Integrating Engineering Geology Into Corridor Earthworks to Improve Efficiency & Productivity

Greg O’Rourke, Executive Director - Rail

This presentation has been produced in

cooperation with 4DGeotechnics

This presentation will:

Explain how using engineering geological techniques will add value to any corridor project

Provide examples of lost value opportunities

Explain why “hard information” often comes too late to impact positively on a project

Introduction

Engineering geology is the application of the

geologic sciences to engineering practice for the purpose of assuring that the geological factors affecting the location, design, construction, operation and maintenance of engineering works are recognised and adequately provided for.

What is Engineering Geology?

The below track component of the railway

(earthworks) normally represents the most variable

component of the fixed infrastructure.

It is normally built out of natural materials on and in

a natural geological setting.

Because it is variable it often presents the most

engineering risk.

Understanding the geology therefore allows us to

predict likely issues and therefore manage this risk

from an early stage of the project.

Why is this important?

Conditions of a site are the product of the

history of the site.

Therefore understanding the geology allows

early anticipation of site ground conditions and likely engineering performance.

Total Geology Concepts

Typical Land Surface

Anticipation of ground conditions leading

to:

– informed corridor selection

– Locking in value

– Less surprises

– Targeted geotechnical investigation

– Collected data on a corridor, not an alignment.

What are the benefits of adopting this approach early?

Geological Knowledge

Framework

100%

50%

Desk Study Mapping Ground

Breaking

Investigations

Supplementary

Ground

Breaking

Investigations

Construction

Dependent

on Approvals

Biggest

decisions on

alignment are

made before

ground

disturbance

Alternative Often Typical Approach…

Designated by the Blue Line

100%

50%

Desk Study Mapping Ground

Breaking

Investigations

Supplementary

Ground

Breaking

Investigations

Construction

Biggest

decisions –

little

information

Main

information

gathering

commences

here A lot of

information

gathering

occurs here

– Surprises!

Recommended approach is:

Introduce engineering geological principals

early

Initially use available information for initial

route selection

Then site inspection followed by detailed

mapping

Total Geology Approach (Typical)

Total Geology Approach (Typical)

Identification of geohazards

Route optimisation and identification of construction materials

Corridor can be selected

Subsurface investigation

Total Geology Approach (Typical)

Develop reference conditions

Apply the observational method

Total geology approach (continued)

An Example

Looking for the

line of least

resistance

The same alignment using published data

Same alignment with aerial photography

Same alignment with geological mapping

Cut through Rock

requires drill and

blast

Likely poor

foundation

conditions

Potential borrow

areas

Potential borrow

areas

Use this information to reduce risk and cost

Alignment moved to

avoid poor

foundations, reduce

drill and blast and take

advantage of an

abundance of good

borrow materials

Using Traditional method

Select alignment based on topography

When able to, approvals allowing, test pit or drill

Depending on where targets are chosen, may discover unfavourable conditions’

No real knowledge on where to move it.

Findings

Lang Hancock Railway

Train

Loadout

Bridge

Site

Lang Hancock Railway

Bridge

replaced with

culverts at

design stage

Void below

surface

discovered

during

construction

Once hard investigatory information is available corridor is

already locked in.

If problems are only discovered when drilling and testpitting

occurs, often too late to do much about it.

Any changes are likely to require further investigation –

expensive and time consuming – or gaps in information are

presented to contractors, leading to potential latent

conditions claims.

Generally more expensive than a total geology approach

without really managing risk properly.

Problems arising from not taking a total geology approach

Adopting total geology approach:

Provides the right information at the right time

Enables informed decision making (eg corridor selection)

Enables risk management to occur, including anticipation of

geohazards and the like.

Provides information to enabling a cost effective site

investigation to take place

Allows changes to be anticipated and modifications to be

made with minimal disruption

Engineers and geologists working together to ensure

beneficial outcomes for all.

Conclusions

John Kennedy and Ian Lewis from 4DG

Acknowledgements