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。     

Peak and residual strength characteristics of cement-treated soil cured under different consolidation conditions

The shear strength of cement-treated soil can be changed by both cementation and consolidation during the early stages of hardening because of cement hydration. Based on the results of triaxial and unconfined compression tests, this paper describes the effects of isotropic and one-dimensional consolidation stress, applied during the curing period, on the undrained peak and residual shear strengths of cement-treated soil. The sample used was a mixture of fine-grained sand and ordinary Portland cement. A consolidated undrained triaxial compression test (ICU) was conducted on the specimens immediately after the cement treatment. Each test was conducted under different consolidation pressures, curing times and delayed loading times. The following conclusions were developed from the results and discussions: (1) the undrained peak shear strength of cement-treated soil, cured under different consolidation conditions, increases with an increase in either the consolidation pressure or the curing time, whereas it gradually decreases with an increase in the delayed loading time. (2) The rate of undrained strength increase resulting from consolidation differs significantly between isotropic and one-dimensional consolidations. (3) For a curing time of between one and seven days, the rate of strength increase by isotropic consolidation exceeds that by one-dimensional consolidation. The simultaneous volumetric change of cement-treated soil during consolidation depends on the stress conditions of the specimen, that is, the difference between isotropic and one-dimensional consolidations. (4) When the test is not conducted under nearly in-situ conditions, the undrained shear strength may be underestimated, depending on the time interval between the cement treatment and the start of consolidation. (5) The shear strength in the residual state is influenced by the consolidation pressure during curing. (6) As the consolidation pressure during curing increases, the specimens exhibit a higher residual strength.     

生物酶改良膨胀土的压缩特性

为探究生物酶改良膨胀土压缩特性,通过一维固结试验,研究了生物酶、石灰、水泥改良膨胀土体孔隙比、压缩系数、单位沉降量与荷载变化规律。探讨了固结压力对生物酶、石灰、水泥改良膨胀土体压缩特性的影响。试验结果表明:生物酶、石灰、水泥改良膨胀土表现出不同的压缩性,主要反映在压缩曲线与压缩系数上;掺生物酶、石灰、水泥都能改善膨胀土的压缩性,其中,生物酶配比为1∶300改良膨胀土的压缩性最小;改良膨胀土的单位沉降量与荷载的关系可用幂函数来表示:si=bpai。     

Model for predicting the unit weight of cement-treated soils

In this paper, a rational method for estimating the unit weight of cement-treated clay is proposed, which takes into account the relationship between the various phases and changes in these phases during curing. The simplest unit weight estimate is the unreacted unit weight which may be used as a lower-bound estimate of the cured unit weight. More accurate estimates of the unit-weight are possible by considering the effects of hydration of the cement-water paste during curing period, using the “drained” and “undrained” estimates of the unit weights. The drained and undrained assumptions refer to the drainage conditions during curing. Both are consistently closer to the measured unit weights than the unreacted unit weight, with undrained assumption having a slightly better agreement. An empirical relationship is also proposed for estimating the effect of the change of volume arising from consolidation during curing. This may be significant if the treated soil layer lies deep in the ground, where the effective stress levels are high. Comparison with unit weight measurements from a soil mixing project indicate that the calculated unit weight agrees well with the range of unit weight measurements for soft clay. For the loose sand, the calculated unit weight is higher than the measured unit weight, possibly owing to the dilation of sand when sheared, ahead of the mixing shaft.     

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.     

Basic parameters governing the behaviour of cement-treated clays

Although extensive research has been conducted on the mechanical behaviour of Portland cement-treated soft clays, there has been less emphasis on the correlation of the observed behaviour with clay mineralogy. In this study, experimental results from the authors have been combined with the data found in the literature to investigate the effect of parameters such as curing time, cement content, moisture content, liquidity index, and mineralogy on the mechanical properties of cement-treated clays. The findings show that undrained shear strength and sensitivity of cemented clays still continue to increase after relatively long curing times; expressions are proposed to predict the strength and sensitivity with time. This parametric study also indicates the relative importance of the activity of the soil, as well as the water–cement ratio, to the mechanical properties of cementitious admixtures. Two new empirical parameters are introduced herein. Based on the results of unconfined compression, undrained triaxial, and oedometer tests on cement-enhanced clays, expressions that use these parameters to predict undrained shear strength, yield stress, and the slope of the compression line are proposed. The observed variations in the mechanical behaviour with respect to mineralogy and the important effect of curing time are explained in terms of the pozzolanic reactions. The possible limitations of applying Abrams׳ law to cement–admixed clays are also discussed.     

