TECHNICAL PAPER

Reliability in the testing and assessing of piling work platforms Fred Fountain, Testing and Analysis Tony Suckling, Balfour Beatty Ground Engineering

Introduction design assumptions is uncertain. propose a safe and sustainable working platforms. Scanning with There have been several instances The method is also slow and protocol for making adequate ground penetrating radar (GPR) is on construction sites of piling rigs laborious and ties up heavy plant so platform assessments, by: a geophysical method using radar and cranes of various types toppling it is unsustainable to carry out many n Identifying a non-destructive pulses to image the subsurface over while operating on un-bound or tests across a platform. means of rapidly surveying a by detecting variations in the weakly-cemented working platforms. Most significantly, investigations platform so as to identify any buried dielectric constants of materials in The current method of designing following rig and crane toppling anomalies, including defects and the ground. To investigate whether piling platforms in the UK identifies incidents have often found that reductions in layer thickness. GPR could be a reliable alternative that the key problem is “punching inherent, isolated areas of weakness n Identifying a reliable but more to static load testing, trials with failure”, but relies heavily on or ground collapse beneath a rapid, representative and simple modern non-specialist equipment modelling assumptions and on working platform have been the method of load testing a platform, were carried out on two sites. site investigation data. In order to actual causes of failure, which to permit the carrying out of many First, attempts were made to certify working platforms at present were not indicated by load testing. such tests as opposed to only one or find and map reinstated trial pits a few plate load bearing tests are For this reason, it is essential that two. located within a piling rig plant yard carried out, and unless there are contractors constructing such (Figure 1). Second, a dimensioned visible problems the test results are platforms carefully inspect and Detection of hidden traverse was made along a roadway usually accepted without question. check sub-grades for any evidence anomalies containing visibly-reinstated service As a result, just about any platform of localised weak areas, such as old It is possible for hidden “soft spots” trenches. passes. The relationship between pits or trenches. and other voids and defects, such as At the first site four trial the data from such testing and the The intent of this paper is to layer thinning, to be present beneath excavations, which were hidden

Figure 1: Attempts were made to find and map reinstated trial pits located within a piling rig plant yard

ground engineering november 2012 29 TECHNICAL PAPER

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30 !"#$%& '%!(%''"(%! %#)'*+'" ,-., Figure 3: Analysis of plate bearing date Cycle 1 Cycle 2

Test location/ k762 Es Ev1 Deflection CBR Evd k762 Es Ev2 Deflection Evd Selected for ID (MPa) (MPA) (MPa) at 350kPa (%) (MPa) (MPa) (MPA) (MPa) at 350kPa (MPa) analysis (mm) (mm) Site 1, Area 1 274.1 441.2 652.2 0.77 69 78.48 1,370.48 – 6,000.0 0.06 78.48 300mm plate Site 1, Area 1 81.2 58.1 63.2 4.94 17 78.48 168.9 129.0 276.9 2.36 78.48 X 610mm plate Site 1, Area 2 68.9 76.9 173.1 4.56 17 45.45 148.9 124.2 211.8 2.29 45.45 X 610mm plate Site 2, Test 1 <21.8 7.2 12.4 36.93 <5 18.49 – – – – 18.49 X 610mm plate Site 2, Test 2 144.4 145.2 450.0 1.99 36 18.49 129.2 148.1 290.3 2.39 18.49 610mm plate Site 2, Test 3 26.9 20.2 49.2 17.88 7 18.49 22.5 66.2 233.8 8.79 18.49 X 610mm plate Site 2, Test 4 78.7 57.8 131.4 5.23 20 18.49 52.6 77.5 200.0 4.71 18.49 610mm plate Site 3, Test 1 106.8 105.3 327.3 3.03 27 45.86 335.3 384.6 900.0 0.82 45.86 610mm plate Site 3, Test 2 127.0 190.5 418.6 2.11 32 45.86 841.2 1,111.1 2,571.4 0.42 45.86 610mm plate Site 3, Test 3 79.8 45.1 125.0 6.04 20 45.86 111.9 143.9 367.3 2.52 45.86 610mm plate Site 3, Test 4 75.3 79.4 189.5 4.25 19 45.86 251.6 370.4 900.0 1.14 45.86 X 610mm plate Site 4, Test 1 105.6 35.8 38.9 6.63 26 4.39 224.3 131.6 257.1 2.09 4.39 610mm plate Site 4, Test 2 45.6 98.0 246.6 4.40 11 58.59 278.0 270.3 692.3 1.01 58.59 X 610mm plate Site 4, Test 3 37.2 109.9 339.6 5.38 9 13.20 122.0 133.3 321.4 2.49 13.20 610mm plate

Site 4, Test 4 50.7 34.7 83.7 8.96 13 66.96 357.1 370.4 900.0 0.75 66.96 X 610mm plate Site 4, 123.1 52.4 124.1 4.39 31 20.95 122.3 136.1 285.7 2.53 20.95 27/03/12 610mm plate

Figure 3 Notes a) “Cycles” refers to parameters determined on the first or second cycle. b) “k762” refers to the modulus (or coefficient) of sub-grade reaction. c) “Es” refers to the secant elastic modulus (without correction for Poisson`s Ratio) from 150 to 350kPa in the 610mm plate tests carried out (with no size conversion) d) “Ev1 and 2” refer to the secant elastic modulus (without correction for Poisson`s Ratio) from 135 to 315kPa in the 610mm plate tests carried out (with no size conversion), on the first and second cycles respectively. e) “Settlement at 350kPa” refers to the mean plate settlement recorded at a load of 350kPa under a 610mm diameter plate .f) “CBR” refers to the equivalent theoretical California Bearing Ratio as calculated from the relevant k762 g) “Evd” as given in blue and repeated is the dynamic modulus as generated by the LWD instrument. h) The data points marked with a green cross under “Selected for Analysis” are the data points considered to be most representative/least anomalous herein as used in linear regression.

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