Within the construction industry, groundwater issues become relevant in four key areas:
Weak ground – When soil such as sand, silt or weak clay contains groundwater which is under pressure, the ground becomes very weak. This is because of the principle of effective stress in which the property of a soil that controls its strength is the total stress on the soil minus the groundwater pore water pressure.When the soil becomes weak, it can flow as seen in a mudslide. Unless treated, this can result in the collapse of the ground, together with surrounding temporary structures, causing structural damage and potential loss of life.
Groundwater Resource – Within the world, groundwater is a vast store of potable water which feeds our rivers and lakes. Carefully designed water well boreholes provide a plentiful supply of potable water to homes and industries. To avoid over abstraction and a loss of the supply of groundwater to neighbouring properties or the natural environment, abstraction boreholes must be carefully designed to ensure a sustainable abstraction.
Groundwater Protection – If a site operation or industrial process is located over a groundwater resource, it is a legal requirement to prevent the contamination of the groundwater aquifer.Aquifer protection measures can be designed using various methods, including the removal of the contamination source to the removal of the pathway between the source and the vulnerable aquifer.
Energy Resource – The ground within the UK is relatively constant temperature, ranging from 9 degrees Celsius in the North to around 13 degrees Celsius in the South. This makes the ground highly suitable for the abstraction of energy for the ground source heating and cooling of buildings.
If groundwater is used for heating by the pumping of groundwater from abstraction boreholes, this is known as an open loop ground source system. Such an open loop system needs permission from the Environment Agency to ensure that the abstraction of the groundwater does not impact on the wider natural resource.
The most common method of ground source heating and cooling is using a closed loop system. Under these conditions, collector pipes are installed in the ground through which flows a thermal transfer fluid which carries the heat from the ground to the heat pump located within the building.
The collector pipes can be installed in both shallow horizontal trenches and vertical boreholes. However, if there is no groundwater present then there is very little energy transferred from the ground. This is because although the ground particles have a high thermal conductivity, it is the groundwater within the pores of the soil matrix that facilitate the movement between the particles themselves. Without the presence of groundwater, the heat will not dissipate through the ground, resulting in a poor energy resource. In the other extreme, if groundwater is actually flowing through past the pipes within the aquifer, this results in an excellent heat energy resource.