Innovations & Contracting in Tunnelling Adaptive Measures & Climate Change

In a world where infrastructure is the linchpin of sustainable development, the fusion of innovation and contracting takes centerstage in the realm of tunneling. This article delves into the critical role of adaptive measures in addressing climate change and the green transformation of infrastructure. Harald Wagner (PhD, PE, ITACET Foundation Trustee), a leading expert in the field, navigates us through the intricate network of systems, from green energy to cutting-edge tunneling technologies. Uniting innovative concepts and contractual practices, this journey paves the way for a more sustainable and resilient future. Explore the intersection of innovation and contracting, where underground infrastructure plays a pivotal role in shaping the world of tomorrow.

Introduction

Infrastructure is that component connecting all UN Sustainable Development Goals (SDGs). One of the ingredients of success in economic development is innovative infrastructure, which is improving incomes, livelihoods and human well-being.

Efficient methods to generate power and transport goods to major markets have allowed economies and societies to develop global export industries that have created jobs and opportunities. High-speed information infrastructure is needed to support innovation in goods and services.

In the future, achieving high-quality infrastructure development can positively impact economic output via higher construction activity and increased employment. A recent massive wave of investment in infrastructure has the potential to be transformative, as it will support economic recovery, address climate change, and embed new technologies and green economic development models for a more sustainable future.

Green Transformation

The Green Transformation consists of 5 active components:

• Green Energy
• Green Infrastructure
• Green Finance
• Green Innovation
• Green Production, Consumption & Waste.

New infrastructure needs to be green in order to be sustainable. Green infrastructure will play a critical role as none of the green transformations can be achieved without some direct or indirect input from infrastructure.

The next phase of infrastructure investment needs restructuring of economies to become sustainable. Economies across the world are shifting from polluting fossil fuel energy production to zero pollution renewable energy, zero-emission vehicles, more efficient infrastructure and smart cities. Financial institutions are beginning to check climate risks.

International infrastructure investment will benefit from globally consistent, transparent baseline standards, which are under development by the new International Sustainability Standards Board.

Network of Systems

Thanks to a network of systems covering communication, energy, transportation, trade, and supply, people can transmit comprehensive information from any global location. To develop such an infrastructure, communication shall preferably be digitized, energy based on renewables, transportation based on clean energy, and supply chains shall work without regulatory friction between countries and continents.

In urban tunnelling, any approach has its limitations in adequately describing the Ground-Structure-Interaction (GSI). Applied approach is of eminent importance in evaluating unforeseeable risks. Tunnel excavation causes disturbance of initial state of stress creating 3-Dimensional-Stress-Regime umbrella like at the tunnel face. Each Simulation of Excavation & Installation of Initial Support shall analyze risks and ground response.

Digital transformation and engineering based on experience helps to fast-track green underground solutions towards the delivery of UN Sustainable Development Goals (SDG). It helps to limit risks in urban tunnelling and supports contacts with infrastructure industry.

Full support is given to “rated criteria” approach at procurement, which has been hailed as a “game changer” for promoting value in procurement. The rated criteria approach underlines the objective of achieving SDG objectives. International procurements shall require use of rated criteria including risk analysis in addition to price as part of bid evaluation.

Assumption Verification

An integral part of tunnelling is data verification by means of in-situ monitoring of design assumptions made regarding the interaction between the ground and initial support. Collapses happen and contractors claim for not reasonably foreseeable. All subsurface physical data described in tender documents are deemed to be foreseeable, and subsurface physical data outside scope of conditions defined in tender documents are deemed to be unforeseeable. Figure 1.


The contractor shall be deemed to have based proposals for excavation and lining works on the subsurface physical conditions and ground reactions described in the tender documents irrespective of any discrepancy or ambiguity that may be found between such conditions and/or reactions and conditions described in any data made available.

Physical conditions mean natural physical conditions and reactions of the ground to excavation encountered, having been unforeseeable and having an adverse effect on the progress increasing cost of execution. It shall be assessed under measurement of excavation and lining works and adjustment of time for completion and contract price. Even under conditions of actual increasing geotechnical observational data, elimination of unforeseeable risks per se would lack factual geotechnical uncertainty in underground construction.

