Showing papers on "Soil stabilization published in 2008"

Strength and Stiffness Response of Coir Fiber-Reinforced Tropical Soil

Abstract: Use of natural fibers in civil engineering construction practice is often advantageous as they are cheap, locally available, biodegradable, and ecofriendly. Among the available natural fibers, coir is produced in large quantities in South Asian countries, such as India, Ceylon, Indonesia, Philippines, etc. and has better mechanical properties, such as tensile strength. In this paper, results on the strength and stiffness behavior of soil reinforced with coir fibers are presented. Soil samples reinforced with coir fibers of different sizes, and made into cylindrical soil specimens were tested in triaxial shear apparatus to determine the strength and stiffness of soil response due to fiber inclusion and the results were compared with that of unreinforced soils. The results show that addition of coir (1-2%) as random reinforcing material increases both strength and stiffness of clay soil considered in the study. In addition, available theoretical models for prediction of strength of fiber-reinforced soil are examined in relation to the results of the present investigation. Analysis shows that the available models are not adequate to capture the strength and stiffness response of coir fiber-reinforced soil. A nonlinear regression model for strength and stiffness response is proposed in the present study.

Soil Property Criteria for Rammed Earth Stabilization

Abstract: This study relates value ranges of natural soil properties (plasticity, texture, and shrinkage) to the degree of predisposition of soils to stabilization for rammed earth wall construction. A total of 219 strength determinations were made on 104 soils compacted and stabilized with cement and/or lime and/or asphalt. Using a 2 MPa compressive strength criterion as the measure of stabilization success, soil property value ranges were related to the proportion of samples exceeding the criterion. Linear shrinkage (LS) and plasticity index (PI) are found to be the best discriminators of soil predisposition, with textural variables being useful secondary discriminators. “Favorable” soils, with stabilization success rates of ≥80% , include those with: (1) LS<6.0% and PI<15% ; and (2) LS 6.0–11.0%, PI 15–30%, and sand content <64% . These soils were stabilized with treatments averaging 4.2% cement and 1.8% lime, with individual treatments ranging from 4–8% total cement and/or lime. “Unfavorable” soils, with stabil...

Durability of Cement Stabilized Low Plasticity Soils

Abstract: Three testing methods for predicting the durability of cement-stabilized soils—the tube suction (TS), 7-day unconfined compression strength (UCS), and wetting–drying durability tests—were tested and compared for their correlations and influence factors using a problematic low plastic silt clay from subgrade commonly encountered in Louisiana. A series of samples was molded at six different cement dosages (2.5, 4.5, 6.5, 8.5, 10.5, and 12.5% by dry weight of the soil) and four different molding moisture contents (15.5, 18.5, 21.5, and 24.5%). The test results indicate that the water–cement ratio of cement-stabilized soil had the dominant influence on the maximum dielectric value (DV), 7-day UCS, and durability of stabilized samples tested, although the dry unit weight of cement-stabilized soil could cause the variation of the results. This study confirms that TS, 7-day UCS, and wetting-drying durability tests are equivalent in predicting durability, and tentative charts to ensuring the durability of cement-...

Predicting the Erosion Rate of Chemically Treated Soil Using a Process Simulation Apparatus for Internal Crack Erosion

Abstract: Chemical stabilization is an effective ground improvement technique for controlling erosion. Two stabilizers, lignosulfonate and cement, were used to study how effectively they could stabilize erodible silty sand collected from Wombeyan Caves, NSW, Australia. To conduct this research, four dosages of cement (0.5, 1, 1.5, and 2%) and four dosages of lignosulfonate (0.1, 0.2, 0.4, and 0.6%) by dry weight of soil were selected. All treated and untreated soil specimens were compacted to 90 and 95% of their maximum dry density to study the effect of compaction level on erodibility. The erosion characteristics of treated and untreated soil samples were investigated using a process simulation apparatus for internal crack erosion designed and built at the University of Wollongong. The findings of this study indicated that both chemical stabilizers increased the resistance to erosion because of their cementing properties. It was also found that the critical shear stress increased linearly with the amount of stabilizer, and the coefficient of soil erosion decreased as a power function of the critical shear stress.

