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目前报道的不少实验成果,在得出粉土热物性指标和某一因素的关系时,并未保持其他影响因素固定不变,因而只能说明粉土热物性指标随影响因素的定性变化趋势。要建立热物性指标与影响因素间的确定性关系和推算公式,需要更为严格的实验,即研究某一影响因素时保持其他因素不变。通过一系列实验,对粉土试样的热导率进行研究,在排除孔隙比、干密度、土样成分等影响因素的情况下,独立分析了粉土的热导率与含水量间的关系。实验结果表明粉土的热导率随含水量的增大而增大,其变化规律与砂土一致,都符合对数变化规律,且整个变化过程可分为两个阶段。同时还分析了粉土的内在传热机制,有效描述和解释粉土热导率随含水量的变化规律。分析结果表明用对数形式来描述粉土热导率与含水量之间的关系是正确的。
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上海地区沉桩阻力估算方法分析探讨 总被引:2,自引:0,他引:2
分析了估算沉桩阻力的必要性。在简单介绍了上海地区土层特性的基础上,按照桩端持力层土层性质和桩侧土性质的不同组合,将上海地区地基土分为4类进行研究。选择了4个具有代表性的已有计算沉桩阻力的计算公式,针对不同地基土类型,分别利用大量工程实测数据对各公式进行了分析研究,结果表明没有一个公式普遍适用于各种地基土。在分析各公式在不同地基土中的优缺点的基础上,提出了推荐使用的以静力触探比贯入阻力Ps值为主要参数,同时考虑土体灵敏度和侧阻力、端阻力深度修正的沉桩阻力估算公式。运用大量的工程实测数据对该公式进行了验证,结果表明对不同的地层组合都比较适合。推荐公式对判定静压桩沉桩可能性和施工设备选型具有参考价值。 相似文献
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地震作用诱发的场地土震陷问题引起了人们广泛关注. 以阜新地区风积土为研究对象,进行了50年超越概率2% 和10% 的地震载荷及等幅正弦载荷作用下风积土的震陷试验,探讨了振动次数、动应力幅值和含水量对风积土震陷系数的影响规律,建立了风积土震陷系数经验公式. 依据分层总和法估算了2 条地震载荷和等幅正弦载荷作用下风积土场地震陷量,并对场地风积土的震陷性进行了评价. 以上研究成果将为阜新地区风积土地基的抗震防震设计提供参考依据,具有重要的工程应用价值. 相似文献
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粉土是介于砂性土和黏性土之间的一种过渡类型土,工程性质既与砂性土不同又与黏性土有较大区别。针对目前还没有合适的室内实验仪器测试粉土临界水力比降和抗渗强度的现状,从试样极限平衡状态出发,对土体进行受力分析,研制了粉土抗渗强度测定设备,研究的实验方法解决了粉土饱和难问题。设计的变水头装置和透明接水容器,保证了粉土抗渗强度测定的可靠性和准确性。多个渗透容器并联成多套装置,可实现多个样本同时测定。对杭州钱塘江粉土的实验结果表明,粉土的临界水力比降与一般砂土有差异。原状样的抗渗强度比击实样高。铺设土工布抗渗层,将大大提高粉土的抗渗强度。研究结果可为粉土地基渗透破坏的防控提供参考。 相似文献
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本文以区域构造应力场的地质力学分析为基础, 结合声发射(AE)法对引水区探洞大理岩定向岩样的地应力实验测定, 对该区地应力场进行了初步研究, 比较了地质力学宏观分析与应力量测结果之间的关系, 探讨了AE法测定地应力存在的问题。 相似文献
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地基弹塑性承载力pcr、p1/4的公式在推导过程中,为方便求解,一般假设地基土体的静止土压力系数K0=1,即把自重应力场看成是静水应力。这一假定实际上人为地增加了地基土的侧向压力,使土体处于加密状态,从而过高地估计了地基承载力。考虑K0≠1的前提下,由地基土中一点的应力状态,根据莫尔-库伦破坏准则,得到该点的临塑、临界荷载的近似公式。该公式修正了一些学者在K0≠1时推导地基弹塑性承载力公式过程中的缺陷,也弥补了现有公式的局限性,得到了土体抗剪强度参数c、φ在不同的K0下对地基临界载荷p1/4的影响,给出了该近似公式的适用条件。 相似文献
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波数-频率域内地基土表面位移Green函数的理论分析 总被引:2,自引:0,他引:2
建立了柱面坐标系下分层弹性半空间地基土模型。利用钟阳刚度矩阵法和Haskell-Thomson传递矩阵法推导出所有分层土体之间的振动传递关系;根据Helmholtz定理将土体的位移向量分解成势函数的形式,推导出弹性半空间表面应力与位移之间的关系;再将分层土体和半空间地基土通过位移与应力之间的关系进行耦合,得到分层弹性半空间地基土模型表面位移与应力之间的关系。结合单位脉冲荷载作用下地基土表面的边界条件,推导出波数-频率域内地基土表面位移Green函数的解析解,用Matlab程序语言对理论进行实现并通过算例对地基土表面位移Green函数的特征进行了分析和总结。 相似文献
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P. Roux de Reilhac F. Bonnefoy J.M. Rousset P. Ferrant 《Journal of Fluids and Structures》2011,27(3):456-466