Modeling compression behavior of cement-treated zinc-contaminated clayey soils

In this paper, the compression behavior of cement-treated soil with various cement contents and zinc concentrations is presented and modeled by the destructuring framework and the concept of the Intrinsic Compression Line (ICL). The void ratio of a cement-treated sample with Zn contamination is the sum of the void ratio sustained by the intrinsic soil fabric (destructured void ratio) and the additional void ratio due to cementation. The compression index at the pre-yield state, C_s, increases as the Zn concentration increases or as the cement content decreases. At the post-yield state, the additional void ratio is inversely proportional to the effective vertical stress. The rate of reduction in the additional void ratio is controlled by the destructuring index, b. The values for b and yield stress are mainly dependent upon the degree of cementation, which is controlled by the cement content and the Zn concentration. Based on a critical analysis of the test data, a practical (simple and rational) method for assessing the compressibility of cement-treated soil with various Zn concentrations is suggested. The proposed predictive method is useful not only for quickly determining compression curves, with acceptable errors, but also for examining the results of tests on cement-treated zinc-contaminated soil.     

Attempt to reproduce the mechanical behavior of cement-treated soil using elasto-plastic model considering soil skeleton structure

The improvement of sand and clay using lime or cement to control solidification is common practice. Among the many constitutive models for solidification proposed for clay and sand, few can reproduce the combined behavior of cement-treated clay and cement-treated sand. Here, four typical experimental results for cement-treated soil have been chosen from the literature to consider the shear and consolidation behavior for clay and sand, especially for a low cement mixing ratio. The elasto-plastic constitutive model was used to simulate this behavior considering the soil skeleton structure.The simulation results obtained using the model agreed with the experimental test results both for the cement-treated clay and the cement-treated sand. In the case of the clays, the experimental results were reproduceable using material constants for elasto-plastic and evolution parameters and only required changes in the initial state values, regardless of whether the soil was treated or untreated. In the case of the sands, the structure decay index of the treated sand became smaller than that of the untreated sand. Moreover, the cement-treated loose sand did not exhibit softening behavior. This was attributed to the slow rate of decay of the highly structured cement-treated loose sand due to the solidification of the cement. The degree of structure and the overconsolidation ratio both increased with higher amounts of admixed cement. The model developed in this study was capable of describing the mechanical behavior of both cement-treated clay and cement-treated sand.     

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。     

A review of the stabilization of tropical lowland peats

The Deep Mixing Method, which involves the formation of in situ stabilized peat columns, is suitable for deep peat stabilization, whereas the mass stabilization technique is used to stabilize the soil of shallow peat deposits instead of the costly and problematic removal and replacement method. The concept of soil-cement stabilization involves the addition of water to cement, resulting in a chemical process known as cement hydration. Stabilization of peat by cement, which requires a significant strength increase in the cement-stabilized peat or organic soil, is attributed largely to physicochemical reactions that include cement hydration, hardening of the resulting cement paste and interactions between soil substances and primary and secondary cementation hydration products. The factors that affect these physicochemical reactions and the interactions of peat soil-cementation products that influence peat stabilization are the amount of solid particles, the water: soil ratio, the quantity of binder, the presence of humic and/or fulvic acids, the soil pH and the amount of organic matter in the peat. With the Air Curing Technique, stabilized peat samples for unconfined compressive strength (UCS) tests were kept at a normal air temperature of 30 ± 2 °C and strengthened by gradual moisture content reduction instead of the usual water-curing technique or water submersion methods that have been common practice in past experiments involving the stabilization of peat with cement. The principle of using the Air Curing Technique to strengthen stabilized peat is that peat soil at its natural moisture content contains sufficient water (water content from 198 to 417 %) that, when mixed with cement, a curing process takes place that causes the stabilized peat soil to gradually lose its moisture content and to become drier and harder throughout the curing period. This process does not require the addition of water.     

水泥、石灰加固淤泥土无侧限抗压强度试验研究

本文阐述了如何对工程中所遇到淤泥质软弱地基土采用水泥、石灰进行加固和进行一系列的物理性能、强度试验,并就水泥、石灰用量和养护龄期对加固土无侧限抗压强度的影响进行分析,提出了强度预测公式,以资借鉴.     

