5 Test procedure

5.1 Equipment checks and calibrations

Prior to each test, a check of dimensions shall be made to ensure that they are within the values given in Table 1. The straightness of the rods shall be checked once on each new site and at least every 20 penetration tests at that site. After each test, a visual check of the straightness of the rods shall be made.

At the test site, the rate of blows, the height of fall, the friction free fall of the hammer, the proper condition of the anvil and the mechanical release devices shall be checked for satisfactory operation which is to be ensured for the whole test series. In addition, the proper functioning of the recording device has to be checked in case automatic recording equipment is used.

The precision of the measuring instruments — if applicable — shall be checked after any damage, overloading or repair and at least once every six months, unless the manufacturer's manual requires shorter inspection intervals. Faulty parts shall be replaced. Calibration records shall be kept together with the equipment.

To check pneumatic dynamic penetrometers, the driving energy per impact (actual energy Emeas) shall be measured directly. When divided by the area of the cone then this shall not deviate from the theoretical value of specific work per blow as specified in Table 1 by more than 3 %. The driving energy per impact shall be checked every six months.

Energy losses occur e.g. due to friction at the hammer (velocity loss compared to the free fall) or due to energy losses during the hammer impact on the anvil. Therefore, for each new driving device the actual energy transmitted to the drive rods should be determined.

NOTE A recommended method to determine the actual energy is given in Annex C.

5.2 Test preparation

In general, dynamic probing is performed from the ground surface.

Dynamic probing test equipment shall be set up with the penetrometer vertical, and in such a way that there will be no displacement during testing. The inclination of the driving mechanism and the driving rod projecting from the ground shall not deviate by more than 2 % from the vertical. If this is not the case, the dynamic probing test shall be stopped. In difficult ground conditions deviations up to 5 % may be allowed and shall be reported.

Trailer-mounted dynamic probing test equipment shall be supported in such a way that the suspension travel of the support trailer cannot influence the test.

The equipment shall be set up with appropriate clearance from structures, piles, boreholes etc., in order to be certain that they will not influence the result of the dynamic probing test.

When carrying out dynamic probing in situations where the rods are free to move laterally, for instance over water or in boreholes, the rods shall be restrained by low-friction supports spaced not greater than 2,0 m apart in order to prevent bending during driving.

5.3 Test execution

The drive rods and the cone shall be driven vertically and without undue bending of the protruding part of the extension rods above the ground.

No load shall be applied to anvil and rods during lifting of the hammer.

The penetrometer shall be continuously driven into the ground. The driving rate shall be kept between 15 and 30 blows per minute. All interruptions longer than 5 minutes shall be recorded.

The rods shall be rotated 11/2turns or until maximum torque is reached at least every 1,0 m penetration. The maximum torque required to turn the rods shall be measured using a torque measuring wrench or an equivalent device and shall be recorded.

During heavy driving, the rods shall be rotated 11/2 turns after every 50 blows to tighten the rod connections.

To decrease skin friction, drilling mud or water may be injected through horizontal or upwards holes in the hollow rods near the cone. A casing may be sometimes used with the same purpose.

The number of blows shall be recorded every 100 mm penetration for the DPL, DPM and DPH and every 100 mm or 200 mm penetration for the DPSH-A and DPSH-B.

The normal operating range of blows should be between N10 = 3 and 50 for DPL, DPM and DPH and between N20 = 5 and 100 for DPSH-A and DPSH-B. For specific purposes, these ranges may be exceeded. In cases beyond these ranges, when the penetration resistance is low, e.g. in soft clays, the penetration depth per blow may be recorded. In hard soils or soft rocks, where the penetration resistance is very high or exceeding the normal range of blows, the penetration for a certain number of blows may be recorded as an alternative to the N-values.

In general, the test should be stopped, if either the number of blows exceeds twice the maximum values given above or the maximum value is exceeded continuously for 1 m penetration.

5.4 Influencing factors

Geotechnical or equipment related factors can influence the selection and operation of the equipment and the results of the tests.

NOTE Examples are given in Annex D.

5.5 Safety requirements

National safety regulations shall be followed; e.g. regulations for:

  • personal health- and safety equipment;
  • clean air, if working in confined spaces;
  • ensuring the safety of the equipment.

ISO 22476-2:2005 Field testing — Part 2: Dynamic probing