Appendix B - Geotechnical Investigation Report

Cone Penetrometer Testing (CPT) and Interpretation:                       There are limitations when using the CPT in that it may not penetrate
The cone penetrometer is sometimes referred to as a Dutch Cone.           obstructions within any fill, thick layers of hard clay and very dense
The test is described in Australian Standard 1289.6.5.1–1999 (R2013)      sand, gravel and weathered bedrock. Normally a ‘dummy’ cone is
‘Methods of Testing Soils for Engineering Purposes, Soil Strength and     pushed through fill to protect the equipment. No information is
Consolidation Tests – Determination of the Static Cone Penetration        recorded by the ‘dummy’ probe.
Resistance of a Soil – Field Test using a Mechanical and Electrical
Cone or Friction-Cone Penetrometer’.                                      Flat Dilatometer Test: The flat dilatometer (DMT), also known as the
                                                                          Marchetti Dilometer comprises a stainless steel blade having a flat,
In the tests, a 35mm or 44mm diameter rod with a conical tip is
                                                                          circular steel membrane mounted flush on one side.
pushed continuously into the soil, the reaction being provided by a
specially designed truck or rig which is fitted with a hydraulic ram      The blade is connected to a control unit at ground surface by a
system. Measurements are made of the end bearing resistance on            pneumatic-electrical tube running through the insertion rods. A gas
the cone and the frictional resistance on a separate 134mm or             tank, connected to the control unit by a pneumatic cable, supplies
165mm long sleeve, immediately behind the cone. Transducers in            the gas pressure required to expand the membrane. The control unit
the tip of the assembly are electrically connected by wires passing       is equipped with a pressure regulator, pressure gauges, an audio-
through the centre of the push rods to an amplifier and recorder unit     visual signal and vent valves.
mounted on the control truck. The CPT does not provide soil sample
                                                                          The blade is advanced into the ground using our CPT rig or one of our
recovery.
                                                                          drilling rigs, and can be driven into the ground using an SPT hammer.
As penetration occurs (at a rate of approximately 20mm per second),       As soon as the blade is in place, the membrane is inflated, and the
the information is output as incremental digital records every 10mm.      pressure required to lift the membrane (approximately 0.1mm) is
The results given in this report have been plotted from the digital       recorded. The pressure then required to lift the centre of the
data.                                                                     membrane by an additional 1mm is recorded. The membrane is then
                                                                          deflated before pushing to the next depth increment, usually
The information provided on the charts comprise:
                                                                          200mm down. The pressure readings are corrected for membrane
 Cone resistance – the actual end bearing force divided by the           stiffness.
    cross sectional area of the cone – expressed in MPa. There are
    two scales presented for the cone resistance. The lower scale         The DMT is used to measure material index (ID), horizontal stress
    has a range of 0 to 5MPa and the main scale has a range of 0 to       index (KD), and dilatometer modulus (ED). Using established
    50MPa. For cone resistance values less than 5MPa, the plot will       correlations, the DMT results can also be used to assess the ‘at rest’
    appear on both scales.                                                earth pressure coefficient (Ko), over-consolidation ratio (OCR),
 Sleeve friction – the frictional force on the sleeve divided by the     undrained shear strength (Cu), friction angle (), coefficient of
    surface area – expressed in kPa.                                      consolidation (Ch), coefficient of permeability (Kh), unit weight (),
                                                                          and vertical drained constrained modulus (M).
 Friction ratio – the ratio of sleeve friction to cone resistance,
    expressed as a percentage.                                            The seismic dilatometer (SDMT) is the combination of the DMT with
                                                                          an add-on seismic module for the measurement of shear wave
    The ratios of the sleeve resistance to cone resistance will vary
                                                                          velocity (Vs). Using established correlations, the SDMT results can
    with the type of soil encountered, with higher relative friction in
                                                                          also be used to assess the small strain modulus (Go).
    clays than in sands. Friction ratios of 1% to 2% are commonly
    encountered in sands and occasionally very soft clays, rising to
                                                                          Portable Dynamic Cone Penetrometers: Portable Dynamic Cone
    4% to 10% in stiff clays and peats. Soil descriptions based on
                                                                          Penetrometer (DCP) tests are carried out by driving a 16mm
    cone resistance and friction ratios are only inferred and must not
                                                                          diameter rod with a 20mm diameter cone end with a 9kg hammer
    be considered as exact.
                                                                          dropping 510mm. The test is described in Australian Standard
Correlations between CPT and SPT values can be developed for both         1289.6.3.2–1997 (R2013) ‘Methods of Testing Soils for Engineering
sands and clays but may be site specific.                                 Purposes, Soil Strength and Consolidation Tests – Determination of
Interpretation of CPT values can be made to empirically derive            the Penetration Resistance of a Soil – 9kg Dynamic Cone
modulus or compressibility values to allow calculation of foundation      Penetrometer Test’.
settlements.                                                              The results are used to assess the relative compaction of fill, the
Stratification can be inferred from the cone and friction traces and      relative density of granular soils, and the strength of cohesive soils.
from experience and information from nearby boreholes etc. Where          Using established correlations, the DCP test results can also be used
shown, this information is presented for general guidance, but must       to assess California Bearing Ratio (CBR).
be regarded as interpretive. The test method provides a continuous        Refusal of the DCP can occur on a variety of materials such as
profile of engineering properties but, where precise information on       obstructions within any fill, tree roots, hard clay, gravel or ironstone,
soil classification is required, direct drilling and sampling may be      cobbles and boulders, and does not necessarily indicate rock level.
preferable.




February 2019                                                       3