4 TUNNEL
4.1 PRIMARY SUPPORT OF SPRAYED CONCRETE LINING TUNNELS
4.1.1 Description
1. The Contractor shall, with due regard to the safety and stability of the Works, above ground buildings and all other structures above and below ground, implement a primary support shell in tunnels immediately following excavation using conventional means (i.e. not by TBM), where applicable.
2. The design of the primary support shell of the sprayed concrete lining tunnels of the Works shall aim at their adequate dimensioning, by appropriately addressing any ground improvement applications ensuring:
(a) The safe construction of the tunnels primary support structure itself;
(b) The sprayed concrete lining shall arrest ground movement;
(c) The primary support shell of the tunnels shall not be considered at all in the design of their final lining.
4.1.2 Sprayed Concrete Tunnel Design and Analysis Methodology
1. A structural analysis shall be performed for each tunnelling class with the following objectives:
(a) To verify that the primary support measures foreseen for this class are sufficient, safe and cause acceptable tunnel wall convergence and ground movements; and
(b) Calculations for the safety factor of the design for this tunnelling class. This shall be achieved by performing a supplementary analysis of a specific tunnelling class, using the geotechnical parameters of the immediately inferior class.
2. The structural analysis shall be performed in two-dimensions (i.e., assuming plane strain conditions). In special cases (e.g. in the design of tunnel intersections or under adverse geotechnical conditions), 3-D analyses shall be performed;
3. Two-dimensional analyses shall include the 3-D effects of the tunnel excavation face by one of the following methods:
(a) Internal pressure reduction method, i.e., by reducing the internal pressure of the excavated cross-section to a value compatible with the wall convergence, at the location where the primary lining is installed; or
(b) Modulus reduction method, i.e., by reducing the modulus of the excavated cross-section to a value compatible with the wall convergence, at the location where the primary lining is installed;
4. The Contractor shall investigate and assess, as necessary, any structures which are below and above the tunnel regarding possible adverse influences on the tunnel works below and address the results of such findings in his design;
5. Given that the presence and the nature of the ground water affect the sprayed concrete lining design, the following factors shall be examined:
(a) The range of groundwater pressures during the construction phase, in short-term and mid-term conditions;
(b) The impact on any structures (i.e. impact on building foundations, subsidence etc.) due to the changed ground water level during the tunnel excavations;
(c) The impact of water on the geomaterials being excavated, such as looseness, disintegration and/or swelling etc;
(d) The design of the appropriate drainage system for the works, regarding short-term and mid-term inflows; and
(e) The local drainage characteristics of the surrounding geomaterials shall be taken into account for the determination of the most appropriate method for excavation and control of the ground water;
4.2 TUNNEL FINAL LINING
4.2.1 General
1. The tunnel final lining structures consist of either the following:
(a) Reinforced cast – in situ concrete; or
(b) Reinforced precast concrete segmental rings.
2. These shall be designed and constructed in a manner, which ensures that any movements and deformations, which may result from the most unfavourable possible loading conditions, will not exceed (in any case) limits beyond which these structures lose their structural capacity and integrity, either during construction or during their prescribed design life of 120 years.
3. Tunnel final linings shall be designed in accordance with the provisions of the Design Specification, entitled “Design Loads”.
4. The primary support shells of the tunnels shall not be considered in the design of the tunnels final lining.
5. The design of tunnels final linings shall not allow for any long term relief and/or effect related to ground arching effects (i.e. full overburden pressure shall be taken into account in the design).
6. The distribution of the lateral ground pressures on to the tunnels final linings shall consider the construction method, the relative rigidity of the lining and the interaction of the lining with the ground. The tunnel final linings shall be designed to withstand the at-rest earth pressure (K0 conditions), unless it can be demonstrated and fully justified to the Engineer that these pressures will not occur in the long term after stress relief caused by the excavation. This may be the case where the overburden height (ground surface to tunnel(s) crown distance) is greater or equal to 3 times the tunnel excavation diameter and the existing ground conditions (overlying and surrounding the tunnel(s)) are homogeneous in terms of their stiffness and shear strength characteristics. Any reduced earth pressures shall not be used in the following cases of ground and groundwater conditions, or other cases directed by the Engineer:
(a) Extensive karstic depression zones.
