Subgrade Course Research Articles

Influence of calcium carbonate sludge on cement-stabilized subgrade quality as investigated by means of electrical resistivity measurements

Calcium carbonate [CaCO3] is a key raw material used in the clarification of sugarcane juice for syrup production. The CaCO3 sludge produced during the clarification process is waste that needs to be stored, creating a geoenvironmental problem. On the other hand, it has been found that cement-stabilized subgrade is a suitable alternative for improving the quality of a subgrade course. This study aimed to investigate the influence of calcium carbonate sludge on the quality of the subgrade. The subgrade was composed of a mixture of 10% to 30% CaCO3 sludge, 1% to 3% of original Portland cement (OPC), and 67% to 100% of unqualified crushed rocks by weight. The modified Proctor method was used to compact soil–cement admixture samples, which were then tested for mechanical properties and electrical resistivity. The Wenner electrode array was used to measure electrical resistivity and compare it to the unconfined compressive strength of 16 different types of soil–cement mixtures after 7 days. The results of experiments show that the basic properties of CaCO3 sludge, when mixed with OPC and packed down, can make the best soil–cement mixture. As a result of this study, electrical resistivity was found to be in good correlation with unconfined compressive strength, thus opening up a time-saving and cost-effective way to check the quality of a soil–cement mixture.

Assessing the key factors affecting the substructure of ballast-less railway track under moving load using a double-beam model and random forest method

In this paper, an approach is presented for analyzing the substructure of a slab track. The approach involves deriving a semi-analytical solution of the double-beam model, which incorporates a visco-elastic connection between two concrete beams and a spring-damping foundation. The model is then subjected to a concentrated moving load with a constant velocity. To more effectively assess the impact of various parameters, a random forest algorithm is utilized. The parameters considered include the spring-dashpot properties of the connection layer and the bedding layer, the thickness of the upper and lower beams, and the velocity of the moving load. The results of the random forest regression show that the stiffness of the intermediate and foundation layers have the greatest influence on the vertical deflection of the upper beam. However, the effect of stiffness of intermediate layer on the deflection and bending moment of the lower beam is found to be marginal. Moreover, for high-speed trains, the velocity of the concentrated moving load substantially changes the extreme responses attributed to the vertical deflection and bending moment. In this context, the damping properties of the interconnection layer and the subgrade course have a greater impact on the responses of the upper and lower beams.

Investigational studies on beneficial effect of geosynthetic reinforcement at an interface of two layered system

The phenomenon of inclusion of geosynthetic reinforcement on California bearing ratio values of two-layered systems along with various[H/4,2H/4,3H/4,5H/4,H/4&2H/4,H/4&3H/4,2H/4&5H/4] thickness configuration and different geosynthetic(geogrid&geotextile)was studied in the laboratory. The thickness of expansive clayey subgrade pavement over a two-layer system of various thickness configuration was computation for unreinforced and reinforced soil layer system. In this investigation thickness configuration of expansive clay soil has been observed. Expansive soils originate in several components of the planet such kind of soil usually comprises of active clay minerals. Geotechnical engineers face several issues while planning groundwork owing to clayey soil due to poor bearing capacity and excessive settlement. Expansive soils are sometimes wet when they are in saturation and these soils rephrase their rigid as they become dry. Expansive clayey are accompanied by less compressive strength and more excessive settlement. This decrease of strength due to moisture results in severe damages to building foundations and roads other vital structures. The utility and efficacy of geosynthetics as a replacement for the sub-grade course for pavements, as a cost-effective approach. Various experiments were conducted on expansive soil with an increase of strength geosynthetics at diverse heights. The foremost aim of this research is to investigate the utilization of Geosynthetics in soil reinforcement applications and to raise the effects of geosynthetic on the strength property of unsaturated soil by carried out the compressive test on the soil samples. The outcomes attained are compared for two treated soil and untreated soil. Without reinforcement the CBR value of clay soil was 2.90. The CBR value is tested by palcing geogrid and geotextile at various heights and it was identified that one layer geogrid palced at H/4 and two layer geotextle was palced at H/4 &2H/4 the distance from the top the CBR test was shows greater values of 2.38 & 2.03 times more than the soil alone.

