CALIBRATION OF THE PERTH SAND PENETROMETER (PSP) FOR SILICA SANDS

• Published in: Iranian journal of science and technology. Transactions of civil engineering Vol. 36; no. C1; p. 13
• Main Authors: Mohammadi, S D, Fityus, S G, Bates, L
• Format: Journal Article
• Language: English
• Published: Shiraz Springer Nature B.V 01.02.2012
• Subjects: Calibration; Charts; Civil engineering; Density; Devices; Friction; Measuring instruments; Penetrometers; Sand; Sand & gravel; Silica; Silicon dioxide; Standard deviation; Studies; Weight reduction; Australia
• ISSN: 2228-6160

Abstract- The blunt tipped "Perth Sand Penetrometer" is used extensively in Australia for characterization of silica sand sites prior to the construction of light weight domestic structures. The hand operated device, which can be readily deployed in fine granular soils at depths up to 5 m, is routinely and successfully used to infer in situ density and internal friction angles in extensive coastal sand deposits. Some calibration charts are presented for a light weight dynamic penetrometer device. The charts presented here are based on the results of 18 calibration chamber tests, performed in a specially constructed chamber, 1m high and 1m in diameter. All tests were performed on silica sand samples were consistently prepared to 3 densities using the sand raining or pluviation technique. The prepared samples were pressurized during testing to simulate overburden effects due to burial at depths up to 5m. Particular account is taken of the effects of rod friction. The pullout tests to estimate rod and anchor friction in sand were used by some researchers (i.g. 11, 14). Whilst able to simulate deep insitu conditions at the tip of the penetrometer rod, the chamber fails to account for the increasing amount of resistance due to rod friction which would occur in deep test situations. That is, in a simulated 5m test, only 1m of rod was actually embedded, so that 4m of side friction on the rods was unaccounted for, rendering the results potentially unconservative. Three approaches were adopted to account for this. Firstly, the relative side friction on embedded rods in loose, medium and dense samples, and simulated depths up to 5m, were assessed by measuring the quasistatic pullout resistance of the rods after driving. This was achieved simply by incorporating a spring balance between the embedded rod and a pullout cable. The load on the balance was recorded as the rod was extracted at a steady rate of about 100mm per second. The arrangement of this method is illustrated in Fig. 5. By interpolating the corrected blow count data in Fig. 9a, a calibration chart relating the density of sand to testing depth and blow counts/150mm has been developed. It is presented in Fig. 10. The plotted points in Fig. 10 have been taken from the corrected results in Fig. 9a. Comparisons of the chart with the results of Glick and Clegg [3] are difficult because of the limited depths considered in that study. However, it is interesting to note that the quoted blow counts for depths of sand between 200 and 750mm, at 80% relative density, are a constant value of 8/150mm (Fig. 11). By comparison, this study determined blow counts ranging from 3/150mm at 200mm to 8/150mm at 750mm in sand at the same density. The constant blow count value for shallow depths in the 1965 study is inconsistent with the results of this study, and the extensive field experience of the authors. The blunt tipped, dynamic PSP is an extremely useful and efficient tool for the characterization of sand sites. Prior to this study, the limited results of Glick and Clegg [3] were the only generally available data for the interpretation of the results of this test. In this study, a calibration chart has been developed for use in the density characterization of clean, dry silica sands up to 5m deep. Whilst the trends in the raw data showed an amount of inconsistency, it is expected that the conservative approach adopted in the analysis of this data has preserved a satisfactory degree of conservatism in the resultant calibration chart. Nevertheless, the inference of insitu density using the PSP and the chart developed here, must, in all cases, be tempered by engineering judgment and experience. Those seeking to characterize sand sites with the PSP must appreciate that the chart is the product of interpolation of a limited data set, and can thus give only a guide to the likely magnitude of insitu densities. In particular, one must be aware that only a small amount of data for loose sands at shallow levels has been used in the formulation of the chart. Thus, any interpretations made in this regard must be assumed to have a significant degree of uncertainty.