Increase In Unconfined Compressive Strength Research Articles

Effect of fiber-reinforcement on the strength of cemented soils

This study aims to verify the differences in the strength of an artificially cemented sandy soil with and without fiber reinforcement. The controlling parameters evaluated were the amount of cement, porosity, moisture content, and voids/cement ratio. A series of unconfined compression tests and suction measures were carried out. The results show that fiber insertion in the cemented soil, for the whole range of cement studied, causes an increase in unconfined compression strength. The UCS increased linearly with the amount of cement and reduced with the increase in porosity ( η) for both the fiber-reinforced and unreinforced specimens. A power function fits well as the relation between unconfined compressive strength (UCS) and porosity (η). Finally, it was shown that the voids/cement ratio is a good parameter in the evaluation of the unconfined compressive strength of the fiber-reinforced and unreinforced cemented soil studied.

The influence of freeze–thaw cycles on the unconfined compressive strength of fiber-reinforced clay

Freeze–thaw cycling is a weathering process that frequently occurs in cold climates. In the freeze state, thermodynamic conditions at temperatures just below 0 °C result in the translocation of water and ice. Consequently, the engineering properties of soils such as permeability, water content, stress–strain behavior, failure strength, elastic modulus , cohesion, and friction angle may be changed. Former studies have been focused on changes in physical and mechanical properties of soil due to freeze–thaw cycles. In this paper, the effect of freeze–thaw cycles on the compressive strength of fiber-reinforced clay is investigated. For this purpose, kaolinite clay reinforced by steel and polypropylene fibers is compacted in a laboratory and exposed to a maximum of 10 closed-system freezing and thawing cycles. The unconfined compressive strength of reinforced and unreinforced specimens is then determined. The results of the study show that for the soil investigated, the increase in the number of freeze–thaw cycles results in the decrease of unconfined compressive strength of clay samples by 20–25%. Moreover, inclusion of fiber in clay samples increases the unconfined compressive strength of soil and decreases the frost heave . Furthermore, the results of the study indicate that fiber addition does not decrease the soil strength against freeze–thaw cycles. Moreover, the study shows that the addition of 3% polypropylene fibers results in the increase of unconfined compressive strength of the soil before and after applying freeze–thaw cycles by 60% to 160% and decrease of frost heave by 70%.

Effect of fibres on the mechanical properties of clayey soil

This paper presents the effect of short, discrete, randomly oriented fibres (natural and synthetic) on the mechanical properties of clayey soils. The mechanical properties investigated include peak unconfined compressive strength, stiffness and ductility. Three types of clayey soil were obtained from the eastern part of Irbid city in northern Jordan. Two types of fibre were used in this study: nylon and palmyra fibres, with aspect ratios (L/d) equal to 75. The clayey soils were mixed with fibres at five different percentages by volume of solid soil particles: 1%, 2%, 3%, 4% and 5%. The results showed that the peak unconfined compressive strength, stiffness and ductility of the clay–fibre mixture increased with fibre content. The post-peak softening in compression resistance decreased with increasing fibre content. The relative unconfined compressive strength increased with fibre content. Palmyra fibre showed a higher increase in the relative unconfined compressive strength than nylon fibre when mixed with clayey soil, for all fibre contents. Furthermore, the clayey soil with a high activity index showed greater improvement when mixed with fibres than that with a low activity index.

Some experiences on the stabilization of Irish peats

This paper presents the findings of a study into the engineering properties of two peats from the Irish Midlands that were mixed with various binders to form a stabilized soil. The study comprised an investigation of the increase in unconfined compressive strength over time achieved using different binders for both peats and a comprehensive series of triaxial and compression tests on one peat when mixed with cement. A stabilized structure (i.e., a stabilized surface layer and a stabilized column) was tested in a large testing chamber in Trinity College to compare the laboratory parameters with those interpreted from the results of the large-scale test. The study showed that the engineering properties of the peat were considerably improved when mixed with some binders, however the degrees of improvement were markedly different for the two peats that had similar organic content. The formation of the stabilized soil structure within the testing chamber significantly reduced the amount of settlement when compared with that interpreted for the untreated soil, and the rate of consolidation was accelerated. A finite element analysis of the recorded behaviour in the large testing chamber showed good agreement between the simulated and the experimental behaviour.Key words: peat, cement, stabilization, compressibility, column.

Cementation of Soils Due to Calcium Carbonate

This study shows that calcium carbonate plays an important role as a cementing agent of soils. The vane shear strength and unconfined compressive strength of sedimentary soils are shown to vary with depth and are strongly dependent on the calcium carbonate content. It was found that an increase in calcium carbonate content caused an increase in soil strength, and that a decrease in soil strength was attributed to the decrease in carbonate content. The cementing effects due to calcium carbonate are quantitatively evaluated in this study. The results show that the increase in soil strength due to calcium carbonate is very high, depending on the type and age of the soils. For example, some alluvial sedimentary soils show an increase in unconfined compressive strength of 64 kPa by an increase of one percent in calcium carbonate.

Perforation of concrete slabs with 48 MPa (7 ksi) and 140 MPa (20 ksi) unconfined compressive strengths

Summary We conducted perforation experiments with 25.4-mm diameter, 0.50-kg, 3.0-caliber-radius-head, ogival-nose rods and 178-mm-thick concrete slabs with 48 MPa (7 ksi) and 140 MPa (20 ksi) unconfined compressive strengths. For impact velocities between 300 and 1100 m/s, our data showed that residual velocities for the 140 MPa concrete were less than 20% lower than that for the 48 MPa concrete. Thus, for a factor of three increase in unconfined compressive strength, we measured relatively minor changes in ballistic perforation performance. We explained these results qualitatively with post-test observations and triaxial material experiments with the 48 and 140 MPa concrete materials.

Sodium chloride as an additive in lime-soil stabilisation : Lees, G; Abdelkader, M O; Hamdani, S K Highway EngrV29, N12, Dec 1982, P2–8

Kaolinitic and montmorrillonitic soils were prepared from commercial quality sand and clay in 10, 30 and 50 per cent clay contents. Lime was added in 2, 4 and 8 per cent by dry weight of soil. The effect on optimum moisture content, maximum dry density and unconfined compressive strength of adding 1, 2 and 3 per cent of sodium chloride during lime treatment was investigated. At 28 days strength gains due to sodium chloride were generally higher in lime-kaolinite than in lime-montmorillonite soils. These amounted to between 100 and 300 per cent increase in unconfined compressive strength over that of the untreated or lime-only treated soils for clay contents between 30 and 50 per cent of the total soil composition. For most soils the optimum salt content for a maximum strength gain appears to be approximately one per cent. (Author/TRRL)