Significance of spatial variability of strength properties of deep cement mixed columns on the stability of embankments

The research work presented in this thesis begins with a study on the post-yield strain-softening behaviour of isolated DCM soil specimens. The consolidation behaviour of DCM soil specimens was numerically simulated using a strain-softening incorporated constitutive model. The results indicated that the numerical model can accurately predict the performance of DCM soil beyond yielding. Then the behaviour of highway embankments improved using DCM technique and loaded in the post-yield region was simulated using 3D and 2D numerical models. The conversion into a plane-strain model based on the equivalent area approach was identified as the best approach to simplify a 3D problem when DCM columns experience post-yield softening. Next, the efficiency of different DCM column configurations on preventing post-yield softening and improving the performance of embankments constructed on soft soil deposits was investigated. DCM wall type improvement, individual DCM columns arranged in a square pattern, individual DCM columns arranged in a triangular pattern, T-shaped DCM columns and application of geosynthetic reinforcement were evaluated under this section

Strength and Equivalent Modulus of Cement Stabilized Lateritic with Partial Replacement by Fly Ash and Rice Husk Ash

The effect of industrial/agricultural waste materials including fly ash (FA) and rice husk ash (RHA) as Portland cement replacement on properties of stabilized lateritic soil as a road construction material is investigated. The compacted lateritic soil samples treated with Portland cement at 1%, 2% and 3% by weight of the dry soil and three different amounts (10%, 20% and 30%) of FA and RHA for replacing cement are prepared and the unconfined compression and cyclic loading tests are conducted on 28 days curing samples. The equivalent modulus (Eeq) defined as the average linear portion from the unloading/reloading cycles, is used to quantify the effects of stress level on the cyclic resistance of the treated lateritic. Based on the compressive strength results, both replacement materials have demonstrated potential applications in lateritic soil stabilization. Overall, the RHA shows a better efficiency than FA for replacement particularly at 2% cement content. Based on cyclic loading tests, the Eeq values increase as the stress level increases for all samples. The FA and RHA notably enhance the Eeq values of cement treated lateritic

Swell and microstructural characteristics of high-plasticity clay blended with cement

This study presents the effect of high plasticity on swell potential, swelling pressure and micro structural characteristics of kaolinite-bentonite mixed clays. Five different combining ratios of kaolinite bentonite mixture of 100:0, 90:10, 75:25, 50:50 and 25:75 in % by weight of dry kaolinite were used. All five synthesised soils were then mixed with 0%, 5% and 8% of cement by weight of dry soil, cured for 28days and subjected to Atterberg limit, one dimensional oedometer and scanning electron microscope test. The inclusions of 5% and 8% cement reduces the plasticity index of the treated soils as the percentage of bentonite increases. The effects of plasticity of treatment with 5% and 8% cement after 28 days curing period, was evaluated, and the results show that reduction in plasticity index resulted to decrease in swell potential and swelling pressure of the kaolinite-bentonite mixed clays. The results of micro-structural analysis of 5% cement treated soils show formation of flocculated fabric and cementation of soil particles, and filling with cementitious compounds of the voids of flocculated fabric in the soil. The reduction in swell can be attributed to the resulting compacted and dense mass of treated soils due to cementation of soil particles and cation exchange. The complex behaviour of swell of high plasticity kaolinite-bentonite mix has been explained using one dimensional oedometer test, by further experimental study and examination of the micro-structure of treated soils

Rheology of Cement Mixed with Hollow Microspheres

Hollow microspheres cement is lightweight cement solution that is designed to have the highest strength ratio and lowest permeability of any cement design at a given slurry density, and rapid compressive strength to reduce Wait on Cement (WOC). Hollow microspheres used to reduce hydrostatic pressure on weak formations and to cement lost circulation zones. Hollow microspheres are produced from a mixture of liquid sodium silicate glass and a foaming agent [2]. For example, carbonates, bicarbonates, sulphates, nitrates, and acids are used as foaming agent. The mass is then dried and crushed. In this study, the focuses are mainly cementing the intermediate and production casing in a single stage using low density cement that was based on hollow microspheres. The objectives of this work is to analysis low density cement in High Pressure High Temperature (HPHT) formation which also includes the lab tests such compressive strength, fluid loss and thickening time test. Hollow microspheres cement is a High Strength, Low Density (HSLD) cement system which suggested for increasing primary cementing success in steam injected, low fracture gradient areas. It is incompressible cement which provides consistent and predictable density from the top of the borehole to the bottom. The hollow microsphere cement system is HSLD acknowledged as a feasible solution because conventional cement designs lose the formation. Advantages of using hollow microspheres cement are that it gives an excellent mud displacement, enhanced mechanical properties, good strength to density ratio and long lasting zonal isolation. A programme is developed using software to test the parameters such as temperature, pressure and density of the cement. Although the microspheres operations can be very complex, hollow microspheres cement has many applications that can justify the increase complexity. Cement slurry using hollow microspheres can be applied in high permeability formations, poorly consolidated formations and HPHT formations