In view of climate change, being an issue of global relevance, there are two major areas of global underground infrastructure network development. One is urban development, which is shifting population from rural areas to urban areas, in many cases into coastal environments. It is expected that after the middle of the 21st century about 2/3 of the world population will be living in cities. Examples of global urbanization can be observed on all continents.

There is a minority of civil engineers on the political stage. Investments into infrastructures are influenced and decided by politicians, who depend on competent advice of civil engineers.

It represents a textbook aiming to support interested public and private decision maker teams to easy understand technological and practical state-of-the-art in advanced tunnelling technologies, considering interactions between contracting, design, and construction.

Innovation Features

Innovation in Underground Technology shall be inspired by nature, where trees are using rocks both on surface and at rock joints to grow. Actual exemplified technical innovations in underground design and construction are featured i.e., by following pioneering techniques.

Innovations in Conventional CTM/NATM Tunnelling

• CLAY/SILT – Soil Stability Improvement
• DOUBLE DECK for Transport Tunnels
• STEEL ARCHES Inclined settlement control
• LOAD DISTRIBUTION Rails and shotcrete
• FINAL LINING with Shotcrete
• MULTIPLE DRIFT binocular metro Stations
• WATERPROOFING Sprayed Membrane
• HYBRID Shallow Tunnelling
• STEEL FIBER reinforced wet processed Shotcrete.

Mechanized TBM Tunnelling

• VERTICAL TRENCH with prefabricated one pass Di Walls
• UNIVERSAL RING Precast one pass liners
• CONTROLLED KINEMATIC- Connectors
• SIMULTANE TUNNELLING-Dig/Support
• FLAT JOINT DESIGN
• SEALING Tunnels with Precast Segments
• CAVERN Construction with Machines
• SINGLE PASS unified precast segments
• UNIFIED Circumferential Joint Connectors
• UNIFIED L-Joint Sliding Guiding Rods
• CONTRACTS with integrated GBR and RMP. Figure 2.

Uniting Technologies

Protruding merit has been achieved by uniting Technologies and Geomechanical Principles of ‘Conventional Tunnelling’, globally recognized as ‘New Austrian Tunnelling Method (NATM)’ with Principles of ‘Mechanized Tunnelling’ (TBM). Innovations reflecting detailed structural components of excavation and support in both technologies, as well as implementation of new contractual practices, resulted in mostly expired intellectual property rights.

Since 1970 there have been intense discussions when it came to evaluation, choice and decision making between NATM/CTM (Conventional Tunnelling Method) and TBM (Tunnel Boring Machine Method), called Mechanized Tunnelling. Since then, a gradual approximation between the two Tunnelling Techniques, accompanied by advanced in-situ observation & monitoring has taken place.

Conventional Tunnelling Method (CTM)NATM - The New Austrian Tunnelling Method - was developed in the 1960s, and is the best known for a number of engineering solutions that use calculated and empirical real-time measurements to provide optimized safe support to the tunnel lining. The main idea is use geological stress of surrounding rock mass to stabilize the tunnel itself, by allowing a measured relaxation and stress reassignment into surrounding rock. Figure 3.

With Conventional Tunnelling, design parameter designation shall be carried out by the clients engineering team, by the consultant’s design offices, or by the construction contractors design team, where the consultant is cooperating closely with the client being finally responsible for design in all phases of the tunnel respectively the cavern project.

Various types of tunnels are dug in types of materials varying from soft clay to hard rock. The method of tunnel construction depends on such factors as the ground conditions, the ground water conditions, the length and diameter of the tunnel drive, the depth of the tunnel, the logistics of supporting the tunnel excavation, the final use and shape of the tunnel and appropriate risk management.

Tunnel Boring Method (TBM): Bored tunnel method is a modern technology, where tunnel boring machines are used which automatically work and make the entire tunneling process easier. It is also a quicker process and good method to build tunnels in high traffic areas. TBM’s are available in different types suitable for different ground conditions. These machines can be used in difficult conditions such as below the water table etc. A special pressurized compartment is provided for TBM to work in below water table conditions. The workers should not enter that compartment except for repair works. Care should be taken while TBM is working. Figure 4.

