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1.
基于孔隙分布模型的垫层料冻胀变形规律探讨 总被引：2，自引：0，他引：2
垫层料冻胀变形过大会影响面板坝的正常使用,研究表明,垫层料冻胀变形量大小与其级配及孔隙分布有关。为了研究寒冷环境下垫层料冻胀变形机制和规律,基于土颗粒为理想球体且完全均匀分布的假定,提出了垫层料孔隙分布模型,确定了等效孔隙直径及等效孔隙数量的计算办法。利用单向固结仪,进行了不同孔隙尺寸和不同孔隙数量垫层料的冻融循环试验,冻胀试验结果表明：垫层料冻胀量大小随孔隙尺寸和孔隙数量变化而变化。存在一个临界孔隙尺寸,小于该尺寸的孔隙越小、小孔隙越多,冻胀量越大;反之,冻胀量越小。基于孔隙分布模型,构造定义了孔隙分布指数,发现垫层料冻胀变形量与孔隙分布指数呈线性正相关关系。研究结果可为工程设计确定合理的垫层料级配提供参考。 相似文献
2.
渠道抗冻胀垫层设计方法研究与数值模拟 总被引：2，自引：0，他引：2
基土换填是常用的抗冻胀措施。目前非冻胀性土缺乏科学标准的定义,换填厚度基本按照经验公式和工程类比确定,不尽科学合理。在对垫层抗冻胀机制的分析基础之上,根据层状土毛管水土水势理论给出了垫层材料的选择依据,结合热阻等效原理在考虑了衬砌结构允许位移的基础上给出了渠道垫层厚度的计算公式,并根据传统算法与该方法对山东打渔张北干渠弧形坡脚梯形渠道进行抗冻胀垫层设计;同时采用ANSYS有限元软件对渠道铺设垫层前后进行热力耦合数值模拟。研究表明,垫层通过改善水分场、温度场削弱了冻胀发生的因素;该垫层算法比传统算法合理、工程造价较低。数值分析表明,渠道冻胀量、冻胀力明显被削减,其中对阴坡的削减可达90%以上。 相似文献
3.
通过现场4桩大压板静载试验,布置土压力盒,测定并分析C桩（刚性桩）桩顶、M桩（亚刚性桩）桩顶和桩间土体应力,计算桩（C桩+M桩）土荷载分担比,分析CM桩复合地基静载试验过程中桩、土的受力特性。通过设置不同垫层厚度,对比大压板试验P-S曲线,结合单桩静载试验,分析CM桩复合地基垫层的破坏模式及垫层效应。试验结果表明,CM桩复合地基工作时C桩桩顶应力集中现象明显,C桩桩土应力比大于10,M桩桩土应力比小于10;随着试验加载,桩土应力比逐渐增大,C桩桩土应力比增大幅度大于M桩;在复合地基设计荷载条件下,桩土荷载分担比接近6:3:1;将M桩和桩间土体视为一整体,即地基处理后相对于C桩的“桩间土”,则桩土荷载分担比为6:4,设计较为合理;随着垫层厚度增大,CM桩复合地基沉降值增大;当C桩成桩质量较好时,垫层破坏模式为C桩桩顶刺入破坏,试验时应合理选取褥垫层的材料和厚度。 相似文献
4.
Clay liners or compacted earthen barriers are important barrier materials used for preventing contaminant transport through soils. A low hydraulic conductivity (k) is a significant parameter that governs the design and construction of clay liners. Compacted expansive clays, which are montmorillonite clays, also have a very low hydraulic conductivity (k). When expansive clays are blended with fly ash, an industrial waste, the hydraulic conductivity (k) further reduces as the ash-clay blends result in increased dry densities at increased fly ash contents. Hence, fly ash-stabilised expansive clay can also be proposed as a unique clay liner material. As expansive clays undergo heave when they come into contact with water, it is necessary to study the heave behaviour of fly ash-stabilised expansive clay liners. This paper presents heave studies on fly ash-stabilised expansive clay liners. Fly ash in different contents by dry weight of the expansive clay was added to the clay, and the ash-clay blend was compacted as a liner overlying a natural field soil layer. Compacted lateritic clay was used for simulating the natural field soil into which contaminants migrate. Calcium chloride (CaCl2) solution of varying concentration (5, 10, 20, 50, 100 and 500 mM) was used as the permeating fluid in the heave studies. The rate of heave and the amount of heave of the fly ash-stabilised expansive clay liners were monitored. Deionised water (DIW) was also used as inundating fluid for comparative study. Heave (mm) decreased with increase in solute concentration for all fly ash contents. For a given solute concentration, heave decreased up to a fly ash content of 20 % and thereafter it increased when the fly ash content was increased to 30 %. Heave of the fly ash-stabilised expansive clay liners was correlated with their permeability, liquid limit (LL) and free swell index (FSI) pertaining to the respective fly ash content and CaCl2 concentration. 相似文献
5.
