4 PRESSUREMETER TEST (PMT)
(1)P The pressuremeter test covers the measurement in situ of the deformation of soils and weak rocks to the expansion of a cylindrical flexible membrane under pressure.
(2)P Four different types of apparatus are specified:
- Ménard pressuremeter (MPM),
- prebored pressuremeters (PBP),
- self-boring pressuremeter (SBP)
- full displacement pressuremeter (FDP).
(3) The PBP and the MPM are lowered into a test hole created specifically for the pressuremeter test.
(4) The SBP is drilled into the ground using an integral cutting head at its lower end such that the probe replaces the material it removes thereby creating its own test hole.
(5) The FDP is usually jacked into the ground with an integral cone at its lower end, thereby creating its own test hole. The MPM may in some instances be jacked or driven into the ground.
(6) PBP, SBP and FDP probes may take a number of forms, therefore descriptions are given in accordance with the type of installation and measuring systems.
(7) Two different basic test procedures are specified: a procedure to obtain a pressuremeter modulus, Em, and limit pressure, plm, that may be used in design procedures formulated for the Ménard pressuremeter; and a procedure to obtain other stiffness and strength parameters.
(8)P The tests shall be carried out in accordance with a test method that complies with the requirements given in this section.
(9)P The test method used shall be reported in detail together with the test results.
(10) The test method may be reported by reference to a standard.
(11) P Any deviations from the requirements given below shall be justified and in particular their influence on the results shall be commented upon.
(1)P pressuremeter: cylindrical device, designed to apply a uniform pressure to the walls of a cavity by means of a flexible membrane. The main components of a pressuremeter are shown in fig. 4.1.
(2)P probe: cilindrical part of the pressuremeter that is inflated and thereby transmits the pressure to the cavity walls. The probe may be lowered into a prebored hole, be bored, jacked or driven into the ground (see fig. 4.1)
(3)P expanding section: part of the probe fitted with the flexible membrane. The expanding section may be subdivided in one or three cells (see fig. 4.1).
(4)P test hole: length of borehole, specifically created for pressuremeter testing. It can be of the same diameter or smaller than the borehole and is created below the base of the borehole.
(5)P cavity: portion of a test hole that is subjected to pressure by the expanding membrane. At the start of a test the diameter of the cavity is the same diameter as the test hole.
(6)P monocell probe: pressuremeter with a single expanding cell.
(7)P tricell probe: pressuremeter with three expanding cells, one of which, the central cell, is the measuring cell.
(8)P volume displacement type pressuremeter: pressuremeter fitted with a volume change gauge to measure the change in volume of the expanding section.
(9)P radial displacement type pressuremeter: pressuremeter fitted with displacement transducers to measure the change in radius or diameter of the expanding section.
(10)P membrane stiffness: pressure required to inflate the membrane in air.
(11)P membrane compression: change in thickness of the membrane as the pressure is increased.
(12)P system expansion: change in volume of the pressuremeter system, excluding the volume change of the probe, as a result of a pressure change.
(13)P applied pressure: is the pressure applied by the pressuremeter to the walls of the cavity in the soil or rock.
(14)P volume change: change in volume of the expanding cavity.
(15)P volumetric strain: change in volume of the cavity with respect to the original volume of either the cavity or the expanding section of the probe.
(16)P cavity strain: change in radius of the cavity with respect to the original radius of the cavity.
(17)P pressuremeter test curve: plot of the variation of the applied pressure with either the cavity strain or volume change or the volumetric strain.
(18) The basic curve can have one of the following forms, shown in figure 4.2. For the MPM test the axes are usually transposed.