Subgrade Strength Research Articles

Kaolinite subgrade strength characteristics variation with RBI Grade 81

The shrinking behaviour of clay soil due to moisture variation causes damage to the foundation of structures, residential, commercial structures and embankment construction. To overcome this problem, the soil needs to be treated to improve its strength and durability of the ground. The best technique is stabilization, which enhances the engineering soil properties, upgrades the shear strength, and reduces the consistency limit. In this present study, Kaolinite clayey subgrade soil is stabilized using Road Building International Grade 81 (RBI), and its effects on the strength characteristics of the soil are studied. Compaction characteristics, Atterberg's limits, Unconfined Compression Strength tests (UCS), and Split Tensile Strength (STS) on the soil samples were performed. The same composites are studied for SEM and XRD results to confirm the morphology of the new compounds formed. Compaction factors increased optimum moisture content (OMC), and the maximum dry density (MDD) decreased with RBI Grade 81 to kaolinite. UCS values increased significantly for the clayey subgrade with the addition of RBI Grade 81. RBI Grade 81 at 8% shows an enhanced upgrade in the clay subgrade's strength compared with the natural kaolinite subgrade. Hence, RBI Grade 81 can be recommended as a potential soil stabilizing agent, particularly for clayey subgrade soil.

Effect of sodium silicate and cement on the improvement of engineering properties of organic soil

The study is aimed at evaluating the effect of adding sodium silicate and cement to organic soil. Geotechnical properties of organic soil are determined before and after the addition of the stabilizing materials, which in this case are cement and sodium silicate. The results obtained after treatment were analyzed and evaluated to determine whether the strength values reached are adequate for strong subgrades for pavement, and airports construction. Organic soil samples used in this study were obtained from Kayseri Free Area in Turkey. Index properties and geotechnical properties of organic soil, which was identified as sample P, were determined and this formed the reference upon which strength improvements of each mix design sample were obtained. Optimum moisture content and maximum dry density of the soil and the various mixes were obtained using standard proctor test. Unconfined compressive tests (UCS), California bearing ratio (CBR), and Falling head permeability tests were used to determine geotechnical properties. UCS tests were conducted on air cured samples for 1, 7, and 28 days. Soaked and unsoaked CBR samples were tested after 1, 7 and 28 days. Hydraulic conductivity was determined using the falling head permeability test. From the experiments, sodium silicate and cement were seen to improve the strength of organic soil and provide acceptable subgrade strength and CBR values. CBR and UCS tests indicated that longer curing periods improved strength even more. Higher values were obtained for 7 days cured samples than for 1-day samples with the highest values being obtained for 28 days cured samples. Design mixes with higher cement and sodium silicate compositions gave the highest values of strength. In conclusion, sodium silicate and cement give positive results when it comes to stabilizing organic soil.

Use of an Eletrokinetic Remediated Soil as a Road Subgrade Material

The soil investigated for suitability checks, as a subgrade material in this study, was a crude oil contaminated (COC) soil treated using an electrokinetic technique. The index properties and compaction characteristics of the electrokinetic remediated (EKR) soil are natural moisture content was 10.97%; The Atterberg limit test showed liquid limit, plastic limit, plasticity index and linear shrinkage of 36.50%, 22.05%,14.45 %, and 4.30%, respectively. The percentage of 62.80% passes 0.075mm sieve with a maximum dry density (MDD) of 1.77 Mg/m3, and the moisture content decreased from 13.2% to 11.81%. The soil is classified as A-6 according to AASHTO classification system and belong to clay of low plasticity CL or OL group according to the Unified Soil Classification System. The unconfined compression strength, (UCS), durability, and California bearing ratio (CBR) of the electrokinetic remediated soil improved marginally from 46.63kN/m2 to 92.64kN/m2; from 18% to 23%; and from 2.55% to 4.05% respectively. However, these results obtained, do not meet the minimum requirement of the Nigerian General Specification. As a result, it is advised for further research, that an EKR soil be stabilized using cement stabilization to achieve the desired subgrade strength.

