Sydney – 14th October 2015

Daniel Clert

North Strathfield Rail Underpass Shallow tunnelling techniques

Northern Sydney Freight

Corridor (NSFC) Program• Remove bottlenecks

and enhance freight

capacity, availability,

reliability and journey

time

• Includes grade

separation, track

amplification and

passing loops2

North Strathfield Rail

Underpass

3

Current

at-grade

crossing

Project scope

4

Delivery partners

Investigations and geotech

Concept design

Detailed Design

5

Review of Environmental

Factors

Signalling concept

Detailed design

6

• Underpass ~ 148m long

Overview

7

2.8% slope on approach2.1% slope on exit

Shallow Cover

Indicative Geological Profile

Siltstone,

Ashfield Shale

Formation

Weathered Shale

Shallow driven tunnel

Ballast and sub-base

Stiff Clay

Tunnel Support

Observation on site: For 6 Mpa: Best case 6hrs, Worst case 12hrs, average 7hrs

Main Options taken:

- Full face excavation.

- Fast Setting (accelerated) Shotcrete

(5% accelerator).

- Permanent Monitoring (survey and

shotcrete).

- Close proximity between Design,

Methodology and Construction teams.

Support Contingency – Lattice Girders

Support Contingency – Steel Sets

Methodology

Surface Layout

19

Overview

Materials: Canopy tubes

Face nails (Face and wall stability)

Cycle Times for a 1.3 m advance

• CANOPY TUBES 2.00 days

• CUT & SC 1 0.85 day

• CUT & SC 2 0.85 day

• CUT & SC 3 0.85 day

• FACE SUPPORT 1.00 day

• CUT & SC 5 0.85 day

• CUT & SC 6 0.85 day

• CUT & SC 7 0.85 day

• CUT & SC 8 0.85 day

• SUB-TOTAL 8.95 days

Progress

The NSRU project was commissioned in June 2015.

5 months ahead of schedule

Tunnel Progress on NSRU

Permit to Tunnel

• Permit to Tunnel issued every 24 hours.

• PTT includes review and analysis of:

• Face Mapping

• Track and Surface monitoring

• In tunnel: Convergence monitoring

• PTT confirms all support from previous 24 hours

installed.

• PTT instructs support requirements for next 24

hours.

Supported Ground: Safety aspects

• No Access under ground that does not have as a

minimum:– Canopy Tubes

– 150mm Shotcrete at 1MPa or greater

• Exclusion zone around the face unless there is as

a minimum:– Face dowels

– 50mm Shotcrete on the face

• No access under shotcrete until it reaches 1MPa.

Shotcrete testing in the tunnel

Verification of 6 Mpa strength with Beam end testing

Face Mapping

External Monitoring: Track

Ground Monitoring Points

Remote access robotic scanned survey data 24 hrs /day

Plan of monitoring surface

Track Monitoring Points

In tunnel monitoring

In tunnel monitoring

Designers Expected Max Settlement = 6 to 8 mm

Daily “Permit To Tunnel” meeting room

Surface settlement: Actual vs Predicted

No alarm triggered during Construction

Outcome

A few other project

elements

44

45

• A 4D project – design, plan and build

around track possessions

Key challenges

46

Key challenges

• 4D project – design, plan and build

around track possessions

Multi-disciplinary

response

47

• Design co-ordination drawings

48

• Construction staging diagrams

Multi-disciplinary

response

49

• Methods Department – managing site

Multi-disciplinary

response

50

• Methods Department – managing site

Multi-disciplinary

response

Questions

51