Transcript Barbara Cosanti

AN INNOVATIVE METHOD TO EVALUATE
DEGREE OF COMPACTION
OF RIVER EMBANKMENTS
USING CPT
BARBARA COSANTI
N. SQUEGLIA
D.C.F. LO PRESTI
University of Pisa – D.E.S.T.eC.
AN INNOVATIVE METHOD TO EVALUATE DEGREE OF COMPACTION OF RIVER EMBANKMENTS USING CPT
AN INNOVATIVE METHOD TO EVALUATE DEGREE OF COMPACTION OF RIVER EMBANKMENTS USING CPT
AN INNOVATIVE METHOD TO EVALUATE DEGREE OF COMPACTION OF RIVER EMBANKMENTS USING CPT
Improving soil strength by increasing the unit weight
Increasing the bearing capacity of foundations
Decreasing the undesirable settlement of structures
Control undesirable volume changes
Reduction in hydraulic conductivity
Increasing the stability of slopes
AN INNOVATIVE METHOD TO EVALUATE DEGREE OF COMPACTION OF RIVER EMBANKMENTS USING CPT
DESIGN
Saturated for only
a short
period of time
POOR
ATTENTION
CAUSES
of
FAILURE
ASSESSMENT
of the
SAFETY DEGREE
Different erosion
mechanisms and
slope instability
Definition of design values
for strength and permeability
characteristics
POOR DEGREE
OF COMPACTION
=
PREDISPOSING
FACTOR
DEPENDENCY ON THE
DEGREE OF
COMPACTION
AN INNOVATIVE METHOD TO EVALUATE DEGREE OF COMPACTION OF RIVER EMBANKMENTS USING CPT
AN INNOVATIVE METHOD TO EVALUATE DEGREE OF COMPACTION OF RIVER EMBANKMENTS USING CPT
EVALUATION OF THE
DEGREE OF COMPACTION
OF RIVER EMBANKMENTS
After completion
CPT TESTS IN LABORATORY
in a mini CC with a mini CPT
using samples at given densities
In situ stress state
when relevant
TIP RESISTANCE TARGET PROFILE
CPT tests in situ
qc LAB
Vs
QUALITY CONTROL
 Existing embankments: evaluation of the degree of compaction
 Embankments under construction: it is possible (a‒priori) to establish
which is the expected qc corresponding to a prescribed density
AN INNOVATIVE METHOD TO EVALUATE DEGREE OF COMPACTION OF RIVER EMBANKMENTS USING CPT
AN INNOVATIVE METHOD TO EVALUATE DEGREE OF COMPACTION OF RIVER EMBANKMENTS USING CPT
The tip resistance is not affected by the tip diameter
qc from CPT (d= 35.7 mm)
qcLAB from mini-CPT (d= 8 mm)
qc [MPa]
Even if:
0
2
4
6
8
0
Normalized velocity
40
Where:
v: velocity of the penetrometer
d: diameter of the penetrometer
cv: coefficient of consolidation of the soil
depth [cm]
(Finnie & Randolph, 1994)
80
mini
120
UNSATURATED
SILT MIXTURES
160
standard
10
AN INNOVATIVE METHOD TO EVALUATE DEGREE OF COMPACTION OF RIVER EMBANKMENTS USING CPT
FOR DRY SAND →
(Baldi et al. 1986, Jamiolkowski et al. 1988, Garizio 1997, Jamiolkowski et al. 2000, 2001)
IN SITU STRESS STATE →
Estimate of the vertical effective stress component v
At-rest earth pressure coefficient → DMT test
(Jamiolkowski et al. 1988)
AN INNOVATIVE METHOD TO EVALUATE DEGREE OF COMPACTION OF RIVER EMBANKMENTS USING CPT
The effects of the mini–chamber sizes can be considered
negligible if:
CC diameter
z
(m)
DMT-A (kPa)
80
90
100
Mini-CPT diameter
110
120
= 40
130
3.00
15d - 53 cm
3.20
30d - 107 cm
3.40
DMT-A base
3.60
DMT blade
location
3.80
4.00
4.20
4.40
CPT at 30d
distance
CPT at 15d
distance
When the horizontal
distance between DMT
and CPT is  20 times
the cone diameter the
DMT is no more
sensitive
to
the
passage of the cone
It is acceptable:
Mini-CPT diameter
Diameter of the biggest particle
4
AN INNOVATIVE METHOD TO EVALUATE DEGREE OF COMPACTION OF RIVER EMBANKMENTS USING CPT
The method has been successfully used in some case histories
qcLAB,90%
qcLAB,80%
(Modified Proctor)
AN INNOVATIVE METHOD TO EVALUATE DEGREE OF COMPACTION OF RIVER EMBANKMENTS USING CPT
partially disturbed
samples
qcLAB,90%
qcLAB,80%
AN INNOVATIVE METHOD TO EVALUATE DEGREE OF COMPACTION OF RIVER EMBANKMENTS USING CPT
AN INNOVATIVE METHOD TO EVALUATE DEGREE OF COMPACTION OF RIVER EMBANKMENTS USING CPT
Developed by the
Geotechnical
Laboratory of the
University of Pisa in
partnership with
Pagani Geotechnical
Equipment
AN INNOVATIVE METHOD TO EVALUATE DEGREE OF COMPACTION OF RIVER EMBANKMENTS USING CPT
THE EQUIPMENT
Diameter = 320 mm; Height = 210 mm
Top boundary → rigid
Lateral and bottom boundaries → flexible →
provided with latex membranes
AN INNOVATIVE METHOD TO EVALUATE DEGREE OF COMPACTION OF RIVER EMBANKMENTS USING CPT
THE EQUIPMENT
The membranes allow the independent
application of horizontal and vertical
stresses through a compressed air system.
