4.7 Dynamic probing tests (DP)

4.7.1 Objectives

(1) The objective of the dynamic probing tests is to determine the resistance of soil and soft rock in-situ to the dynamic penetration of a cone.

(2)P A hammer of a given mass and falling height shall be used to drive the cone. The penetration resistance is defined as the number of blows required to drive the penetrometer over a defined distance. A continuous record shall be provided with respect to depth. No samples are recovered.

(3) The test results should be used particularly for the determination of a soil profile together with results from sampling by drilling and excavations according to Section 3 or as a relative comparison of other in-situ tests.

(4) The results may also be used for the determination of the strength and deformation properties of soil, generally of the coarse type but also possibly in fine soil, through appropriate correlations.

(5) The results can also be used to determine the depth to very dense ground layers indicating for instance the length of end bearing piles.

4.7.2 Specific requirements

(1)P For planning the specific test programme for a project, in addition to the requirements given in 4.2.1, the type of required DP test according to EN ISO 22476-2, shall be decided upon.

(2)P The tests shall be carried out and reported in accordance with EN ISO 22476-2.

NOTE Five procedures are available according to EN ISO 22476-2, covering a wide range of specific work per blow: DPL, DPM, DPH, DPSH-A and DPSH-B as follows.

Dynamic probing light (DPL) : test representing the lower end of the mass range of dynamic penetrometers.

Blow count: N10L.

  • Dynamic probing medium (DPM) : test representing the medium mass range of dynamic penetrometers. Blow count: N10M.
  • Dynamic probing heavy (DPH) : test representing the medium to very heavy mass range of dynamic penetrometers. Blow count: N10H.

Dynamic probing super heavy (DPSH-A and DPSH-B) : tests representing the upper end of the mass range of dynamic penetrometers closely related to the dimensions of the SPT. Blow count: N10SA, or N20SA, N10SB or N20SB.

(3)P Any deviation from the requirements given in EN ISO 22476-2 shall be justified and in particular its influence on the results of the test shall be commented upon.

NOTE Deviations exist with respect to:

  • falling height and hammer mass;
  • dimensions of the cone: e.g. an area of 10 cm2 for the DPM cone, instead of 15 cm2 as specified in EN ISO 22476-2:2005, clause 4.

(4) In locations with special difficulties of accessibility, lighter equipment and procedures other than those specified in EN ISO 22476-2 may be used.

4.7.3 Evaluation of test results

(1)P In addition to the requirements given in 4.2, the field and test reports according to EN ISO 22476-2 shall be used for evaluation purposes.

(2)P Possible geotechnical and equipment influences on the penetration resistance according to EN ISO 22476-2:2005, 5.4 shall be considered in evaluating the test results.

4.7.4 Use of test results and derived values

(1) For coarse soil, it is possible to obtain correlations with some geotechnical parameters and field tests. The correlations may be used in a quantitative evaluation for foundation design, provided the friction along the rods is negligible, or duly corrected.

(2) For fine soil, the quantitative use of the results should be employed only under well-known local conditions and supported by specific correlations. The skin friction during the test is a factor of special concern with this type of soil and should be duly taken into account.

(3) Several correlations have been established among the different dynamic probing tests and between them and other tests or geotechnical parameters. In some cases the friction along the rods has been eliminated or corrected, but the actual energy transmitted to the probe has not been measured. Therefore they cannot be considered valid in general.

NOTE 1 Examples of such correlations are included in Annex G.

NOTE 2 The correlations given in Annex G should be considered as conservative estimates.

(4) If an analytical method for bearing resistance of spread foundations is used, the angle of shearing resistance (φ') of coarse soil may be determined from the number of blows and the corresponding density index (ID) with correlations.

NOTE 1 An example of an analytical method is given in EN 1997-1:2004, D.4.

NOTE 2 Such correlations for the determination of φ' are given as examples in G.1 and G.2.

(5) If a theoretical elastic method is applied to calculate the settlements of spread foundations, the oedometer modulus (Eoed) derived from the number of blows may be used.

NOTE 1 Examples of theoretical elastic methods arc given in EN 1997-1:2004, Annex F.

NOTE 2 Corresponding examples of correlations for the determination of the oedometer modulus are given in G.3.

(6) If well-established correlations between ultimate compressive resistance from static pile load tests (see EN 1997-1:2004, and cone penetration resistance (qc) in coarse soil are used for the design, qc may be estimated from N10 or N20 values using established relationships.

NOTE 1 Examples for DPH correlations are given in G.4.

NOTE 2 An example of correlations between the results of different dynamic probing tests is given in G.5.

Eurocode 7: Geotechnical design — Part 2: Ground investigation and testing