共查询到20条相似文献，搜索用时 234 毫秒
1.
在综合分析现有水平荷载作用下桩基分析方法的基础上,建立了考虑桩侧土体受力状态的斜坡刚性桩力学模型;根据极限平衡原理,建立横向荷载作用下斜坡刚性桩弯矩和应力平衡方程;引入考虑斜坡影响的p-y曲线方法,提出了综合考虑桩侧土体极限承载力与水平抗力系数沿深度呈线性增加的侧向极限承载力与土体抗力承载力系数计算方法,同时,将该方法应用于计算实例,通过与已有有限元和理论计算方法对比分析,计算结果验证了本文方法的合理性与可行性;并利用该方法,分析了斜坡坡角、桩土接触面系数以及地基水平抗力系数对斜坡刚性桩承载特性的影响因素。分析表明:斜坡的坡角、桩土接触面系数对侧向荷载作用下斜坡刚性桩的荷载位移曲线影响明显,而桩侧土的抗力系数对侧向荷载作用下斜坡刚性桩的荷载位移曲线影响不明显。 相似文献
2.
工程中基桩大多处于复杂的成层地基中,鲜有位于单一土层中,从宏观角度出发,引入初始地基比例系数,提出了基于m法的双曲线型p-y曲线。某现场7根试桩地基土非线性显著,实测和理论计算的地面处桩身水平位移水平荷载关系曲线均呈良好的二次抛物线关系,且理论与实测曲线吻合良好,验证了本文p-y曲线模型。地基土非线性对桩身最大弯矩、桩侧地基土压力影响显著,不容忽略。工程实际中采用m法计算基桩最大弯矩值偏小,建议乘以1.05~1.25的系数,以计入地基土非线性影响。 相似文献
3.
鉴于当前焊接接头疲劳评估曲线只适用于单轴加载情况,基于缺口应力法对焊接接头进行了多轴疲劳分析。通过联合焊接接头的多轴疲劳试验名义应力数据和有限元法所计算的缺口应力集中系数,获得了5种焊接接头的各向缺口应力;根据Von Mises、ⅡW和EESH 3种多轴疲劳准则计算出等效缺口应力并将其统一在同一坐标系统下;最后采用最小二乘法拟合出适用于多轴疲劳评估的缺口寿命曲线。与ⅡW标准推荐的单轴曲线相比,这些多轴缺口疲劳曲线具有更低的倾斜度和更高的疲劳等级,即多轴加载时明显降低了103~106次中周范围内的疲劳强度值,而对106~107次高周疲劳范围的影响则相对有限。 相似文献
4.
给出了小剪切变形下的基桩P-Δ效应和大剪切变形下支座P-Δ效应计算的杆单元刚度矩阵方程。假定杆单元弯曲变形位移函数为三次幂函数,剪切变形函数为线性函数,根据有限元法一般原理,推导了一种同时计入竖向力径向剪切分力剪切变形和水平力剪切变形的P-Δ效应杆单元刚度方程,推导了一种仅计入竖向力径向剪切分力剪切变形而忽略水平力剪切变形的P-Δ效应杆单元刚度方程,推导了一种仅计入水平力剪切变形而忽略竖向力径向剪切分力剪切变形的P-Δ效应杆单元刚度方程。计入水平力剪切变形而忽略竖向力径向剪切分力剪切变形的P-Δ效应杆单元可良好的模拟支座在大剪切变形下的偏心工作特性,能实时计入其偏心弯矩影响,为实时计入支座偏心特性的结构动静力分析提供了理论支撑。最后通过自编MATLAB程序进行算例分析,结果表明,计入支座大剪切变下的P-Δ效应后,基桩内力位移和地基土压力均显著增大。基桩自身剪切变形对桩身内力位移和地基土压力影响较小,可以忽略。 相似文献
5.
碎石土因特殊的工程特性而被科研人员关注,但对大粒径、粉质粘土填充、稍密状态下碎石土的力学性能涉足较少。根据该类型碎石土特点及大量勘察结果配置出两种比较典型级配的稍密碎石土,通过大型直剪试验仪测定了不同含水率状态下碎石土试样的抗剪强度,绘制剪应力与水平位移的关系图,通过一元回归得出稍密碎石的抗剪强度指标c、φ值,分析了不同含水率、不同级配对稍密碎石土抗剪性能的影响。结果表明：随着含水率的增大,碎石土粘聚力总体呈减小趋势,但变化趋势具有显著的阶段性且和粉质粘土的含量有关,含水率变化对碎石土内摩擦角的影响较小。用规范推荐方法计算了该类型碎石土地基承载力,并与地方规范经验取值和勘察工程实践取值进行了对比,结果表明：含水率对地基承载力影响较大,且与碎石土填充物的粉质粘土含量有关,粉质粘土含量越高,承载力影响越大。 相似文献
6.
