Soaked California Bearing Ratio Values Research Articles

Application of Gum Arabic on the Geotechnical Properties of Subgrade Materials

This study investigates the impact of Gum Arabic on the geotechnical properties of subgrade soil materials, a non-traditional soil stabilization technique. Given the need for sustainable and locally available alternatives in road construction, the study aims to assess how different percentages of Gum Arabic affect the physical and mechanical behavior of soil. The research aims to provide sustainable and locally available alternatives in road construction. Three soil samples were treated with varying percentages of Gum Arabic, (1.5%, 3%, 6% and 12%), and standard geotechnical tests were conducted under both soaked and unsoaked conditions. The results showed that the average natural moisture content of the soils was 7.9%, 2.2%, and 4.6%. The addition of Gum Arabic increased the peak maximum dry density of the soil samples by 8.02%, 1.88, and 7.88%. The maximum unsoaked California Bearing Ratio (CBR) values of soil samples were 32.1%, 81.7%, and 48.7%, respectively. Whereas, maximum soaked CBR values of soils S1, S2 and S3 obtained at 1.5%, 6% and 1.5% additions of gum Arabic were 8.4%, 28.7% and 16.9% respectively. The study recommends using 3% Gum Arabic to improve the CBR property of soil samples. The application of Gum Arabic showed significant improvements in soil behavior under both soaked and unsoaked conditions.

A new method for CBR prediction using fuzzy set theory

California Bearing Ratio (CBR) values of the subgrade soils are key parameters in highway route survey and project design. However, in order to calculate the CBR value, time-consuming and specialized tests must be performed in the laboratory or in the field. In this study, a model based on Fuzzy set theory is proposed to predict the CBR value of soils. The geological characteristics of the fine-sized aggregate in soils are considered as the key parameter in the prediction model.For this purpose, novel Fuzzy membership functions are defined. Logarithmic interpolation approach, which takes into account the Atterberg limits and Proctor parameters of the soils, was used to determine the membership degrees of the gravel and sand sized aggregates forming the soil. The membership degrees of fine-sized aggregates were determined by basic sigmoid membership function according to the type of clay they contain. In order to verify the accuracy of the model, the calculated results were compared with the soaked CBR values obtained from laboratory tests and it was found that there was a high correlation (R2=0.86) between each other. Considering the obtained results together, it was determined that the effect of variables such as the geological class to which the aggregates forming the soil belong, which have the potential to affect the CBR value of the soils, on the results of the CBR prediction models can be eliminated by means of membership functions.

Design of sustainable bituminous concrete pavement with cement–treated granular layers constructed on stabilized subgrade

Purpose Designing a sustainable bituminous concrete with long-term performance is a challenging problem. In addition, strength of the subgrade has a crucial impact on pavement design. This paper aims to concentrate on subgrade soil stabilization with granite dust powder (GDP) and crumb rubber powder (CRP) to improve the engineering properties of the soil. Further design of bituminous concrete pavement with cement-treated layers in base and subbase course layers was carried out with life cycle cost analysis and life cycle assessment for 1 km of a four-lane national highway. Design/methodology/approach Subgrade soil stabilized with GDP and CRP is characterized as per Indian Standards (IS)-2720 to determine the optimum dosage. Further, the mechanistic-empirical pavement design was carried out using Indian Road Congress-37 (2018), analyzed using IITPAVE software and validated with ANSYS software. The life cycle cost analysis is carried out using the net present value method, and the life cycle assessment is performed according to the cradle-to-grave approach. Findings A soil mix comprising 10% GDP and 2.5% CRP yielded a soaked California bearing ratio value of 6.58%. In addition, the design of bituminous concrete pavement with cement-treated granular layers showed a 26.9% reduction in life cycle cost and 59.4% reduction in total carbon footprint per kilometer compared to the pavement with traditional aggregate layers. Originality/value The research on subgrade stabilization with sustainable materials like GDP and CRP incorporating mechanistic empirical pavement design, life cycle cost analysis and life cycle assessment is limited. Overall, the study recommends the use of GDP and CRP to stabilize soil for subgrade application and incorporate cement-treated granular layers, which offer economic and environmental benefits compared to traditional pavement construction.

