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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 7

Onshore testing


Before the cone penetration tests start, the client should define (on
paper) the aim of the tests. Are the tests for stratification, pile design or
settlement prediction of soft layers etc? A clear strategy for executing
the tests should be determined in discussion with the contractor.
Existing data from boreholes or geotechnical maps should be made
available. The locations of the test should be marked, and the
coordinates and altitude of all the test locations should be recorded. If
possible, the groundwater levels should be measured beforehand.
The day rate for a thrust machine exceeds £1000; it is therefore very
important to undertake all the necessary preparations prior to its arrival
on site to ensure maximum production time.
General preparations 
 Table Required data before start of tests 
 Accessibility of test location (by road/through fields? locked farm
gates? has permission of the
site owner been obtained? etc)
if in doubt, ask for a site visit
before cone penetration company's
staff arrive
 Is the test location clearly marked,
numbered and the co-ordinates

CPT number:
Co-ordinates: x =
                    y =
                    z =
Grid reference:

 Level of groundwater Metres BGL:                                                      

Stratum from borehole:
(if available) 
Anticipated termination of CPT:

Layer   Depth   Soil type   Unit weight 
 Location of borehole No        Co-ordinates
            x =
            y =
            z =
Grid reference:     
CPT tests
To set up tests the following steps are taken: 
 Position rig over test location 
 2 Level thrust machine using the hydraulic jacks 
 3 Load the computer with test number, client's name etc 
 4 Enter on the computer if there is pre-drilling
 5 Connect cone penetrometer to first thrust rod 
 6 Lower the penetrometer by means of the hydraulic rams to just above ground level 
 7 Check the zero readings for loads, inclination and depth 
 8 Commence the test attaining a rate of 20 mm/sec 
 9 Stop thrust every metre to connect the next rod 
 10  Finish test at scheduled depth or refusal (inclination, tip resistance, sleeve friction too high, or total force too much due to hard rock) 
 11 In case of cobbles or boulders resulting in a refusal, move rig 1m and record new position, before repeating the test 
 12 Remove the penetrometer, disconnecting and restacking the rods 
 13 Check the zero readings just above ground level 
 14 Save test data in computer 
 15 Enter test details and results on day report
 16 Remove rig 

Dissipation tests

  • The purpose of a dissipation test is to evaluate the factor of
    consolidation (settlement). To do this, the level of the groundwater
    table must be known
  • Dissipation tests are only useful in clays. It is therefore necessary to
    research the stratum, first, by using a CPT or CPTU
  • When only one dissipation test will be made at a location, the best
    position to do the test is vertically midway in the clay layer
  • In soft or loose soils, pre-drilling should be taken down to the
    groundwater table. The pre-drilled hole should be filled to ground
    level with water if the pore pressure is to be measured using a watersaturated
    system. If the groundwater table is located at great depth,
    the pore pressure system should be saturated with glycerine or
    silicone oil
  • The choice of the filter location is between U1 and U2. A filter at U3 is
    used only in combination with U2. Both filter locations U1 and U2 have
    advantages and disadvantages:
    ♦ U1 gives larger positive porewater pressure, even in heavily over-
    consolidated clays, but the filter is more prone to damage and wear
    ♦ with U2, the filter is much less prone to damage, but in heavily
    over-consolidated clays, very low (or even negative) porewater
    pressure may be produced 
  • At present the location of the filter is not standardised. The ISSMGE
    reference test procedures[1] refer to the location behind the cone, U2,
    as the preferred location
  • During the dissipation test the push rods can be locked or unlocked
    (in the push/pull clamp). The ISSMGE reference test procedures do
    not give a preferred procedure.

For t50, the test can be stopped when the pore pressure is dissipated
until a pressure ut = 0.5(ui + u0) is obtained. Where u0 is the groundwater
pressure and ui is the pore pressure at the start of the test. Where u0 is
unknown, it is safe to stop at 0.5 ui.
Figure 65 shows typical test results for U1 and U2.
Since procedure (locked or not locked) and location of filters U1 and U2
influence the test results, it is important that the client gives written

Figure 66 shows an example of how to calculate and where to stop the
dissipation test for t50.


Figure 65  Typical dissipation curves  

Figure 66
  Dissipation test (t50
ui = initial pore water pressure U1 or U2 
uo = in-situ porewater pressure before penetration 
When uo is unknown, test should be stopped at 0.5ui
ui = 250 kPa  uo = 50kPa (5m of water)
Test to be stopped at 0.5 (250 + 50)= 150kPa or at 0.5 x 250 = 125 kPa if uo is unknown

 Table 5  Control scheme for recommended maintenance routines
(from IRTP, 2001[1], Table A1.1)
 Checking routine 

Start of

Start of

End of

Every 3rd

 Verticality of thrust

 Penetration rate 

 Safety functions 


 Push rods 


 Gaps and seals 


 Zero drift  




 Function control 



 CPT and CPTU     100-200 m/day for CPT 
 Dissipation test, t50     0.5-1.0 hours, depending on permeability
 Mostap soil sampling     0.5-1.0 hours per metre-sample,
    depending on depth 
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