为了研究灰分对煤自燃能力的影响作用,利用绝热氧化实验装置对不同灰分含量煤样进行升温氧化实验,采用R70、TCPT、B 3种指标表征灰分含量对煤样自发氧化过程的影响。结果表明：1）灰分含量越大,煤样低温氧化阶段温升速率越小,温升加速点温度越高,煤样的自发氧化过程越慢,煤越不易自燃;灰分含量大于40%后,煤自燃倾向性快速减弱。温升加速点是反应微观信息的零活化能温度的宏观累计结果,具有直观且滞后的特点。灰分越大,滞后越明显,温差越大。2）R70、TCPT、B 3种指标与灰分关系表现为二次函数。R70和TCPT两种指标显示灰分越大,自燃倾向性越弱,与实践经验相符。受水分权重影响,B指标显示煤样在灰分小于40%时,灰分越大,煤样自燃倾向性越强,这与实践经验相悖。因此,B在判定灰分对煤样自燃倾向性的影响时具有一定的局限性。 相似文献
7.
人工环境实验室对温度的控制精度低于工艺性环境要求,但冬季若采用分体式空调制热模式控制,实验室温度的波动范围过大,影响采集实验数据的准确性。提出冬季采用空调制冷模式联合电取暖器稳定人工环境实验室内温度的新方法,在背景实验中将新方法和传统空调制热温度控制方法进行对比,结果表明：采用新方法能大幅度提高人工环境实验房间温度的稳定性。为对新方法中空调的设定制冷温度与电取暖器功率匹配问题做进一步研究而进行探究试验,实验结果表明：空调制冷量Q1、测试房间热负荷Q2、电取暖器功率Q3和测试房间其他设备功率Q4存在匹配关系,当空调设定温度相同时,|Q1+Q2-Q3-Q4|值越小,人工环境实验室内温度波动频率越稳定,振幅越小。 相似文献
8.
为完善圆钢管混凝土轴压长柱极限承载力的计算理论,对比分析了中国国家标准GB 50936-2014和CECS 28：2012中轴压短柱极限承载力的N0计算公式,并把GB 50936-2014中基于套箍系数的N0计算公式改写成统一的形式,提出了基于正则长细比的轴压长柱的稳定系数计算式,并通过36个试件的对比,对计算式的精度和适用范围进行了分析。研究表明,现行国标GB 50936-2014中基于套箍系数的N0计算公式更为精确,基于N0计算公式和本文的稳定系数,可以计算得到更为精确的轴压长柱的极限承载力。 相似文献
9.
利用一组物料、热量守衡式及其他有关约束关系,建立了氢还原竖炉模拟模型,可定量考察消耗量、生成量和氮气、CO兑入成分、DRI金属化率、入炉煤气温度等的关系。模拟结果表明：兑入CO可使入炉煤气量从纯氢还原的1650 N·m3左右下降到1200 N·m3左右;当CO和H2的体积之比V（CO）/V（H2）约为0.6时,氮气兑入量约为0,竖炉能量利用最佳;当V（CO）/V（H2）体积比为0.3时,最佳氮气兑入成分约为11%;纯氢还原最佳氮气兑入成分约为25%;兑入氮气可以减少入炉氢气的量,但不能减少入炉气体的总量。对氢还原竖炉模拟结果可为其工艺设计、操作和节能等提供参考信息。 相似文献
10.
传统边坡可靠度分析往往在岩土参数服从线性Mohr-Coulomb（简称线性M-C）破坏准则的假设条件下进行,并且常常采用极限平衡法或有限元法计算安全系数。然而,岩土介质破坏准则具有一定的非线性。为能更加实际地描述岩土破坏机理和得到严格精确的解,基于非线性Mohr-Coulomb（简称非线性M-C）破坏准则,结合极限分析上限法和蒙特卡洛法,进行边坡可靠度上限分析。当非线性参数m=1时,与等效的线性M-C破坏准则进行对比计算,验证了方法的可行性。同时,将初始粘聚力、内摩擦角arctan（c0/σt）和非线性参数作为随机变量且服从截断正态分布,进行了参数变异性和敏感性影响分析。研究表明：非线性M-C破坏准则下,边坡可靠度随初始粘聚力、内摩擦角arctan（c0/σt）和非线性参数变异性的增大而减小;边坡可靠度随初始粘聚力和内摩擦角arctan（c0/σt）的增大而增大,随非线性参数的增大而减小。 相似文献
11.