An Investigation on the Potential of Cellulose for Soil Stabilization

The construction industry remains a significant contributor to global carbon emissions. Several sustainable alternatives have emerged to overcome this issue in geotechnical engineering. In this study, cellulose, an abundant biopolymer, is investigated for its potential to modify geotechnical properties favourably. Sodium carboxymethyl cellulose (NaCMC) is an anionic ether derivative of natural cellulose with good binding and moisture-retaining capacity. Experimental investigations were conducted on organic silt stabilized with 0.25% to 1.00% NaCMC, and the results indicate that unconfined compression strength (UCS) increased by 76.7% with 0.5% NaCMC treated soil after 28 days. Hydraulic conductivity (HC) of the 0.5% NaCMC treated soil decreased by 91.7% after 28 days, and the additives suppressed the compression index of the soil by 50%. The California bearing ratio (CBR) test indicated that the additive improved the subgrade strength by 33.2%, improving it from very poor to a fair sub-grade material. Microstructural analysis using a scanning electron microscope (SEM) and chemical investigation using x-ray diffraction (XRD) indicates that NaCMC’s interaction with soil did not form any new chemical compounds. However, the viscous nature of the material formed fibrous threads that bind the soil to enhance the geotechnical properties, establishing itself as a prominent stabilizer for ground improvement applications.

Performance Evaluation of Lime, Cement and Alkali-Activated Binder in Fiber-Reinforced Expansive Subgrade Soil: A Comparative Study

Abstract Expansive subgrade soils show early distresses causing distortion and premature failure to pavement structures. In the present study, an attempt is made to enhance the subgrade strength characteristics of the expansive soil by treatment with an alkali-activated binder (AAB) and reinforcement with four types of fibers (polypropylene [PF], glass, hemp, and coir fiber [CF]). The research also compares the effectiveness of fiber reinforcement in geopolymerized alkaline soil with the traditional lime and cement binders. AAB is produced by the reaction in an alkaline activator of sodium silicate and sodium hydroxide with aluminosilicate precursors (Class-F fly ash and slag) by maintaining a 0.4 water-to-solid ratio. The effect of varying dosages of fibers and slag/fly ash ratio in the alkaline, lime, and cemented soil mixture on unconfined compressive strength (UCS), split tensile strength (STS), and flexural and penetration resistance is evaluated through a series of geomechanical and microstructural characterization tests. California bearing ratio (CBR) and flexural strength (Sf) are chosen as a subgrade strength performance indicator for fiber-reinforced soil. It is observed that PF-AAB soil shows higher interfacial bonding with strong interlocking density and tensile cracking resistance. The combined inclusion of fiber reinforcement (> 0.5 %) with 0.66 slags/fly ash ratio (S40 F60) in the alkaline mixture increased the subgrade strength performance indicator (flexural and elasticity) by around 35 %–40 % over the lime-cement soil-fiber mixture. The corresponding CBR, UCS, and STS values were also found to have increased by 55 %–65 %. Furthermore, the uncertainties associated with subgrade strength failure are predicted in the form of the CBR reliability index using Monte Carlo simulation through a nonlinear regression model developed from experimental results. The study shows that the optimum dosages of fiber reinforcement and slag/fly ash are essential factors for regulating the volumetric instability and tensile cracks of expansive soil.

