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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.

Overview

Speakers

Jared Jiang
Senior Engineering Geologist, Mott MacDonald NZ

Duration

30 min

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Video transcript

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(upbeat music)

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Hi everyone, welcome.

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My name is Jared.

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I’m the Senior Engineering Geologist for Mott MacDonald,

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I’m based in New Zealand.

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So my talk today

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is about how we have used the Leapfrog Works

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to visualize and detect potential underground clashes.

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

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to illustrate how we have utilized Leapfrog

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for the ground stabilization works

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of the Forrestfield Link in west Perth, Western Australia.

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Next slide.

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So a bit of a presentation overview.

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

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and how Mott MacDonald was involved in this project,

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and what ground stabilization design

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and construction solutions we formulated for this project.

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So this talk will also include

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how we have utilized the capability of Leapfrog Works

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for data storage, design planning, design execution,

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and design verification throughout this project.

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So this will follow by a quick summary

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on my personal user experience

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with Leapfrog during the project.

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Next slide, please.

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So here’s a background story of this project,

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the Forrestfield Airport Link Metro line

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comprises twin segmentally lined TBM tunnels

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of a nominal 6.1 diameter with the cross passages between

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at approximately 200 meters along the alignment

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for easy access between tunnels.

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So it is a fairly easy type of tunnel construction

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around the world.

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So the site is located

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towards the western end of the alignment

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near the Perth Airport

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as shown in this figure here,

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the problematic section of the tunnel

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is associated with the cross passage number 12,

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shown in the yellow cross

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towards the very end of the alignment

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on the right.

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So during the construction stage,

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a piping event occurred

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during the excavation of the cross passage

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and the water was gushing into the cross passage

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through the pre-grouted ground around it.

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So this event resulted in some sediment and defamation

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of the installed tunnel lining on the excavation site.

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Basically,

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these events reduced the water pressure

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within the surrounding soil

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

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Luckily, the movement only occurred

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on one of the twin tunnel at this location.

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So the in-flow water brought in sediments,

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you know, into the tunnel and potentially created voids

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around the tunnel extrados,

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by how much, we don’t know,

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that’s always a mystery.

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It’s always going to be a mystery.

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So Mott MacDonald was commissioned by the DNC contract,

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that’s the design or construction contract

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of the Forrestfield Airport Link Metro tunnel project,

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as a specialist to work on the reinstatement works

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for the tunnel lining and cross passage.

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Next slide, please.

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As you can see the dash line here

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is a perfect circle,

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and the solid line around it

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is from the survey data,

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shows the outline of the deformed tunnel lining.

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The defamation created a deviation of up to 600 millimeters

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from the original design in some places.

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

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certain parts of the tunnel freely

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without touching the lining and the utilities.

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The cross passage here is a typically minor structure

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constructed after the TBMs has gone through.

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Next slide, please.

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So we were contracted to carry out the design

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and construction of the remedial works.

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So as we have carried out appropriate investigations,

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including geo-technical, geo-physical testings

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and other necessary survey works

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to basically get a better picture

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of the potential issues and challenges that lie there.

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Long story short, so after the investigation

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and weighing all the challenges,

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we believe that permeation grouting

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is really the only ground improvement design solutions

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for this typical type of geological conditions.

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The ground surrounded tunnel and cross passage,

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there is silty sandy materials.

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The ground water level is fairly constant,

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sort of fluctuated between four to five meters

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below the existing ground level,

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and the tunnel

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is about between 9 to 16 meters below ground.

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So next slide, please.

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

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they’ve already carried out various prevention measures

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to stop further damages to the tunnel and cross passages.

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So we have been given the information,

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including the following

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historical, any historical investigation data,

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historical ground improvement works,

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some as-built plans.

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Also the compaction grout they carried out from the surface.

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We were also given some existing utility information,

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including, and also some laser scan surveys

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of the internal tunnel, internal geometry.

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Some point cloud data,

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scans of the tunnel and cross passage

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at the affected location.

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Also, the temporary works

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support locations,

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some of the struts and bracings

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to support the tunnel from further damage.

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

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Next slide, please.

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So together with all the information,

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investigation works that we have done

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also all the information that I’ve just mentioned,

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

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And with my involvement

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briefly, in the past with Leapfrog,

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we ended up

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deciding to use Leapfrog,

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not just to store all the information

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

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Next slide, please.

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So with me knowing what the Leapfrog can do

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from, you know, clash detection perspective,

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we also decided to do the modeling

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of a grouting design

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and modeling of the permeation grout data

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during the design and construction stage.