(b) Extensive highly weathered formations.
(c) Formations with high swelling potential.
(d) Areas of high groundwater pressures of “artesian nature”.
7. The design of the tunnels final linings shall consider the full hydrostatic groundwater pressures, with consideration of the maximum long – term levels of the existing groundwater tables (design groundwater level).
8. Tunnel final linings shall be designed to resist grouting pressure.
9. The design of the tunnels final linings shall comply with the safety requirements of Eurocode 2 (EN1992) for concrete structures, Eurocode 3 (EN 1993) for steel structures and Eurocode 7 part 1 (EN1997-1) in terms of the applicable partial factors and design approaches.
10. Specifically, for fire safety, the design of the tunnels final linings shall comply with the fire safety requirements mentioned in the Design Specification, entitled: ‘Fire Protection and Life Safety Requirements’.
11. For the seismic analysis of the tunnels final linings, this shall comply with the relevant provisions of the Design Specifications, entitled: ‘Tunnel Design Specification’.
4.2.2 Minimum Design Requirements
1. Concrete intended for use in the tunnels shall comply with the specifications of QCS and EN 206 (with the most conservative standard prevailing in the case of conflict) and for:
(a) Cast in-situ concrete structures the minimum design concrete class shall be C30/37 and the reinforcement shall consist of high ductility bar of minimum category B500C; and
(b) The tunnels’ precast segmental lining, the minimum design concrete class shall be C40/50 and the reinforcement shall consist of high ductility bar of minimum category B500C, or approved alternative reinforcement.
2. For the design of the reinforced precast concrete segmental rings, the following are essential:
(a) Segmental linings shall be designed not only for the ground and groundwater pressures, but also for all handling, transportation, stacking and erection forces with an allowance for impact. In addition segmental linings shall be designed to resist all forces which may be applied by the equipment used for this;
3. For segmental linings, the design shall take into consideration the contact stresses at the joints and the bending caused by the loads eccentricity at the joints. The strains imposed on to the concrete shall be received by specially placed reinforcement in the area of the segment’s face (area where pressure is exerted by the TBM thrust jacks);
4. The layout of the structure and the interaction between the structural members shall be such as to ensure a robust and stable structure. Adequate jointing between precast elements or between precast members and cast in-situ structures shall be achieved using appropriate reinforcement and/or special ties in order to ensure their stability and waterproofing, even when subjected to accidental stresses (such as excessive impact, fire, etc.) and possible differential pressures of the supports.
4.2.3 Minimum Construction Requirements Applicable in the Design
1. Continuous end-to-end cracking of the concrete is not permitted. The Contractor shall document and justify minimum reinforcement requirements, subject to a SONO from the Engineer.
2. Depending on the soil and ground water aggressiveness, which will be identified after the appropriate sampling and testing, all necessary measures shall be taken, consistent with the overall design life of the Works and as reasonably determined by the Contractor, in order to ensure reduced permeability and increased resistance of the final lining. These measures shall be submitted to the Engineer for a SONO and include (indicatively but not limited to) special concrete mix (admixtures, special cement etc.), construction measures (larger concrete cover, additional surface reinforcement, curing etc.), special design (limitation of cracking etc.), coating of the exterior surface of the lining, by using special resistant materials, special reinforcement, special resistant waterproofing gaskets (for segmental lining) or waterstops (for cast in- situ lining).
3. The presence of a primary support lining shall not be taken into consideration for determining which surface is in contact with water or soil or with lean concrete.
4. In all areas of the Works, for which there is a provision for cross-passages and the connection of the TBM tunnel to shafts, recesses for E/M installations, etc., specific parts of the precast segments of the main tunnel shall be cut. Cuts shall be made in the main TBM tunnel with precision after installation of the TBM tunnel segments, using the undisturbed cutting method, and shall be made only at the intersection of the connecting tunnel with the main TBM tunnel and geometrically correspond to the outer perimeter of the connecting tunnel. The entire procedure shall be performed diligently so as not to cause any damage, displacement, loosening or disconnection of the precast segments of the main tunnel. All relevant designs shall follow and incorporate this method.
