3.4 Test procedure

3.4.1 Calibration and checks

(1)P All measuring devices shall provide reliable and accurate measurements.

(2) All measuring devices should be calibrated every 3000 m of CPT sounding or at least every 6 months or after repair.

(3)P For a CPTU the filter, its sensing device and all fluid spaces shall be filled with a deaired fluid before each test and precautions shall be taken to ensure full saturation of the whole system.

(4) The wear of the cone and of the friction sleeve should be checked regularly to ensure that they satisfy the tolerances. Examples of tolerances are given in the documents listed in Annex M.

(5) The seals should be checked for the presence of soil particles and be cleaned.

(6) If a friction reducer is used, it should be located at a sufficient distance above the penetrometer tip so as not to influence the measurements.

3.4.2 Performing the test

(1)P The penetration shall be performed with no rotation, no vibrations, nor blows, and the direction of the thrust shall be vertical.

(2) The axis of the push rods should at the surface not deviate, more than 2 % from vertical.

(3)P The rate of penetration shall be (20 ± 5) mm/s.

(4)P The penetration depth of the cone shall be measured with an inaccuracy not exceeding 0,2 m and the depth interval between the readings shall not exceed 0,1 m.

3.5 Interpretation of the results

(1)Results of CPT and CPTU may be used for determining stratification, classifying soils and determining properties of a wide range of soils and soft rocks, provided penetration is possible.

(2) In a CPTU the total (corrected) cone resistance qt and pore pressure ratio Bq, should be determined with qc and u measured at the same level.

(3) For interpretation of the results of a CPTU the pore pressure u0 and the total vertical stress σv0 existing in the ground before the test should be used. u0 is be the equilibrium pore pressure; σv0 may be determined from the unit weights of the ground layers.

(4) When CPT results are used for classifying soils, the classification should be based at least on cone resistance, local unit side friction and friction ratio (or friction index). A better classification is obtained by performing CPTU and using total (corrected) cone resistance qt, generated pore pressure) u and pore pressure ratio Bq, (and/or local unit side friction and friction ratio or index, if relevant).

3.6 Reporting of the results

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

  • apparatus used, type of tip used;
  • date of calibrations;
  • zero readings of measuring devices;
  • system of measurement (electric, mechanical or hydraulic);
  • the depth over which a friction reducer or push rods with a reduced diameter have been used;
  • the depth of the start of the test;
  • the depth of water in the hole or of the water table when available;
  • graphs of the following results, with depth, on an arithmetic scale:
  • cone resistance: qc;
  • local unit side friction: fs, when relevant;
  • total side friction resistance Qst when relevant;
  • friction ratio: Rf, or friction index: If, when relevant;
  • observations of the operator such as incidents, procedure details not included in the test method which might have an influence on the tests results.

(2)P For a CPTU the report shall also include:

  • cone area factor: a,
  • graphs of the following results, with depth, on an arithmetic scale:
  • penetration pore water pressure: u;
  • total (corrected) cone resistance: qt (replacing qc);
  • pore pressure ratio: Bq.

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