Natural Gradient Boosting for Probabilistic Prediction of Soaked CBR Values Using an Explainable Artificial Intelligence Approach

The California bearing ratio (CBR) value of subgrade is the most used parameter for dimensioning flexible and rigid pavements. The test for determining the CBR value is typically conducted under soaked conditions and is costly, labour-intensive, and time-consuming. Machine learning (ML) techniques have been recently implemented in engineering practice to predict the CBR value from the soil index properties with satisfactory results. However, they provide only deterministic predictions, which do not account for the aleatoric uncertainty linked to input variables and the epistemic uncertainty inherent in the model itself. This work addresses this limitation by introducing an ML model based on the natural gradient boosting (NGBoost) algorithm, becoming the first study to estimate the soaked CBR value from this probabilistic perspective. A database of 2130 soaked CBR tests was compiled for this study. The NGBoost model showcased robust predictive performance, establishing itself as a reliable and effective algorithm for predicting the soaked CBR value. Furthermore, it produced probabilistic CBR predictions as probability density functions, facilitating the establishment of reliable confidence intervals, representing a notable improvement compared to conventional deterministic models. Finally, the Shapley additive explanations method was implemented to investigate the interpretability of the proposed model.

Experimental study on strength, durability, hydraulic and toxicity characteristics of soil treated with mine tailings based geopolymers for sustainable road subgrade application

This article explores the utilization potential of three distinct mine tailings (MT) viz.; red mud (RM), iron tailings (FeT), and zinc tailings (ZT) as geopolymer binders to stabilize the soil for road subgrade application. The strength and durability of soil treated with various MT-based geopolymers are examined through a succession of unconfined compressive strength (UCS), California bearing ratio (CBR) and alternate wetting-drying tests respectively. Furthermore, permeability tests are also conducted to examine the hydraulic response of soil amended with MT-based geopolymers. Finally, leaching study is performed to examine the geo-environmental implications of various geopolymer specimens. The experimental results reveal that the UCS of untreated soil is increased from 0.39 MPa to 5.24 MPa, 5.13 MPa and 3.78 MPa with the use of RM, FeT, and ZT-based geopolymers respectively. The study further shows a 26-fold, 19-fold, and 15.8-fold increase in the soaked CBR values of soil when it is stabilized with RM, FeT, and ZT-based geopolymers respectively. In contrast to untreated soil, soil stabilized with MT-based geopolymers exhibit excellent weathering resistance to alternate wetting-drying cycles showcasing its exceptional durability under challenging environmental conditions. Irrespective of the MT content, curing environment, and the alkali activator concentrations, soil treated with MT-based geopolymers is found to satisfy both the strength (i.e. UCS = 0.75–1.5 MPa and CBR > 5%) as well as durability criteria (i.e. % loss in mass < 10%) specified by Indian Road Congress for subgrade soil. Moreover, the leaching study shows the concentrations of toxic elements (Zn, Cd, Fe, Pb, Ni etc.) to be within the permissible limits specified by USEPA thereby dispelling any environmental concerns associated with the use of MT-based geopolymers.

CBR Correlation with Index and Compaction Properties of Soil

California Bearing Ratio (CBR) is widely used in the design of roads to indicate the bearing capacity of subgrade as well as each layer of the flexible pavement system. However, the procedure for obtaining the CBR value is often considered complicated and time-consuming, thus; some correlations were developed by previous researchers between the CBR value and index properties such as fine content (w), liquid limit (LL), and plasticity index (PI) of the soil, as well as between the CBR value and compaction properties i.e., optimum moisture content (OMC) and maximum dry density (MDD). This study was conducted to evaluate the applicability of the published correlation on the soil obtained in Palembang and the surrounding areas. In this case, 30 sets of secondary data were collected and selected from past projects. In addition, laboratory tests were conducted on five sets of samples for verification purposes. The laboratory tests include a wet sieve to obtain fine content, Atterberg limits to determine soil’s plasticity, and a standard Proctor test to obtain OMC and MDD. Analysis shows that with modifications, some published correlations could be used to predict unsoaked and soaked CBR values for soils in Palembang. Furthermore, two correlations were developed between the CBR values and compaction properties of the soil based on statistical analysis of the collected data.