5. Tunnels shall be checked for uplift using:
(a) The dead loads;
(b) All permanent loads; and,
(c) The uplift groundwater pressures.
6. Regarding ground water levels, the Contractor’s calculations shall be based on the worst-case scenario likely to occur within the design life of the Works, as this will be estimated on the basis of the appropriately evaluated hydrogeological data (including predictions about ground water fluctuations during the design life of the Works). Any possible effects from the presence of the structure on the groundwater flow shall be considered in the calculations.
7. Where necessary, a construction sequence adequately safeguarding against uplift during all stages of construction shall be indicated on appropriate drawings.
8. The tunnels’ uplift safety factor shall be determined on the basis of paragraph 2.4.7.4 and 10.2 of EN1997-1.
4.2.4 Submissions
1. The design of tunnel final lining shall include, but not be limited to the design report, the calculations, any documents related to additional checking or annexes of the calculations, the construction drawings and any other supporting material needed for the better substantiation of the design.
2. The design report shall include at least the following items:
(a) Table with the basic design assumptions;
(b) Table with the geotechnical and geometrical characteristics of the soil stratigraphy, as well as sketches of the geotechnical cross-sections;
(c) A separate chapter in which the structural analysis models shall be clearly described and fully substantiated. This chapter shall contain a detailed description of the individual components of the various models, such as their geometry, their supporting and coupling conditions, the moment of inertia and elastoplastic properties of all members, as well as the properties of any springs or elements used for the simulation of the ground – tunnel interaction;
(d) A separate chapter presenting and justifying in detail all loads exerted onto the model and all loading combinations used in the design, in accordance to the provisions of the Design Specification, entitled: ‘Design Loads’;
(e) A separate chapter describing, justifying, evaluating and presenting in detail the results of the calculations and the dimensioning of all structural members. For this scope, and as a minimum requirement, the following shall be included:
(i) moments, shear and normal forces,
(ii) the deformed structural model including values of the calculated deformations
(iii) the calculated reinforcement for each structural element.
4.3 EFFECT OF TUNNELLING ON SURROUNDING STRUCTURES
4.3.1 General
1. Description
(a) This specification includes the minimum requirements for the assessment of the degree of risk relating to the damage of buildings and structures, caused by the tunnelling works.
(b) A detailed methodology for risk assessment is described in the Annex of this specification.
2. Definitions
(a) The zone of influence of tunnelling is the volume of geomaterial influenced by the tunnelling operations. Any buildings or other structures located within this zone shall be subject to the provisions of this specification, in relation to the assessment of risk of damage. The minimum zone of influence for a specific tunnel cross-section, is shown in the following sketch.
Figure 4.1
Minimum Influence Zone
(b) Tensile Strain (e) in a structure is the average tensile strain, defined as the average strain over a gauge length of one metre.
(c) Critical Tensile Strain (ecrit) is the tensile strain causing visible cracking in masonry and blockwork.
(d) Volume loss (or Ground Loss - GL) is the ratio of the volume (.V) of geomaterial excavated in excess of the theoretical tunnel volume divided by the theoretical tunnel volume (Vo).
(e) The following drawings provide the definitions of rotation (.), angular strain (a), relative deflection (.), and deflection ratio (./L), tilt (.), and relative rotation (ß):
Figure 4.2
Definition of Parameters
Rotation or slope, ., and angular strain, a.
Relative deflection, ., and deflection ratio, ./L.
present
Tilt, ., and relative rotation, ß (angular distortion)
4.3.2 Classification of Damage of Buildings and buried structures due to Tunnelling
1. Buildings with surface foundations
(a) The risk assessment shall be based on the following classification of damage. Three broad categories of building damage shall be considered that affect:
(i) Visual appearance or aesthetics.
(ii) Serviceability or function; and
(iii) Stability.
(b) From the above three broad categories of damage, six specific categories of damage (numbered 0 to 5 in increasing severity) are defined, as described in Table 4.1. Normally categories 0, 1 and 2 relate to “aesthetic” damage, categories 3 and 4 relate to “serviceability” damage and category 5 represents damage affecting “stability”.
