Annex J

(Informative)

# Flat dilatometer test (DMT)

(1) This Annex gives an example of correlations between Eoed and DMT results. These correlations may be used to determine the value of the one-dimensional tangent modulus (Eoed = dσ/dε) from results of DMT tests, through:

Eoed = RM×EDMT

in which RM is estimated either on the basis of local experience or using the following relationships:

if IDMT ≤ 0,6; then RM = 0,14 + 2,36 lgKDMT

if 0,6 < IDMT < 3,0; then RM = RM0 + (2,5 – RM0)lg KDMT, in which

RM0 = 0,14 + 0,15(IDMT – 0,6); if IDMT ≥ 3; then RM = 0,5 + 2lgKDMT if KDMT > 10; then RM = 0,32 +2,18 lg KDMT

if values of RM < 0,85 are obtained in the above relationships, RM is taken to be equal to 0,85.

where

IDMT
is material index from the flat dilatometer index
KDMT
is the horizontal stress index from the flat dilatometer test

Annex K

(informative)

## K.1 Example of deriving the value of undrained shear strength

(1) This is an example of deriving the undrained shear strength (cu), which can be obtained using the following equation: where

pu
is the ultimate contact pressure from the PLT results;
γ×z
is the total stress (density times depth) at test level when the test is conducted in a borehole with a diameter smaller than three limes the diameter or width of the plate;
Nc
is the bearing capacity factor; for circular plates:
Nc = 6
(typically for PLT on the subsoil surface);
Nc = 9
(typically for PLT in boreholes of depths greater than four times the diameter or width of the plate).

## K.2 Example of deriving the value of the plate settlement modulus

(1) This is an example of deriving the plate settlement modulus EPLT (secant modulus).

(2) For loading tests made at ground level or in an excavation where the bottom width/diameter is at least five times the plate diameter, the plate settlement modulus (EPLT) may be calculated from the general equation: where

Δp
is the selected range of applied contact pressure considered;
Δs
is the change in total settlement for the corresponding change in the applied contact pressure Δp including creep settlements;
b
is the diameter of the plate;
v
is Poisson's ratio for the conditions of the test.

(3) If not determined in other ways, v is equal to 0,5 for undrained conditions in fine soil and 0,3 for coarse soil.

(4) If the test is made at the base of a borehole, the value of EPLT may be calculated from the equation: where

Cz
is a depth correction factor; it is defined as the ratio of the depth load to settlement of the corresponding surface load.; an example for suggested values is given in Figure K.1.  Figure K.1 – Depth correction factor Cz as a function of plate diameter b and depth z for PLT results obtained with a uniform circular load at the base of an unlined shaft ## K.3 Example of deriving the value of coefficient of sub-grade reaction

(1) This is an example of deriving the coefficient of sub-grade reaction (ks) which may be calculated from the equation: where

Δp
is the selected range of applied contact pressure considered;
Δs
is the change in settlement for the corresponding change in applied contact pressure Δp including creep settlements.

(2) The dimensions of the loading plate should be stated, when calculating values of ks.

## K.4 Example of a method to calculate the settlement of spread foundations in sand

(1) This is an example of deriving settlements directly. The settlements of a footing in sand may be derived empirically according to the relations given in Figure K.3, if the ground beneath the footing to a depth larger than two times the width is the same as the ground beneath the plate (see Figure K.2). Key

b1
width of the test plate
b
width of the foundation
p
s1
is settlement measured in PLT
s
is predicted settlement for the footing
• 1 test plate
• 2 footing
• 3 influenced zones
Figure K.2 – Influenced area beneath a test plate and a footing Key

b/b1
is width ratio
s/s1
is settlement ratio
• 1 loose
• 2 medium dense
• 3 dense
Figure K.3 – Graph for calculations of settlement based on plate loading tests

NOTE This example was published by Bergdahl el al (1993). For additional information and examples, see X.3.8.

Eurocode 7: Geotechnical design — Part 2: Ground investigation and testing