Use of Chemically Stabilized Soil as Cushion Material below Light Weight Structures Founded on Expansive Soils

Abstract: Among the several remedial techniques suggested to combat the damages caused by expansive soils, the use of sand cushion and cohesive nonswelling (CNS) soil cushion were widely accepted, especially for light weight structures such as floorings, pavements, and canal linings, which cover large areas. CNS cushion is preferred to sand cushion in view of the sceptical performance of sand cushion at several work sites. However, various investigators have reported the nonavailability of suitable CNS materials at many project sites and in such circumstances, it is also suggested to prepare the artificial CNS materials by mixing suitable admixtures to the native clay. The present work deals with the modification of black cotton soil using Ca Cl2 and rice-husk-ash (RHA), which resulted in two favorable combinations of soil +0.5% Ca Cl2 +8% RHA and soil +1% Ca Cl2 +6% RHA with nonswelling properties, while retaining high unconfined compressive strength values. The mix of soil +0.5% Ca Cl2 +8% RHA was taken for furth...

Mitigation of Liquefaction Potential of Silty Sands

Abstract: Mitigation of liquefaction potential of soils with fines contents greater than 15 to 20 percent usually requires special adaptation of the dynamic densification methods — Deep Dynamic Compaction, Explosive Compaction, Vibro-Compaction, Compaction Piles — that are ordinarily used to improve loose, clean cohesionless soils. However, these methods can be used to attain the needed improvement in many soils if closely spaced vertical sand, gravel, or prefabricated (wick) drains are installed prior to construction. Soil-cement columns or walls installed by deep soil mixing or jet grouting can be used to provide both reinforcement and containment of liquefied soil. Removal and replacement of liquefiable silty and clayey soils using compaction, admixture stabilization or substitution by another 'material; e.g., roller compacted concrete, is also possible; however, the cost may be high, and consideration must be given to dewatering needs and the stability of open excavations. Mitigation of the liquefaction potential of high fines content sandy and silty soils using permeation grouting is not feasible because the low hydraulic conductivity of such soils.

Sulfate Induced Heave in Oklahoma Soils due to Lime Stabilization

Abstract: Sulfate-induced heave in lime-stabilized soils is a serious problem that can cause costly infrastructure damage if not addressed and occurs when lime is added to soil containing sulfate. Lime, a common soil stabilizer, is mixed with expansive soils to make them non-expansive. However, when a certain amount of sulfate is present naturally in the soil, in the form of gypsum (CaSO 4 ⋅2H 2 O), the addition of lime (CaO) and water (H 2 O) will form a highly expansive mineral, ettringite (Ca 6 Al 2 (SO 4 ) 3 (OH) 12 ⋅26H 2 O) and cause excessive swelling. When exposed to water, ettringite can expand up to 250% and the resulting lime/soil mixture becomes more expansive than the natural soil; affecting and often destroying infrastructure. The purpose of this research was to determine a threshold level of sulfate in Oklahoma soils, above which adverse reactions occur as a result of lime stabilization. The volume change behavior of three natural Oklahoma soil samples, with and without a lime additive, was analyzed with free swell tests and a parallel gypsum solubility study on manufactured soils was performed. The preliminary data shows that the level of sulfates at which adverse reactions occur with the addition of lime in Oklahoma soils lies between 200 ppm and 8500 ppm, and researchers are continuing work to narrow this range. The results of the gypsum solubility study with manufactured soils have led to a faster and more comprehensive method for measuring sulfate content in natural soils.

Behavior of Stabilized Peat Soils in Unconfined Compression Tests

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.

