4.5 Interpretation

4.5.1 Data reduction of pressuremeter tests

(1)P The applied pressure, corrected for membrane stiffness if necessary, shall be converted to stress.

(2)P If a radial displacement type pressuremeter is used, the displacement readings shall be converted to cavity strain and, if testing weak rock, corrected for membrane compression and thinning.

(3)P If a volume displacement type pressuremeter is used (e.g. Ménard) then the volume reading shall be corrected for system expansion.

4.5.2 Interpretation of the Ménard test

(1)P A plot of corrected volume change against corrected applied pressure expressed in stress shall be produced.

(2)P The Ménard pressuremeter modulus E_m and limit pressure p_LM shall be determined using the method illustrated in figure 4.3.

(3)P p_lm is defined as the pressure required to double the total volume of the cavity from the point (p_r, V_r) (see fig. 4.3). The pressure p_r is the pressure where d(ΔV)/dp is a minimum and V, is the corresponding value of the injected volume. V_c is the deflated volume of the probe.

Figure 4.3: Interpretation of E_M and p_lm for an MPM test

4.6 Reporting the results

(1)P The following information shall be submitted prior to starting site work:

full details of the pressuremeter and testing equipment;
details of the proposed drilling equipment and flushing medium to be used for drilling boreholes;
description of the methods of carrying out all the drilling operations for forming test holes;
typical test data sheets and forms for presenting final results;
reference description of the methods for carrying out the tests.

(2)P In addition to the requirements given in 2.6 the report shall include the following information to be submitted for each test on request:

depth of the top and bottom of the test hole, and depth of the displacement measurement axes;
details of bored, drilling (and self-drilling if applicable), including date and time of start and finish of all drilling, description and estimate of any drilling fluid returns and depth and size of casing used, if any;
the output of the transducers recorded prior to and during installation and on removal from the borehole for any PBP;
tabulated output of the transducers during a test, if required, time of start and finish of test and rates of stress and/or strain on magnetic media;
the calibration results used to convert the test data to engineering units;
tabulated calibrated test data on magnetic media on request if applicable;
a plot of applied pressure against the volumetric or average cavity strain expressed as a percentage.

(3)P All information shall be presented. All graphical plots shall be presented on a scale which sensibly fills the entire page.

(4)P Values of E_M and p_LM if a Ménard test is carried out shall be submitted.

(5) In table 4.1 a list of additional plots is given.

Table 4.1: A list of additional plots

Probe	Ground type	Abscissa	Ordinate
radial displacement type
self-bored, pushed in	all	cavity strain for each arm	applied pressure
prebored	all	cavity strain for each pair of arms	applied pressure
self bored	all	initial cavity strain for each arm	applied pressure
all	all	cavity strain for unload- reload cycle for each arm	applied pressure
all	clay	logarithm of cavity strain for each arm	applied pressure
all	sands	natural logarithm of current cavity strain for each arm	natural logarithm of effective applied pressure
volume displacement type (except MPM)^*)
prebored	all	volume change	applied pressure
prebored	all	rate of change of volume	applied pressure
^*) For MPM tests the pressure is plotted as abscissa and the volume change as ordinate.

4.7 Derived values of geotechnical parameters

(1)P When an indirect or analytical method is used the geotechnical parameters of shear strength and shear modulus shall be derived from the pressuremeter curve.

(2)P When a direct or semi-empirical method is used all the features of the method shall be taken into account.

4.7.1 Derived values for the calculation of bearing capacity resistance of spread foundations

(1) When the sample semi-empirical method of annex C in ENV 1997-1 is used the specification for the Ménard pressuremeter may be followed.

(2) An example of the calculation of the bearing resistance is given in annex C.1.

(3) When the sample analytical method of annex B in ENV 1997-1 is used, the strength of the soil may be determined using empirical and theoretical methods but only on the basis of local experience.

(4) The angle of shearing resistance, φ', may be determined from an SBP test in non cohesive soils by theoretical methods and from FDP and PBP tests using empirical correlations but only on the basis of local experience.

4.7.2 Derived values for the calculation of settlement of spread foundations

(1) The settlement of spread foundations may be determined from stress controlled tests (Ménard method, see 4.4.3.1) using a semi-empirical method.

(2) An example of the calculation of the settlement of a spread foundation is given in annex C.2.

(3) When the sample analytical methods of annex D in ENV 1997-1 are used, the stiffness of the soil may be determined using theoretical methods but only on the basis of local experience.

4.7.3 Pile foundations

(1) The ultimate bearing resistance of piles may be evaluated directly from stress controlled tests (Ménard method, see 4.4.3.1).

(2) An example of the calculation of the ultimate bearing resistance is given in annex C.3.

(3) When the ultimate bearing resistance of a pile is evaluated indirectly from pressuremeter test results an analytical method may be applied to derive values of base and shaft resistance based on local experience.