The Pressuremeter

1

• The Pressuremeter
• and
• Foundation
• Engineering
• Professor Trevor Smith
• Department of Civil and
• Environmental Engineering
• Portland State University

The Pressuremeter and Foundation Engineering
2
Topics

• 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
3
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 AM 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
4
Equipment and Procedures

• Original Menard 3 cell units require
  nitrogen/water control units and are stress level
  controlled-estimates 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 devices- NX
  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
5
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
6
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
7
Cavity Expansion Theory

• 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 ?P/?V, Eo 2G (1?).
• In plasticity PL Poh Su(1LnG/Su)- in granular
  material dilatancy prevents easy relationships to
  f. Use Pl directly in design.
• Cohesive behavior Eo/Plgt12, granular 7lt Eo/Pllt12

?0.33
The Pressuremeter and Foundation Engineering
8
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
  ffriction angles most direct equations assume no
  volume change. Widely used empirical f Pl
  chart from Menard.

e.g. Su/Pa0.21 Pl/Pa 0.75 to UCBriaud (1985)
The Pressuremeter and Foundation Engineering
9
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
10
Foundation Design-Serviceability
First term from elastic distortion and second
term all round spherical squeeze.
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 ev distribution. Ec/a is a corrected
consolidation modulus.
PMT Pile settlement methods have shown 95
probability that s lt 1.25 Dia (lognormal)
The Pressuremeter and Foundation Engineering
11
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 1990s 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
12
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
13
Practice Case History Lateral Load Deflection
Predictions on Bonneville Dam JFBS

• Four feet sq. concrete flumes, supported on 10
  feet diameter shafts carry juveniles gt250 feet to
  midstream away from predator fish. High and low
  level.
• Shafts on 120 feet spacing, 70 feet stick up
  above M/l- embedded 100 feet into 50 feet of silt
  and sand overlying gravels produce M/l rotations
  and deflections-tolerable flume deflection 2
  feet.
• Flood frequency offer submerged horizontal repeat
  monotonic loads to shafts. P-y and cyclic problem

The Pressuremeter and Foundation Engineering
14
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
15
Questions?
The Pressuremeter and Foundation Engineering
16
(No Transcript)
17
No collapse
slight collapse
Moderate collapse
severe collapse
18
(No Transcript)
19
(No Transcript)
20
(No Transcript)
21
?0.33
The Pressuremeter and Foundation Engineering
22
pics
23
(No Transcript)