Fibre-reinforced cemented soils compressive and tensile strength assessment as a function of filament length

This study aims to develop a dosage methodology based on tensile and compressive strength for artificially cemented fibre reinforced soils considering filament length. The controlling parameters evaluated were the fibre length (l), the cement content (C), the porosity (η) and the porosity/cement ratio (η/C_iv). A number of unconfined compression and split tensile tests were carried out in the present work. The results show that fibre insertion in the cemented soil, for the whole range of cement content studied, and the increase of reinforcement length improve unconfined compressive and split tensile strengths. It was shown that the porosity/cement ratio, in which volumetric cementitious material content is adjusted by an exponent (0.28 for all the fibre-reinforced and non-reinforced cemented soil mixtures) to end in unique correlations for each mixture, is a good parameter in the evaluation of the unconfined compressive and split tensile strength of the fibre-reinforced and non-reinforced cemented soil studied. Analysis of variance (ANOVA) performed on the results of a factorial experiment considering the effect of adjusted cement content, fibre length and porosity showed that all of these factors are significant in affecting the measured changes in split tensile and unconfined compressive strength values. Finally, unique dosage relationships could be achieved linking the unconfined compressive strength (q_u) and the split tensile strength (q_t) of the sandy soil studied with porosity/cement ratio (η/C_iv) and fibre length (l).     

Modelling tensile/compressive strength ratio of artificially cemented clean sand

The present work proposes a new theoretical model for predicting both the splitting tensile strength (q_t) and the compressive strength (q_u) of artificially cemented sand and assesses their ratio for a given material. The proposed model is based on the concept of the superposition of the failure strength contributions of the sand and cement phases. The sand matrix obeys the concept of critical state soil mechanics, while the strength of the cemented phase can be described using the Drucker-Prager failure criterion. The analytical solutions are compared against the results of tests on three different types of cemented clean sand cured for different time periods. While the analytical relation fits the experimental data well, it also provides a theoretical basis for the explanation of some features related to the experimentally derived strength relationships for cemented clean sand. The value of the power relationship between the strength and the porosity/cement ratio index seems to be governed by the soil matrix properties, while the interdependency of the strength and the curing time can also be captured. For a given cemented sand, the model equally confirms the existence of a unique tensile/compressive strength ratio (q_t/q_u), independent of the curing time and primarily governed by the compressive to tensile strength ratio (or the friction properties) of the cement. It is also confirmed that the q_t/q_u ratio changes within a narrow range for different frictional properties of the cementing phase.     

Modelling tensile/compressive strength ratio of fibre reinforced cemented soils

The present work proposes a theoretical model for predicting the splitting tensile strength (q_t) - unconfined compressive strength (q_u) ratio of artificially cemented fibre reinforced soils. The proposed developments are based on the concept of superposition of failure strength contributions of the soil, cement and fibres phases. The soil matrix obeys the critical state soil mechanics concept, while the strength of the cemented phase can be described using the Drucker-Prager failure criterion and fibres contribution to strength is related to the composite deformation. The proposed developments are challenged to simulate the experimental results for fibre reinforced cemented Botucatu residual soil, for 7 days of cure. While the proposed analytical relation fits well the experimental data for this material, it also provides a theoretical explanation for some features of the experimentally derived strength relationships for artificially fibre reinforced cemented clean sands. A parametric study to analyse the effect of adding different fibre contents and fibre properties is provided. The proposed modelling developments also confirm the existence of a rather constant q_t/q_u ratio with moulding density, cement and fibre contents .     

Effects of porosity,dry unit weight,cement content and void/cement ratio on unconfined compressive strength of roof tile waste-silty soil mixtures

