Gravity induced near-surface stresses in long-symmetric ridge-valley systems

Patterns of near-surface gravity and tectonically-induced stresses within ridge-valley systems greatly illuminate our understanding of important geodynamic processes as well as design of experiments to elucidate them. This paper presents analytical results derived for a number of geometrical configurations and range of mechanical properties of a ridge-valley system using the elastic solution of McTigue and Mei. The study reveals (i) the presence of non-zero compressive stresses near the ridge crests, which decrease with increasing Poisson's ratio (μ) and reduce to zero at ridge crests for μ=0·5 and that (ii) the central tensional regime characterizing a valley becomes narrower due to the presence of two ridges; and decreases with increasing μ, becoming compressive at depth. For all geometrical parameters considered, all components of stress show concentration at the outer flanks of the ridges and increase with depth approaching a standard state of stress.     

水库诱发地震评价研究

本文是在总结了水库地震的基本情况和主要特征后,以工程地质学理论为基础,并结合地震地质学,对水库地震进行了评价。其目的是为了确保大坝施工期与建成后的安全运行,并根据库坝区的诱震地质条件,正确评价诱发地震的可能性及其可能造成的危害,为工程建设采取合理的对策提供依据。其步骤分为三步：水库地震可能性评价、水库地震危险性评价与水库地震监测和预测研究。其内容为区域工程地质、构造地质、水文地质、地震与水库地震监测,并依据世界水库地震资料的对比分析,总结出：构造断裂型、地表卸荷型与岩溶塌陷型3种主要水库地震类型的判据。其评价方法,主要是对水库地震综合性分区评价及水库地震强度的评价方法进行了详细的论述,具有较高的实用价值。     

水库诱发地震评价研究

本文是在总结了水库地震的基本情况和主要特征后,以工程地质学理论为基础,并结合地震地质学,对水库地震进行了评价.其目的是为了确保大坝施工期与建成后的安全运行,并根据库坝区的诱震地质条件,正确评价诱发地震的可能性及其可能造成的危害,为工程建设采取合理的对策提供依据.其步骤分为3步:水库地震可能性评价、水库地震危险性评价与水库地震监测和预测研究.其内容为区域工程地质、构造地质、水文地质、地震与水库地震监测,并依据世界水库地震资料的对比分析,总结出:构造断裂型、地表卸荷型与岩溶塌陷型3种主要水库地震类型的判据.其评价方法,主要是对水库地震综合性分区评价及水库地震强度的评价方法进行了详细的论述,具有较高的实用价值.     

Risk assessment of workers exposed to noise pollution in a textile plant

In order to assess the risks associated with worker’s hearing loss, due to exposure to noise pollution, at the Boroujerd Textile Factory a cross sectional study was conducted. 60 workers from the Spinning and Weaving workshops and official staff were randomly selected as case and control groups and their hearing were tested by audiometry. The audiometric results revealed that amongst workers being exposed to the noise pollution in the Spinning and Weaving Workshops there is a distinct increase in the number of cases of hearing loss at high frequencies. There also appears to be a slight bias towards hearing loss in the left ear, in preference to the right in addition, those who have worked for longer than 16 years are subjected to hearing loss even at low frequencies conversely, the office workers (the control group) seem to suffer little or no hearing loss at low frequencies at all, but after approximately 10 years of service there may be some hearing loss, but only at higher frequencies, which could be attributed to presbycusis. Also, the t-test (statistical hypothesis test) results verified the significant difference among both groups at high frequencies. The questionnaire results indicated that workers feel symptoms such as headache, no sense centralization, excitement, nervousness, vertigo. Hence, controlling procedures seem to be essential to protect workers from noise disorders.     

双圆盾构掘进施工扰动土体附加应力分析

应用弹性力学Mindlin解建立了双圆盾构掘进引起土体附加应力积分表达式。运用复化Gauss-Legendre数值积分公 式,定量分析了双圆盾构正面推力、盾构与土体侧摩阻力对土体扰动的程度及范围。分析表明,双圆盾构掘进对土体扰动具有区域性特征,盾构机上部表现为背土挤土,侧面则表现为挤压剪切效应,并且侧摩阻力对土体的扰动程度更大。所得结论对于双圆盾构穿越临近地下管线或建筑物桩基的施工提供理论依据。     

Assessment of noise exposure and associated health risk in school environment

Noise exposure has become one of the most important factors in determining the quality of life in indoor environments. This paper assesses and analyzes noise exposure levels at school and preschool classrooms with different indoor environments. The sound level [A-weighting equivalent steady sound level L _Aeq (dBA)] was measured using a CEL-63× digital sound level meter. The noise level measurements were performed inside two preschools at three classrooms (an activity room, classroom KG1 and classroom KG2) and three schools at different classrooms, starting from grade 1 to grade 12. The logarithmic average noise levels (L _{Aeq avg}) and the 8-h average noise exposure level (L _{EX, 8-h}) were estimated for each classroom. Furthermore, health risk issues associated with the exposure to high noise levels were investigated using a questionnaire and an interview with more than 250 teachers at the preschools and the schools. Then, the results were analyzed using different statistical tools and were compared with the World Health Organization, Occupational Health and Safety and National Institute for Occupational Safety and Health standards. Also, the results were compared with those from different countries worldwide. The study results show that the 8-h average noise exposure level exceeded the allowable limits in some schools, which indicates that students and teachers can face a serious health effects from noise exposure. The comparisons show that the values of noise levels in Kuwait are higher than those in different countries. The maximum value of noise levels was found in secondary schools. The health problems found during the survey are potentially associated with issues related to hearing, voice, headache and the physiological function of teachers.     