Laboratory Procedure to Obtain Well-Mixed Soil Binder Samples of Medium Stiff to Stiff Expansive Clayey Soil for Deep Soil Mixing Simulation

Abstract: This paper presents a laboratory procedure to prepare well-mixed soil binder samples for simulation of deep soil mixing to stabilize medium stiff to stiff expansive clayey soils. Two natural clays were selected, and stabilized with lime, cement, and combinations of both at various proportions and dosages. Results obtained from tests conducted on identical specimens showed that the current soil-binder mixing and specimen preparation procedures have yielded homogenous and uniform treated clayey specimens. Engineering properties measured on the treated soil specimens were analyzed and ranked to arrive at the optimum binder dosages for field implementation. Concurrent mineralogical studies on selected specimens using X-ray diffraction and scanning electron micrograph studies revealed the presence of pozzalonic compounds and interwoven threads in the treated samples indicative of the mixing and stabilizing phenomenon. The recommended chemical dosages were later implemented in a field deep mixing study to construct two test pads. Several in situ wet grab samples were collected from the treated ground and were subjected to strength and stiffness tests in the laboratory. Comparisons between test results from field cores and laboratory fabricated specimens showed a good match suggesting that the formulated test protocol has provided a reasonable simulation of the DM process.

Efficacy of Cement-stabilized Fly Ash Cushion in Arresting Heave of Expansive Soils

Abstract: Expansive clays swell and shrink seasonally when subjected to changes in the moisture regime causing substantial distress to the structures built in them. Techniques like sand cushion and cohesive non-swelling soil (CNS) layer have been tried to arrest heave and consequent damages to structures. Sand cushion has been proved to be counter-productive. Studies have indicated that even though CNS layer was effective initially, it became less effective after the first cycle of swelling and shrinkage. Research carried out by the authors, using cement-stabilized fly ash as a cushioning material, has shown that it was quite effective in arresting heave. Fly ash cushion, stabilized with 10% cement with thickness equal to that of the expansive soil bed reduces heave by about 75% in the first instance. With subsequent swell-shrink cycles, the performance further improves, unlike in the case of a black cotton soil provided with a CNS cushion. At the end of fourth cycle of swelling, the reduction in the amount of heave is as high as 99.1%.

Deep Soil Mixing Technology for Mitigation of Pavement Roughness

Abstract: The effectiveness of Deep Soil Mixing (DSM) treatment method was evaluated in terms of reducing heave movements of underlying expansive soils. Several binder types were used to treat expansive soils and these methods are considered in a laboratory investigation to select the appropriate binders for field DSM studies. Laboratory studies indicated that a combined binder treatment approach of using lime and cement was the appropriate method for field studies. Two pilot scale test sections were then designed and installed on DSM soil columns. Anchor rods were used to fasten a biaxial geogrid to the DSM columns. Surcharge equivalent to loads from base and surface layers was placed on top of the DSM-geogrid sections through a fill placement. These treated test sections along with control sections on untreated soils were instrumented and monitored. Monitored results showed that soil shrink-swell related movements and pressures in both vertical and lateral directions were considerably less than those recorded in the untreated soil sections. Nondestructive studies using seismic methods showed the enhancements of shear strength in the treated zones. Overall, this research resulted in the development of a design methodology for stabilizing expansive clayey soils at considerable depths using DSM column treatment.

Combined Lime and Cement Treatment of Expansive Soils with Low to Medium Soluble Sulfate Levels

Abstract: Expansive soils are considered as one of the major natural hazards causing billions of dollars of damage annually to various civil infrastructures built over them. Several methods have been attempted to stabilize expansive soils with some success. One method using combined lime and cement additives shows some promise, with initial lime treatment improving the workability and the subsequent cement treatment improving the strength and resilient properties of the same subsoil. However, the efficiency of this method has not yet been extensively studied. Hence, an attempt is made in the present research to evaluate the suitability of combined lime and cement treatment in stabilizing expansive clays of the city of Arlington, Texas. This paper covers two of the test pavement sections built on combined lime and cement treated subgrades. Laboratory test results including unconfined compression strength, free swell tests and linear shrinkage tests were first conducted to evaluate the property enhancements. Field sections built on combined treated subsoils were monitored and surveyed to study the heave related movements and cracking.

