吸力对非饱和膨胀土抗剪强度及剪胀特性的影响

利用非饱和土直剪仪进行原状样和压实样的控制吸力直剪试验以研究吸力对非饱和膨胀土抗剪强度和剪胀性状的影响。试验结果表明:该膨胀土原状样和压实样的剪胀势随着吸力增加而增大。吸力对该膨胀土抗剪强度的贡献可归结于两种不同的机理:①吸力使得土体中粒间有效应力增加;②吸力对土体剪胀势的贡献。由于吸力对土体剪胀势的贡献,吸力对该膨胀土峰值强度的贡献大于其对峰后软化强度的贡献。当吸力相同时,原状样的峰值强度和剪胀势均高于压实样,这与原状样中铁锰结核的胶结作用有关。吸力对该膨胀土抗剪强度的贡献高于压实高岭土。     

微生物对膨胀土自由膨胀率的研究

地球表面的土体里含有丰富活跃的微生物,是地质环境中重要的组成部分.采用混合平板法从膨胀土和农田土壤中分离出菌株,制成固体菌剂.利用自由膨胀率试验,对接入不同菌剂并经不同时间培养的膨胀土进行测试.结果表明,加入微生物菌剂后膨胀土的自由膨胀率有明显改善,由原来的70％降低至48％,降幅达32％,将膨胀土由中等膨胀土变为弱膨胀土.     

Analysis of strength development in cement-stabilized silty clay from microstructural considerations

This paper analyzes the strength development in cement-stabilized silty clay based on microstructural considerations. A qualitative and quantitative study on the microstructure is carried out using a scanning electron microscope, mercury intrusion pore size distribution measurements, and thermal gravity analysis. Three influential factors in this investigation are water content, curing time, and cement content. Cement stabilization improves the soil structure by increasing inter-cluster cementation bonding and reducing the pore space. As the cement content increases for a given water content, three zones of improvement are observed: active, inert and deterioration zones. The active zone is the most effective for stabilization where the cementitious products increase with cement content and fill the pore space. In the active zone, the effective mixing state is achieved when the water content is 1.2 times the optimum water content. In this state, the strength is the greatest because of the highest quantity of cementitious products. In the short stabilization period, the volume of large pores (larger than 0.1 μm) increases because of the input of coarser particles (unhydrated cement particles) while the volume of small pores (smaller than 0.1 μm) decreases because of the solidification of the cement gel (hydrated cement). With time, the large pores are filled with the cementitious products; thus, the small pore volume increases, and the total pore volume decreases. This causes the strength development over time.     

Effect of electric arc furnace dust on the properties of OPC and blended cement concretes

This paper presents results of a study conducted to evaluate the mechanical properties and durability characteristics of ordinary Portland cement (OPC) and blended cement (silica fume and fly ash) concrete specimens prepared with electric arc furnace dust (EAFD). Concrete specimens were prepared with and without EAFD. In the silica fume cement concrete, silica fume constituted 8% of the total cementitious material while fly ash cement concrete contained 30% fly ash. EAFD was added as 2% replacement of cement in the OPC concrete and 2% replacement of the total cementitious content in the blended cement concretes. Mechanical properties, such as compressive strength, drying shrinkage, initial and final setting time, and slump retention were determined. The durability characteristics were evaluated by measuring water absorption, chloride permeability, and reinforcement corrosion. The initial and final setting time and slump retention increased due to the incorporation of EAFD in both OPC and blended cement concretes. The drying shrinkage of EAFD cement concrete specimens was more than that of concrete specimens without EAFD. The incorporation of EAFD was beneficial to OPC concrete in terms of strength gain while such a gain was not noted in the blended cement concretes. However, the strength differential between the blended cement concretes with EAFD and the corresponding concretes without EAFD was not that significant. The water absorption and chloride permeability, however, decreased due to the incorporation of EAFD in both the OPC and blended cement concretes. The corrosion resistance of OPC and blended cement concrete specimens increased due to the addition of EAFD.     

Influence of applying overburden stress during curing on the unconfined compressive strength of cement-stabilized clay

In the case of cement-stabilized soils cured under the influence of overburden stress, it is necessary to consider two different timelines of cementation and consolidation, along which the structures of stabilized soils evolve. These two timelines are interrelated and ought not to be considered separately, especially in the early stage of curing when significant structural changes occur. In this study, the strength and deformation characteristics of cement-stabilized clay subjected to overburden stress during curing was investigated using an unconfined compression test apparatus. For this purpose, three types of specimens were prepared by stabilizing very soft clay with different amounts of cement. Overburden stress was applied for three different time durations during curing. In the series of unconfined compression tests conducted on the specimens with no overburden stress applied during curing, the axial stress initially increases rapidly, then was maintained before finally dropping. In the series of tests with overburden stress applied during curing, the axial stress continues to increase gradually before rapidly declining. The values of unconfined compressive strength are larger for the specimens subjected to overburden stress during curing. The values of the unconfined compressive strength also increase linearly as the duration of applied overburden stress increases. The increase in strength apparently occurs due to increasing dry density accompanied by a decrease in the water content due to the drainage of pore water during the application of overburden stress.     