(c) The system of classification in Table 4.1 is based on ease of repair of the visible damages.
(d) In order to classify visible damages it is necessary, when carrying out the survey, to assess what type of work would be required to repair the damage both externally and internally. The Contractor shall take into account the following points:
(i) The classification relates only to the visible damage at a given time and not to its cause or possible progression which are separate issues;
(ii) Damage shall not be classified solely based on crack width. Ease of repair shall be a key factor in determining the category of damages;
(iii) The classification was developed for brickwork or blockwork and stone masonry. It can be adapted for other forms of cladding. It is not intended to apply to reinforced concrete structural elements. However, as cracking of in-fill brick walls of frame structures are usually more critical than the structural damage of the structural frames, the method can also be used for assessing the risk of cracking of the brick wall in-fills of frame structures;
(iv) In cases where damage could lead to corrosion, penetration or leakage of harmful liquids and gases or structural failure, the Contractor shall follow the same methodology but shall propose more stringent criteria and /or ranking to the Engineer for a SONO.
(e) Besides defining the numerical categories of damage, Table 4.1 also lists the “normal degree of severity” associated with each category. The descriptions of severity given in Table 4.1 refer to standard domestic and office buildings. In special cases such as for a building with valuable or sensitive finishes, this ranking of severity of damage may not be appropriate. In this case, the Contractor shall propose the same methodology but more stringent criteria and /or ranking to the Engineer for a SONO.
Table 4.1
Classification of visible damage to walls
Classification of visible damage to walls with particular reference to ease of repair of plaster and brickwork or masonry
Category
of damage
Normal degree
of severity
Description of typical damage (Ease of repair is underlined) Note: Crack width is only one factor in assessing category of damage and shall not be used on its own as a direct measure of it.
0
Negligible
Hairline cracks less than about 0,1 mm
1
Very slight
Fine cracks which are easily treated during normal decoration. Damage generally restricted to internal wall finishes. Close inspection may reveal some cracks in external brickwork or masonry. Typical crack widths up to 1 mm.
2
Slight
Cracks easily filled. Re-decoration probably required. Recurrent cracks can be masked by suitable linings. Cracks may be visible externally and some repointing may be required to ensure watertightness. Doors and windows may stick slightly. Typical crack widths up to 5 mm.
3
Moderate
The cracks require some opening up and can be patched by a mason. Repointing of external brickwork and possibly a small amount of brickwork to be replaced. Doors and windows sticking. Service pipes may fracture. Watertightness often impaired. Typical crack widths are 5 to 15 mm or several > 3 mm.
4
Severe
Extensive repair work involving breaking-out and replacing sections of walls, especially over doors and windows. Windows and door frames distorted, floor sloping noticeably1. Walls leaning1 or building noticeably, some loss of bearing in beams. Service pipes disrupted. Typical crack widths are 15 to 25 mm, but also depends on the number of cracks.
Classification of visible damage to walls with particular reference to ease of repair of plaster and brickwork or masonry
Category
of damage
Normal degree
of severity
Description of typical damage (Ease of repair is underlined) Note: Crack width is only one factor in assessing category of damage and shall not be used on its own as a direct measure of it.
5
Very severe
This requires a major repair job involving partial or complete rebuilding. Beams loose bearing, walls lean badly and require shoring. Windows broken with distortion. Danger of instability. Typical crack widths are greater than 25 mm, but depends on the number of cracks.
1. Local deviation of slope, from the horizontal or vertical, of more than 1/100 will normally be clearly visible. Overall deviations in excess of 1/150 are undesirable.
2. Table 4.2 gives the relationship between the category of damage, the limiting tensile strain (elim) and the maximum acceptable values of “green field” settlements and settlement troughs.
