Meeting minutes and resources

Isle of Wight Council

Minutes: Leeson Road Borehole Discussion

Friday 26 July 2024

Hybrid meeting – MSTeams and Conference Room 6, County Hall, Newport

Attendees

Isle of Wight Council (IWC)

• Phill Jordan – Leader of the Council and Cabinet Member for Highways and Transport
• Rodney Downer – Ward Member Wroxall, Lowtherville & Bonchurch
• Michelle Love – Service Director Transport and Community Saftey
• Natasha Dix – Service Director Waste, Environment and Planning Services (CHAIR)
• Alan White – Group Engineer – Highways PFI Contract Management Team

Jacobs UK (supporting IWC)

• Roger Moore - Jacobs Senior Expert - Professor Emeritus, Applied Geomorphology, Global Principal – Geoscience and Engineering Geology, Tunnel and Ground Engineering (RM)

Island Roads Services (IRS)

• Rob Gillespie – Chief Executive Officer

Ringway Island Roads Limited (RIR)

• Stephen Ashman – Operations Director
• Joanne Saunders - Business/Structures Manager

Ventnor Town Council (VTS)

• Katherine Baldwin – Town Clerk

Public Attendees

• Julian Rodley
• Chris Innis
• Richard Ferraro
• Ken Oliver
• David Groocock
• Martin Simpson
• Steve McLoughlin
• James Attrill

Apologies

• Edward Blake – Ward Member Ventnor and St Lawrence
• Clare Mosdel – Conservative Group Leader & Ward Member Newchurch, Havenstreet and Ashey
• Colin Rowland – Strategic Director Community Services
• Steve Cooper – Mayor of Ventnor

1 Introductions and apologies

• Parties introduced themselves.
• Apologies were noted.
• Request made for minutes to be circulated post meeting.
• IWC noted there was not an appointed note taker the room requested participants permission to record and transcribe the meeting in teams for the purpose of preparing notes/minutes.

All attendees agreed – Transcript is annexed to these minutes.

2 Opening Remarks from the Chair

ND opened the meeting and reminded all attendees that this meeting is to present the current plan for the installation on monitoring equipment via boreholes on Leeson Road to enable an early warning system and automated closure system. This activity supports the desire to keep Leeson Road open safely into the future.

A second meeting will be help in September to discuss the long-term views on landslide management in the Undercliff.

3 Presentation from Ringway Island Roads Limited

JS presented the annex PowerPoint presentation ‘Leeson Road Reopening, Ground Investigation Proposals’

Parameters of ground investigation

JS set out the parameters for the ground investigation as follows:

• 3 Boreholes will be to a depth of a minimum of 85m below lesson road (c.120m above datum) targeting beyond the Gault to the Carstone/Monks Bay Sandstone
• 1 borehole will be rotary open-hole (RO) borehole to 30m.
• 3no dynamic sampling with rotary core follow-on (DS+RC) boreholes each to 85mbgl, including detailed logging of cores and samples.
• Inclinometers installed to the base of two DS+RC boreholes.
• Multiple vibrating wire piezometers (VWR), fully grouted, to be installed in one DS+RC and one RO borehole.
• In situ downhole geophysics – Natural Gamma logging - in each DS+RC borehole.
• Groundwater and inclinometer monitoring.
• Geotechnical laboratory testing.
• Production of a factual report and AGS Data.

SM raised a query on the lining that will be used in the boreholes. Discussion on grouting, cement, and bentonite and sleeving took place.

SA confirmed Boreholes will be at least 85 meters below ground level current proposal is to place them in the road.

Discussion on the location and size of equipment that will be required for works took place. Rig will be large (shown on slides) and require safe working space around it.

RM set out when this is tendered, we should ensure the quality of the drillers and understand their experience of drilling in the undercliff – worked with the council in 2005 when so much was learnt.

SA set out experience working in the Undercliff drilling the boreholes for the Niton Undercliff drainage scheme and how that technical knowledge and lesson learnt from that scheme have fed into his specification. Currently not specified air or water drilling will let the contractors provide that advice in the tenders. Looking at a 10-week programme

Tenders are being discussed with two parties at this time.

SMcL agreed drilling slowly and properly to get quality results.

SA set out the intention to send cores for the whole length for logging and verification.