One of the conventional ways to improve the mechanical behavior of soils is to mix them with cementing agents such as cement, lime and fly ash. Recently, introduction to alternative materials or sub-products that can be adopted to improve the soil strength is of paramount importance. Therefore, the present study aims to investigate the effects of porosity (η), dry unit weight (γ_d) of molding, cement content (C) and porosity/volumetric cement content ratio (η/C_iv) or void/cement ratio on the unconfined compressive strength (q_u or UCS) of silty soil–roof tile waste (RT) mixtures. Soil samples are molded into four different dry unit weights (i.e. 13 kN/m³, 13.67 kN/m³, 14.33 kN/m³ and 15 kN/m³) using 3%, 6% and 9% cement and 5%, 15% and 30% RT. The results show that with the addition of cement, the strength of the RT–soil mixtures increases in a linear manner. On the other hand, the addition of RT decreases q_u of the samples at a constant percentage of cement, and the decrease in porosity can increase q_u. A dosage equation is derived from the experimental data using the porosity/volumetric cement content ratio (η/C_iv) where the control variables are the moisture content, crushed tile content, cement content and porosity.     

Optimizing the evolution of strength for lime-stabilized rammed soil

In the present study,unconfined compressive strength(q_u)values of two lime-treated soils(soil 1 and 2)with curing times of 28 d,90 d and 360 d were optimized.The influence of void/lime ratio was represented by the porosity/volumetric lime content ratio(η/L_(iv))as the main parameter.η/L_(iv) represents the volume of void influenced by compaction effort and lime volume.The evolution of qu was analyzed for each soil using the coefficient of determination as the optimization parameter.Aiming at providing adjustments to the mechanical resistance values,the η/L_(iv) parameter was modified to η/L_(iv)~C using the adjustment exponent C(to make q_u-η/L_(iv) variation rates compatible).The results show that with the decrease of η/L_(iv)~C.qu increases potentially and the optimized values of C were 0.14-0.18.The mechanical resistance data show similar trends between q_u and η/L_(iv)~C for the studied silty soil-ground lime mixtures,which were cured at ambient temperature(23±2)℃ with different curing times of 28—360 d.Finally,optimized equations were presented using the normalized strengths and the proposed optimization model,which show 6% error and 95% acceptability on average.     

The effects of curing time and temperature on stiffness,strength and durability of sand-environment friendly binder blends

Agricultural-industrial wastes, like rice-husk ash (RHA) and carbide lime (CL), have great potential applications in such earthworks as the stabilization of slopes and pavement layers and the spread footings and bed of pipelines, particularly in the regions near where the waste is produced. Present research evaluates the potential use of RHA mixed with CL as a binder, improving strength, stiffness and durability properties of a uniform sand. Two different curing temperatures, 23 °C and 40 °C, and curing periods, 7 and 28 days, of compacted sand-RHA-CL blends (distinct dry unit weights and contents of RHA and CL) were evaluated to determine the importance of these changes on the reactions between the materials. The experimental program aims to assess the following parameters: initial shear modulus (G₀), unconfined compressive strength (q_u), and accumulated loss of mass (ALM). Studies have been carried out to quantify these parameters as a function of a novel index called porosity/volumetric binder content (η/B_iv). The results showed higher values of G₀ and q_u, as well as a small rate of ALM with reduction of porosity and with rise of the environment friendly binder content. The latter is achieved either by increasing eith the RHA or the CL content. The curing temperature acts as a catalyser, accelerating the pozzolanic reactions between RHA and CL. Longer curing periods also benefit reactions between materials by enhancing their geotechnical properties. An analysis of variance (ANOVA) was carried and the results showed the dry unit weight, RHA content and curing type are significantly effect the strength results. It was also possible to verify that curing for 28 days at 23 °C and for 7 days at 40 °C are statistically equivalent in terms of strength. The G₀ results after weathering cycles tended to decrease in specimens at a 40 °C curing temperature and increase in specimens at a 23 °C curing temperature.     

Measurement of Soil Tensile Strength and Factors Affecting its Measurements

This paper describes the tensile strength measured for three kinds of statically compacted unsaturated soils; mixtures of clay ~ silt ~ sand, Narita-sand and Kanto loam. Specimens were directly prepared either under controlled compaction stress or under controlled dry density by statically compacting them within the tensile mold of the apparatus. Image analysis was done to show the normality of tensile force to the tensile failure plane. Tensile strengths (q_t) were compared with the unconfined compressive strengths (q_u) for silt ~ sand mixture, clay ~ sand mixture, clay ~ silt mixture and Narita sand, respectively. Increment in tensile strength (also q_u/q_t ratio) with the increase in the percentage and decrease in the size of finer soils could be seen. Effects of number of compaction layers and tensile pulling rates on the q_t were also examined. Increase in the tensile strength with the increase in the number of compaction layers was observed; and it was suggested to prepare the unsaturated compacted specimen by 3 to 4 layers compaction. Increase in tensile strength of 0.3 kPa and 0.003 kPa per one cycle of logarithm of tensile pulling rate was observed for clay ~ sand-4 (1:3) and clay ~ sand-5 (3:1) for the pulling rate of 0.01 to 1.0 mm/min.     