Editorial: Special Issue on Smart and Green Infrastructures with Optimum Life Cycle Solutions

Editorial: Special Issue on Smart and Green Infrastructures with Optimum Life Cycle Solutions

Evaluation of effect of moisture on fatigue performance of pavement designed with recycled asphalt mixtures

The moisture resistance of dense- and gap-graded bituminous mixes prepared with the replacement of virgin aggregates and fresh bitumen with reclaimed asphalt pavement (RAP) was evaluated using indirect tensile strength (ITS) and resilient modulus ( Mr). The mechanistic analysis was performed to estimate the effect of moisture resistance on the fatigue performance of thin and thick pavement sections designed with dense- and gap-graded bituminous mixes. The ITS ratio and Mr ratio results indicate that the resilient modulus ratio is more sensitive to moisture damage in bituminous mixes than the ITS ratio. In addition, the results of the fatigue life ratio indicated that the gap-graded mix prepared with different RAP content has better resistance to moisture-related cracking in thick pavement sections than the dense-graded mix. However, the effectiveness of gap-graded and dense-graded mixes prepared with different RAP content on moisture-related cracking depended on the subgrade strength for thin pavement sections.

Design of Rigid Pavement for Oke- Omi Road, Ibadan, Nigeria

Rigid pavements are often preferred to flexible types due to their higher durability and ease of maintenance also to reduce early road failure and increase its longevity. This study redesigned a deteriorated segment of Oke-Omi flexible road pavement as a rigid pavement. The pavement thickness was derived using the American Association of State Highway and Transportation Officials (AASHTO) design method. A programme using a spreadsheet was developed to facilitate the design process. The sieve analysis result showed that the soil was poorly graded. The soil has a low plasticity index of 28.1% (liquid limit 46.2%, plastic limit 18.1%); the Maximum Dry Density and Optimum Moisture Content were 1999 g/cm3 and 10.8% respectively. The California Bearing Ratio of the soil was 48.43% which shows that the subgrade strength was adequate. The computed Estimated Single Axle Load (ESAL) for both the base year and the projected year are 6.74x106 and 100x106 single axle respectively. The design process yielded the pavement thickness of 240 mm and 380 mm for the base year (2017) and projected year (2037) respectively. A rigid pavement of adequate thickness was designed for the deteriorated segment of the Oke-Omi road.

Literature Review on Effects of Saturation on Soil Subgrade Strength

Abstract: Subgrade is the layer of soil on which the subbase or pavement is constructed, give support to the remaining part of the pavement system. It is critical for highway engineers to begin a subgrade with a California Bearing Ratio (CBR) value of at least 10. Lot of Researches shows that if a subgrade has a CBR value less than 10, the subbase material will divert under traffic loadings in the same way as the subgrade and cause pavement degradation. The subbase, the layer of aggregate material just below the pavement, gives drainage and stability to the pavement. Undrained water in the pavement substantiate layers can freeze and expand, rising internal pressures on the pavement structure. Additionally, flowing water can move soil particles that clog drains and, in fusion with traffic, pump fines from the subbase or subgrade. It is therefore essential that highway engineers develop a strong, permeable subbase with longitudinal subdrains. This paper provides a literature review on effects of saturation on soil subgrade strength.

A Study on Effects of Saturation on Soil Subgrade Strength

A Study on Effects of Saturation on Soil Subgrade Strength

β-Glucan as a Sustainable Alternative to Stabilize Pavement Subgrade.

Beta glucan (β-Glucan), a polysaccharide biopolymer, is used to improve the subgrade strength of clayey soils in an attempt to advocate a sustainable, carbon-neutral, and eco-friendly stabilizer. A design thickness catalog was developed for a three-layered flexible pavement using 3D finite element analysis (FEA) and layered elastic analysis. The analyses were performed for β-glucan-treated fine-grained soils with varying traffic intensities based on a mechanistic design philosophy conforming to IRC: 37-2018. Genetic programming (GP) was employed to obtain equations governing the rutting and fatigue failure in pavements. Thirty-nine datasets were used in the determination and analysis of critical strains governing the failure of a flexible pavement. Energy-dispersive X-ray spectroscopy (EDS), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), Zetasizer analysis, and pH tests of the β-glucan-treated soil revealed the mechanism of strength improvement of the fine-grained soils. The savings in cost for a 1 km stretch of the pavement were estimated to be 14.3%.

