偏高岭土协同石灰钝化红黏土水敏性的机制

红黏土水敏性强,添加石灰等碱性材料处治后,能获得即刻的改良效果,但由于红黏土呈弱酸性,石灰改良后其长期性能会衰减。为提高石灰稳定红黏土（简称La+L）的长期性能,添加偏高岭土（4%）协同石灰（5%）稳定红黏土（简称La+L+MK）,改善其水敏性和酸?碱互损作用。制备8种初始含水率的压实试样（初始孔隙比相同）,养护到预定时间后开展无侧限抗压强度试验,同时,测定试样的钙离子浓度、电导率和pH值。结果表明：初始含水率为26%左右时,改良土的无侧限抗压强度最高,初始含水率偏高或偏低都不利于改良土的强度增长。究其原因,试样偏干时,缺少水分,石灰水化不充分,不能形成游离态钙离子,无法进行火山灰反应,颗粒之间无法形成胶结;试样偏湿时,火山灰反应形成的胶结强度不及过量水分引起的基质吸力丧失量。试样的钙离子浓度和电导率变化规律,证实了以上原因解释的猜想。当然,添加偏高岭土后,能够显著改善偏湿状态下的石灰土强度。即使浸水饱和后,相对石灰改良土,也能够保持较高的强度,充分证明偏高岭土能够有效降低石灰土水敏性,提高其耐久性。偏高岭土直接提供了大量硅、铝氧化物,且将土体pH值降到有利于硅、铝氧化物溶解的碱性范围,加速火山灰反应,缓减或抑制石灰?红黏土的互损作用。     

Compressibility behaviour of lime-stabilized clay

Lime stabilization reactions result in the formation of inter-particle cementation bonds that improves strength and reduce compressibility of clay soils. Though several studies in the past have focused on the impact of lime stabilization on the strength behaviour, few studies have examined the impact of lime stabilization on the compressibility behaviour of clay soils. The present study examines the compressibility behaviour of lime-stabilized soils in light of the frameworks proposed for saturated cemented clays. Cementation bonds formed during the lime stabilization reactions imparted yield stress in the range of 3900–5200 kPa to the artificially cemented specimens. The compression behaviour of these artificially cemented specimens in the pre-yield stress and post-yield stress regions conformed to the framework proposed for saturated cemented soils.     

用石灰粉煤灰稳定煤矸石的初步研究

煤矸石是一种特殊的软质粗粒土,在中国堆存达70亿吨,年增加1.5亿吨。若煤矸石用做道路基层材料可行,则有助于减少煤矸石占地,降低污染环境。为此,拟定了10种不同配合比,进行了石灰粉煤灰综合稳定试验,测试了煤矸石混合料的无侧限抗压强度、抗压回弹模量及温缩系数等指标,并进行了分析,得到了石灰粉煤灰比为1：2及二灰含量约为30 %的初步配合比。结果显示煤矸石可以用于低等级道路基层和高等级道路底基层。     

改良膨胀土筑堤技术研究

利用改良膨胀土作为高速公路路堤填筑材料是宁淮高速公路需要解决的主要问题。尽管室内试验论证可以用石灰改良膨胀土性质,但现场石灰改良土施工还要解决三大问题：石灰拌和均匀性和石灰含量的检测问题、现场压实方法和压实度控制问题、现场压实改良土的胀缩性和强度是否满足高等级公路路床和路基的要求问题。结合宁淮高速公路先导段施工,设计了试验段进行现场试验。试验结果表明,通过合理的施工工艺、有力的质量控制,改良膨胀土能够满足设计要求。改良土已经不具有膨胀土性质,胀缩性低,CBR强度高,是良好的路堤填筑材料。     

水氯镁石-石灰乳沉淀法制备氢氧化镁工艺优化

就石灰乳-水氯镁石沉淀法制备氢氧化镁工艺进行了总结,在前人研究工作的基础上,探讨了沉淀反应温度、晶种添加量、沉淀反应搅拌速度等工艺条件对氢氧化镁沉淀品质及性能的影响,给出了试验结果;并对已有工艺条件进行了优化,使得到的氢氧化镁具有较好的粒度和纯度,改进后的工艺有较好的工业前景和利用价值。     

Sulphate Attack in Lime-Treated Marine Clay

ABSTRACT

The use of lime to improve the properties of soft clays is not new. Recently the deep lime mixing technique has been extended to coastal regions for improving the behavior of weak marine clays. But lime treatment technique should be approached carefully for clay containing a high percentage of sodium sulphate. The presence of sulphate in lime-treated clays may result in high swelling due to the formation of the expansive mineral, ettringite. A limited study of lime-treated marine clays has shown a need to further explore the formation of ettringite and its stability with time. In this article, a laboratory investigation was carried out to examine the influence of sodium and calcium sulphates on the behavior of lime column treated marine clay. Scanning electron microscopy (SEM) was used to identify the formation of various reaction products, including ettringite. Test results indicate that the formation of ettringite in the lime-sodium sulphate-clay system adversely affects the engineering behavior of the marine clay, whereas the addition of calcium sulphate significantly improves the engineering characteristics of the soil.     

