Ground Improvement Project –Large water storage tanks

Carrington NSWDouglas Partners’ Technical Seminar 2019

Scott McFarlane & Richard Merifield

Background

• Douglas Partners are a trusted consultant to PWCS;

• PWCS needed to upgrade their stormwater management system;

• PWCS engaged GHD as the design consultant (civil, hydraulic, mechanical,

electrical & geotechnical);

• PWCS provided GHD previous nearby geotechnical data (by DP) to assist

GHD with conceptual geotechnical ground improvement options for tank;

• PWCS provided DP the concept geotechnical design options by GHD to

develop scope of works (i.e. data report).

Stormwater Management System

• Manage stormwater to minimise

off-site uncontrolled discharge;

• Above ground steel tanks;

• Supported on concrete slab;

• Tank 1 – 20 m dia, 11 m high, 5Ml;

• Tank 2 – 32 m dia, 11 m high, 8 Ml;

• Tank 3 – 32 m dia, 11 m high, 8 Ml;

• Pipeline to connect into existing

pond. Trench to be excavated

adjacent to rail line.

Previous Data

Soft Clay VL Sand

Very Stiff to Hard Clay

Dense Sand

Clay / Silt and Sand

Stiff Clay

Fill

Rock-40

-30

-20

-10

-0

GHD Concept Ground Improvement Options

Ground

Improvement

Option

Do nothing Preload CFA piles Driven Piles Cutter Soil

Mixing (CSM)

Design Details - 8 m high

preload

(3 month

wait)

600 mm dia;

Installed to

>35 m,

3 m c/c

400 mm sq;

Installed to

>35 m,

2.5 m c/c

CSM to 35 m

15% area

replacement

ratio

Estimated

Post

Construction

Settlement

(mm)

700 250

to

300

5 to 10 5 to 10 With preload:

20 mm

Without:

100 mm

Constraints Settlement Space,

time

Depth of

piles, ASS

Depth of

Piles

Depth of Piles

PWCS – very risk adverse with any ground improvement (past experience)

DP DifferenceCalculation of the Settlements and Vertical Stresses beneath Uniformly Loaded, Flexible, Rectangular Footings on Multi Layered Elastic SolidLimitns: 1.Maximum 10 layers, 10 flexible footings, 4 cross sections

2.Units: metres and kPa3.Enter data in coloured cells & adjust settlement plot axes4.Settlements & stresses calculated along Xsections at Zdepth

Footing Uniform No. X ordinate Y ordinate X ordinate Y ordinate Pressure1 0.00 0.00 32.00 32.00 120.002345678910

Xsection Xord left Yord left Xord right Yord right Zdepth1 0.00 0.00 32.00 32.00 0.00234

Max Settlement along Xsections = 250 mmSoil Layer Base Depth Layer Thick Soil Moduli Psn's Ratio Description

1 2.00 2.00 40000.00 0.35 gravel2 4.00 2.00 2000.00 0.35 clay3 5.00 1.00 25000.00 0.35 sand4 10.00 5.00 5000.00 0.35 sand5 15.00 5.00 60000.00 0.35 sand6 23.00 8.00 12000.00 0.30 clay7 37.00 14.00 15000.00 0.30 clay8910

version 1.1 © Douglas Partners Pty Ltd Date: Calcs by: Check:CLIENT: PWCSPROJECT: Carrington Project No: NALOCATION: PWCS Bore No: NA

Coords closest to Origin Coords far from Origin

0.00

5.00

10.00

15.00

20.00

25.00

30.00

35.00

0.00 5.00 10.00 15.00 20.00 25.00 30.00 35.00

Layout of Uniformly Loaded, Flexible Footings

Ftg1 Ftg2 Ftg3 Ftg4 Ftg5Ftg6 Ftg7 Ftg8 Xsect1 Xsect2Xsect3 Ftg9 Ftg10 Xsect4

0.000

0.050

0.100

0.150

0.200

0.250

0.300

0.00 5.00 10.00 15.00 20.00 25.00 30.00 35.00

250 mm

DP Revised Scope• Investigation – Provide data to

GHD to undertake Design;

• Parallel modelling to compare

with GHD design;

• Review technical specification;

• Review tenders methodology;

• Review preferred tenderers

design, QA and alternate design.

