Influence of fines content on the anti-frost properties of coarse-grained soil

This paper aims to determine the optimal fines content of coarse-grained soil required to simultaneously achieve weaker frost susceptibility and better bearing capacity. We studied the frost susceptibility and strength properties of coarse-grained soil by means of frost heaving tests and static triaxial tests, and the results are as follows： （1） the freezing temperature of coarse-grained soil decreased gradually and then leveled off with incremental increases in the percent content of fines; （2） the fines content proved to be an important factor influencing the frost heave susceptibility and strength properties of coarse-grained soil. With incremental increases in the percent content of fines, the frost heave ratio increased gradually and the cohesion function of fines effectively enhanced the shear strength of coarse-grained soil before freeze-thaw, but the frost susceptibility of fines weakened the shear strength of coarse-grained soil after freeze-thaw; （3） with increasing numbers of freeze-thaw cycles, the shear strength of coarse-grained soil decreased and then stabilized after the ninth freeze-thaw cycle, and therefore the mechanical indexes of the ninth freeze-thaw cycle are recommended for the engi- neering design values; and （4） considering frost susceptibility and strength properties as a whole, the optimal fines content of 5% is recommended for railway sub,fade coarse-~rained soil fillings in frozen re^ions.

基于原型监测的分离式加筋土桥台工作性能数值分析

依托明巢高速公路分离式加筋土桥台工程原型监测,用FLAC2D软件建立桥台数值模型,并将数值模拟得到的桥台受力及变形情况与桥台原型监测结果进行对比验证.考虑到填料类型及其压实工序与填料力学性能的相关性,模拟分析了填料内摩擦角对加筋土桥台工作性能的影响.结果表明:随着填料内摩擦角的增大,分离式桥台的水平土压力和竖向土压力都有所减少,并且竖向位移、水平位移及筋材应变也有所减少;当填料内摩擦角增大到一定程度时,其对承载性能的优化作用有所减少;工程中选取加筋土填料时,根据现场施工情况确定填料的内摩擦角,并权衡工作性能及经济效益,做出合理的选择.

浅谈轻质填料在路基中的应用

为减少路基沉降,通常采用轻质填料填筑路堤,其中常用的填料有粉煤灰、土工泡沫塑料和泡沫轻质土。通过工程实例,介绍了这3种填料在路堤中的填筑方法,并结合不同路堤高度、不同填料的工后沉降量及工程造价,对工程设计方案进行了比选。

工程渣土再生填料长期浸水性能试验研究

工程渣土再生填料浸水条件下的性能衰减是一个复杂过程,分析掌握其衰减规律具有重要意义。通过浸水试验,研究了工程渣土再生填料试件在室内静荷载作用下,浸水时长7~360d范围内的抗压强度和质量变化。试验数据表明,浸水条件下,工程渣土再生填料保持了前期强度增长较快、后期平缓的增长趋势,同时试件完整性较好。综合来看,在长时间浸水条件下,工程渣土再生填料可保持良好的路用性能,符合沿海地区道路工程使用要求。

渗流作用下多级配土石混合填料的结构演化规律

渗流是引起土石混合填料中细颗粒流失,致使土体结构变化引起路基变形及失稳的关键因素。采用自行研发的颗粒流失试验装置,对不同级配的土石混合填料进行渗流试验,监测渗流作用下填料的透水质量、细颗粒流失量和沉降量的变化过程,分析土体结构演变过程;采用PFC^(3D)(Particle Flow Code in 3D)对细颗粒流失过程进行数值模拟,分析填料孔隙和粒径动态变化特性。研究结果表明:透水质量和细颗粒流失率可以反映土石混合填料结构对水分的敏感程度。填料骨架结构对水分的敏感程度越低,可及时有效地排出水分,渗流对结构的破坏越小。渗流条件下土石混合填料的结构演化过程可分为细颗粒快速流失、骨架重塑和相对稳定3个阶段,其中骨架重塑阶段是引起其结构演化的关键阶段。细颗粒快速流失阶段,每小时透水量增长速率较快,细颗粒大量流失,沉降量很小;骨架重塑阶段,每小时透水量变化速率减缓,细颗粒流失量减少,但骨架结构重组导致颗粒产生明显的相对位移,沉降量增长较快;相对稳定阶段,每小时透水量变化缓慢,沉降量基本保持不变。颗粒流失数值模拟的过程表明细颗粒组分的迁移引起填料孔隙率产生变化,致使土体结构发生改变。上述结果表明,在所研究的几种填料中,n=0.55级配下土石混合填料的骨架结构最稳定,对水分的敏感性最弱。

