We have published an update about the tunnelling aspect of the proposed LTC before, including details of the Tunnel Boring Machine that would be used, if the LTC goes ahead. Now National Highways/LTC are talking about whether to use one or two Tunnel Boring Machines .
We’ve been told previously that the tunnelling would take 4.5 to 5 years, and would be done using two Tunnel Boring Machines, starting from the North side of the River Thames, with spoil coming out the back of the Tunnel Boring Machines (TBM) to where it would largely be used north of the river.
Now it seems they are proposing they may start tunnelling from the north and possibly then turn the TBM around on the south side of the river, and turn it back across to north of the river, with the spoil that ends up south of the river from the TBM being taken back through the first tunnel.
Of course they appear to be saying a change from 2 TBMs to 1 TBM wouldn’t have any negative effects, and even go so far as to claim it would reduce carbon emissions by 38,000 tonnes. However, as we read the update in the consultation booklet, what we were reading just generated lots of questions to send through to NH/LTC, which we’ve shared below.
We will comment further on this update as we hear back from NH with more info and answers to our questions!
If you have any questions or need any of the info in the consultation booklet explained or clarified please email NH/LTC on firstname.lastname@example.org or call them using 0300123 5000. (Remember if you call that is an answering service and they will simply take your details and ask someone to call you back, you won’t get instant answers)
The consultation booklet says that it will be up to the contractor to decide whether 1 or 2 tunnel boring machines would be used, if LTC goes ahead. But please do consider commenting on this in your response to the Minor Refinements Consultation too. Deadline 23:59 on Mon 19th June 2023.
TCAG questions to NH/LTC on Tunnel Boring Machines
Q1. Please advise what the estimated cost of using two TBMs would be, and also what the estimated cost of using 1 TBM would be.
“We are currently in the process of procuring the delivery partner for the Tunnels and Approach Roads contract. We anticipate cost savings could be derived from using one tunnel boring machine (TBM), however costs will not be firmed up until the procurement is completed. No decision has been taken on whether one or two TBMs would be used.”
Q2. Please provide details of how material use would be reduced. What exactly does this mean?
“In this context material means manufacturing one TBM rather than two. This would reduce the use of the materials needed to build a TBM, such as steel.“
Q3. Please advise how the reduction of 38,000 tonnes of carbon emissions has been calculated, since you would still be completing two tunnels and therefore the same amount of work must need to be done regardless of whether it is done with 1 or 2 TBMs?
“The reduction in carbon emissions relates to the reduction in machinery required for one TBM, for example the reduced TBM steel required to build one TBM rather than two.“
Q4. If 1 TBM were used, what process would be used in regard to the slurry treatment and segment production facilities? Surely you would need to have slurry treatment and segment production facilities set up on both sides of the river at one time or another as they would need to be on the side the TBM starts off from?
“Slurry treatment and tunnel segment production remains the same as described in the Environmental Statement Chapter 2 – Project Description [APP-140]. Please refer to paragraphs 2.7.147 to 2.7.150. All tunnel production activities remain within the North portal, and slurry from the northbound tunnel drive would be pumped through a pipe network to the north portal through the tunnel that would already have been constructed by the southbound drive.“
Q5. When it is stated that if one Tunnel Boring Machine was used the spoil from the second tunnel would be taken back through the first tunnel to the north of the river, please can someone advise how it would be taken back?
“The spoil arising from the tunnelling process, as described in the consultation material, will be a slurry of chalk and water, which is fluid and can be pumped through pipelines. The excavation arisings from the tunnelling, suspended in a water-based slurry as detailed in the Environmental Statement Chapter 2 – Project Description [APP-140], Paragraph 2.7.147 will be pumped via a pipe network from the cutter head back to the slurry treatment plant (STP) which is located within the North portal. This process remains unchanged for a single TBM, with the pipeline passing through the first tunnel during the construction of the second tunnel.“
Q6. Please provide details of how many additional vehicle movements would be generated taking the spoil back through the tunnel to the north of the river.
“None, as the material would be pumped through the tunnel.”
Q7. Please provide details of how much additional emissions would be generated taking the spoil back through the tunnel to the north of the river.