SMcL and RM opened the concept of alternative approaches to coring, sampling and testing.

Both set out from their professional perspectives that the upper greensand bench in well studied and known geology and does not necessarily require logging and sampling.

They raised the suggestion of using sample windows in the upper geology and selectively targeting the layers for logging and scientific testing. This could potentially save on drilling costs in the upper green sand and provide funding to go a litter deeper.

RG – Stated RIR are open to this discussion, queried what advantage does it give?

RM – is save a lot of time and money, if you are coring 3 to 4 of these with continuous logging the expense is enormous.

SMcL – set out he believes we think we (indicates RM and Himself) are agreed the upper parts not of interest it is malm rock, debris and reworked debris – so you would sample capture there.

Discussion held on the methodologies of capturing 3 directional information in drilling practice. Methodologies of capturing information to inform understanding of the orientation of the slip planes. SMcL suggested multiple core samples from 3 differing boreholes at the same horizons of interest can assist in this. Jacobs raised the use of a televiewer that essentially takes a three-dimensional photograph that does not rely on taking samples back to the lab as it is instant digital data.

Suggestions of depth carried between 110 and 130 meters moving the conversation into the ground model developed by Jacobs.

4 Jacobs – Geological Section Slide (slide annexed)

Figure 4-1 Smugglers Tearoom Geological Section Showing Pre-2023 Landslide Event Ground Profile

RM presented the Jacobs ground model

The dash lines show a degree of uncertainty. The brown lines mark the base of the clay and the contact with the Monks Bay Sandstone formerly known as Carstone.

Below the Monk's Bay Formation, we've got potentially a confined aquifer system within the lower green sand, which is known as the Sandrock. That becomes more important in the Undercliff but here in Bonchurch because the Sandrock is exposed in the sea cliffs that it free drains. It is not confined; it's not generating artesian pressures.

Whereas that situation is a little different in the Undercliff because this horizon dips below sea level. So, the whole system becomes quite confined.

Focusing on Bonchurch then we believe based on the previous drilling that we did in 2002, that this is primarily an upper system landslide system seated in the Gault Clay. The interesting characteristics of the failure in December was the sheer vertical movement at the rear of the scarp of almost 100m. The vertical settle raised the question of how the geology accommodates the sudden drop of 100m. An interpretation of this failure points initially that the failure was in the higher levels of the Gault, but the verticality of the rear scarp suggested the movement could be at the base of the Gault.

SMcL Note to all this is not just solids issue it is a liquids issue in the solifluxation of the Gault.

RM We know from the geomorphological evidence is that failure actually initiated around the mid-slope. So, the displacement of that central part of this landslide pre-existing landslide would have opened up quite a large tension crack at the back here, which then allowed the Cliff to basically drop into the ground.

RM thinks from the best judgement and in all bounds and probability, we're looking at failure towards the base of the Gault Clay. Leeson Rd is about 130 metres above ordnance datum.

So you could take a borehole down around 80 metres, which would reach 45/50 metres I suspect. Query if this depth would pick up any displacement at the base of the gault?

SA clarified it is the intention is to get to the bottom of the gault clay.

RM stated if you're going to do that, I think you're looking at a minimum of 110 metres.

SA confirmed the intention has always been to go below the Gault with 85m as a minimum, but drilling is intended through to the top of the Monks Bay Sandstone.

RM ideally there should be two piezometers below the Monks Bay sandstone. The pressures in the Sand rock will have a hydrostatic groundwater system above the Gault. So, you would have separate piezometers located in the upper level.

SA set out that appreciating what was discussed earlier about sampling in the upper sections, we we've almost got like a Cliff face now. IR keen to understand how that material performs independently of any movement from the Gault Clay, because there is now a cliff standing that could fail through other mechanisms. The thinking behind doing the sampling in the higher levels is focused on that performance risk.

RG questioned if whet Steve and Roger is saying is that the existing data would give us that information already?

SMcL Martin has spent a lot longer looking at this than I and we have a new geological term called Soup and Croutons – basically settled debris and blocks inside the chalky debris.

