Pressure Meters
Pressure Meter is a meter constructed to measure the at-rest horizontal earth pressure. The pressure meter has two major components.The first component is a read-out unit that remains above ground. The second component of the pressure meter is a probe that is inserted into the borehole to read the pressure.
A man named Louis Menard in 1955 first brought the pressure meter to the forefront. He started the first production of it in France in 1957.
How it works
The probe of the pressure meter is inserted into the borehole and is supported at test depth. The probe is an inflatable flexible membrane which applies even pressure to the walls of the borehole as it expands. As the pressure increases and the membrane expands, the walls of the borehole begin to deform. The pressure inside the probe is held constant for a specific period of time and the increase in volume required to maintain the pressure is recorded.There are two types of tests that can be performed with the pressure meter. The stress controlled test increases pressure in equal increments while the strain controlled test increases the volume in equal increments.
How it is used
The pressure meter is used to test hard clays, dense sands and weathered rock which cannot be tested with push equipment. It allows engineers to design foundations that will be stable in these conditions. There are three different types of pressure meters.The borehole pressure meter is the most common and has a probe that is inserted into a preformed hole . The second type of pressure meter is called a self-boring pressure meter. The self-boring pressure meter has a probe that is self boarded into the ground to prevent disturbance. The third pressure meter is called a cone pressure meter. The cone pressure meter has a cone shaped probe that is inserted into the base of the borehole, it then displaces the soil into the cone of the probe which causes less disturbance to the soil to get a more accurate reading. Different soil types sometimes require different types of pressure meter tests.