Settlement due to Consolidation
H. Ohta
ABSTRACT: Settlement of the trial embankments placed on the campus of Asian Institute of Technology by (a) Akagi and (b) Ohta is discussed based on the performance of various settlement estimate techniques. Since these embankments were placed close to each other, mechanical parameters of the subsoil should be identical in both cases and therefore gives good chance to check the appropriateness and reliability of parameter estimation procedure. In addition to comparing the settlement estimate methods, proposed is a laboratory technique to estimate the in-situ effective stress state. This technique gives information on the change in effective stress state due to the progress of consolidation settlement.
KEYWORDS: Consolidation, Settlement, Deformation, Soft clay
A Simulation of Surface Runoff and Infiltration due to Torrential Rainfall Based on Field Monitoring Results at a Slope Comprising Weathered Granite
H. Ohtsu, H. Masuda, T. Kitaoka, K. Takahashi, M. Yabe, S. Soralump and Y. Maeda
ABSTRACT: The frequency of rainfall-triggered slope failure has recently been increasing in Asian countries. One plausible reason for the increased frequency is climate change. It is therefore a pressing issue to clarify the mechanism of infiltration, causing slope failure. From such a viewpoint, this study investigated the relationship of the runoff, the infiltration and the surface retention due to torrential rainfall by means of one-dimensional tank model analysis using the results of field measurement conducted in Phuket, Thailand. The results showed that the infiltration is temporally retained by the surface retention at the beginning of rainfall, including immediately after and that the time rate of the infiltration is affected by the rainfall intensity. Furthermore, this study investigated the applicability of the proposed method, which deals with the infiltration simulated by one-dimensional tank model analysis, by comparing with the measured values and the results of conventional method.
KEYWORDS: Slope, Seepage analysis, One-dimensional tank model
Calcium Carbide Residue – A Cementing Agent for Sustainable Soil Stabilization
S. Horpibulsuk, A. Kampala, C. Phetchuay, A. Udomchai, and A. Arulrajah
ABSTRACT: The high unit cost and energy intensive process in the production of Portland cement are the driving forces for the need to seek for alternative cementitious additives. Calcium Carbide Residue (CCR) has been recently introduced as a sustainable cementing agent. The recent research on the engineering properties of CCR stabilized clay as a subbase/base materials is reviewed and presented in this paper. CCR alone as well as a mixture of CCR and fly ash (FA) can be used for soil stabilization instead of ordinary Portland cement. The suitable ingredient of CCR, FA and clay results in a moderately high strength and durable geomaterial. The CCR fixation point obtained from the index test is proved as a practical indicator for determining the CCR content to obtain the required engineering properties. For a particular CCR content, the optimum water content is the most appropriate in terms of strength, swelling and durability against wetting and drying (wd) cycles. Significant strength and durability improvement is noticed when FA is utilized with CCR. The input FA at optimal content reacts with the excessive Ca(OH)2 from the CCR and this results in a significant improvement of the strength and durability. The strength analysis shows that the durability is directly related to the unsoaked strength (prior to the w-d cycles). Consequently, the relationship between the w-d cycle strength and unsoaked strength is proposed. It is useful for the quick determination of the unsoaked strength for mix design to attain the target strength at the design service life.
KEYWORDS: Calcium carbide residue, Fly ash, Strength, Swelling, Durability, Stabilized clay
Soil Parameter Optimization of the NGI-ADP Constitutive Model for Bangkok Soft Clay
B. Ukritchon and T. Boonyatee
ABSTRACT: This paper studies the NGI-ADP soil model, which can realistically simulate the anisotropic undrained stress strain responses and undrained shear strengths of clays. The model requires direct input parameters of undrained shear strengths and failure shear strains, including triaxial compression test, triaxial extension test and direct simple shear. However, parametric studies in this paper clearly show that trial-and-error testing of some input parameters is necessary in order to determine the optimal set of input parameters. The paper proposes the equations of anisotropic stress strain curves of this soil model and the technique of soil parameter optimization so that the optimal set of input parameters can be determined automatically and efficiently. The technique of soil parameter optimization is based on the statistical approach of least squares where proposed stress strain curves are used to compute model predictions. Finally, the proposed technique of soil parameter optimization of the NGI-ADP model is employed to determine the optimal set of input parameters for Bangkok soft clay.