Effect of using recycled aggregates as road subbase materials: A case study from Kuwait City

In the State of Kuwait, the rise of the construction industry increases the construction and demolition activities and generates large amounts of aggregates. This study focuses on the use of recycled aggregates as road sub-base materials. Two different types of recycled aggregates have been used; namely, recycled concrete aggregates (RCA) and reclaimed asphalt pavement (RAP). Three mixtures are formed: control mix, RCA mix, and RAP mix. California Bearing Ratio (CBR) value was used as an acceptance criterion to evaluate the performance of the mixes. Results of CBR test were compared with the minimum limit of CBR value of road sub-base set by the Ministry of Public Work (MPW) specifications (MPW, 2012; section 3), (minimum 30%). The soaked CBR values of the control mix and RCA mix were equal to 73% and 80%, respectively, and they satisfy MPW specification (2012). While the soaked CBR value of RAP mix was equal to 29%, and it did not conform with MPW CBR limit for road sub-base (minimum 30%). The performance of RAP mix was enhanced by following two different scenarios. In the first scenario, the amount of RAP aggregates was decreased by mixing RAP with fresh aggregates. In the second scenario, cement was added to the RAP mix with two dosages, 2% and 4%. Both scenarios gave CBR values that meets the MPW requirement. It was concluded that RCA can be used as sub-base material, while RAP aggregates can be used as sub-base material when mixed with fresh aggregates or by adding cement as a modifier.

Pemanfaatan Bioplastik dari Limbah Tandan Kosong Kelapa Sawit untuk Peningkatan Nilai CBR (California Bearing Ratio) Tanah Lempung

The massive increase in palm oil production in Indonesia has created problems in the large volume of palm oil processing waste that must be managed. One of the efforts made to reduce this impact is by reusing the empty fruit bunches waste of palm oil as a material for making bioplastics. This bioplastic is then used to improve soil bearing capacity by increasing the CBR (California Bearing Ratio) value in expansive clay soils. The effectiveness of the use of bioplastics was measured by comparing the test results of laboratory CBR values of soil samples mixed with bioplastics with varying levels of 0%, 4%, 10%, and 15%, respectively. The test results showed that samples that had been treated with bioplastics had a greater soaked CBR value than sample without bioplastics. The highest soaked CBR value obtained was 21.14%, namely in sample with 10% bioplastic content. Bioplastic from empty fruit bunches of palm oil has the potential to be developed as a material to improve soil bearing capacity.

Laboratory investigation to identify subgrade soil in Maharashtra to satisfy reinforcement need for pavement design

Pavement research manifests the field test to stimulate the field condition wherein the lab test quickly acquires the results. Researchers faced difficulty achieving uniformity upon testing the natural subgrade soil, but the artificial subgrade controls trafficking and design parameters like subgrade california bearing ratio (CBR). In this paper, four different soil samples collected from Maharashtra were tested to identify the subgrade soil that satisfies the pavement's need for reinforcement. The article discusses the results and highlights the predominant tests performed by following Indian standard (IS) codes like CBR, swelling pressure, hydrometer test, and other engineering properties tests. Sample #4 is black cotton soil, basically montmorillonite clay. Results reveal that sample #4 identified as CH as per IS soil classification showed the swelling pressure as 40kN/m2, proving that the soil is challenging and expansive with the need for reinforcement in pavement design as the soaked CBR value is 2.23%.

Engineering behavior of municipal solid waste incinerated bottom ash with the addition of lime

The paper identifies the physio-chemical properties of incinerated bottom ash procured from waste incineration and treatment facility. The key factors responsible for its limited use as raw material have been identified. The stabilization process can successfully control these limitations using lime as the stabilizing agent. The properties of the stabilized product for 3, 5, and 7 % of lime addition have been compared with the untreated bottom ash. A series of Unconfined Compressive Strength (UCS), Split Tensile Strength (STS), and California Bearing Ratio (CBR) tests were performed for the experimental investigations on the improvement of strength characteristics. The specimens were prepared at the Optimum moisture content (OMC). Maximum dry density (MDD) values were calculated using Indian Standard light compaction tests and kept under curing for 3,7,14, and 28 days. The results suggest better strength in the stabilized specimen with higher lime contents as the pozzolanic action results in 124 kPa for STS value for 7 % lime content under curing for 28 days. The best results for UCS were also produced, where an increase of more than 3859 % strength was noticed. The soaked CBR values showed well-stipulated results with more comparative strength gain than in unsoaked conditions. The analysis of Mineral and Microstructure in Municipal solid waste incinerated bottom Ash (MSW-IBA) is carried out through FESEM and XRD testing.

