Tremie refers to a method of pouring concrete underwater, or in dry spaces deep underground. Tremie may also refer to the main piece of equipment used to direct the pour of this concrete. A tremie pour allows the concrete to set up and dry successfully, and helps to keep moisture away from the wet concrete mix.
The tremie method of pouring concrete is often used during bridge construction, or to set piles needed to support footers and foundations in water or unstable soil. First, contractors build a standard form out of metal or composite materials. This form must match the size and shape of the object being constructed. A metal plate is fastened to one end of the form, then the entire object is lowered until it reaches the sea floor. The plate at the base of the form should be firmly attached so no water can enter the form.
Next, installers lowers a grout pipe, or tremie down into the base of the form. One end of the pipe must remain close to the sea floor, while the other end features a large bin or hopper to catch the freshly-mixed concrete. A concrete mixing truck empties the mixture into the hopper, and the wet concrete travels down the length of the tremie to fill the base of the form. Installers must keep the bottom of the grout pipe in contact with the fresh concrete at all times for best results.
After the pour is complete, the pipe is lifted up and out of the form. The concrete is allowed to dry based on the type of mixture used, and tests may be performed to determine whether the concrete has safely cured. Depending on the application, the forms may be removed or simply left in place.
The tremie method is also used to seal underground well casings. Sealing around the well with concrete or grout prevents the well from caving in on itself, and also keeps unwanted surface water from contaminating the water supply. The tremie pumps wet concrete into the base around the well casing until the mixture reaches ground level. Once the grout pipe has been removed, installers simply drill through the base of the casing and surrounding concrete to access water for the well.
Some may wonder why the tremie is needed at all. While it is possible to simply pour concrete into a form from above the water level, this generally results in a very poor finished product. The falling concrete is no longer mixed properly once it settles into the base of the form, resulting in voids or air pockets that could lead to failure.
