Weymouth Harbour Wall Repairs – final stage

Anyone who read our previous blogs on the Weymouth Harbour wall repairs will assume the works finished on 23rd December last year. However, unforeseen problems in the pile driving phase caused delays. These prevented some overlapping tasks, which may now stretch until mid February. It is helpful to compare pile driving to archeology – one never really know what’s down there!

Infilling waling beam trench and gap-filling between the piles

We started writing these particular blogs because we feel repair and strengthening of areas of the Harbour are essential works. The aim is to maintain the beauty and functions of our working Harbour, for years to come. Knights Brown Construction and Dorset Council have been informing affected local businesses but sometimes have been overtaken by events. In any event, the contractors and local authority have been MUCH more informative and responsive than during the ill-fated repairs to the old Condor Ferries Berth 3 back in 2012/3.

Shuttering for the concrete capping (8th January)

At the time of writing (11th January), remaining works included the last capping beam concrete pour and replacing the Ferry Steps. Then there are – levelling, making good, reinstating safety railings, resurfacing and clearing the site. We hope to add a few photos in later updates to this post during these concluding works, as they arise. We may be able to add a short video clip of the finished result. Then we shall be back to blogs about visiting luxury superyachts, Naval vessels, Tall Ships and Harbourside events, such as the Seafood Festival.

Updates (after 11th January)

Update on 15th January: Yesterday’s storm (Brendan) slowed work on the site but more backfilling and welder-cutting for pipe egress was attempted. The wind was swaying the crane alarmingly and work had to be halted in the afternoon. (No pictures – far too wet and windy!)

31st January 2020 – The large crane (Old Squeaky) was dismantled (using another box-crane) and disappeared from site around 11:30 a.m. It transpires, the crane may not have been causing TV interference after all. At least we can now investigate other possible causes, having eliminated the most obvious suspect.

Storm Ciara rattling and tipping over barriers around the site – courtesy of Roundhouse Hotel, Weymouth
One of 15 double-passes by streetsweeper 13th February – road still a mud bath when Storm Dennis hit us – courtesy of Roundhouse Hotel, Weymouth

Storm Ciara caused quite a stir last weekend (8th/9th/10th February,. There were gusts of wind up to 60mph and lots of rain. Some site barriers toppled in places and crashed against Roundhouse walls. The worst of the weather was not filmed due to even worse wind and rain later, naturally. (Film clips courtesy of Roundhouse Hotel Weymouth).

Week ending 14th February

Removing barriers and re-opening the road to traffic – 14th February

There remain a few more finishing jobs and complete site clearance is not expected for another week. Safety railings will be added later (etc). However, the repairs are essentially complete and are looking quite tidy.

Update – 31st May 2020

General view of the repaired area
General view of the repaired area

We promised a few photos of the finished Harbour Wall repair area. We had to wait for the Covid-19 restrictions to permit the works. But here it is and very good it looks too. The final effect is very smart and makes for an attractive feature for residents and visitors alike.

The new Ferry Steps
The new Ferry Steps
The seating area is part of the new amenity
The seating area is part of the new amenity
View from the benches towards Weymouth Inner Harbour
View from the benches towards Weymouth Inner Harbour

Weymouth Harbour Wall repairs – Update at mid-stage

Without recapping all the data in the previous post, we would like to update further work on the Weymouth Harbour Wall repairs at the midway stage (last week of pile-driving?) During 19th November, the contractors swiftly moved the piling jig another 10 metres or so along the Harbour Wall repairs site to the final position (Western end, 74m).

Very quickly, the piling rig was then fitted with piling guides and another 6 piles were lowered into position. Ancillary work onvolved spot-welding and cutting where the “ears” of the “staples” were deformed and manually “knocking” the piles into alignment, against the wind and crane movements till they could slide smoothly into place. Below is a “sequence” (actually compiled from 2 adjacent pile emplacements).

You can easily see from the above why the Council and the Contractors advised us to close for the duration of the works! (See here for a contemporary update from Weymouth Harbour website). We are also being kept informed regularly by Dorset Council, in turn advised by Knights Brown Construction, the contractors. Also, note the dust and grime adhered to the outside of the windows. Together with extra internal dust generated by pile driving vibrations, this is another reason for closing our business during the works. Latterly, we have discovered TV interference effects.

Self-explanatory, really. Aligning the piles and hammer before “tapping” then into stable locations. Then the sustained piling begins. Expected to take a few days. Note how much construction dust and dirt has been accreted onto the outside of the windows!

Note the occasional transient excursion in vibration records below. In this example, the peak-to-peak transient was approximately + 50 to – 80 mGal, or about MMI 4 (possible damage). Peak-to-peak the gap was about 130 mGal – or MMI 5 (persons may lose balance, significant building damage) – BUT – it was only a transient, not continuous, not repeated many times and not resonant – so no observable damage likely.

A couple of small items were vibrated off shelves

Also note, our measurements are NOT accurate, NOT ground displacement figures and NOT directly relatable to MMI values. MMI itself is a scale more usually associated with earthquake events (running from 1 – no effects, to 12 – total destruction). We only use these results as rough indicators.