Table 4.2
Relationship between categories of damage
Relationship between category of damage, Limiting tensile strain (elim) and maximum acceptable “green field” ground settlements
Category of damage
Normal degree of severity
Limiting tensile strain (elim) (%)
Approximately equivalent ground settlements and slopes (after Rankin 1988)
Max slope of ground* (.S/L)
Max settlement of building (mm)*(S)
0
Negligible
0 – 0.05
1
Very slight
0.05 – 0.075
less than 1/500
less than 10
2
Slight
0.075 – 0.15
1/500 to 1/200
10 to 50
3
Moderate
0.15 – 0.3
1/200 to 1/50
50 to 75
4 to 5
Severe to very severe
Greater than 0.3
1/200 to 1/50
greater than 75
(*) These columns indicate “green field” settlements and settlement trough slopes.
4.3.3 Methodology for Assessing the Risk of Damage to Buildings due to Tunnelling
1 General
(a) The Contractor shall apply the following methodology for assessing the risk of damage of buildings due to tunnelling. The methodology includes three consecutive stages as described below.
2. Stage 1: Preliminary Risk Assessment
(a) A preliminary risk assessment shall be performed prior to the beginning of tunnelling.
(b) Using the tunnel alignment and depths, the zone of influence of the Works shall be determined.
(c) A Ground Loss (GL) value shall be selected for each tunnel section, due to tunnelling and the specifics of the tunnel excavation method and shall be submitted to the Engineer for a Statement of No Objection. The Contractor is also referred to the Materials and Workmanship Specification, Clause 13.1.2, Selection of TBM.
(d) The contours of surface settlements (for “greenfield” conditions) shall be determined over the surface part of the zone of influence.
(e) Using the above contours of surface settlements, the differential settlement (.S) and tilt (.S / L) shall be determined for each building within the zone of influence of the Works.
(f) Preliminary limiting values of the differential settlement (.) and slope (./L) shall be assessed for each building based on the type of structure, age, structural condition, span width, etc. As an indication, for good quality, average size, reinforced concrete buildings, the limiting differential settlement can be about 10mm and the limiting slope about 1/500. The above indications on limit settlements apply to common constructions. They should not be applied to unusual structures or buildings including high rise buildings or those for which the load intensity is highly non-uniform.
(g) Buildings with settlement (.S) and tilt (.S / L) smaller than the limiting values mentioned previously can be assumed to have negligible risk of damage and be excluded from the following stages of risk assessment.
(h) All other buildings within the zone of influence of the Works shall be subjected to the following two stages of risk assessment.
(i) The following two stages of risk assessment shall also be performed for all very sensitive and important buildings (including high rise buildings) inside the zone of influence of the Works, regardless of the results of stage 1 risk assessment.
3. Stage 2: Second Stage Risk Assessment
(a) This stage of risk assessment shall be performed prior to the beginning of tunnelling.
(b) It shall include all buildings within the zone of influence of the Works exceeding the limiting values of differential settlement (.S) or tilt (.S / L) of stage 1 assessment as well as all very sensitive and important buildings inside the zone of influence of the Works.
(c) The second stage risk assessment will be based on calculated maximum tensile strains and comparison with the corresponding limits for each category of damage in Table 4.2.
(d) Specifically the second stage risk assessment shall be based upon either:
(i) The facade of any building is represented by a simple beam whose foundations follow the ‘greenfield’ displacements caused by the tunnel excavation. These displacements are calculated from the settlement trough, as described above; or
(ii) The maximum tensile strains shall be calculated using the methodology described in the annex to this specification. The approach of Potts and Addenbrooke (1997) can also be included at this stage, to account for the structural stiffness in more detail. Ref : “A structure's influence on tunnelling-induced ground movements”, by D M Potts and T I Addenbrooke, Proceedings of the ICE - Geotechnical Engineering, Volume 125, Issue 2, April 1997, pages 109 – 125.
(iii) For each building under assessment, using Tables 4.1 and 4.2 and the calculated maximum tensile strains, an appropriate category of damage shall be assigned to each such building.
(e) Figure 4.3 shows an interaction graph for the case of a beam with L/H=1. The Contractor shall make his own assessment of the damage classification for all buildings, by deriving all necessary figures, similar to Figure 4.3, by considering the geometrical characteristics and the structural type of the buildings.
