HOW ARE DIAPHRAGM WALLS CONSTRUCTED?
What is the grab's role as an equipment in this?
Diaphragm walls are constructed in three main stages:
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Excavation from top to bottom
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Installation of Reinforcement
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Placing concrete
The grab, attached to a carrier equipment is for excavating a trench for the wall
EXCAVATION PROCESS
The excavation (and thus the subsequent construction) for the continuous diaphragm wall is carried out panel wise. The panels are constructed independently, with inert earth on either end are classified as primary panels. Others, with at least one constructed panel on either side are classified as secondary panels.
Excavation of diaphragm wall is carried out by a grab (clampshell). The panel thickness is dictated by the width of the grab. To guide the excavation of the diaphragm walls in soil, a concrete guide wall is constructed first. The initial excavation is done by placing the grab between two faces of guide wall. It helps in ensuring the correctness of diaphragm wall in x and y dimensions.
The initial excavation till the bottom of guide wall is known as initial bite. After initial bite, the grab is positioned in one location in the horizontal plane and excavation progresses along the depth of the diaphragm. This is said as one full bite. Generally, the length of a panel is quite larger than the jaw size of a grab. Thus excavation for one panel includes multiple bites. (See illustration no.2 in the exhibit above)
