Patent GB-1430239-A (GB)
Title: In-situ testing of materials
IPC: G01N33/24
Filed: 1972-07-12
Abstract: 1430239 Boring earth &c NATIONAL RESEARCH DEVELOPMENT CORP 25 July 1973 [12 July 1972] 32574/72 Heading E1F [Also in Division G1] Soil drilling and testing apparatus comprises a tube 14, Fig. 1, provided with a cutting edge 18, cutting blades 16 mounted on a hollow drive shaft 15 down thro' which flushing water is pumped to push the loose drilled soil up thro' passage 21, and one or more flush fitting load cells such as 51, 100 adapted to continuously measure stress and/or strain characteristics of the soil. The load cell 51 comprises a panel recessed into but integral with a tube 26, Figs. 4, 4a, four webs 24 being left after machining, each being arranged to support an electrical strain gauge. A face plate 23 flush with the surface of the barrel 14 is then fixed and sealed over the panel and the load cell can be used to record and balance any in situ lateral stress by altering the pressure of gas confined between tubes 22, 26, Fig. 1, the electrical resistance gauges on webs 24 indicating zero when the pressures are equal. The axial shear stress on the cell face 23 can be measured by recording the difference in forces on strain gauges carried by the upper and lower pairs of webs 24. The other cell 100 which measures the compressive strength, stiffness and/or consolidation characteristics, comprises a thin rubber membrane 31 held on reduced diameter roughened portions 30 by end clamps 32, 33. If the membrane is held tight against the tube the external diameter of the device is everywhere the same. The membrane may be extended by dry nitrogen circulated therethrough and thro' cell 51 by pipes 46, 48 to remove moisture from the electric strain gauges, and the extension of the membrane 31 is measured by spring pressed pivoted arms such as 38, 38' Fig. 2, the bending of the springs 40' being sensed by strain gauges (not shown). The behaviour of the soil depends on the speed at which it is loaded, that is, upon the rate at which the membrane is expanded, so the speed at which the compression tests are carried out will depend on the purposes of the tests and to conditions simulated so as to be similar to those when actual operations e.g. pile driving, take place. Accordingly the membrane is flush fitted with one or more pore water pressure cells which will indicate whether the soil is behaving as a drained or undrained soil. The cells comprise slabs of porous stone the inner surfaces of which are acted upon by liquid trapped against the stones by an inner diaphragm. The pore pressure of water in the soil is transmitted by liquid in the porous stone to the liquid trapped between the membrane and inner diaphragm, and movements of the diaphragm are read off from an electrical strain gauge to give pressure differences between the inflating gas for the membrane and the pore water pressure on the outer surface of the stone. The tests are performed by expanding the membrane in small increments of pressure or volume and may employ alone either the expanding membrane 31 or the load cell 51 on bauxite slurry, fly ash slurry or asphalt or bitumen or materials stored in silos. In a modification the membrane may be displaced inwardly instead of outwardly.