Structural inspection of quay and harbour walls

A wall is fine until the seabed leaves.

Everything a quay wall does depends on what is under it, and the ground can go for years before anything shows above the water.

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02

Two thirds of it is never seen.

The part that gets looked at is the part that is easy to look at. The rest is a structure nobody has laid a hand on since it was built.

9 mCoping to seabed at low water, on our stretch

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Three things end a wall.

  • The seabed washing out from under the toe
  • Joints opening until the fill behind runs out through them
  • Ties and anchors going, which shows as the coping moving
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Metre by metre, on the wall.

A diver on the face with a tape and a probe, from the coping to the toe, along the whole length, and a chainage against every finding.

Everything below is what that produces

What a shift is

The numbers the day is built around.

None of these are ours to choose. They are the water, and the plan is written to fit them.

0.3Metres of visibility on a good day hereWhich is why the inspection is done by hand and the camera is for the record afterwards
2 hThe slack window either side of high waterOutside it the tide takes a diver off the wall faster than they can work
45Minutes of bottom time at nine metresOn air, with the ascent and the surface interval planned around it
120Metres of wall in a working dayTwo divers, one in the water, one dressed and on the deck
03

At three tenths of a metre, looking is not the sense you use.

From the surface down the page is the wall as the diver reads it, which is by hand.

One wall, one survey

The east quay, end to end.

Every finding sits at the metre it was found at. That is what makes a report worth having: not that there is a defect, but where.

The east quay, end to end.
  1. 01

    Coping displaced, 25 mm

    The top course has moved seaward and the joint behind it has opened. On its own it is nothing. With anything below it, it is the tie.

    Chainage 13 m

  2. 02

    Open joint, 40 mm

    A finger goes in to the second knuckle and comes out with fill on it. The wall is losing what is behind it through the front.

    Chainage 44 m

  3. 03

    Scour, 1.2 m under the toe

    The seabed has gone from under the base for about four metres of length. This is the one that decides whether the quay works next season.

    Chainage 74 m

  4. 04

    Sound

    The last thirty metres are tight, the toe is buried and the joints are full. Saying so is half of what the survey is for.

    Chainage 104 m to the end

Asked every time

Before you take a wall out of service.

Why not send an ROV down instead?

Because at three tenths of a metre of visibility a camera sees three tenths of a metre. An ROV is good on a clear deep structure and it is honest to say so. On a silty harbour wall the survey is tactile: a hand along the joint, a probe into the fill, a tape from the coping. We fly a camera too, for the record, and it records what the diver already found.

What do we actually get?

A chainage drawing of the face with every finding on it, photographs and video against each one, a written condition grade per ten metre panel, and a page at the front that says which of it needs doing this year. It is written to be handed to an engineer, not to be admired.

How long does a wall like ours take?

About a metre a minute in the water, so a hundred and twenty metres is a working day, plus a day either side for the tides and the write up. A wall with a lot of findings takes longer, because each one is measured rather than noted.

What if you find something serious?

You hear it that afternoon on the phone, not in three weeks in a document. If it is a load restriction we say so before we leave the site. We have no interest in a finding that arrives too late to act on.

Enquire

Tell us about the wall.

Where it is, roughly how long, when it was last looked at, and whether anything has moved. We will come back with a tide window and a price for the length.