The Pressuremeter
and
Foundation
Engineering
Professor Trevor Smith
Department of Civil and
Environmental Engineering
Portland State University
The Pressuremeter and Foundation Engineering
Topics
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Historical Perspectives
Equipment and Procedures
Drilling Procedures
PMT Parameters
Cavity Expansion Theory
Soil Properties
Foundation Design-Ultimate
Foundation Design-Serviceability
Case Histories: Collapsible Soil Predictions of Settlement,
and Bonneville JFBS shafts under lateral load
The Pressuremeter and Foundation Engineering
Historical Perspective
• 1933 Kogler in Germany chain driven-little development
•1955 Louis Menard in France develops the 3 cell
pneumatic/hydraulic 3 cell prebored PMT and begins the work
on direct design rules-published in 1963
• 1959 Fukuoka in Japan develops the K-Value meter
•1965 Jezequel and other in France develop self boring
•1966 Higher pressure PMT in Japan called OYO meter
•1971 Hughes and wroth at Cambridge university perfect the
Cam-Ko-Meter as self boring on board instrumentation
•1978 First book published called The Pressuremeter and
Foundation Engineering
•1982 Briaud and Smith at Texas A&M develop rugged hydraulic
TEXAM units with single cell probe
•1982-present worldwide developments of PMT-CPT
•1988 ASTM D4719-87 standard for PMT covering equipment,
drilling techniques, testing and accuracy.
•82,86,90,95 Dedicated International conferences contain BOK
The Pressuremeter and Foundation Engineering
Equipment and Procedures
•Original Menard 3 cell units require nitrogen/water control units and are stress level controlledestimates made of the total pressure, PL, and steps of PL/10 made. ASTM procedure A.
•Hydraulic single cell probes require simple units using strain controlled volume injection. ASTM
procedure A or B.
• The typical probe sizes are EX, AX, BX, and NX (32mm, 50mm, 63mm, 72mm) for prebored devicesNX only for selfboring devices. Prebored dominates the north American market to either ASTM
procedure A or B.
•Menard ($30k) and Texam ($15k) devices for soil typically maximum pressure of 4 MPa (40 tsf) and
OYO and others in rock up to 20MPa.
•With prebored holes of diameter, Dh, 1.03 D ≤ Dh ≤ 1.2D must be carefully prebored for each test!
The Pressuremeter and Foundation Engineering
Drilling Procedures
•Both 2- 15/16 and 3 -1/8 inch roller bits have proved
useful for hole preparation. In addition coring through
dense gravels is a possibility
•Each test section must be drilled and tested as
quickly as practical. You cannot drill ahead and
prepare multiple sections.
•Typically roller bits in sand and drag bits, or roller
bits, work well in clay. Avoid end downward mud
circulation.
• The hole stability and tolerance is the #1 priority for
good data. No reaming or washing is allowed because
of scour. The lowest pump pressure and rotation
speed is desirable. ASTM specs maximum of 60-rpm
drill string rotation, and 30 psi down pressure and 4
gal/min circulation.
• NEVER wash, or ream the hole to remove excess
cuttings. The over drilling of the test section to allow
for 6 inch to 12 inch sump is better to allow excess
cuttings to collect. The Probe does not test the bore
hole bottom, only the side wall.
The Pressuremeter and Foundation Engineering
PMT Parameters
After corrections for membrane stiffness
and volume losses in supply tubing - net
cylindrical cavity expansion
True limit pressure, PL, at infinite
expansion, practical limit pressure, Pl, at
double cavity (41% radial increase).
Expansion passes through Ko and reveals
the linear expansion behavior-thus
modulus, Eo, before yield, Py, at borehole
wall is initiated and Pl reached. We may
cycle-creep-conduct Eo studies to variable
strain or stress level etc.
So mechanics tells us the net increase in
pressure beyond Poh (Ko), which is Pl*, is
related to foundation bearing capacity-and
settlement design to distribution of Eo and
the loading shape.
The Pressuremeter and Foundation Engineering
Cavity Expansion Theory
ν=0.33
A surprising amount is known of the behavior
of soils under cylindrical expansion:
•Yield begins on the borehole wall first and
propagates into the soil mass.
•Stress and strains decay radialy away from the
borehole as the R2. Radial strain is compressive
and circumferential strain is negative.
•To avoid tensile failure unload/reload loops
must satisfy certain conditions.
