Deep Trenching - General

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The advantage of deep trenching machines or dewatering machines is the relatively easy and high installation speed of an effective dewatering system compared to any alternative methods.  Furthermore, using such trenching machines to install other underground systems eliminates the need for dewatering and trench-shoring as all workers remain above ground.  The trencher makes a relatively narrow slit in the earth so the wide open cuts typical of conventional excavation are no longer necessary.  This is very important when working with contaminated soils that require disposal or which could expose workers to unnecessary hazards.  The need for expensive steel sheeting or other support structures is eliminated, resulting in faster completion.  Over the years the use of trenching equipment has become increasingly popular due to the economics of using a trencher compared to other techniques and also to the increase in potential applications for deep trenchers.

The principle of horizontal dewatering is quite simple.  Instead of installing a vertical well in the soil, say, every 2.50 metres, one long perforated pipe is laid horizontally at the most desirable depth.  This means there are no wells to create obstacles in the working-strip.  If the filter tube has a sufficiently large diameter, it may also serve to transmit the water entering via the perforation. 

 

There is also no need for the vacuum pipes on the surface.  To carry off the water, a vacuum pump is connected to the end of the filter tube.  By bending the filter tube towards the edge of the working strip and connecting it there to the pump, the whole working area is free of obstacles.  During vacuum-pumping, the water in the filter tube is carried off which results in a lowering of the groundwater level near the filter tube.  In this way the groundwater level can be lowered to such a depth that the bottom of the trench to be dug will lie above the new level.  As far as the stability of the sides of the trench is concerned, the groundwater will no longer pose any problem.  After digging the trench and installing the transmission pipeline, there are only the pumps to be removed.  The filter tube is plugged at its inlet above the ground and remains completely intact in the soil.

 

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