渠基土在冻融循环作用下的变形和应力变化特征 总被引：1，自引：1，他引：0
受季节性气候变化和昼夜交替的影响,处于寒区的地表浅层土体不可避免地会发生冻融循环作用。冻结过程引起土体的膨胀变形,融化过程引起土体的压缩沉降变形。同时冻融交替变化会诱发渠基土的结构与物理力学性质发生显著改变,从而危害工程设施的服役性。土体所处的应力环境是影响冻融过程中土体变形发展的关键因素。为了研究不同上覆荷载条件下冻融循环过程对寒区渠基土变形与冻胀应力发展特性的影响,开展了一系列冻融循环试验。结果表明：在上覆荷载为10 kPa时,冻融循环会使土体产生膨胀变形;当上覆荷载为50 kPa或100 kPa时,冻融循环会使土体产生非常明显的固结沉降,且上覆荷载越大,沉降量也会越大。随着冻融循环次数的增加,土体在其所处的应力环境下逐渐形成相对稳定的固结结构,单次冻融过程中产生的冻胀量与融化固结量趋于相等,即冻融稳定系数趋于1。在不同上覆荷载条件下固结稳定后,保持试样两端约束的位移不变,发现土体冻融过程中产生的最大竖向冻胀应力随冻融循环次数的增加不断衰减,且冻胀应力的发展与孔隙水压力的变化具有一致性。因此,通过对恒定上覆荷载条件下冻融过程中正冻与正融界面附近孔隙水压力分布的研究,可揭示冻融过程中土体变形发展的内应力机理。 相似文献
6.
桩承加筋路堤中路堤与褥垫层共同作用理论分析 总被引：1，自引：0，他引：1
从桩承加筋路堤中加筋褥垫层与路堤填土共同作用的实际情况出发,利用弹性力学对路堤填土单元进行了力学平衡分析,同时考虑到加筋褥垫层的工作状态类似于连续梁板的特性,根据PCC桩承加筋路堤的设计参数及现场测试结果,将现浇混凝土薄壁管桩（PCC）桩承加筋路堤中的加筋褥垫层视为弹性薄板,再根据薄板小挠度理论,推导出了桩土差异沉降等计算公式。又根据填土与褥垫层变形协调、应力连续的条件,在忽略褥垫层材料本身压缩量的前提下将加筋褥垫层变形分析与填土变形分析相结合,提出了求解填土等沉面高度、桩土应力、桩土差异沉降的方法,最后通过与现场实测结果对比,验证了方法的正确性。 相似文献
7.
8.
在现场试验的基础上,利用FLAC3D建立数值模拟模型,分别改变复合地基的褥垫层、持力层和桩体材料的模量,计算采用不同模量时复合地基的沉降以及桩土的应力,分析模量变化对复合地基承载力和沉降的影响规律。结果表明,褥垫层的材料和模量影响到桩间土承载力的发挥,褥垫层宜采用级配砂石,模量取值范围为20～50MPa。持力层模量增大可以提高复合地基承载力减小沉降,因此水泥土搅拌桩的桩端要进入到具有一定硬度的土层中,除软弱土外,其他土层做持力层其强度对复合地基承载力和沉降的影响不大。在一定范围内增大桩模量可以有效提高复合地基承载力减小沉降,采用水泥土搅拌桩加固软土地基时,桩的模量不要过大,建议取值范围为200～400MPa。 相似文献
9.
