ABSTRACT
Example 9. 11 A pressuremeter test was carried out at a site at a depth of 7 m below the ground surface. The water table level was at a depth of 1.5 m. The average unit weight of saturated soil is 17.3 kN/m3. The corrected pressuremeter curve is given in Fig. Ex. 9.11 and the depleted volume of the probe is V
=535 cm3• Determine the following. (a) The coefficient of earth pressure for the at-rest condition (b) The Menard pressuremeter modulus Em (c) The undrained shear strength cu' Assume that poh = P om in this case
Solution From Fig. Ex 9.11, Poh =P om =105 kPa The effective overburden pressure is
pb = 17.3 x 7 - 5.5 x 9.81 = 67.2 kPa The effective horizontal pressure is
P~h = 105 - 5.5 x 9.81 =51.0 kPa (a) From Eq (9.21)
(b) From Eq (9.25)
O-.:;;--r.----------a..----I--~_.-.--...a.--'"""----~----' 200 400 600 800 1000
Figure Ex. 9.11
From Fig. Ex 9.11 vf = 200 cm
3 Pf= 530 kPa V
o = 160 cm3 P
om = 105 kPa
200+160 From Eq (9.24) Vm =535 + =715cm32
lip = 530 -105 =10.625 liv 200-160
Now Em = 2.66 X 715 X 10.625 = 20,208 kPa
(c) From Eq (9.26)
From Fig Ex 9.11
845 Therefore Cu =9 =94 kPa From Eq (9.27)
C =EL+ 25 = 845 +25 =109.5 kPa u 10 10
9.10 THE FLAT DILATOMETER TEST The flat dilatometer is an in-situ testing device developed in Italy by Marchetti (1980). It is a penetration device that includes a lateral expansion arrangement after penetration. The test, therefore, combines many of the features contained in the cone penetration test and the pressuremeter test. This test has been extensively used for reliable, economical and rapid in-situ determination of geotechnical parameters. The flat plate dilatometer (Fig. 9.21) consists of a stainless steel blade with a flat circular expandable membrane of 60 mm diameter on one side of the stainless steel plate, a short distance above the sharpened tip. The size of the plate is 220 mm long, 95 mm wide and 14 mm thick. When at rest the external surface of the circular membrane is flush with the surrounding flat surface of the blade.
