CHARACTERIZATION OF GRANULAR SOILS AS PAVEMENT MATERIALS (original) (raw)
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Rational Approach to the Evaluation of Soils for Low-Volume Roads
Transportation Research Record: Journal of the Transportation Research Board, 2011
Given the paramount importance of soils in unsurfaced or thinly surfaced roads, it seems worthwhile to evaluate soils on the basis of both pavement and soil mechanics. Such a rational approach is used to discuss the mechanical behavior of a residual soil found in southern Brazil. The experimental program included tests traditionally used in pavement engineering, such as grain size distribution, Atterberg limits, compaction, California bearing ratio, resilient modulus, and permanent deformation under repeated loading. The influence of water content and compaction degree on soil strength and stiffness was quantified. In addition, direct shear tests were performed to define shear strength parameters that were used to verify layer safety against failure. Water retention curves, which relate soil suction to saturation degree, were used to analyze permanent deformation evolution under repeated loads. The interpretation of test results confirmed the suitability of the suggested approach fo...
JOURNAL OF CIVIL ENGINEERING AND MANAGEMENT, 2019
The bearing capacity of subsoils is particularly important due to the intensive development of road and airfield pavements. Subgrade is classified due to frost susceptibility as non-frost-susceptible, low-frost-susceptible or frost-susceptible. Presented research included laboratory tests of low-frost-susceptible soils with limited potential for direct use. The main objective of this paper was focused on the study of changes of compactibility parameters and the CBR (Californian Bearing Ratio) values of silty sand (Pπ). For this purpose, seventeen soil samples with various fine fractions content (of 1.6% to 24.2%), were composed. Laboratory tests, based on soaked soil samples, encompassed the Proctor Compaction test and the CBR test. Additionally, measurements of moisture content in soaked soil samples before and after the penetration test and the displacement of annular surcharge rings while penetration test, were performed. Obtained results allowed for conclusions that penetration ...
Mechanical behaviour of a compacted well-graded granular material with and without cement
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Cement additions improve the performance of granular soils. However, most literature examples of cement additions are in poorly graded sands, either to mimic the behaviour of sandstones or to accentuate the mechanical differences between cemented and uncemented soils. In this article, the behaviour of a well graded granular soil, used for base and sub-base of roads, was studied by doing triaxial tests on cemented and uncemented samples. Samples were compacted to achieve a dense fabric and tested at stresses commonly used in practice. Sieving was used to understand if breakage is important and to determine the grain size distributions of the samples after compaction and shearing. The results show that the addition of small percentages of cement greatly increase stiffness and dilation. Thereby, generating larger strengths; this is particularly important at low confining stresses in roads and parking areas, where this material is commonly used. At large strains, the results show that different Critical State Lines exist for both the uncemented and cemented soils. Each line has a different slope, which is believed to be the result of the evolution of the grain size distribution of the cemented soil. The normalised data indicate that a unique state boundary surface can be determined for all three tested soils.
EVALUATION OF SOAKED AND UNSOAKED CBR VALUES OF SOIL BASED ON THE COMPACTION CHARACTERISTICS
Subgrade of a pavement should be strong enough to give adequate support to the pavement and for supporting and distributing the wheel loads. The design and behaviour of a flexible pavement depends mainly on the stability of the subgrade soil, which can be increased by compacting the soil at optimum moisture content (OMC) thus achieving maximum dry density (MDD). In this study, Modified Proctor Compaction Test (MPCT) was conducted by giving 5 different number of blows per layer so as to establish a relationship of compaction energy with OMC & MDD. Also, OMC and MDD are one of the most important parameters influencing California Bearing Ratio (CBR) test. CBR is a penetration test used for evaluating the mechanical strength of subgrade soil and for determining the thickness of the pavement required. Determination of soaked and unsoaked CBR value for a soil is time consuming and a laborious process. Hence in this paper an attempt has been made to arrive at regression equations to correlate soaked and unsoaked CBR values for the silty clay (CL) soil with the compaction characteristics, so that based on OMC and MDD, CBR value of soil can be predicted thus avoiding the time consuming process of conducting CBR tests. The soil sample used in this project was a disturbed sample collected from Thiruporur District in Chennai.
Such as the other developing countries, in Turkey, in-situ quality control/quality assurance (QC/QA) of granular pavement layers (subgrade, subbase and base) still relies on their density and moisture measurements. With shifting from empirical to mechanistic-empirical methods in pavement design over last decades, it became essential to change the QC/QA procedures of compacted granular materials from unit weight-based to stiffness/strength based criteria. Since the unit weight criteria unable to provide sufficient information about the engineering properties of granular layers, a missing link occurs between the design and quality control. Dynamic Cone Penetrometer (DCP) is a non-destructive, effective, fast and reliable testing method which is used to determine the stiffness/strength properties of granular pavement layers and subgrade. After DCP test is performed the penetration indexes (PI) of each layer is calculated. DCP-PI is usually correlated with California bearing ratio (CBR) values and Elastic Modulus to assess mechanical properties of Materials. Considerable research has been conducted to develop an empirical relationship between the DCP-PI values and the CBR and Elastic Modulus for a wide range of pavement and subgrade materials. In this study, series of laboratory tests were performed on two different types of base material and two different types of subgrade soil to determine their physical and mechanical properties. These materials compacted with various depths in 1.00x1.40 m steel boxes to simulate granular pavements. The target densities were determined according to laboratory compaction test of each material. After the specimen compaction procedure DCP test was performed and the PI was defined for each layer according to DCP test results. The correlations in the literature were used to calculate the CBR and Elastic modulus of the layers. The calculated values compared with laboratory CBR tests and the Repeated Load Triaxle Test (RLTT) results.
