在一个城市的下水道建筑工地
﻿At a city's sewer construction site
形成了流沙
a quicksand condition developed
把一个工人拖到地里
pulling a worker into the ground
事情是这样的
This is what happened
一个新的升降机站正在建造中
A new lift station was being built
升降机站把废水从较低的高度移到较高的高度
Lift stations facilitate the flow of waste water
从而促进废水的流动
by moving it from a lower to a higher elevation
升降机站将安装在地面以下
The lift station was to be installed
约7米的地方
about 7 metres below grade
原工程图纸建议
The original engineering drawings for the project
开挖深度略低于最终施工深度
proposed an open cut excavation
to a depth of just below the final construction
该市委托编写了一份岩土工程报告
The city commissioned a geotechnical report
报告1，项目情况
- Report 1 - for the project
但后来这个项目被搁置了
but then put the project on hold
多年后，当项目重新启动
Years later, when the project was restarted
该市委托编写报告2
the city commissioned Report 2
一份对比报告1的最新岩土技术报告
an updated geotechnical report that took into account Report 1
为了确定土壤分层
To determine the soil layering
在报告1中，三个钻孔钻至6.1米
three boreholes had been drilled to 6.1 metres for Report 1
一个钻孔至9.1米，用于报告2
and one borehole to 9.1 metres for Report 2
这些报告给人的印象是
The reports gave the impression
在拟建的升降机站的底部
that down at the base of the proposed lift station
会有一层厚厚的淤泥
there would be a substantial layer of silt
在淤泥层上面，有一层粗砂
and just above it，a layer of coarse sand
地下水在约2.3米处被发现
Groundwater was found at about 2.3 metres
因此需要从现场
making removal of water from the site
或所谓的排水系统中清除水
or what is known as dewatering necessary
该城市提供了项目信息
The city provided project information
包括向总承包商A公司提交的报告2
including Report 2 to Firm A, the prime contractor
规划和建造决定
The planning and construction decisions were based on
是根据对报告1和2所提供的
the understanding of the subsurface conditions
地下条件的了解作出的
provided by Reports 1 and 2
然而，钻孔还不够深
However, the boreholes had not gone deep enough
他们提供的数据
The data from them was inadequate
不足以制定有效的排水计划
for creating an effective dewatering plan
根据施工中地下水的降低情况，一个实用指南
According to Groundwater Lowering in Construction:A Practical Guide
钻孔的深度
boreholes should penetrate to
应为开挖深度的1.5至2倍
a depth of 1.5 to 2 times the depth of the excavation.
根据所提供的报告
Based on the reports provided
公司A构思了脱水和支撑的概念
Firm A conceived a dewatering and shoring concept
使用开放式钢沉箱
using an open steel caisson
而不是用一个完全开放的切口
instead of going with an open cut to full depth
就在地下水之上
An open cut was made to about 2 metres
挖了一个2米左右的缺口
just above the groundwater
然后将由三个环形截面组成的沉箱
Then a caisson，made up of three ring-shaped sections
打入土壤中
was driven into the soil
它的墙壁形成了一道屏障
Its walls created a barrier to prevent groundwater and soil
防止地下水和土壤进入沉箱的两侧
from entering the sides of the caisson.
半不透水的淤泥层
The silt layer, being semi-impervious
会减少下面地下水的渗透
would reduce groundwater penetration from below.
除了沉箱
In addition to the caisson
脱水系统有3个其他要素:
the dewatering system had 3 other elements:
几十个降水井点进行预排水
Dozens of dewatering well-points for pre-drainage
即在开挖前降低地下水位
which is the lowering of groundwater levels before excavating
安装两根6米深的
Two slotted steel pipes
有槽钢管作额外的预排水
that were installed 6 metres deep for additional pre-drainage
以及允许监测地下水位
and to allow monitoring of the groundwater level
把两个潜水泵放置在沉箱中
And two submersion pumps placed in the caisson
以清除渗入其中的地下水
to remove groundwater that leaked into it
排水系统以高流量
The dewatering system pumped ground water
连续抽运场地的地下水
from the site continuously, at high volume
事件发生的当天
On the day of the incident
大部分的泥土已经从沉箱中取出
most of the soil had already been removed from inside the caisson
人们正在开动潜水泵来降低里面的水位
The submersion pumps were being run to lower the water level inside it
沉箱四周的碎石提供了良好的行走道路
Crushed stone around the caisson provided a good walking surface
工人1一直在调整潜水泵的管道
Worker 1 had been adjusting the pipes for the submersion pumps
后来，他看到水位
Afterward, he saw that the water level
已经下降到几乎沉箱的底部
had gone down to almost the bottom of the caisson
他跨出了一步
He took a step
他的脚下沉，然后被拉到地面下
His foot sank, and then he was pulled into the ground
工人2号和3号看到
Workers 2 and 3 saw the water in the caisson
沉箱里的水开始沸腾，水位迅速上升
start to boil and that the level of the water was rising quickly
他们抓住了工人1的手和胳膊
They grabbed Worker 1's hands and arms
工人3号开始被拉下来
Worker 3 began to be pulled down
他放开了对工人1的控制
He released his hold on Worker 1
从坍塌的地方出来
got out of the collapsing area
然后试着把材料铲走
and then tried shovelling material away
但它不断地塌陷进洞里
but it kept collapsing into the hole
然后他拨打911，并且去关闭水泵
He then called 9-1-1 and went to shut down the pumps
工人4到了
Worker 4 arrived
几分钟后
Minutes later
工人1的头顶大约在水面下一米
the top of Worker 1's head was about a metre below the surface
工人1的胳膊下系着一根吊带
A lifting strap was looped under Worker 1's arms
并且绑在脱水管上
and tied to the dewatering manifold
他一动不动地躺在
Completely immobile, he was stretched
皮带和拉他下来的重物之间
between the strap and the weight of the material pulling him down
最后，他把脚从靴子里挪了出来
Eventually, he was able to wiggle his feet out of his boots
在其他工人的帮助下被解救了
and was freed with the help of the other workers
是什么导致了这一事件?