Use of slag (with cement) for improving the performance of expansive soil of road pavement subgrade

The study presented in this paper evaluates the suitability of using slag (with cement) as a stabilizer, for improving the performance of expansive subgrade soil in road pavement. Several laboratory tests were conducted to determine the geotechnical engineering characteristics of the expansive soil and associated mechanical engineering performance. The tests conducted include the particle size distribution, standard Proctor compaction, Atterberg’s limits, free swelling, permeability, California bearing ratio (CBR), unconfined compressive strength (UCS), and repeated load triaxial (RLT). In this study, the use of slag (with cement) as a stabilizer followed three proportion schemes, and the selection of a specific stabilizer proportion was determined based on UCS value that satisfies the required standard as a subgrade for road pavement. The results recommended a stabilizer proportion for the soil studied to be 13.5% slag + 1.5% cement at 28 days curing time. This mixture resulted in a remarkable increase in the UCS value of eight times higher than the UCS value of the non-stabilized soil. The CBR value of the mixture was four times higher than the minimum required value for design of road pavement. The study presented herein confirmed that the exploitation of the by-product material of slag can indeed be useful, both in terms of improving the performance of the subgrade soil for road pavement and sparing the environment a spread of significant potential pollutant

Mass Stabilization as a Ground Improvement Method for Soft Peaty

Construction of road embankments or other infrastructures on soft peat is a challenge. The main problems are high compressibility and rather low undrained shear strength of peat. Mass stabilization provides a solution to improve the properties of a peaty subgrade. Mass stabilization is a ground improvement method, where hardened soil mass is created by adding binder into soil and by controlled in situ mixing. Mass stabilization poses an alternative solution for conventional mass replacement or other techniques, which leave peat in place. The chapter deals with mass stabilization of soft peat soil. Specific attention is paid to design, research and construction considerations, and experience obtained during last three decades. Peat properties before and after stabilization, design methods including pre-testing, stabilization technique and machinery, quality control methods and practices, binder technology, long-term performance of mass stabilized peat, environmental effects, feasibility, applications, and limitations are all presented and discussed in this chapter. The long-term observations (during the last 25 years) have shown that the strength of stabilized peat has continued to increase in average 1.6 times from the strength of 30 days. Therefore, mass stabilization has proven to be a flexible ground improvement method for peat layers with maximum thickness of 8 m

Rheology of Cement Mixed with Hollow Microspheres

Hollow microspheres cement is lightweight cement solution that is designed to have the highest strength ratio and lowest permeability of any cement design at a given slurry density, and rapid compressive strength to reduce Wait on Cement (WOC). Hollow microspheres used to reduce hydrostatic pressure on weak formations and to cement lost circulation zones. Hollow microspheres are produced from a mixture of liquid sodium silicate glass and a foaming agent [2]. For example, carbonates, bicarbonates, sulphates, nitrates, and acids are used as foaming agent. The mass is then dried and crushed. In this study, the focuses are mainly cementing the intermediate and production casing in a single stage using low density cement that was based on hollow microspheres. The objectives of this work is to analysis low density cement in High Pressure High Temperature (HPHT) formation which also includes the lab tests such compressive strength, fluid loss and thickening time test. Hollow microspheres cement is a High Strength, Low Density (HSLD) cement system which suggested for increasing primary cementing success in steam injected, low fracture gradient areas. It is incompressible cement which provides consistent and predictable density from the top of the borehole to the bottom. The hollow microsphere cement system is HSLD acknowledged as a feasible solution because conventional cement designs lose the formation. Advantages of using hollow microspheres cement are that it gives an excellent mud displacement, enhanced mechanical properties, good strength to density ratio and long lasting zonal isolation. A programme is developed using software to test the parameters such as temperature, pressure and density of the cement. Although the microspheres operations can be very complex, hollow microspheres cement has many applications that can justify the increase complexity. Cement slurry using hollow microspheres can be applied in high permeability formations, poorly consolidated formations and HPHT formations