Supervision of tunnelling constructions and software used for their evaluation

Supervision is a common instrument for controlling constructions of tunnels. In order to suit relevant project’s purposes a supervision procedure is modified by local conditions, habits, codes and ways of allocating of a particular tunnelling project. The duties of tunnel supervision are specified in an agreement with the client and they can include a wide range of activities. On large scale tunnelling projects the supervision tasks are performed by a high number of people of different professions. Teamwork, smooth communication and coordination are required in order to successfully fulfil supervision tasks. The efficiency and quality of tunnel supervision work are enhanced when specialized software applications are used. Such applications should allow on-line data management and the prompt evaluation, reporting and sharing of relevant construction information and other aspects. The client is provided with an as-built database that contains all the relevant information related to a construction process, which is a valuable tool for the claim management as well as for the evaluation of structure defects that can occur in the future. As a result, the level of risks related to tunnel constructions is decreased.


Introduction
Tunnels are being constructed in an environment whose parameters are explored in details only locally priory to the commencement of construction. Therefore, changes to the expected geotechnical conditions are not rare when constructing a tunnel. Contractors adopt an excavation method and rock support as per given conditions in order to construct a tunnel in time manner and quality as per the contract's conditions. The final product, a tunnel, must serve without defects for its entire service life.
There is a large amount of data related to tunnel excavation, geotechnical conditions and rock support obtained a during tunnel construction period. These data are essential not only for the prompt evaluation of rock mass conditions, the determination of excavation and rock support measures and payments, but lately they form a base for the claim management as well as the analysis of possible defects of the structure.
The defects of a tunnel structure or the necessity of its improvement may appear during the operation of a tunnel. The knowledge of an excavation process, geotechnical conditions, used rock support and any complications that happened in the course of tunnelling are vital for choosing a correct remedial action. The later analyses of the conditions are more difficult because tunnel lining covers the surrounding rock mass. The experienced clients incorporated an obligation to provide a database of as-built information into their contract with the supervision and/or the contractor.

Supervision scope of work
Supervision work in tunnelling projects, based on the contract between clients and supervisions, can include, but is not limited to, the below listed tasks: • Check of quality and quantity of contractor's tunnelling work including excavation process and installed rock support • Regular evaluation of tunnel excavations and contractor's performance • Geological mapping • Determination of excavation classes and/or instructions of rock support • Check of health and safety and compliance with environmental regulations • Quality tests of construction material • Design check, proposal of design improvements according to actual conditions; exceptionally designing • Check of the contractor's technical documentation including method statements, as built drawings etc. and proposing improvements • Financial matters -regular check of payment applications, claim management and quasiarbitrator • Client's representation • Regular and ad hoc reports and analyses, Final Report • Holding meetings Some of the above listed tunnel supervision activities are described in more details in the following chapters. Tools used by a supervision to perform the tasks are presented, including the example of an on-line software system specialized in tunnel supervision purposes.

Excavation classes
According to contract conditions the supervision role can include the mapping of geological conditions, the determination of excavation classes and the check/control of rock support to be installed. It is of extreme importance to carry out this work properly because of health and safety reasons, technological reasons and not least economic reasons.
Clients pay contractors for the actual provided work as per contract conditions. In case of tunnel excavations the payments are often made as a cost per linear meter of a tunnel for a particular excavation class. The excavation classes are specified by their excavation methods and used rock support according to geotechnical conditions. There are two kinds of classes -expected (prior to construction) and actual (as built). The construction schedule is based on the expected excavation classes. The difference between expected excavation classes and actual excavation classes has significant influence on both project cost and schedule. Refer to Table 1 for an example which presents the difference between actual and expected excavation classes of a 4km long railway tunnel in the Czech Republic and its influence on project cost.
When the actual geotechnical conditions lie within the limits specified in the contract, it is usually relatively easy to agree on a difference/change between expected excavation classes and actual excavation classes. The impact on construction schedule and cost is then automatically evaluated according to predefined conditions. However, when geotechnical conditions are outside the limits of the contract, then the agreement on additional work and its payment is sometimes difficult to reach, taking into account the fact of not predefined influence on construction schedule and cost.
In both cases -the actual geotechnical conditions are a) within or b) outside the expected limitsproper unambiguous specification of the excavation classes needs to be clearly stated in the contract. There are usually more aspects with the impact on determination of excavation classes. The determination of excavation classes must be carried out by experienced personnel in tunnelling. Unfortunately, sometimes the definition of excavation classes is vague, ambiguous and unthorough. Furthermore, sometimes the specification of expected geotechnical conditions and their limits is incomplete and vague and/or with mistakes. It is wise to define expected geotechnical conditions and their limits in a special document. Such a document is often called Geotechnical Baseline Report (GBR) [2]. However, it is often a case that GBR or a similar document is not provided, especially when projects are located outside Western Europe and North America.