Waleed Abdelmoghny Metwaly Ogila 《Environmental Earth Sciences》2016,75(24):1493
Expansive soils are considered as a potential natural hazard if they are not adequately treated. Expansive soils have high potential for shrinking and swelling under changing moisture conditions and cause extensive damages to engineering infrastructures. This study is concerned with the suitability of natural ornamental limestone dust to reduce the swelling characteristics of high expansive soils. The results are revealed that the swelling pressure and percent of heave are greatly decreased with increasing the inserted core diameters and mixing percentages of limestone dust. The average reduction percent values of swelling pressure and percent of heave are increased from 2.21% to 43.09% and from 2.56% to 45.64%, respectively, for treated soil samples with increase in limestone dust core diameters from 5 mm to 20 mm (1% to 16% of total soil area). The average reduction percent values of swelling pressure and heave percent are increased from 10.29% to 70.73% and from 22.29% to 82.90%, respectively, for treated soil samples with increase in limestone dust mixing percentages from 10% to 30%. The results are revealed that the enhancement in swelling characteristics of high expansive soils that are treated by ornamental limestone dust is mostly attributed to the replacement of high expansive fine clay particles by non-expansive and non-plastic coarse limestone dust particles, and to the presence of a considerable amount of free lime in limestone dust (4.97% as [Ca(OH)2]) that is responsible for converting the high expansive soils to less expansive soils by pozzolanic reaction. The mixing treatment method is more suitable for surficial and shallow foundation high expansive soil beds, while the compacted limestone dust piles “inserted limestone dust core method” are more suitable for deep foundation high expansive soil beds. 相似文献
10.
国内外沉管隧道先铺基础多采用碎石作为垫层材料,目前尚无采用卵石的先例。卵石和碎石在表面光滑度、排列接触方式、颗粒间天然空隙率等物理特性的差异性将影响其力学性能表现。通过物理模型试验和数值模拟计算,对卵石和碎石垫层的力学变形特性进行对比分析。研究表明：（1）两种材料垫层压缩曲线均呈两阶段反弯曲线变化趋势,相同荷载条件下卵石垫层压缩量较碎石高,总体割线模量较碎石低约30%。（2）垫层厚度由0.8 m变为1 m时,卵石垫层割线模量增加了13.0%,碎石垫层割线模量增加了2.2%;卵石垫层力学变形性能对垫层厚度的变化较碎石垫层更敏感。（3）预压荷载由52.5 kPa增加到84 kPa时,卵石垫层割线模量增加了23.5%,碎石垫层割线模量增加了7.6%;预压荷载越大,卵石垫层能更早达到拐点从而表现出更稳定的力学性能;增加预压荷载对卵石垫层整体力学变形性能的改善较碎石垫层更明显。（4）随沟宽增大,垫层模量在前期再压缩阶段出现模量提高,而在全加载期内总体表现为模量降低;在全荷载范围内卵石垫层对垄沟尺寸变化的敏感度低于碎石垫层。（5）碎石垫层的整体力学性能优于卵石垫层,但两种垫层材料对结构沉降和受力状态的影响相对有限;在对施工偏差敏感度充分分析的基础上,卵石可替代碎石作为沉管隧道垫层材料。（6）开展卵石级配试验研究,获取最佳卵石级配,是未来研究方向。 相似文献
11.
级配碎石作为季节性冻土地区高铁路基基床表层填料,其防冻胀问题尤为关键。为研究在不同条件下级配碎石的冻胀特性,选取不同的含水率、细颗粒含量、冷端温度和压实度进行了室内封闭系统冻胀正交试验。结果表明,在不同因素、不同水平的组合时,级配碎石有不同程度的冻胀。当级配碎石含水率为5%时,试样的冻胀率较小;当含水率超过7%时,大部分试样冻胀率超过1%。对冻胀过程中试样温度场、冻结深度、冻胀变形过程和冻后试样含水率分布进行了分析,发现冻后试样冷端位置的含水率高于初始含水率,暖端位置的含水率低于初始含水率。当以冻胀率作为参考序列,其他试验条件作为比较序列时,灰色关联度分析结果表明,影响级配碎石冻胀率的主要是含水率,其次为细颗粒含量、压实度及冷端温度,其关联度相差不大。并得出了最有利于冻胀发展的组合。为满足寒区高速铁路变形量的要求,提出以控制级配碎石含水率小于5%为指标。 相似文献
12.
根据静载荷试验和数值模拟的结果,研究垫层厚度对水泥土搅拌桩复合地基沉降的影响规律。针对珠海地区广泛存在的淤泥质土,进行了天然地基和4种垫层厚度的水泥土搅拌桩复合地基现场静载荷试验。在地基中预埋沉降管和沉降磁环,利用带刻度的探头感应加载过程中沉降磁环位置的变化,获取地基的分层沉降量,据此分析复合地基的沉降规律。在现场试验的基础上,对水泥土搅拌桩4桩复合地基进行了数值分析,将数值计算得到的不同垫层厚度复合地基中桩、土的分层沉降进行比较,结果表明垫层的设置减小了桩的沉降量,但过厚的垫层不能够有效地提高复合地基的承载力,反而会增大沉降。建议对褥垫层厚度的选取,除了要综合承载力和沉降两方面因素之外,还要考虑实际的地质条件。垫层厚度可取20～40 cm,当淤泥层位于桩身中部以下取高值,位于桩身中上部取低值。 相似文献
13.
