Subgrade Strength Research Articles

Strength Evaluation of Soil Subgrade Using In-situ Tests

Flexible pavements in many countries including India are designed on the basis of laboratory California Bearing Ratio (CBR). During construction to ascertain that the design stipulations are met with, one has to check in-situ CBR. For testing in-situ CBR, undisturbed samples are taken and are then tested in the laboratory. Collection of undisturbed sample from soil subgrade that is essentially non-plastic in nature, is near to impossible and further more determination of CBR is a time consuming and sensitive to many parameters, such as relative density, particle size, texture, moisture content and confinement pressure etc.. Thus, during execution stage, it becomes very difficult to ascertain whether the design stipulation has been achieved or not. In this study an effort has been made to evaluate the subgrade strength by conducting in-situ tests using Dynamic Cone Penetrometer (DCP) and Light Weight Deflectometer (LWD) on various locations shown in (Figure 1), of an under-construction road, that is on the service bank of Sirhind Canal, in Punjab, India. The road is tested at fifteen different locations; representative samples of soil were collected from all the fifteen locations and tested in the laboratory for Grain Size Analysis, Atterberg Limits (Liquid Limit, Plastic Limit), Maximum Dry Density (MDD), Optimum Moisture Content, and Laboratory CBR at 97 percent of modified MDD, to find correlations.

Geosynthetic subgrade stabilization – Field testing and design method calibration

Abstract Geogrids and geotextiles are used routinely to stabilize weak subgrade soils during road construction. Typical subgrade stabilization applications are temporary haul roads or unpaved low-volume roads, but can also include paved roads built on poorer foundation materials. Full-scale test sections were constructed, trafficked and monitored to compare the relative operational performance of geosynthetics used as subgrade stabilization, as well as determine which material properties were most related to performance. Unpaved test sections were constructed using twelve geosynthetics consisting of a variety of geogrids and geotextiles. Multiple control test sections were also built to evaluate the effect that subgrade strength, base course thickness, and/or presence of the geosynthetic had on performance. Even though the geotextile materials used during this study showed good performance as subgrade stabilization, material properties associated with their performance was difficult to establish due to the limited number of test sections and lack of relevant tests to properly characterize these types of materials for this application. Using longitudinal rut as the primary indicator of performance, it was determined through a linear regression analysis that the stiffness of the geogrid junctions in the cross-machine direction correlated best with performance in this application and under these conditions. Using this knowledge, the design equation associated with the Giroud–Han method was calibrated to make geogrid junction stiffness in the cross-machine direction the primary property of the geosynthetic, thereby replacing geogrid aperture stability modulus. The calibration and verification of this method is described herein.

Factors Influencing Deformations of Geocell-Reinforced Recycled Asphalt Pavement Bases under Cyclic Loading

AbstractA significant amount of recycled asphalt pavement (RAP) material is produced from flexible pavement rehabilitation projects. RAP can be used as a base course material for sustainable pavement construction. Performance of a pavement largely depends on the strength of its foundation, which consists of the subgrade and base course layers. Geocell was used in this study to increase the strength of RAP bases. Nine large-scale laboratory cyclic plate loading tests were conducted on unreinforced and geocell-reinforced RAP bases with three different thicknesses (150, 230, and 300 mm) over weak and moderate subgrades to investigate the influence of geocell confinement, base course thickness, base course strength, and subgrade strength on permanent and resilient deformations of RAP bases. The subgrade was prepared by mixing Kansas River sand with kaolin and compacted at weak [target California bearing ratio (CBR)=2%] and moderate (target CBR=5%) strengths. The test results showed that geocell confinement im...

