Penetrometer

Abstract: Recognition of the importance of soil compaction is increasing, but instrument cost, measurement repeatability, and data interpretation limit its measurement on agricultural and rangelands. The dynamic penetrometer described here follows American Society of Agricultural Engineers standards, but replaces the proving ring with a strike plate, a shaft extension, and a sliding hammer. The penetrometer cone is pushed into the soil by successive hammer blows. Penetration resistance is calculated as the work by the soil needed to stop cone movement divided by the penetration distance. The work by the soil is defined as the kinetic energy of the hammer when it impacts the strike plate. Construction cost is approximately $100 to $150. The standard drop height and hammer mass ensure measurements are consistent between operators.

Abstract: A theory, based on cavity expansion and stress rotation analyses, is developed for computing the cone penetration resistance of sand. The sand is modeled as a nonlinear elastic-plastic material. The theory can be used for analysis of calibration chamber tests, as it takes full account of chamber size and boundary conditions. The theory was used to calculate values of cone penetration resistance for the conditions corresponding to each of about 400 cone penetration tests performed in different calibration chambers. The chamber diameters range from 0.76 to 1.20 m and the cone penetrometer diameters from 1 to 3.57 cm. The samples were prepared of different sands at different densities and stresses. The agreement between theoretical and experimental values was better than ±30% in most cases.

Abstract: USE OF A FLAT-ENDED PENETROMETER, AS SUGGESTED BY RANANATHAN, RUNS INTO PRACTICAL DIFFICULTIES. WITHOUT THE POSITIVE GUIDE OF THE CONE POINT, THE TIP MAY DRIFT UNPREDICTABLY, A SERIOUS PROBLEM AT SOUNDINGS IN EXCESS OF ABOUT 50 FEET. FURTHERMORE, THE FLAT TIP, INSTEAD OF SHEDDING SOIL DURING ITS ADVANCE, AS DOES THE CONE TIP, TENDS TO TRAP AND CARRY DOWN ITS OWN SOIL PLUG. THE RESEARCH OF GIELLY, LAREAL, AND SANGLERAT INTO PREDICTING THE COMPRESSIBILITY OF COHESIVE SOILS USING STATIC CONE PENTROMETER DATA SUGGESTS THAT THE DRAINED COMPRESSIBILITY OF COHESIVE SOILS MAY RELATE TO THE UNDRAINED STRENGTH CHARACTERISTICS OF SUCH SOILS. THE ENERGY EXPENDED TO ADVANCE THE CONE PENETROMETER, RESULTING IN RADIAL EXPANSION OF A CYLINDER EQUAL TO THE DIAMETER OF THE PENETROMETER TIP, MAY HAVE A FUNDAMENTAL RELATIONSHIP TO THE DISRUPTION AND COMPRESSIBILITY OF THE STRUCTURE OF ANY SOIL. THE CASE STUDIES PRESENTED BY WEBB AND MELVILL ARE A VALUABLE CONTRIBUTION. A MODEL STUDY MADE IN 1968 BY ANNE TOPSHOJ AND SUPERVISED BY THE AUTHOR INVESTIGATED THE RATIO OF EDGE/CENTER SETTLEMENT FOR A FLEXIBLE, UNIFORMLY LOADED, CIRCULAR AREA OF 4.1 INCHES DIAMETER PLACED ON THE SURFACE OF A DRY, UNIFORM, MEDIUM QUARTZ SAND AT A RELATIVE DENSITY OF ABOUT 25%. SHE ALSO TESTED A RIGID PLATE OF THE SAME DIAMETER PLACED ON A LATEX SHEET ON THE SURFACE OF THE SAME SAND IN THE SAME CONDITION AND LOADED TO THE SAME TOTAL LOAD. THE BEARING OF THIS WORK ON THE RESEARCH OF WEBB AND MELVILL IS ILLUSTRATED AND DISCUSSED.

Abstract: This paper discusses the effects of penetration rate on the penetration resistance in soft clay for various shaped penetrometers (cone, T-bar, ball, and plate) and for T-bars with different aspect ratios. Constant rate (“normal”) and variable rate (“twitch”) penetration tests, where the penetration rate was successively halved over eight steps with the penetrometer advanced by one or two diameters in each step, were undertaken in the beam centrifuge at the University of Western Australia. The tests were conducted on samples reconstituted from clay collected from the Burswood site in Western Australia. The twitch tests showed higher penetration resistance than the corresponding normal tests after the penetration rate had been reduced by a factor of 16 due to cumulative effects of partial consolidation. The penetration rate at which the resistance started to increase due to partial consolidation was used to estimate the consolidation coefficient, cv , of the reconstituted clay. The interpreted cv values wer...