蒙特卡洛模型在现代黄河三角洲浅层沉积物压实速率模拟中的应用

APPLICATION OF MONTE CARLO MODEL TO SIMULATION OF COMPACTION RATES OF SHALLOW SEDIMENTS IN THE MODERN YELLOW RIVER DELTA

在进行黄河三角洲浅层沉积物固结压实研究中,过去传统的方法通常基于钻孔和剖面,进行局部计算分析。为克服钻孔分布不均的局限性需研究整个现代黄河三角洲地区浅层沉积物的压实沉降特征,基于1987年黄河三角洲地区综合工程地质勘察获取的钻孔资料,采用了数学地质中的蒙特卡洛方法,结合土力学的分层总和法对整个现代黄河三角洲浅层沉积物的压实速率进行模拟,并分析了压实模拟的具体影响因素。结果表明当前浅层沉积物的90%累积概率(P90)的压实速率变化范围为0.18~9.07mm/a,影响模拟沉积层的压实速率主要因素为沉积物的初始孔隙比、压缩系数和平均沉积速率,上述要素均与压实速率呈显著正相关,软土层应是浅沉积地层压实沉降的主要贡献层。提出按照时间序列分别对不同流路时期叶瓣进行模拟,更符合现代黄河三角洲地区的沉积环境和历史,并对比23个地面沉降水准监测数据,定量分离了浅层沉积物固结压实分量,其约占沉降总量的13%。

The traditional methods used in the study of shallow sediment compaction,which is one of the important contributors to land subsidence,are usually based on drillings and profile measurement with local computation in the Yellow River Deltaic area.In order to overcome the methodological limitation and restriction in past studies,the Monte Carlo approach and the stratified summation method are adopted.With the borehole data obtained from the Project on Comprehensive Engineering Geological and Hydrogeological Survey in 1987,we numerically modeled the shallow sediments of the whole delta,calculated the compaction rates and analyzed the influence factors of compaction simulation.The results show that the present compaction rates vary in a range from 0.18mm/a to 9.07mm/a.The influence factors of compaction rates are mainly the geotechnical parameters,such as initial porosity and compressibility and the average net accumulation rates,both of which are significantly and positively correlated with the present compaction rates,and the soft layer is the major contributor to the sediment compaction and land subsidence.The results are fit to the history of the Yellow River delta if simulations are made for lobes with time.Combined with the ground subsidence level monitoring data,it is found that the contribution of consolidation and compaction of shallow sediments accounts for about 13% of the total settlement.