Explosive impulse on plates

This paper describes a series of very small scale model tests that were conducted in support of a full scale test program conducted by the Army Research Laboratory at Aberdeen, Maryland for the US Navy to investigate the impulse delivered to a military vehicle by a buried land mine. The full scale tests were conducted in July of 2004 and investigated the effect of various parameters on the impulse delivered. The vehicle was represented by a steel plate and depth of burial, standoff distance, and explosive size (up to 10 pounds of TNT) were changed in the seven tests conducted for the Navy. The full scale tests were conducted in saturated sand. The tests described in this paper used a maximum charge size of 3.3 gm of RDX and PETN. Each of the tests conducted for the Navy were simulated by the small scale tests and a prediction of the impulse that would be measured for each of the tests was made. The small scale tests (as well as the full scale tests results) were also used by the developers of various numerical codes that were also used to predict the impuse that would be measured in the full scale test series.This paper is accompanied by a paper by Taylor et al. (Taylor, L. C., Skaggs, R. R. and Gault, W., 2005, Vertical impulse measurement of mines buried in saturated sand, Fragblast, International Journal for Blasting and Fragmentation, 9, 19-28) in this issue of FRAGBLAST. In the next issue of FRAGBLAST several additional papers will be published. These will be the results of the numerical codes that were used to predict the impulse.     

抛石基床爆夯振动效应监测与分析

根据对广西钦州港二期码头爆夯监测,分析了爆夯产生的振动速度和冲击波超压变化规律。结果表明,实测质点振动速度衰减规律与规范提供的经验公式基本相同;由于自由面反射的稀疏波作用,实测冲击波超压值远小于经验公式提供的结果;分析结果还表明,由于冲击波的脉动作用,即使在一次起爆（不分段）情况下,振动速度和冲击波超压波形也会产生多次振动现象,其振动强度越来越小;另外,由于稀疏波作用,在相同的爆炸条件下,测点入水深度越大,其冲击波超压值越高;测点入水深度越小,冲击波超压值越低。该分析结果可为类似工程提供借鉴。     

Timing effects on the fragmentation of small scale blocks of granodiorite

A series of small scale tests, simulating multi-hole blasts have been performed to establish the effect of delays on blast fragmentation. The blasts were performed in high quality granodiorite blocks, which were cut from stone prepared by dimensional stone quarry operations. The pattern used was equilateral triangular, with a distance of 10.2 cm between boreholes, which had a diameter of 11 mm, were loaded with detonating cord and the coupling medium was water. The delays used were achieved using different lengths of detonating cord for the cases of delays between 0 and 100 μs between holes and a sequential blasting machine firing seismic detonators for larger delays up to 4 ms. All fragments were collected and screened. The experiments showed that the worst fragmentation was achieved with simultaneous initiation of all charges. Fragmentation improved with the delay time between holes up to 1 ms between holes. If the experiments are scaled up, the results show that in granodiorite, fragmentation optimization requires delays of few milliseconds per metre of burden. The findings, agree with previously published work, involving larger scale experiments and other rock types.     

平邑县矿山地质环境保护与治理机制探索

平邑县高度重视日益突出的矿山地质环境问题,不断加强矿山地质环境保护与治理工作力度,通过推进矿山公园建设、严格采矿权审批程序及开展矿山地质环境治理总体规划等,对保护矿业遗迹、保护矿山地质环境等工作起到积极作用,并取得了较好的社会效益、经济效益和环境效益。     

Use of alternative conceptual models to assess the impact of a buried valley on groundwater vulnerability

A buried valley incised into a sequence of pre-Quaternary sediments is shown to seriously affect the vulnerability of groundwater. Often the existence of buried valleys is not known or is not described explicitly in a hydrogeological model. In the present study, two numerical groundwater models, representing two alternative conceptual models, were produced to help quantify the effect of the valley on groundwater vulnerability. One model included the buried valley and the other did not. Both models were subjected to calibration and were found to describe hydraulic head and river discharge equally well. Even though the two models showed similar calibration statistics; fluxes, travel paths and travel times were affected by the inclusion of the buried valley. The recharge area and the groundwater age of potential abstraction wells placed in the pre-Quaternary deep aquifers surrounding the buried valley were different for the two models, with significantly higher vulnerability when the valley was included in the model. Based on the results of the present study, it is concluded that a buried valley may not always be detectable when calibrating a wrong conceptual model. If reliable results should be obtained a good geological model has to be constructed.     

岩石受荷载变形的电阻率曲线分析

电阻率是岩石的重要物理参数,对研究岩石的固有特性和赋存状态有着重要的作用。选取砂岩、灰岩、泥岩和花岗岩为代表岩样,进行受荷载条件下的电阻率曲线分析,得到了电阻率的临界点,其电阻率临界点的应力比值范围为70%~85%,对应于岩石应力应变中的屈服点。分析发现,电阻率临界点具有方向性,岩石电阻率临界点可以用于判断岩石的屈服点和应变状态。     

黄河水下三角洲沉积物强度变化原位测试研究

研究区位于1964～1976年黄河由刁口入海时形成的水下三角洲叶瓣上。1995年为石油开采在潮坪上构筑的交通设施对波浪形成良好的屏障。在屏障两侧各选一典型研究区，于1999年和2002年进行了大量对比性现场原位土工测试，探讨了波浪对黄河口沉积物的次生改造作用，结果表明：(1)较强的波浪荷载作用，不会提高海底沉积物的表层强度，只是导致不均匀程度随水动力作用的时间增长有所加大：(2)较强的波浪荷载作用，使得海底表层沉积物之下一定深度范围内土体强度提高，形成强度硬层：(3)海底沉积物强度沿着剖面线在平面上呈现周期性或间隔性变化。     

基于加载动力效应对孔压滞后现象的一个解释

在底部可测孔压的固结仪内进行单面排水固结试验时,观测到试样底部的孔压可出现滞后现象。为分析其原因,考虑加载引起的动力效应,建立以竖向应变为求解对象的一维动力固结方程,并用有限差分法进行求解。引入新指标CD来综合考虑试样压缩模量、渗透系数、密度以及土样厚度等4个参数对动力效应的影响,探讨了该指标对固结过程中孔隙水压力的影响。计算结果表明,瞬时加载引起的动力效应是引起试样内孔压滞后的一个原因,并且对于压缩模量或渗透系数较大的试样,更易出现孔压滞后现象,同时动力效应对固结度的影响则主要体现在固结的前期。最后讨论了固结分析时可以忽略动力效应的范围。     

摩擦桩沉降变形规律及承载力确定的探讨

在现场的桩基垂直静载荷试验基础上 ,进行荷载传递机理分析和沉降变形的阶段性划分 ,探讨了确定单桩竖向承载力的新方法 ,为工程合理、充分地利用承载力提供参考。     

基坑开挖对邻近地下管线影响的变形控制标准

基坑开挖会引起邻近区域地埋管线的附加受力和变形,甚至会引起管线的开裂破坏。基于位移控制理论,对板式支护体系由于基坑开挖而引起的周边自由土体位移场的分布规律进行了探讨,通过位移控制两阶段简化分析方法与位移控制有限元方法的对比,验证了简化方法的合理性。其次对最近修订的《上海市基坑工程技术规范》的基坑环境保护标准进行了探讨,利用简化方法通过算例计算以分析其仍需改进的方面,在此基础上,基于地下管线的自身承受能力,提出了基坑开挖对管线保护的变形控制标准,给出了为保证管线正常使用,基坑开挖深度与基坑允许侧向变形的关系,从而可以为基坑开挖环境影响评价标准的建设提供相应的理论依据。