4.8 Weight sounding test (WST)
(1) The objective of the weight sounding test is the determination of the resistance of soil in situ to the static and/or rotational penetration of a screw-shaped point.
(2)P The weight sounding test shall be made as a static sounding in soft soil if the penetration resistance is less than 1 kN. If the resistance exceeds 1 kN, the penetrometer shall be rotated, manually or mechanically, and the number of half-turns for a given depth of penetration recorded. A continuous record is provided with respect to depth but no samples are recovered.
NOTE Further information on a procedure, presentation and evaluation for the WST can be found in CEN ISO/TS 22476-10, (see X.3.5).
(3) The weight sounding test should primarily be used to give a continuous soil profile and an indication of the layer sequence. The penetrability in even stiff clays and dense sands is good.
(4) The weight sounding test may also be used to estimate the density index of coarse soil.
(5) The results can also be used to determine the depth to very dense ground layers indicating the length of end bearing piles.
4.8.2 Specific requirements
(1) The tests should be carried out and reported in accordance with a recognised method.
(2)P Any deviation from the requirements in the method referred to in (1) shall be justified and in particular its influence on the results of the test shall be commented upon.
NOTE Further information on a procedure, presentation and evaluation for the weight sounding lest can be found in CEN ISO/TS 22476-10.
4.8.3 Evaluation of test results
(1)P The requirements given in 4.2 shall be followed for the evaluation of the test results.
(2) In addition, the field and test reports, according to the method referred to in 4.8.2 (1), should be used for evaluation purposes.
NOTE Further information on aprocedure, presentation and evaluation for weight sounding test can be found in CEN ISO/TS 22476-10.
(3) The following influences can affect the evaluation of the results.
- The variations of the resistance with depth can depend on the variations in the soil layer sequence.
- In very soft to firm clays, the resistance is often less than 1 kN or approximately constant and less than 10 half-turns per 0,2 m of penetration.
- As the sensitivity of the clay also influences the penetration resistance, the strength of the clay cannot be determined directly from the penetration resistance without a calibration for each site.
- In very loose to loose sediments of sill and sand, rather low and constant penetration resistances are obtained. In medium dense to dense silts and fine sands, higher (10 to 30 half-turns per 0,2 m of penetration) resistances are obtained, which remain approximately constant with depth.
- In sand and gravel sediments, the variation in penetration resistances increases with the grain size.
- In silty sands and coarse gravel, a high penetration resistance does not always correspond to higher density or strength and deformation properties.
4.8.4 Use of test results and derived values
(1)P When the bearing resistance or the settlement of a spread foundation is derived from weight sounding test results, an analytical design method shall be used.
(2) If an analytical method for bearing resistance is used, the angle of shearing resistance φ'may be determined from correlations with weight sounding resistance.
NOTE Examples of analytical methods are given in EN 1997-1:2004, Annex D.
(3) Such correlations should be based upon comparable experience, relevant to the design situation.
NOTE Annex H presents an example correlation, derived for quartz and feldspar sands in a European region.
(4) If an adjusted elasticity method is used for calculating settlements of spread foundations from weight sounding results, the drained (long term) Young's modulus of elasticity (E') may be determined from weight sounding resistance on the basis of local experience. In the case of quartz and feldspar sands, for example, the angle of shearing resistance (φ') may be estimated from the weight sounding resistance.
NOTE 1 Such an adjusted elasticity method is given in EN 1997-1:2004, Annex F.
NOTE 2 Examples for correlations 10 estimate the drained (long term) Young's modulus of elasticity (E') and the angle of shearing resistance (φ') of quartz and feldspar sands are given in Annex H.
(5) In coarse soil, the weight sounding resistance may also be used in direct estimation of the bearing capacity of spread foundation and piles.
(6) In fine soil, the weight sounding resistance may be used to estimate the undrained shear strength of soil, based on local experience, considering the sensitivity of the soil and water conditions in the borehole.
4.9 Field vane test (FVT)
(1) The objectives of the field vane test are the measurement of the resistance to rotation in-situ of a vane installed in soft fine soil for the determination of the undrained shear strength and the sensitivity.
(2)P The field vane test shall be carried out with a rectangular vane, consisting of four plates fixed at 90° angles to each other, pushed into the soil to the desired depth and rotated.
(3) The field vane test may also be used for the determination of the undrained shear strength in stiff clays, silts and glacial clays. The reliability of test results varies depending on the type of soil.
(4) After extensive rotation of the vane, whereby the soil along the failure surface becomes thoroughly remoulded, the remoulded shear strength value can be measured and the soil's sensitivity can be calculated.
4.9.2 Specific requirements
(1) The tests should be earned out and reported in accordance with requirements given in EN ISO 22476-9.
(2)P Any deviation from the requirements given in EN ISO 22476-9 shall be justified, and in particular its influence on the results of the test shall be commented upon.
4.9.3 Evaluation of test results
(1)P In addition to the requirements given in 4.2, the field and the test reports according to EN ISO 22476-9 shall be used for evaluation purposes.
(2) The results of other field test, e.g. from CPT, SPT, WST or DP if conducted, should be available and considered.
4.9.4 Use of test results and derived values
(1)P If the bearing resistance of a spread foundation, the ultimate compressive or tensile resistance of piles or stability of slopes are derived based on vane test results, an analytical design method shall be used.
(2)P In order to obtain derived values for the undrained shear strength from field vane test results, the test result (cfv) shall be corrected based on:
The correction factor µ shall be determined based on local experience.
(3) Existing correction factors are usually related to the liquid limit plasticity index, the effective vertical stress or the degree of consolidation.
NOTE Annex I gives examples of such correction factors.