钢筋混凝土（RC）板与一定厚度的土颗粒缓冲层组合结构被广泛用于山区高位单体及群发性崩塌落石的防治,为研究此类防护结构在落石作用下的冲击力衰减规律及RC板的破坏模式,开展了室外系列落石冲击试验。结果表明,增大缓冲层厚度能够有效减小最大冲击力,峰值加速度随缓冲层厚度减小而增大,尤其在缓冲层厚度为0.1 m及0.2 m时,最大值急剧增大,峰值加速度与缓冲层厚度的变化满足指数函数关系;根据量纲分析原理得到缓冲层最大冲击深度与动能的平方成正比、与最大入射冲击力成反比的计算公式,且与实测值较吻合;入射冲击力在缓冲层内的衰减率随缓冲层厚度的增加以指数函数递增,在0.6 m缓冲层厚度下可使峰值冲击力衰减70%左右;随累积冲击能级的增大,RC板经历了弯曲起裂及扩展、次级弯曲裂纹和剪裂纹产生及跨中弯曲裂纹贯通的过程,试验结束时RC板整体表现出典型的弯曲破坏特征。 相似文献
14.
A study of orthogonal design tests on frost-heaving characteristics of graded crushed rockEI北大核心CSCD
Seasonally frozen soil is distributed widely in the Northeast China. The prevention measures against the frost heave of graded crushed rock, which is used as the filler of surface layer in subgrade, are crucial to high-speed railway constructed in seasonally frozen soil region due to the strict requirements of subgrade deformation. In order to study the frost heave characteristics of graded crushed rock under different conditions, water content, fine content, cooling temperature and compaction are chosen as influential factors of frost heave characteristics. The closed system laboratory frost heave experiments have been performed based on the orthogonal design, showing that different frost heave amounts appear in different combinations of factors and levels. The frost heave ratio of most graded crushed rock samples is small when water content is 5%, and it exceeds 1% when water content is above 7%. The temperature field, frozen depth, frost heave deformation process and water content distribution in sample after freezing are analyzed. It is found that the water content is greater than the initial water content at the cold side, and is lower than initial water content at the warm side. Using the frost heave ratio as a reference sequence and other factors as comparison sequences, the correlation degrees among water content, fine content, compaction, temperature at cold side and frost heave ratio are analyzed with the gray correlation method. The results from this analysis indicate that water content produces the most significant effect on the frost heave ratio of graded crushed rock. The water content of graded crushed rock should be maintained below 5% in order to prevent frost heave development in the cold regions. 相似文献
15.
Swelling behavior of expansive soil has always created problems in the field of geotechnical engineering. Generally, the method used to assess the swelling potential of expansive soil from its plasticity index, shrinkage limit and colloidal content. Alternative way to evaluate swelling behavior is from its expansive index (EI) and swelling pressure value. The present study investigates the reduction of EI and swelling pressure for kaolinite and bentonite clay when mixed with various percentages of Ottawa sand and Class C fly ash. The percentages of Ottawa sand and Class C fly ash used were 0–50 % by weight. The results show that there is a significant reduction in the swelling properties of expansive soil with the addition of Ottawa sand and Class C fly ash. The reduction in EI ranged approximately from 10 to 50 and 4 to 49 % for kaolinite and bentonite clay, respectively. Also the maximum swelling pressure of kaolinite and bentonite clay decreased approximately 93 and 64 %, respectively with the addition of various percentages of Ottawa sand and Class C fly ash. Standard index properties test viz., liquid limit, plastic limit and linear shrinkage test were conducted to see the characteristics of expansive soil when mixed with less expansive sand and fly ash. Also, for these expansive soils one dimensional consolidation test have been conducted with sand and fly ash mixtures and the results were compared with pure kaolinite and bentonite clay. 相似文献
16.