Laboratory Investigation of Hot Mix Asphalt Behaviour for Mechanistic-Empirical Pavement Design in Tropical Countries
T. Chompoorat and S. Likitlersuang
ABSTRACT: To enhance the quality and efficiency of road design and construction it is necessary to elevate the comprehensive behaviour of the materials employed. Southeast Asian including Thailand, located in the tropical zone usually experiences an extreme weather condition of hot temperature and high humidity. This severe environmental condition is believed that it could reduce the performance and accelerate the aging process of the pavement. The material widely used in the construction of pavement in the Southeast Asian countries and perhaps all over the word is an asphaltic concrete mixed from the AC 60/70 asphalt binder and aggregates. Referring to the theory of mechanic it can be concluded that the asphaltic concrete is a thermo-visco-elastic material which its principle behaviours are caused by strain rate and temperature. To understand the mechanical behaviour of asphaltic concrete, this research aims to integrate the mechanical properties of asphaltic concrete, including stress-strain-strength characteristic, permanent deformation, and moisture damage. The experiments were run through an unconfined compression, an indirect tensile, a resilient modulus, and a dynamic creep tests under various temperatures and different strain rates. The results from this study lead to a high level of understanding in mechanical behaviours and failure mechanism influenced by strain rate and temperature as well as moisture. Moreover, the outcome of this research can be used to define the mechanistic-empirical equations for damage prediction. This research could hopefully enhance the development of pavement design in Thailand based on mechanistic design concept.
KEYWORDS: Pavements and roads, Laboratory Tests, Hot Mix Asphalt, Strength, Creep, Moisture damage
Slope Stability and Pore-Water Pressure Regime in Response to Rainfall: A Case Study of Granitic Fill Slope in Northern Thailand
A. Jotisankasa, K. Mahannopkul and A. Sawangsuriya
ABSTRACT: Spatial and temporal variations of pore water pressure within slopes in response to rainfall that lead to slope failure, are one of the major uncertainties in evaluating slope stability. This paper reports on the study of slope stability with respect to pore water pressure variation with rainfall during actual failure in September 2011. The studied slope, situated near the peak of Doi-Inthanon national park, Northern Thailand, consisted of granitic residual soil fill that suffered from soil erosion and shallow failure. The KU-tensiometers were installed to monitor both pore water pressure and suction in the slope. Various laboratory and field tests were conducted, namely, direct shear tests on both fully saturated and unsaturated soils, soil water characteristic curve, and field infiltration tests. Two-dimensional (2-D) Back analysis of slope stability, for failure event in 2011 suggested that the critical pore water pressure distribution can be assigned to the ru value of about 0.43 or u=0.43γH. Based on three dimensional (3-D) stability analysis, the pore water pressure can be 30% higher when compared with the 2-D analysis. 2-D Finite Element seepage analysis appeared to capture general trend of pore-water pressure change reasonably well. However, it seemed to underpredict the pore-water pressure at failure especially for depth greater than 2 meters.
KEYWORDS: Slope stability, Pore-water pressure, Rainfall, Suction, Granitic soil
Evaluation of the Hydraulic Conductivity of Clayey Soil Mixed with Calcium-Bentonite Using Odeometer Tests
R.D. Fan, Y.J. Du, S.Y. Liu and Y.L. Yang
ABSTRACT: The hydraulic conductivity of clayey soil/Calcium-bentonite backfills for vertical cutoff wall is evaluated based on a series of oedometer tests. Kaolin is used as the control clayey soil, and the Ca-bentonite content is set at 0, 5%, 10% and 15%. The results reveal that the hydraulic conductivity are significantly affected by the bentonite content, with a hydraulic conductivity that is generally lower than 10−9 m/s. Three empirical methods are assessed to predict the hydraulic conductivity based on e and eL (or wL). The predicted values of hydraulic conductivity are found to fall in the range of 1/3 to 3 times those evaluated values. However, the equation based on the frameworks of the Kozeny-Carman (KC) equation is shown to estimate the hydraulic conductivity for both the kaolin-bentonite backfills in this study and the sandy soil-bentonite backfills from earlier reported study with reasonable accuracy.
