叠加于弧后前陆盆地挠曲沉降之上的另一类沉降——动力沉降

弧后前陆盆地挠曲沉降包括逆冲负载沉降和盆地沉积物负载沉降。叠加于挠曲沉降之上还存在另一类沉降,即动力沉降。动力沉降是动力地形的一种,即动力地形低。动力地形一般认为具有两种成因,一种为与超大陆集聚和分散有关的动力地形,另一种为与大洋板片俯冲有关的动力地形。由大洋板块俯冲产生的动力沉降往往分布于弧后前陆盆地区,其幅度、波长与板块俯冲角度、俯冲速率、俯冲板块在地幔中通过的位置和俯冲岩石圈的热年代密切相关。将通过弧后前陆盆地沉积地层的去压实得到的总沉降减去盆地模拟获得的逆冲带负载和盆地沉积物负载沉降可以得到剩余沉降,即动力沉降。从地层资料中定量分离出动力沉降为改进和限制长期以来悬而未决的由洋壳俯冲导致的地幔-粘性流动构造模型提供理论基础和实际资料。     

Mining subsidence engineering

If large, continuous cavities are created underground, as for example in coal mining, the layers of rock over the deposit generally break and subside. The subsidence can be reduced in amount and severity by filling in, or “stowing,” the mine cavity with waste material. In the course of subsiding, the land surface deforms into a generally flat, plate-shaped trough, the edge of which travels ahead of the mine working. The effects of mining may simultaneously cause a structure to subside, tilt, bend, and be extended or compressed, with extension and compression sometimes alternating. Areas turned into swamp or placed permanently under groundwater have to be kept drained.     

天津地区构造沉降及控沉远景问题

使用第四纪地质、统计地貌学和历史水准点调查等手段,研究了天津地区的构造沉降背景,讨论了控制地面沉降远景目标问题。研究工作使用天津地区第一海相层底板埋深、全新统地层钻孔、深层基岩标和历史水准点等一系列资料,获得天津市和邻近地区构造沉降的平均速率为1.7mm a左右。研究还发现了基底构造沉降背景具有这样一些规律:(1)从西部到东部沿海,区内沉降有逐渐增加的趋势。(2)沿海河发育了一条北西方向的构造沉降异常带。(3)以海河为界,沉降分布的方向不同,北部为北西西向,南部为北东方向,整体活动规律反映了活动断裂和基底构造的控制作用。     

Land subsidence in China

Land subsidence in China occurs in different regions. It is primarily caused by excessive groundwater withdrawal. Other reasons for the subsidence include the oil, warm groundwater withdrawal and the neotectonic movement. The common characteristics of land subsidence in China are slow, accumulative, irreversible, and other unique properties. The range of subsidence still keeps extending and the accumulative subsidence increasing though some measures taken. Adjustment of the aquifer exploitation practice is a subsidiary way to control land subsidence, but it cannot solve this problem completely. In a specfic way of groundwater changing, the contribution of a certain soil layer to the total subsidence depends on its compressibility and thickness. Besides the elasticity, both cohesive soil layers (aquitards) and sand layers (aquifers) are observed to be plastic and creep when the groundwater level fluctuates in a specific way, which often leads to subsidence delay.     

上海地面沉降监控中心

1 前言 上海自二十世纪六十年代初开始系统的开展地面沉降研究工作,至今已积累了大量的监测数据资料,近年来地面沉降监测设施不断完善,至2000年底已建成了覆盖全市范围的具有高新技术全新的地面沉降监测网络。     

Sinkhole subsidence due to mining

This paper reviews the modes of formation of sinkhole subsidence associated with mining activities, drawing on examples in India. Sinkhole (pot-hole) subsidence is an abrupt local depression at the surface which can be hazardous to life and property due to its tendency to occur without warning. Shallow extraction, weak overburden and geological discontinuities are the main factors which cause them. Sinkholes occur due to the failure of a mine roof which migrates through the overlying strata until the failure zone intercepts the unconsolidated overburden. Alternatively they may occur by the creation of cavities in the overburden following the inflow of sand and soil from the overlying weathered and friable strata through faults. Overburden cavities eventually cave in and sinkholes appear at the surface. Sinkholing phenomena can be controlled to some extent by proper design of mining supports and construction of walls to create a barrier around an area prone to sinkholes in bord and pillar workings. Backfilling and grouting can be used to stabilize abandoned underground workings.     

Design considerations for subsidence control

Summary Subsidence planning and control must be an integral part of mine design in order to minimize the economic impact of underground mining on the surface. Precalculation of surface deformations which may cause damage to surface structures must be performed and damage criteria must be established, if the response of structures to such movements is to be determined and the extent of damages to be assessed. In this paper the Surface Deformation Prediction System (SDPS), which can be used to predict accurately the vertical and horizontal parameters of surface movements due to underground mining, is discussed. The Subsidence Response Modelling Program (SRMP), which can be applied to evaluate the response of buildings to subsidence-induced movements, is also reviewed. Finally, an example is presented demonstrating the applicability of these techniques for subsidence design and control.     