Construction schedule
The supervision shall monitor and evaluate the actual progress of tunnel excavations and should continuously compare it with the scheduled progress. It is an advantage when the supervision is capable of predicting of the future progress of excavations based on statistical methods. Such methods use data from the already excavated sections of tunnels and take into account the effects of actual encountered geological conditions, delays, maintenance periods, learning curve etc. It is a demanding task which needs a special software but when available, then the supervision is able to keep the construction schedule under tight, continuous and realistic control. An example of construction schedule of a 4km long railway tunnel is shown in Figure 1.  Figure 1 shows that that the actual excavation progress b) was delayed in comparison with the originally planned progress a) by 86 days (horizontal offset), which represented 1080m (vertical offset). However, due to aggravated geotechnical conditions, represented in higher/heavier excavation classes with slow advance rate, the progress was delayed by 20 days, which is a horizontal difference between the curves a) and c). The rest of the delay, i.e. 66 days, is on the account of unforeseen geotechnical conditions, unexpected events, learning curve, contractor's delays including breakdowns and extensive maintenance etc.
When these delays are claimed by a contractor, it is up to a supervision to confirm or determine their owner. Having known the high cost of daywork -66 days were equal to approx. 2.5 million EUR in the above mentioned project -it is of the critical importance to follow and record the activities and delays in details during the tunnelling.
Due to the amount of data it is necessary to use a special software application. One of such applications is mentioned in Chapter 7. The application analyzes events, i.e. activities and delays, for any time in the past. The Figure 2 presents a simple chart showing partition of main activities and delays during construction of a 14km long headrace tunnel in Iceland [1]. The tunnel was excavated by a 7.6m diameter hardrock open type TBM, see Figure 3. A noticeable amount of time was spent on the activity No. 7) Utilities, which included repairs of a conveyor belt. As the tunnel conveyor was getting longer, breakdowns in the conveyor belt happened more often and thus the excavation progress became considerably slower. The breakage of the conveyor belt was caused by an insufficient number of installed boosters. Having identified and quantified the true cause of the deceleration of the excavation progress, the issue could be further addressed.

Quality of tunnel structure
A tunnel structure should be constructed as specified in the design in order to fulfil its operational function during its entire service life. The final structure sometimes more or less varies in comparison with the design. There can be more reasons for the variation, such as for example the change in supplied materials, the different procedure of excavation, etc. It is necessary to have all the changes properly documented including the reasons for changes with all relevant records.
In cases when the variation in construction is not agreed, it is required to issue a special form called in many countries "Non-conformance Report" (NCR). The tunnelling industry regularly uses the NCR as a way to keep the track of deviation and work that fails to meet specifications and standards. A NCR should minimally include the information on what exactly went wrong and in which place, what the main reasons were, why the work did not meet specifications and what remedial action should be taken. A NCR is open until the time when the remedial works are undertaken and agreed, after which the NCR is closed. All NCRs shall be closed until a tunnel is handed over for operation to a client.
The remedial actions that are needed for closing NCRs are often time consuming and expensive. Refer to Table 2 and Figure 4 that present an example of time lost and money wastage due to the collapse of rock support and surrounded rock mass during the excavation of a 28km long headrace tunnel in Pakistan. The event happened because the contractor did not comply with rock support specifications. Having all relevant information including NCRs properly recorded the supervision was able to defend the client against the later false contractor's claim for "suddenly worsen geotechnical conditions". It is interesting to note that the direct cost of remedial measures is often much less expensive when compared with the estimated income from a project operation.    Depending on the reasons remedial actions could be paid solely by a contractor, a client or expenses can be shared between them. It is a supervision who has to guide this process. Contractors usually try to include the provided remedial works into claims regardless true reasons. Therefore, it is of a paramount importance to keep all the necessary relevant information related to NCRs. Furthermore, contractors are often directly penalized for any issued NCR according to contract conditions.
There can be plenty of information and documents related to any single NCR. Speaking of tunnels that are often several kilometres long and constructed for a period of couple of years, the amount of