Strength Of Subgrade Research Articles

Subgrade Feasibility Analysis for Tourist Access Roads in Senggani Gorge, Tulungagung Using Laboratory CBR Testing

Highways have an important role in the economic and tourism sectors, providing easy accessibility and accelerating regional growth. Senggani Gorge, a tourist attraction in Nglurup Hamlet, Sentang District, Tulungagung Regency, is the main attraction with the charm of waterfalls and natural coffee plantations in the highlands. However, accessibility constraints arise because the path to the tourist attraction is still slippery and bumpy clay. Clay soil conditions pose access difficulties, so more research is needed to understand the potential use of clay soil as a base layer of road pavement. This study focused on a research system that involved soil sampling on the access road to Senggani Gorge. Experimental methods were used to evaluate the effect of using clay subgrades on such tourist road access. The laboratory CBR test was conducted to test the strength of clay subgrade in road pavement construction, with the main aim to determine the impact of its use on tourist access to Senggani Gorge in Tulungagung. The results showed the percentage of CBR in collision variations 10, 25, and 56, as well as a comparison with research in Nglurup Hamlet which reached a CBR value of 27%. These findings are expected to provide a dimension of comparison and generalization of results, broadening understanding of the use of clay soils as road construction materials in various locations.

Unconfined compressive strength of subgrade stabilized with coconut shell ash and lime in variation to curing time

Abstract Many construction projects have encountered issues where the soil does not meet the necessary specifications for use as a subgrade layer. The high compressibility and low shear strength of these soils can lead to significant distortion when exposed to traffic loads. To address these issues, this study evaluated the impact of using natural additives namely coconut shell ash (CSA) admixed with lime. The research looked at how different types of treated soil and the quantity of chemicals used impacted the effectiveness of these additives. Variation portions of 2 %, 4 %, 6 %, 8 % and 10 % CSA with a constant 6% lime were used in the investigation. The study also examined how different variations of CSA and lime impacted the soil’s mechanical properties. Unconfined compressive strength (UCS) test was incorporated with curing times of 7, 14 and 28 days. The study's results found that using a combination of CSA and lime effectively improved the soil’s strength and durability. It conclusion, treated soil admixed with 6 % CSA and 6 % lime significantly improved the UCS as the value achieved 230.82 kN/m2 at 7 days. It's proven that untreated soil is more susceptible to water compared to treated soil.

Resilient response and strength of highly expansive clay subgrade stabilized with recycled concrete aggregate and granulated blast furnace slag

In urban areas, due to urban development and lack of space, roads may be built on the expansive clay subgrade. Expansive clay soils increase in volume when in contact with water and shrink by losing water. Recycled concrete aggregates (RCA) are one of the components of construction and demolition (C&D) wastes that can be used instead of natural resources in road construction projects. In this research, a combined method of mechanical and chemical stabilization was used to evaluate the use of RCA as a mechanical stabilizer and granulated blast furnace slag (GBS) as a chemical stabilizer to improve the strength and resilience characteristics of expansive clay subgrade. Laboratory results showed that adding RCA wastes to expansive clay subgrade reduced atterberg limits (LL, PL, and PI) and optimum water content (OWC) and increased the maximum dry density (MDD), California bearing ratio (CBR), and uniaxial compression strength (UCS). Expansive clay subgrade with 20 % RCA was treated with GBS chemical stabilizer in order to achieve a minimum 7 days target strength of 1.7 MPa for subbase application. A series of repeated load triaxial (RLT) tests were performed according to the AASHTO T307 procedure and resilient modulus (Mr) values of the stabilized clay subgrade specimen were evaluated at different curing times under cyclic loading. Also, the proposed Mechanistic-Empirical pavement design Guide (MEPDG) model was used to predict Mr values in different confining and deviator stresses which showed a good correlation with the measured Mr values. Finally, the improvement of the clay subgrade stabilized with RCA and GBS was also supported by SEM analysis. The results obtained from this research showed that the use of RCA, in addition to reducing disposed waste and environmental pollution, can improve the physical and mechanical characteristics of expansive clay Subgrade layers.

Subgrade soil stabilization using geosynthetics: A critical review

The construction of roads has been highly impacted due to weak subgrade. During the design phase of road, the index properties and various investigations required to check the strength of subgrade. In different types of soil subgrade, subjected to its weak strength, various types of stabilization have been performing throughout the world. Geosynthetic materials are now a days become a research interest for stabilization of weak soil. It acts as reenforcing agent in soil subgrade. Geotextiles, geogrids, steel fibers, etc. are some types of geosynthetics which helps to distribute the loads on pavement structure more efficiently. According to studies, it improves the soil subgrade's effective bearing capacity and serves as an alternate method of economic stability. Geotextile may also be used as reinforcement in asphalt overlays to mitigate the reflection cracking. Geotextiles also aid in enhancing the base course's flexural stiffness, which lowers the maximum vertical load on the subgrade. The stability of subgrade soil under the effect of geosynthetic materials contributes to an increase in bearing capacity.