Comparative studies of lightweight deflectometer and Benkelman beam deflectometer in low volume roads

Abstract A comparative subgrade moduli study is carried out by static and dynamic deflection methods using lightweight deflectometer and conventional Benkelman beam deflectometer on low volume road. Field and laboratory tests are performed at 40 test locations on in-service road of 2 km stretch that contains three common types of cohesive soils (CH, CI, and CL). Pavement static and dynamic responses are estimated to ascertain static, backcalculated, and composite moduli of subgrade. The backcalculated and composite moduli of subgrade is validated at given moisture content using repeated triaxial test. Static moduli values are on lower side as compared with dynamic moduli values whereas the composite, and laboratory moduli of subgrade are approximately consistent with 2% to 7% variation, respectively. Correlation analyses between static and dynamic moduli of different types of subgrade soils depict good correlation of determination (R2) varies between 0.75 and 0.91. Subsequently, validation of static moduli with California bearing ratio (CBR) related subgrade moduli shows moderate correlation of 0.67 to 0.74 whereas dynamic moduli shows good correlation of 0.74 to 0.93 for different types of soils, respectively. Therefore, the comparative analysis shows that lightweight deflectometer provides reliable subgrade moduli values, and it can be used as a quick subgrade strength evaluating tool for low volume roads.

Impact of Rice Husk Ash on Soil Stability (Including Micro Level Investigation)

Objectives: In this study, the change in behavior of subgrade soil after apply rice husk ash which is an environmental pollutant was observed. Methods/Statistical Analysis: Some sample of subgrade soil was taken and mixed with various amount of rice husk ash (1%, 2%, 4%, 6%, 8% and 10%). Did some experimental tests like OMC, MDD, CBR to determine the changes on subgrade strength properties with RHA content also to study its impact in better way, did SEM and EDS tests of untreated soil as well as treated soil. Findings: From the experimental works it is observed that addition of rice husk ash shows increase in OMC value whereas decrease in MDD value and Upto 6% rice husk content CBR is increasing after that it start decreasing. In other hand from SEM and EDS test decrease in void ration and breaking of montmorillonite has observed. Applications/Improvements: Since mixing of rice husk ash with soil shows improvement in CBR value and reduces the void so it can be use for sub-base construction as it will reduce the thickness and cost of pavement.

Designing low-volume roads using the dynamic cone penetrometer

The paper describes an environmentally optimised approach to the design of low-volume roads (LVRs) in which the in situ strengths of the subgrade and pavement layers at the anticipated in-service moisture condition are used for design rather than soaked values. It describes how the assumptions and simplifications inherent in the more traditional California bearing ratio (CBR)-based methods of design tend to produce less-than-optimum solutions compared with the dynamic cone penetrometer (DCP) method. DCP measurements are much more reliable than CBR measurements and are also quick to perform; hence, a relatively large number of measurements of subgrade strengths (for new roads) and pavement layer strengths and thicknesses (for upgrading projects) can be obtained, thereby reducing risks of inadequate data for design purposes. Research has shown how material specifications for LVRs can be relaxed and the paper shows how this aspect is integrated into DCP design methods. The paper reviews the alternative methods of DCP design, summarises the advantages of these methods and recommends some improvements.

On-Field Assessment of Sub-Grade Uniformity Using DCP

Abstract One of the key parameters for the performance of a pavement is uniformity of its sub-grade. In situ assessment for the uniformity of the sub-grade is commonly carried out by measuring the density of soil mass. Measurement of the density is done by cutting a core from the soil mass. According to ASTM D6951-09 (2009) the soil density may be estimated if the soil type and moisture content are known from the dynamic cone penetrometer (DCP) penetration rate. The DCP test is a soil-penetration test that is used for the measurement of sub-grade strength. In this paper, empirical correlations were developed for estimation of in situ density of the sub-grade material from DCP penetration rate and moisture content. These relations were developed using multi-linear regression analysis for different soils, namely Black Cotton Soil, Yellow Soil, and Moorum (lateritic soil). It also developed a generalized correlation for density using a power function model.

