软岩地区钻孔嵌岩灌注桩承载力确定的探讨

单桩承载力的确定,在桩基础的设计中占有重要地位。但在软岩地区由于地层岩性的不同,单桩承载力的实际工作性状与国家规范的规定之间不尽相同。根据实测资料对软岩地区的单桩承载力的确定方法进行探讨,综合考虑嵌岩段侧阻力与端阻力之间的相互协调对嵌岩段所能提供的承载力的影响,提出一种新的计算方法,并结合工程实例,进行验证。     

桂西南岩溶生态脆弱区生态承载力分析及可持续发展状况评价——以广西平果县为例

以平果县这一典型岩溶生态脆弱区为例,依据1990、1995、2000及2002年的调查统计数据,对区域生态系统的生态足迹和生态承载力进行测算,并以测算结果为依据,对区域生态系统可持续发展状况进行评价。结果表明,在1990年、1995年、2000年、2002年,平果县区域生态足迹呈不断增加的趋势,人均生态足迹从0．8004hkm^2增加至1．4444hkm^2,净增加了0．644hkm^2;生态承载力总体也呈增长的趋势,2002年比1990年增长了26．83％,其增长值主要来源于森林（果园）面积的增加,而耕地和草地的面积却呈现负增长。区域生态承载力阈值很小,远低于广西区及全国的同期水平;除森林（果园）表现为轻微生态盈余外,耕地、草地、水域均表现为生态赤字,以致区域生态总体表现为较大的生态赤字,且呈逐渐增加趋势,表明区域生物生产土地面积的需求量已经严重超过区域生态系统的承载能力,区域可持续发展的前景不容乐观。[      

Assessment of disaster resilience capacity of hillslope communities with high risk for geological hazards

This study presents a novel preparedness assessment method for assessing hazard mitigation and environmental planning of hillslope communities. A professional questionnaire was utilized to weight each indicator. Communities in Hsinchu, Taichung and Nantou counties with debris flow hazards were taken as study samples. Debris flow risk and landslide susceptibility for each community were determined using Geographic Information System (GIS) technology and logistic regression analysis. Thus, a novel risk assessment method for evaluating disaster resilience capacity of hillslope communities was established. This method was then applied to assess casualties caused by Typhoon Herb in 1996 and Typhoon Mindulle in 2004. Additionally, the analytical results generated by this assessment method were discussed with the aim of developing references for implementation of risk analysis, increasing the effectiveness of disaster mitigation, and reducing future loss of life and property.     

Use of sinkhole and specific capacity distributions to assess vertical gradients in a karst aquifer

The carbonate-rock aquifer in the Great Valley, West Virginia, USA, was evaluated using a database of 687 sinkholes and 350 specific capacity tests to assess structural, lithologic, and topographic influences on the groundwater flow system. The enhanced permeability of the aquifer is characterized in part by the many sinkholes, springs, and solutionally enlarged fractures throughout the valley. Yet, vertical components of subsurface flow in this highly heterogeneous aquifer are currently not well understood. To address this problem, this study examines the apparent relation between geologic features of the aquifer and two spatial indices of enhanced permeability attributed to aquifer karstification: (1) the distribution of sinkholes and (2) the occurrence of wells with relatively high specific capacity. Statistical results indicate that sinkholes (funnel and collapse) occur primarily along cleavage and bedding planes parallel to subparallel to strike where lateral or downward vertical gradients are highest. Conversely, high specific capacity values are common along prominent joints perpendicular or oblique to strike. The similarity of the latter distribution to that of springs suggests these fractures are areas of upward-convergent flow. These differences between sinkhole and high specific capacity distributions suggest vertical flow components are primarily controlled by the orientation of geologic structure and associated subsurface fracturing.     