Manual air pressure regulators for the
vertical and horizontal stresses.
All the possible chamber boundary conditions can be applied:
- BC1 = h = cost; v = cost
- BC2 = h = 0; v = 0
- BC3 = h = 0; v = cost
- BC4 = h = cost; v = 0.
AN INNOVATIVE METHOD TO EVALUATE DEGREE OF COMPACTION OF RIVER EMBANKMENTS USING CPT
THE EQUIPMENT
step by step electric motor
aluminum frame
locking system
AN INNOVATIVE METHOD TO EVALUATE DEGREE OF COMPACTION OF RIVER EMBANKMENTS USING CPT
THE EQUIPMENT
Mini CPT:
- 60° conical tip
- cone diameter = 8 mm
- external sleeve
- standard rate of 20 mm/s
- load cell external to the cone
AN INNOVATIVE METHOD TO EVALUATE DEGREE OF COMPACTION OF RIVER EMBANKMENTS USING CPT
AN INNOVATIVE METHOD TO EVALUATE DEGREE OF COMPACTION OF RIVER EMBANKMENTS USING CPT
AN INNOVATIVE METHOD TO EVALUATE DEGREE OF COMPACTION OF RIVER EMBANKMENTS USING CPT
CRUSHED SAND
FINE GRAINED SOILS
(Calibration material)
(Building materials)
d50 = 0,5 mm Cu = 2
min = 1,419 kg/dm3 ; max = 1,663 kg/dm3
Dry
sand
samples
are
reconstituted inside the CC to a
given DR by pluvial deposit.
A4; dmax = 18.2 kN/m3; wopt=13.2%
A4; dmax = 19.5 kg/m3; wopt=10.8%
A6; dmax = 20.5 kN/m3; wopt=9.43%
AN INNOVATIVE METHOD TO EVALUATE DEGREE OF COMPACTION OF RIVER EMBANKMENTS USING CPT
FINE GRAINED SOILS
 Fine grained soil samples are reconstituted in
5 layers at a known unit weight using static
compaction (hydraulic ram) in a mold
 The compaction effort, required to consolidate
each layer and the sample, is registered:
AN INNOVATIVE METHOD TO EVALUATE DEGREE OF COMPACTION OF RIVER EMBANKMENTS USING CPT
AN INNOVATIVE METHOD TO EVALUATE DEGREE OF COMPACTION OF RIVER EMBANKMENTS USING CPT
TIP RESISTANCE
STRESS DEPENDENCE
AN INNOVATIVE METHOD TO EVALUATE DEGREE OF COMPACTION OF RIVER EMBANKMENTS USING CPT
TIP RESISTANCE
STRESS DEPENDENCE
AN INNOVATIVE METHOD TO EVALUATE DEGREE OF COMPACTION OF RIVER EMBANKMENTS USING CPT
TIP RESISTANCE
STRESS DEPENDENCE
h
AN INNOVATIVE METHOD TO EVALUATE DEGREE OF COMPACTION OF RIVER EMBANKMENTS USING CPT
DD; PC; →
d = 8092%dmax (Modified Proctor)
w = wopt
FR →
d = 80%dmax (Modified Proctor)
w= 4; 8; 12%
Suction → evaluated according to
Aubertin et al. (2003)
AN INNOVATIVE METHOD TO EVALUATE DEGREE OF COMPACTION OF RIVER EMBANKMENTS USING CPT
There is a clear relationship
between tip resistance ‒ degree
of compaction ‒ compaction
energy, while, confinement
pressures and suction have
little effect on the tip resistance
AN INNOVATIVE METHOD TO EVALUATE DEGREE OF COMPACTION OF RIVER EMBANKMENTS USING CPT
FR →
d = 80%dmax (Modified Proctor)
w= 4; 8; 12%
(wopt  10%)
AN INNOVATIVE METHOD TO EVALUATE DEGREE OF COMPACTION OF RIVER EMBANKMENTS USING CPT
CPT E2 FREDDANA
Qc ( MPa )
0
5
10
15
0
100
20
25
Very high values of qc in the
shallower
layers
of
the
embankments
Z ( cm )
200
300
EVAPO - TRANSPIRATION
PHENOMENA (DESSICATION)
400
500
600
CPT E2
Variation of tip
resistance with
water content
AN INNOVATIVE METHOD TO EVALUATE DEGREE OF COMPACTION OF RIVER EMBANKMENTS USING CPT
Laboratory tests
AN INNOVATIVE METHOD TO EVALUATE DEGREE OF COMPACTION OF RIVER EMBANKMENTS USING CPT
CPTu
LFWD
Correlation
between Ed and qc
Average qc measured
within the influence depth
for the LFWD
(approximately 1.5 times
the diameter
of the loading plate = 45cm)
AN INNOVATIVE METHOD TO EVALUATE DEGREE OF COMPACTION OF RIVER EMBANKMENTS USING CPT
As the water content decreases,
Ed value increases
AN INNOVATIVE METHOD TO EVALUATE DEGREE OF COMPACTION OF RIVER EMBANKMENTS USING CPT
For a given soil and water content:
 a correlation exists between qc and soil density that
can be used to define a target tip resistance profile
 it is possible to predict the dry density from the
measured qc irrespective of the boundary stresses