Discussion followed on the historic boreholes of the undercliff and known geology of both the relic landslide and the in-situ geology behind the Undercliff. SMcL has requested by FOI from Southern water and the Military the data from confidential boreholes above the Undercliff. Currently not enough data to establish a working 3D model of the Sandrock formation beneath the Monks Bay Sandstone. Ask for IR and the council to consider going to 130m boreholes for that information to provide the dip of the stratigraphy. Only another 20m as the formation dip could be deciphered to 1.5 to 2 degrees.

RM your point about the structure the chert and malm beds are the seriously hard stuff and we know from the ground model where you can expect that – so the difficult drilling will be in the early part. Our experience is that you can air mist most of the Chert/Malm/Passage beds but as soon as you enter the Gault you will have to go over to a polymer. SMcL agreed a PHP inhibiting polymer will stop the clays expanding – probably best to go with PHB for all of it otherwise using two drilling rigs.

SA Island roads and the council have had discussions on this. What you've put in on the table, it's wider than the scope that island roads are looking at. Our concern is the road and how do we monitor that road and make sure it's safe for use. That that is our primary focus rather than the bigger picture, which is a slightly wider scope that would come more Natasha and the whole coastal to understand the wider area. But the remit that's behind this is establishing parameters and monitoring that allows us to safely open the road and put it back into use.

May have to accept that one day we may not be able to use the road. What you are suggesting I understand and is probably a good idea but does scope creep from current plans.

RM Would strongly recommend at least one of these boreholes goes down 110 metres, so I'm suggesting there so that you can get the in-situ monitoring by the in inclinometer. We need to monitor what's happening at that interface with monks by sandstone. For resilience earlier, something you know well, what happens if something the equipment malfunctions, then you've lost the value. Would suggest two as a security, but you may get away with just doing that rather than doing four, which may be a little over the top.

RF raised a concern that the council and Island roads have generally been asking themselves only one question – that being what we do to open the road without spending lots of money. It seems a missed opportunity to plan for substantial engineering interventions. If all you're doing here in your more limited scope, is to get information to reassure you that you can open the road safely for the time being without doing major engineering works then, in my view, that is insufficient and it's insufficient for the communities, and it's insufficient for the South white in terms of the transport situation that we face, that road is vital and it's vital that it is secured. Is that you know from my own experience and I'm not an engineer, as I've said, that I've worked with major engineers, national and international major projects. My own view is that there will be an engineering solution to that road and there is an opportunity now for you to get the data and to get the information in the bank to enable high quality engineers to be able to review the situation for the longer term solution.

I think it would be an appalling everybody's time, frankly, if that additional information is not secured.

RG Your point is very well made, Mr Ferrara, and that that was partially the reason for doing the full recovery of what comes out of the boreholes to add to the geological profile information in the limited scope that we are working on regarding the opening of these roads. If we drill boreholes, let's get as much information detailed information as we can to add to the suite of information already there. I don't know about sample capture if that gives an adequate amount to add to the already borehole profiles that we've got from this during then, OK, well that's so that's an alternative.

SMcL, it does, add that if I explain further, the call will give you some of the structure. But if the structure is not oriented in 3D, then you have no idea what it actually means. So yes, we've got structure. So, what who gets you can't make any conclusions from it. You can make some inferences, but there are no definitive conclusions to be made.

RG So as I say, I think that, you know, all of this discussion is really helpful because it allows us to take away and discuss with others and also with the Council as to what exactly in scope of the lease and road investigation in order to reopen it safely and what additional information can we achieve from that operation to add to the wider piece.

RF I mentioned that a quick postscript to that. I mean I would have thought that in order to satisfy yourselves that you were getting all the information that would be necessary for deep engineering, design works to be carried out, then there ought to be serious engineers in the room advising you what information they want and as far as I'm concerned, you know if this goes ahead without that high level input of engineering knowledge, then I think you are at risk of not capturing sufficient information.

RG just to be clear, we work with high level engineers of similar peerage to Roger every day of the week on this project.

RF Are they advising you on what would be required in terms of information capture in order to properly assess the engineering solutions for securing leasing Rd long term.

RG no

RF then I think that should be and that is the scope of what we are tasked with investigating at the moment is the scope of the investigation that will give us the information required to safely reopen the roadways and what monitoring should be in place to give us the early warnings.

RF I formally request that that scope be extended so that the longer-term solutions can be properly and rapidly investigated.