The specific properties of soft clay are characterized by higher void ratio, lower permeability and higher compressibility, the consolidation settlement of soft clay is affected by the imposed stress history, the stress paths, the consolidation pressure and the soil properties. In this paper, the porous media theory based on the mixture theory was applied in the study on the consolidation settlement of soft clay, which was more rigorous than the conventional consolidation settlement theory and the coupling between soil and water can be taken into account in the analysis. 相似文献
12.
13.
To investigate the effect of consolidation soft soil, three groups of model tests were designed. The first group was PVC pile-net composite foundation, the second was pile-cap-net composite foundation, and the third was PVC and sand pile composite foundation. Butter was coated and plastic membrane was covered on inner side wall of model cast to reduce border effect. The gauges were glued with epoxy on the surface of the model with PVC piles and geogrids to measure the stress of PVC piles and geogrids. Soil pressure cells were installed in the middle of piles and the top of the sand piles, and dial indicators were installed in the middle of road and road shoulder to measure deformations. It is that shown: 1) as for the distribution of the road settlement and the differential settlement, the settlements of the third group are the largest and those of the second group are the least; 2) in terms of the stress ratio of PVC pile and soil, the values of the first group and the third group are similar, while the value of the second group is much larger; 3) the change of geogrid strain is disorderly. There are periodic peaks in the strain of geogrid of pile top and periodic troughs in the soil between the piles. The geogrid strain of the second group measured in the corresponding spot is much larger than those of the other two groups. The results of three groups of tests illustrate that if the condition is permitted, it would be the best to adopt the scheme of pile-cap-net composite foundation, which has better reinforcement effect for soft soil. 相似文献
14.
Stress of diaphragm wall is analyzed by plane finite element method for high earth-rockfill dams built on deep soil foundation. The differences of stress are studied with two kinds of different constitutive models, i.e. elastic model and nonlinear elastic model, and meanwhile, the influences of the height of dam and diaphragm wall for this two constitutive models are also compared. The results show that, the variation laws of the stress of diaphragm wall are similar for both of the models. But, the stress computed by nonlinear elastic model is much smaller than elastic model does. Under the condition of low stress, the results are similar for the two models, but have big differences for high stress. In addition, for this two models, with the increasing of height of dam and diaphragm wall, the maximal values of the stress are increasing constantly, and relative error of the maximal value of the stress as well, which have the linear relation with the height of dam and diaphragm wall. So, for the conditions of high dams or deep soil foundations, nonlinear elastic model is the right one to use because of the high stress of diaphragm wall. 相似文献
15.
Maize (Zea mays L.) is one of the most important crops worldwide and is a model organism among cereal crops. Abiotic and biotic stresses are often present simultaneously and severely influence maize production, causing great yield losses worldwide. Therefore, the selection and cultivation of stress-tolerant maize lines that adapt to various stresses is instrumental in addressing the problem of yield losses caused by stress. The maize mesocotyl is the crucial organ that pushes shoots out of deep water or soil after seed germination. It has a simple anatomy and exhibits rapid growth in the dark. In this article, we reviewed the studies on the elongation of the maize mesocotyl and the actions of phytohormones, especially under deep-sowing conditions, and emphasized the role of the maize mesocotyl in response to environmental stress and deep-sowing tolerance. We propose that the maize mesocotyl can serve as a selection organ for evaluating stress tolerance at the early seedling stage. We also identify future research fields that need further investigation in studies of the maize mesocotyl. 相似文献
16.
3种质地土壤上As胁迫对小麦灌浆期旗叶光合特性的影响 总被引：2，自引：0，他引：2
为了深入探讨壤土、黏土、沙土3种主要农田土壤质地条件下As胁迫对小麦的影响差异,研究了小麦灌浆期的根长、分蘖、分生根数目、干物质量等形态指标及旗叶的净光合速率(Pn)、气孔导度(Gs)、胞间CO2浓度(Ci)、蒸腾速率(Tr)、水分利用率(WUE)、叶绿素含量等光合特性指标。结果表明:当As≤15 mg/kg时,小麦受到的胁迫作用不明显;当As≥30 mg/kg时,小麦则开始呈现出根长降低,分生根数目减少等明显的胁迫效应。当As≥30 mg/kg时,在壤土和黏土条件下生长的小麦根长较长,分生根数目较多,并且小麦旗叶的Pn、Gs、Ci、WUE、叶绿素相对含量较沙土条件下高。As胁迫对3种质地土壤上小麦植株干物质量影响不同,壤土上As≥30 mg/kg时、黏土上则As≥45 mg/kg时及沙土上各处理As胁迫下,小麦干物质量出现明显降低。总的来说,壤土和黏土条件可以在一定程度上缓解小麦所受到的As胁迫作用,而沙土对As胁迫缓解效果较差。因此,选择适宜的土壤质地种植小麦,能有效缓解As对小麦植株的胁迫作用。 相似文献
17.