非饱和膨胀土变形和强度特性的三轴试验研究

为了研究吸力变化对非饱和膨胀土变形和抗剪强度特性的影响,利用三套新研制的双压力室非饱和土三轴仪,进行一系列吸湿试验、等吸力压缩固结试验和等吸力剪切试验。试验土样取自鄂西北的中膨胀性土,采用静力压实方法制备试样。试验成果表明:该非饱和膨胀土在低围压吸湿过程中的体变性状呈明显的屈服特性,因此验证了Barcelona膨胀土本构模型中SD屈服包线的存在。在等向压缩固结过程中,该非饱和膨胀土的屈服应力随吸力增加而增大,而屈服后的压缩系数随吸力增大而减少,表明吸力对土体具有硬化作用。该非饱和膨胀土的有效内摩擦角不随吸力变化而变化,吸力对抗剪强度的贡献(似凝聚力)随吸力呈非线性增加,吸力对该膨胀土抗剪强度的贡献明显高于压实高岭土和砂性土。     

击实膨胀土的循环膨胀特性研究

主要研究了干湿循环对击实膨胀土胀缩特性的影响。研究结果表明,击实膨胀土的胀缩变形并不是完全可逆的,随干湿循环的发展,膨胀土的膨胀速率加快,绝对膨胀率总是增大而相对膨胀率则降低。这种变化在第Ⅱ、Ⅲ级循环时最明显,第Ⅲ级循环后便趋于稳定。这些变化特性主要是粘粒集聚、微结构改变的结果。     

细度对电炉钢渣活性指数的影响

通过试验研究电炉钢渣(熔炼渣和精炼渣)细度与活性的关系.研究表明:无论是熔炼渣还是精炼渣,活性指数都随钢渣细度增加而显著增加.能够满足GB/T20491-2006{(用于水泥和混凝土中的钢渣粉>中规定的Ⅱ级钢渣活性指数要求.电炉精炼渣并没有表现出比熔炼渣更高的活性,两者的活性指数-比表面积关系曲线几乎重合.     

Hydromechanical behavior of unsaturated expansive clay under repetitive loading

Compacted layers of expansive soils are used in different engineering projects,such as subgrades,engineered clay barriers,and buffers for radioactive waste disposal.These layers are exposed to a variety of stresses and wetting conditions during field serviceability.Coupling between hydraulic and mechanical repeated loading provides insight understanding to the induced progressive deformation of expansive clay.This study was conducted to investigate the hydromechanical behavior of unsaturated compacted expansive clay under repeated loadingeunloading (RLU) conditions.Two series of onedimensional (1D) oedometer tests were conducted under controlled matric suction up to 1500 k Pa using the axis translation technique (Fredlund soil-water characteristic curve device,SWC-150).The first test series was carried out at different levels of controlled matric suction for non-repeated loading eunloading (NRLU) cycles.RLU cycles were applied in the second test series at different repetitivestress levels and under different levels of matric suction.The results indicated increasing axial wetting strain ε_a(s),axial swell pressure s_s(s),compression index C_c(s),and swell index C_s(s) with suction reduction.The estimated loadecollapse (LC) curves obtained from NRLU series (LCN) and RLU series (LCR)indicated increasing yield stress s_y(s) with increasing suction.This is attributed to the developed apparent cohesion between soil particles,which in turn rigidifies the material response.Applying repetitive loading induced a notable reduction of compression index C_c(s) at the same level of suction,whereas swell index C_s(s) seems to be independent of repetitive loading.Finally,repetitive loading exceeding initial yield stresses results in plastic hardening and,hence,enlargement of yield stress locus(i.e.LC_R curve).     

Effect of grain size on the strength characteristics of cement-stabilized lateritic soils

Lateritic soils are readily available all over Nigeria and as such have attracterd several research studies in recent times, the obvious aim being its utilization in the construction industry. This paper gives an account of the work done to further classify the usefulness and limitations of lateritic soils.Cement was used as the stabilizer and the lateritic soils used were obtained from the Ifewara deposits located about 10 km along Ife-Ifewara Road. A sieve analysis of the sample was made. Five different grain size ranges, from coarse to fine, were extracted from the samples. Cubes were moulded by mixing each grain size range with cement in five different proportions, the optimum water/cement ratio of each mix proportion being determined beforehand. The compressive strengths of the cubes were determined after 7, 21, and 28 days of curing in water, respectively. It was established that the higher the laterite/cement ratio, the lesser the compressive strength, and that the finer the grain size range, the higher the compressive strength. Finally, it was observed that cubes made using laterite/cement mix proportions 1:1 and 3:1 kept gaining strength with age while the others were losing strength.     