Transient excusrion captured 19th November, ca 5pm, around + 50 milliGal and – 80 milliGal

Pile driving vibrations and resulting damage to nearby structures is a long investigated subject and surprisingly complex (Some accessible texts are – http://onlinepubs.trb.org/Onlinepubs/hrr/1967/155/155-002.pdf https://www.diva-portal.org/smash/get/diva2:610771/FULLTEXT02.pdf https://en.wikipedia.org/wiki/Pile_driver )

Update: 22nd November

We shall not bore you with another series of vibration graphs – just some typical data as the crew near completion of the piling stage (about 12 metres distant).

About +40 and -30 mGals.
Note the sound spectrum is very wide, reflections and reverberations spreading the spectrum

As with the vibration graphs, the sound level graphs are NOT accurate and depend significantly on factors such as microphone quality, sampling rate and software rendering. As a very rough guideline, the sound and vibrations are disturbingly loud indoors and sufficient to dislodge some items from shelves, rattle toilet seats, windows, doors, floorboards and plumbing against fixings. However, we see no significant damage yet.

Room scenter damaged shaken off table

Weymouth Harbour wall repairs

Brief notes at 6-week stage (16th November 2019)

After 6 weeks and despite many signs stating the road is closed, we still get up to 1000’s of pedestrians and drivers who refuse to believe the road is actually closed!

Initial survey

Before commencing the Harbour Wall repairs, it was necessary to establish the existing condition – of the wall and nearbyconstructions and busines premises. There was a preliminary survey in several phases. This was carried out prior to work commencing (30th September) with a main aim of checking external condition of nearby buildings. This would enable any damage caused by pile-driving and related operations to be determined

There was then an internal survey using old-fashioned methods (camera and clipboard). (peter.christie@dorsetcouncil.gov.uk).

Demolishimg the old kiosk building @ Ferry Steps

The next phase of Harbour Wall repairs was to demolish the old storage and sales kiosk, built above the waling beam next to the Ferry Steps. Initially, the building was shrouded in temporary sheeting, checking for and removing any potentially hazardous materials. Then the “JCB” moved in a flattened the site in short order.

Further work includes replacing parts of the existing waling beam (anchoring structure for the tie-rods holding existing and new sheet piles in place – the tie rods are alleged to extend some 23 metres underneath the adjacent buildings).

Pile Driving operations

The main work involved pile-driving new sheet piles about 0.5m from the existing wall surface profile, about 18m into the subsoil. Originally, it was suggested a 4.5 Tonne hammer would be used to start the piles into position, followed by a more substantial (45 tonne?) ship-mounted hammer to drive the piles fully home. We have no specific information (as public) but we think the current hammer is a half-tonne hydraulic type – the noise is quite substantial and vibrations presently lie around 20 – 50 milliGals.

The piles will be cut as needed for drainage and tie-rod fixings. The gap will be back-filled with reinforced concrete, with ancillary works to fix in new sections of waling beam. The whole project is being (part?) funded from a £1.9 million Coastal Regeneration Scheme opening the way for the Harbourside Redevelopment Scheme(ca £3.3million?). When the repairs are completed, there are plans for new Harbourmaster and fishing buildings plus a scenic walkway around the Peninsula perimeter. Any flood defences would be funded from a different scheme.

Vibrations

Discussions of vibrations arising from pile driving and consequent effects on nearby structures tend to get a bit complex. In very general terms, ground displacements of 2mm/sec or more poses some risk of minor damage to older buildings (such as Listed Grade 2 Aaran House), while displacements above about 5mm/sec may cause significant damage. Hammer weights about 0.5 Tonne and frequencies about 1/sec tend to fall into the range of MMI (Modified Mercalli Index) 3 (noticeable but very little damage) while “heavier” impacts and higher frequencies can push perceived effects up to MMI 4 (minor damage) or even MMI 5 (significant damage, difficulty maintaining balance). The Council advised us to close for the duration and we took their advice.

Above, we see a few graphs of accelerometer readings vs time, during the early weeks of pile driving. Note the acceleraometer was not too accurate or sensitive and the sampling rate was low – which may cause some peaks to be “missed”. Using the archaic non-SI unit, the Gal, we can see background levels around 2 milliGal, rising to around 50 milliGal, as the operations got nearer. There is no easy relationship between Gals and mm/sec ground displacements but the MMI scale would suggest 30 to 50 milliGal = MMI 3, roughly. We have observed only slight plaster cracking and a little dust fall.

Closure of Esplanade to Custom House Quay road and pavement junction

Meantime, up to 2,000 pedestrians per day and 100’s of motorists are “visiting” the site, at least as far as the road closure next to The Roundhouse b&b. It is quite amusing to see all those stern faces crumple into astonishment when they find out a half-dozen “road closed” and “diversion” signs were not just dumped for fun and the road into Custom House Quay really is closed (6 weeks till now: another 6 weeks to go approximately).

The Council (DCC, formerly WPBC) have advised the nearest properties to close during the period of works, for safety, noise and disruption reasons. Hence, we are closed (since 1st October) till the Christmas period (scheduled completion 23rd December). We are hoping for compensation due to business interruption.

Reopening in 2020 – early in January

We apologise for any inconvenience to guests who would have wished to book our guesthouse this autumn, but the works were essential and closure was unavoidable. It was only a few years ago a section next to Condor Ferry Berth collapsed. Allegedly that was in relatively sound condition compared to the current repair section. Of course, public safety is paramount and works have continued as rapidly as feasible. We thank all our guests for visiting us in the past and we hope to see you all again next year. Happy Holidays!

(See mid-stage update)