What led to this incident?
含水层是一种自然形成的地下岩层
An aquifer is a naturally occurring underground layer of rock
水很容易通过它流动
through which water can easily flow
在项目区域下方
Underneath the project area
不止一个，而是两个含水层
there was not just one, but two aquifers
上含水层和下含水层
an upper aquifer and a lower aquifer
与上含水层不同，下含水层处于高压状态
Unlike the upper aquifer, the lower aquifer was under pressure.
报告1和2的钻孔探测到了上部含水层
The boreholes from Reports 1 and 2 had detected the upper aquifer
但他们没有深入到足够深的地方去探测下面的那个
but they hadn't gone deep enough to detect the lower one
结果，排水系统太浅
As a result, the dewatering system was too shallow
无法减少下层含水层的水量
to reduce the water from the lower aquifer
蓄水层都被确定在第三份报告，报告3中
Both aquifers had been identified in a third report，Report 3
但市政府没有向A公司提供这份报告
but the city had failed to provide this report to Firm A
因为土是从沉箱里取出来的
As the soil was removed from inside the caisson
从沉箱底部的土壤中
a proportional amount of holding weight
移除一定比例土壤的保持重量
was removed from the soil at the bottom of the caisson
随着这个过程的进行
As this process continued
地下水渗入沉箱
groundwater infiltrated the caisson
取代了排出的土壤体积
replacing the volume of removed soil
水暂时为下层土壤
The water temporarily provided
提供了置换持重
replacement holding weight for the lower-layer soils
同时平衡了沉箱内部
and also equalized the hydrostatic pressure
与地下水之间的静水压力
between the caisson interior and the groundwater
就在事件发生之前
Right before the incident
水从沉箱里抽出来
the water was pumped out of the caisson
这样就去掉了承重
This removed the holding weight
增加了沉箱内外的静水压差
and increased the hydrostatic pressure differential
between the outside and the inside of the caisson
压差导致了接下来发生的事情
The pressure differential contributed to what happened next
一些潜在的机制或机制的组合
Several potential mechanisms or a combination of mechanisms
可能导致流沙的形成
may have led to the quicksand condition
一个可能的机制是
One potential mechanism is that the caisson
沉箱从未完全穿透东侧的淤泥层
never fully penetrated the silt layer on the east side
可能是因为西边的土层比东边高
possibly because the layer was higher on the west side than the east
而在工人所站的位置
and that the coarse sand layer
下方深处的粗砂层
bore the full force of the pressure differential
承受着压差的全部力量
deep below where the worker was standing
它迅速向下陷下
and it rapidly let go downwards.
或者，淤泥层可能已经隆起
Alternatively, the silt layer may have heaved up
释放来自较低含水层的压水
releasing pressurized water from the lower aquifer
最后，在积极的脱水活动中
Finally, the whole ground system
精细的土壤颗粒被冲刷掉
may have been destabilized from the washing out of fine soil grains
可能破坏了整个地面系统的稳定
during the aggressive dewatering activities
虽然导致流沙形成的
Although the exact mechanism
确切机理还不能确定
that resulted in the quicksand condition couldn't be determined
在每种情况下
the differential between the hydrostatic pressure
沉箱内外的静水压力都存在差异
inside and outside the caisson was present in each case
这可能也是一个原因
and was likely a factor.
没有同事的帮助
Without the help of his co-workers
工人1的情况本可能变得更糟
Worker 1's situation could have turned out much worse
他的靴子至今仍在地下
His boots remain underground to this day
无论你的建设项目是电梯站，还是高楼大厦
Whether your construction project is a lift station、a high rise
或者其他依赖于稳定土壤条件的结构
or other structure that depends on stable soil conditions
要知道地下水的流动
know that the movement of groundwater
会产生潜在的致命危险
can create potentially deadly hazards