Fly Ash-Calcium Chloride Stabilization in Road Construction

Abstract: Both fly ash and calcium chloride have been used in a wide variety of roadway construction applications. Engineering applications of both Class C and Class F fly ashes include portland cement concrete, soil and road base stabilization, flowable fills, grouts, structural fills, and asphalt filler. Until recently, the primary roadway application for calcium chloride has been as a dust-controlling agent on unsurfaced roads. Ongoing research at Texas A&M and Texas Transportation Institute has concluded that when the two are strategically combined within a roadway mix design, their individual mineralogical and physicochemical characteristics interact to further enhance the service performance of the roadway. Although the fines content in the roadbed composition is critical, there is a synergistic effect on the strength generated when calcium chloride is added along with fly ash. This synergistic blending of fly ash and calcium chloride is referred to as "surface-activated stabilization"

Forensic Investigation of Pavement Premature Failure due to Soil Sulfate-Induced Heave

Abstract: Current practice does not recommend stabilizing high sulfate-bearing soils using calcium-based stabilizers due to high potential swell and low retained unconfined compressive strength. In this technical note, a series of tests has demonstrated that a combination of lime and fly ash (Class F) proved to be the most suitable stabilizer for a high sulfate-bearing soil, and a combination of lime and slag seemed to be the most effective stabilizer for a moderate sulfate-bearing soil in terms of retained unconfined compressive strength and three-dimensional free swell potential.

Hazardous Waste Pollution Prevention Using Clay with Admixtures

Abstract: Landfill is the most commonly used method for disposal of waste materials since it is one of the least expensive methods. In order to dispose of any hazardous material to a landfill, a liner is used, which protects the underlying land and groundwater since it acts as a barrier to fluid movement. Of the various methods available for providing improved and more effective properties of landfills, methods involving the use of bentonite, cement, lime, gypsum, etc., have been explored in the laboratory. The aim is to overcome the problem and deficiencies of the existing liners. It is observed from the experimental results that the metal concentrations of the input waste solution can be reduced to 80-98% using a soil-cement admixture, 60-95% using a soil-gypsum mixture, 45-95% using a soil-bentonite mixture, 50-90% for soil, 35-80% using a soil-lime mixture, as liner materials. The permeation rate of different metals through the different soil-admixture media depends on various factors. A simple mathematical treatment of the phenomenon related to the permeation of liquid through the admixture of the clay and other components has been developed. The experimental results show satisfactory agreement with the predictions.