A Study on Effects of Saturation on Soil Subgrade Strength

Abstract: The design of the pavement layers to be laid over sub grade soil starts off with the estimation of sub grade strength and the volume of traffic to be carried. Design of the various pavement layers are very much dependent on the strength of the sub grade soil over which they are going to be laid. Sub grade strength is mostly expressed in terms of CBR (California Bearing Ratio). Weaker sub grade essentially requires thicker layers whereas stronger sub grade goes well with thinner pavement layers. The sub grade is always subjected to change in saturation level due to precipitation, capillary action, flood or abrupt rise or subtidal of water table. Change in moisture level in sub grade causes change in the sub grade strength. And it becomes quite essential for an engineer to understand the exact nature of dependence of sub grade strength on moisture variation. An understanding of the dependence of the CBR strength of local soils on water content will contribute towards better design and maintenance practices. Normally CBR test is an easy and well adopted method conducted on soil samples to measure the strength of sub grade. However, many other tests are also considered for assessing the sub grade strength. The strength of soil, used for sub grade may vary largely on the amount of saturation in it, i.e. Amount of water exposed to the soil. Hence, in this study an attempt has been made to vary the degree of soaking and hence the saturation level in various types of soils and study the engineering properties of soils including CBR at different saturation levels. It is observed that for coarse grained soil, worst engineering properties are observed after three days of soaking and for fine grained soils, the same is found at the end of four days

Assessment of Geologic Effect of Road Submergence Depths on Soil Subgrade Strength in Eket, South-South Nigeria

Road submergence is a common occurrence in Eket, South-South Nigeria, resulting in massive outlays for road construction and alimony. Fundamentally, the delineation of roadway structures is based on the strength of consolidated soil avowed as the subgrade. Consequently, the subgrade is the in situ material upon which the roadway structure is placed. It is necessary to know the modes of damage to roads caused by submergence. This study assesses the effect of road submergence depths and the extent of submergences on the subgrade strength of soil samples carried out on the Uquo Eket road that was intensely defective by the deluge. Coherent and frictional soil material types were tested for California Bearing ratio (CBR), mechanical analysis, Atterberg limit determination, and moisture density tests, respectively. CBR tests were done at various elevations of submersion, including common drenching limit, elongated deluge, and resoluteness of its suitability. Atterberg limit determination and mechanical analysis tests categorized and determined the applicability of studious soil as subgrade substantial. For elongated duration deluges, the depth and extent of submergence of subgrade strength show a lower value. Moreover, mechanical and Atterberg limit determination tests indicate a rapid and high-resolution occurrence of delegation for the elongated duration.

Behavior of Soil Subgrade Strength with Saturation

Behavior of Soil Subgrade Strength with Saturation

Impact of Subgrade Strength on Pavement Performance

Based on the standard design of flexible pavement structure conducted in Turkey, only subbase course layer is affected by the variation of subgrade strength and other pavement layers (wearing course, binder course, asphalt concrete (AC) base course, and crushed stone base course) are not influenced by the variation of subgrade strength. Therefore, the aim of this study is to investigate the impact of subgrade strength on flexible pavement distresses. To achieve the objectives, firstly, three different flexible pavement structures designed using the Turkish Flexible Pavement Design Guide 2008 were chosen and secondly, the effect of variation of subgrade strength [5 to 50 California Breading Ratio (CBR)] on pavement performance (rutting and fatigue cracking) for three different traffic levels [5000, 10000, and 15000 average annual daily truck traffic (AADTT)] for climatic condition of Izmir region using AASHTOWare Pavement ME Design v2.5.5 were analyzed. The results of the study show that, reducing subgrade CBR values from 50 to 5 CBR resulted in an increase by 3.7mm in total rutting depth and 5.6% in alligator cracking magnitude. Also, results demonstrated that the influence of subgrade strength on rutting within asphalt concrete layers (AC rutting) is negligible. By contrast, increasing subgrade CBR value from 5 to 50 resulted in a significant increase (65.1 to 314.7 m/km) in longitudinal cracking magnitude while thermal (transverse) cracking is not sensitive to the variation of subgrade CBR values. This study can assist highway agencies and individual pavement designers in the design a more practical pavement.