SENSITIVITY ANALYSIS ON FLEXIBLE ROAD PAVEMENT LIFE CYCLE COST MODEL

Sensitivity analysis is a tool used in the assessment of a model’s performance. This study examined the application of sensitivity analysis on a developed flexible pavement life cycle cost model using varying discount rate. The study area is Effurun, Uvwie Local Government Area of Delta State of Nigeria. In order to determine one of the vital geotechnical engineering properties (i.e. California Bearing Ratio) of the soil samples required for this study, soil samples were taken from the subgrade of the study area using the disturbed sampling method. The laboratory test was carried out at geotechnical laboratory in Warri and in accordance with AASTHO 1993 to determine the subgrade strength. Existing data such as maintenance records, vehicular traffic counts, material costs, discount rate and pavement design data were sourced from the Delta State Ministry of Works, Effurun. These acquired data and CBR results of 5% and 6% were used for the design of three competing flexible pavement systems and Bill of Engineering Measurements obtained. These were used for the evaluation of the Life-Cycle Costs (LCCs) using present worth cost (PWC) method; varying discount rates in MS Excel spread sheets for a design life of 20 years. Regression modeling of the three scenarios was done with sensitivity analysis carried out on the developed model. The project age was used as its independent variable, while discount rate is a secondary independent variable varied by ±4%, ±8% and ±12% of the initial discount rate of 5.4% applied with the accuracy of 95%. The coefficient of determination (R 2 ) for the Hot Rolled Asphalt (HRA), Interlocking Concrete Pavement Block (ICPB) and Do-nothing models are 0.97, 0.95 and 0.99 respectively indicating a robustness of the developed models. The graphs produced from the sensitivity analysis indicate a decrease in life cycle cost with increasing interest rate for the alternatives. These results are vital for the economic evaluation of flexible pavement and transportation systems. http://dx.doi.org/10.4314/njt.v35i2.7

Experimental Investigation on the Effect of HDPE Fibres on the Subgrade Strength of Black Cotton Soil

Experimental Investigation on the Effect of HDPE Fibres on the Subgrade Strength of Black Cotton Soil

ROAD SUBGRADE STRENGTH UNDER VARIOUS FLOODING EVENT

Flooding and water inundation could result in great damage to road pavements. In principle, the design of pavement structure is based on the strength of compacted soil known as subgrade or road foundation. Therefore, subgrade is the major significant part of road structural systems. When roads are inundated for a long time or repeatedly, the materials in each layer of road structure become saturated, and then the original condition of subgrade soils will be compromised. This study investigated the effect on sub-grade strength and properties due to road submergence period and repeated submergence of road structural systems. Two types of soil that are normally used as the embankment soils in road construction, which can be categorized as cohesive and cohesionless materials were used in this study. California Bearing Ratio (CBR) test and Oedometer consolidation test were carried out on the various categories of inundation and loading conditions including repeated inundation. The findings indicated that the strength of subgrade materials were affected differently depending of inundation period and number of repeated inundation.

Behavior of Geogrid Reinforced Foundation Systems Supported on Clay Subgrades of Different Strengths

This paper presents an experimental study investigating the behaviour of geogrid reinforced sand-clay foundation systems with clay subgrades of different strengths. Model tests were carried out on a circular footing of 150 mm diameter (D) resting on 1 × 1 × 1 m foundation bed having clay subgrades of different undrained shear strengths (c u), ranging from 7 to 60 kPa. Different series of laboratory model tests were performed on homogeneous and layered foundation systems. The layered systems were comprised of dense sand of varying layer thicknesses (H = 0.63–2.19D) overlying the clay subgrades. Pressure-settlement responses obtained indicated that the foundation performances were largely influenced by footing settlement (s/D %), layer thickness (H), and subgrade strengths (c u). The results indicated that the planar geogrid reinforcement, placed at the sand-clay interface, can substantially improve the performance of the foundation beds depending on layer thickness and subgrade strength. A maximum of about 5.6-fold improvement in bearing capacity was observed in the study, for very soft clay subgrade of 7 kPa.