Numerical and experimental direct shear tests for coarse-grained soils

The presence of particles larger than the permissible dimensions of conventional laboratory specimens causes difficulty in the determination of shear strength of coarse-grained soils. In this research, the influence of particle size on shear strength of coarse-grained soils was investigated by resorting to experimental tests in different scale and numerical simulations based on discrete element method （DEM）. Experimental tests on such soil specimens were based on using the techniques designated as ＂parallel＂ and ＂scalping＂ to prepare gradation of samples in view of the limitation of laboratory specimen size. As a second approach, the direct shear test was numerically simulated on assemblies of elliptical particles. The behaviors of samples under experimental and numerical tests are presented and compared, indicating that the modification of sample gradation has a significant influence on the mechanical properties of coarse-grained soils. It is noted that the shear strengths of samples produced by the scalping method are higher than samples by the parallel method. The scalping method for preparing specimens for direct shear test is therefore recommended. The micromechanical behavior of assemblies under direct shear test is also discussed and the effects of stress level on sample behavior are investigated.

水泥粉煤灰改良粗粒土路基填料力学与收缩特性

河北省西北地区特殊气候环境下,经上部荷载作用基床底层收缩变形产生的裂隙向上扩展使得路基表层产生裂缝。针对这一问题,本文以该地区路基改良粗粒土填料为研究对象,分析其力学特性与收缩特性,并提出新的抗裂评价指标,综合评价填料工程适用性。结果表明:掺入粉煤灰后水泥改良填料力学性能降低,但填料拉压比增大;水泥掺量越低填料抗干缩性能越好,掺入粉煤灰填料抗干缩性能进一步改善,但粉煤灰存在最佳掺量;填料最大温缩应变随温度的循环逐渐增加,第3次温度循环后趋于平稳,填料对温度变化敏感度降低;从能量角度提出综合抗裂系数,得出水泥粉煤灰改良填料综合抗裂性优于水泥改良填料。

Using a modified direct shear apparatus to explore gap and size effects on shear resistance of coarse-grained soil

This work used a modified direct shear apparatus, created newly by the authors, to explore effects of the gap between shear box halves and specimen size on the shear resistance of coarse-grained soil. The shear boxes of this apparatus were assembled from a series of steel structures capable of superimposition and nesting. Such characteristics facilitated variation of specimen size in both diameter and height. The new device can also maintain a constant gap during shearing. We performed a series of gap-effect and size-effect tests for two uniformly graded, coarse^grained soil samples. The test results showed that both the gap space and specimen size bad significant influences on shear resistance of the coarse-grained soil. Further, analysis of variations in shear strength indices led to a reasonable gap dimension and specimen size of the two soil samples.

颗粒细长比对粗粒土填料振动压实特性的影响

本文旨在探究粗颗粒(粒径d>5 mm)细长比对粗粒土填料振动压实特性的影响机制,深入揭示粗粒土填料振动压实机理。首先,基于优化Viola-Jones算法建立颗粒形状采集系统,通过几何算法量化粗颗粒细长比;其次,基于自研智能振动压实仪,选择3组不同细长比的粗粒土填料,开展大型振动压实试验,并通过物理-力学指标揭示细长比与粗粒土压实特性之间的相关性;最后,建立振动压实离散元数值模型,并通过孔隙率、颗粒应力以及颗粒运动特性等细观指标揭示细长比对粗粒土填料压实特性的影响机制。研究结果表明:在振动压实过程中,存在最优细长比使粗粒土填料密度最大,粗粒土填料承载力随细长比增加而增加;在数值模型中,粗粒土填料内部孔隙率随细长比增加而减小;细长比越小,颗粒应力越集中,导致颗粒破碎现象越显著,同时,颗粒运动也越剧烈,其中,细颗粒运动位移比粗颗粒的大。

