Cement-mixed Gravel Research Articles

Field studies on low and fast compressibility of cement-mixed gravel in railway embankment construction.

The cement-mixed gravel, which is used in the construction of railway embankment, is a relatively more expensive material compared to sandy soil. Having said that, it is used where small residual settlement is required for example, abutment transition zone, due to characteristic of higher strength than sandy soil. In this paper, the time-dependent settlement were evaluated using field data measured over a long period of time at two RSR (Reinforced Subgrade for Railways) construction sites using two different backfill materials (sandy soil and cement-mixed gravel). The embankment settlement with cement-mixed gravel as a backfill material was reduced by 78% compared to that with sandy soil. Further, the period for stabilizing the embankment before installation of the railway track was significantly reduced with cement-mixed gravel as a backfill material.

Evaluation of Horizontal Subgrade Reaction Modulus for Integral Abutment Based on Changes in Buffering Zone Stiffness

The buffering zone, which can control the stiffness of the backfill material, is applied at the integral abutment (IA) to reduce the horizontal earth pressure on the abutment and decrease the residual settlement at the transition zone. Numerical analyses are performed to evaluate the horizontal subgrade reaction modulus based on the stiffness change in the buffering zone. A 1 m section from the back of the abutment is set as the buffering zone, and materials such as sandy soil, gravel, and cement-mixed gravel are applied differently. By implementing the buffering zone, the passive and active coefficients of the horizontal subgrade reaction decrease by 28% and 31% at the height of 6.8 m. respectively. Hence, the possibility of adjusting the horizontal subgrade reaction of the IA by changing the stiffness of the buffering zone is confirmed.

<b>Proposal of Constructional Countermeasures for the Widening of Embankments with a Focus on Their High Stability</b>

The improvement rate of countermeasures adopted in constructing a second track on an embankment on soft ground is determined empirically due to unknown factors such as the deformation properties of soft ground. In this study, centrifuge model tests were performed to grasp the deformation properties of soft ground for such construction cases. Based on the test result, a new countermeasure was proposed, which has high horizontal support performance and combines deep mixing wall-type ground improvements and cement-mixed gravel. The proposed method having the same improvement rate as deep mixing was confirmed as being able to reduce the deformation of the embankment and the surrounding ground.

Factors Affecting the Mechanical Properties of Cement-Mixed Gravel

A study has been conducted to investigate the mechanical properties of cement-mixed gravel using the unconfined compression test and the tensile test. Basic factors including the curing period, the water-binder ratio, the cement content, and the strain rate were evaluated. Ordinary Portland cement with fly ash was employed as the cementation agent for preparing cemented samples. The results indicate that the unconfined compressive strength, the deformation modulus, and the tensile strength increase with the increase in the curing period. The ratio of tensile strength to unconfined compressive strength has no distinct change after 7 days. An optimum water-binder ratio can be obtained. The unconfined compressive strength and deformation modulus decrease as the water-binder ratio decreases and increase from the optimum water-binder ratio. With the increasing of the cement content, the unconfined compressive strength increases distinctly, the deformation modulus increases significantly when the cement content is less than 4% and then increased slowly, and the failure strain increases to a peak value and then decreases. With the increasing of the strain rate, the unconfined compressive strength increases slightly and the deformation modulus increases slowly. The failure strain decreases with an increase in the strain rate.

A New Method to Simulate Stress–Strain Relations from Multiple-Step Loading Triaxial Compression Test Results

Abstract Multiple-step loading (ML) on a single specimen can be used to determine the peak compressive strengths at different confining pressures (σ′hS) of cement-mixed gravel (CMG) very similar to those obtained by single-step loading (SL) drained triaxial compression (TC) tests. However, only the unload/reload stress–strain relations at different σ′hS (except for the primary loading one at the first step) can be obtained from a ML test and the reloading relations become softer with an increase in the negative irreversible axial strain increment that has taken place during respective immediately preceding unloading regimes. This effect gradually decreased during reloading while it totally disappeared once large-scale yielding started. An empirical equation was developed to derive undamaged reloading stress–strain curves (URCs) by removing the damage effects from ML TC test measured reloading curves (MRCs). A new simple method was developed in the framework of proportional rule to simulate primary loading curves (PLCs) at different σ′hS from the MRCs from a given ML TC test using a correlation factor. A practical procedure for simulation of PLCs in a ML test were established and applied to generate PLCs in a ML test increasing σ′h and a ML test decreasing σ′h. The method was validated by comparing the PLCs simulated from the results of a pair of ML tests increasing and decreasing σ′h with those measured in a set of SL TC tests at different σ′hS.