Stabilization of Pavement Sub Grade with Stone Dust, Fly Ash and Tire Rubber to Withstand the Fatigue and Rutting

The existing practice of subgrade has been modified with the unique type of subgrade that can withstand running traffic >20msa with 90% reliability. This can be achieved by adding fly ash, stone dust and tire rubber to pavement subgrade. This modified subgrade Mix was prepared to improve the strength of subgrade. Conventional and modified subgrade pavement mixes were tested with CBR values and the resilient modulus of conventional and modified subgrade has been found as per IRC 37-2008. Plate load test has been carried out in the laboratory with the continuous loads on the subgrade and the moduli of subgrade reaction obtained finally were compared analytically using IIT Pave software. The optimal mix proportion of Modified subgrade denotes (subgrade soil with 22% Stone Dust, 4% Fly Ash and 2% Tire Rubber). The modified subgrade in flexible pavement showed an increase in bearing capacity, resilient modulus (Mr) and modulus of subgrade reaction (k) which gave fruitful results with the optimum mix proportion with stone dust, fly ash and tire rubber. The usage of these materials in the construction of pavements decreases the industrial waste, minimizes the environmental pollution, decreases the pavement thickness as well as increases the pavement life.

Strength and compaction characteristics of kaolin clay blended with industrial wastes

The long-term stability of the construction over soil depends significantly on the strength of the ground. Swelling and shrinkage characteristics of expansive fine-grained soil causes volumetric changes followed by distress and damage to the structures resting on it. One of the most popular and cost-effective methods of improving soil is adding admixtures. Utilization of industrial wastes in soil stabilization is a cost effective and environment friendly solution. In this study, two types of industrial wastes, copper slag and pond ash, are used with the aim of improving the strength and compaction characteristics of subgrade. So, the work is focused on evaluating the compaction and strength characteristics of Kaolin clay (KC) blended with Copper Slag (CS) and Pond Ash (PA). For the compaction characteristics, modified proctor compaction tests were conducted and to study the strength characteristics, Unconfined compressive strength (UCS) and split tensile strength (STS) tests were conducted. In Total, 14 different mix combinations were used in this study. From the test results, it has been observed that blending KC with PA and CS not only improved its compaction characteristics but strength too.

Laboratory Assessment of Coir Geotextile Mats Under Wheel Load Conditions for Low-Volume Roads (LVRs)

The present study brought out the effort and quantifies the use of geotextile in Low-Volume Roads over the weak subgrade. The Low-Volume Roads (LVRs) play a key role in the economic growth of rural area as well as helps in developing the country. The construction of these LVRs over the weak strength of soil subgrade is a challenging task for civil engineering to provide the safe and smooth flow of traffic, and such soil is revealed that the Black Cotton soil (BC). The weak soil subgrade consists the finer particles like clay and silt showing poor shear strength, bearing capacity, and California bearing ration values. It poses several serious problems to the LVRs. To arrest these problems many of the conventional techniques were adopted in pavement application. But these techniques are nor economical and neither eco-friendly. To reduce this problem, the cost of construction, and to provide a longer duration, geosynthetics are introduced as an alternate material in pavement application in the last few decades. In the umbrella of geosynthetics, the geotextile is gaining attention for its utilization in pavement constructions. The study found the coir composite mats performed better reinforcement and improved the strength of the pavements. This study concluded that the use of coir geotextile mats with appropriate of sub-base soil at the suitable position at H/4 with morrum soil improved the performance of the LVRs with 200mm thickness of mould over the 400 mm thickness of the mould. It is indicate a decrease in construction and maintenance costs of the LVRs.

