Trapping of sustained turbidity currents by intraslope minibasins

Depositional turbidity currents have filled many intraslope minibasins with sediment creating targets for petroleum exploration. The dynamics of sustained turbidity currents and their depositional characteristics are investigated in a scaled physical model of a minibasin. Each turbidity current deposited a downstream thinning wedge of sediment near the inlet. Farther downstream the turbidity current was ponded by a barrier. The ponded part of the turbidity current was separated from the sediment‐free water above by a relatively sharp, horizontal settling interface indicating highly Froude‐subcritical flow. The very slow moving flow within the ponded zone created conditions for the passive rainout of suspended sediment onto the bed. In the lower part of the ponded zone, the concentration and mean grain‐size of the sediment in suspension tended to be relatively uniform in both the vertical and streamwise directions. As a result, the deposit emplaced in the ponded zone showed only a weak tendency toward downstream fining and was passively draped over the bed in such a way that irregularities in the inerodible bed were accurately reflected. The discharge of suspended sediment overflowing the downstream end of the minibasin was significantly less than the inflow discharge, resulting in basin sediment trapping efficiencies >95%. A simple model is developed to predict the trapping of sediment within the basin based on the relative magnitudes of the input discharge of turbid water and the detrainment discharge of water across the settling interface. This model shows a limiting case in which an intraslope basin captures 100% of the sediment from a ponded turbidity current, even through a succession of sustained flow events, until sediment deposition raises the settling interface above the downstream lip of the minibasin. This same process defines one of the mechanisms for minibasin filling in nature, and, when this mechanism is operative, the trap efficiency of sediment can be expected to be high until the minibasin is substantially filled with sediment.     

基坑肥槽积水对构筑物地下室的危害

随着高层建筑的大量兴建,与之配套的地下室也越挖越深,继而出现了地下室底板和外墙渗漏现象,造成了巨大的经济损失和社会影响.以贵州某高层建筑为例,在介绍场地的工程地质及水文地质条件的基础上,通过现场抽水试验过程中的水位观测,认为安装在地下室的自动泵长期抽出的水没有排到场地以外的城市排水系统中,而是在肥槽中不断循环,肥槽中水位长期高于地下水位,其积水又渗入地下室,是造成地下室底板破裂的主要原因.经过将大气降水、施工用水及工人生活用水等及时排到场外的城市排水系统中等措施,最终解决了基坑肥槽积水问题,为以后施工相似工程具有一定的借鉴作用.     

基于矿井排水的水文地质参数识别

由于强烈的非均质性,如何识别岩溶裂隙含水层水文地质参数是一个由来已久的难题。本文利用焦作矿区、荥巩矿区及永夏矿区生产矿井大流量、长时间的排水资料进行识别岩溶裂隙水含水层的水文地质参数,计算结果发现：K值均在100m/d量级上,μ＊值均在10^-3量级上,与孔隙含水层的值相当;用识别的参数预算矿井涌水量与区域降雨补给量接近,回报水位及给定条件下排水量误差均不超过2%。结果表明,可以用渗流理论模型对管道流、裂隙流进行概化处理。研究成果提出矿区岩溶裂隙地下水参数计算的新方法,为防控矿坑突水、安全生产提供了新思路。