The Effect of Diatomaceous Earth Addition on CBR Values of Glee Geunteng Soil in Aceh Besar, Aceh Province, Indonesia

The soil which is the platform often used for construction activities needs the strength to resist loads. However, its physical and mechanical properties are sometimes naturally limited and this implies there is a need for improvement and stabilization. Therefore, this study uses diatomaceous earth, which is a natural pozzolanic material classified as a type of Supplementary Cementing Materials (SCM), as an additive. The chemical stabilization was conducted by mixing the soil with stabilizing materials such as cement, lime, fly ash or others that have the ability to change the chemical composition and combination of soil. It is important to note that diatomaceous earth has similar properties as other pozzolanic materials such as fly ash and metakaolin powder and this is the reason it is expected to function as a soil stabilizing agent needed to improve soil properties. This study was conducted using the soil from Glee Geunteng in Peukan Bada as well as the diatomaceous earth obtained from Lambeureunut Village, Aceh Besar Regency, Aceh Province, Indonesia. The main purpose was to determine the California Bearing Ratio (CBR) value of the Glee Geunteng soil mixed with diatomaceous earth at 5, 10, 15, and 20% dry weight of the soil. The CBR test consisted of unsoaked CBR, soaked CBR testing at 4 days, and swelling properties of CBR with a variety of diatomaceous earth mixtures. Glee Geunteng soil was classified as A-6 Group Index 3 based on the AASHTO soil classification and as the SC (silty clay) soil according to the USCS classification. The results showed that the unsoaked CBR value reduced from 35.96% for the natural Glee Geunteng soil to 31.65% for the soil mixed with 20% diatomaceous earth material. A similar trend was observed for the soaked CBR value with a reduction from 15.57% to 6.98%. The decrease in CBR value was perceived to be caused by the very small silica content (SiO2 ) in diatomaceous earth material with 42.09% compared to the 86% in the material obtained from another source in the previous research by Hidayati.

Effect of mining tailing waste on properties of cement stabilized black cotton soil

In most cases, not all available materials for road construction do meet the nominal requirements, as such; stabilization becomes necessary. This study presents the results of a laboratory experiments carried out to assess the effect of mining tailing waste (MTW) as an admixture to ordinary Portland cement (OPC) stabilized Black Cotton Soil (BCS). The MTW was obtained from a tin mining site in Bukuru, Jos South LGA of Plateau State, Nigeria, while the BCS was obtained along Kanawa-Jauro-Gotel road, in Yemaltu-Deba, Gombe, Nigeria. The specimens were prepared by admixing the four blends of OPC stabilized BCS (using 0, 4, 6, and 8% OPC) with stepped percentage of MTW(0, 5, 10, 15 and 20%) by dry weight of BCS. Atterberg’s limits, Sieve analysis, Compaction, soaked California Bearing Ratio (CBR) and Unconfined Compressive Strength (UCS) test were carried out on the natural and stabilized BCS. The BCS classifies A – 7 – 6 (40) and CH (high plasticity clay) according to the American Association of State Highway and Transport Officials (AASHTO M 145-2012) and the Unified Soil Classification System (ASTM D 2487-2011), respectively. Addition of MTW to OPC stabilized BCS affected the compaction characteristics and improved both the soaked CBR, and the UCS. The optimum blend was achieved with 20% MTW admixed to BCS stabilized with 8% OPC which gave a 4-days soaked CBR value of 35% and a 7 days cured UCS value of 1273 kN/m2. This satisfies the sub-base requirements of the Nigerian general specifications. Thus, this study recommends the use of 20% MTW with 8% OPC for BCS stabilization.