邯郸强膨胀土三向膨胀力特性试验研究

对在不同干密度、初始含水率、温度下的邯郸强膨胀土和复合改性后的膨胀土进行三向膨胀力试验研究。结果表明,在试验条件范围(干密度:1.2,1.35,1.5,1.65 g/cm~3;初始含水率:15%,18%,21%,24%;温度:20℃,35℃,45℃,55℃,65℃)内,竖向与水平向膨胀力的比值随干密度增加而增加,干密度等于1.2g/cm~3时,比值接近1;干密度是决定平衡时间的关键因素,干密度越大的试样膨胀平衡时间越长,且所有试样平衡时间都在3000 min内;在室内常温(20℃左右)和初始含水率相同时,竖向膨胀力随干密度呈指数关系递增;相同温度和干密度下,随着初始含水率增加,三向膨胀力皆呈线性减小的规律,且三向膨胀力与初始含水率关系曲线的斜率随干密度线性递增;经过0.8%PVA(聚乙烯醇)+5%KCl(氯化钾)的混合溶液改性,并添加0.6%聚丙烯纤维后的土样竖向膨胀力下降33.3%,0.8%PVA+4%CaO(氧化钙)的混合溶液改性的土样竖向膨胀力下降16.7%。未改性和经过0.8%PVA+4%CaO的混合溶液改性的土样竖向膨胀力随着温度的升高而减小,经过0.8%PVA+5%KCl的混合溶液改性,并添加0.6%聚丙烯纤维后的土样随着温度升高竖向膨胀力先增加,温度大于45℃后逐渐减小。     

脱湿状态对膨胀土膨胀变形和强度特性的影响

非饱和膨胀土的脱湿状态对土中水分散失速率影响较大,不同的脱湿速率又会使膨胀土呈现不同的工程性状。通过控制恒温恒湿箱的温湿度工作参数,设置不同的脱湿环境制备土样,进行土工试验,深入认识脱湿状态对膨胀土膨胀变形和抗剪强度的影响。将饱和土样脱湿到设定的不同含水率,进行有荷载膨胀率试验,结果表明:在相对湿度越大的环境下,脱湿速率越小,土体膨胀率越大;起始含水率和上部荷载越小,土体膨胀变形越大。将不同起始含水率的土样膨胀完全后放入直剪仪,进行固结直剪试验,结果表明:脱湿到不同含水率的试样,脱湿速率越小,土体越密实膨胀后的抗剪强度越大;上部荷载存在可提高土体的抗剪强度,起始含水率越小上部荷载越大土样的抗剪强度越高。研究结果可为大气作用下膨胀土边坡的防护设计提供参考,有助于对自然气候环境下膨胀土边坡的灾变进行预警,并可优化膨胀土边坡的施工方案。     

Phosphorus removal by electric arc furnace steel slag and serpentinite

Electric arc furnace (EAF) steel slag and serpentinite were tested in columns either alone or mixed with limestone to determine their capacity to remove phosphorus (P) from a solution containing initially 20mg P/L (for 114 days) than 400mg P/L (for 21 days). EAF steel slag was nearly 100% efficient due to specific P adsorption onto metal hydroxides and precipitation of hydroxyapatite. Serpentinite also showed a good performance that decreased with time, adsorption appearing to be the dominant mechanism for P removal. Mixing limestone with these two materials did not improve their performance and in the case of serpentinite, it actually even decreased it. In 114 days of experimentation, serpentinite alone and the mixture of serpentinite and limestone removed 1.0mg P/g while in 180 days of experimentation, EAF steel slag and the mixture of slag and limestone removed an average of 2.2mg P/g, without attaining their maximum P removal potential. The void hydraulic retention time (HRTv) was a key factor for growing hydroxyapatite crystals and had a significant effect on P removal efficiency by EAF steel slag. A temporary increase in HRTv caused by clogging resulted in an increase in EAF steel slag efficiency (from 80% to almost 100%) towards the end of investigation. Results from this study indicate that the use of EAF steel slag in constructed wetlands or filter beds is a promising solution for P removal via adsorption and precipitation mechanisms.     

