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 .     

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).     

Effects of lime addition on geotechnical properties of sedimentary soil in Curitiba,Brazil

The soil of the Guabirotuba geological formation(Paraná Basin, Brazil) has physico-mechanical properties which are not suitable for its utilization in pavement construction, in protection of hillsides and slopes, or as shallow foundation support. Treatment of this soil by lime addition would improve its usability. The present context intends to determine the ratio between the splitting tensile strength(q_t)and the unconfined compressive strength(q_u) of clayey soil in the metropolitan region of Curitiba City,which has been treated with different lime contents and curing times. The control parameters evaluated include lime content(L), curing time(t), moisture content(w), and ratio of porosity to volumetric lime content(η/L_v). It was observed that the q_t/q_u ratio is between 0.17 and 0.2 in relation to the curing time,and an exponential relation exists between them. Meanwhile, the unconfined compressive strength of lime-treated soil was found to be approximately four times the initial value.     

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.     

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。     

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.     

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.     

污水环境对水泥土力学性能的影响试验研究

由于多数地下水泥土工程直接与地下腐蚀性介质环境接触,必将导致水泥土材料的逐步劣化甚至失效破坏。以某市区工地附近明渠排放的污水作为侵蚀性介质,制作了不同水泥掺量的水泥土试件,通过对比试验,研究了污水环境和清水环境下不同水泥掺量、不同龄期的水泥土抗压强度和抗剪强度。结果表明,在污水或清水环境下,相同水泥掺量水泥土30 d 龄期的抗压强度几乎相等,随着龄期的增加其抗压强度均逐步增大,但污水环境下其抗压强度增长的幅度明显小于清水环境,90 d 后清水环境的水泥土抗压强度不再增长,而污水环境的抗压强度开始降低;污水环境和清水环境下的水泥土内摩擦角和黏聚力随龄期、水泥掺量的增加均逐步增大,污水环境下龄期90 d后的内摩擦角和黏聚力均开始降低。     

浸水条件下水泥砂土力学性能的试验研究

通过对不同水泥掺入比、不同龄期的水泥砂土在浸水和不浸水条件下的无侧限抗压试验,分析了浸水对水泥砂土的各项力学性能的影响,以及水泥砂土的无侧限抗压强度和模量随水泥掺入比及龄期的变化规律,并对水泥砂土全应力应变曲线的特性进行了总结。     

聚丙烯纤维水泥稳定碎石抗压强度试验研究

在大量试验研究的基础上,对试件养护龄期、聚丙烯纤维体积掺量以及水泥掺量的变化对聚丙烯纤维水泥稳定碎石抗压强度的影响进行分析。结果表明:聚丙烯纤维的掺加对水泥稳定碎石抗压强度有一定的增加;随着试验龄期的增长,抗压强度不断增长;在聚丙烯纤维掺量体积分数小于1‰的范围内,随着纤维体积分数的增加,水泥稳定碎石抗压强度和抗拉强度均有增加的趋势;随着水泥掺量的增加,聚丙烯纤维水泥稳定碎石抗压强度基本呈线性增加。     

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.     

Strength Development in Cement Stabilized Low Plasticity and Coarse Grained Soils: Laboratory and Field Study

Laboratory and field strength development of cement stabilized coarse-grained soils are studied in this paper. A phenomenological model to assess the laboratory strength development is developed. The model is divided into the dry and the wet sides of optimum water content. At the optimum and on the wet side of optimum, the strength development in cement stabilized soils at a particular curing time is dependent only upon the soil-water/cement ratio, w/C, which can reflect the combined effects of water content and cement content. It is moreover premised that the relationship between strength and water content is symmetrical around the optimum water content (OWC) in the range of 0.8 to 1.2 times the OWC. The proposed model is useful for assessing the strength development wherein water content, cement content and compaction energy vary over a wide range. Only the test result of a single laboratory trial is needed. From the field study, it is found that the field roller-compacted strength, q_ufr is lower than the laboratory strength, q_ul under the same dry unit weight, soil-water/cement ratio and curing time due to several field factors. The ratio q_ufr/q_ul varies from 50 to 100%. Non-uniformity in mixing soil with cement is realized by the ratio of field hand-compacted strength to laboratory strength, q_ufh/q_ul ranging from 0.75 to 1.2. For most data, the field roller-compacted strength is 55 to 100% the field hand-compacted strength. This might be caused by the difference in compaction method and curing condition between laboratory and field stabilization. From this field observation and the proposed model, a practical procedure for repairing damaged roads using the pavement recycling technique is introduced. The procedure consists of the determination of cement content, the execution of the field stabilization and the examination of the field strength. It can save on sampling and laboratory testing and hence cost.     

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.     

