Performance of an earth wall stabilized with bearing reinforcements

This article presents the performance of a fully instrumented test wall reinforced with bearing reinforcement. Bearing reinforcement is an inextensible earth reinforcement. It is composed of a longitudinal member and transverse members. The longitudinal member is a deformed steel bar and the transverse members are a set of equal steel angles. The test wall was 6 m high, 9 m long at the top, 6 m wide at the top, and 12 m long, 21 m wide at the base and was constructed on a hard stratum. The facing panels were made of segmental concrete block which measured 1.50 × 1.50 × 0.14 m in dimension. From the full-scale test results, the bearing stress distribution is a trapezoid shape as generally assumed for the examination of the external stability of MSE walls. The tilt of the bearing reinforcement earth (BRE) wall indicates that the BRE wall behaves as a rigid body. The coefficients of earth pressure decrease with depth and approach the active state at deeper reinforcement level. From the variation in the stiffness factor as a function of depth and lateral earth pressure, the bearing reinforcement has a stiffness factor of K/K_a = 1.7, which is much lower than that of steel grids and metal strips. The lower tension (coefficient of lateral earth pressure) reduces the cross-sectional area of the longitudinal members and hence cost effectiveness. The maximum tension line (possible failure plane) of the BRE wall is bilinear, similarly to the coherent gravity structure hypothesis, which is commonly used for the analysis of inextensible reinforcements. Finally, the suggested method of designing the BRE wall is presented. It has been successfully used to design several BRE walls founded on the hard stratum in different areas in Thailand.     

Environmental impacts of utilizing waste steel slag aggregates as recycled road construction materials

Slag is an industrial waste generated during the steelmaking process. Electric arc furnace slag (EAFS) and ladle furnace slag (LFS) are both produced at different stages of steelmaking process, respectively, in electric arc furnaces and refining ladle furnaces. As part of this research, an extensive suite of engineering and environmental tests were undertaken on steel slag aggregates to evaluate their potential usage as road construction materials. The engineering assessment included particle size distribution, hydrometer, organic content, flakiness index, Atterberg limits, particle density, water absorption, pH, minimum and maximum dry densities with a vibrating table, modified compaction, California bearing ratio (CBR) and Los Angeles abrasion tests. In addition, a suite of environmental tests comprising total and leachable heavy metal tests were undertaken on both types of steel slag aggregates. From an environmental perspective, EAFS and LFS were found to pose no environmental risks for use as aggregates in roadwork applications. The engineering properties of LFS aggregates with its satisfactory geotechnical and environmental results, particularly its high CBR values, indicated that the material was ideal for usage as a construction material in roadwork applications such as pavement base/subbases and engineering fills. EAFS, with its comparatively lower CBR value, was found to be only suitable to use as a construction material for pavement subbases and engineering fills. The usage of steel slag aggregates in roadwork applications would bring about a practical end-of-life alternative for their sustainable reuse and possibly divert large amount of these waste materials from landfills.     

Compaction behavior of fine-grained soils,lateritic soils and crushed rocks

This paper studies compaction characteristics and California Bearing Ratio, CBR values of fine-grained soils, lateritic soils and crushed rocks. All test data were collated from the Bureau of Rural Road 6, the Department of Rural Roads, Thailand. The Ohio's and the modified Ohio's curves can predict satisfactorily the compaction curves of the fine-grained soils, and lateritic soils and crushed rocks consistent with the grade B of the American Association of State Highway and Transportation Officials (AASHTO) requirement. The CBR value of a specific soil is directly related to the relative dry unit weight (the ratio of dry unit weight to maximum dry unit weight, γ_d/γ_d,max). The field compaction result of a fine-grained soil at the optimum water content, OWC, shows that initially the dry unit weight increases rapidly with the number of roller passes and the relationship between dry unit weight and number of roller passes is represented by the logarithm function. Finally, the dry unit weight reaches a constant value, which is close to the laboratory maximum dry unit weight. Even with a large number of roller passes (compaction energy), the dry unit weight cannot be enhanced further because the soil state approaches the zero air void state. In practice, the excess roller pass is thus not economic. Based on the analysis of the test data, the field compaction procedure for road embankment and pavement constructions, which includes the material selection and the construction control, is suggested. It is useful in terms of both engineering and economic viewpoints.     

Strength development in silty clay stabilized with calcium carbide residue and fly ash

Calcium carbide residue (CCR) and fly ash (FA) are waste products from acetylene gas factories and power plants, respectively. The mixture of CCR and FA can produce a cementitious material because CCR contains a large amount of Ca(OH)₂ while FA is a pozzolanic material. Soil stabilization by CCR is classified using three zones: active, inert and deterioration. In the active zone, the natural pozzolanic material in the soil is adequate to produce a pozzolanic reaction. Hence, the input of FA into this zone does not significantly improve strength. Strength in the inert zone can be significantly increased by adding FA. FA improves the densification and pozzolanic reaction. The deterioration zone is not recommended for use in practice, even with the input of FA. The unsoundness due to free lime hinders strength development. Although the soaked and unsoaked strengths depend mainly on the CCR and FA contents, most of the ratios of soaked strength to unsoaked strength vary between 0.45 and 0.65. It is proved that a mixture of CCR and FA can be used for soil stabilization instead of ordinary Portland cement. The possible mechanism regarding the control of strength development presented in this paper can be applied to other clayey soils stabilized with different cementitious materials produced from Ca(OH)₂-rich and pozzolanic materials. This putative mechanism is also fundamental for further studies involving the development of rational dosage methodologies.     