Machine learning approach for predicting and evaluating California bearing ratio of stabilized soil containing industrial waste

The California bearing ratio (CBR) is one of the important indexes, which is used to represent the strength of subgrade or subbases of pavement. In general, the CBR can be determined through experiments both in the laboratory and field. However, the determination of the CBR is time and cost-consuming as well as low accuracy due to the disturbance of samples and limitations of preparation in the laboratory. Thus, this study estimates the CBR of stabilized soil using twelve machine learning techniques (6 single models and 6 hybrid models). The single models include artificial neural network (ANN), gradient boosting (GB), extreme gradient boosting (XGB), random forest (RF), support vector machine (SVM), and K-nearest neighbors (KNN), while the six hybrid models are a combination of these single models and random restart hill-climbing optimization (RRHC). Twelve models are constructed based on eleven input variables, including cement, Atterberg's limits, optimum moisture content (OMC), maximum dry density (MDD), and dust and ashes. To evaluate the performance of the proposed models, four popular statistical indexes namely mean absolute error (MAE), root mean square error (RMSE), mean absolute percentage error (MAPE), and determination coefficient (R2) were used. The results indicate that among twelve models, four models using GB, RRHC_XGB, RRHC_RF, and RF had a high prediction accuracy (R2 > 0.98) and outperformed than other remaining models. Among these four models, the model using RF has the highest prediction accuracy (R2 = 0.9817, RMSE = 2.3970, MAE = 1.1682, MAPE = 0.0666). According to the result of feature importance analysis using Sklearn permutation importance, SHapley Additive exPlanation (SHAP), individual conditional expectation (ICE), and partial dependence plots-2D, cement and plasticity index (PI) are two most important variables affecting the CBR prediction of stabilized soil. Where, PI was found to be a very crucial factor, which improved the prediction ability of the models compared to the results of previous studies. The results also reveal that when cement content is larger than 2%, there is an insignificant influence of the cement on the CBR of stabilized soil. The value of PI smaller than 15% has a vital impact on the CBR for any values of cement, dust, and ashes. Furthermore, the results also indicate that dust and ash content have less effect on the CBR of stabilized soil. In summary, it can be concluded that this study provides an insightful assessment of the CBR prediction of stabilized soil, and the results of this study can fill the gap in the literature and provide practical knowledge and application on the CBR of stabilized soil.

Application of automated cone penetrometer for railway investigation using correlations with DCPI and deflection modulus

Portable in-situ devices have been used for characterizing low accessible field, such as the railway subgrade. In this study, the automated cone penetrometer (ACP) was designed for the application on the railway subgrade. ACP is composed of the cone tip, driving rod, and hydraulic hammer system. The hydraulic motor lifts and drops the 294.3 N hammer from a height of 200 mm such that the potential energy of 58.9 N m impacts the driving rod. The N-value (NACP) from the ACP test was compared with the dynamic cone penetration index (DCPI) from the dynamic cone penetrometer (DCP) test. The test results show that the NACP and DCPI profiles show opposite trend owing to the inverse concept of the unit. From the correlation of DCPI and NACP, the limitation of DCPI reveals owing the minimum manually measured value of 1 mm/blow. Additionally, the evaluation of the deflection modulus (EFWD) using NACP is more efficient than that using DCPI. Based on the result of this study, we suggest that ACP can be used for strength and stiffness evaluation of railway subgrade rapidly and reliably.

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

Influence of Freeze–Thaw Cycles on Physical and Mechanical Properties of Cement-Treated Silty Sand

The problem of weak ground conditions is currently of great interest, as with the rapid development of infrastructure, researchers are trying to cope with the improvement of problematic soil properties to build structures on it. In cold regions, the problem of weak soils is further exacerbated by freeze–thaw cycling. For the improvement of soil properties, the soil stabilization method using ordinary Portland Cement (OPC) is commonly applied, but it produces a significant amount of carbon dioxide emissions. Therefore, the purpose of this research study is to present laboratory testing results for the evaluation of soil treatment using Calcium Sulfoaluminate (CSA) cement that has a lesser carbon footprint. On stabilized soil specimens cured for 3, 7, and 14 days and subjected to freeze–thaw cycles, unconfined compressive strength (UCS) and ultrasonic pulse velocity (UPV) testing were performed. Samples were prepared at optimum moisture content using different cement content, 3%, 5%, and 7%. Applying the results from the UCS test, the strength loss/gain and resilient modulus of treated soil were obtained. The test results show that the strength and pulse velocity values decreased with the increase of freeze–thaw cycles. However, improvement in soil performance can be observed with the increase in cement content. Overall, the use of CSA as a stabilizer for silty sand would be useful to achieve sufficient strength of subgrade.

Research article on Correlations of CBR-A Literature

This paper summarizes the ongoing researches about the California bearing ratio which is most use in direct method to assess the stiffness modulus and shear strength of sub grade in the design of flexible pavement. Many studies regarding CBR values of different types of soil , that have been carried out earlier were studied, it has been found that CBR value varies with different properties possessed by the soil.CBR value of soil depends on many factors like maximum dry density (MDD),optimum moisture content(OMC),liquid limit(LL), unconfined compressive strength, percent fines etc. Determination of CBR is a bit lengthy and time consuming process so a correlation can be developed between the CBR values and Index properties of soil, so that the sub grade strength can be determined.