Effect of Electrolyte Lignin and Fly Ash in Stabilizing Black Cotton Soil

Subgrade is one of the important layers of any pavement. It must be able to support loads transmitted from pavement structure without excessive deformation under adverse climatic and traffic conditions. In this investigation, laboratory studies were carried out to evaluate the influence of a commercial electrolyte lignin stabilizer (ELS), fly ash (FA) and a combination of both, on black cotton (BC) soil procured from North Karnataka region in India. Basic geotechnical and engineering properties like unconfined compressive strength (UCS), California bearing ratio (CBR), etc. were determined for both untreated and treated soil. Dynamic repeated load test was conducted to examine the fatigue behaviour of the soil. Durability of the soil was checked by wet-dry (WD) and freeze-thaw (FT) cycle tests, and swelling properties by free swell index test. From the studies, it was observed that consistency limits, dry density, UCS and CBR values were improved for treated soil, with curing periods of 1, 7 and 28 days. Weight loss in FT test was less than 14 % for 12 cycles, which ensures that the stabilized soil has become durable. But none of the samples were observed to be withstanding above five cycles in wet-dry test. Soil stabilized with ELS and FA showed better results compared to soil with only ELS. Swelling was reduced to a great extent with 28 days curing period for the former one. From the experimental results, it can be concluded that this chemical can be used as a stabilizer for existing BC soil in site to enhance its subgrade strength.

Study on Flexible Pavement Failures in Soft Soil Tropical Regions

Road network system experienced rapid upgrowth since ages ago and it started developing in Malaysia during the colonization of British due to its significant impacts in transportation field. Flexible pavement, the major road network in Malaysia, has been deteriorating by various types of distresses which cause descending serviceability of the pavement structure. This paper discusses the pavement condition assessment carried out in Sarawak and Sabah, Malaysia to have design solutions for flexible pavement failures. Field tests were conducted to examine the subgrade strength of existing roads in Sarawak at various failure locations, to assess the impact of subgrade strength on pavement failures. Research outcomes from field condition assessment and subgrade testing showed that the critical causes of pavement failures are inadequate design and maintenance of drainage system and shoulder cross fall, along with inadequate pavement thickness provided by may be assuming the conservative value of soil strength at optimum moisture content, whereas the exiting and expected subgrade strengths at equilibrium moisture content are far below. Our further research shows that stabilized existing recycled asphalt and base materials to use as a sub-base along with bitumen stabilized open graded base in the pavement composition may be a viable solution for pavement failures.

Analysis of structural performance and sustainability of airport concrete pavements incorporating blast furnace slag

Abstract In this study, the effects of various blast furnace slag (BFS) contents on the performance of cement pastes and pavement were investigated at two levels, the micro and the macro. At the micro level, the strength and chemical properties of cement pastes containing various percentages of BFS and subjected to different water curing periods were evaluated. At the macro level, the structural and sustainability performance of airport concrete pavements were studied. In this regard, several structural design charts were developed to determine the thickness of the concrete slab required to withstand traffic loadings for various versions of aircraft design and subgrade strengths. The sustainability of the concrete pavements was assessed in terms of fuel requirements and greenhouse gas (GHG) emissions. In addition, a simple graphical method was proposed for comparing structural and environmental performance of concrete pavements with respect to BFS content, subgrade strength, different versions of the aircraft design, fuel requirements and GHG emissions for pavement construction. Based on the results obtained using the proposed method and the structural and sustainability analyses, scenarios are suggested for choosing preliminary BFS content.

Fatigue and rutting strain analysis on lime stabilized subgrades to develop a pavement design chart

Roadbeds made up of weak coastal subgrade soil, subjected to changes in moisture contents due to seasonal wetting and drying or due to any other reason, undergo volumetric changes leading to pavement deterioration. Two important factors that govern pavement design are soil subgrade strength and traffic loading. There has been a move towards the use of the mechanistic approach in pavement design in many developed countries. The scope of this study is to increase the subgrade strength with the addition of lime to fulfill design specification, this leads to economy in the structural thicknesses of the pavement on subgrade strengths of 2%, 3% and 4% CBR values with traffic intensities of 1, 5, 10, 20 and 30million standard axles. In this study, a multilayer elastic analysis using KENLAYER computer program was carried out to determine the tensile strain at the bottom of bituminous, lime stabilized layers and compressive strain on lime stabilized subgrades. Also, the design catalogues have been developed for the above subgrade strengths.