Stress–strain relations of cement-mixed gravelly soil from multiple-step triaxial compression test results

The peak compressive strengths at different confining pressures of cement-mixed gravel (CMG) that are very similar to those obtained by single-step loading (SL) drained triaxial compression (TC) tests using multiple specimens can be obtained by a multiple-step loading (ML) test using a single specimen. However, only the unload/reload stress–strain relations at different confining pressures (except for the primary loading pressure at the first step) can be obtained from an ML test, and the reloading relations become softer with the increases in negative irreversible axial strain increments that have taken place during the respective immediately preceding unloading regimes. This phenomenon is formulated by a unique empirical equation for the CMG tests. Undamaged reloading stress–strain curves (URCs) were inferred by removing the damage effects from measured reloading curves (MRCs) in the ML TC test based on this correlation. A method was developed within the framework of the proportional rule to infer primary loading curves (PLCs) at different confining pressures from the URCs and the PLC at the first step obtained from a given ML TC test. A procedure was formulated to modify the PLCs obtained by this procedure based on the PLCs measured at stresses exceeding the yield stress for large-scale yielding during reloading at different confining pressures in the ML test. This method was validated by comparing the PLCs obtained from the results of a pair of ML tests, increasing and decreasing the confining pressure, with those obtained from a set of SL TC tests at different confining pressures.

Effects of Curing Period and Stress Conditions on the Strength and Deformation Characteristics of Cement-mixed Soil

ABSTRACT The effects of long-term curing on the strength and deformation characteristics of compacted cement-mixed soil were evaluated. A series of unconfined compression tests and drained triaxial compression (TC) tests were performed on moist cement-mixed sand compacted at various water contents, wi, and cured at unconfined conditions for different periods up to more than eight years. TC tests were performed on cement-mixed gravel compacted at the optimum water content. The ageing effects on the compressive strength, qmax, from the present study were compared to those with various types of cement-mixed soils and concretes from the literature. An increase in qmax of cement-mixed soil continues for a very long period, up to several years, unlike ordinary concrete. This result indicates that the compressive strength at 28 days of cement-mixed soil, usually employed as the design strength, may largely underestimate the long-term strength. The increasing rate with time of the initial stiffness at small strains becomes continuously smaller than qmax with time. A large high-stiffness stress zone develops when monotonic loading is restarted at a certain high strain rate after some long sustained loading. This stress size is much larger than the one in the case without ageing effects. By positive interactions between the ageing effect and the inviscid yielding, qmax exhibits a larger extra gain when cured longer at more anisotropic stress states.

Several Factors Affecting the Strength and Deformation Characteristics of Cement-Mixed Gravel

ABSTRACT Related to the construction of a new type bridge abutment having the backfill of cement-mixed gravel, effects of moulding water content, wi, compaction energy level, cement-to-gravel ratio by weight, c/g, and curing period on the stress-strain behaviour of compacted cement-mixed gravel and their correlations were investigated. A series of drained triaxial compression tests were performed on a well-graded gravel of crushed sandstone from a quarry mixed with ordinary Portland cement. Possible effects of inherent anisotropy produced by compaction in different directions were evaluated to a limited extent. The following results were obtained. With a fixed c/g, the maximum compressive strength is attained when compacted at wi=the optimum water content, wopt, for a given compaction energy level, while the compressive strength is not an unique function of compacted dry density of solid, ρd (or compacted void ratio, e). These trends of behaviour are analysed in terms of positive effects of higher ρd (or lower e) of cement-mixed gravel and an associated increase in the cement amount per total volume for a fixed c/g as well as effects of the amount and strength of cement paste, both being a function of moulding water content. The benefits of compaction at wi=wopt for a fixed compaction energy level in achieving higher compressive strengths increase with an increase in c/g and the curing period. The pre-peak stress-strain behaviour tends to become more linear with curing period. The effects of in-herent anisotropy are not as significant as those with air-pluviated unbound sand.

Strength and Deformation Properties of Compacted Cement-Mixed Gravel Evaluated by Triaxial Compression Tests

To achieve as possible as a high cost-effective construction of important civil engineering structures, such as bridge abutments, using cement-mixed gravel (CMG) for the backfill, a series of drained triaxial compression (TC) tests were performed on CMG specimens. Two types of well-graded gravels were used. Axial and lateral strains were measured locally on the lateral surface of solid cylindrical specimens. It was found that, for a same cement to gravel ratio by weight, the peak strength qmax tends to become the maximum when compacted at the optimum water content, w opt, for a given compaction energy level. This trend is due largely to the smallest compacted void ratio and partly due to the largest cement content per unit volume associated with the maximum dry density. The other influencing factors include an incidental optimum combination of strength and amount of cement paste that may be attained when compacted at w = wopt· The relationship between the ratio of "qmax at a certain molding water content, w" to "qmax at wopt, qmax.OMC" and the normalized deviation ratio of w from “wopt, | w- wopt | / wopt” is rather unique whether compacted at dry or wet of optimum, for different compaction energies and for the two types of gravel. It is also shown that the initial Young's modulus tends to become the maximum when compacted at wopt while the pre-peak stiffness and post-peak ductility generally increase with an increase in the molding water content. Based on the test results, it is recommended to compact a given type of cement-mixed gravel around at wopt ensuring that the compaction is not made dry of optimum for a given compaction energy.

Ageing Effects Developed During Creep And Extremely Slow Monotonic Straining Of Cement-Mixed Gravel

Ageing Effects Developed During Creep And Extremely Slow Monotonic Straining Of Cement-Mixed Gravel