Effect of Metakaolin on Strength Properties of Lateritic Soil Intended for Use as Road Construction Material

An excellent all-weather road is essential in providing reliable transportation services that comprise social and economic development elements. However, in most cases, the road has to be constructed on a soft foundation soil where large deformations usually occur, which causes increases in maintenance costs and leads to interruption of traffic service, especially during the wet season. It is necessary to stabilize or improve the in-situ soils. This study explores the potential of using metakaolin to improve the geotechnical properties of lateritic soil for road construction materials. The soil classifies as A-6(4) and CL according to the American Association of State Highway and Transport Officials and the Unified Soil Classification System. The soil was treated with 5, 17.5 and 30 % concentrations of metakaolin by dry weight and was compacted using three compaction energies: British Standard Light (BSL), West African Standard (WAS) and British Standard Heavy (BSH). California Bearing Ratio (CBR) and Unconfined Compressive Strength (UCS) tests were carried out to evaluate the effect of metakaolin on the soil investigated. Results showed a general improvement in the engineering properties of the soil with an increase in metakaolin content, particularly when compacted at the BSH energy level. However, the results did not meet the 1500-3000 kN/m 2 7 days UCS criterion stipulated by the Nigerian General Specification for road base courses. However, 30 % lateritic soil/metakaolin blended soil compacted using WAS and BSH energy levels suffice for use as sub-base in road construction, having met the 750-1500 kN/m 2 7 days UCS criterion stipulated by the Nigerian General Specification. The Peak CBR value for the treated soil, compacted using the three energy levels of BSL, WAS, and BSH, occurred at 30 % metakaolin concentration with corresponding soaked CBR values of 17, 23 and 31 %. The Nigerian General Specification recommends a nominal strength criterion of a soaked CBR value of 30 and 80 % to be attained by material to be used as sub-base and base course in road construction. Based on the above criterion, only the 30 % metakaolin treated blend compacted at the BSH energy level met the 30 % requirement for sub-base materials.

Evaluation of the Effect of RAP and Lime on Geotechnical Properties of Clayey Soil

Abstract: Road network plays a large role in the rapid development of the economy of a country, providing connectivity to remote areas for various transportation activities. India ranks second in the world in terms of length of road network after the United States. The major road network in the urban locality consists of bituminous pavements periodically resurfaced during maintenance. From the milling process, reclaimed asphalt pavement (RAP) is obtained. Additionally, RAP can be used for the utilization of recycled asphalt pavement (RAP) materials in subgrade soil. Reclaimed Asphalt Pavement (RAP) is being used in this case study to stabilize the subgrade soil collected from Crop Research Center (CRC), Govind Ballabh Pant University, Tanda Range, Uttarakhand (29°01'09.7"N, 79°28'55.9"E). To conduct the experimental program, a variable amount of RAP percentages viz., 5, 10, 15, and 20%, and different percentages of lime i.e., 2, 4, 6, and 8% were mixed with natural soil. Based on gradation, Standard Proctor Test (SPT), Unconfined Compressive Strength (UCS), California Bearing Ratio (CBR), and Specific gravity, the characteristics of RAP-soils with added lime were evaluated. For soil mixture including 10% RAP and 4% lime, a maximum MDD of 19.04 and a percentage increase in compaction of 11.93% was observed. OMC value was observed as 11.35%, which further decreased as RAP content increased. Due to RAP containing coarse aggregate, a higher CBR value was obtained due to the harder sample surface. For all soil mixers of 15% RAP and 4% lime, unsoaked CBR and soaked CBR values were found to be 31.39% and 18.69% respectively. Percentage increases in their respective CBR values were 868.83% and 662.86%. for every percentage of lime variation, maximum CBR was obtained at 15% RAP, and maximum CBR value for soaked CBR was obtained for soil with 15% RAP and 2% lime, whereas for unsoaked CBR, it was obtained for soil with 15% RAP and 4% lime. Maximum UCS values of 412.45 kN/m2 , 606.81 kN/m2 and 857.62 kN/m2 were observed on 3rd, 7th and 14th days for soil mix with 15% RAP and 4% lime, with percentage increase of 291.17%, 249.40% and 387.78% respectively. Based on the results of the study, RAP materials can be effectively used in the soil subgrade, sub-base, and base of flexible pavements, reducing the cost of construction. Keywords: Reclaimed Asphalt Pavement (RAP), Lime, CBR, SPT, UCS, OMC, MDD.