We consider the transient water wave technique for the experimental determination of response amplitude operators (RAOs) of a floating structure. The main advantage of this technique, which consists of generating a wave focused near the model and analyzing the resulting motions, is that only a single test is required to accurately estimate the RAOs in a wide frequency range. The focused wave, however, may produce nonlinear effects. We thus propose an improved method in which the response is linearized by means of crest and trough focusing. The method is applied to a model barge and compared to other classical methods such as regular, random and transient waves. Based on criteria like accuracy, time required and ease of use, the focused wave technique appears to provide many advantages to determine RAOs. 相似文献
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针对河南某岩石碎渣高填方路堤,提出了夯击能1000kN·m、虚铺厚度1.5m的强夯施工工艺,对试验段进行了现场检测:地质雷达波形较好地反映强夯后虚铺层厚度的减小幅度,并可判断强夯水平有效加固范围为4m,瑞利波速沿深度变化比较均匀,平均值达到了310m·s-1,重型动力触探结果表明试验段达到中密程度,灌水法测得的固体体积率都达到了83%以上,上述检测结果说明强夯的加固效果比较理想。采用ABAQUS有限元分析软件,将夯锤简化为刚性体,通过施加竖向初速度的方式模拟了强夯作用,结合雷达测试结果,认为夯沉量20mm可作为强夯的有效加固范围,最后模拟了存在涵洞结构物的路堤的强夯作用,指出涵洞上方路堤厚度必须达到8m以上,才能保证强夯安全作业。 相似文献
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This paper examines an asymptotic analysis for predicting sound fields above a rigid-frame porous medium, the so-called non-locally reacting porous medium. Their solutions can be represented by a direct wave term, a reflected wave term and a diffraction wave term. Exact and analytical solutions are available for the direct wave and the reflected wave from a perfectly hard ground. In the contrary, the diffraction wave term can only be cast in an integral form that is amenable to approximate analysis. A modified saddle-point method is explored to evaluate the diffraction integral asymptotically. Three different types of non-locally reacting surfaces, which are an extended reaction, a hard-backed layer, and an impedance-backed layer, were considered. The sound fields above these porous surfaces have the same form but they are different by an augmented diffraction term in the solutions. The analytical formula for the total sound fields, which can be stated in a closed form, offer a physically interpretable solution comprising of a direct wave and ground reflected wave terms. This latter term can further be split into a specularly reflected plane wave and ground wave components. A series of numerical comparisons have been conducted to validate the asymptotic analyses presented in this study. It has been demonstrated that the overall sound fields can be predicted well by the formula for all incidence angles and for a wide range of non-locally reacting porous surfaces. 相似文献
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Accurate estimation of blast loads on structures is essential for reliable predictions of structural response and damage.