深层搅拌桩强度的影响因素与改善措施

影响深层搅拌桩强度的主要因素为水泥实际掺入比、养护龄期、土样含水量、土体搅拌均匀程度、复搅深度是否合理、外加剂选择是否合适、土体围压和水泥强度等级等。通过分析这些影响因素，探讨了提高深层搅拌桩桩体强度和单桩承载力的方法。     

水泥基流态土固化剂的试验研究

为制备性能优良水泥基流态土固化剂,通过研究水泥基流态土固化剂中拌合用水与回填土的比例、固化剂掺量与回填土质量的比例和水泥基流态土固化剂的组成,确定水泥基流态土固化剂的最佳掺量,探讨增强固化土抗压强度的方法.采用扫描电子显微镜(SEM)观测水泥基流态土固化剂的微观结构和水化产物,分析水泥基流态土固化剂的加固机理.研究表明...     

甲基纤维素对新拌水泥浆体性能的影响

探讨了甲基纤维素对新拌水泥浆体若干性能的影响，并将其与水灰比和水泥品种的影响进行了比较。结果表明：甲基纤维素有显著的增稠和提高水泥浆体保水性的作用，有较小的增塑、缓凝效果；甲基纤维素引气效果明显，因此应用中需特别考虑其对材料强度的影响。     

广州南沙地区软土采用水泥和粉煤灰固化试验研究

通过室内试验,研究广州市南沙地区软土采用水泥和粉煤灰加固力学特性。考虑水灰比、水泥粉煤灰混合固化剂掺量、粉煤灰掺量的变化对固化土无侧限抗压强度的影响,建立固化土强度-龄期一系列函数公式。研究显示:水泥起到提高固化土强度的主要作用,粉煤灰的掺量应有所限制;对于不同的混合固化剂配比,有各自的最佳水灰比。水灰比小于0.5,加大混合固化剂掺量不能显著提高固化土强度。广州南沙软土采用水泥粉煤灰搅拌桩加固,混合固化剂掺量取15%~18%,粉煤灰掺量取20%~30%,水灰比取0.53左右,比较合理。     

快硬硫铝酸盐水泥混凝土强度与灰水比关系公式的试验研究

根据试验结果所建立的强度与灰水比关系公式。并对该公式进行了综合分析和比较。     

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。     

水泥粉喷桩桩体水泥黑土力学性质试验研究

根据原状黑土、不同水泥掺入比和养护龄期人工配制的水泥黑土试块、水泥粉喷桩桩体钻芯试件的物理力学性质测试数据以及水泥黑土X射线衍射 (XRD)和扫描电镜 (SEM)测试结果 ,分析了水泥粉喷桩桩体水泥黑土无侧限抗压强度和模量随水泥掺入比及养护龄期的变化规律、水泥黑土强度形成机理以及室内外水泥黑土无侧限抗压强度相关关系 ,提出了水泥粉喷桩桩体水泥黑土的水泥掺入比建议值     

低掺量水泥土物理力学特性试验研究

通过界限含水量试验研究了不同掺量水泥对水泥土液、塑限的影响,利用无侧限抗压强度实验研究了水泥土在饱水养生条件下的强度特性,并得出了一些对工程有益的结论。     

Utilization of carbide slag-activated ground granulated blastfurnace slag to treat gypseous soil

Treating gypseous soils with lime or cement may induce remarkable swelling, resulting in the deterioration of pavement subgrade or other foundation layers. To mitigate this swelling, two industry by-products, carbide slag (CS) and ground granulated blastfurnace slag (GGBS), were utilized in this study. The CS was used to activate the GGBS, which was used to treat an artificial gypseous soil with different binder contents and CS:GGBS ratios, compared to ordinary Portland cement. The treated soils were soaked after a 7-day curing period. A series of tests was performed to examine the properties of the treated soils, including swelling, strength, water content, X-ray diffraction (XRD), scanning electron microscopy (SEM), and mercury intrusion porosimetry (MIP). It was found that the CS-GGBS-treated soils experienced slightly higher swelling (0.2%–1.0%) than the cement-treated soils (0.1%–0.3%) during the 7-day curing period. However, the following soaking process significantly increased the swelling of the cement-treated soils (>5.0%), caused cracks on the specimen surface, and reduced the strength, whilst the swelling of the CS-GGBS-treated soils after soaking was much lower (<0.3%), no cracks were observed, and the decrease in the soaking-induced strength was much less. The XRD, SEM, and MIP results indicated that the formation of ettringite was primarily responsible for the swelling. For the CS-GGBS-treated soils, the activation of GGBS and the formation of ettringite at an early age (within 7 days) rapidly consumed the Ca(OH)₂ in the CS; and hence, the further formation of ettringite after soaking was very limited. For the cement-treated soils, the cement hydration continuously supplied Ca(OH)₂ for the ettringite formation until completion, resulting in longer and higher swelling after soaking.