Small Strain Stiffness and Non-Linear Stress-Strain Behaviour of Cement-Mixed Gravelly Soil

The stiffness at small strains and non-linear stress-strain relation of compacted cement-mixed well-graded gravelly soil as well as the ageing effects were evaluated by drained triaxial compression tests on compacted moist specimens cured for different periods at isotropic and different anisotropic stress states. In all the tests, the initial stress-strain relation at small strains less than about 0.001% was essentially elastic and the initial Young's modulus, E₀, was essentially the same as the E_eq value evaluated by applying unload/reload cycles under otherwise the same conditions. The E_eq values were rather independent of strain rate. The E_eq value from the first unload/reload cycle applied during otherwise continuous ML became noticeably lower than the elastic modulus evaluated at the same stress state, more as approaching the peak stress state. After a number of small unload/reload cycles and long sustained loading, the E_eq value became closer to the elastic modulus due to a decrease in the viscous effects. The ratio of E₀ to the compressive strength (q_max) was similar to that of concrete but noticeably larger than those of uncompacted cement-mixed soil, sedimentary softrock and unbound gravelly soil. Both E₀ and q_max increased with time by ageing, while the E₀/q_max ratio decreased with time. When ML was restarted at a constant strain rate after ageing with a shear stress, the tangent stiffness became very high for a large stress range with a substantial change in the non-linearity of stress-strain relation.     

花岗石锈斑的清洗

去除舍铁高的花岗石中锈斑，可以提高其商品价值，给企业带来良好经济效益。在处理液中添加柠檬酸或磺基水杨酸，可有效地提高除锈效果。在处理液中添加高效附着剂，可提高处理液在石材表面驻留和反应时间，对节约处理费用效果明显。     

计入初始应变项的平面梁单元非线性刚度矩阵

开展平面结构几何非线性分析时经常会遇到杆件含有初始应力力或初始应变的情况。由于非线性刚度矩阵中舍有节点位移，矩阵运算量大，给刚度矩阵的推导带来很大困难。根据平面梁单元几何非线性方程，采用计入初始应力和初始应变项的一般性线弹性应力应变关系，导出了相应的切线刚度矩阵，利用MATLAB数学工具箱，给出了含有初始应力和初始应变的所有刚度矩阵的显式表达式，为程序编制奠定了基础。     

住宅室温模拟和实测数据的一致性分析

通过对住宅内某个测试房间模拟计算室温与实测室温的一致性分析,研究了天空背景辐射、太阳辐射、邻室室温等扰量对室内热状况的影响程度,并反推计算得到了测试房间与室外的逐时通风换气量。同时,一致性分析又说明了模拟软件DeST反映住宅室内热状况变化规律的准确性和合理性。     

岩土小应变问题研究进展

岩土小应变情况下表现出许多与一般中大应变实验不同的特性.现场测试表明岩土工程中应变一般都比较小.因而近年来岩土小应变问题受到重视.本文对当前岩土小应变力学行为实验研究与本构模型研究进展进行了较为系统的描述.提出了合理描述岩土小应变力学特性需要进一步研究的几个问题.     

不同强夯加固方案的现场量测与分析

结合某工程地基处理实例,对不同强夯加固方案的现场量测(包括地面变形、超静孔隙水压力和地面振动加速度)结果进行详细的分析探讨,提出了应用强夯技术加固饱和软土地基的可行性及若干有效的辅助措施.     

黄土粘弹性性质的室内外试验分析

基于粘弹性力学理论,室内外试验分析不同静力荷载作用下黄土的粘弹性特征,结合三参量单元的蠕变模型和黄土试验装置推导出适合于黄土变形的蠕变方程式.通过自制室内试验设备,测试黄土试件在10kg-100kg十个不同等级静力荷载作用下的应变,采用数据分析软件并结合蠕变方程式对沉降曲线进行模拟,得到不同荷载作用下黄土蠕变方程式的两个关键系数,通过这些系数可以分析黄土的非线性粘弹性性质并可预测不同填筑高度下黄土路基工后不同时间的沉降量.黄土在静力荷载作用下的蠕变表明:其应力应变特征具有粘弹性性质,采用表征非线性粘弹性特征的三参量固体模型能够较好地模拟黄土的沉降规律.     