Current practice in blast effect analysis and design estimates blast loads primarily based on empirical formulae obtained
from field blast tests. Due to the limited availability of test data, those empirical formulae are usually applicable to the
case that the reflection surface of the structure is big enough so that no wave diffraction around the structure exists. They
will overestimate the blast loads on structure columns without infill walls around them, which are very common in the modern
buildings, especially for the ground floor columns. For a standalone column, the initial reflected pressure may be quickly
relieved at the edge of the column, and the column will be engulfed with the blast wave due to diffraction. Therefore, the
interaction between the blast wave and structure is important for such columns. The blast loads on such columns will be different
from those obtained in field blasting tests on walls. There is no method in the open literature to estimate blast loads on
standalone columns. In the present study, interactions between blast waves and structure columns are simulated using AUTODYN
3D. The influence of the scaled distance of the blast, column stiffness, ratio of the supported mass to the column mass, and
column dimension and geometry, on the blast wave–column interaction is investigated. Based on the numerical simulation results,
some formulae are proposed to estimate the blast pressure, impulse, and the reflected pressure time history on standalone
structure columns.
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基于水平土拱效应的桩间挡土板土压力计算研究 总被引:4,自引:0,他引:4
基于``平板开缝-装配-焊接'工艺制备了以高聚物为基体的Kagome等蜂窝结构,并开展
了Kagome, 正三角形和菱形蜂窝结构的面内准静态压缩力学行为实验研究,实验过程中应用
CCD图像采集系统和图像相关法对试件进行了全场位移监测. 另外对比传统正六边形蜂窝,
采用数值分析技术,模拟了低速冲击下不同蜂窝结构坍塌行为. 实验结果和数值模拟均
揭示了在材料用量和结构尺寸完全相同的情况下,Kagome蜂窝结构的面内能量吸收性能优于
其它3种蜂窝结构,并发现了Kagome蜂窝压缩变形时所特有的局部蜂窝旋转变形. 研究结果
表明改变蜂窝形状和周期性排布会对蜂窝结构整体的变形模式以及能量吸收性能产生较大的
影响. 相似文献
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贵州石漠化地区棕黄色粘性土团聚体稳定性研究 总被引:1,自引:0,他引:1
唐益群〓张晓晖〓佘恬钰〓杨〓坪〓王建秀 《力学学报》2009,17(6):817-822
以贵州省普定县碳酸盐岩石漠化研究试验区(陈旗村)的棕黄色粘性土为研究对象,考虑了初始含水率和浸润时间两个影响因素,对研究区土体中占绝对优势的>5mm的大颗粒团聚体进行了共计16组湿筛法试验。结果表明:棕黄色粘性土团聚体遇水破裂的过程主要发生在被浸润初期,初始含水率越小的土壤,经雨水浸润后,大颗粒团聚体破裂得越快越彻底;而原本就比较湿润的土体,团聚体的稳定性则较好。因此,对碳酸盐岩石地区石漠化的防治,应着重考虑气候长期干燥、蒸发量对水土流失的影响。
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Jarosaw Pytka 《Journal of Terramechanics》2009,46(5):241-249
Strain gage pressure transducers are most frequently used for soil stress state determinations. Their construction, rugged and mechanically resistant, enables them to measure stresses within a wide range (up to 500 kPa) in harsh conditions. Output signals are easily readable and stable. The accuracy of the measurements, however, depends upon proper design and calibration before use in soil. This paper contains information on design considerations and results from calibration tests of transducers of two membrane diameters: 20 and 30 mm. The calibration test stand, as well as calibration procedures, are described in detail. For calibration tests, natural soils were used, as well as steel balls, to simulate the effect of the aggregated structures of arable soils and grain materials. The calibration method considered different soil types as well as soil water content. Soil and its water content were found to have an effect on output scale factor. 相似文献
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西南喀斯特地区的石漠化已经严重影响了人民正常的生产生活。水土流失是石漠化过程中一个关键环节。喀斯特地区地表广泛覆盖的红粘土在降雨条件下随着含水量的增加和人工垦殖的影响,剪切强度会产生变化,更易发生水土流失。本文以贵州普定石漠化研究区(陈旗村)的红粘土为例,以原状土模拟未经扰动的土样,以重塑土来模拟经过开垦被扰动后的土样,设计了原状土和重塑土在不同含水量下的直剪试验,初步地研究了这一变化规律。结果表明:在含水量大于35%时,石漠化地区红粘土粘聚力和内摩擦角均随着含水量的增加显著降低;在同一含水量水平下,原状土的抗剪强度明显优于重塑土,且随着含水量的增加,重塑土的强度衰减较之原状土快许多,表明了经过人工垦殖后的红粘土在降雨条件下更易发生水土流失。
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