Validity of sand dunes sediments as a fine aggregates for roads works: a case study on sand dunes sediments, Al-Nasiriya city, southern Iraq

In light of the development and urban growth of the city of Al-Nasiriya, the road construction sector consumes the largest amount of aggregates. The research aims to study suitability of the sediments of the sand dunes extending on one side of the international road between Nasiriya – Baghdad near the check point of Fadak as fine aggregate used for the purposes of roads construction. The results of the geotechnical evaluation of physical properties showed that the grain size analysis of the fine aggregate did not meet the requirements of the Iraqi specification and according to these results, the aggregate needs to modify. Based on liquid limits and plasticity indices and according to Iraqi specification the deposits are suitable for using as sub-grade course materials and to construct the shoulders of the road but not suitable for using as sub-base course materials. While the results of chemical tests indicate that incompatibility of the rates of organic matters and calcium carbonates with Iraqi specification. On the other hand, the chemical analysis of the sediments showed that the rates of the chlorides, sulfates, gypsum, total soluble salts and pH they were within acceptable limits of standard specifications. The mineral components of the soils were characterized by clay minerals (kaolinite and montmorillonite) and non-clay minerals (quartz, feldspar, and calcite).

Geotechnical Properties of Rubber Reinforced Cemented Clayey Soil

This paper focuses on the effect two forms of waste rubber tyres of granulate (Rg) and fibre (Rf) categories on the compaction–strength–consolidation–swell–durability behaviour of uncemented/cemented clayey soil. The effect of incorporation of five proportions 0%, 2.5%, 5%, 7.5% and 10% Rg/Rf (by weight of soil) and three proportions 0%, 3% and 6% cement (by weight of soil) was assessed. Reduction in maximum dry unit weight (γmax) and optimum water content (ωopt) of clayey soil and cemented clayey soil was observed with the incorporation of ruuber granulates (Rg) and rubber fibres (Rf). Both unconfined compressive strength (UCS) and split tensile strength (STS) of the clayey soil were primarily controlled by the amount of cement and waste rubber tyres and it was found to be decreased with the enhancement in rubber content. But addition of Rg and Rf was found to improve the ductility and strain hardening behaviour of cemented clayey soil, prosperously under unconfined compression. Inclusion Rg was found to be ineffective to overshadow the brittleness of the cemented clayey soil subjected to tensile loads. The inclusion of higher rubber content had lowered the strength of cemented significantly. Decline in the California bearing ratio (CBR) value, swelling pressure (σs) and increment in the compression index (Cc) and weight loss during wet/dry cycles were observed with the incorporation of Rg and Rf in cemented clayey soil. The results of all performed tests were cross checked and compared with various Indian standards to reach at the optimum dose of Rg and Rf that can be added to cemented clayey soil for its possible applications in back filling, construction of embankment (for rural roads), sub-grade course, sub-base course and slide slope of canal. The form of waste rubber tyre i.e. Rg and Rf had significant effect on the geotechnical characteristics of cemented clayey soil. Overall, Rf had outperformed the Rg, considering all evaluated geotechnical properties. Maximum dose of Rg and Rf to be added in cemented clayey soil should not be more than 5% and 7.5%, respectively.

Failure modes and mechanisms of pavements in saline foundations

Saline soil causes problems for the construction of airfield pavements and results in some pavement failure modes that are different from or more serious than failure modes in non-saline soil. Through an investigation of several typical airports in China, the failure modes of airfield pavements were determined in this study as mainly blow-ups, faulting, slab cracking and black spots. These failures are mainly attributed to the subgrade course, cement-stabilising aggregate base course (CSABC) and concrete surface course subjected to different levels of sulfate and chloride attack. Salt-heaving experiments were conducted for the subgrade and base courses, while salt corrosion experiments were performed for the surface course. The results indicate that the salt-heaving pressure of soils not only increases with an increase in dry density of the soil and the content of sodium sulfate, but also varies with water content and reaches a maximum value at the optimum soil moisture. The compressive strength of the CSABC was found to increase first and then decrease as the contents of sulfate and chloride salt reached threshold contents of 0·3% and 0·2%, respectively. In addition, the impacts of sulfates on the flexural strength, dynamic modulus of elasticity and mass loss of concrete were found to be proportional to sulfate content.

