dewatering
 

Dewatering

M&R Integrated Services Ltd provides dewatering through vertical well-points in cooperation with MOS Grondwater techniek. A large Dutch company with over 100 years experience in dewatering. They have executed many large international contracts including Nigeria for EGTL Escravos in 2005

Our partnership enables us to:

• Provide soil engineering capability
• Provide deep-well and horizontal dewatering.
• Execute large scale projects

Together we are able to execute large jobs and provide Clients with complete dewatering solutions. As our standard we provide vertical well-point dewatering and this can be mobilized directly from our yard in Warri, whilst equipment required for deep-well and horizontal dewatering will need to be mobilized from the Netherlands.

In November 2012 M&R Integrated Services Ltd signed a major contract with Gramen Petroserve Nigeria Ltd, where M&R will provide dewatering services to enable excavations for foundation installation.

The construction of pipelines, buildings and civil engineering works generally involves excavations and the digging of trenches. These may be of such depth that especially during the wet season the bottom is below the water table. Because of this (especially in permeable soils such as red sand), the ground water will flow into the trench or excavation through the bottom and sides, and will fill it to a certain depth. To enable work in such excavations to be carried out under dry conditions, this water has to be removed or be prevented from entering through the bottom and slopes of the excavation.

The vertical wellpoint dewatering system works by the aid of vertical wellpoints connected to a headerpipe system and a dewatering pump the whereby the ground water is artificially and temporarily lowered.

Wellpoint sketch

Groundwater dewatering comprises various technologies to lower a groundwater table by pumping groundwater out of the ground. It is the opposite from 'open dewatering', where the groundwater is catched after its entrance into an excavation.

Dependant of composition of the subsoil, outflow of water from the ground into open air can cause transport of soil particles. This will cause washing out, leading to loss of slope-stability. Another aspect is the geotechnical fact that soil stability can be improved by lowering of the groundwater table. Finally, uncontrolled water pressure under an excavation can lead to heaving of the bottom of excavation and start of spontanious, free flowing wells. These are the major reasons why the use of groundwater dewatering can be necessary or desirable, when excavating below groundwater level.

Excavation depths up to 6m can be handled with a single stage well point system. If excavations are deeper either deepwells (not currently available) or a multistage system is required as per below:

multistage wellpoint

The wellpoint dewatering system in comparison with other dewatering systems is:

  • Applicable in most type of soils
  • A flexible system
  • Effective and efficient
  • Easily to adapt depending on dewatering results achieved

Typical Equipment

Most of our pumps are GEHO® ZD pumps, The GEHO® ZD pump is a a twin cylinder, quadruple-acting crankshaft driven vacuum piston pump. The crank timing produces a moderate pulsating type action that prevents clogging of the wellpoint strainers and achieves priming from greater depths. The ZD pump range is developed and manufactured by Weir Minerals Netherlands b.v. Pumps are driven either diesel or electrically driven and capacities range from 45 to 90 m3/hr

More particularly in wellpoint drainage and dewatering, these pumps have come into widespread use because they perform their duty reliably under all conditions, with a minimum of attention and maintenance. Further, they are the most economical pumps for wellpoint drainage operations as they have an extremely high efficiency of about 92% resulting in a very low horse power motor requirement of only 7,5 kW. This means when operating with diesel engines you can comfortable use a one cylinder engine compared to a 3-cylinder of 22 Kw before.

Fuel saving per pump can go up to 27,500 liters per year per pump!!

Another main advantage in pumping water from dewatering wells is that they develop a pulsating vacuum, causing the water and/or air to be snatched out of the ground, as it were. Since this effect is beneficial to the stability of the bottom and slopes of the excavation, the reciprocating pump can indeed claim to be a universal pump suitable for horizontal drainage, for drainage from wells with free gravity inflow, or functioning on the vacuum principle. Thanks to their dual (duplex) form of construction, these pumps are characterized by very steady operation. A major advantage is that the capacity remains constant despite any increase in suction and/or delivery head. This is in marked contrast with centrifugal pumps, whose capacity shows a marked decrease if the suction head or delivery head is increased while the relatively high installed power remains viable. The piston pump is selfpriming and can handle therefor water and air without the need of an addional vacuum pump.Because of their smooth operation andslow running at a low rate of about 65 - 70 strokes per minute the pumps have by far the longest life-time for these wellpoint drainage applications. 

pumps

Header pipelines

 

 Dewatering in practice 

Wellpoints are jetted into the soil and each wellpoint is connected to a 4 inch header HDPE pipe to collect the water and pumped by pistonpumps creating a vacuum. The water is pumped away which creates lowering of the groundwater table.

Sequence of a typical small scale dewatering project

 

 Dig01

dig02

 dig03

 dig04

 dig05

 dig06