土体小应变特性的研究进展

大量实测资料表明 ,在工程实际中大部分土体的变形在 0 0 1%～ 0 3%之间。但由于仪器精度的限制及人们意识的不足 ,直到近年来人们才逐渐意识到研究小应变土体特性的重要性 ,本文较为系统地介绍了这方面的研究情况     

Laboratory and Field Investigations of Polymer and Crumb Rubber Modified Bitumen

In this paper, properties of new kind of modified bitumen are presented. Bituminous binder was modified with mix modification using polymer and additive of crumb rubber. Terminal blend process at the refinery was applied to produce the mixed modified binder. Laboratory tests were focused on the characterization of the properties of 45/80-55 CR binder with comparison to reference 50/70 and conventional polymer modified 45/80-55 bitumen. Based on conventional binder tests such as penetration, softening point and Fraass breaking point as well as BBR （bending beam rheometer） and DSR （dynamic shear rheometer） tests, rheological properties were investigated. For determination of stability of the polymer and crumb rubber, modified bitumen tube testing method was used. Based on the results analysis, improvement of the viscoelastic properties of polymer and crumb rubber modified bitumen was observed. Conventional properties and stability tests showed that it is possible to pass standard requirements for polymer modified bitumen. Mixed modification and terminal blend allow to use crumb rubber as a modifier with elimination of the separation of crumb rubber during transportation and storage at high temperature. In this paper, experience from filed sections with use of the asphalt mixture with new kind of modified bitumen is presented.     

Effects of Geosynthetic Reinforcement Type on the Strength and Stiffness of Reinforced Sand in Plane Strain Compression

The effects of geosynthetic reinforcement type on the strength and stiffness of reinforced sand were evaluated by performing a series of drained plane strain compression tests on large sand specimens. The reinforcement type is described in terms of the degree of unification of the constituting components (for geocomposites) as well as the tensile strength and stiffness, the covering ratio and others (for geocomposites and geogrids). Sand specimens reinforced with different geosynthetic reinforcement types exhibited significantly different reinforcing effects. A geocomposite made of a woven geotextile sheet sandwiched firmly with two sheets of non-woven geotextile, having a 100% effective covering ratio, exhibited reinforcing effects higher than typical stiff and strong geogrids. With some geocomposite types, the reinforcing effects increase substantially by better unifying longitudinally arranged stiff and strong yarns and non-woven geotextile sheets. When fixed firm to the yarns, the non-woven geotextile sheets function like the transversal members of a geogrid by locally transmitting load activated by interaction with the backfill to the yarns. These geocomposites can exhibit reinforcing effects equivalent to those with stiff and strong geogrids. Local strain fields of the specimens are presented to show that, for reinforced sand, the peak stress state reached is always associated with the development of shear band(s) in the sand and a higher peak strength is achieved when the strain localisation starts at a larger global axial strain due to better reinforcing effects.     

白垩系地层冻结壁冻融全过程温度场现场实测研究

目前西部地区矿井建设普遍采用冻结法凿井,但对白垩系地层冻结特性了解不清,特别是融化过程尚未有可靠资料作为参考.文章以西部地区某在建井筒选择代表性地层为研究对象,开展冻结壁温度场冻结、融化全过程现场实测,通过二者结果对比,得出西部地区冻结壁温度场冻融过程分布规律,为以后类似地层冻结法凿井提供参考.     

FRP锚杆工程特性的室内外试验研究

纤维增强塑料(简称FRP)筋是一种新型的复合材料,本文介绍了FRP锚杆的特点,同时通过室内试验和现场试验,对其拉拔破坏模式、粘结强度、拉拔承载力、锚固反应与钢锚杆进行了对比分析,阐述其锚具设计方法和施工质量检测方法。试验证明,FRP锚杆具有良好的力学性能,能够满足边坡锚固的设计要求,具有很高的推广应用价值和广阔的发展前景。     

地下室长侧墙混凝土早期温度场及应变场分布特性试验研究

混凝土早期变形及约束引起的地下室侧墙混凝土开裂现象是工程中的常见问题.通过预埋温度与应变传感器的方法,对实际工程中侧墙混凝土早龄期的温度与应变的变化规律进行了监测.研究结果表明,地下室侧墙混凝土浇筑后,温度的变化都有一潜伏期,此后温度急剧上升直至达到最大温升,之后开始降温并趋于外界温度.同时研究也表明,混凝土内部温度是...     

