stabilized with cement columns formed by DMM. The results of consolidation test, scanning electron micrographs (SEM) and energy dispersive x-ray spectrometer (EDX) showed that the compressibility of peats can be improved significantly by the installation of cement stabilized columns. The amount of cement used to form the column was observed to influence the engineering behaviour of treated tropical peats and it had more influence on sapric peat than on hemic and fibrous peats.

Improvement of Settlement Problems of Fibrous Peat

The distribution of peat deposits can be found in many countries and peat-land constituents from 5 to 8% of earth land surface, where approximately 60% of the wetlands are peat. An increasing growth of the population leads to the necessity of peat-land utilization for development purposes. This article describes a laboratory study on the effect of different binders on the settlement of fibrous peat. The effect of the sodium silicate, ordinary Portland cement and kaolinite on the settlement of peat is investigated through Rowe Cell consolidation test. At the end of this study, it is shown by increasing sodium silicate (within 2.5%), cement and kaolinite on treated peat, they are able to improve settlement of fibrous peat much more than conventional binders like pure cement

Stabilization of tropical peat by chemical grout

Peats have low shear strength and high deformation characteristics. Cement, sometimes with other industrial binders, is widely used for the stabilization of peats by deep mixing. However, peats lack a favorable structure for the chemical reactions, coupled with high moisture content that is acidic in nature. So, the efficiency of the binders is low making it an expensive option. This paper presents the effectiveness of using calcium chloride and kaolinite in cement-sodium silicate grout for improving the strength of tropical peat. The change in shear strength of the treated samples was evaluated by the vane shear test and moisture content test. The microstructural changes were evaluated by scanning electron microscopy and energy dispersive x-ray spectrometer analysis. Calcium chloride seemed to have different effects on the shear strength of peat and was observed to play an important role in the effectiveness of the chemical stabilizers. Experimental results showed that kaolinite (more than 10%) has a crucial rule in increasing the shear strength of peat. It was observed that sodium silicate within 3% and cement has favorable effect on the shear strength of peat and induce a decrease in the moisture content of mixtures consisting of peat and themselves and also lead to some favorable changes in the microstructure.