English

s: Generally the soil quality improvements through stabilization include better soil gradation, reduction of plasticity index or swelling potential, and increases in durability and in strength. The tensile strength and stiffness of a soil layer can be improved through the use of additives and thereby permit a reduction in the thickness of the stabilized layer and overlying layers within the pavement system. According to Sherwood (1995) and Little (1999), lime stabilization can be used to either modify or stabilize clays. The strength of lime mixture depends to a great extent on the quantity of lime added above lime fixation point. (i.e. it changes the Plasticity Index of soil). In this experiment Indian A-7a type black cotton sol is used. In this paper soil subgrade characteristics are determined by using 0%, 2%, 4%,6%, 8%, 10%, 12%, lime ( by weight of soil) stabilization techniques & a graphical representation is made % of stabilization Vs optimum moisture content & maximum dry density values. But some time in the field OMC of soil, especially black cotton soil changes very rapidly in this case the advantage of this graph is one can easily get a rough idea about changes soil characteristics due to applications of lime stabilization, when the soil becomes highly plastic to non plastic. Finally a semi empirical formula is made to get an idea about OMC & Maximum Dry Density values of A-7a type Indian black cotton soil (As per Highway Research Board of India) due to application of lime stabilization within range of 0 to 12% of lime by weight of soil. This paper also help full to determine how the subgrade strength varies with lime stabilization. KYE WORDS: Sub-grade Soil Stabilization, Lime Stabilization, Changes in Soil Characteristics due to Lime Stabilization, Establishment of Semi Empirical Formula, Limitations

Experimental Research on Influencing Factors of Remolded Fine Soil Strength

In order to research on the influence law of fine soil strength affected by plasticity index, moisture content,compactness, the unconfined compressive resilient modulus of the soil is as the evaluation index of remolded soil strength. Three fine soils with different plasticity index are selected from field. Test scheme was obtained with the method of orthogonal design. By the static molding method,the soil sample was compacted from the prescriptive moisture content and compactness. The unconfined compressive resilient modulus of the soil sample were tested respectively. The experiments show that sort of influencing factors is plasticity index, moisture content, compactness. With the increase of plasticity index, remolded soil strength increases and increasing extent is significantly large. With the increase of moisture content, remolded soil strength decreases and increasing extent is larger. With the increase of compactness, soil subgrade strength increases, but increasing extent is significantly small.The exponential function is adopted for multiple nonlinear fitting. The relationship between the unconfined compressive resilient modulus and plasticity index, moisture content, compactness is obtained and shows a good correlation.

The Applied Research of Cement-Soil in the Road and Bridge Design

Based on the actual design and construction experience, the application of cement-soil in road and bridge foundation is designed. First of all, the basic parameters of foundation soil are determined through coring; then, the mix proportion of cement-soil is designed; Finally, the structural design is conducted on cement-soil according to different usages. The results show that using the cement-soil to improve the road and bridge subgrade, it can not only effectively improve the subgrade strength and durability, but also be convenient for construction, save a lot of building materials and reduce the project cost, which has a great guiding significance on the design and construction of the bridge.

Different Gradations Cement Improved Phyllite Test Analysis

The paper analyzed the phyllite properties in the highway from Shiyan-Tianshui the eastern An-kang 25th section through the related indoor and outdoor testing. As the on-site filler CBR value didnt meet highway subgrade filling on the filler mechanical properties, and it should be improved with cement. The engineering and compaction properties were analyzed under different cement doses and gradation combinations, whose result was shown that selecting the improved phyllite gradation composition of 5% cement content and 60% stone content was the optimal. In that it could not only meet subgrade strength design requirement and the on-site application, but also be the most economical and reasonable.

Sustainable pavement construction by the use of recycled glass

The construction of pavements is usually based on different national and international standards. As a result the pavement design all over the world normally consists of different granular base layers and different asphalt or concrete layers. The overall thickness of the pavement construction depends on many different parameters e.g. traffic loads, number of passes, and subgrade strength. Especially at the construction of pavements across soft soils large settlements occur which often results in damages to the pavement layers. Besides the improvement of the soft subgrade material by soil improvement methods, cut and cover construction or hydraulically bonded base layers the vertical loads on the soft subgrade can be reduced by the use of light infill materials. One of those materials can be called as glass foam gravel and is produced from recycled glass. As another alternative of the asphalt and concrete layers glass asphalt can be used. The main advantage of this product compared to asphalt and concrete is the permeability without any loss of bearing capacity. The use of both sustainable materials for the construction of pavements is described in the paper.