“None, as the material would be pumped through the tunnel.“
Q8. If vehicles are used to transport spoil to the northern side, using the first tunnel, will the tunnel be used by two way traffic, or would the returning vehicles use a different route?
“As above, vehicles will not be used.”
Q9. Please signpost us to which DCO application documents you are referring to when you state “The overall construction programme set out in the DCO application would remain the same”.
“Please refer to the Plate 2.13 on page 147 in the Environmental Statement Chapter 2 – Project Description [APP-140].”
Q10. The consultation booklet states that “the construction works required at the northern tunnel entrance before the tunnelling can start would be smaller in scale, allowing tunnelling to start approximately 10 months earlier in the programme”. Please advise how works can be smaller in size, as presumably the same amount of work ultimately would need to be done to create two tunnels. What are the works you mention? How does it take 10 months less and how can you start sooner?
“The size of the initial portal structure will be smaller to launch a single TBM (approximately half the size). The remainder of the structure will be excavated for receipt of the returning TBM, but this will be undertaken after the TBM launch.“
Q11. Please advise how many staff would be used if two TBMs were to be used, and also how many staff would be used if one TBM were to be used.
“Please refer to the Workers Accommodation Report [APP-551] for information on estimated worker numbers for TBM(s). Numbers for one TBM will be slightly lower associated with the reduction in the number of TBMs.“
Q12. Whilst you may use fewer staff if only using one TBM, surely they would be needed for twice as long?
“The TBM crew would be required for longer, however they form a small proportion of the number of staff that would be employed at the northern tunnel compound.”
Q13. How many extra staff would be needed to turn the TBM round for the return journey back to the north side of the river?
“This work will be completed by the same tunnel contract workers. There are no additional workers required.”
Q14. Please provide details of the staffing patterns for each option, with one TBM and with 2 TBM.
“Staffing patterns will be determined by the Delivery Partner.”
Q15. Would the workers accommodation all still be on the north side of the river?
Q16. Would any additional set up/units etc be needed south of the river if only 1 TBM is used?
Q17. Please provide details of what change to the numbers of staff vehicles over the construction period there would be. Again surely the number of vehicle movements would not be reduced overall?
“As noted within the consultation booklet, there would be an overall reduction in movements related to the tunnelling activities if a single TBM was chosen. As the remainder of the construction programme and movements would not be affected by this change, this means that overall the total number of vehicle movements would reduce.“
Q18. Please provide data on how many journeys would be made to both the northern and southern compounds for each option of using 1 or 2 TBMs.
“The two TBM assessment provides an assessment of the reasonable worst case number of journeys, which is set out in Chapter 8 of 7.9 Transport Assessment [APP-529]. Please refer to Question 17 which provides information on how this changes if a single TBM were to be used“
Q19. Please provide information and data on the increase in journeys related to construction in the second year. How many, and how this is calculated for instance
“As set out in the consultation booklet the change to a single TBM would not have any materially new or different environmental effects arising compared to those presented in the DCO Application. The forecast impact of the construction of the Project remains as is set out in Chapter 8 of 7.9 Transport Assessment (TA) [APP-529]. The assessment within the TA makes a number of assumptions which are set out at paragraph 8.1.7; as such it is considered this assessment represents a reasonable worst case.“
Q20. How can the traffic during the most intensive construction phase be slightly lower than compared with using 2 TBMs?
“As noted within the consultation booklet, use of a single TBM would require fewer staff, therefore there would be fewer vehicle trips.”
Q21. How much lower would it be? How do you make that calculation?
“As set out in the consultation booklet the change to a single TBM would not have any materially new or different environmental effects arising compared to those presented in the DCO Application. As set out in the answer to Question 17, the number of movements would reduce overall. Details of how the construction assessment has been developed is set out in Chapter 8 of 7.9 Transport Assessment [APP-529].”
Q22. When do you consider the most intensive construction phase to be?
“The proposed construction programme would be complex in nature, lasting for a number of years and covering a wide area. Given its complexity, there is no one phase that is most intensive in all locations. The forecast impact of the construction of the Project remains as is set out in Chapter 8 of 7.9 Transport Assessment [APP-529].“
Q23. When you have previously quoted tunnelling would take 4.5-5 years was this with both TBMs tunnelling at the same time simultaneously, or sending one through, then setting it back up north of the river to do the second tunnel?