Prediction of Cbr Values From Compaction, Gradation and Plasticity Characteristics of Red Soils
CBR is an important parameter in assessing the strength of flexible pavement layers. Estimation of CBR values from laboratory methods are time consuming and laborious. In this aspect indirect methods play useful role in supporting the quality of estimation of CBR values. In the present study red soil samples of coarse grained nature are used in predicting compaction characteristics such as optimum moisture content and maximum dry density. These models with R2 values are in the range of 0.51 to 0.58 have obtained using grain size distribution, consistency as independent variable.
Preparation, Characterization and Modeling of Unbound Granular Materials for Road Foundations
Applied sciences, 2018
A wide range of granular soils were laboratory prepared as base and sub-base materials in flexible pavements technology. The samples were produced according to the requirements defined in the Spanish General Technical Specifications for Roads and Bridge Works (PG-3), which links to the American Unified Soil Classification System (USCS). The lab-prepared granular soils were characterized by means of particle size distribution, Atterberg limits, non-standard Proctor and California Bearing Ratio (CBR). The determination of CBR has been performed considering the evolution of the penetrability up to one, two, three and four days of immersion. The results show that repeatable values within an acceptable degree of accuracy can be obtained, which indicates good quality laboratory testing conditions. Detailed analytical study is performed on the relationship between CBR index and maximum dry density, finding that a predicting model can be obtained from density variation to estimate representative CBR values for design. The results were compiled in a decision matrix using the Analytical Hierarchy Process (AHP) to estimate a California bearing ratio value (CBR) versus maximum dry density.
Assessment of Compression Behaviour of Compacted Soils
IAEME Publication, 2020
The soil compaction is an important engineering application in many geotechnical issues related infrastructure development. Millions of cubic meters of soils are subject to compaction all over the world in the construction of flyovers, embankments, roads and irrigation structures. Compaction improves the stability, strength characteristics and reduces the permeability. Though the strength development as a result of compaction is well studied, compressibility characteristics need much closer examination for enabling better comprehension in the analysis and design of soil structures. A limited experimental investigation is taken up in the present study to understand the compressibility behaviour of compacted soils. The soils from eight different locations in the region of Tirupati have been selected based on inherent variations represented by grain size and plasticity characteristics for the purpose of the study. The soils are classified predominantly as Clayey Sands (SC) to Clay with High Compressibility (CH) as per Indian Standard classification (IS 1498-1970) [4]. The oedometer compression tests are conducted on soils compacted to Proctor's maximum dry density as per IS 2720 Part-7 1980 [11]. The compressibility behaviour is analysed and a step wise procedure is proposed for assessing the compressibility behaviour of compacted soils for use by practicing engineers.
Use of the Soil Modulus for Compaction Control of Compacted Soils
Proceedings of the International Conference on Ground Improvement & Ground Control, 2012
Insufficient compaction conditions can cause significant roadway infrastructure maintenance costs. Conventional compaction control, using nuclear methods, is based on the discrete in situ determination of the dry density and moisture content. Recently, there has been an increase interest in alternative methods for compaction control using intelligent compaction technologies. This method enables the continuous measurement of the soil modulus and the degree of compaction on the layer that is being compacted. Thus, the efficiency of the compaction process can be maximized. Although the adoption of this method is very promising, it constitutes a change of project specification for the contractors (i.e. use of the soil modulus instead of the dry unit weight). Furthermore, the role of dry unit weight, moisture content and matric suction on the soil modulus is still not well understood. This paper presents a review study of the effect of soil types, prepared under standard the same Proctor compaction energy, on the small-strain shear modulus. The results suggest that there seems to be a close relationship between the fines content and small strain shear modulus on the dry side of the optimum, whereas, its effect seems less evident on the wet side of the optimum.
Use of an elastoplastic framework for the understanding of the CBR test for fine and coarse soils
Geotechnical Engineering in the XXI Century: Lessons learned and future challenges, 2019
The present paper shows the understanding of factors that influence the value of the CBR test for fine and granular soils. This is important because the CBR test is frequently used in the design and evaluation of pavements. Nowadays, CBR tests are correlated with the resilient module, which is a key parameter in the current mechanistic methods of pavement design. However, the results indicate a large number of correlations depending on the modulus of elasticity and the plasticity indexes of the material that lead to a large dispersion of the results using these correlations. The above indicates that there are several variables that have not been taken into account in the correlations. The purpose of this study is to show how the value of the CBR test is a function of other variables such as the size and shape of the particles, the crushing, the compaction energy and the elastic behavior of the material. These variables were evaluated through FEM (Finite Element Method) simulations while varying several geotechnical parameters known in practical geotechnics. These simulations in FEM include a linear elastic model, a failure criterion (elastoplastic model), with isotropic hardening, in addition these were prepared for granular and fine soils. The results show that the CBR depends not only on the Young's modulus (a parameter commonly used to correlate with the CBR), but also seems to depend on the compressibility due to the crushing of particles and the energy of compaction. Finally, this paper provides ideas that improve the understanding of the variables that lead to high or low CBR values for fine and granular materials.