Exploration on mechanical test method of improved loess under dry-wet cycles

The stability of loess subgrade is affected by many factors. Dry-wet cycle is a common factor that causes damage to the strength of loess subgrade. In order to study the influence of dry-wet cycle on the stability of loess subgrade, reveal the mechanism of dry-wet cycle damage to the strength of loess subgrade It is necessary to sample the loess soil samples in this area, and perform compaction test, dry-wet cycle test, unconfined compression test and scanning electron microscope test on the soil sample to analyze the influence of dry-wet cycle on the strength and microstructure of loess soil. . In this way, the potential relationship between the microstructure and the strength of the soil can be obtained. The results show that the loess drywet cycle causes the loess's tensile strength and compressive strength to decrease with the increase of the number of dry-wet cycles. The dry-wet cycle effect gradually reduces the shear structural strength of the undisturbed loess and eventually disappears. Scanning electron microscope tests found that the humidification process caused slight movement of the particles, while the drying process resulted in permanent deformation of small pores.

Experimental assessment of coir geotextile to improve the strength of weak subgrade at different load conditions

The stabilization of weak subgrade soil with natural geotextile fiber is a cost-effective to improve the stability of the low-volume roads (LVRs). The coir geotextile is naturally available eco-friendly and biodegradable material having the high strength and durability compared to the other natural material. The present study, the test were conducted to determine the effectiveness of coir fiber and coir geotextile mats under the static and dynamic loading condition by using the CBR and WTT respectively. The inclusion of the coir geotextile fiber to the BC soil subgrade improved the load bearing capacity in soaked and un-soaked condition. The study was also conducted with two types of the coir mats under the repeated loading condition with help of the fabricated mould. It has two layer flexible pavement system like subgrade and sub-base are prepared according to CBR Standard. From the results, it was concluded that the provided coir geotextile mats helps in the slow settlement, reduce the permanent deformation/rut improved the performance of the roads. The placement of coir geotextile in both the test (CBR and WTT) showed the significant improved in reinforced section improved the service life of the flexible pavement structure with lower cost of maintenance.

Prediction of CBR using dynamic cone penetrometer index

Nowadays, construction of new roads and upgradation of existing roads are booming as a part of infrastructural development in India. Subgrade strength plays an important role in the design and construction of pavement. California bearing ratio (CBR) test is used to measure the strength of subgrade and most of the highway agencies design the pavement section using CBR value of the subgrade. The conduction of CBR test consumes more effort and time as it involves soil sampling, preparation of soil specimens, soaking for 96 h and testing. Also, the laboratory assessment of CBR does not simulate the in-situ soil properties (mainly moisture and density) and the laboratory CBR sometimes may be higher than the CBR of the soil under in-situ condition as compaction is carried out in a confined rigid mould. In this study, dynamic cone penetrometer (DCP) index is used to predict the subgrade CBR values. A total of eight soil samples were collected from two different sites and the various engineering properties are determined. To know the effect of density, moisture content, fines content and CBR on the dynamic cone penetration index (DCPI), a series of laboratory compaction tests, CBR tests and DCP tests are conducted. The available correlations are verified for their predictability of CBR values and the correlations suitable for the local soils are recommended.

Strengthening Soft Clayey Subgrade Soil Layer Using Cement Kiln Dust and Palm Kernel Ash Materials

The product materials which are generated from industrial manufacturing are used to enhance the engineering and chemical properties of soil. There are three phases of soil improvement are improvement without the addition of any other material, adding certain materials, and providing reinforcement. This study used materials product from industrial and waste materials as additives to improve the physical properties and strength of clayey soil subgrade under foundation and flexible pavement structure. This study has been investigated the effect of isolated and combined Cement Kiln Dust (CKD) and Palm Kernel Ash (PKA) materials on strength of clayey soil as tested by California Bearing Ratio (CBR) test. Various percentages of CKD and PKA materials were added to clayey soil samples to determine the optimum percent of CKD and PKA. The results showed that CKD and PKA have improved soil strength at the optimum compound percent of CKD content was 8% and PKA was 2% by weight of dry soil.