New binary paper/wood industry waste blend for solidification/stabilisation of problematic soil subgrade: macro-micro study

This article presents the potential application of paper/wood industry waste by-products, i.e. lignosulphonate (LS) in conjunction with lime (LM) [i.e. LS-based cementing admixture (LSCA)] to mitigate desiccation induced cracking and mechanical vulnerabilities of expansive soil subgrade. The results showed that the LSCA and lime (LM) significantly ameliorated the soil consistency, subgrade strength characteristics (i.e. California bearing ratio and resilient modulus), and completely mitigated the swelling potential with enhanced resistance against Sr . Moreover, the LSCA and LM notably reduced the 3D-volumetric shrinkage and crack intensity factor (CIF) by 90.1 and 87.4%, respectively. The mineralogical and microstructural analyses manifested that the LSCA induced new cementitious compounds (i.e. hydrates of calcium silicate and calcium aluminate), and substantially enhanced the interlocking among the soil particles compared to the untreated and LS-treated soils. Besides, pavement thickness analyses showed that the LSCA treated subgrade, omits the provision of sand cushion and sub-base course promoting road material conservation.

Consideration of a Tack Coat Bond Strength Test to Minimize the Potential for Slippage Failures on Flexible Airfield Pavements

Slippage failures on flexible pavements are a potential problem for airports given the large wheel loads and high tire pressures of modern aircraft. While not common, when slippage failures do occur the impact can be significant on flexible pavement performance. This paper has three components: (1) case studies of slippage failures that have occurred on airfield pavements; (2) a literature review of relevant interlayer bond strength test procedures; and (3) the results of an analytical, field, and laboratory research investigation. Component (3) was conducted to assess the suitability of interface bond strength tests to evaluate the sufficiency of interlayer bond strength between lifts of asphalt pavement, either new construction or an overlay of existing pavement. The analytical study found that for a fully bonded pavement (no-slip condition), subgrade strength was the primary factor affecting horizontal stress at the interface followed by wheel load. Field cores were obtained from recently constructed asphalt pavements and brought to the laboratory for monotonic direct shear testing to determine bond strength as well as monotonic indirect tensile testing to determine mixture strength. Testing was conducted at 77°F (25°C) and 136°F (58°C). Results showed better repeatability at room temperature with similar relative performance ranking to the critical case high temperature test. Bond strength was influenced by in-place mixture density. Overall, the bond strength test method was practicable for use in field laboratories for acceptance testing.

Pengaruh Kondisi Tanah Terhadap Kerusakan Dengan Menggunakan Metode Road Condition Index (RCI) Pada Ruas Jalan Pronoyudo Kecamatan Junrejo-Kota Batu

Subgrade with poor strength and stability would cause the pavement to deform and crack easily. Different locations have different subgrade conditions. Different soil characteristics in different locations call for different treatment or stabilization measures. Poor subgrade strength is observed in Pronoyudo Street in Junrejo Sub-District, Batu City. This is evidenced by the cracked and chipped asphalt surface. The method used to determine the type and level of road damage in the study was Road Condition Index (RCI), while subgrade strength or CBR (California Bearing Ratio) was determined using DCP. In addition, sieve analysis was also performed for foundation material as well as testing water content and subgrade plasticity. Observations were made along 1,000 m (1 km) which was divided into 200 sq m. The analysis results showed a mean Road Condition Index (RCI) of 6.96% and the mean CBR value using the DCP tool was 2.48% (< 5%) with a DDT value of 3.39. A routine or periodic maintenance program is deemed to be the right management method for Pronoyudo Street in Junrejo Sub-District in Batu City. Therefore, overall, the program that has been carried out for road maintenance is in accordance with the results of research analysis and Public Works Ministerial Decree No. 13/PRT/M/2011.