Three dimensional slope stability analysis and failure mechanism

Abstract: of thesis entitled THREE DIMENSIONAL SLOPE STABILITY ANALYSIS AND FAILURE MECHANISM submitted by Wen-Bing Wei for the degree of Doctor of Philosophy at The Hong Kong Polytechnic University in July 2008 For slope stability problem, two-dimensional analysis is commonly used for simplicity, though all slope failures are three-dimensional (3D) in nature. There are only limited applications of 3D analysis due to the various limitations of three-dimensional slope stability methods. Recently, there are various important progresses for 3D analysis. 3D limit equilibrium method (LEM) for general asymmetrical problem together with innovative optimization method for locating the general critical 3D failure surface has recently been developed. In addition, 3D strength reduction method (SRM) can now be conducted within a tolerable duration. Until now, there is still a lack of detailed investigation of 3D slope stability failure mechanism and the application of 3D LEM and SRM under different 3D conditions. This study aims to conduct an extensive threedimensional slope stability analysis and to investigate the failure mechanism under different situations. The 3D effect considered in this study includes the important factors such as slope geometry, boundary conditions, water, soil nail and pile. Both the LEM and SRM are conducted in this study, and some interesting differences between these two methods are discovered. It is concluded that both methods have their own merits and limitations, and a good understanding of these methods are required before a good solution can be obtained. The suitability of these two methods under different conditions is investigated and precautions when these methods are applied are suggested. In this study, some results which appear to be different from common understanding are obtained. Some of the results are also different from published studies, and careful investigations have revealed that the present detailed studies have provided a better and more reasonable understanding about the failure and stabilization mechanism. For example, for a simple slope extending to infinity, the critical slip surface is still basically two-dimensional until the external loading is large to induce a threedimensional failure. The failure mechanisms due to the self weight of soil and external loads are actually different. The discretization domain required for SRM analysis is found to decrease with the increase of external loads which is also out of expectation. The distribution of tension force in soil nail is found to be influenced by the state of the slope (service state, limit state) and the failure modes (external failure, internal failure). In general, the line of the maximum tension may not correspond to the critical slip surface as commonly believed, except when the failure mode is an internal tensile failure. For slope supported with one row of piles, the slip surface is divided into two parts when the pile spacing is very small, and these two parts gradually become connected to form a clear single slip surface mechanism with the increase of pile spacing. The point of maximum shear force in the pile which is commonly used to determine the location of the slip surface in traditional design is found to be not a valid assumption, and this is important for design of slopes reinforced with piles. Some engineers have questioned the disturbance of the seepage pattern due to the presence of soil nails and piles. Such blocking effect is however found to be negligible. With the detailed study on 3D failure and stabilization mechanism, a clearer and better understanding of three-dimensional slope failure has been achieved in the present study. LIST OF PUBLICATIONS Wei, W. B., Cheng, Y. M., and Li, L. (2008). Three-dimensional slope failure analysis by the strength reduction and limit equilibrium methods. Computers and Geotechnics, In Press. Wei, W. B. and Cheng, Y. M. (2008). Soil nailed slope by the strength reduction and limit equilibrium methods, submitted to International Journal for Numerical and Analytical Method in Geomechanics. Wei, W. B. and Cheng, Y. M. (2008). Strength reduction analysis for slope reinforced with one row of piles, submitted to Journal of Geotechnical and Geoenvironmental Engineering. Wei, W. B. and Cheng, Y. M. (2008). Stability analysis of slope with water flow by strength reduction method, submitted to Soils and Foundations. Cheng, Y. M., Lansivaara, T., and Wei, W. B. (2008). Reply to Comments on “Twodimensional slope stability analysis by limit equilibrium and strength reduction methods”. Computers and Geotechnics, Vol. 35, No.2, 309-311 Cheng, Y. M., Lansivaara, T., and Wei, W. B. (2007). Two-dimensional slope stability analysis by limit equilibrium and strength reduction methods. Computers and Geotechnics, Vol. 34, No.3, 137-150 Wei, W. B. and Cheng, Y. M. (2007). Strength reduction method for three dimensional slope stability analysis. 60 Canadian Geotechnical Conference and 8 Joint CGS/IAH-CNC Groundwater Conference (Ottawa, Ontario, Canada, October 2124, 2007), 815-820 Cheng, Y. M., Wei, W. B., and Lansivaara T. (2006). Factors of safety by limit equilibrium and strength reduction methods. Numerical Methods in Geotechnical Engineering – Schweiger (ed.), Sixth European Conference on Numerical Methods in Geotechnical Engineering (Graz, Austria, 6-8 September 2006), 485-490

Rapid Assessment of Cement and Fiber-Stabilized Soil Using Roller-Integrated Compaction Monitoring

Abstract: Test sections of high-early strength (Type III) portland cement and polypropylene monofilament fibers were constructed at the Bradshaw Field Training Area in the Northern Territory (NT), Australia as part of a Joint Rapid Airfield Construction (JRAC) project. Aprons, taxiways, and a helipad were stabilized using these materials in combination with screened native soil. The purpose of the test sections was to (a) evaluate the resulting properties for different stabilization dosage rates; (b) develop construction methods, criteria (including limits), and quality control guidelines; and (c) provide a hands-on training opportunity for the joint United States and Australia military construction team. Testing and monitoring consisted of roller-integrated compaction monitoring (global position systems monitoring pass coverages and compaction machine values) and in situ testing, which included dynamic cone penetration tests, Clegg impact tests, and light-weight deflectometer tests. After the test sections, constr...

