DEVELOPMENT OF THE UBC SELF-BORING PRESSUREMETER . PRESSUREMETERS. PROCEEDINGS OF THE THIRD INTERNATIONAL SYMPOSIUM, ORGANISED BY THE BRITISH GEOTECHNICAL SOCIETY, OXFORD UNIVERSITY, APRIL 2-6, 1990

The design considerations, development and evaluation of a jetting self-boring pressuremeter are described. Special features include downhole digital data acquisition/processing, low membrane correction, membrane protection and alternate jetting systems. The downhole instrumentation provides a separate amplifier for each transducer, permitting the use of the A/D converter for each channel. Data is transmitted to the surface in digitized format, thus eliminating the effects of transmission line noise. The surface personal computer allows viewing of the data in engineering units as the test proceeds, as well as providing a real-time graphical presentation of the test. A new lantern has been designed that allows the use of thin membranes with a very low membrane pressure correction for work in soft soils. Two jetting systems have been developed and are being evaluated. The initial system was a central jetting system. The central rod is provided with 3 sets of small vanes for stability and a tip in which a series of 2.4 mm holes has been drilled. The alternate design is called the "Showerhead". Near the bottom of the pressuremeter the mud passes to the outer wall through 4 radial holes, and then passes through 12 channels to form a circle of jets aimed inward away from the cutting shoe. For the covering abstract of the conference, see IRRD 838295. (Author/TRRL)