Experimental Research on Dynamic Shear Modular Ratio and Damping Ratio of Sandy Gravel Soil

The dynamic shear modulus ratio and damping ratio of sandy gravel are important parameters for the seismic response analysis of valley geomorphic sites,which have an important impact on the determination of design ground motion parameters. In this paper,the dynamic triaxial test of sandy gravels has been performed based on the project of the Shangluo Seismic Microzonation. Combined with the other results of sandy gravel,the recommended results of slightly dense,medium dense and dense sandy gravel were obtained. By building the typical site model,the influence of the dynamic shear modulus ratio and the damping ratio uncertainty on the seismic response of the site is studied. The results show that the uncertainty of the average of the dynamic shear modulus ratio and the damping ratio ± 1 times the standard deviation has little effect on the peak acceleration of the sandy gravel site,and the rationality of the grouping and statistical results is explained. Under different probability levels,the change in the shear modulus ratio and damping ratio leads to a significant difference in the high frequency response spectrum.The response spectrum of 0. 04-0. 1s ranges from about 20%,but it has little effect on the long period spectrum of more than 1. 0s. The study of dynamic shear modulus ratio and damping ratio of sandy gravel has the ability to improve the reliability of the designing ground motion parameters.

单双向循环荷载作用下砂砾料动模量和阻尼比试验研究

通过大型振动三轴试验,研究了单双向循环荷载作用下砂砾料动弹性模量和阻尼比的变化规律,分析围压和径向循环动应力对砂砾料动力参数的影响。研究结果表明:在双向振动三轴试验中,砂砾料的轴向动应变受径向动应力的影响较小,动应变主要与施加的轴向动应力大小有关;单双向振动下砂砾料的动弹性模量均随着动应变的增大而逐渐降低,双向振动时砂砾料动弹性模量随动应变的衰减速率基本不变,在相同动应变下双向振动的动模量均低于单向振动;砂砾料在双向振动时的阻尼比大于单向振动,双向振动时消耗的动应变能更大。通过对两种试验条件下的最大动弹性模量、动模量比进行分析,建立了表述单双向试验条件下最大动弹性模量的换算关系式和双向振动试验中动模量比和动应变的修正模型。

Equal Volumes of Sand and Gravel Concrete Mix Ratios in Cameroon and Its Effect on Concrete Compressive Strength

In recent years, the rationalization of concrete mix ratios which batches equal volumes of sand and gravel in building projects has been gaining grounds in the Cameroon construction industry. The main objective of this study is therefore to investigate if the concrete produced with rationalized mix ratio can be adopted as conventional mix ratio in terms of minimum required compression strength of concrete for buildings. Specifically this work compared the conventional mix ratio of 350 kg of cement: 400 liters of sand: 800 liters of gravel for a cubic meter and the rationalized batch of 350 kg of cement: 600 liters of sand: 600 liters of 5/15 gravel, 15/25 gravel and a combination of 5/15 + 15/25 gravel. Average compressive tests’results for both the conventional and the rationalized mix ratios were found to meet the minimum compressive strength of 65% at 7 days, 90% at 14 days and 99% at 28 days for gravel size combination 5/15 + 15/25. Single size gravel of 5/15 and 15/25 did not meet the minimum required compressive strength of 20 N/mm2 for the rationalized mix ratio at 28 days curing based on the minimum compressive strength required, this study arrives at the conclusion that the equal volumes of sand and gravel mix ratio of 350 kg/m3 of cement: 600 liters of sand: 600 liters of gravel mix ratio can be adopted as a conventional concrete mix ratio for gravel size 5/15 + 15/25.

橡胶砾石级配对筋土界面循环剪切特性的影响

橡胶砾石作为基础填料,具有低剪切刚度、高阻尼比的特性。为了研究土工格栅-橡胶砾石的循环剪切特性,利用室内动态直剪仪进行了一系列直剪试验,分析了4种橡胶砾石颗粒级配(级配不良GR1、GR4,级配良好GR2、GR3)、3种橡胶配比(10%、30%、60%)、3种竖向应力(30、60、90 kPa)下土工格栅-橡胶砾石界面的剪应力-剪切位移关系和体变特性。试验结果表明:在循环剪切过程中,各橡胶砾石级配均表现出剪切硬化的特点,但其抗剪强度与纯砾石相比均出现不同程度的降低;橡胶砾石抗剪强度随着竖向应力的增加而增大,4种级配土中GR2表现出最高的抗剪强度,但相较于纯砾石其抗剪强度约下降9%;界面最大竖向位移与竖向应力和橡胶含量成正相关,2种连续级配土GR2和GR3的界面竖向位移较小;在同一颗粒级配下,剪切频率和剪切位移幅值越大,混合土界面峰值剪应力越大;筋土界面剪切刚度随着循环次数的增加而增大,随着橡胶含量的增大而减小,而阻尼比与剪切刚度呈相反的规律。