Evaluation and Field Verification of Strength and Structural Improvement of Chemically Stabilized Subgrade Soil

Abstract: Often subgrade soils exhibit properties, particularly strength and/or volume change properties that limit their performance as a support element for pavements. Typical problems include shrink-swell, settlement, collapse, erosion or simply insufficient strength. A common approach to subgrade soil support or stability problems involves chemical modification or stabilization with additives such as lime (hydrated or quick), fly ash (Class C from lignite coal), cement kiln dust (CKD) or Portland cement. Other additives are available, but this group constitutes the major products or by-products used on roadway construction in Oklahoma. The type and amount of chemical additive is dependent on the purpose or function of the treated material (i.e., improved physical properties or improved strength) and selection is based on accepted or standardized procedures. Questions then arise with regard to chemically treated subgrade soils about the rate of development and ultimate value of improvement. The purpose of this research is to develop relationships between rate of development and magnitude of strength (or physical property) improvement for chemically treated subgrade soils. The research project involved laboratory and field studies of the influence of cementitious additives on the strength and structural improvement of stabilized subgrade soils. Laboratory tests for measuring strength and structural improvement (e.g. UCS and MR) were conducted on field mixed treated soils and laboratory mixed treated and untreated soil samples. UCS and MR tests were conducted on samples varying curing time (field and laboratory mixed) and percent additive used (laboratory mixed). A series of field tests (Nuclear w-γ, stiffness gauge, portable FWD, Dynamic Cone Pentrometer, and PANDA Pentrometer) were conducted at five field test sites on the untreated subgrade soils and on the treated subgrade soil with curing time as allowed by the construction schedule. The research project collected a large volume of both laboratory and field data which are summarized in the appendixes (5) to this report.

The Role of Nanotechnology for theDevelopment of Sustainable Concrete

Abstract: The present paper addresses several topics in regard to the sustainable design and use of concrete and the role of nanotechnology. First, major features concerning the sustainable aspects of the material concrete are summarized. Then the major constituent, from an environmental point of view, cement is discussed in detail, particularly the hydration and application of slag cement. The intelligent combining of mineral oxides, which are found in clinker, slag, fly ashes etc., is designated as mineral oxide engineering. It results among others in environmentally friendly binders, recipes for soil stabilization (new building products), and impermeable/durable concretes. Subsequently, the mix design of concrete is treated, whereby distinction is made between self-compacting concrete and earth-moist concrete. By combining the particle sizes of all components, so including the powders (cement, fillers), optimum mixes in regard to workability/compactability and hardened state properties are obtained. This so-called particle size engineering results in concretes that meet all technical requirements, but that also make optimum use of the cement it is containing. This paper concludes with summarizing the opportunities and challenges involved with the introduction of both approaches, viz. mineral oxide engineering and particle size engineering, in the construction industry.

Alkaline swelling and consequences of alkalization of clayey bed soils

Abstract: Results of investigation of interaction between sodium hydroxide and a clayey soil are described, and the inadmissibility of the alkali used as a reagent for soil stabilization is demonstrated.

Stabilization of peat by deep mixing method: A critical review of the state of practice

Abstract: The purpose of this paper is to advance the knowledge on peat soil stabilization by critically examining and documenting the current state of practice. Deep Mixing method is emphasised on column type techniques using lime/cement. This paper is essentially a comprehensive review of available academic literature on deep soil stabilization utilizing this approach. Deep mixing with lime or lime-cement column and combined soil stabilization with vertical columns (CSV) methods are discussed and to illustrate applications of these methods in a variety of conditions, several case histories are presented.