Land subsidence in Tianjin,China

Land subsidence has been affecting Tianjin for the past 50 years. It leads to comprehensive detrimental effects on society, the economy and natural environment. Overpumping of groundwater is the main cause. In 2008, the maximum cumulative subsidence reached 3.22 m and the total affected area nearly 8,000 km². The subsidence reached its most critical state in the early 1980s when it occurred at a rate as high as 110 mm/year. At the same time, groundwater extraction had also reached a maximum of 1,200 million m³. By importing the Luan River to Tianjin and restricting exploitation of groundwater, hydraulic heads gradually recovered after 1986 in all aquifers, and this has continued to the present in the second aquifer. The subsidence rate in urban areas dropped to 10–15 mm/year. The area of groundwater extraction expanded to the suburban area with economic growth in the 1990s, and it was shifted to the third and fourth aquifers. At present, with a subsidence rate of 30–40 mm/year, four new suburban subsidence centers have been formed. Several measures were adopted to mitigate and prevent land subsidence disasters. These included restricting groundwater exploitation, groundwater injection, prohibiting use in the specific zone, a pricing policy for water resources, advocating water-saving technology, and strict enforcement of groundwater laws. Although the subsidence area is still increasing slowly, the subsidence rate is being controlled.     

Land subsidence in Bangkok, Thailand

Land subsidence from deep well pumping has been affecting Bangkok for the past 35 years. Its impact is particularly critical because of the flat low-lying topography and the presence of a thick soft clay layer at the ground surface that augment flood risk and foundation engineering problems, respectively. The subsidence reached its most critical state in the early 1980s when it occurred at a rate as high as 120 mm/year. The rate decreased in the subsequent period but the subsidence-affected area expanded following the growth of the city. Despite various attempts implemented to remedy the crisis, groundwater pumping from the thick aquifer system underneath the city continued to increase from 1.2 million m³/day in the early 1980s to more than 2.0 million m³/day at the turn of the century. Piezometric levels in the main aquifer layers had been drawn down by as much as 65 m. Monitoring data showed a clear correlation between the subsidence and piezometric drawdown. The data suggested that for 1 m³ of groundwater pumped out in Bangkok Plain, approximately 0.10 m³ of ground loss occurred at the surface. Significant development has been made in numerical methods for prediction of differential settlements between building foundations caused by the piezometric drawdown in the aquifers. The strict mitigation measures adopted recently, comprising a pricing policy for groundwater management, an expansion of tap water supply, and strict enforcement of groundwater laws, have resulted in a marked drop in groundwater use. However, the land subsidence will continue for a long while owing to the time-dependent consolidation behavior of the soft clay layer and clay aquitards.     

地下水开采—地面沉降模型研究

本文建立三维流支－－一维非线性固结地面沉降模型,在混合井流,降雨滞后补给,初始水头形成,人为边界刻画,水流－固结耦合及软土层固结滞后于地下水开采层水头变化等方面有所改进,所建模型用于苏州市,模拟出若干地面沉降重要特征,地面沉降中心偏离地下水漏斗中心,地面沉降动态滞后于地下水的水头动态,软土层渗透系数随固结过程的变化及头在软土层中的传递特征。     

Detection of subsidence conditions by photogeology

A variety of air-photo interpretation criteria need to be used for detecting areas of potential subsidence. An initial step is to search for past failures showing on air photographs, to establish the cause and to interpret the boundaries of the environment that might be affected. Causes detectable include karstic terrain, areas liable to piping, or containing concealed peat, old shafts, and stratiform or vein workings. Airborne imaging conditions can be selected to improve the possibility of detection in some situations.

The technique can indicate situations where risks are high, but cannot be used to map with certainty voids liable to collapse.     

抽汲流体引起的地面沉降——D.C.海姆博士(澳)第二讲摘登

在第一讲里,我们讨论了抽汲流体引起沉降的现象,描述了地面沉降与现场其它现象是如何相互关联的,特别是沉降与砂层中水位变动的相关性以及与受应力作用的含水层,或者含水层内粘土单元体(粘土透镜体或粘土夹层)的存在的相关性。在第二讲里,我们要讨论抽汲流体引起沉降的机理,以及介绍沉降垂直分量随时间变化的成功模拟。在这里,一维固结理论起着关键的作用。地下水文地质学的一个主要课题是如何预测地面沉降。含水体系压缩的不可恢复部分几乎全发生在其中的细粒沉积物中。在含水体系力学里,滞水体的作用是非常重要的。     

锡西—澄南典型地面沉降区地面沉降风险评价

选择长三角苏锡常地面沉降最为典型地段—无锡西部至江阴南部地区,系统分析了地面沉降现状及成因机理,建立了地面沉降风险评价指标体系。结合该区实际对体系中的评价指标进行了优选,依据地面沉降分层标监测数据、各评价指标要素对地面沉降灾害的贡献率分别对地面沉降易发性和易损性指标权重进行了修正。在地面沉降易发性、易损性评价基础上,利用GIS进行了地面沉降风险评价,根据评价结果提出了地面沉降风险控制规划建议。