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Lyceum 2021 | Together Towards Tomorrow

Jared will present a case study and discuss how he’s used Leapfrog Works for ground investigation and design of ground stabilisation measures around tunnel annulus.



Jared Jiang
Senior Engineering Geologist, Mott MacDonald NZ


30 min

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Video transcript

(upbeat music)

Hi everyone, welcome.

My name is Jared.

I’m the Senior Engineering Geologist for Mott MacDonald,

I’m based in New Zealand.

So my talk today

is about how we have used the Leapfrog Works

to visualize and detect potential underground clashes.

In this talk, I will show you a past project example

to illustrate how we have utilized Leapfrog

for the ground stabilization works

of the Forrestfield Link in west Perth, Western Australia.

Next slide.

So a bit of a presentation overview.

First, I’ll give a bit of a background story of the project,

and how Mott MacDonald was involved in this project,

and what ground stabilization design

and construction solutions we formulated for this project.

So this talk will also include

how we have utilized the capability of Leapfrog Works

for data storage, design planning, design execution,

and design verification throughout this project.

So this will follow by a quick summary

on my personal user experience

with Leapfrog during the project.

Next slide, please.

So here’s a background story of this project,

the Forrestfield Airport Link Metro line

comprises twin segmentally lined TBM tunnels

of a nominal 6.1 diameter with the cross passages between

at approximately 200 meters along the alignment

for easy access between tunnels.

So it is a fairly easy type of tunnel construction

around the world.

So the site is located

towards the western end of the alignment

near the Perth Airport

as shown in this figure here,

the problematic section of the tunnel

is associated with the cross passage number 12,

shown in the yellow cross

towards the very end of the alignment

on the right.

So during the construction stage,

a piping event occurred

during the excavation of the cross passage

and the water was gushing into the cross passage

through the pre-grouted ground around it.

So this event resulted in some sediment and defamation

of the installed tunnel lining on the excavation site.


these events reduced the water pressure

within the surrounding soil

and has caused a bit of a movement of the segmental lining.

Luckily, the movement only occurred

on one of the twin tunnel at this location.

So the in-flow water brought in sediments,

you know, into the tunnel and potentially created voids

around the tunnel extrados,

by how much, we don’t know,

that’s always a mystery.

It’s always going to be a mystery.

So Mott MacDonald was commissioned by the DNC contract,

that’s the design or construction contract

of the Forrestfield Airport Link Metro tunnel project,

as a specialist to work on the reinstatement works

for the tunnel lining and cross passage.

Next slide, please.

As you can see the dash line here

is a perfect circle,

and the solid line around it

is from the survey data,

shows the outline of the deformed tunnel lining.

The defamation created a deviation of up to 600 millimeters

from the original design in some places.

As a result, the train was not able to pass through

certain parts of the tunnel freely

without touching the lining and the utilities.

The cross passage here is a typically minor structure

constructed after the TBMs has gone through.

Next slide, please.

So we were contracted to carry out the design

and construction of the remedial works.

So as we have carried out appropriate investigations,

including geo-technical, geo-physical testings

and other necessary survey works

to basically get a better picture

of the potential issues and challenges that lie there.

Long story short, so after the investigation

and weighing all the challenges,

we believe that permeation grouting

is really the only ground improvement design solutions

for this typical type of geological conditions.

The ground surrounded tunnel and cross passage,

there is silty sandy materials.

The ground water level is fairly constant,

sort of fluctuated between four to five meters

below the existing ground level,

and the tunnel

is about between 9 to 16 meters below ground.

So next slide, please.

So before we got involved, the people came before us,

they’ve already carried out various prevention measures

to stop further damages to the tunnel and cross passages.

So we have been given the information,

including the following

historical, any historical investigation data,

historical ground improvement works,

some as-built plans.

Also the compaction grout they carried out from the surface.

We were also given some existing utility information,

including, and also some laser scan surveys

of the internal tunnel, internal geometry.

Some point cloud data,

scans of the tunnel and cross passage

at the affected location.

Also, the temporary works

support locations,

some of the struts and bracings

to support the tunnel from further damage.

We were also provided with CAD designs, 2D and 3D files.

Next slide, please.

So together with all the information,

investigation works that we have done

also all the information that I’ve just mentioned,

as you can see it, there’s a lot of information.

And with my involvement

briefly, in the past with Leapfrog,

we ended up

deciding to use Leapfrog,

not just to store all the information

you know, above, and also to do the geological modeling.