SA - The analysis of the wider coastal requirements is not something that sits with Island Roads, it's definitely a sensible suggestion, but unfortunately it isn't our decision to make.

RF I think that decision does need to be made.

ND what we will take away from today and the advice has been provided from Stephen and Roger is that conversation that we will as a Council have with Island Roads as partners, as to how we can relook at that specification, where those savings are and the value of that additional information that there has to be something to be agreed in a contractual conversation.

RG set out that in the context of the early warning of future failure of Leeson Road in order to open it safely we would need to have full confidence in the historical data rather than the current data that we would not be capturing by making that saving. We have to consider that in the round and how that all fits together with the reasonableness of decision to be made on the reopening.

ND set out that the council is balancing the long term social economic need as long as well as the long-term solution needs to ensure that we can have the road reopened as long as possible that we can reopen the road as soon as possible.

JR - Blindingly obvious to me and to most people who live in that there is a clear existential threat from an economic point of view or from a well-being point of view of many thousands of people and many livelihoods and many local businesses. The risk is clear, the existential risk. I have to absolutely support exactly what's been said here that not to go the extra mile here when we're already incurring a serious investment in terms of the brief so far to not drive forward and go as deep and broad and to broaden the scope would be the miss opportunity that's been identified by Richard and Steven and Roger and just about everybody around this table so.

To me, it would be so fallacious not to do that.

ND - as we have said, there's intention was never to stop bang on 80 basis or 85 metres. The intention has always been to get into below the clay and to the Monks Bay Sandstone.

JR – asked if this is medium- and long-term solution territory?

ND The information that we get from that is not just for the scope of Island Roads, they will use these boreholes for their data monitoring. The council will use the same data to talk to the Environment Agency about long-term coastal solutions.

ND reminded all that we can discuss the long-term strategy for coastal schemes and the undercliff in the second meeting at which the EA will attend in September. The EA are looking at the long-term coastal schemes for Ventnor.

EA coastal Schemes

General discussion about the EA coastal Schemes followed along with a discussion about developing long list and shortlist options from the borehole data to use to seek funding for the longer term. Needing the right data now to inform the future being the key point.

RF set out is this a serious opportunity to get the relevant data that is required not just for that simple question can we open the road without spending lots of money short term, but also to nail it for the full engineering design exercise and options appraisal which he has requested the council undertake which will require establishing broad based costs for securing that road. In his experience in the past working with government and dealing with funding streams and so on and so forth. Basically, if you don't have an idea of what your cost is likely to be, then you can't really have a conversation with the government. The only way you're going to get an idea of what your cost is going to be too long term secure Leeson Road is to design it or to design options for it, which will give you a range of costs which will go to government with and say this is where we're at and this is what we need. You have to have the data; you have to do the engineering work. You have to design it and you have to cost it. If you don't start that chain of events. Now we must get the right data now to feed that whole process. Otherwise, that whole process either will never happen or will be delayed and delayed and delayed.

RM responded to RFs statement to set out from the engineering background, what really is required here is an option appraisal and you would not be investing at this stage in very expensive drilling boreholes in support of an options appraisal because that appraisal will go through like a sifting process long list, short list to preferred scheme and once you get to that preferred scheme, then start to design it.

You develop the reference design preliminary design and then you would probably commission further geotechnical investigations to support that design process.

RM set out that to provide some assurance what I'm seeing here today, the proposals will not only satisfy the requirements of island roads in terms of their fund, but I think this will generate huge value in terms of improving our understanding of the ground model.

In other words, all these dashed lines hopefully will become more solid lines.

I do believe this is going to provide a huge value to take forward that your point is right in the longer term that requires a set of data and that knowledge that we are all saying is required.

RM – to provide assurance from what I am seeing proposed here today I see that this exercise will provide the data and information to inform longer term research and options.

SMcL – Raises two questions.

There are 4 boreholes one is 30 m deep, could it go further south on the landslip debris it would be a relatively short borehole and could intersect with the Sandrock.

 Request for quotation your about to put out I think you need to vary the boundary definition to bring down the cost.

RM – from experience drilling on the landslip itself would cost c.£500k just to secure access the landslide itself before you started drilling which would negate not drilling at the back – it is a nice principle but at this time not cost effective. It is also a health a safety matter.

SA – wo have commissioned a LIDAR survey which will give accurate topographical data and repeat survey will show movement.