重载铁路基床级配碎石动弹性模量及颗粒破碎试验研究

针对级配碎石的动力特性以及颗粒破碎性质,采用室内动三轴试验,研究其在循环荷载作用下循环应力比(cyclic stress ratio,CSR)、围压以及加载次数对累积动应变、动弹性模量、颗粒形状系数和颗粒破碎的影响。研究结果表明,不同CSR条件下,加载次数达到10000次时,累积动应变基本完成。随着加载次数的增加,不同CSR下的动弹性模量逐渐减小,滞回圈面积逐渐增加后保持稳定。低围压下,CSR对动弹性模量影响不显著,动弹性模量增加幅度较少;高围压下,动弹性模量随着CSR的增加而增长较大。循环荷载作用下,颗粒破碎方式主要为研磨;颗粒粒径越大,试验后的颗粒形状系数球度越大,颗粒越靠近球形,其轮廓线越圆滑。当CSR小于0.3时,影响颗粒破碎的主要因素为动应力大小,而围压影响不显著;当CSR大于0.3时,颗粒破碎主要因素受动应力和围压共同影响。

不同母土对水泥土微观结构及强度的影响

为探究多元变量组合差异下水泥土强度的变化规律,以江西省内常见的黏性土、砂性土和砂砾土为研究对象,在不同配合比方案下开展无侧限抗压强度试验,并通过SEM测试分析水泥土微观结构。试验结果表明,在母土为最优含水状态下的三种水泥土中,水泥掺入比为21%(质量分数,下同)、水灰比为0.5、土质含砂砾率为100%的水泥土抗压强度最高,其C-S-H凝胶含量较多,孔隙数量较少,砂砾基质的粒状骨架较多。

戈壁滩地区水稳砂砾材料组成设计与工艺控制

以新疆G575线巴哈公路项目为依托,通过室内水泥稳定砂砾基层配合比设计、收缩性能试验研究,结合试验段试铺及施工工艺参数指标分析,提出适合戈壁滩地区的水泥稳定砂砾基层组成设计及相关施工工艺,可为同类条件施工项目提供参考。

基于空隙率数值模拟的水稳碎石级配研究

为了确定空隙率最小的CTB-30水泥稳定碎石级配,通过简化模型参数构建了离散元PFC3D的空隙率数值试验模型,粗集料级配采用数值试验确定,细集料级配通过i法确定,确定了空隙率最小的CTB-30级配,对CTB-30级配进行了力学性能验证与芯样强度测试。结果表明:19~31.5 mm、9.5~19 mm与4.75~9.5 mm三档集料空隙率最小的配比为42∶28∶30,i为0.75时细集料空隙率最小,粗、细集料的最佳比例为67∶33。采用重型击实法成型试件,在5%的水泥剂量下,与骨架密实级配中值、悬浮密实级配中值相比,空隙率最小的CTB-30级配的最佳含水率分别降低0.2%、0.4%,最大干密度分别提高0.018 g/cm^(3)、0.039 g/cm^(3),无侧限抗压强度分别增加3.8%、9.1%,劈裂强度分别增加5.7%、3.4%。通过试验段总结了施工要点,芯样检测结果超过室内试验结果,施工观感符合预期。

高液限黏土质砾承载比强度特性试验研究

高液限黏土质砾属于非均匀、非均质、非连续的混合多相特殊地质材料,其承载比(CBR)强度特性较一般细粒黏土或粗粒填料有较大差异。因此,以我国西南地区某高速公路典型的高液限黏土质砾为研究对象,开展了不同含水率、不同细粒土含量和不同击实功下的CBR试验研究。其结果表明:高液限黏土质砾的CBR强度受颗粒组成、含水率和击实功等因素的综合影响,仅改变单一因素并不一定能提高CBR值;高液限黏土质砾的CBR强度变化比纯黏性土剧烈,受含水率影响更为明显;若不计算砾石的吸水量,高液限黏土质砾中黏土的含水率超过其液限时,黏土起着润滑作用,将明显降低高液限黏土质砾的CBR值;当高液限黏土质砾在最佳含水率时,其CBR值大于8%,可用于路基各层位的填筑;高液限黏土质砾路基碾压施工过程中,需突破以最佳含水率作为碾压含水率控制标准的传统模式,可在对其细粒土含量、压实度、含水率等因素综合考量的基础上,确定最优的碾压参数控制标准。该研究成果可为高液限黏土质砾的合理有效利用提供理论和技术支撑。

