3 CONE PENETRATION AND PIEZOCONE TESTS – CPT(U)

3.1 General

(1)P The cone penetration test (CPT) consists of pushing vertically into the soil, at a relatively slow and constant rate, a penetrometer which comprises a series of rods terminated by a penetrometer tip comprising a cone and a cylindrical shaft and measuring the penetration resistance of the cone as well as, possibly, the local friction on a sleeve located in the cylindrical shaft.

(2)P The piezocone test (CPTU) is a CPT which includes the measurement of the pore water pressure during penetration at the level of the base of the cone.

(3)P This section covers mainly electric penetrometers.

(4)P The tests shall be carried out in accordance with a method that complies with the essential requirements given in this section.

(5)P The test method used shall be reported in detail with the test results.

(6) The test method may be reported by reference to a standard.

(7)P Any deviation from the requirements given below shall be justified and in particular its influence on the results shall be commented upon.

(8) Experience of deviations exists with respect to:

• size of the cone;
• use of mechanical or hydraulic penetrometers.

3.2 Definitions

For the purpose of this prestandard the following definitions related to CPT and CPTU apply:

(1)P penetrometer tip: The main parts of the penetrometer tip are defined in figure 3.1.

(2)P cone resistance (q_c): the measured axial force Q_c acting on the cone divided by the total area of the base of the cone A_c;

(3)P local unit side friction (f_s): the measured frictional force Q_s acting on the sleeve divided by its area

(4)P friction ratio (R_f): f_c/q_c where q_c and f_s are determined at the same depth, expressed as a percentage

(5)P friction index (I_f): q_c/f_s where q_c and f_s are determined at the same depth.

(6)P For CPTU the following additional parameters are defined.

(7)P cone area factor (a): A_N/A_C, where A_N is the net area of the cone (see figure 3.2)

(8)P penetration pore pressure (u): the pore pressure measured during penetration on the cylindrical part of the cone, just above the conical part of the cone (see figure 3.1)

(9)P generated pore pressure (Δu): u – u₀, where u₀ is the pore pressure existing in the ground before the penetration test at the level of the cone;

(10)P total (corrected) cone resistance (q_t): q_c + u (1 – a)

(11)P pore pressure ratio B_q: Δu/(q_t - F_v0), where F_v0 is the total vertical stress existing in the ground before the penetration test at the level of the cone.