Index And Engineering Properties Of Subgrade Soils: A Study In Areka Town, Wolaita Zone, Southern Ethiopia

Civil engineering structures are designed from the knowledge of soil properties at the given site. This research work is for the Investigation of index and engineering properties of Areka town subgrade soils. To investigate these ten test pits were selected by dividing the total area of the town in to ten parts based on the expansion potential of the town and the current distribution of the gravel road according to the municipality of Areka town. The soil samples per pit up to 3m depth, were collected from open pits by direct manual excavation. During field testing, field density and natural moisture content tests were done.[15] The laboratory tests that were carried out includes natural moisture content, particle size distribution, specific gravity, Atterberg limits (LL and PL), compaction (OMC and MDD), CBR and CBR swelling potential tests were conducted. From the results that were obtained for grain size analysis, Atterberg limits and from soil classification systems (USCS and AASHTO). According to the results of this research, Natural Moisture content ranged between 8.0-12.0%, field dry density ranged between 1.66 – 1.87( g/cc) , gravel fraction between 9.18-16.19 %, sand fraction between 22.30-54.26 %, silt fraction between 15.82-47.69 %, Clay fraction between 9.0-35.5%, Specific Gravity ranges between 2.58-2.78, Plasticity Index between 8.21- 14.61%,, GI ranges from 4 to 11 and for the soil classification under A-4, A-6, A-7-5 and A-7-6 according to AASHTO M145 and inorganic silts of medium compressibility according to unified soil classification system and the OMC ranges from 10.14% to 21.37 %, MDD ranges from 1.77 g/cc to 1.98g/cc, CBR swell ranges from 1.42- 1.92% and CBR value ranges from 6.31-8.76 (%) as the test result indicate that CBR swelling potential values were below 2%, therefore they were good to use as a subgrade soil for pavement construction [6]. The CBR values for the soil samples were above 5% so they were good to use as a subgrade soil for pavement construction [11]. From all soil samples the subgrade strength class based on CBR value TP1, TP6, TP9, TP10 were S3; and the remaining were S4 [7].; thus, the subgrade soil has good bearing capacity for the pavement construction based on [4].

Strength and settlement of subgrade soil in southern part of Kangeyam block

Subgrade must typically be capable of supporting weights transmitted from the pavement or building structure. The relative compaction, optimum moisture content, and type of soil everything have an influence on bearing capacity. A good subgrade can withstand a large amount of loading without an excessive deformation. When subjected to heavy moisture or freezing temperatures, most soils experience some volume change. In case of pavement, highway pavements eventually rest on native soil, the subgrade serves as the foundation material for the pavement construction (subgrade). As a result, the features of subgrade have an impact on the performance of pavement. It is therefore critical for an engineer to comprehend the precise nature of the relationship between subgrade strength and settlement characteristics due tomoisture fluctuation. This paper represents that the soil sample taken in and around southern part of Kangeyam block (Kangeyam, Ganapathipalayam, Alangadu, Sampanthanpalayam, Sivanmalai, Periyailliyam, Padiyur, Veeranaampalayam, Vattamalai, Aratholuvu) was tested and experimented for its index and engineering properties. The index properties test includes specific gravity, sieve analysis, OMC (optimum moisture content) and MDD (maximum dry density) was conducted for classification of soil. Since the soil samples collected was predominantly identified sand of various gradation, the engineering properties test such as direct shear test was conducted to evaluate their shear strength properties. The subgrade strength of the soil samples was estimated by conducting CBR (California Bearing Ratio) test. In addition, the settlement of soil samples was evaluated as flexible pavement. The results of the tests data were entered in GIS (Geographical Information System) to describe the data as spatial representation mapping for the zone. This will ensure that the numerous subgrade qualities found throughout the zone are evaluated for safety and referred for future approaches.