“The duration referred to relates to the tunnel construction as a whole and includes fit out and commissioning”
Q24. How long would it take one TBM to tunnel each tunnel?
“The indicative tunnelling programme remains consistent with the programme shown in Plate 2.13 on page 147 in the Environmental Statement Chapter 2 – Project Description [APP-140].“
Q25. How long would it take to turn the TBM around, if only one is used?
“The indicative tunnelling programme remains consistent with the programme shown in Plate 2.13 on page 147 in the Environmental Statement Chapter 2 – Project Description [APP-140]. The duration of the turn around will be determined by the Delivery Partner.“
Q26. How long would the overall tunnelling be expected to take?
“The indicative tunnelling programme remains consistent with the programme shown in Plate 2.13 on page 147 in the Environmental Statement Chapter 2 – Project Description [APP-140].”
Q27. Please provide details of the process involved in setting up, turning, and dismantling the TBMs. Would cranes be needed at both ends? How long would the cranes be set up for? What would the additional vehicle movements associated with the cranes be?
“There is no change to the process for setting up or dismantling the TBMs. The TBM will be turned around using temporary moveable platforms. There are no additional fixed cranes required to turn the TBM around and no additional vehicle movements required for cranes.“
Q28. Please provide further details of the negative impacts to those living south of the river, as clearly there would be a significant difference between them having the TBMs arrive south of the river compared to having one TBM that needs to be turned around and then all the spoil arriving south of the river and having to be taken back to the northern side.
“The TBM will be turned around within the southern portal structure. There are no changes to the impacts already assessed for those residents south of the river associated with the turnaround of the TBM or a south-north tunnel drive. Please refer to Q5 for details on the slurry movement.“
Q29. Will you be questioning the shortlisted contractors on whether they will use 1 or 2 TBMs prior to awarding the tunnels contract?
“The bidders will set out their proposed construction methods in their tender submissions.”
Q30. If not how can you fully assess which contractor to award the contract to, as this must impact things like costing etc in tenders?
“The bidders’ submissions will be assessed against a number of set criterion determined as part of the procurement process.“
Q31. Please advise whether the ‘minimal changes’ that would alter the air quality would result in a worsening or improvements of air quality.
“The reference to minimal changes means that a single TBM methodology does not change the conclusion of the air quality construction phase assessment already presented in the Environmental Statement (Refer to Chapter 5 – Air Quality [APP-143]) and no materially new or different significant effects were anticipated as a result of using a single TBM.”
Q32. Please provide details of how you have assessed and reached your conclusion.
“Potential impacts were assessed against those detailed in the relevant chapters of the Environmental Statement to determine if the change in tunnelling methodology presented a change in significant effects or introduced any materially new or materially different environmental effects to those identified in the Environmental Statement. Please refer to the construction related environmental assessment of using a single TBM approach provided in the consultation materials.”
Q33. How can you say that the construction works required at the northern tunnel entrance before the tunnelling can start would be smaller in scale, but also say there would be no change to the impacts in regard to effects on cultural heritage?
“As set out in the consultation booklet the change to a single TBM would not have any materially new or different environmental effects arising compared to those presented in the DCO Application.”
Q34. How can there be no change in noise and vibration if you were to use 1 TBM as there would be additional noise and vibration associated with taking the spoil from south of the river to north of the river?
“Please refer to Q5“
Q35. Considering the additional spoil movement, how can you say it would not impact people’s health and wellbeing with that happening right on their doorstep?
“Please refer to Q5“
Q36. Where will the water supply for the TBM come from south of the river, if only 1 TBM were used?
“Water supply for tunnelling operations remains unchanged and will be serviced from the northern portal. Please refer to Environmental Statement Chapter 2 – Project Description [APP-140] paragraph 2.6.138 b.”
Q37. What has prompted you to suddenly start considering whether to use 1 or 2 TBMs after so many years of planning and consultation?