MS asked RM on the ground model section what is below the dashed red line under the word landslide debris?

RM clarified it is just landslide debris, the dashed line indicated two different stages of landslide debris / movement of debris.

MS – Martin raised that he has surveyed this with Steven and on behalf of Bruce who has spent a lot of time looking at these beds in the field. Martins stated his interpretation is different to this one (ref Jacob’s slide). Fundamentally, it's not completely different, but the details are a lot different. Some of that will be solved by the boreholes, for example, the thickness of the gault. We’ve got the thickness of the gault there at 50 metres, there's some slight dispute on that. So, the geologists, the two factions, if you like, a disagreeing slightly on the details, which does have an impact on how you solve the problem. I welcome the opportunity to talk to Roger with Bruce at the end of August.

MS requests the Council talk to his group about potentially funding our research or talking to them before we consider other options.

ND – That is not a conversation for today, but we will have it with you.

RG – reminds all parties that the scop we are looking at requires acuity of data, the more data the better. Need to back the option that gives the most reasonable data and acuity of data to provide the grounding for the safe reopening of Leeson Road. That is our scope, but we need to place our acuity in the data that backs that decision.

MS sets out that we all agree at least on one thing that at least one of the boreholes needs to be 110m long.

ND set out that we have all agreed and said in our different ways that we have always intended to go beneath the Gault Clay. It is a known factor, and it is what we are planning to do.

SA agrees and sets out that the driller will know when it changes from clay to sandstone as it will get harder to drill and will probably go a meter of more into that sandstone.

SMcL Requests that the drilling goes deeper into the Monks Bay Sandstone a mater or more to really nail down the beds. Economic case to save money in the top by not sampling whole core provides coast capacity to go deeper in the Sandrock below the Monks Bay Sandstone.

ND and RIR state that discussion will be taken outside between the council and RIR & IRSL.

RF requests that SMcL although not part of this meeting topic, explains what he has talked about in the past about drainage.

ND requests we save discussions on the long-term landslide risk strategies for the September meeting as it is a long topic to unpack.

SA and SMcL agree to have a separate technical chat about drilling.

SA provided assurance to RF that serious engineers are involved in every stage, Atkins (commissioned by IRSL) reports are signed off by Steven Fort, who has worked on the Island with Roger for quiet some time, previously for Rendall Geotechnics.

Group confirm Jacobs are commissioned by IWC to advise the council and Atkins are separately appointed by IRSL to advise Island Roads

RM set out he worked with Steven Fort at Highpoint Rendall in the 90s when Alan Clarke was the head of Geotechnics and then moved onto work for Halcrow who advisors to the council coastal management team were, Halcrow were then bought by an American Company 2M who were then bought by Jacobs.

RG clarifies that no party is working in isolation and from the beginning of this the parties have been working to peer review and challenge the proposals coming forward.

SA also confirms his engineering expertise having joined Island Roads from leading the work in Niton Undercliff working with Steven Fort and Alan Clarke installing the drainage and syphon system, he was the person that installed all of that equipment a site contractor.

MS askes JS to place the overhead picture back on screen to discuss where the group thinks the next piece of the landslide will fail? He believes it to be the triangle of green.

All parties agree, RM states this is already set out in papers.

MS asks if the road is in-situ geology on the greensand bench.

RM agreed that it appears so. However, he is not seeing evidence of pre-failure or stress fractures on the road they are all seaward of the road.

MS asks if the stress fractures are caused by exposure?

RM sets out the stress fractures are guided by the jointing in the upper greensand blocks [looking at ariel picture over 72A] they are very clear blocks, and they are following the joints.

SA sets out that in the pictures below the tearooms you can see the fractures.

MS looking back at the ariel of 72A, questions if RM is calling this (lower garden) the greensand bench.

RM sort of it is a bot complex as there is a lot of chalk debris draped over the surface which is probably late quaternary early Holocene – there is a drape of reworked chalk where the field is and further up you can see the bans of the chert in the green sand structure.

SA questions if we could drill on the field at the back corner.

RM says we already did that in 2002.

SA set out data hasn’t been captured from that borehole because of property owners denying access.

RF questioned if the council are working to acquire via compulsory purchase all relevant properties that could be used in the future for an engineering scheme.