Elasto‐plastic seepage‐induced stresses due to tunneling

When tunneling is carried out beneath the groundwater table, hydraulic boundary is altered, resulting in seepage entering into the tunnel. The development of flow into the tunnel induces seepage stresses in the ground and the lining is subjected to additional loads. This can often cause fine particles to move, which clog the filter resulting in the long‐term hydraulic deterioration of the drainage system. However, the effect of seepage force is generally not considered in the analysis of tunnel. While several elastic solutions have been proposed by assuming seepage in an elastic medium, stress solutions have not been considered for the seepage force in a porous elasto‐plastic medium. This paper documents a study that investigates the stress behavior, caused by seepage, of a tunnel in an elasto‐plastic ground and its effects on the tunnel and ground. New elasto‐plastic solutions that adopt the Mohr–Coulomb failure criterion are proposed for a circular tunnel under radial flow conditions. A simple solution based on the hydraulic gradient obtained from a numerical parametric study is also proposed for practical use. It should be noted that the simple equation is useful for acquiring additional insight into a problem on a tunnel under drainage, because only a minimal computational effort is needed and considerable economic benefits can be gained by using it in the preliminary stage of tunnel design. The proposed equations were partly validated by numerical analysis, and their applicability is illustrated and discussed using an example problem. Comments on the tunnel analysis are also provided. Copyright © 2010 John Wiley & Sons, Ltd.     

盾构法隧道施工引起土体位移与应力的镜像分析方法

盾构法隧道施工会引起隧道周围一定范围土体的位移,对土体位移进行较为准确地分析,对于控制隧道周围土体位移量和减小过大位移对既有建筑物及管线带来的危害十分重要。隧道周围土体的位移是由地层损失引起的,并且与注浆量有很大关系。根据地层损失与注浆量的空间分布规律,应用镜像方法原理,对盾构法隧道推进产生的土体位移与应力进行空间分析,得到隧道周围土体的位移与应力分布,计算结果与天津地铁施工过程的现场实测结果对比表明,该方法行之有效。     

An analytical solution for stresses induced by a post-tensioned anchor in rocks containing two perpendicular joint sets

A new analytical approach for the analysis of stress around a post-tensioned anchor in rock with two perpendicular joint sets is presented. The solution considers nonlinear shear stresses developed along the anchor bond length as well as debonding at the tendon–grout interface. The bearing plate effects are also considered in the analyses. The following assumptions are made: (1) homogeneous and orthotropic elastic rock; (2) half-space rock mass with plane strain conditions; (3) trilinear bond-slip model for the behavior of the tendon–grout interface; (4) an elastic anchor. The employed methodology is to decompose the anchor problem into two problems of simpler loadings: stresses produced under a rigid bearing plate and stresses induced by interfacial shear stresses mobilized along the bond length. Based on the proposed solution, an illustrative example is given and the results show that a large compressive region is formed around the anchor free length. Tensile stress concentrations are also observed around the bond length and near the rock surface outside the bearing plate. A parametric study is also conducted to investigate the effects of joint properties on the induced stresses. The results show that as the number of joints intersecting the anchor axis increases, the magnitude of compressive stresses in the free zone decreases, while the size of compression zone around the anchor increases. To verify the results of the analytical approach, a comparison is made with numerical results obtained by using the finite element method. The analytical solutions compare very well with the results obtained by numerical method.     

地基剪切模量对列车引起的动应力的影响

为了分析地基剪切模量对列车引起的地基动应力的影响,利用移动荷载作用下弹性半空间内部的应力响应解,计算了两种不同速度、不同地基剪切模量时,列车引起的地基表面反力和地基动应力。在两种速度下,反力最大值均随地基剪切模量的增大不断增大。不同速度时,地基剪切模量对动应力的影响是不同的。     

Assessment of potential risks induced by increasing extreme precipitation under climate change

Natural Hazards - A warmer climate has caused more extreme climate events like the heatwave or extreme precipitation, which has led to a large number of lives and economic losses. In this study, we...     

Friction effect on stresses in ensiled granular media

We develop, in this paper, an analytical approach of continuous medium type which improves the theory of Janssen and other existing approaches of the same type. This approach allows to calculate the stresses in any point of the ensiled granular medium and to represent as well qualitatively as quantitatively the stress saturation effect. The influence of the friction angles is studied.     

Lithomorphic stresses and cleavage of loess

Lateral stresses existing in soil deposits are important clues to recent stress history because they tend to remain “locked in” following adjustments in the overburden load: Thus a high lateral stress is partly retained following a reduction in vertical stress, as by glacial melting or erosion. Conversely, during loess deposition a low lateral stress should be retained if the soil structure is preserved under increasing vertical stress. This has not previously been verified in the field because of the difficulty of measuring lateral stresses in situ in an hydrocollapsible material.