基于响应面分析胶凝砂砾石材料渗透性能研究

为研究不同配合比对胶凝砂砾石渗透性能的影响,选取3个因素(粉煤灰掺量、水胶比、砂率),利用响应面法对试验结果进行影响因素的显著性分析,得出胶凝砂砾石渗透系数对单因素和两两因素交互作用的敏感程度。结果表明:粉煤灰、砂率对渗透系数呈现出极强敏感强度,水胶比对渗透系数敏感强度最低;另外因素之间的两两交互作用对渗透性能的影响从高到低依次为水胶比和砂率、粉煤灰和砂率、粉煤灰和水胶比;通过响应面数学模型得出最优配合比为粉煤灰掺量为22 kg/m^(3)、砂率为20%、水胶比为1.0。

砾石土路基封层材料性能及施工技术要点

利用砾石土路基封层对公路路基进行处理能显著提升公路综合性能。对某公路建设基本情况进行介绍,分析了封层材料的原材料性质并设计了配合比,对材料基本性能进行试验研究。将材料应用到工程实践中,从水泥稳定土封层施工以及石灰稳定砾石土施工两个层面详细介绍了施工技术要点,有效积累了理论和实践经验,对于提升施工技术水平具有一定的现实意义。

Frost heave control of fine round gravel fillings in deep seasonal frozen regions

Fine round gravel soil is widely employed in the subgrade of high and thawing. The lower the fines content in fine round gravel soil, but compaction difficulty increases. This study is to obtain the speed railways in cold regions to prevent frost heaving the smaller the quantities of frost heaving and thawing, optimum fines content and limited frost heaving and thawing. The fine round gravel soil filling （FRGSF） used in the Harbin-Qiqihaer Passenger Dedicated Line is taken as the study object. Influence of fines content on optimum water content, maximum dry density and frost heaving properties of FRGSF were studied by means of compaction and frost heaving tests. Results show that the maximum dry density of the FRGSF increases first and then decreases with an increase of fines content, namely there is an optimum fines content for easy compaction. The method of surface-vibratory instrument is fit for coarse-grained soils, and wet state of coarse-grained soil is in favor of compaction. Considering the relationship of fines content with maximum dry density and the frost heaving ratio of FRGSF, the fines content should be limited to within the range of 9%-10%, so that the frost heaving ratio is less than 1%, and the FRGSF is easily compacted. Water supply is proved to be an important factor influencing the amount of frost heaving of FRGSF. We also conclude that in the field, it is imperative to control waterproofing and drainage measures.

加筋碎石桩复合地基工作状态影响因素分析

为制定合理的软土地基加筋碎石桩处治方案,采用有限元软件进行数值模拟分析。通过对比不同条件下的复合地基沉降量计算结果,分析不同因素对复合地基工作状态的影响。研究认为:在考虑经济性的情况下,建议桩土模量比选择为25,加筋体刚度取800kN/m,加筋体长度取1/2 H,并优先选择内摩擦角大的碎石。

Stress Ratio-Strain Relation of Pile and Soil in Composite Foundation

A series of triaxial compression tests were arried out by means of composite-reinforced soil samples to simulate the interaction between soil and pile. The samples are made of gravel or lime-soil with different length at the center. The experiment indicates that the strength of the composite samples can not be obtained by superimposure of reinforcing pile and soil simply according to their replacement proportion. It also indicates the law for stress ratio of reinforcing column to soil. The stress ratio of reinforcing column to soil increases and reaches peak rapidly while load and strain is small. Then the ratio decreases. This law is in accordance with the measuring resuits in construction site.

包裹碎石桩在粉质黏土地基中的承载特性研究

为了探究包裹碎石桩对粉质黏土地基的加固效果,基于模型试验和数值模拟方法,对包裹碎石桩与传统碎石桩复合地基承载力特性进行了研究,并分析了碎石模量、碎石内摩擦角和土工格栅刚度等参数对包裹碎石桩复合地基承载及变形的影响。结果表明:传统碎石桩复合地基在荷载小于20 kPa时,沉降增大不明显。当荷载大于30 kPa时,沉降迅速增大,复合地基失稳破坏;在一定的粒径范围内,相同级配下,碎石粒径越大,碎石桩整体变形越小,承载能力越高;包裹碎石桩的碎石模量在高应力状况下,对复合地基沉降的影响效果较为明显。当桩土模量比大于30时,其对复合地基的沉降影响逐渐减弱;增大碎石内摩擦角能有效增大桩土应力比,并提高桩身应力传递效率。随着内摩擦角的增大,复合地基的沉降逐渐减小,在高荷载水平下,其影响效果更加明显;土工格栅的包裹能减少复合地基沉降,但影响程度有限,当包裹刚度J>1000 kN/m时,对沉降的影响逐渐减弱。

