水泥改良软土次固结变形特性试验研究_贺建清.pdf

第 20 卷 第 3 期2023 年 3 月铁道科学与工程学报Journal of Railway Science and EngineeringVolume 20 Number 3March 2023水泥改良软土次固结变形特性试验研究贺建清1,2，任虎程2，胡惠华3，吴昊天2，王朦2(1.水能资源利用关键技术湖南省重点实验室，湖南 长沙 410014；2.湖南科技大学 岩土工程稳定控制与健康监测省重点实验室，湖南 湘潭 411201；3.湖南省交通规划勘察设计院有限公司，湖南 长沙 410200)摘要：人工配制不同水泥掺量的水泥土，进行一维固结蠕变试验，研究水泥掺量对水泥土次固结特性的影响；测定水泥土吸附结合水含量，确定吸附结合水含量与水泥掺量的关系，探究水泥对软土次固结特性的影响机制。研究结果表明，水泥土的结构强度随着水泥掺入比的增加而增大，水泥掺入比低于10%，其增速缓慢；超过10%，增速明显。水泥土的主固结时间几乎不受固结压力影响，随着水泥掺入比增大明显减小。水泥改良软土的次固结系数C与固结压力p的关系曲线在结构强度附近存在峰值点，起始阶段，次固结系数随着固结压力增加逐渐增大；超过峰值后，随着固结压力增加先是明显减小，最后逐渐趋近于基本不再变化的常数。施加的固结压力低于水泥土的结构强度时，e-lg t关系曲线近似呈直线，主、次固结界限模糊，主、次固结划分点难以确定；超过水泥土的结构强度时，e-lg t关系曲线呈反S形，固结压力越大，线形特征越明显，主、次固结分界点越清晰。水泥土的次固结系数C与压缩指数Cc的比值近似为一常数，水泥土的C/Cc值明显低于原状土，几乎不到原状土C/Cc值的一半，C/Cc值与水泥掺入比aw呈线性递减关系。水泥土的吸附结合水含量Wg与水泥掺入比aw呈良好的线性递减关系，水泥掺量增加，吸附结合水含量变小，结合水膜变薄，流变相物质体积占比相应减少，改良后的软土随着流变相物质的减少，整体性质呈现出次固结特性变弱的趋势。关键词：软土；水泥土；水泥掺入比；次固结特性；影响机制中图分类号：TU43 文献标志码：A 文章编号：1672-7029（2023）03-0941-09Experimental study on secondary consolidation deformation characteristics of cement modified soft soilHE Jianqing1,2,REN Hucheng2,HU Huihua3,WU Haotian2,WANG Meng2(1.Hunan Provincial Key Laboratory of Hydropower Development Key Technology,Changsha 410014，China;2.Hunan Provincial Key Laboratory of Geotechnical Engineering for Stability Control and Health Monitoring,Hunan University of Science and Technology,Xiangtan 411201,China;3.Hunan Provincial Communications Planning,Survey&Design Institute Co.,Ltd.,Changsha 410200,China)Abstract:Cement soils with different cement contents were artificially prepared.One-dimensional consolidation 收稿日期：2022-04-01基金项目：国家自然科学基金资助项目(52078211)；湖南省自然科学基金资助项目(2021JJ30252)；湖南省重点实验室开放基金资助项目(PKLHD201903)通信作者：贺建清(1964)，男，湖南湘乡人，教授，博士，从事土力学与地基基础方面的科研与教学工作；Email：DOI:10.19713/ki.43-1423/u.T20220632铁 道 科 学 与 工 程 学 报2023 年 3月creep test was carried out to study the influence of cement content on the secondary consolidation characteristics of cement soil.The adsorbed bound water content of cement soil was measured.The relationship between adsorbed bound water content and cement content was determined to explore the influence mechanism of cement on the secondary consolidation characteristics of soft soil.The results show that the structural strength of cement soil increases with the increase of cement mixing ratio.The growth rate is slow when the cement mixture ratio is less than 10%.When cement is added more than 10%,the growth rate is obvious.The main consolidation time of cement soil is almost not affected by the consolidation pressure,and decreases significantly with the increase of cement mixing ratio.Besides,the relationship curve between secondary consolidation coefficient C and consolidation pressure p of cement-improved soft soil has a peak point near the structural strength,at the initial stage,the secondary consolidation coefficient increases gradually with the increase of consolidation pressure.When the peak value is exceeded,with the increase of consolidation pressure,the consolidation pressure decreases significantly at first and then gradually approaches a constant which is almost unchanged.In addition,when the applied consolidation pressure is lower than the structural strength of cement soil,the e-lg t curve is approximately linear,the boundary of primary and secondary consolidation is fuzzy.The division point of primary and secondary consolidation is difficult to determine.When it exceeds the structural strength of cement soil,the e-lg t relationship curve is anti-S-shaped.At this time,the greater the consolidation pressure is,the more obvious the linear characteristics are,the clearer the demarcation point between primary and secondary consolidation.Moreover,the ratio of secondary consolidation coefficient C to compression index Cc of cement soil is approximately a constant,which is almost half of the C/Cc value of undisturbed soil.The C/Cc value decreases linearly with the cement mixing ratio aw.Furthermore,the adsorbed bound water content Wg of the cement soil shows a good linear decreasing relationship with the cement incorporation ratio aw.With the increase of cement content,the content of adsorbed bound water becomes smaller,the bound water film becomes thinner,and the proportion of the volume of the rheological phase material decreases accordingly,the overall properties of the improved soft soil show a trend of weakening the secondary consolidation characteristics with the decrease of the rheological phase material.Key words:soft soil;cement soil;cement mixture ratio;secondary consolidation characteristics;influence mechanism 软土地基广泛分布在沿海、河流两岸及湖泊地区。在软土地基上直接修建建(构)筑物，易出现由土体次固结引起的工后沉降，严重影响建(构)筑物的正常使用。次固结是指受压土体在超静孔隙水压力消散后由于土粒表面结合水膜的蠕变、土粒结构的重新排列等因素所引起的变形随时间长期变化的过程12。利用超载预压法克服软土次固结变形是目前控制软土地基工后沉降相对经济、有效的处理措施，在某种意义上，是一种物理处理方法3。除此之外，工程实际中常通过在软土中掺入水泥或石灰等材料进行化学改性，以达到提高软土地基承载力、减少沉降的目的。深层水泥搅拌桩(DCM)法因具有布桩灵活、施工技术成熟、造价经济等优点已被广泛应用于软土地基加固工程中。DCM法加固软土地基的主要目的如果是为了提高地基的承载力或者加固边坡，水泥掺量一般较高，水泥土的固结微不足道；如果是为控制建(构)筑物沉降变形，水泥掺量一般较低，水泥土复合地基的固结沉降不容忽视4。在以往的工程实践中，只考虑了水泥土地基的主固结沉降变形，忽略了次固结沉降变形，如软土地区桥头地基虽然进行