3.3 Equipment

3.3.1 Apparatus

(1)P The apparatus shall comprise:

  • thrust machine;
  • push rods;
  • penetrometer tip;
  • measuring/recording equipment.

(2)P The thrust machine shall push the rods into the soil at a constant rate of penetration. It shall be stabilised in such a way that it does not move significantly during the pushing action.

(3)P The push rods shall be assembled tightly in order to form a rigid-jointed series with a continuous straight axis.

(4) In order to prevent buckling, guides and/or casings should be provided for the free part of the push rods above the soil, in very soft layers situated above a highly resistant layer and for the part of the push rods in water.

(5) Before loading, push rods should be straight so that the maximum deflection of a point on a 1 m push rod, from a straight line through the ends, does not exceed 1 mm for the 5 lowest push rods and 2 mm for the remainder.

(6)P The penetrometer tip terminates the series of rods. It shall have a cone and shaft with the same axis as the series of push rods.

(7)P When the penetrometer tip includes a friction sleeve, it shall have the same axis and shall be located immediately above the cone.

(8)P The apex angle of the cone θ shall be 60°.

(9) The assessment of the derived values in 3.7 is based on the nominal total area of the base AC = 1000 mm2.

(10) When cones having a base AC different from 1000 mm2 are used, careful attention should be given to size effects.

(11) In Annex M documents have been listed that give examples of the description of the geometry, tolerances and surface roughness of the cone, friction sleeve and shaft, as well as the geometry of gaps, geometry and deformability of seals. It is recommended that these should be used.

(12)P For CPTU a filter element for pore water pressure measurement is incorporated into the cylindrical part of the cone. Its diameter shall not be less than the diameter of the cylindrical part of the cone and not more than the diameter of the friction sleeve, if applied.

(13) The use of additional filter elements placed at other locations is not in contradiction with the minimum requirements given in this section.

(14) For CPTU the geometry of the cone should be such that:

  • the height he of the cylindrical part including the height hu of the filter element is: 7,0 mm ≤ he ≤ 10,0 mm,
  • the diameter du of the filter element is: dcdudc + 0,2 mm


dc is the diameter of the cylindrical part of the cone

and the seal in the gap should be such that the remaining area Ai (see figure 3.3) is as small as possible.

Remaining area Ai for a piezocone test CPTU
Figure 3.3: Remaining area Ai for a piezocone test CPTU

3.3.2 Measuring equipment

(1)P The apparatus for CPT or CPTU shall include suitable measuring devices with suitable data transmission and data recording systems. The recorded data shall always be accessible on the site.

(2) Devices for measuring the following quantities should be used, when relevant:

  • total penetration force Qt;
  • axial force Qc, acting on the cone, linked to the cone;
  • frictional force Qs,acting on the friction sleeve, linked to the friction sleeve (alternatively, sum of the forces Qc + Qs, acting on the cone and on the friction sleeve, linked to the cone and friction sleeve);
  • inclination and penetration rate of the cone;
  • in a CPTU penetration pore pressure u relative to a known pressure, linked to the filter element in the cone.

(3) If electric measuring devices are built into the tip, they should be temperature compensated.

(4) The sensing devices for measuring cone resistance and local side friction should be designed in such a way that eccentricity of the load does not affect the readings.

(5)P The inaccuracy of the measurements shall not exceed 5 % of the measured value.

Eurocode 7 Geotechnical design — Part 3: Design assisted by fieldtesting