Different Types of Earth Pressure Cells, Their Applications and Construction of Isobar Diagram Using Them-14

During the backfill of trenches in earth dams, a plug, approximately 0.5 meter (2 feet) in width, made of a mixture of 5% bentonite (by volume) from an approved source and exhibiting a free swell factor of approximately 600%, and 95% embankment material, can be placed in the trenches at intervals of not greater than 20 meters (50 feet). The purpose of the bentonite plugs is to reduce the possibility of water seepage through the embankment core along the back filled trenches. The cable may be marked by using labels. For an individual cable the identification number should be taped near the end of the cable. Additional cable labels might be specified at regular intervals along the cable to aid in identification if cables need to dug up for splicing, etc.

2.8 Installation of Contact ("fat-back") Pressure Cell

Earth Pressure Cells which are used for the measurement of earth pressures on structures. In backfills for piers, piles, bridge abutments, retaining walls, culverts and other structures the cells may be installed either inside a concrete structure being poured or directly on the surface of an existing structure.

Figure 2.9 - Attachment to Concrete Form

2.9 Installation in Poured Concrete:

When pouring concrete the cells can be held to the forms using nails and the lugs welded to the edge of the cell. The cell is positioned so that the thin pressure sensitive plate is directly against the concrete form (Figure 2.9.). The plates are nailed to form lightly in such a manner that they engage the concrete sufficiently so that they do not pull out of the concrete when the forms are removed. The cable is routed inside the concrete to a convenient readout location or to a block out inside where excess cable can be coiled. The cable is protected from damage during concrete placement and vibration, by tying it to adjacent rebars.