Mechanized Tunnelling Technology is used to highly automate the entire tunnelling process, reducing tunnelling costs. In certain predominantly urban applications, tunnel boring is viewed as quick and cost-effective alternative to laying surface rails and roads. Disadvantages of mechanized tunnelling arise from usually large size equipment - difficulty of transporting the large machine to the site, or (alternatively) high cost of assembling on-site. Figure 5.

Cut & Cover Technology in construction is generally used to build shallow tunnels. In this method, a trench is cut in the soil and it is covered by some support which can be capable of bearing load on it. The cutting can be done by two methods. One is bottom-up method in which a tunnel is excavated under the surface using ground support. Another method is the top-down method in which the side support walls are constructed first by slurry walling method or contiguous bored piling. The roof is placed on the top of the walls and excavation is carried out. Finally, the base slab is constructed.

As technologies have pros and cons, it is fair to state that tunnelling techniques have benefitted from each other. The fields of competition have shifted from Geomechanics towards Contract, Schedule, Cost, Geotechnical Baselines and Risk Management, and Innovation in Contracting.

Creating Contracts

The stakeholders in the contract are the owner/employer, the contractor, and the engineer being the employer’s representative, whereas contractual clear relationships shall be established between employer and engineer as well as between employer and contractor. There shall be only an administrational relation between contractor and engineer. For settlement of disputes, a dispute adjudication board shall be established above employer and contractor.

Contracting shall be featured by balanced terms and clauses, allowing for application of common laws including civil laws. They shall be widely applicable under various project delivery and contracting concepts. More specific provisions shall be included regarding obligations of parties and their rights. Management procedures shall correspond with the latest developments. Late payment problems shall be tackled as well as the role of the engineer shall be updated.

To best keep control of projects, the responsibility of the client must include proper organization in various design phases and his involvement in main project aspects in order to make good choices of most suitable conditions of contract. Upon project analysis, subject and type of contract (construction only, design & build, etc.), risk sharing (construct or be involved in design), intended management of contract/project, type/method of payment, shall be decided.

Cardinal Objectives

Objectives of innovative infrastructure construction contracts are

• Construction of Project itself
• Support for Capacity Building
• Institutional Strengthening of developer
• Increase Supply - energy/addition of renewable, low-carbon energy
• Strengthen Sustainability - economically, environmentally, socially.

Summary

Innovative Tunnel projects shall start with a comprehensive investigation of ground conditions by collecting samples from boreholes and by using geophysical techniques. An informed choice can then be made of means and methods for excavation and ground support. In investigating various routes, horizontal and vertical alignments optimization of best ground conditions and water influence shall be achieved.

Independent from the choice of tunnelling technology, Conventional Tunnelling or Mechanized Tunnelling, young tunnel engineers are advised to use as geotechnical key factor “stand-up time”, being the amount of time, a newly excavated cavern can support itself prior to any added structural support.

Knowing this key parameter allows the design engineers to determine, how far an excavation can proceed before support is needed, which in turn affects the speed, efficiency, and cost of construction.This assumption presumes that the contractor is experienced and able to implement support at conditions specified in the contract documents. Conditions encountered at the tunnel face and conditions defined in the GBR (Geotechnical Baseline Report) are to be compared and evaluated.

Financing institutions are advised to engage competent/experienced Consultants in support of the owner to review/improve the management systems and processes, especially with respect to schedule, contract and risk management.

Bibliography

• H. Wagner. “Tunnel Construction Technologies & Risk Practices – Inevitable Risks of Collapses in Construction”. Tunnelling Asia 2022. International Conference on Underground Space – The Need of the Day. Page 97 – 110. Mumbai/India, June 27-28, 2022.
• H. Wagner. “Urban Underground Space Sustaining Life Cycles”. ITA-AITES World Tunnelling Congress WTC 2022. Copenhagen 2 – 8 September 2022.
• H. Wagner. “The Genesis of Underground Engineering”. NBM&CW Tunnelling Technology Publication. October 2022.