浅谈水泥稳定土强度的影响因素

论述了水泥稳定土所能达到的强度和水稳性之间的关系 ,指出其强度是随着原土的组成以及水泥类型和用量而发生较大的变化 ,对它的影响因素进行了分析和探讨。     

高含水率疏浚淤泥平板贯入剪切强度试验研究

针对中国缺乏高含水率疏浚淤泥不排水强度的有效测试方法的现状,引进了Tan课题组提出的平板贯入剪切试验方法,对分布于中国不同地区的3种疏浚淤泥进行了系列平板贯入剪切试验,分析了加载速率对不排水强度测试结果的影响以及贯入深度随贯入时间的变化规律,完善了平板贯入剪切试验测试方法。基于平板贯入剪切试验数据,分析了疏浚淤泥的不排水强度性状和主要影响因素,导入含水率与液限之比对各种疏浚淤泥的不排水强度进行归一化分析,验证了平板贯入剪切试验测试方法的有效性,为该测试方法应用于中国疏浚淤泥的强度测试奠定了基础。     

Mix design and performance analysis of asphalt concretes with electric arc furnace slag

The paper presents the results of a laboratory study, aimed at verifying the possibility to use two particular typologies of electric arc furnace (EAF) steel slags, in substitution of the natural aggregates, in the composition of wearing course asphalt concrete for flexible pavements. The experimental research has been articulated in a preliminary study of the chemical, leaching, physical, and mechanical properties of the EAF steel slag, and in the following mix design and performance characterisation of the bituminous conglomerates, through gyratory compaction tests, permanent deformations tests, Stiffness Modulus tests at various temperatures, fatigue tests and indirect tensile strength tests. All the mixtures with EAF slag have satisfied the requisites for acceptance in the road sector technical standards, thus resulting as suitable for use in the construction of road infrastructures, moreover presenting higher mechanical characteristics than those of the corresponding asphalts with full natural aggregate.     

碱性氧化剂对水泥固化淤泥强度的影响研究

为消除淤泥中有机质对水泥固化淤泥的不利影响,提出了氧化降解有机质、减薄双电层厚度、维持pH值稳定等对策来提高水泥固化淤泥的强度。采用高铁酸钾和碳酸氢钠作为碱性氧化剂,配合水泥对淤泥进行固化处理。通过无侧限抗压强度试验,初步了解碱性氧化剂对水泥固化淤泥强度的影响规律,并利用有机元素试验、动电电位试验、比表面积试验和SEM等手段,进一步探究碱性氧化剂的固化机理。研究结果表明:掺碱性氧化剂的水泥固化淤泥7d无侧限抗压强度达到了1.536 MPa。碳酸氢钠通过中和有机酸,维持水泥固化淤泥为p H=9～10的碱性环境;该条件下,高铁酸钾能高效降解有机质,除去黏土颗粒表面聚合态的有机质胶膜,有利于SiO_2与Al_2O_3游离于孔隙溶液中,促进水泥水化产物的生成。同时,孔隙溶液中游离的高价阳离子与黏土颗粒表面低价阳离子交换吸附,减薄双电层厚度,引起土颗粒的絮凝团聚。     

水泥改性黄土的抗液化特性与机制

以改性处理减轻饱和黄土的液化势为目标,通过对不同配比的水泥改性黄土进行SEM细观结构测试和动三轴液化试验,研究了水泥改性黄土的液化特征,得出了不同配比水泥改性黄土的动残余应变和动孔隙水压力发展趋势,分析了水泥固化饱和黄土的物化机制,并基于试验结果,提出了水泥改性黄土的最佳配比。结果表明:水泥改性处理在黄土中形成了凝块状胶接结构,优化了土中孔隙分布,增大了土体的结构强度;水泥对土体的密实效应、掺加水泥导致的细粒增加和离子交换对黄土结构的胶结效应和黏粒增加对土中游离水的吸附作用共同提高了水泥改性黄土地基的抗液化稳定性;水泥掺量大于3%后,水泥改性黄土的动残余应变和孔隙水压力随着振次的增加均增长缓慢,且在m=5%时峰值最小,表明5%是水泥改性黄土地基抗液化处理的最佳配比。     

地聚合物对水泥固化土强度的影响及其机理分析

采用无侧限抗压强度、电镜扫描(SEM)和压汞(MIP)等试验方法,分析研究了地聚合物—偏高岭土(metakaolin)对水泥土的力学强度的影响规律,探讨了其改善水泥土强度的机理,并根据现场测试验证了实用性和经济性。试验结果表明:地聚合物掺入水泥土后,水泥土的无侧限抗压强度得到了大幅度的提高,然而强度与地聚合物掺量之间并非单一线性增加关系,而是由活性区域和惰性区域组成,转折点对应的MK掺量为3%;微观试验结果表明地聚合物掺入能产生更多的胶结物,使水泥土结构更加致密;基于试验数据给出了地聚合物掺量与水泥土强度增长的评价公式。现场测试结果和工程造价分析均表明了地聚合物具有较大的工程实用性。