Heat capacity and phase equilibria of wadeite-type K2Si4O9

The low-temperature heat capacity (C _p) of Si-wadeite (K₂Si₄O₉) synthesized with a piston cylinder device was measured over the range of 5–303 K using the heat capacity option of a physical properties measurement system. The entropy of Si-wadeite at standard temperature and pressure calculated from the measured heat capacity data is 253.8 ± 0.6 J mol⁻¹ K⁻¹, which is considerably larger than some of the previous estimated values. The calculated phase transition boundaries in the system K₂O–Al₂O₃–SiO₂ are generally consistent with previous experimental results. Together with our calculated phase boundaries, seven multi-anvil experiments at 1,400 K and 6.0–7.7 GPa suggest that no equilibrium stability field of kalsilite + coesite intervenes between the stability field of sanidine and that of coesite + kyanite + Si-wadeite, in contrast to previous predictions. First-order approximations were undertaken to calculate the phase diagram in the system K₂Si₄O₉ at lower pressure and temperature. Large discrepancies were shown between the calculated diagram compared with previously published versions, suggesting that further experimental or/and calorimetric work is needed to better constrain the low-pressure phase relations of the K₂Si₄O₉ polymorphs. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

竖向高荷载作用下大直径超长钻孔灌注桩承载性能试验

通过机场—西华高速大直径超长钻孔灌注桩大吨位竖向单桩静载试验,分析了该地区大直径超长钻孔灌注桩的承载性状以及荷载传递机理。试验结果表明:试桩的Q-S曲线呈缓变型,桩端承载力占总荷载的比例均<10%,即均表现为摩擦桩特性;试桩的侧摩阻力自上而下逐步发挥,侧摩阻力和桩端阻力异步发挥且互相耦合;大直径超长钻孔灌注桩桩侧摩阻力的发挥与土层性质、土层埋深及桩顶荷载水平有关;在高荷载作用下桩侧上部土层摩阻力具有不同程度的软化现象,而中下部土层侧摩阻力具有不同程度的强化现象,甚至即使在最大加载情况下,桩身下部土层的侧摩阻力也并未完全发挥,因此在根据规范计算超长桩承载力时,不同深度土层的侧摩阻力应乘以相应不同的修正系数。     

瞬变电磁法在彬州市某煤矿采空区勘查中的应用

采用地面瞬变电磁法对拟建搬迁安置小区是否存在煤矿采空区进行勘查,运用未充水采空区、充水采空区分别在视电阻率断面图上呈现相对高阻、低阻异常的地球物理标志,结合地面地质灾害调查成果,较为准确的确定了彬州市某煤矿采空区具体位置,并推断塌陷过渡带范围。     

特定场地下土工构筑物的几何可靠性分析

针对特定场地下土工构筑物的正常使用极限状态,采用近年发展的几何可靠性方法计算了多种构筑物的可靠度指标。考虑同一场地下的钻孔灌注桩、抗浮锚杆和CFG桩单桩加载变形测试曲线的离散性,各曲线回归参数呈现差异并可作为随机变量,进而探讨了各曲线回归参数间的相关性及联合分布特性。基于这些回归参数的联合发散概率密度等值线,即随机变量刚好达到极限承载能力状态,该几何可靠性算法可在随机变量的原始空间求得土工构筑物的可靠度指标。通过比对该几何可靠度指标与常规的一次可靠性算法成果,验证了该几何可靠性计算技术的可行性。计算表明,几何可靠性评价模型实施简便,易于被工程技术人员接受。     

资源环境承载协调理论与评价方法

资源环境承载能力评价是进行国土空间规划和用途管控的基础性工作,越来越受到国家重视。在资源环境承载能力研究实践中,以自然资源环境系统及其与社会经济系统的关系为主要研究对象,创新性提出了"资源环境承载协调理论",并基于此理论初步建立了不同空间尺度的地质资源环境承载能力评价技术方法,构建了地质环境、地下水资源、矿产资源等不同资源环境要素的承载能力评价指标体系,包括承载本底评价指标和承载状态评价指标。规范了不同尺度的资源与环境承载能力评价流程,为有序推动全国、区域及市县尺度的自然单元和行政单元的地质资源环境承载能力评价工作提供了强有力的。     

砾卵石层中预制桩的承载性状研究

依据59根桩静载荷试验实测结果和桩侧相关土层的标贯试验成果,反算出砾卵石持力层中预制桩的极限桩端阻力,结合7根桩身埋设有应力计的预制桩桩端阻力的实测成果,分析了砾卵石层中的预制桩的桩端阻力、桩端荷载分担比例及端阻充分发挥所需的桩端位移。通过对121根以砾卵石为持力层的预制桩的静载试验成果与静压法施工终压力的比较,分析了砾卵石层中静压预制桩的施工终压力与极限承载力的关系。