Specification Best Practice th July 2017 The Slate ...

PCA Waterproofing Conference 2017 Design – Specification – Best Practice 6th July 2017 The Slate, University of Warwick, Coventry, CV4 7SH

APPLICATION OF ARTIFICIAL GROUND FREEZING (AGF)

Alan Auld

BSc PhD CEng PEng FICE FIMMM

Engineering Consultant

1. What artificial ground freezing (AGF) is2. What AGF does3. AGF - freezing systems4. How the process works5. Ground investigation required6. Design and installation of the freeze7. Frozen ground behaviour prediction8. Recent examples of AGF

CONTENTS

1. WHAT ARTIFICIAL GROUND FREEZING (AGF) IS

AGF is not a method for water proofing buildings but it is a means of preventing water ingress into excavations to allow buildings to be constructed

1. It increases the strength (and hence the stability)of water-bearing low strength soils (sands, silts and clays) and prevents groundwater ingress during excavation i.e. shallow excavations, shafts and tunnels

2. It prevents groundwater ingress into deepexcavations in hard rock i.e. deep shafts

2. WHAT AGF DOES

1. Calcium Chloride (Brine) Freezing(Brine circulated at between -25ºC to -35ºC)

2. Liquid Nitrogen Freezing(LN exhausts at -190ºC – rapid freeze)

3. AGF - FREEZING SYSTEMS

4. HOW THE PROCESS WORKS

Point to emphasize – AGF is a two part operation:Contractor based operation – freeze hole drilling, freeze tube installation and freezing plantGround engineering based operation – frozen ground behaviour evaluation

Establishing a freeze wall

5. GROUND INVESTIGATION REQUIRED

1.BH strata sequence, types, elevation, thickness2. Strata strength and stability3. Groundwater elevation, movement and salinity4. In situ tests, SPT, CPT, permeability5. Rock core fracture state, TCR, SCR, RQD, FI6. Lab tests on core samples

Ground freezing contractor’s specialist expertise:1. Coolant type (brine or LNG)2. Refrigeration plant capacity3. Coolant temp. and flow rates4. Freeze tube configuration and brine main layout5. Freeze hole drilling and casing installation6. Ground temperature monitoring

6. DESIGN AND INSTALLATION OF THE FREEZE

6. DESIGN AND INSTALLATION OF THE FREEZE

Ground freezing contractor’s specialist expertise:1. Coolant type (brine or LNG)2. Refrigeration plant capacity3. Coolant temp. and flow rates4. Freeze tube and brine main feed configuration

5. Freeze hole drilling and casing installation6. Ground temperature monitoring

1. Thermal design2. Structural design3. Heave and thaw settlement

7. FROZEN GROUND BEHAVIOUR PREDICTION

Prediction of freeze growth rates through the ground to confirm:1. Min. time before excavation can take place2. When all ground is completely frozen3. Predicted frozen ground growth rates compared

with actual rates observed by in situ temp.monitoring

THERMAL DESIGN

Design information required:

1. Freezing coolant temperature2. Initial ground temperature3. Radius of freeze tubes4. Unfrozen and frozen ground thermal

conductivities and heat capacities

THERMAL DESIGN (Continued)

1. Calculation of freeze wall growth and hence itsthickness for design

2. Estimate of power required which determinesthe number of refrigeration units needed

THERMAL DESIGN (Continued)

Finite Element Mesh - 3D Isometric Section

Finite Element Mesh - 3D Cross-Section

Freeze-Wall growth – 3 DaysTemperature Gradient +120C to -1960C

Freeze-Wall growth – 21 Days

1. Design loads2. Frozen ground properties:

UCS, shear strength, tensile strength, Eand creep behaviour

3. Structural design calculations for frozen groundstructure including predicted deformation duringexcavation

STRUCTURAL DESIGN

1. Heave occurs predominantly in clay soils

2. Predictions can be made based on soil frostsusceptibility recommendations

GROUND HEAVE AND THAW SETTLEMENT PREDICTIONS

1.Dorney Bridge, Maidenhead, Berkshire, boxjacking - 1998

2. Histadrut Road crossing for the Kishon DrainageAuthority, Haifa, Israel – twin jacked box culverts- 2000

RECENT EXAMPLES OF AGF

Dorney Bridge, Maidenhead, Berkshire

Box jacking - 1998

Histadrut Road crossing for the Kishon Drainage Authority, Haifa, Israel

Twin jacked box culverts - 2000

SUMMARY COMMENTS1. The examples shown are jobs we have undertaken

for the Nottingham based ground freezing

contractor, The British Drilling & Freezing

Company Ltd, as the engineer for the frozen

ground behaviour predictions

2. They relate to shafts and tunnels

3. Depending upon the situation, AGF can be used

also for the construction of deep basements