粒类料直剪试验强度尺寸效应及剪切带特性研究

中粗砾料地基抗剪强度指标多采用经验或通过大型直剪试验获取。为了探索不同粒径砾类料适合的剪力仪尺寸,将5种不同最大粒径的砾类料与4种尺寸剪力仪进行组合试验,以大型直剪试验结果为基准值,研究各组合试验强度尺寸效应和剪切带特征。试验结果表明,试样抗剪强度及指标参数均随径径比增加先减小后趋于稳定,试样最大粒径越大,强度尺寸效应越显著。同径径比下,随着法向应力增加,抗剪强度与基准值间差异逐渐增大,尤其以最大粒径较大者显著。最大粒径2~10mm试样可选用Φ150mm剪力仪,最大粒径10~20mm试样宜选用Φ250mm剪力仪,最大粒径20~40 mm试样宜选用Φ350 mm剪力仪。试样剪切带宽度与颗粒粒径成正比,与法向应力成反比。

大位移、大斜度井压裂充填工艺设计及应用

大位移、大斜度井压裂充填存在着防砂管柱下入困难、现场作业风险高,难度大等特点。文章以渤海某油田为例,针对大位移大斜度井压裂充填工艺设计、管柱下入模拟分析、摩阻计算三方面进行设计。并将井斜为84.12°,水垂比为3.13的A1井进行应用案例分析,选用3.88大通径一次多层充填防砂管柱,大大提高了作业效率;采用Landmark软件对防砂筛管下入摩阻进行计算,分析下入的可行性,优化钻杆方案,使充填效率较设计提升30%;针对层温度低的特点,提出了使用低温酶破胶剂来提高反排效率;最后对相关压裂充填施工工艺参数进行设计,采用低砂比,大排量充填,从而形成短宽缝,达到很好的充填效果。

复合型暗管外包滤料防淤堵试验研究

灌溉回归水再利用问题是西北干旱、半干旱地区农业灌溉亟待解决的问题,已有研究表明,由管壁裹土工布+砂砾石复合的农田排水暗管外包料的滤土、排水效果显著。为探究该类外包滤料的防淤堵情况,结合宁夏银北灌区暗管排水循环利用问题,采用砂砾石、沸石、炉渣材料和当地常用管壁外裹土工布构造了排水暗管的复合型外包滤料结构,通过室内土柱渗透试验,分析研究了复合型外包滤料的防淤堵性状与评价方法。试验结果表明,复合型外包滤料的防淤堵效果优于仅铺设土工布的情况,而传统砂砾石与吸附性材料之间的防淤堵效果存在细微差别;复合型外包滤料可以使用沸石、炉渣等吸附材料代替砂砾石,但应满足滤料的级配条件,在C_(u)>4的同时不宜缺少小粒径滤料;滤料部分的水力梯度值占复合型外包滤料的总体水力梯度值的百分比更大;考虑外包滤料内部各结构权重的改进梯度比方法用于分析判断暗管外包滤料的防淤堵情况是可行的。

Experiments of Multi-element Composite Foundation with Steel Pipe Pile and Gravel Pile

A set of serf-developed apparatus for foundation physical model were utilized to conduct model tests of the multi-element composite foundation with a steel pipe pile and several gravel piles. Some load-bearing characteristics of the multi-element Composite foundation, including the curves of foundation settlement, stresses of piles, pile-soil stress ratio, and load-sharing ratio of piles and soil, were obtained to study its working performances in silty sand soil. The experimental results revealed that the multi-element composite foundation with steel pipe pile and gravel pile contributed more than the gravel pile composite foundation in improving the bearing capacity of the silty fine sand.

不同加载比时砂砾料动模量和阻尼比变化规律研究

为探究加载比和围压对砂砾料动力特性的影响,通过大型动三轴试验,研究不同加载比和围压作用下砂砾料动模量和阻尼比的变化规律。研究结果表明:(1)随着加载比的增大,动应变显著增大,孔压明显上升,最大阻尼比增大;(2)试验数据更能反映出阻尼比随动剪应变发展的变化规律,综合考虑各动力参数的变化,建议砂砾料动模量和阻尼比试验的加载比选择范围为1.5~2.0;(3)采用分段拟合法对动应变小于0.01%和大于0.01%的试验数据进行拟合,直线与试验点的拟合度均大于0.96,分段拟合不同试验条件下砂砾料本构关系更为合理;(4)不同试验条件下动剪切模量比与参考剪应变具有良好的归一性,通过二元线性回归得到砂砾料最大动剪切模量关于围压和加载比的经验公式。该方法可为砂砾料动三轴试验及数据处理提供参考。