Parameters Controlling Strength of Industrial Waste-Lime Amended Soil

Unconfined compression tests and suction measurements were carried out in the present work on sandy specimens with distinct Class F fly ash amounts, lime contents, porosities and curing periods to assess key parameters controlling strength of fly ash-lime amended soil. A special effort has been allocated in order to develop a dosage methodology for fly ash-lime improved soils based in a rational criterion, as it exists in the concrete technology where the water/cement ratio plays a fundamental role in the assessment of the target strength. The results show that the unconfined compressive strength (UCS) increased linearly with the amount of lime for soil-fly ash-lime mixtures at all curing time periods studied. A power function fits better the relation UCS-porosity for soil-fly ash-lime mixtures. The bigger the amount of fly ash and the curing time, the larger the UCS for any given porosity and lime content. Finally, the porosity/volumetric lime content ratio, in which volumetric lime content is adjusted by a coefficient (in this case a unique value-0.12-was found for all soil-fly ash-lime mixtures and all curing periods studied) to end in single correlations for each curing period, show to be a good parameter in the evaluation of the unconfined compressive strength of the soil studied (UCS varies non-linearly with the porosity/volumetric lime content ratio in the case of fly ash-lime addition).     

Use of fall cone test as measurement of shear strength for soft clay materials

A fall cone test (FCT) was carried out to obtain the undrained shear strength (s_u), and to measure the sensitivity (S_t) of intact and remolded samples from several sites in Japan. The value of s_u from FCT was compared with half of the unconfined compression strength (q_u/2), which is a standard way to evaluate s_u for practical design in Japan. It is found that s_u from FCT is neither related with q_u/2 nor used directly as a design value. S_t was also obtained by field and laboratory vane tests. A comparison study revealed that S_t by FCT is as much as 10 times larger than that by the field vane. The large difference in S_t measured by different testing methods can be attributed to remolding methods. That is, the remold condition for FCT was created by kneading the sample in a plastic bag by hand, while in the field vane, the ground was remolded by 30 turns of the vane blade. This indicates that the degree of the reduction in strength caused by the turn of the vane blade is less significant than that caused by remolding by kneading.     

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

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, w_i, 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, q_max, from the present study were compared to those with various types of cement-mixed soils and concretes from the literature. An increase in q_max 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 q_max 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, q_max exhibits a larger extra gain when cured longer at more anisotropic stress states.     

石灰粉煤灰稳定黄土的无侧限抗压强度研究

以石灰粉煤灰稳定黄土为对象,通过标准击实试验、无侧限抗压强度试验,研究养护龄期和石灰粉煤灰掺量对稳定黄土最佳含水率、最大干密度及无侧限抗压强度的影响。结果表明,随石灰粉煤灰掺量的增加,稳定黄土最佳含水率增大,最大干密度减小;石灰粉煤灰掺量一定时,随粉煤灰掺量的增加,最大干密度增大,最佳含水率减小;无侧限抗压强度随养护龄期的增长、石灰粉煤灰掺量的增加而增大。通过对试验数据的拟合回归,建立了稳定黄土无侧限抗压强度与孔隙率、粉煤灰与石灰的比值（F/L）及石灰粉煤灰总体积掺量的关系。     

The role of carbide lime and fly ash blends on the geotechnical properties of clay soils