Application of lignin-based by-product stabilized silty soil in highway subgrade: A field investigation

Lignin is a by-product of paper and timber industry, and it has not been fully utilized in both developed and developing countries. Improper disposal or storage of lignin is not only a waste of natural resources, but also posing significant risk to public health and the environment. Sustainable reuse options for lignin in civil engineering infrastructures, such as road embankments and dam foundations, have been recently evaluated by laboratory testing. However, up to now studies on the actual filed performance of lignin in stabilizing silty soils in highway subgrade have been noticed to be quite limited. With this in view, a field trial was carried out to verify the viability of using lignin stabilized silty soil as a highway subgrade course material. Traditional soil stabilizer, quicklime, was selected as a control chemical mixture in the field trial for comparison purposes. The construction procedures of the subgrade silty soil stabilized by lignin and quicklime in field Sections were presented. A series of field tests, including California Bearing Ratio (CBR) test, resilient modulus (Ep) test, Benkelman beam deflection test, and dynamic cone penetrometer (DCP) test were carried out after the subgrade construction to investigate the effects of the curing time and additive content on the mechanical properties and bearing capacity of the stabilized silt. In addition, moisture content and compaction degree tests were conducted to evaluate the quality of the compacted subgrade soils. The test results indicate that at the bottom zone of the filled soil layers with 96% degree of compaction, the 12% lignin stabilized silt exhibits superior mechanical performances (i.e., higher value of CBR and Ep, and lower values of resilient deflection (Hr) and DCP Index) than the 8% quicklime stabilized silt after 15 days of curing. Under the same additive content (i.e., 8%), the bearing capacity of lignin stabilized silt is slightly lower relative to the quicklime stabilized one. The field trial results reveal that as a stabilizer of the subgrade soil, lignin has negligible environmental influences and induces low construction costs. The use of lignin as a stabilization chemical mixture for silty soil may be one of the viable answers to the reuse of biobased organic by-product in civil engineering. The outcome of this study is of great significance for the development of nontraditional, cost-effective, and environmentally friendly soil stabilizer in solidification/stabilization technology.

Field evaluation of soft highway subgrade soil stabilized with calcium carbide residue

Calcium carbide residue (CCR) is a by-product of acetylene gas production. Stockpiles of CCR continue to accumulate worldwide, in both developed and developing countries. Sustainable reuse options for CCR in civil infrastructures, such as road embankments, have been recently evaluated in the laboratory. However, to date there are limited studies on the actual field performance of CCR in stabilizing clayey soils in highway subgrades. In this study, a field trial was conducted to ascertain the viability of using CCR stabilized clayey soil as a highway subgrade course material. Quicklime was selected as a control binder in the field trial for comparison purposes. The construction procedures of the CCR and quicklime stabilizations in two field sections are presented. A series of field tests, including California Bearing Ratio (CBR) test, plate loading test, Benkelman beam deflection test, and dynamic cone penetrometer (DCP) test were undertaken after the embankment construction. The results indicated that in the top zone of the filled soil layers with 94% degree of compaction, the CCR stabilized subgrade soil exhibited higher values of CBR and resilient modulus, and lower values of resilient deflection and DCP Index relative to the quicklime stabilized soil. The field trial results indicated that CCR had negligible environmental effects and furthermore resulted in low construction costs. Based on the field test results, CCR was found to be a viable alternative binder for stabilizing soft subgrade soils. The outcomes of this research are significant from engineering, economic and environmental perspectives.