The Geotechnics of Ipswich Chord - Institution of Civil ... · Systems Civils & Earthworks. 5 ... The Geotechnics of Ipswich Chord • Ground investigation completed by others at

Geotechnics in the Rail Industry - 12th May 2015• Jane Collins (Arup, Design Geotechnical CRE)

• Sam Moss (Arup, Lead Geotechnical Designer)

The Geotechnics of Ipswich Chord

2

Outline of Presentation

• Background

• Outline of scheme

• Core requirements

• Ground conditions

• Earthworks

• Bridges

• Connection to existing lines

• Summary


3 The Geotechnics of Ipswich Chord

Project Background

• Forms part of the Felistowe to Nuneaton Freight Enhancements Project

• Ipswich Chord identified as an key CP4 business plan commitment

• Avoids the need to travel via London, avoids “run round “ in Ipswich with

associated restrictions on standage.

• First project to be delivered by Network Rail under a Development Consent Order

4

Ipswich Chord – Design & Build Team Structure


Gfg

Southern Region MAFA

Design & Build Contractor

Multi

Disciplinary

Design

Signalling

Install and Test

Civils

Pryor (Earthworks)

Bachy Soletanche (Piling)

VibroMenard (ground

treatment)

Mabey (Steelwork)

+ others…..Rail

Systems

Civils &

Earthworks

5

Ipswich Chord – Scheme Elements


• 1.3km twin-track chord (Bacon Factory Curve) between

LTN1 and ESK

• new 6m high embankment to support the new alignment

• two new double junctions at either end

• two new underbridges and widening of existing underbridge

• Replacement of existing life expired UB 404

• Associated S&C, Signalling, Civil Engineering, M&E and

Telecoms

LTN1

embankment widening retaining wall widening

ESK/BFC

tie-in

6

Ipswich Chord – Geotechnical Challenges


• Ground investigation completed by others at Form A - limited by programme and site access

• Delays in confirmation of DCO resulted in < 3 months for detailed design

• Supplementary ground investigation was undertaken in parallel with detailed design

greater extent of soft ground beneath embankment

buried glacial channel

• Poor condition of existing earthworks (ESK in particular)

• Access to critical area of site for earthworks delayed > 6 months due to negotiations with

landowner

7

Site History & Ground Conditions


8

Chord Earthworks Optioneering

Earthwork Construction Period

- 18 months assumed

- Actual 8 months!


Vibro concrete columns

or stone columns

Excavate & Replace

9

Chord Earthworks


• Controlled Modulus Column (CMC) & load transfer mattress

• Settlement monitoring during & post-construction

Cross- section

from Form B &

or VM Form B

to show typical

construction

Graph/table to

show Form A vs

CMC treated

settlement

CMC Treatment


Earthworks Monitoring

• settlement within CIV071 limits

• CMC treatment performed better

than predicted.

31/03/2013

open to traffic

predicted settlement

fill height

12 months < 5mm settlement

12 months < 10mm settlement

11

Ipswich Chord - Infrastructure


Sproughton Rd Bridge River Gipping Bridge

Retaining Wall

Underpass

Boss Hall Junction: Bridge 404

LTN1


Bridge 404

services

temporary

support

foundations

offline

temporary

supports

13

River Gipping West Bridge


existing

new

14

ESK & BFC tie in


• Transition from CMC treated embankment to embankment widening

• risk of differential settlement

CMC treated

embankmentembankment widening

• Geotextile used to mitigate against differential settlement

• Settlement & track monitoring during & post construction

Ultra high strength &

stiffness geotextile

15

• Good TBI

• Sub-formation verification

testing

• Sub-formation geogrid

• Sub-grade geo-composite

• Type 1 sub-ballast

Granular embankment fill

Cohesive embankment fill

Geocomposite

Geogrid

Type 1

Boss Hall Junction - Trackbed Design


16

Ipswich Rail Enhancements: Summary


• Challenging programme – start on site 3-months from award of the contract!

• Challenging ground conditions, including (but not limited to):

• Soft ground beneath embankment

• Buried glacial channel

• Highly Constrained Site

• Live railway - majority of structures & embankment widening works undertaken without

possessions (adjacent line open working)

• Existing ‘Poor’ earthworks

• Access issues

• Three things helped the project succeed:

• Common Design Models - including services

• Close relationships between Design and Construction CRE’s, and the NR PE’s

- A commitment to each other to do everything in our power to get it done

17

The finished product – opened to traffic 31/3/14


18

Network Rail Partnership Awards 2014


Winner: Best Large Project

Documents

The Geotechnics of Ipswich Chord - Institution of Civil ... · Systems Civils & Earthworks. 5 ... The Geotechnics of Ipswich Chord • Ground investigation completed by others at