Carbide lime is a by-product obtained during the manufacturing of acetylene from the reaction of calcium carbide and water. A major portion of carbide lime is dumped in waste deposition areas, creating an environmental problem. Carbide lime and fly ash have possible applications in slope stabilization, subgrade improvement of roads, and soil treatments under shallow foundations. A series of Atterberg limits tests, compaction tests, unconfined compressive strength tests, ultrasonic pulse velocity tests, and wetting–drying tests were performed on carbide lime and fly ash treated clay soils to evaluate the effects of additive content, curing time, strength development, and the effects of wetting and drying. A total of 8% of carbide lime constituted the fixation point, and peak strength was achieved at 12% carbide lime content. A total amount of 25% additive was found as a threshold changing the Atterberg limits. Test results indicated that the strength of the treated soil improved by the existence of carbide lime and fly ash; best performance was observed in 28-day specimens with 10% carbide lime and 20% fly ash content reaching to 8 times larger strength than untreated soil. The failure patterns of the specimens reflected the curing time and wetting–drying effects. Although, the application of wetting–drying cycles deteriorated the treated soil, the presence of carbide lime partially prevented the strength loss. New relationships between normalized strength and curing time depending on carbide lime content were proposed. Furthermore, a linear relationship between the unconfined compressive strength and the ultrasonic pulse velocity of the treated soils was established.

     

A Slope Stability Analysis Considering Undrained Strength Anisotropy of Natural Clay Deposits

The effects of sites and plasticity index (I_p) on the inherent strength anisotropy of eleven different clay deposits are quantitatively examined by the unconfined compression test using a small size specimen with a different angle of inclination to the vertical. A new method for a slope stability analysis, taking the effects of the IASIA method (Inherent And Stress Induced Anisotropies) into consideration, is proposed. The applicability of the IASIA method and the optimum embankment design are examined through case histories of embankment failures on soft soils. The undrained strength anisotropy cannot be estimated by parameters such as the I_p value because of the complicated relationship with the factors influencing undrained anisotropic strength. It must be directly measured. The IASIA method was recommended from a study of a failed embankment. The probability of failure (P_f) and consumer's risk (P_c) from half of the unconfined compressive strength (q_u/2) were (2.5~25.5)% and (4.7~42.3)% less than those of the Iwai q_u/2_(IASIA) and Urayasu q_u/2_(IASIA). Therefore, the design results were underestimated by disregarding strength anisotropies. If, P_f and P_c were considered, the C_t values increased. However, the P_c values drastically decreased to 24.8% from 54.3% concerning the 75-mm sampler and n increased, thus avoiding latent risks. These mean that the IASIA method can be used for optimum embankment design based on performance provisions.     

Characterizing cyclic and static moduli and strength of compacted pavement subgrade soils considering moisture variation

Compacted soils are widely used as the subgrade layer for pavements. Knowledge of the mechanical properties of subgrade soils under cyclic and static loading conditions and their variation under the influence of environmental factors is required for the rational design of pavements based on mechanistic methods. This paper presents an experimental investigation of the cyclic and static moduli and the strength properties of seven different compacted Canadian subgrade soils considering the variation in the post-compaction moisture content. Cyclic triaxial tests were performed to reliably determine the resilient modulus (M_R). Unconfined compression tests, which allow an unloading-reloading loop at 1% strain, were performed to determine the deviator stress (S_u1%) at 1% strain, the reloading elastic modulus (E_1%) at 1% strain and the unconfined compressive strength (q_u) at failure. The physical properties, the chemical and mineralogical compositions, and the soil-water characteristics of these soils were also determined. Relationships were developed to predict the M_R from the S_u1%, E_1%, q_u and soil physical properties for the investigated subgrade soils because the experimental determination of M_R is both expensive and time-consuming. The studies presented in this paper provide useful information and approaches that can be used to promote the implementation of mechanistic pavement design methods using simple techniques.     

含盐量与固化材料掺量对固化盐渍土抗压强度的影响

为解决滨海盐渍土的低强度和大变形问题,采用水泥、石灰、SH固土剂固化盐渍土,研究含盐量、固化材料掺量、养护龄期和浸泡用水对固化土抗压强度的影响.结果证实:含盐量大于1%,固化土抗压强度随含盐量的增加而减小;掺加水泥、石灰、SH固土剂均可提高土的强度和水稳性;随养护龄期的增加,固化土的抗压强度增加;石灰固化土和SH固土剂...     