ND – not the council is not at this time looking a compulsory purchase and is not in a position to discuss wat those private property owners are doing with their land.

RF set out that he believes, and engineering solution would require unfettered access to that land under various ownerships at this time and is very surprised to hear the council is not securing that land.

SA returned to the question of the back scarp and where the failure is.

Parties agree the current backscarp will continue to progress back to complete the curve between smugglers haven and 72A as set out in Jacobs’s report.

RM sets out these areas have pre-failed, the cracks in Smugglers Haven car park which are still growing, but further east of this figure (towards Shanklin) there is less evidence of pre-failure, and it seems relatively stable.

SMcL asked what it is that disturbs RM?

RM set out it is principally the bottom-up failure and loss of support.

MS asked if IR filled in the four cracks in smugglers have car park?

SA stated no one has deliberately filled them in.

MS asserted they have been filled in with a sandy material.

Much confusion, no one has filled them in, it is likely sand/fines have washed into the cracks during rainfall.

MS asked if this is where 7mm if movement was detected.

SA clarifies that there is not an extensometer that has measure 7mm of movement, there is an inclinometer that is showing it is tilting by 7mm per meter but these need to be measured over time as there can be environmental impacts over these.

Went on to explain the tiltmeters and what they measure. Confirming they are not exactly still and are showing steady small movements.

MS queries on behalf on Bruce Denness if a Borehole could be relocated north side of the road to be absolutely sure this is in situ geology.

Parties discuss the expense and difficulty of building a ledge into the hill to site a rig within an SSSI.

MS stated the concern is assuming the road in on in situ geology.

RM sets out that it would be his interpretation that it is in situ. We can see the line of the geology across the undercliff and recorded the top as the greensand bench. I am 99 per cent confident that Lesson Road in in situ.

MS asks if that extends to gills cliff road where there is an exposure of chert beds.

RM – no that’s different, it is below the graben and is all displaced. Gills cliff is not in situ, it is below the graben and is all moving.

MS asked if any of this information is to be made public?

RM says this is all well known and has been written up in various papers over the years and on the maps.

MS queries what maps

RM sets out the Ventnor Park Landslide system that Gills Cliff sits within. There is a softening Graben that Gills Cliff is seaward of and there is good evidence that is has been moving for at least 150 years. Every year it is probably moving 40mm seaward.

ND opens the relevant geological maps of the Undercliff.

Long conversation and discussion as RM explain the ground behaviour and geomorphological maps of the undercliff and demonstrates the relic landslides and the in-situ geology across central Ventnor to Bonchurch.

ND offers to make the maps available to this who wish them.

Winding up, all parties round up their views on the need for data capture to inform the monitoring and the future of the road.

Question raised as to if the road will be immediately reopen following the boreholes.

ND confirms that that intention is to reopen as soon as possible. Caveat that we cannot plan for unknown factors.

Brief discussion on the equipment’s monitoring regime and how it will inform the early warning system.

SA sets out that the data monitoring and thresholds will become increasingly sophisticated over time – a responsive automatic closure system will be in place based on thresholds.

SMcL queries why no action was taken when the instrumentation in Nov 23 showed movement?

SA explained the old monitoring equipment was not automatically feeding back but was manually collected monthly.

RM the key learning from the December failure is the need for live data to be appropriately reactive in the future.

MS queried if the road will be closed for 10 weeks.

SA confirmed yes that is the current strategy.

RM asked what was the rationale for locations.

SA set out there are services to avoid in the road and key locations to gather data from, ideally the boreholes would go in the footway, but there are services in there to avoid.

Rig needs space to work safely.

IRSL will consider these locations if achievable for one of the Boreholes.

Technical conversation on the uses of flexible and rigid Bentonite mixes in the boreholes

RM asked if BH 1 could go on the vacant properties – ND clarified they have said no.

RM queries if using the landslide car park or the green adjoining the team room could be used as the geotechnical data would be as valuable as the data from the road and it would reduce the impact.

SA, we have looked at the area of highest impact to the road.

RM I wouldn’t move 3 and 4 next to the team rooms the other long one could go further up the road, could very easily get a rig in the car park if that saves 2 weeks of closure. Just moving one there is a time saving. That’s my challenge to Island Roads

No further queries raised.

Meeting Ends