7.4 Test procedure

7.4.1 Use of preboring and casing

(1)P The possible need to prebore through the upper stiff or dense soil layers shall be estimated in each case.

(2) Preboring is often required through a dry crust or through a fill in order to minimize skin friction along the rods.

7.4.2 Manual weight sounding

(1)P When the penetrometer is used as a static penetrometer in soft soils the rod shall be loaded in steps using the following standard loads: 0 kN, 0,05 kN, 0,15 kN, 0,25 kN, 0,50 kN, 0,75 kN, 1,0 kN. The maximum standard load is 1,0 kN.

(2)P The load shall be adjusted in the standard steps to give a rate of penetration of about 50 mm per second.

(3)P If the penetration resistance exceeds 1 kN or the penetration rate at 1 kN is less than 20 mm per second the rod shall be rotated. The load of 1 kN is maintained and the number of half turns required to give 0,2 m of penetration shall be counted.

(4)P The rod must not be rotated when the penetration resistance is less than 1 kN.

(5) The sounding may be terminated by striking the rod with a hammer or by dropping some of the weights onto the clamp in order to check that the refusal is not temporary.

7.4.3 Mechanized weight sounding

(1)P The test shall be carried out in a similar manner as for the manual sounding. The rate of rotation shall not exceed 50 turns per minute.

(2) The rate of rotation should be between 15 and 40 turns per minute.

(3) The applied load should be measured by a dynamometer or a measuring cell attached to the machine.

(4)P During the sounding, vibrations from the engine shall be kept in such level, that it does not affect the measured penetration resistance.

7.5 Interpretation of test results

(1)P The penetration resistance is given by the standard loads in stages (kN) and when rotated, loaded with the maximum standard load, by the number of halfturns per 200 mm of penetration.

(2) Differences between manual and mechanical operated tests may occur. Where this may be the case, e.g. when estimating the relative density of loose cohesionless soils, comparisons between manual and mechanized tests are recommended.

(3) The penetration resistance is strongly influenced by the shaft friction of the rods.

7.6 Reporting of the test results

(1)P In addition to the requirements given in 2.6 the test report shall include the following information:

  • sounding method;
  • the type of the loading device;
  • the type of the rotating equipment and the rate of rotation;
  • preboring, diameter and depth of the borehole, if preboring is used;
  • diameter of the casing tube and depth of casing, if used;
  • diameter of the rods;
  • the penetration depth for every standard load during the static sounding phase;
  • the number of halfturns required for every 0,2 m of penetration during the rotating phase; in cases when a full section of 0,2 m is not penetrated the number of halfturns and corresponding penetration;
  • the depth of penetration and number of blows during driving if the penetrometer is driven by blows of a hammer or some of the weights;
  • interruptions during the test;
  • all observations which may help in the interpretation of the test results.

7.7 Derived values of geotechnical parameters

(1)P When the bearing capacity or the settlement of a spread foundation is evaluated from weight sounding test results and analytical method shall be used.

(2) When the sample analytical method for bearing capacity in annex B of ENV 1997-1 is used, the angle of shearing resistance N' may be determined from correlations with weight sounding resistance. Such correlations should be based upon comparable experience, relevant to the design situation. Annex F presents a sample correlation, derived for quartz and feldspar in a European region.

(3) When the theoretical elastic method in annex D of ENV 1997-1 is used for calculating settlements of spread foundations from weight sounding results, the drained (long term) Young's modulus Em may be determined from weight sounding resistance on the basis of local experience. In the case of quartz and feldspar sands derived values as in annex F, for example, may be used to estimate a value of the angle of shearing resistance N' from the weight sounding resistance.

(4) In cohesionless soils the weight sounding resistance may be used also in direct estimation of the bearing capacity of spread foundation and piles.

(5) In cohesive soils the weight sounding resistance may be used to estimate the undrained shear strength of soil, based on local experience, considering the sensitivity of the soil and water conditions in the borehole.

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