察尔汗盐湖地区盐渍土微观结构及其力学与强度表现

为探明察尔汗盐湖区盐渍土的微观结构特征及其力学与强度表现,从盐湖区采集9组不同含盐量的盐渍土样品,对盐渍土进行电镜扫描、直接剪切试验和抗压强度试验,从微观结构上分析了盐渍土的力学与强度表现,提出了察尔汗盐湖区盐渍土颗粒骨架的连结形式。研究结果表明,不同含盐量的盐渍土微观结构形式不同,盐渍土颗粒骨架之间的连结有3种形式:1)点式接触、2)堆叠接触、3)盐晶体胶结;微观结构越密实,盐晶体胶结作用越强,盐渍土表现出越高力学与强度特性;盐晶体的胶结作用是影响盐溃土力学与强度特性的显著因素;无侧限抗压强度显著变化的含盐量拐点为45.74%。     

Determination of long-term strength of frozen loess after numerous freeze-thaw cycles

In order to determine the changing rule of long-term frozen soil strength and elucidate the connection between long-term strength and soil physical properties,frozen loess was subjected to 4,6,8,10,and 50 freeze-thaw cycles,under closed-state conditions in a constant-temperature box.The frozen samples were tested on a spherical template indenter,and the results show that under the effect of repeated freeze-thaw cycles,the long-term strength of frozen loess decreased; changes in the mechanical property indices were highly unstable during the first 10 cycles; the soil strength and density were the greatest at the eighth cycle while the void ratio was the smallest; and after eight cycles all of the indices had less fluctuation and certain rising or falling tendencies.By converting the number of freeze-thaw cycles into elapsed time in the tests,three different forecasting methods of long-term soil strength could be assessed and the soil equivalent cohesive force after 10 years,20 years,or 30 years could be estimated.     

The underground application of Magnetic Resonance Soundings

The potential application of MRS technology in locating waterbearing fractures in underground mines is studied. The determination of the presence of water ahead of mining is important to prevent accidents and to ensure higher efficiency in mining operations. In the usual surface based measurements, with horizontal loop and water layer, the geometry of the problem can be summarized by the value of the inclination of the Earth magnetic field. For MRS measurements under the geometric conditions associated with underground mining, where the loop is non-horizontal, the geometry can be described in an effective inclination that can be expressed in terms of the Earth magnetic inclination and declination, together with two further parameters that characterize the orientation of the mine wall. We examine the consequences of the different geometries on the MRS signal. Since the loop size is severely restricted in underground conditions, the feasible target depth is also severely limited. The consequences of the fractured hard rock aquifer conditions, typical of deep mining or tunneling environments, are also examined. The overall conclusion is that in underground MRS applications the signal strength is too small to enable the practical identification of fractures containing large volumes of water ahead of the mining face.     

干湿循环下含盐量变化对遗址土剪切强度影响的试验研究

中国西北干旱和半干旱地区集中降雨和强烈蒸发的特殊气候环境加剧了对土遗址的破坏。以掺入不同含量Na2SO4和NaCl的重塑土样为研究对象,通过室内模拟开放系统下干湿循环过程,并采用声波测试,反映含盐类遗址土在干湿循环下的劣化过程;测试多次循环后的遗址土剪切强度随含盐量的变化规律,并从盐类性质及波速两方面分析了干湿循环对遗址土剪切强度的作用机理。结果表明:在含水率一定的情况下纵波波速随干湿循环次数的增加而减小;干湿循环后的土体黏聚力随着盐分含量的增加呈下降趋势,内摩擦角则出现先增大后减小的现象;纵波波速与黏聚力随着含盐量的增长整体变化趋势有较好的相关性,与内摩擦角的相关性则表现为纵波波速的间断性和内摩擦角阶段性的契合。     

直剪强度指标的可靠度统计方法

矩法和线性回归法能得到较为准确的岩土抗剪强度指标的均值,但是在统计标准差或变异系数时,矩法常常面临样本容量偏小而导致变异系数偏大的困难,而常规线性回归法无法给出实际所需的抗剪强度指标的标准差。本文从可靠度理论出发,利用正交标准化变量空间中原点到极限状态线最短距离为可靠指标的原理,提出了一种利用Excel规划求解功能求解抗剪强度参数的简便方法。将这一方法应用于91组404个水利水电岩土工程二类岩体与混凝土胶结面大型直剪试验结果的统计中,并将结果与其它方法进行了对比。     

昆明黏性土动力特性试验研究

对昆明地区黏性土进行室内的共振柱试验和动三轴试验,初步研究了该地区黏性土的动力特性,得出了不同初始固结比下黏性土的动强度曲线,比较了黏土与粉质黏土的动强度受固结应力比的差异,并对黏性土的动强度与破坏时其振动周数之间的关系曲线进行了拟合,给出了其数学表达式根据试验所得动强度包线的特征和动强度参数,分析了黏性土强度参数的变...     

甘肃武都典型夯土民房承重墙体抗剪强度试验研究

武都是甘肃省典型夯土民房使用地区.试验中使用武都当地常用土料,完全按照当地施工工艺夯筑两片夯土墙体试件,利用伪静力方法研究墙体抗剪强度.结果显示:(1)上覆荷载对夯土墙体的水平承载力和变形影响较大,随着上覆荷载从10 kN增加到18 kN,开裂荷载和极限荷载分别增加了217％和359％,极限顶点位移则降低了30％;(2)在水平往复荷载的作用下,夯土墙体始终沿着夯土层间水平和垂直接触裂缝处产生破坏,最终碎裂成块体.最后提出了使用铁丝网来加固现存夯土民房承重墙体的建议.     

砖墙-钢筋混凝土墙组合结构震害预测方法

建筑物震害预测对于制定城市防震减灾规划意义重大,对于我国高烈度区建造的砖墙-钢筋混凝土剪力墙组合结构,目前没有成熟的震害预测方法.为了预测西昌市砖墙-钢筋混凝土剪力墙组合结构建筑物在不同地震烈度下可能发生的震害程度,通过分析该种结构在不同地震作用下的受力特点,提出以结构薄弱层的楼层屈服强度系数为指标进行震害预测,并结合...     

内圆外方复合钢管混凝土短柱轴压承载力试验研究

为研究内圆外方复合钢管混凝土柱的轴压承载力,完成了10个试件的轴心受压试验。试验结果表明:达到峰值承载力时,方钢管纵向已屈服、横向尚未屈服;试件的破坏形态为方钢管向外鼓曲、沿纵向局部撕裂,方钢管与圆钢管之间的混凝土已经酥松、局部压碎;大部分试件即使纵向平均压应变达到0.11,尚能承担不小于其峰值承载力70%的轴力;压缩刚度的计算值平均为实测值的83.6%。采用钢管仅提供轴压承载力、不提供横向约束的假定计算得到的试件的轴压承载力,与试验结果符合最好。     

冻土抗拉强度与冻温及含水率关系的试验研究

通过用CBR-l型承载比试验仪实测不同冻结温度和不同含水率下冻土的强度,建立了抗拉强度与冻结温度和含水率关系的数学模型,并进行了科学的分析,找出之间变化的规律：含水率在14％-25％且一定时,温度在0℃— -20℃内抗拉强度随着冻结温度的降低而逐渐增加,在-20℃达到抗拉强度最大值;而冻结温度在-20℃以下,抗拉强度随...