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Published By Lankelma

Lankelma is the foremost contractor for onshore in-situ soil testing in the UK. An acknowledged specialist in CPT, Lankelma also offers a worldwide consultancy and training service.

A.P. van den Berg develops, designs and manufactures geotechnical and environmental soil investigation equipment for onshore and offshore applications. Specialists in CPT systems and equipment.


Gardline Geosciences offers worldwide marine geotechnics, in-house consutancy and services with marine investigations ranging from nearshore to full ocean depth (down to 3000m).

About the Author

Hans Brouwer studied civil engineering at Delft University in The Netherlands. He has worked as a part-time lecturer at Amsterdam Polytechnic and was senior partner in a structural engineering consultancy. He has written a standard textbook in Dutch about the design of building foundations. He now lives in England where he writes technical textbooks in English, hopefully to reach a bigger readership.

Chapter 4

Part 1: Special cones: geotechnical cones

Seismic cone

          SEISMIC CONE   4.3 
Figure 21  Seismic cone configuration (above),
test result (below)
Ground surface motions
The seismic cone (Figure 20) measures the shear wave velocity of the soil being investigated. Together with a knowledge of the soil saturated unit weight, the shear wave velocity allows an assessment of the small strain shear modulus (G0) and the constrained modulus (M0) to be made. The small strain shear modulus is an essential input for rediction of groundsurface motions from earthquake excitation, evaluation of foundations for vibrating equipment, offshore structures  ehaviour during wave loading, and for prediction of deformations around excavations.
The seismic cone is available in 10 and 15 cm2 areas. The cone usually consists of a piezocone unit – measuring the geotechnical parameters qc, fs and U2 – with a receiver for the seismic measurements above it.
A schematic diagram, with the layout of the standard technique using a seismic cone, is shown in Figure 21.
The extra equipment needed, in addition to the built in seismometer, is a memory oscilloscope
and an impulse source with a trigger for the oscilloscope. The source can consist of a steel beam for shear (S) wave generation or a flat plate for compression (P) wave generation.   
The moduli G0 and M0 can be determined from the following:
G0 = ρ(Vs)2 (kN/m2)
M0= ρ(Vp)2 (kN/m2)
where: ρ = the soil mass density (kg/m3)
          Vs = shear wave velocity (m/sec)
          Vp = compression wave velocity (m/sec)
The shear wave source usually consists of a beam pressed against the
ground by the weight of the CPT vehicle and a hammer. Normally the
seismic cone penetrometer is pushed into the ground and penetration
is stopped at 1 m intervals. During the pause in penetration, a shear
wave is generated at the ground surface and the time required for the
shear wave to reach the seismometer in the cone penetrometer is
measured. The shear wave is generated by hitting the beam end
horizontally with the hammer in the direction of the long axis. The
computer in the CPT rig collects and processes all the data from the
CPT or CPTU. The seismic source for offshore testing is a hydraulic
underwater shear wave box.
Sonic cone
Lankelma Ltd is developing a new seismic tool for cone penetration
testing. The sonic cone will allow in-situ testing of primary and shear
waves without a surface source. It combines a standard piezocone with
an acoustic velocity-logging tool. Acoustic velocity logging uses
mechanical energy in the form of pulses or continuous waves of
acoustical frequencies to investigate the surrounding material.
The simplest form of the sonic logging tool involves an acoustic pulse
travelling from the transmitter through the soil, as a compression (P)
wave, to the receiver which is a fixed distance from the transmitter. The
pulse also travels up along the wall of the housing as a boundary wave. 
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