Compression Rates of Untreated and Stabilized Peat Soils

Abstract: Characterized by high initial void ratio, organic content and water holding capacity, fibrous peat exhibits high compressibility and low shear strength. Consequently, formation of deep fibrous peat layer often poses difficulties in construction. In practice, compressibility of deep fibrous peat layer can be reduced by deep soil stabilization technique. The technique is developed in such a way that dry binders are mixed with in situ peat soil to form columnar reinforcement in the deep peat ground prior to preloading. Preloading simulations of both untreated and stabilized peats were carried out in laboratory by loading of both soils using standard oedometer consolidation apparatus. Ordinary Portland cement, ground granulated blast furnace slag and siliceous sand were used to stabilize the soil. Analysis on the time-compression curves from the tests revealed that coefficients of vertical consolidation (cv of both soils were best predicted using square root of t52.6 method when compared to those evaluated using conventional curve fitting methods. Main reason for this is the experimental time-compression curves for the method best fit its theoretical curve. In addition, the method predicts cv of soil at 52.6 average degree of consolidation, which is less likely to be affected by secondary compression that usually occurs concurrently at the later stage of soil primary consolidation.

Evaluation, Selection and Assessment of Guidelines for Chemical Stabilization of Tropical Residual Soils

Abstract: Soil stabilization has been widely used as an alternative to substitute the lacking of suitable materials on site. Guidelines and standards have been developed to assist practitioners in designing structures such as road by mean of stabilization. This paper presents the results of an investigation aimed at evaluating and assessing the suitable guidelines for the stabilization of tropical residual soils. Two types of tropical residual soils namely granite residual and sedimentary residual soil were tested by using conventional methods practiced in Malaysiaand two guidelines, namely the TRL and PWD were evaluated. From the results of this study, it appeared that the TRL gave a simplified and satisfactory route in selection of suitable binder for the stabilization processes of tropical residual soils.

Improving the Tensile Strength and Toughness of a Soil-Cement-Fly Ash Pavement Subgrade with Recycled HDPE Strips

Abstract: Cementitious stabilization of soil and base is a common practice for improving the strength and stability of pavement foundations. However, the resultant stabilized material has a brittle matrix with strong potential for developing tensile cracks under repeated traffic loadings. This phenomenon often leads to reflection cracking in asphalt overlays which are underlain by cemented base or subgrade layers. An experimental investigation was conducted to evaluate the split tensile load- deformation-strength and toughness properties of a granular soil chemically stabilized with cement and fly ash, and mechanically reinforced with recycled plastic strips (High Density Poly Ethylene or HDPE) obtained from post consumer products. As an extension to the ASTM C 496 procedures for split tension tests, two lateral linear variable differential transformers were attached to measure the tensile deformation of the horizontal diameter due to loading in the orthogonal direction; this method permitted an evaluation of the fiber toughening action under split tension. It was found that the inclusion of HDPE strips does not meaningfully improve the tensile strength, but significantly enhances the toughness properties, which may be beneficial in delaying the propagation of traffic-induced tensile cracks in pavement applications.

Recent Developments in Ground Improvement for Mitigation of Seismic Risk to Existing Embankment Dams

Abstract: The ma jority of large embankment dams in the United States in operation today were constructed over half a century ago - before major earthquakes in 1964 jump-started geotechnical earthquake engineering and initiated systematic evaluations of the seismic stability of these earth structures and the soil deposits on which they are built. Many dams have required strengthening owing to increased levels of anticipated shaking or inadequate resistance of the embankment or foundation materials. Soil stabilization and ground improvement methods have included buttress fills, removal and replacement of weak foundation soils, deep dynamic compaction, vibro-compaction, vibro-replacement, explosive compaction, deep soil mixing, jet grouting, compaction grouting, and permeation grouting. In most cases the design strategy is to strengthen the dam to prevent vertical crest deformations that would exceed the freeboard and transverse cracking to depths greater than the remaining freeboard after the earthquake. Special attention must also be given to assuring that seepage paths cannot form along conduits or other discontinuities. In many cases stabilization to prevent excessive upstream deformations is costly and difficult, so in recent years there have been several cases where ground improvement and construction of stabilizing trenches and berms has been confined to the downstream slope and foundation area.