The prefabricated pile,driven in soft clay,can squeeze the soil laterally in a certain scope around the pile,and the void ratio is reduced significantly;consequently,the shear bearing capacity is raised.But the soil parameter,which is used to estimate the capacity of pile,is reduced according to the soil state before the pile was driven.Then,a certain difference appears when the pile is working.The calculation result usually is partial to conservative.This paper analyzes the squeezing mechanism of the pile using the theory of cylindrical cavities expansion.And a formula,which is used to estimate the increment of shear bearing capacity of soil around the pile when excess pore water pressure from pile driving distributes completely,is presented based on the unique relation between the shear bearing capacity and the density of the soil.This formula can be used to estimate the final ultimate-bearing capacity of the pile.The calculated results by the proposed formula are in good agreement with those of the site measurement. 相似文献
18.
Changes in nutritive value of alfalfa (Medicago × varia T. Martyn) and Festulolium (Festulolium braunii (K. Richt) A. Camus) under drought stress 
下载免费PDF全文
下载免费PDF全文 Legume–grass mixtures showed a weaker response to adverse environmental conditions than to monocultures. A yield decrease due to the scarcity of water is well documented, while the impact on the food value is inconsistent. Therefore, we undertook studies to assess the impact of water deficit in the soil on the content of the nutrients in alfalfa and Festulolium grown in monoculture and in mixture. A pot experiment was carried out in 2012–2014 in a completely randomized design, with four replications. The research was carried out at two levels of soil moisture: 70% field water capacity FWC (optimal conditions) and 40% FWC (drought stress). We found that the effect of drought stress on the food value of alfalfa and Festulolium was smaller than on the yield. Water deficit caused a significant yield decrease, the biggest in alfalfa in monoculture. Drought stress significantly reduced the content of crude fibre, the contents of crude protein and crude fat tended to increase. The influence of stress on water‐soluble carbohydrates content was not determined. Nutrient content was varied depending on a species. Introducing alfalfa as a component to a mixture with Festulolium caused a significant yield increase and improved the nutritional value of dry matter. 相似文献
19.
《Soil Technology》1991,4(4):319-327
Because of the very low soil solution ionic strengths in highly weathered soils, clay particles can be readily dispersed under the impact of raindrops. The clay fraction of many soils is dispersible under the combined effects of mechanical disturbance and low electrolyte concentration. This clay dispersion results in fine particle segregation at the soil surface, with clay particles moving into and blocking soil pores resulting in the formation of a highly impervious crust which reduces infiltration. Because the clay is dispersed, the particles usually orient themselves in a laminar fashion as they settle. As a result, runoff is substantially increased, giving rise to soil erosion. The crusts formed in this manner often have very high strengths which prevent or substantially reduce crop emergence. The formation of such crusts can be prevented by the application of relatively low rates of by-product gypsum such as phosphogypsum on the soil surface which produces sufficient electrolyte in solution during raindrop impact to maintain the clay particles in a flocculated condition. The results of a number of experiments in which different soils were treated with phosphogypsum are discussed to illustrate the effects of electrolyte concentration, level of sodium and other factors on the formation of surface crusts and the consequent runoff and erosion. As a result of the application of phosphogypsum to the soil surface, a laminar orientation of clay particles at the surface is prevented, which allows a much greater proportion of the rainfall to enter the soil. Any crusts formed are thus much weaker and do not reduce seedling emergence. This type of crust formation can also be prevented by reducing raindrop impact through the use of mulches. This phenomenon occurs on many soils not normally considered to suffer from chemically-induced physical problems, which points to the importance of considering chemical as well as physical processes in the evaluation of potential runoff and erosion. 相似文献
20.
考虑降水、支护结构变形以及基坑隆起3个因素引起的基坑周围土体的沉降,根据降水引起土体沉降的机理,运用修正的分层总和法单独计算出由降水引起的周围土体沉降。通过研究基坑开挖引起坑外土体沉降的规律,推导出由基坑开挖引起的坑外土体沉降理论公式。把降水引起的沉降及基坑开挖引起的沉降进行叠加,加入修正系数,最终以简化的理论公式合理地计算出基坑周围土体沉降。具体工程验证表明,推导的理论解析解与实测数据十分接近,能有效预估基坑周围土体沉降,为施工方案编制提供可靠的理论依据,最大限度减少基坑施工对周围环境的影响。 相似文献