A geoenvironmental application of burned wastewater sludge ash in soil stabilization 总被引：1，自引：1，他引：0
This paper studied the use of burned sludge ash as a soil stabilizing agent. The sludge ash was obtained from a public wastewater treatment plant, and it was burned at 550 °C. Different percentages of burned sludge ash were mixed with three different types of clayey soil. A laboratory study consisting of Atterberg’s limits test, unconfined compressive strength test, standard proctor density test, and swelling pressure test were carried out on samples treated with burned sludge at different percentages by dry weight of the clayey soils. The results show that the addition of 7.5 % of the burned sludge ash by the dry weight of the soil will increase the unconfined compressive strength and maximum dry density and also decrease the swelling pressure and the swell potential of the soil. The addition of percentage higher than 7.5 % by dry weight of the soil decreases both the maximum dry density and the unconfined compressive strength; as a result it showed less effectiveness in stabilizing the soil. The conclusion of this research revealed that the burned sludge ash can be used as a promising material for soil stabilization. 相似文献
17.
碎石垫层强度与变形特性试验研究和有限元分析 总被引：1，自引：0，他引：1
碎石垫层已广泛应用于土木工程各个领域,但碎石垫层的强度与变形特性尚不十分清楚,需要进一步研究。通过对5种不同厚度碎石垫层在高应力下的室内模型试验和有限元分析,揭示了不同厚度碎石垫层的强度特性和变形特征。通过有限元分析与试验结果的对比分析,得出了不同厚度的碎石垫层荷载与沉降变形、竖向应力与侧向约束力都近似呈线性变化。碎石垫层的厚度对沉降大小有一定影响,在其他条件相同的情况下,碎石垫层越厚,沉降越大。在一定荷载作用下,碎石垫层在较短的时间内自身压缩变形已基本趋于稳定,而后随时间的增加,其压缩变形量很小。提出了一种测定碎石类土侧压力系数、泊松比及变形模量的试验测定方法,以期为测定其他类别土的侧压力系数、泊松比及变形模量提供参考。 相似文献
18.
兰新第二双线是世界上第一条修建在高海拔季节冻土区的高速铁路,路基填料采用通常认为是冻胀非敏感性材料的粗颗粒土（A、B组填料）。基于2015-2017年军马场-民乐区间（长约38 km）运营期现场监测发现,部分路段仍有较大冻胀量发生,对列车高速运营存在安全隐患。现场监测结果表明：该区间高铁路基平均冻结期为5个月,最大冻深介于3.0~3.8 m,约是天然冻深的2倍,路基2.7 m以上地层最大冻胀量可达27.5 mm。0~0.5 m级配碎石层含水量很低,控制在4%以内,暖季较高,寒季由于冻结而降低;0.5 m以下地层含水量相对较高,介于8%~15%之间,暖季较低,寒季较高,呈现“正弦”式分布,且随着路基深度增加而逐渐减小。路基冻胀发展过程大致可分为三个线性阶段,其中第二阶段（12月中下旬至次年1月中旬）为冻胀发展最快时期,历时约20天可达到稳定冻胀量。 相似文献
19.
《Geomechanics and Geoengineering》2013,8(2):175-181
Expansive soils swell on absorbing water and shrink on evaporation thereof. Because of this alternate swelling and shrinkage, civil engineering structures founded in them are severely damaged. For counteracting the problems of expansive soils, different innovative techniques were suggested. Stabilization of expansive clays with various additives has also met with considerable success. This paper presents, by comparison, the effect of lime and fly ash on free swell index (FSI), swell potential, swelling pressure, coefficient of consolidation, compression index, secondary consolidation characteristics and shear strength. Lime content (weight of lime/weight of dry soil) was varied as 0%, 2%, 4%?and 6%?and fly ash content (weight of fly ash/weight of dry soil) as 0%, 10%?and 20%. A fly ash content of 20%?showed significant reduction in swell potential, swelling pressure, compression index and secondary consolidation characteristics and resulted in increase in maximum dry density and shear strength. Swell potential and swelling pressure decreased with increase in lime content also. Further, consolidation characteristics improved. Compaction characteristics and unconfined compression strength improved at 4%?lime and reduced at 6%?lime. 相似文献
20.
桩体复合地基柔性垫层的效用研究 总被引：25，自引：4，他引：21
从阐述复合地基与桩基之间的区别入手,通过对桩体刺入垫层的研究,寻找在桩头呈理想球形孔条件下,垫层、桩体、桩间土三者模量与刺入量之间的关系,进而讨论了在刺入模式下的加固区复合模量计算问题。还讨论了复合地基桩上材料最优发挥状态问题,力图寻找最佳的桩土荷载分担比。 相似文献