CPT tests

CPT static penetrometric testing (mechanical type) essentially consists of measuring the resistance to insertion of a mechanical bit of standardised dimensions and characteristics, as it is driven into the ground at a constant speed (2 cm/sec).

In tests with the Begemann mechanical bit, the values Qc (bit resistance), Fs (side friction) and Qt (total resistance) are measured via a load cell and shown on the display of the electronic acquisition board.

Penetrometers which can be used for CPT tests

CPT tests Penetrometers Selector Acquisition system
Manual Hydraulic Manual Automatic
100 kN TG 63 – 100
200 kN TG 63 – 200
200 kN TG 73 – 200

 

Key
■ Standard
□ Optional
◇ Not available

Selector

In order to control the movement of the Begemann bit, the driving rods, which act on the various components of the bit, are telescopic. An enlargement ring can be installed on the external set of rods to decrease the friction on the rods, facilitating their insertion.
The load cell, which measures the driving insertion force, is installed inside a removable unit called the “selector“, which presses alternately on the inner and outer rod.

Two types of selector exist:

  • Manual selector
    Before starting a driving stage, the operator must manually operate a lever which prepares the selector for the command of the inner or outer rod.
  • Hydraulic selector
    During the driving stage the rods are operated automatically by a hydraulic command. The operator must simply control the driving movements for insertion of the rods.

Aquisition system

The values measured by the load cell are acquired by an electronic device fixed to the selector, known as the “Acquisition system”.

TGAS11

The values acquired by the load cell are shown on the display of the TGAS11 unit.
The operator must manually write down the readings displayed during insertion: 

  • RP = First reading made, relating to insertion of the bit only.
  • RP+RL = Second reading made, relating to the insertion of the bit + side sleeve.
  • RT = Third reading made, relating to the insertion of the outer rods.

The TGSW01 software allows calculation of the bit force, side friction and total resistance values. The RP/RL ratio (Begemann 1965 ratio) and RL/RP ratio (Schmertmann 1978 ratio – FR%) are also calculated.

TGAS05v2

The values acquired by the load cell are shown on the display of the TGAS05v2 unit.
The operator can download the readings after performing the CPT test: 

  • RP = First reading made, relating to insertion of the bit only.
  • RP+RL = Second reading made, relating to the insertion of the bit + side sleeve.
  • RT = Third reading made, relating to the insertion of the outer rods.

The TGSW01 software allows calculation of the bit force, side friction and total resistance values. The RP/RL ratio (Begemann 1965 ratio) and RL/RP ratio (Schmertmann 1978 ratio – FR%) are also calculated.

 

Pagani Geotechnical Equipment also supplies the accessories (Begemann bits, rods, load cells) necessary for performing CPT tests.

Penetrometers