Strength Development in Cement Admixed Bangkok Clay: Laboratory and Field Investigations

The in-situ deep mixing technique has been established as an effective means to effect columnar inclusions into soft Bangkok clay to enhance bearing capacity and reduce settlement. In this paper, an attempt is made to identify the critical factors governing the strength development in cement admixed Bangkok clay in both the laboratory and the field. It is found that clay-water/cement ratio, w_c/C is the prime parameter controlling the laboratory strength development when the liquidity index varies between 1 and 2. Based on this parameter and Abrams' law, the strength prediction equation for various curing times and combinations of clay water content and cement content is proposed and verified. This will help minimize the number of trials necessary to arrive at the quantity of cement to be admixed. Besides the w_c/C, the strength of deep mixing column is controlled by the execution and curing conditions. For low strength improvement (laboratory 28-day strength less than 1,500 kPa), the field strength of the deep mixing columns, q_uf, made up from both dry and wet mixing methods is higher than 0.6 times the laboratory strength, q_ul. The q_uf/q_ul ratios for the wet mixing columns are generally higher than those for the dry mixing columns. This higher strength ratio is due to the dissipation of the excess water in the column (consolidation) caused by the field stress. The water to cement ratio, W/C, of 1.0 is recommended for the wet mixing method of the soft Bangkok clay. A fast installation rate was shown to provide high quality for low strength columns. Suggestions are made for improving the deep mixing of soft Bangkok clay, which are very useful both from economic and engineering viewpoints.     

The potential micro-hydropower projects in Nakhon Ratchasima province,Thailand

At present, fossil fuel energy is commonly used in developing countries, including Thailand. The tendency to use fossil fuel energy is continuously increasing, and the price of fossil fuels is rising. Thus, renewable energy is of interest. Hydropower is one of the oldest renewable energy forms known and one of the best solutions for providing electricity to rural communities. The present paper aims to determine the potential micro-hydropower sites that could provide more than 50 kW but not over 10 MW in Nakhon Ratchasima Province, Thailand. Both reservoir and run-of-the-river schemes are considered for the assessment of potential micro-hydropower sites. For the reservoir scheme, the discharge in the reservoir is employed for generating micro-hydropower electricity. This installation can be carried out without major modifications to the dam. The run-of-the-river scheme diverts water flow from the river mainstream to the intake via a pressure pipe or an open canal, which is then conveyed to the turbine via a penstock to generate electricity. The results showed that there are 6 suitable projects for the reservoir scheme and 11 suitable projects for the run-of-the-river. The maximum power load was 6000 kW and 320 kW for the reservoir and the run-of-the-river schemes, respectively. Hydropower from the run-of-the-river scheme is more suitable than hydropower from the reservoir scheme because of the many mountains in this province. The designed head for the run-of-the-river scheme is thus generally higher than that for the reservoir scheme. Because stream flow during the dry season is very low, electricity can only be produced in the wet season. This research is a pilot study to determine the potential sites of micro-hydropower projects.     

Marginal lateritic soil/crushed slag blends as an engineering fill material

Lateritic soil (LS) with suitable mechanical properties is commonly used as the subbase and as engineering fill material in roads. However, LS is becoming increasingly scarce as a source for road projects. The usage of marginal LS as a pavement subbase and engineering fill material leads to some challenging issues that this research seeks to address. This paper evaluates the possibility of using crushed slag (CS), a waste by-product, as a replacement material to stabilize marginal LS for engineering fill applications. An investigation was undertaken on the physical and mechanical properties of the LS/CS blends at various CS replacement contents. The laboratory evaluation program included particle size distribution, specific gravity, water absorption, Los Angeles (LA) abrasion, Atterberg limit, California Bearing Ratio (CBR) and swelling tests. CS replacement was found to reduce the fine content and increase the abrasion resistance of the marginal LS, resulting in a reduction in liquid limit, plasticity index, LA abrasion and particle breakage. With increases in the CS replacement content, a marked improvement in the physical properties of the blends was found, including increased soaked CBR and reduced swelling. Normalized CBR_CS/CBR₀ and S_CS/S₀ and CS replacement relationships were developed in this research. CBR_CS and S_CS are the CBR and swelling values at various CS replacement contents, respectively and CBR₀ and S₀ are the CBR₀ and swelling values at a 0% CS replacement content, respectively. The results are expected to be of interest to both geotechnical and pavement practitioners. The physical and mechanical properties of the blends with a minimum of 10% CS replacement content were found to meet the national local road authority requirements for engineering fill material.