Tests were conducted at two sites in Missouri river valley loess using theK_o Stepped Blade, which uses data extrapolation to give stress on a zero thickness blade. In basal loess where the moisture content was at or above the liquid limit,K_o = 1.0 ± 0.02. In the upper to middle loess zoneK_o is as low as 0.2 to 0.4, lower than the values of 0.4 to 0.5 that would be expected if the soil were normally consolidated. Near the ground surface, lateral stresses are higher soK_o > 1, attributed to post-depositional weathering and the presence of smectite clay minerals. The vertical sequence of lateral stress from high to low to high again should contribute a tension-induced cleavage if lateral confinement is removed by excavation or erosion. This stress condition is most pronounced in loess close to its source, where the potential tension zone was found to extend to a depth of about 7 m compared to 4 m at the other site. Loess cleavage appears to result from stress relief and is not a unique directional property of this material.     

压力型锚杆锚固段的应力分布规律研究

根据Kelvin解,推导了压力型锚杆锚固段的弹性黏结应力和正应力分布方程。在推导过程中,考虑了三向应力状态对锚固段黏结应力的提高作用。经过与现场试验实测数据的对比分析,验证了理论计算公式的可靠性。采用软质岩体条件下的参数,对锚固段应力分布进行了计算,总结了岩石条件下锚固段应力分布特点,并分析了各种岩土参数变化对锚固段应力分布的影响,为压力型锚杆的进一步理论研究和工程实践提供了基础。     

预剪应力作用下原状黄土动力特性试验研究

以陕西武功地区原状黄土为对象,在不同含水率与不同初始平均主应力下进行动扭剪三轴试验,研究了预剪应力作用下原状黄土动剪切模量与阻尼比的变化规律。结果表明：原状黄土动剪切模量随动剪应变变化的整体趋势并未因存在预剪应力作用而发生改变;存在预剪应力作用时,含水率与初始平均主应力对原状黄土动剪切模量的影响程度降低;含水率与初始平均主应力对预剪应力作用下原状黄土的初始动剪切模量具有显著的影响;存在预剪应力作用时原状黄土的阻尼比随动剪应变的增大先减小而后缓慢增大,其值总体上在0.20～0.35之间;现有的半对数坐标进行直线方程拟合的方法已不再适用于存在预剪应力作用时原状黄土阻尼比的计算;含水率对原状黄土阻尼比随动剪应变变化规律的影响呈现出含水率越大、阻尼比越大的趋势;初始平均主应力对原状黄土阻尼比随动剪应变变化的影响规律不明显。     

库水动态对沿岸路基应力的影响

基于室内物理模拟试验和FLAC数值模拟方法,对沿河（库）路基岩土体内部的孔隙水应力和总应力在河（库）水位动态变化条件下的变化特征进行了研究,两种模拟方法得出的结果是一致的。研究表明,水位上升阶段,总应力和孔隙水应力的总体变化趋势是增大的,但是总应力增大的幅度小,因而有效应力的总体变化趋势是减小的;水位下降阶段,总应力也略有减小,但由于孔隙水应力的大幅度减小,使得填土内有效应力总体上是增大变化的。同时,用FLAC数值模拟方法,能够很好地研究数据的规律性和掌握数据的连续性。因此,用FLAC有限差分法可以有效地模拟沿河（岸）路基在各种水力边界条件下应力场和渗流场的变化情况。     

随采地震噪声衰减研究

鉴于煤矿井下环境的封闭性及对安全生产的高要求特点,炸药震源在煤矿井下地震勘探施工中存在众多局限性,而以采煤机作为震源可以规避炸药震源的许多固有缺陷,具有可以在不影响回采工作面正常作业的情况下对工作面内部构造及应力开展实时探测的优势。但由于采煤机产生的能量远小于炸药震源,因此采集到信号的质量通常受到环境噪声影响,通过分析大量实际数据发现噪声中能量占比较多的为单频噪声和随机噪声,严重影响探测精度。为提高随采地震数据信噪比,提出了同时衰减单频噪声和随机噪声的方法,首先基于互相关技术在构建常规炮集记录的同时衰减单频噪声,然后通过小波变换衰减随机和残余单频噪声,通过模拟数据和实际数据证实,该方法可以在很大程度上提高信号的信噪比。     

列车引起的地基动应力特性

为分析列车引起的地基动应力特性,用移动荷载作用下的弹性地基Euler-Bernoulli梁模型计算得到地基表面与路堤之间的反力。将其视为作用于地基表面的移动面荷载,以单位移动荷载引起的半空间地基内部应力解为基础,对反力在作用空间上进行积分,得到了列车速度小于地基中Rayleigh波速时列车荷载在地基中引起的稳态应力响应解答。给出了应力随空间坐标和时间的变化,分析了应力的特性及分布规律。发现列车经过时在地基中产生的动应力是循环应力,具有明显的偏移应力。竖向动应力的影响范围随着列车速度的增大而不断增大。