Influence of Increasing Cement Content on some Geotechnical Properties of selected Lateritic Soils of Western Niger Delta on Sapele-Agbor Road, Nigeria

This study is aimed at determining the influence of stabilization by percentage increase in volume of cement on Geotechnical properties of some lateritic soils obtained from two borrow pits along Agbor-Sapele road, Western Niger Delta, Nigeria. The soils are classified as A-7-6 and A-7-5 with high percentage of Fines, averaging 60.43%. These natural soil samples falls short of the Federal Ministry of Works Standard based on grain size and consistency limits. The values of 1950.91 Kg/m3 and 22.70% obtained for maximum dry density (MDD) and optimum moisture content (OMC) when soil was treated at 10% by volume of cement, reveals the fact that higher unconfined compressive strength (UCS) values would be noticeable at 10% by volume addition of cement with increasing energy level of compaction, than that to be obtained at 5% by volume of addition of cement with MDD of 1933.80 Kg/m3 and OMC 22.78%. When the soaked California Bearing Ratio (CBR) values for treated soils were considered, the reduction in soaked CBR value is minimal at 10%, with an average of 76.33% than that obtained at 5% by volume of cement with an average of 78.45%, compacted at varying energy level. In general, the study result clearly reveals that increasing cement content would result in improved strength characteristics even as permeability decreased from 6.744x10-8 mm/s to 6.129 x 10-8 mm/s across the compaction level of the stabilized soil samples.

Utilization of reclaimed asphalt pavement (RAP) as granular sub-base material in road construction

Currently, the scarcity of natural resources has been a significant impact on the construction industry. The demand for fresh aggregate becoming huge due to the increase in the construction of pavement and fulfilling the aggregate requirement is a great concern. In this research, an effort has been shaped to assess the feasibility of the use of Reclaimed Asphalt Pavement (RAP) material for improving the strength properties of the granular sub-base (GSB) layer. RAP aggregate was partially and fully replaced with fresh aggregate in different percentages to test various strength properties. Efforts were being made to improve the strength of the GSB layer by using RAP concerning soaked California Bearing Ratio (CBR) by blending with natural aggregates (NA). To know the best of mix proportions, RAP was partially and fully replaced with virgin aggregate in varying percentages such as 0%, 25%, 35%, 45%, 55%, 65%, and 75%. Modified compaction tests were performed on 100 % RAP and mixtures containing various percentages of RAP to establish the optimum water content for CBR sample preparation. Soaked CBR value was determined at 7 days, 14 days to see the effect of RAP on the GSB mixes. It was observed from the results that the soaked CBR value of RAP improves from 32% over 100% when it is mixed with natural aggregates in varying percentages and made it appropriate for utilizing it as a sub-base of flexible pavement. Depending upon the experimental outcomes, it was deduced that RAP in the sub-base layer is limited to 55% which has exquisite properties as natural aggregates utilized in the road sub-base.

EVALUATION OF ENGINEERING PROPERTIES OF THERMAL POWER PLANT WASTE FOR SUBGRADE TREATMENT

Soft cohesive soils have low strength, high plasticity, and a large expansion ratio making them unsuitable as a road subgrade. This study aims to evaluate the potential of power plant waste (fly ash) from the Barapukuria Thermal Power Plant, Dinajpur, Bangladesh to improve the characteristics of such soft cohesive soil. X-ray fluorescence test conducted to classify the power plant fly ash and the type was identified as “Class F” according to “American Association of State Highway and Transportation Officials” and "American Society for Testing and Materials". Laboratory tests were conducted on clay soil obtained from Dinajpur region modified by the collected power plant waste. As the Class F fly ash has low cementing property, 3% cement was added with it. Cement mixed soil was modified with 5%, 10%, 15%, and 20% fly ash respectively. Specific Gravity, Atterberg limits, Modified Proctor Compaction, Unconfined Compressive Strength (UCS) and California Bearing Ratio (CBR) tests were conducted. The study reveals that there is a decrease in specific gravity, dry density, and plasticity index with the addition of power plant waste. On the other hand, there is an increase in optimum moisture content, UCS, and CBR value. UCS and CBR values were found to be improved remarkably. Soaked CBR value of soil is found to be improved from 2.79% to 92.59% when treated with 5% fly ash and 3% cement. The UCS value of this modified soil was 560.36 kPa. The stabilized soil thus obtained meets the requirements for subgrade as specified by the Local Government Engineering Department (LGED)’s design manual (2005), Bangladesh. Since there is a possibility of leaching by dumping a large quantity of fly ash in the pond, the use of fly ash from the power plants to improve soft cohesive soils for road subgrade may be an environment-friendly alternative to its disposal in the ponds.