Stiffness evaluation of compacted geo-materials using crosshole-type dynamic cone penetrometer (CDP), rPLT, and LFWD

Evaluation of the strength and stiffness of compacted geo-materials is required to ensure that it has sufficient bearing capacity and stiffness to the acting loads. In this study, a crosshole-type dynamic cone penetrometer (CDP) was applied to investigate the strength and stiffness characteristics of a compacted subgrade. The CDP characterizes the subgrade strength by the penetration index (CDPI) and evaluates the stiffness by the shear wave velocity (Vs) and maximum shear modulus (Gmax). CDP tests were conducted at three testing points. Repetitive plate loading tests (rPLTs) and light falling weight deflectometer (LFWD) tests were conducted as standard testing methods for the stiffness estimation of the subgrade. Experimental results show that while the rPLT and LFWD evaluate the equivalent elastic moduli (Ev1, Ev2, and Evd) within the influence zone, the CDP provides the CDPI, Vs, and Gmax along the depth. Linear relationships between the Gmax and the equivalent elastic moduli are constructed. The strain levels corresponding to Ev1, Ev2, and Evd are estimated. This study demonstrates that the CDP is an effective testing method for both strength and stiffness evaluations of the subgrade along the depth.

Efficient computational techniques for predicting the California bearing ratio of soil in soaked conditions

California bearing ratio (CBR) is one of the important parameters that is used to express the strength of the pavement subgrade of railways, roadways, and airport runways. CBR is usually determined in the laboratory in soaked conditions, which is an exhaustive and time-consuming process. Therefore, to sidestep the operation of conducting actual laboratory tests, this study presents the development of four efficient soft computing techniques, namely multivariate adaptive regression splines with piecewise linear models (MARS-L), multivariate adaptive regression splines with piecewise cubic models (MARS-C), Gaussian process regression, and genetic programming. For this purpose, a wide range of experimental results of soaked CBR was collected from an ongoing railway project of Indian Railways. Three explicit expressions are proposed to estimate the CBR of soils in soaked conditions. Separate laboratory experiments were performed to evaluate the generalization capabilities of the developed models. Furthermore, simulated datasets were used to validate the feasibility of the best-performing model. Experimental results reveal that the proposed MARS-L model attained the most accurate prediction (R2 = 0.9686 and RMSE = 0.0359 against separate laboratory experiments) in predicting the soaked CBR at all stages. Based on the accuracies attained, the proposed MARS-L model is very potential to be an alternate solution to estimate the CBR value in different phases of civil engineering projects.

Durability-Aimed Design Criteria of Cement-Stabilized Loess Subgrade for Railway

The subgrade is the foundation of railway construction, so its strength and stability are very important to ensure the safety and stability of a train. Loess is widely distributed in northwestern China, and it must be stabilized before being used in railway subgrade construction because loess is sensitive to water. Railway subgrade withstands not only the train load but also repeated attacks from the environment and climate because it has to be exposed to natural environment after construction. Therefore, the strength of cement-stabilized loess deteriorates continuously because of the above factors. Taking account of long-term stability, the influences of load on the cement-stabilized loess as well as the strength reduction laws of cement-stabilized loess under wet–dry cycling and freeze–thaw cycling were analyzed in this study. Additionally, the respective reduction coefficients were obtained. Finally, the strength design criteria of cement-stabilized loess subgrade were put forward based on railway subgrade durability by analyzing the obtained reduction coefficients and the critical dynamic strength of railway subgrade.

Testing and Evaluation on Dynamic Response of a New Modified Soil Subgrade under Freeze-Thaw Cycles

Abstract Dynamic response analysis is an effective method of evaluating the strength, deformation, and stability of subgrade under repeated vehicle traffic loads. It is usually premised on the results of a field test, which not only requires a lot of manpower and money but also can be easily affected by extraneous factors. In this study, a laboratory test was conducted in order to examine the dynamic response of a new type subgrade: silty clay (SC) modified by fly ash and crumb rubber (RFS). A novel tester was adopted in order to simulate and impulse traffic loads with different vehicle speeds/weights on subgrade materials. In addition, the dynamic stress and acceleration responses of RFS and SC were analyzed under varying speeds and axle loads under 0–5 freeze-thaw (F-T) cycles. Thereafter, scanning electron microscope tests were conducted to bring about clarity regarding the effect on the internal structural changes of two test soils in order to elaborate on the reasons for these dynamic response changes. According to the findings of these tests, the dynamic stability of SC is better than the RFS before F-T cycles. However, the RFS provides better resistance to F-T dynamic stability as the F-T cycle goes on. In particular, the RFS is more suitable for subgrade filling in seasonally frozen regions. Against this backdrop, the current article proposes a convenient method to evaluate the dynamic response of subgrade in laboratory, besides providing a reference for the dynamic characteristics of RFS.