• In elasticity the shear modulus is measured:
G= Vav ΔP/ΔV, Eo = 2G (1+υ).
•In plasticity PL= Poh+ Su(1+LnG/Su)- in granular
material dilatancy prevents easy relationships
to φ. Use Pl directly in design.
•Cohesive behavior Eo/Pl*>12, granular 7<
Eo/Pl*<12
The Pressuremeter and Foundation Engineering
Soil Properties
•Following ASTM standards provides undrained behavior in
cohesive soils and drained in cohesionless soils. Recall no
control over drainage is available-but pwp can be measured
for research purposes.
•Reliable measurements of Su possible but not φfriction
angles –most direct equations assume no volume change.
Widely used empirical φ – Pl* chart from Menard.
e.g. Su/Pa=0.21 [ Pl*/Pa] 0.75 to UC…Briaud (1985)
The Pressuremeter and Foundation Engineering
Foundation Design-Ultimate
Bearing capacity and settlement can clearly be seen
as a function of the lateral support from the
surrounding soil. Obvious in sands-not so in clays.
PMT direct design place the foundation at He
equivalent depth, in equivalent limit soil Ple*.
Capacity is the pressure to cause settlement of B/10
Design methods for pile Qs and Qp are
shown of superior reliability-Qult not QL
Design charts for the k factor in sand,
stilts and clays from load tests. Unique
geometric factors for inclined and slopes.
Strip footings use k/1.2
The Pressuremeter and Foundation Engineering
Foundation Design-Serviceability
First term from elastic distortion and second
term all round spherical squeeze.
PMT Pile settlement methods
have shown 95% probability that
s < 1.25% Dia (lognormal)
Consolidation based settlement applies to soil
layers with high spherical stresses-most settlement
in uniform soils is ‘elastic’ based from deviatoric
stresses and is much deeper.
PMT seeks to separate these and uses Ec and Ed as
weighted averages over different depths- using the
εv distribution. Ec/α is a ‘corrected’ consolidation
modulus.
The Pressuremeter and Foundation Engineering
Research Case History:
Collapsible Soil Predictions
of Settlement
•Colluvium deposits from flash floods in the arid west
threaten valuable agricultural land and the
infrastructure. These are meta-stable soils-often silty
sandy gravels- triggered by moisture and/or stress
changes illustrated by dramatic settlements.
•NCRs (formally SCS) in 1990’s had problems with
relicensing debris basin dams due to visible cracking
•Sinkholes in the basin, longitudinal and transverse
cracking with cracks up to 150mm –uncertain stability
with an impoundment
The Pressuremeter and Foundation Engineering
Research Case History:
Collapsible Soil Predictions of Settlement
•A comprehensive set of PMT based collapse
test field procedures and FEM modeling
recommendations to study retrofit options
•New settlement methods to replace the
double oedometer tests for all soil types
The Pressuremeter and Foundation Engineering
Practice Case History: Lateral Load
Deflection Predictions on Bonneville Dam JFBS
•Four feet sq. concrete flumes, supported on 10 feet
diameter shafts carry juveniles >250 feet to midstream
away from predator fish. High and low level.
• Shafts on 120 feet spacing, 70 feet stick up above M/lembedded 100 feet into 50 feet of silt and sand
overlying gravels produce M/l rotations and deflectionstolerable flume deflection 2 feet.
•Flood frequency offer submerged horizontal repeat
monotonic loads to shafts. P-y and cyclic problem
The Pressuremeter and Foundation Engineering
Practice Case History: Lateral Load
Deflections Predictions on Bonneville JFBS
•Use of PMT gave expansion response in silts, sands and gravels
to construct P-y curves following (F-y)+ (Q-y) principles.
•Range of shaft top deflections and rotations with initial LPILE
analysis gave concern on design life issues and tripped full scale
load testing- via cables in tension.
•Poor load test performance would trip enhancement option 40 feet drag collars through silt and loose sand.
•LPILE subroutines with conservative properties proved to
under predict movements-PMT P-y methods better match to
measured response.
•PMT predictions accepted with cyclic power law decay. No Drag
collar s required for 50 year life and $1.5M saving
The Pressuremeter and Foundation Engineering
Questions?
The Pressuremeter and Foundation Engineering
No collapse
slight collapse
Moderate collapse
severe collapse
ν=0.33
The Pressuremeter and Foundation Engineering