Next slide, please.

So with me knowing what the Leapfrog can do

from, you know, clash detection perspective,

we also decided to do the modeling

of a grouting design

and modeling of the permeation grout data

during the design and construction stage.

So just by adding some value to this project.

Next slide, please.

I’ll just go straight into the modeling stuff we did.

So this slide shows the historical events

undertaken on the surface prior to our involvement.

This includes area photographs of the subject location

before and after the incident.

As you can see the formation of the surface sinkhole

and the concrete trucks trying to temporary

fill this void on the left.

Following this work,

they did a couple of CPTs around the area.

Next slide, please.

So the temporary prevention measures,

including compaction grout from the surface,

this slide shows the extent

of the compaction grouting works.

You can vaguely see the tunnel and the jet grout blocks

to the left of the sinkhole above the cross passage.

Next slide, please.

So this is the latest scan works in blue

from within a tunnel.

So the gray solids is the 3D tunnel design.

This survey works was attempting

to determine the level of distortion of the linings.

This is looking,

next slide, please.

So this is looking down

onto the cross passage,

and as you can see, it appears that the cross passage

has been constructed in a place it was not intended to.

Next slide, please.

So this is also looking down views

shows the intensity data from a point cloud scan

also confirms the as-built location of the cross passage.

Next slide.

So I thought, our investigation,

we have proposed five boreholes in the locations indicated

in the picture on the left.

Also, we also done some geo-physical surveys,


MASW, cross hole seismics

and horizontal seismics within the tunnel,

in order to determine the condition of the soil

surrounding a tunnel lining and cross passages.

Next slide, please.

So from the investigation data,

we constructed simplified ground models

to assist the design.

Next slide, please.

We have determined that permeation grouting

by means of injecting pressurized cement

through the vertical and inclined holes

is the suitable solution in this kind of geology.

So the permeation grout

is required from both surface and from within the tunnel.

The design planning was also, was mostly done in 2D CAD,

but later on was transferred into Leapfrog for fine tuning,

in order to make sure that the design

does not intersect or punch through

the existing segmental lining.

And also it does not overlap with any underground services

and the existing jet grout block.

Next slide, please.

Next slide, please.

So we also carried out a point cloud

scan of the

internals beyond the effected tunnel sections

and we tried to import the point cloud data into Leapfrog

to visualize the potential clashes of the grout design

at the tunnel invert level.

Next slide, please.

So as you can see,

there are a lot of internal bracings and struts,

you know, as part of the temporary works

to support the tunnel from further distorted.

However, we weren’t able to incorporate

the RGB data from the survey when we worked on this project.

So we did the old fashioned way

in Civil 3D.

Next slide, please.

As you can see,

in Civil 3D,

we super imposed the point cloud data to our 2D design

to make sure that there’s no clash

between the grouting holes

and the existing bracings and struts.

Next slide, please.

So this is the finished product

of the grouting design looking up,

and the red color is the surface grouting holes,

and cyan color is the ones from the tunnel invert level.

The black dots are the laser scan points.


next slide, please.

So this is just looking from a different perspective

and the green blocks are the existing jet grout blocks.

Next slide, please.

So this is looking down as mentioned before,

and we didn’t want to re-grout the jet grout block.

So there is no grouting holes proposed

within that green block.

Next slide, please.

So this is just looking up from below.

Next slide, please.

So we also used Leapfrog to visualize

the as-built grouting holes.

As you can see, the picture on the left is the design

and on the left, oh, it’s on the right,

is the as-built holes.

Especially, the incline holes

as you can see, that they are not as perfectly drafted

compared to the design ones.

Next slide, please.

So the modeling of the injected volume

with the borehole interval data was

also being used here.

As you can see, this picture showing here

shows the injected volume greater than 200 liters

at various depth with a gradual color scale,

as a legend,

also shows the places received a secondary grout

or additional grout.

As you can see, closely,

in the area where the holes are slightly larger

than the one above.

So next slide, please.

So in summary,

we have used Leapfrog to store all our project related data

and visualize the survey data

to help us make our design and construction decisions.

Especially in clash detections, design planning

and design execution.

So now, the Leapfrog can take RGB data

and intensity data columns,

which opens a door for importing

point cloud data in the future.

Also, I wish

that I knew

how to, you know, use the numerical modeling functions

in the past when I did the project.

So this is something

for me to think about for our future projects.

So this brings my talk to a conclusion.

Thanks, thanks very much.

(upbeat music)