InvestigationGeotechnical Risks

• Soft clay layer?

• Sand stratum?

• Deeper clay?

• Ground water?

• Rock strength?

Subsurface ProfileTank 1 – 20 m dia Tank 2 – 32 m dia

Design & Analysis

Tank Design Loads

Design Life = 50 years

Serviceability Criteria• Max settlement at centre ≤ 100 mm;

• Max settlement around perimeter ≤ 100 mm;

• Max settlement between centre and edge ≤ 40 mm;

• Max edge to edge tilt ≤ 30 mm;

• Differential settlement ≤ 1 in 500.

Conceptual Time-Settlement Behaviour

Max Total Settlement: Case 1 – 300 mmCase 2 – 225 mm

Initial Ground Improvement Options• No Ground Improvement;

• Piles with Pile Transfer Layer (PTL);

• Deep Soil Mixing (GHD preference);

• Tank Interaction (3D analysis).

7

10

11

12

5

2

45

45

45

45 50

50

50

50

55

55

55

55

60

60

60

60

65

65

65

65

70

7070

70 70

70

70

75

75

75

75

75

75

80

80

80

80

80

80

80

80

80

80

80

80

80

80

85

8585

85 85

85

85 85

8585

7

10

11

12

5

2

495051

5253

53

53

54

54

54

55

5555

55

55

56

56

56

5656

57

57

57

57

57

58

58

58

58

58

59

59

59

59

59

60

60

6060

61

61

61

61

62

62

62

63

63

64

64

6566

67

68

Max Total Settlement: Case 1 – 80 mmCase 2 – 60 mm

Max Total Settlement: Case 1 – 71 mmCase 2 – 53 mm

Max Total Settlement: Case 1 – 76 mm

Initial Tender Review – Mix Soil Option• Large QA component in design spec by GHD:

• Sampling and lab mix design to

determine strength properties;

• Additional CPTs;

• Trial sites (curing time);

• Core sampling of mixed soil;

• Lab testing during mixing;

• Column Penetration Test or Pull-out

resistance test.

• 1 m preload.

Alternative Tender – Rigid Inclusions• Concrete Injected Columns (CIC);

• Controlled Modulus Columns (CMC);

• Controlled Stiffness Columns (CSC).

a) A “unit cell” axisymmetric model consisting of the CSC and its surrounding soils was analysed;

b) Based on the results from a), an equivalent set of soil properties was generated;

c) Using the result from b), a larger model was generated.

Plaxis 2D Unit Cell Model of CSC

Plaxis 2D axisymmetric model (half model) with equivalent composite CSC/Soil Zone

Tank Total Settlement mmSustained Constant Load – 120 kPa

Keller Prediction DP Prediction

Tank 1 (20 m dia) 74 62Tank 2 (32 m dia) 86 71

QA During Construction• Proof rolling & Plate Load Testing rather than

density testing of working platform;

• Additional CPTs;

• Concrete testing (by others);

• Review of concrete takes & penetration depths;

• Plate load testing of installed columns

(similar to pile test)

Plate Load Testing – Working Platform

Installation of Trial Columns

Installation of Trial Columns

Production Rate of Columns

0

10

20

30

40

50

60

050

100150200250300350400450

5/18/201

8

5/20/201

8

5/22/201

8

5/24/201

8

5/26/201

8

5/28/201

8

5/30/201

8

6/1/20

18

6/3/20

18

6/5/20

18

6/7/20

18

Num

ber o

f Met

res

Noof

Pile

s per

day

Stats No. Metres per day

No. of Piles per Day

Range 72 – 400 8 – 53Average 264 35

Column Load Testing (10 MPa – 7 days)

Typical Column Load Test Result

050

100150200250300350400

0 5 10 15 20

Pile

Load

(kN)

Deflection (mm)

Column Diameter – 0.4 mColumn Depth – 7.5 m

Total No. of Column Tests – 9Range of Max Deflection – 2.1 to 28 mm

Thanks to All Involved with this Project

310.5

66.25

487.5

41.75

Ground Test

Melbourne Lab

Newcastle Geo

Newcastle Lab