Prediction of four-days Soaked California Bearing Ratio (CBR) Values from Soil Index Properties

California Bearing Ratio (CBR) laboratory testing is the conventional method for determining soaked strengths of pavement subgrades. The test requires careful preparation of soil samples followed by four days of water soaking before penetrating the samples using a standard plunger at prescribed rates to set depths. When the number of samples becomes large the determination of soaked CBR values becomes cumbersome as the test is laborious and time consuming. This study aimed at establishing an alternative way of determining soaked CBR by developing a model that would be used for estimating soaked CBR of fine- and coarse- grained soils without performing the CBR test. This has been achieved by correlating CBR values compacted at 95% Maximum Dry Density (MDD) with the soil index properties. The results show that soaked CBR values of fine-grained soils significantly correlate with specific gravity of soil (GS), Plasticity index (PI) and the grading modulus (GM) of the soil that yields a degree of determination of R2 = 0.91 and for coarse grained (A-2 type) soil, the soaked CBR values significantly correlate with specific gravity of soil and percentage of fines passing 0.075mm sieve size that yields a degree of determination of R2= 0.94.

Influence and correlation of maximum dry density on soaked & unsoaked CBR of soil

Preparation of subgrade plays an significant role in construction of roads as it acts as the foundation to the flexible pavement. The soil subgrade can be utilized to its full extent only if it is well compacted, the subgrade strength is related to the CBR of soil. Determination of stiffness modulus and shear strength of the subgrade using California bearing ratio (CBR) test. The CBR values be contingent on the nature & other properties of soil. CBR test is very laborious, time overwhelming & always be performed on moulded soil samples which makes it difficult to get accurate values and also to implement in reality. In the present study the authors have made an attempt to calculate the CBR values and the index properties of the soil and to develop a relationship between them so that one can obtain reliable CBR values in less time. The authors have collected the samples from Chickballapur district, India and correlated unsoaked and soaked CBR value with maximum dry density, optimum moisture content, percentage fines, liquid limit and unconfined compressive strength etc. Experimental outcomes indicates that the soil properties influence the CBR value of soil. Correlations are developed between the California bearing ratio and maximum dry density with satisfactory R2 values with which CBR values can be predicted.

Predicting soaked CBR of SC subgrade from dry density for light and heavy compaction

Laboratory California Bearing Ratio (CBR) test is an arduous and lengthy process to determine the CBR strength of the soil. CBR value of subgrade soil plays an important role in the design of flexible pavement. CBR strength of soil can be determined in dry/unsoaked condition and in soaked condition. Soaked CBR value of the subgrade is usually preferred for designing flexible pavements as it gives the CBR strength of subgrade soil under worst case scenario of a pavement being submerged under water for a minimum period of 4 days during floods. Generally, in the lab soaking of the prepared specimen is done for a period of 96 h or 4 days in case of soaked CBR test. While constructing a pavement lot of CBR tests have to be carried out on the subgrade soil at different locations along the length of the pavement. As conducting soaked CBR test requires minimum of 4 days, this will result in lot of delay in the execution of project and ultimately will result in increase in cost of construction. Thus the objective of the present experimental work is to correlate by means of Simple Linear Regression Analysis (SLRA), the soaked CBR value of SC (Clayey Sand) soil with the dry density (DD) of SC soil attained using light and heavy compaction. So that based on the empirical correlations, soaked CBR strength of the subgrade soil consisting of SC soil can be easily predicted from the DD of the subgrade soil without actually conducting the CBR test in the laboratory. Also in this study, an effort has been made to investigate the effect of varying compaction energies on the soaked CBR strength of the SC soil.