Experimental study on mechanical and frost heave behaviors of silty clay improved by polyvinyl alcohol and polypropylene fiber

Silty clay is widely used as subgrade filler in cold regions,which suffer from frost heave in winter and mud pumping in spring.In this study,polyvinyl alcohol(PVA)and polypropylene(PP)fiber were used to improve the mechanical and frost heave behavior of silty clay in cold regions,and the direct shear test and one-dimensional frost heave test were employed in studying improvement effects.Moreover,improvement mechanisms of PVA and PP fiber were analyzed based on test results.The main findings are as follows.(1)Both PP and PVA can heighten the strength of silty clay and suppress frost heave,but the PVA solution has a more decisive influence on improving mechanical properties than PP fiber.(2)The improvement mechanism of the PVA solution is cementing.The improvement effect of 2%PVA solution is the best,which can increase the shear strength by approximately 40%–60%at different stress levels and decrease the frost heave ratio from 0.89%to 0.16%at optimal water content.(3)For 2%PVA improved samples,0.25%PP fiber can further increase soil cohesion by approximately 20–30 kPa at different stress levels and further decrease the frost heave ratio from 0.16%to 0.07%at optimal water content.The improvement effect is neglectable when the PP fiber content exceeds 0.25%.Overall,2%PVA with 0.25%PP fiber is the optimum combination to improve silty clay in cold regions.

高地下水位地区花岗岩残积土路堤填料改良试验研究

以广西南宁-湛江高速公路南宁至博白那卜段工程为依托,考虑到高地下水位地区花岗岩残积土绝大部分须进行改良才能作为路堤填料,通过水泥、石灰、水泥与石灰复掺改良对比试验,分析浸水时间对改良花岗岩残积土路堤填料工程特性的影响,结合试验结果建议:采用4%水泥与3%石灰复掺改良花岗岩残积土的方案。

高速铁路盐渍土路基填料复掺改良试验研究

利用复掺水泥+S95级矿粉+煤系偏高岭土(CMK)方式对取自包银铁路的盐渍土进行改良试验,结果表明:掺入CMK能明显改善土体结构,增强密实度和稳定性,提高强度和抗渗性能,固结物含量、强度随CMK掺量增加呈先增大后减小变化特征,渗透系数随CMK掺量增加呈先减小后增大变化特征;随着CMK掺量提升,最优含水率逐渐增大,土体内部的孔隙水含量增加,土体的导电性随之增大,电阻率随着CMK掺量增加而减小;盐渍土∶水泥∶S95级矿粉∶CMK=90∶2∶6∶2为最佳的路基改良处治方案,其固结物含量最高,强度可提高数倍,抗渗性提升一个数量级以上,电阻率提升2.8~3.3倍。

铁尾矿砂改良膨胀土填料工程特性研究

为保证膨胀土填料路用工程性质良好,选用铁尾矿砂处治膨胀土填料,并通过室内试验研究了铁尾矿砂改良膨胀土填料击实特性、膨胀特性、力学特性和水稳定性。结果表明,随掺砂率增大,铁尾矿砂改良膨胀土最大干密度逐渐提高,最佳含水率逐渐降低;随掺砂率增加,铁尾矿砂改良膨胀土膨胀性减弱,掺砂率增加10%,改良膨胀土自由膨胀率和膨胀力分别平均降低17.2%、22.2%;在掺砂率30%时,铁尾矿砂改良膨胀土力学特性和水稳定性最优,较素膨胀土水稳系数约提高16.1%。建议铁尾矿砂改良膨胀土最佳掺砂率为30%。

生物质焚烧灰渣资源化技术分析与应用

本研究综述了生物质焚烧灰渣理化特性、处置现状,并对其在建材利用、填料、肥料/土壤改良剂中的资源化利用现状、应用前景及应用效果进行了分析与试验研究。

基于连续压实及动态变形模量检测技术的土石混填路基压实质量研究

以静乐丰润至兴县黑峪口高速公路高填方路基填筑为背景,通过现场试验,对不同碾压遍数及松铺厚度条件下,高填方土石混填路基的连续压实值VCV及动态变形模量值进行研究,结果表明:(1)当土石混填路基的松铺厚度一定时,随着碾压遍数的增加,连续压实值VCV呈现增加的趋势,且连续压实值VCV在碾压前期增加速度较快,后期缓慢;(2)松铺厚度为50~60 cm,碾压遍数为5遍时可达到较好的经济效果;(3)路基松铺厚度为50 cm及60 cm时,连续压实值VCV与动态变形模量相关性系数分别为0.714、0.760,松铺厚度为70 cm时,两者离散性较大。