Unconfined compressive strength and ductility of fiber-reinforced cemented sand

A series of unconfined compression tests were performed on specimens of fiber-reinforced cemented sand (FRCS) to evaluate how fiber inclusion affects the measured strength and ductility characteristics of cemented sand. Lightly cemented sand with three different cement ratios (2, 4, and 6% by weight of soil) was mixed with four different fiber ratios (0, 0.3, 0.6, and 1% by weight of soil) and then compacted into a cylindrical specimen. Polyvinyl alcohol (PVA) fiber, which adheres well to cement, was randomly distributed throughout the cemented sand. The test results indicate that the inclusion of PVA fiber has a significant effect on both the unconfined compressive strength (UCS) and the axial strain at peak strength. The increase in the UCS was most apparent in the 2% cemented specimen wherein the UCS increased more than three times as the fiber ratio increased up to 1%. The ductile behavior of the FRCS is quantified by the deformability index, D, which is a ratio of the axial strain at peak strength of fiber-reinforced specimen to that of non-fiber-reinforced specimen. In the cases of 1% fiber ratio, the values of D were greater than four, regardless of cement ratios.     

Mixture design concept and mechanical characteristics of PS ash–cement-treated clay based on the water absorption and retention performance of PS ash

In an attempt to reduce environmental impact, paper sludge ash (PS ash) has recently been studied for its complementary reuse with cement for soil stabilization. In order to establish the optimal mixture design for combining PS ash and cement in soils, a detailed investigation into the stabilizing mechanism is required. To assess the combined effects of PS ash and cement on the strength development of stabilized clay soil, referred to as PS ash–cement-treated clay, a new critical parameter, the unabsorbed and unretained clay-water/cement ratio W*/C, was proposed. To determine W*/C, a new testing method for evaluating the water absorption and retention performance of PS ash was developed. It was revealed that the water absorption and retention rate W_ab of PS ash increased with curing time. Unconfined compression tests conducted on the PS ash–cement-treated clay with various water-cement–PS ash mixture proportions and different curing times affirmed that the strength development was fundamentally governed by the parameter W*/C. This suggests that the water absorption and retention rate W_ab obtained by the developed method is an essential material parameter in the mixture design for the PS ash–cement-treated clay. It was also found that the effect of the hybrid treatment method, which uses both cement and PS ash, was better than that of the method which uses cement alone, particularly under high W*/C conditions. This indicates that the water absorption and retention performance of PS ash can be fully utilized when the mixture has sufficient unabsorbed and unretained water for cement hydration.     

花岗岩残积土的水泥处治实验研究

对花岗岩残积土试样进行水泥浆处治初步实验研究,经处治后的花岗岩残积土,其抗崩解性能显著改善,浸泡在水中数日不会崩解;同样其抗压强度也得到显著提高,当水泥掺量大于10%之后,试块强度反而随着水泥掺量的增加而降低;浸水后的试块,其强度基本是随着水泥掺量的增加而增大;未浸水试块强度基本呈随水灰比增大而降低的趋势,而水灰比及养护龄期对浸水试块的强度影响不明显。     

Durability against wetting-drying cycles for cement-stabilized reclaimed asphalt pavement blended with crushed rock

Pavement rehabilitation and reconstruction generate large quantities of reclaimed asphalt pavement (RAP). The improvement of the engineering properties of this RAP is required in order to enable it for use as environmentally friendly alternative construction material in road pavements. The durability of RAP when blended with crushed rock (CR) and stabilized with Portland cement was investigated in this paper. The CR replacement was found to improve the compactibility and durability of the stabilized RAP/CR material. For a particular RAP:CR ratio, the compaction curves of cement-stabilized RAP/CR blends were found to be essentially the same for all cement contents, but different for unstabilized blends; i.e., the maximum dry unit weight of cement-stabilized RAP/CR blends is higher than that of unstabilized RAP-CR blends. The wetting-drying (w-d) cycles led to a loss in weight of the cement-stabilized RCA/CR blends and to a subsequent reduction in strength. The w-d cycle strengths (q_u(w-d)) for a state of compaction (dry side, wet side or optimum water content) at any w-d cycle could be approximated from the corresponding initial soaked strength (prior to w-d tests) (q_u0). The q_u0 of cement-stabilized RAP/CR blends increased with an increasing CR replacement and an increasing cement content. Assuming that the CR replacement also results in an increasing cement content, w/[C(1?+?kCR_c)] was proposed as a critical parameter for developing q_u0 and q_u(w-d) predictive equations where w is the water content at the optimum water content, C is the cement content, k is the replacement efficiency, and CR_c is the CR content. Based on the q_u(w-d) predictive equation developed here, a design procedure for the laboratory mixing of cement-stabilized RAP/CR blends was proposed, which would be valuable for an accurate determination of the ingredients (RAP:CR ratio and cement content) required to attain the necessary strength at the design service life.     

上海奉贤粉质粘土与水泥加固体的强度试验研究

以上海奉贤区粉质粘土与水泥混合后的加固体为研究对象,对其进行了多组无侧限抗压强度试验,通过对试验数据的整理分析,得出了以下两方面的结果：不同掺量下无侧限抗压强度与龄期的关系;不同龄期的无侧限抗压强度与掺量的关系。     

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.