“The assessment of 2 TBMs provides an assessment of a reasonable worst case and provides the flexibility to use 1 or 2 TBMs, provided the impact is no greater than that assessed in the DCO documentation. As set out in the consultation document if we are granted permission to build LTC then our contractors would determine whether to use 1 or 2 TBMs.“
Q38. Have you carried out any meetings or discussions with HS2 in regard to the tunnelling sinkholes and bubbling and foaming above tunnelling activities so you can ensure nothing similar happens if LTC goes ahead, especially considering latest reports suggest the issues are related to the chalk in the ground where the HS2 tunnelling is taking place, when so much of the proposed LTC route is through chalky ground too?
“We regularly meet with other major projects to learn lessons across different programmes relating to a range of matters. HS2 have confirmed their investigations are ongoing.”
A few more questions in addition to the previous ones on TBM:
Q39. Our understanding is that the haul road was going to be put in place prior to tunnelling beginning. If it is being proposed that the start of tunnelling could potentially be bought forward by 10 months can someone please confirm whether this would still be after the haul road has been created, if LTC goes ahead?
“There is no change to the timing of the construction of the haul road. Tunnelling will commence after the haul road is sufficiently completed to enable the delivery of construction equipment for the northern portal and TBM construction. “
Q40. Can you please share the predicted timeline on the tunnelling within the construction period if only one TBM were to be used please.
“The timeline for tunnelling remains consistent with the indicative programme provided in Plate 2.13 on page 147 in the Environmental Statement Chapter 2 – Project Description [APP-140]. “
Q41. The ‘Cultural Heritage’ section of the table on page 31 in the construction booklet refers to adverse effects in relation to the construction of the northern tunnel entrance. Please can someone clarify whether there would any effects in relation to the southern tunnel entrance.
“There is no change to the southern tunnel entrance as a result of using a single TBM and as such, no changes to the cultural heritage assessment in the Environmental Statement. “
Q42. The ‘Landscape and Visual’ section of the table on page 31 in the consultation booklet refers to impacts of the southern tunnel entrance compound etc. Please can someone provide similar details for north of the river too.
“There are no new or different landscape and visual effects anticipated in the northern compound.“
Q43. The continuation of the ‘Material Assets and Waste’ section of the table on page 32 in the consultation booklet states that “A single TBM would still generate the same volume of material…..” Yet the ‘Material Assets and Waste’ section of the table on page 17 states “No new or different significant effects are anticipated” and “There would be a minor reduction in material use associated with this change. There would also be a minor reduction in construction waste generated and material excavated during construction. Please can someone clarify as this appears to be contradictory.
“The reference to material on Page 32 relates to the slurry material generated during tunnelling and the associated use of tunnel material. The reference on page 17 relates to the proposed change to the limits of deviation for the northern portal headwall. The clarification on tunnelling methodology and the proposed change to the limits of deviation for the northern portal headwall are not connected and there is no contradiction as the two statements are unrelated.“
Q44. Please can someone advise whether the TBM/s would be rented or bought, if LTC goes ahead?
“The TBMs would be procured by the Delivery Partner. It will be a matter for them which procurement route they choose.”
Q45. If rented, how can it be considered a cost saving to use only one as it would need to be rented twice as long?
“Irrespective of the procurement mechanism taken by the Delivery Partner there would be savings from the use of only 1 TBM both in terms of its procurement and operation.”
Q46. If bought, please provide the estimated cost, and what would be done with the TBM/s after LTC is constructed (if it goes ahead)?
“Costs for TBMs will form part of the bids for the Tunnels and Approaches contract. The TBMs would likely be dismantled and recycled at the end of construction, however that is a matter for the appointed delivery partner.”
Northern Tunnel Portal changes – click here
LTC Tunnel – click here
Taken from the DCO application documents (so subject to change if NH submit changes):
2.12 Tunnel Area Plan (APP-042) – click here
2.15 Tunnel Limits of Deviation Plans (APP-046) – click here
6.3. Environmental Statement – Appendix 9.1 – Assessment of Ground-Borne Noise and Vibration, and Underwater Noise from the Tunnel Boring Machine at Marine Receptors (APP-420) – click here