Using fiber and liquid polymer to improve the behaviour of cement-stabilized soft clay

This work studies the effect of using two types of polymer (fibers and liquid) to enhance the strength of cemented soft clay. Four polymer contents were used (0, 0.1, 0.2, 0.5 and 1% by dry weight of the soil) to investigate the unconfined compressive strength, q_un of soft clay mixed with three cement contents (5, 10 and 15%). For wide understanding to the polymer/cemented soil behaviour several factors were considered in this study such as curing time, dry unit weight, the mixture workability and the behaviour after disturbance. This investigation revealed that both fibers and liquid polymers can improve the cemented soft clay strength, however the fiber mechanism in improving the mixture is totally different than the liquid. Increasing the fiber content shall increase q_un till a peak point at fiber content of 0.5%, where the strength started to reduce after. The mixture workability has been improved with increasing the liquid polymer content, and reduced with increasing the fiber content. Fibers can be used to raise up the strength of disturbed cemented soft clay up to 240% by using fiber content of 0.5%. Both fibers and liquid polymers showed a remarkable mechanically, economically and environmentally dominance to be used as additive to cement in improving the soft clay.     

二灰稳定材料强度分析

通过大量的室内试验 ,分析了石灰、粉煤灰土、粉煤灰砂砾的无侧限抗压强度随石灰剂量、养护温度、龄期的增长规律 ,并给出了其回归关系。总结出了二灰稳定材料的强度规律以及对施工的指导意义。     

水泥土搅拌桩止水帷幕工程特性研究

水泥土搅拌桩作为基坑止水帷幕已经得到了广泛应用,为了更深入的理解作为止水帷幕的水泥土的工程特性,通过对不同水泥掺入量的水泥土无侧限抗压强度和渗透系数的室内试验研究,利用CBR-1承载比试验仪和TSS-2柔性壁三轴渗透仪对水泥土进行了无侧限抗压强度和渗透试验,分析了养护龄期及水泥掺入量对水泥土的无侧限抗压强度和渗透系数的影响。试验结果表明,水泥土的无侧限抗压强度随养护龄期和水泥掺入量的增大而增大,并通过曲线的拟合,得出了无侧限抗压强度的预测公式;渗透系数随养护龄期和水泥掺入量的增大而减少,通过数据对比得出28天之后水泥土渗透系数主要是受水泥掺入量的影响。     

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.     

Mechanical Properties of Lightweight Treated Soil Cured in Water Pressure

An artificial lightweight soil has been developed as a backfill to reduce the earth pressure behind port and harbor structures. To reduce the unit weight lightening ingredient such as air foam or EPS beads is mixed within slurry of dredged soft clay, while cement is used as stabilizer to warrant compressive strength. This experimental study aims to characterize the strength and deformation properties of lightweight treated soil cured in water pressure. Samples of two types of lightweight treated soil mixed with air foam or EPS were cured under various pressures, and subjected to undrained shearing tests on triaxial apparatus modified to detect volumetric change. Though high pressures inevitably compress lightener and consequently incur increment in unit weight, pressured curing did not reduce the compressive strength, q_max = (σ_a-σ_c)_max. It was also found that the deformation modulus E₅₀ greatly decreases with relative confining pressure σ_c/q_max. The lightweight soils maintained relatively large residual strengths, showing no significant sign of brittle failure as often confronted in unconfined compression test. It was observed that the critical state line exists when subjected to ultimate strains, and that the peak deviator stress envelop was identified in effective stress path plane for air foam mixed cases alone. K₀-consolidation tests were conducted on modified triaxial apparatus, showing that K₀ values from the quasi one dimensional tests decline to as small as 0.1 to 0.15 around axial strain of 0.5~1% at near yielding points. Poisson's ratios based on both undrained shearing and K₀-consolidation are compared in consistent tendency with minimal values of 0.1 to 0.2 near the identical yielding points. Yet it is revealed from the obtained compression curves that the compressibility increases drastically by some 100-fold when comparing before and after yielding for lightweight treated soil. This fact strikes the importance of not overloading lightweight treated soil by its compressive strength.