浅析基桩低应变法现场检测技术

低应变法检测桩身完整性的技术建立在一维弹性波动理论基础上，具有方法快速、费用低、结果比较可靠等特点，因而广受检测单位和建设单位的欢迎。在实际工程应用过程中，如何进一步改进现场检测方法、提高检测质量直接关系到基桩质量和安全控制。笔者结合自身工作经验，从五个方面，提出了自身的见解。     

台风“韦帕”风场实测及风致输电塔振动响应

给出了台风"韦帕"经过时,在典型的农村地貌上进行的多点边界层风特性以及风致输电塔振动的实测结果.基于风速数据,重点分析了风特性各项参数的空间均匀性,包括平均风速和风向、风剖面参数、湍流强度、阵风因子、湍流积分尺度和脉动风谱、竖向衰减系数以及水平相干性.采集了榆电塔横担和塔头塔身连接处垂直线路方向的振动加速度.基于振动数据,应用Hilbert-Huang变换(HHT)方法识别了输电塔垂直线路方向第1、2阶模态的自振频率和阻尼比.结果表明,自振频率识别结果与有限元计算结果比较接近,阻尼比识别结果远大于一般钢结构的阻尼比.     

Field Measurements of Ventilation and Ventilation Effectiveness in an Office/Library Building

Mechanical ventalation system performance involves the provision of adequate amuunts of outdoor air, uniform distribution of ventilation air within the occupied space, and the maintenance of thermal comfort. Standard measurement techniques exist to evaluate thermal comfort and air change rates in mechanically ventilated buildings; procedures to evaluate air distribution or ventilation effectiveness in the field are still being developed. This paper presents measuremetlts of air change rates and ventilation effectivenes in an office/library building in Washington, DC. The tracer gas decay technique was used to measure whole building air change rates. The air change rates during the measurement period were essentially constant at about 0.8 air changes per hour, somewhat below the design specification and above the minimum recmmmded in ASHRAE Standard 62-1989. Ventilation effectiveness was investigated at several locations within the building through the measurement of local tracer gas decay rate and mean local age of air. The ventilation effectiveness measurements serve as an investigation of the applicability of the m e a s u r r n procedures employed, providing insight into the measurement issue of establishing initial conditions, the spatial variation in test results within a building, and the repeatabildy between tests. The results of the ventilation effectiveness meusurements are consistent with good distrhtion of the outdoor air by the ventilation system and good mixing within the occupied space.     

北京光彩大厦深基坑开挖现场监测与理论分析

由北京光彩大厦深基坑开挖过程中的监测结果及机理分析,得出以下结论:实施早期降水可在基坑整体刚度形成前有效利用基质吸力减小桩顶的侧移量;支护结构整体空间刚度的较早形成可以有效减小基坑的水平侧移;锚杆张拉锁定值小,在锚固体侧可引起负摩阻力;由实测值总结得出摩阻力值在锚固体侧的分布呈二次函数关系;桩身最大位移可能发生在桩身刚度较弱的截面;支护结构与土相互作用的结果,造成土压力实测值与经典理论计算值在分布规律上存在较大的差别。     

基于波场等效的节理面刚度参数取值研究

节理岩体中的节理面往往有一定厚度,如果采用无厚度的线性节理模型分析,其刚度参数的确定非常困难。通过分析弹性波穿过节理面时的波场效应,建立了基于节理后振动强度相等的波场等效法,用于确定带厚度节理的刚度参数,并分析了各因素对弹性波在节理上传播的影响。结果表明:线性节理面的刚度参数是节理岩体的固有属性,与外界荷载无关,采用波场等效法计算刚度参数可行;在弹性波范围内,这种等效参数与入射波频率、入射角等因素关系不大。该方法可用于有厚度节理面动强度参数的确定与分析,完善现有的节理面刚度取值方法。