KEYWORDS: Backfill, Bentonite, Cutoff wall, Hydraulic conductivity, Soil-bentonite
Undrained Shear Strength of Very Soft to Medium Stiff Bangkok Clay from Various Laboratory Tests
W. Ratananikom, S. Yimsiri and S. Likitlersuang
ABSTRACT: “The values of undrained shear strength of undisturbed Bangkok Clay specimens are investigated by various laboratory tests, i.e. (i) unconfined compression test, (ii) unconsolidated undrained triaxial test, (iii) isotropically consolidated undrained triaxial compression/extension tests, (iv) Ko-consolidated undrained triaxial compression/extension tests, (v) direct shear test, (vi) direct simple shear test, (vii) laboratory vane test, and (viii) triaxial vane test. The experimental data are obtained from laboratory tests performed in this study and collected from previous published studies. The soil layers of interest in this study are very soft to medium stiff clays which are located between 2-14 m depth below ground surface. The variations of undrained shear strength with depth and their degree of scattering are presented and discussed. The interrelationships among undrained shear strengths from various laboratory tests are analyzed and relevant discussions are made. The validity of various empirical and theoretical relationships for predicting undrained shear strength of Bangkok Clay are evaluated. Various approaches for estimation of mobilized undrained shear strength for embankment stability analysis are investigated and the most suitable approach for embankment stability analysis and design on Bangkok subsoils is finally suggested.”
KEYWORDS: Laboratory tests; Shear strength; Clays; Embankments
A Review on Design of Pile Foundations in Bangkok
T. Boonyatee, J. Tongjarukae, T. Uaworakunchai and B. Ukritchon
ABSTRACT: A review was made on the design of pile foundations in Bangkok area. Particular attention was paid on design parameters based on local practice which had been reported during 1985 to 2012. An additional study was made on thirty six static load tests on instrumented piles, which were larger and longer than ones in the past. Parameters for the determination of bearing capacity and settlement were back analyzed and compared with those in the literature. Noteworthy studies in the past as well as findings in this study were then summarized and discussed.
KEYWORDS: Pile foundations, Bangkok, Bearing capacity, Settlement, Design parameters
Structured Cam Clay Model with Cementation Effect
S. Horpibulsuk and M.D. Liu
ABSTRACT: In this paper, the theoretical framework of the Structured Cam Clay (SCC) model is extended to describe the behaviour of cemented clay. An operative mean effective stress parameter for soils with cohesion/cementation is introduced to include the influence of cementation on the strength and the deformation of cohesive soils. For simplicity, the removal of cementation is assumed to take place during the process of the rearrangement of soil particles to form the final critical state of deformation. Based on experimental observation, a simple destructuring function is proposed for the removal of cementation structure; especially, for artificially strongly-cemented clays. The model is suitable for describing the behaviour of clays in reconstituted, naturally structured, and artificially cemented states under monotonic loading or with simple stress reversal. The revised model is then employed to simulate the behaviour of cemented clays with various degrees of cementation and confining stresses. It is seen that main features of the complicated behaviour of cemented clays can be represented reasonably well by the model. Some studies on model parameters are also presented.
KEYWORDS: Clays, Cementation, Soil structure, Strength, Constitutive relations
Evaluation of Strength of Soft Ground Improved by Vacuum Consolidation
T. Shibata, S. Nishimura, M. Fujii and A. Murakami
ABSTRACT: This paper presents the numerical evaluation of the strength and stability of a ground improved via vacuum consolidation combined with a preloading embankment. To assess the stability of soft grounds, the undrained shear strength is definitely required. A numerical analysis is desirable for predicting the strength of the improved ground, and the elasto-plastic FEM for soil-water coupled problems, incorporating the SYS Cam-clay model, is adopted in two dimensions. The compression index of clay and the coefficient of permeability of organic soil, which are the primary factors for evaluating the ground behavior, are identified through an inverse analysis from the measured settlements. As the inverse approach, the particle filter is employed to account for the strong nonlinearity of the ground behavior. A stability analysis of the slip surface method is performed based on the evaluated undrained shear strength to assess the effect of the ground improvement on the construction of earth structures. The results show the validity of the ground improvement using vacuum consolidation with a preloading embankment.