Coastal Pollution Mitigation with Lime and Zero Valent Iron

The Taiwan Strait region has many miles of coastline, and the Taiwan Straits Tunnel (TST) project faces many potential pollution problems as construction proceeds through sensitive areas. Conventional approaches for pollution mitigation require further examination. The recent development of nanoscale particle technology has shown distinct advantages for contaminant attenuation and ground improvement. This paper is focused on trace metals and is part of the overall effort to develop the nanoscale particle technology. Trace metals in ground and surface waters represent a continued threat to human and ecological health. One of the difficulties in removing toxic concentrations of trace metals from solution is the variable oxidation state and amphoteric nature of multiple constituents. In particular, while cationic metals (e.g., Pb²⁺, Cd²⁺, Ni²⁺) may be rendered less mobile under high pH conditions, anionic metals (e.g., AsO₄ ^3?, CrO₄ ^2?, SeO₄ ^2?)may become more mobile. The objective of this research was to evaluate the sorption of both cationic and anionic trace elements, including arsenic (As), cadmium (Cd), chromium (Cr) and selenium (Se) under batch conditions. Mixtures of a local residual soil were tested alone and in combination with lime and zero valent iron. It was hypothesized that lime would raise the pH and precipitate positively charged metals while zero valent iron would create reducing conditions favorable to the immobilization of negatively charged metals. Results indicate that the use of lime and/or zero valent iron can increase the sorption capacity of soil. Compared to the baseline soil, sorption capacity increased with addition of lime for arsenic and cadmium while it decreased for chromium and selenium. In the case of zero valent iron addition, sorption capacity increased for cadmium, chromium and selenium, while showing no change for arsenic. When both lime and zero valent iron were used, the sorption capacity increased for all metals tested. These results suggest that the combined use of lime and zero valent iron may serve as an alternative treatment technology for removing trace metals from contaminated water systems.     

Effect of Pollutants on the Physical and Engineering Behavior of Lime-Treated Marine Clay

Abstract

Rapid industrial growth and increasing population has resulted in the discharge of wastes into the ocean, wastes which ultimately reach the seabed and contaminate the marine sediments. The soil-contaminants interaction, and their associated physico chemical properties with sediments control the behavior of marine clays. Marine clay deposits of low strength and high compressibility are located in many coastal and offshore areas. There are several foundation problems encountered in these weak marine clays. In this study, experimental work was carried out in the laboratory to stabilize soft marine clays using the lime column technique. Also the lime-induced effects on the physical and engineering behavior of marine clays in sulfate-contaminated marine environment was investigated. Consolidation tests indicate that compressibility of the lime-treated samples was reduced to 1/2–1/3 of the virgin soil after 45 days treatment. The test results also suggest that the lime column technique can be conveniently used to improve the behavior of contaminated marine clay deposits.     

Lime Stabilization of Soils Underlying a Salt Evaporation Pond: A Laboratory Study

The purpose of this article is to investigate a possible use of lime for the stabilization of base soils underlying salt evaporation ponds in Çamalt? Solar Marine Salt Plant. The plant is located on the old Gediz River Delta, on the north shore of the Izmir Bay-Turkey, where alluvial deltaic soft marine sediments constitute the local soil condition. The low bearing capacity of the pond base soils results in some problems on the mechanical harvest of the solar salt. Therefore, stabilization was taken into consideration for improving the productivity of the salt plant. For this purpose, bench-scale laboratory tests were performed on the specimens that had been sampled from the bases of the salt evaporation pond to investigate the influence of lime on the unconfined compressive strength (UCS) of these marine sediments. By interpreting the pH test results and consistency limits of the lime stabilized soils, optimum lime content was determined as 8%. The verification of the long-term pozzolanic reactions for the optimum lime content was conducted by performing UCS tests with up to six months curing periods, along with the microstructural analysis through X-ray diffraction analysis (XRD) and a scanning electron microscope (SEM). Long-term tests revealed that the optimum lime content successfully sustained the required pozzolanic reactions, and a strength gain of 500% was achieved for a six-month curing period.     

含盐量对石灰固化滨海盐渍土稠度和击实性能的影响

随着含盐量的增加,滨海盐渍土中的盐分结晶形成了更多的盐颗粒,使石灰固化土的稠度指标发生变化,总体上分阶段逐渐下降。含盐量的增加使得石灰固化土的不均匀系数增大,且随着养护龄期的增加而增大。增加土的含盐量,则石灰固化土悬液的电导率随之增加,但电导率几乎不随养护龄期而变化,这表明氯盐没有参与石灰的固化反应,只是吸附在土颗粒的表面或存在土孔隙中,石灰固化后的盐渍土仍然具有一定的吸湿软化性。重型击实试验结果证实,增加含盐量使石灰土混合料的最大干密度略有降低,最优含水率则几乎不变,因此,施工中可不考虑含盐量对石灰固化滨海盐渍土现场碾压效果的影响。