4.1 Cone penetrometer
The cone penetrometer has internal load sensors for the measurement of force on the cone (cone resistance), side friction on the friction sleeve (sleeve friction) and, if applicable, pore pressure at one or several locations on the surface of the cone penetrometer. An internal inclinometer is included for measurement of the inclination of the penetrometer to meet the requirements of the application classes 1, 2 and 3 as given in Table 2.
NOTE 1 Other sensors can be included in the cone penetrometer. The axis of all parts of the cone penetrometer shall be coincident.
Cone penetrometers should ideally have a net area ratio approaching 1, taking into account the robustness of the cone penetrometer.
NOTE 2 Net area ratio, a,varies between 0,5 and 0,9 for commonly used cone penetrometers.
The cross-sectional area of the top end of the friction sleeve shall not be smaller than the cross-sectional area of the lower end.
The dimensional tolerances are operational tolerances. Manufacturing tolerances should be stricter.
The tolerance on surface roughness is a manufacturing tolerance.
4.3 Surface roughness
The surface roughness as mentioned in 4.4 and 4.5 refers to average roughness, Ra, determined by a surface profile comparator according to ISO 8503, or equivalent. The intention of the surface roughness requirement is to prevent the use of an "unusually smooth" and "unusually rough" cone or friction sleeve. Steel, including hardened steel, is subject to wear in soil fin particular sands) and the friction sleeve develops its own roughness with use. It is therefore important that the roughness at manufacture approaches the roughness acquired upon use. It is believed that the surface roughness requirement will usually be met in practice for common types of steel used for penetrometer manufacture and for common ground conditions (sand and clay). The effort required for metrological confirmation can thus be limited in practice.
The cone consists of a conical part and a cylindrical extension. The cone shall have a nominal apex angle of 60°. The cross-sectional area of the cone shall be 1 000 mm2, which corresponds to a diameter of 35,7 mm.
Depending on ground conditions, cones with a diameter between 25 mm (Ac = 500 mm2) and 50 mm (Ac = 2 000 mm2) may be used for special purposes, without the application of correction factors. In this case, the geometry of the cone shall be adjusted proportionally to the diameter. The geometry of the friction sleeve should be adjusted to obtain comparable results. The use of a cone with Ac ≠ 1 000 mm2 shall be reported.
The diameter of the cylindrical part shall be within the tolerance requirement as shown in Figure 4:
35,3 mm ≤ dc ≤ 36,0 mm The length of the cylindrical extension shall be within the following tolerance requirement:
7,0 mm ≤ he ≤ 10,0 mm The height of the conical section shall be within the following tolerance requirement:
24,0 mm ≤ hc ≤ 31,2 mm
If a filter is put at position u2, the diameter of the filter element itself may be larger than the required dimensions (see also 4.5 and 4.4).
The cone should be manufactured to a surface roughness of Ra < 5 µm.
The cone shall not be used if a visual check indicates that it is asymmetrically worn or unusually rough, even if it otherwise fulfils the tolerance requirements.
- 1 minimum shape of the cone after wear
- 2 maximum shape of the cone
4.5 Friction sleeve
The friction sleeve shall be placed just above the cone. The distance due to gaps and soil seals shall not be more than 5,0 mm.
The nominal surface area shall be 15 000 mm2. Tolerance requirements are shown in Figure 5.
Friction sleeves with an external diameter between 25 mm and 50 mm may be used for special purposes if used with cones of the corresponding diameter without the application of correction factors. The ratio of the length and the diameter should preferably be 3,75. Ratios of 3 to 5 are allowable.
The diameter of the friction sleeve, d2, shall be equal to the diameter of the cone, dc, with a tolerance of 0 mm to +0,35 mm.
Dimensions in millimetres
ls length of friction sleeve
d2 diameter of friction sleeve
ad2 ≥ dc; d2 < (dc + 0,35); d2 < 36,1
b As = 15 000 mm2
The geometry and tolerances of the friction sleeve shall be within the tolerance requirement as shown in Figure 5:
dc ≤ d2 < (dc + 0,35) mm and
d2 < 36,1 mm The length of the cylindrical part shall be within the following tolerance requirement:
132,5 mm < ls ≤ 135,0 mm
The friction sleeve shall be manufactured to a surface roughness of Ra = 0,4 µm ± 0,25 µm, measured in the longitudinal direction.
The friction sleeve shall not be used if a visual check indicates that it is scratched, asymmetrically worn or unusually rough, even if it otherwise fulfils the tolerance requirements.