KEYWORDS: Undrained shear strength, Vacuum consolidation, Stability analysis
Chemical Stabilization of Loess in Northeast Thailand Using the Mixture of Calcined Marble Dust Waste and Sugarcane Bagasse Ash Waste
P. Julphunthong
ABSTRACT: The main objective of this study was to investigate the possibility of utilizing calcined marble dust waste and sugarcane bagasse ash waste as the chemical stabilizer for loess. Loess is widely distributed throughout the northeast area of Thailand. This soil type has a large loss of shear strength and a significant increase in compressibility upon wetting, which are obstructive behaviors for construction materials. The study was divided into two sections. The first section dealt with the study of synthesizing cementitious materials from calcined marble dust waste and sugarcane bagasse ash waste. The second section focused on studying the stabilization of loess. This consisted of observing the effect of stabilizer on the basic properties of soil-stabilizer mixtures and the improvement in its mechanical properties. The additive ratios of stabilizer which were studied were between 0-25 percent by weight. The physical and chemical properties of loess, calcined marble dust waste and sugarcane bagasse ash waste were studied by X-ray diffraction, X-ray fluorescence, thermogravimetric analyzer, differential thermal analysis, laser diffraction particle size analyzer, Brunauer, Emmett and Teller, transmission electron microscope and scanning electron microscope analytical techniques. After analyzing the physical and chemical properties of the stabilizing materials, the sugarcane bagasse ash waste and the marble dust waste which was calcined at 1000 oC for 2 h, mixed with the ratio of 1:1, and then selected as the stabilizer for loess improvement. It was found that the liquid limit and plastic limit of the treated soils had been decreased with the percentage increase of stabilizer. The optimum moisture content tended to increase while the maximum dry density was reduced. This corresponded to an increasing of the stabilizer fraction. By adding stabilizer at 25%, the soaked and unsoaked California bearing-ratio were increased by about 185% and 140%, respectively. Unconfined compressive strength of specimens with 25% stabilizer was dramatically increased with 28 days curing time.
KEYWORDS: Loess, Calcined marble dust waste, Sugarcane bagasse ash waste, Cementitious materials
Numerical Analyses of Piled Raft Foundation in Soft Soil Using 3D-FEM
K. Watcharasawe, P. Kitiyodom and P. Jongpradist
ABSTRACT: In recent years, the piled raft foundation has been widely accepted as one of the most economical methods of foundation systems. To evaluate the possibility of implementing this system in a very soft ground condition, this research performed the numerical analyses of the piled raft and pile group foundation systems for low-rise (8-storey) and high-rise (25-storey) buildings with 1-2 basement levels in subsoil conditions of the central part of Thailand, using three-dimensional Finite Element Method. The soils are modelled with Hardening Soil model and Mohr-Coulomb model. Evaluations of the performances of piled raft foundation, i.e., the load sharing ratio of piles, settlement behaviours in both the foundation system and the raft are discussed in comparison with those of the pile group. With limited cases considered and assumptions in this study, the results suggest the potential of using the piled raft system for low-rise building having 2 levels of basement. With this condition, the raft can carry some bearing capacity from pile around 20%. However, the safety factor of piles in the foundation design seems to play a key role on the effectiveness of the piled raft foundation as well and should be further studied.
KEYWORDS: Piled rafts, 3D FEM, Soft soil, Piled-raft load sharing
Investigation of Shrinkage and Swelling Behaviour of Expansive/Non-Expansive Clay Mixtures
S. Por, S. Likitlersuang and S. Nishimura
ABSTRACT: This paper presents an investigation of physical and engineering properties of expansive clays prepared by reconstituting Na-montmorillonite bentonite mixed with natural non-swelling Bangkok clay. The Bangkok clay contents were varied to 0, 20, 40, 60, 80 and 100% by weight. This investigation aims at highlighting the influence of the non-swelling clay content on physical and mechanical properties of the mixture by paying particular attention to its effect on shrinkage and swelling potential. The basic physical properties were determined, along with the unconfined compression, oedometer, compaction and CBR characteristics. The linear shrinkage bar tests and swelling tests were also performed to observe the areal shrinkage and vertical swelling strains. In addition, a microstructure investigation was conducted through X-Ray diffractometer (XRD) and scanning electron microscope (SEM) observations. By increasing the Bangkok clay content in the mixture clays, the compressive strength and CBR values were markedly increased, while the plasticity and the swelling and shrinkage strains were reduced significantly. Correlations were established between the index properties and other properties such as the maximum dry density (MDD), the optimum moisture content (OMC), the CBR, the compression index (Cc), and the swelling index (Cs). These correlations were tested against data from some previous studies on other soil types including natural expansive clays and found to be applicable satisfactorily in most cases. It was also found that a relatively large increase of non-swelling clay content is necessary to obtain markedly larger strength, while the plasticity is greatly reduced by a minor increase. The above findings will be useful in designing earth works where locally occurring expansive clays are desired to be used with minimum improvements.
KEYWORDS: Shrinkage, Laboratory tests, Expansive soil, Bentonite, Bangkok Clay