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So just by adding some value to this project.

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Next slide, please.

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

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So this slide shows the historical events

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undertaken on the surface prior to our involvement.

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This includes area photographs of the subject location

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before and after the incident.

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As you can see the formation of the surface sinkhole

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and the concrete trucks trying to temporary

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fill this void on the left.

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Following this work,

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they did a couple of CPTs around the area.

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Next slide, please.

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So the temporary prevention measures,

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including compaction grout from the surface,

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this slide shows the extent

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of the compaction grouting works.

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You can vaguely see the tunnel and the jet grout blocks

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to the left of the sinkhole above the cross passage.

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Next slide, please.

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So this is the latest scan works in blue

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from within a tunnel.

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So the gray solids is the 3D tunnel design.

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This survey works was attempting

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to determine the level of distortion of the linings.

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This is looking,

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next slide, please.

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So this is looking down

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onto the cross passage,

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

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

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Next slide, please.

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So this is also looking down views

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shows the intensity data from a point cloud scan

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

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Next slide.

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So I thought, our investigation,

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we have proposed five boreholes in the locations indicated

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in the picture on the left.

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Also, we also done some geo-physical surveys,

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including

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MASW, cross hole seismics

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and horizontal seismics within the tunnel,

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in order to determine the condition of the soil

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surrounding a tunnel lining and cross passages.

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Next slide, please.

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So from the investigation data,

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we constructed simplified ground models

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to assist the design.

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Next slide, please.

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We have determined that permeation grouting

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by means of injecting pressurized cement

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through the vertical and inclined holes

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is the suitable solution in this kind of geology.

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So the permeation grout

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is required from both surface and from within the tunnel.

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

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but later on was transferred into Leapfrog for fine tuning,

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in order to make sure that the design

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does not intersect or punch through

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the existing segmental lining.

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And also it does not overlap with any underground services

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and the existing jet grout block.

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Next slide, please.

[00:10:18.378]
Next slide, please.

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So we also carried out a point cloud

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scan of the

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internals beyond the effected tunnel sections

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and we tried to import the point cloud data into Leapfrog

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to visualize the potential clashes of the grout design

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at the tunnel invert level.

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Next slide, please.

[00:10:47.282]
So as you can see,

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there are a lot of internal bracings and struts,

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you know, as part of the temporary works

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to support the tunnel from further distorted.

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However, we weren’t able to incorporate

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

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So we did the old fashioned way

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in Civil 3D.

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Next slide, please.

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As you can see,

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in Civil 3D,

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

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to make sure that there’s no clash

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between the grouting holes

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and the existing bracings and struts.

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Next slide, please.

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So this is the finished product

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of the grouting design looking up,

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and the red color is the surface grouting holes,

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

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The black dots are the laser scan points.

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So

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next slide, please.

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So this is just looking from a different perspective

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and the green blocks are the existing jet grout blocks.

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Next slide, please.

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So this is looking down as mentioned before,

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

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So there is no grouting holes proposed

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within that green block.

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Next slide, please.

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So this is just looking up from below.

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Next slide, please.

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So we also used Leapfrog to visualize

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the as-built grouting holes.

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

[00:12:31.300]
and on the left, oh, it’s on the right,

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is the as-built holes.

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Especially, the incline holes

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

[00:12:41.210]
compared to the design ones.

[00:12:43.020]
Next slide, please.

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So the modeling of the injected volume

[00:12:49.580]
with the borehole interval data was

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also being used here.

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As you can see, this picture showing here

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shows the injected volume greater than 200 liters

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at various depth with a gradual color scale,

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as a legend,

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also shows the places received a secondary grout

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or additional grout.

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As you can see, closely,

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in the area where the holes are slightly larger

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than the one above.

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So next slide, please.

[00:13:32.120]
So in summary,

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we have used Leapfrog to store all our project related data

[00:13:36.750]
and visualize the survey data

[00:13:38.320]
to help us make our design and construction decisions.

[00:13:42.210]
Especially in clash detections, design planning

[00:13:45.520]
and design execution.

[00:13:48.110]
So now, the Leapfrog can take RGB data

[00:13:51.250]
and intensity data columns,

[00:13:53.430]
which opens a door for importing

[00:13:55.390]
point cloud data in the future.

[00:13:57.590]
Also, I wish

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that I knew

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how to, you know, use the numerical modeling functions

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in the past when I did the project.

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So this is something

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for me to think about for our future projects.

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So this brings my talk to a conclusion.

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Thanks, thanks very much.

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(upbeat music)