采用地基加固用高强钢管的SP-锚杆和SP-土钉

锚杆是隧道的关键支护构件。POSCO集团与韩国材料公司共同开发了SP-锚杆和SP-土钉等钢建材产品,这两类产品均采用了屈服强度800 MPa的钢管,其重量相当于普通锚杆的50%,强度则提高了2倍以上,不仅利于施工,在安装后还可以最大程度地提高安全性,大大降低了安全事故的风险。另外,通过中空钢管向内部灌注砂浆,加固效果更为理想。

气泡轻质土在陡坡高路堤中的应用研究

随着学者对气泡轻质土理论和应用的深入研究,气泡轻质土在项目建设中的应用越来越广泛。在道路加宽工程建设中,尤其是软土地基、征地拆迁困难、用地费用高的路段,对气泡轻质土的需求不断增大,且优势较明显,具有广阔的发展前景。文章基于气泡轻质土的性能特点,结合气泡轻质土在陡坡高路堤中的工程应用案例,掌握其具体施工工艺要点,通过研究结论推动气泡轻质土在工程行业建设中创造更好的经济社会效益,为今后该新材料新工艺在建设项目中的有效应用提供指导。

南宁外环膨胀土路基处治技术及设计方案研究

拟建南宁外环路穿越膨胀土分布区,若实施刚性支挡难以保证开挖边坡稳定,沿用弃土换填方案填筑路堤至少需废240万方,使工程投资大增并严重破坏生态环境,为此,研究运用膨胀土处治新技术进行路基工程设计。通过系统土性、填料性质试验,论证了物理处治技术修建膨胀土路堤的可行性;采取FLAC和极限平衡分析,获得实施柔性支护前后典型膨胀土堑坡的稳定性。基于试验、理论分析并借鉴交通部西部膨胀土项目的成功经验,提出两种封闭包盖措施填筑南宁膨胀土下路堤、不同边界条件下的路堑边坡柔性支护设计方案。对比分析表明,采用新技术效益明显,能实现南宁外环高速路安全、经济、节能环保的修建目标。

戈壁粗粒土填料填筑铁路路基压实评价指标研究

选取兰新铁路第二双线4个具有代表性的路基试验段,进行戈壁粗粒土填筑路基的压实质量评价指标研究。研究表明:粗粒土填料填筑路基的孔隙率偏小,但现有规范规定的孔隙率标准偏大,起不到控制路基密实度的作用,因此提出用填料的细颗粒室内击实试验得到的孔隙率换算整体孔隙率的方法控制粗粒土填筑路基的密实度;K30能较好地反映填料的塑性变形,且对压实质量敏感,比Ev2更适合作为路基压实质量的评价指标;Ev2/Ev1控制路基压实质量的实质是Ev1在起作用;规范不应用统一的Ev2/Ev1标准,而应根据填料的粗颗粒含量制定相应的Ev2/Ev1标准,填料的粗颗粒含量越多,填筑的路基的弹性变形量越小,Ev2/Ev1的规范标准应越大;Ev1的测试深度比K30大,且塑性变形在总变形中的比例也大,因此可以考虑将Ev1设定为路基压实质量的评价指标。

土石混填料台背回填柔性加筋注浆技术加固试验研究

通过采用柔性加筋注浆技术处理台后回填土现场试验研究并结合室内试验的方式,研究了柔性加筋注浆新技术处理湘西红砂岩土石混填台背的施工工艺特性、加固实现机制和加固效果。现场试验及质量测试表明,水平柔性加筋注浆新技术处理湘西红砂岩土石混填台背施工工艺简单、加固效果良好,具有较好的开发应用价值。同时,现场试验过程取得大量施工参数和试验数据,为改进该新技术的设计计算及施工参数、完善施工工艺获得素材;对有效预防和减少桥头跳车现象的发生,保证行车的舒适和安全也提供了可供选择的新方式。