2.2 Earth Pressure Cell Design
Earth Pressure Cells are constructed from two stainless steel plates welded together around the periphery so as to leave a narrow space between them. This space is completely filled with deaired hydraulic oil which is connected hydraulically to a pressure transducer where the oil pressure is converted to an electrical signal which is transmitted through a signal cable to the readout location.
In general Earth Pressure Cells use an all welded construction so that the space confining the oil is entirely metal not requiring 'O' rings which tend to trap air and reduce the cell stiffness. The oil is de-aired using a Nold DeAerator™ which materially improves the fluid stiffness and the performance of the cell. The pressure transducer normally employed which is available in several different pressure ranges. The cable is attached to the transducer in an ealed, water-resistant manner. For earth pressure cells located inside a soil mass the cable may be armored and provided with strain relief at the cell to reduce the likelihood of pull-out.
2.3 Earth Pressure Cell Construction
Major components of the rectangular and circular Earth Pressure Cells are shown in Figures 2.4 through 2.5, respectively.
The Earth Pressure Cells may be rectangular or circular in shape. The standard size for the rectangular Model 4800 is 150 mm × 250 mm (6" × 10"), for the circular it is 230 mm (9") in diameter. Standard thickness for both styles is 6 mm (aspect ration > 20). For laboratory tests smaller, thinner cells can be manufactured.
|Figure 2.4 - Rectangular Earth Pressure Cell|
|Figure 2.5 - Circular Earth Pressure Cell|