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Water Control in Construction
Transcript of Water Control in Construction
Post Construction Run Off has Two major effects
Increase in pollutants form new impermeable ground
Increased Dispersion into water systems from man made systems
Plot Attenuation ,Water Retention and Water Cleansing Plot attenuation is used to Slow down water ingress to a natural system
Older projects had the opinion that as long as water was away from the site and into an existing water system it was ok.
New opinion to use attenuation to slow down water before it reaches natural stream
Water Retention is where water is maintained on site and reused can be used in domestic and commercial situations
Uses mainly rain water from roofs ( grey water)
Water is mainly used to flush toilets and water plants
Water Cleansing is where water has pollutants removed before it is allowed to disperse into the purposed water course
This can be done per plot as a silt trap or in a scheme system
http://blogs.bootsnall.com/old_travel_blogs/rob/archives/man%20swimming%20by%20slum.jpg Plot Attenuation Plot attenuation systems are used to control the flow of water into a water course Water Retention This design for Water filtration uses a vortex technology to remove sediments and oils from water before it is discharged into the water system.
The vortex created also slows down the water by removing some of the Kinetic Energy .
This system would be suitable for larger housing schemes with one manhole being able to take 50 Houses
Prevention of ground water Ground water can be kept out either permanently such as in long term waterproofing for a basement, or temporarily such as to ease work during excavation.
The 2 mains ways in which this is achieved are shown below:
Sheet Piling Diaphragm Walls In addition the ground water can be further controlled by:
Well point system
Sides of excavation keep dry by providing row of well point Sump Pumping
Sump pit provided inside the lowest level of the basement to collect water and remove by pump Grouting Grouting is often used to stop the penetration of water in sub-soil with high permeability, such as in fissured and jointed rock strata.
Row's of holes are bored in the soil and, usually cement grout, is injected under high pressure. The cement grout will penetrate into the voids of the sub-soil and form somewhat an impermeable curtain vertically separating the ground water.
The pump facilities for injecting of the grout. can be seen here.
Cement grout is usually a mixture of cement and water, or cement and sand under ratio maximum 1:4. Sometimes chemical grout can be used to form a gel which can increase strength and reduce permeability of soil. (eg. Sodium silicate + calcium chloride = calcium silicate, which is a silica gel)
Pipe for grout injection in soil
Grey Water Recycling Around 1/3 of all a buildings water is used for flushing WC. Grey water, waste water from showers and wash hand basins, can be collected in a re-use system & treated to a standard suitable for WC flushing
Problems may arise when the water is stored as it quickly deteriorates as the bacteria multiply
Systems address this problem by filtration and treatment of the stored grey water. There must also be a way of protecting the mains water against contamination by backflow, to comply with the water supply regulations 1999
Facts and figures
Greywater recycling has the potential to save a third of a buildings mains water usage
They are initially expensive, therefore a saving isn’t instantly seen in most cases
Systems will cost in the region of £3,000, with a small billed charge for running costs such as electricity.
The main benefits are social as they are extremely beneficial to the environment, as they reduce both the pressure on water resources and the quantity of sewage requiring treatment. This gives off a good public image for a construction company which can be a valuable publicity tool.
Rainwater Harvesting Rainwater harvesting is simply the process of collecting water once it has fallen onto roofs and then storing that water in tanks until they are required for re-use
When required the water is pumped to the point of use, thus displacing what would otherwise be a demand for mains water
Recently water demand has started to exceed supply and localised flooding has become an issue, industry experts are now starting to adjust to recognising the important role rainwater harvesting has to play in alleviating both these problems
Rainwater is captured from the roof and brought to a central point, via normal guttering and downpipes, to enter a storage tank (frequently located underground), where it is filtered on entry. A highly efficient and reliable submersible pump delivers the water to a service on demand.
The size of the tank is determined by considering the amount of water available for storage (combination of roof size & local average rainfall) and the amount of water likely to be used (combination of buildings occupancy and function in this case a construction site occupied by various employees and management)
Reed Beds The bed is lined with carpet and pond liner and filled with layers of gravel and pea gravel with a thin layer of sand at the surface. Reed beds are categorised as horizontal beds where the water enters at one end and flows horizontally to the outlet collector and vertical beds where the water flows down vertically through the bed. The vertical beds fill and empty as they work oxygenating the bed as they do so. The horizontal beds stay full most of the time and rely on the reeds pulling oxygen down into their roots to feed the aerobic microorganisms that keep the water smelling fresh
Grey Water Rainwater Harvesting Reed bed construction 1 Reed bed construction 2 Reed bed construction 3 The impact of groundwater on a construction project can be enormous. Water effects the design of the structure, the construction procedures, and ultimately the overall project cost. We have seen water problems of unexpected severity cause major delays. A high proportion of claims and litigation in construction arises from water problems. The ever increasing trend of population growth and population concentration has seen land values soaring, creating a demand for very limited sites that were once thought of as unsuitable. On these sites groundwater is often the problem that must be solved.
Construction of new and improved infrastructures in cities must be carried out while minimizing disruption to the existing services and infrastructure. This often makes it too difficult to use the traditional methods of dewatering. Engineers have modified the wellpointing system by installing inverted o horizontal wells.
Electro-osmosis is suitable for use in very low permeability soils such as silts or clays where groundwater movement under pumping would be exceedingly slow. An electric current is passed through a series of anodes and cathodes in the ground. This causes movement of the water from electrical potential gradients rather than hydraulic gradients. The potential gradient causes positively charged ions and pore water around the soil particles to migrate from the anode to the cathode, where the small volumes of water created and be pumped away by wellpoints or ejectors. This method can reduce the moisture content of the soil, therefore increasing its strength. As well as a groundwater control method it is very much a ground strengthening method. To further increase the stability of the soil elector-chemical stabilisation can be used, where chemical stabilisers are added to the anodes to permanently increase the strength of the soil.
PRESENTATION ON GROUNDWATER CONTROL DURING CONSTRUCTION
WATER CONTROL DURING CONSTRUCTION
WHICH PROCESS DO YOU USE?
The advances in modern technologies to remove groundwater before and during construction over the last 20 years have meant there are many varieties of methods available on the market.
This variety has made it quite a difficult to choose the correct system for the purpose intended. We have evaluated each of the systems available and their ’fitness for purpose’.
SUMP AND PUMP
We are all very familiar with the traditional sump and pump method. Is best suited for small and generally not too deep excavations
Table for overview.
The table demonstrates the depth of excavations against he permeability of soil. We can see that with the greater permeability of the soil
Adam Twatt 0505921 Tom Cairns 0601629 Daryl "the Dazzler " Neill 0600129
A series of extracting wells around the perimeter of the excavations to reduced water table in the localised area. The water is drawn away to a main point for disposal either on site or by other means.
Stuart MacGregor 0914206 1 2 3 4 Matthew Killicoat 0917397 Project Kinmundy Heights, Peterhead
Main Contractor Deveron Homes
Photos 1 + 2 = Typical swale formed
Photos 3 + 4 = Heavy rain causing swale to flood