Figure 4.3
Example of interaction diagram
Figure 4.3. Example of interaction diagram relating (./L)/elim to eh/elim for the case of an isotropic beam with L/H = 1
4. Stage 3: Detailed Evaluation of Risk Assessment
(a) This stage of risk assessment shall be performed only for buildings categorized as “Category of Damage” 3, 4 or 5 during stage 2 risk assessment as well as for all very sensitive and very important buildings within the zone of influence of the Works.
(b) Each building has to be considered in its own right and requires a detailed structural survey. This survey shall consider:
(i) The geotechnical conditions, sub-surface profile and ground-water conditions;
(ii) The stiffness of the building (timber, masonry or framed buildings);
(iii) The foundation type; and
(iv) The sensitivity and usage of the building.
(c) Following the structural surveys, each building will be analyzed by considering the tunnelling sequence, three-dimensional aspects, specific building details and geomaterial/structure interaction.
(d) For buildings remaining in damage category 3 or higher, the Contractor shall perform special designs as described below.
(e) Typically, these designs shall be performed using numerical analyses to include the geomaterial – structure interaction and non-linear geomaterial effects due to ground deformations caused by tunnelling.
(f) These designs shall either include improvement of the ground and/or reinforcement of the building foundations. The objective of the designs shall be to reduce the damage category of the building to a value 2 or lower.
(g) The Contractor shall perform the above designs and submit them to the Engineer for a SONO.
(h) For building on pile foundations requiring stage 3 risk assessment, detailed evaluation shall be performed using numerical analyses to include the geomaterial – structure – pile foundation interaction. Typically, non-linear analyses shall be performed including skin friction and lateral loading of the piles due to ground deformations caused by tunnelling. The Contractor shall perform the above designs and submit them to the Engineer for a SONO.
(i) Regardless of the results of the stage 3 analyses, buildings originally classified in damage categories 2 and above shall be monitored by instrumentation installed prior to tunnelling according to the Materials and Workmanship Specification.
(j) The instrumentation details for all buildings which at their stage 3 risk assessment have a category of damage 3 or higher shall be presented in the improvement /reinforcement design to be prepared by the Contractor.
4.4 SAFEGUARDING TUNNEL CORRIDORS
4.4.1 Metro Corridor planning stage:
1. The planning corridor width for the Metro Tunnels comprises:
(a) The outlined tunnel structure;
(b) The construction tolerance zone;
(c) The exclusion zone;
(d) The alignment adjustment zone; and
(e) The minimum distance between two adjacent tunnel tubes.
2. Definition of outlined tunnel structure:
(a) For the segmental tunnel lining an outer diameter of 7.5m has been assumed.
3. Definition construction tolerance zone:
(a) For the shield driven tunnels a construction tolerance of 0.5m will be taken into account. The construction tolerance zone is defined as a square with equal sides of 8.5m.
4. Definition of exclusion zones:
(a) For third parties no structures shall be closer than 5m horizontally, 6m from the top and 3 m from the bottom of the outlined construction tolerance zone. For planned structures intruding into this zone approvals from the Employer must be obtained.
5. Definition of alignment adjustment zones:
(a) The Employer is retaining the flexibility to move tunnels 3m horizontally and vertically 3m towards Ground Level. The zone underneath the tunnels is defined infinite to safeguard maximum flexibility.
6. The outline of the Metro Corridor is compulsory for all parties and will be added into the Urban Integration Plans. In certain locations the full tolerance may not be required. The Engineer will advise accordingly.
7. The parameters described above are depicted in Figures 4.4 and 4.5 below.
Figure 4.4
Limit of deviation for general Tunnel arrangement
Figure 4.5
Limit of deviation for Twin Tunnel arrangement
4.5 TUNNEL EXCAVATIONS WITH TBM
4.5.1 General
1. The key issues for the Contractor to manage for the construction of tunnels using tunnelling equipment include:
(a) its availability/performance/reliability/serviceability;
(b) assembly, use, removal, with the required equipment;
(c) cutter disc wear;
(d) its stopping periods;
(e) the availability of the correctly certified technical human resources and the supply of all materials needed.
(f) TBM work shall be performed in line with international best practice and the conditions at the Site, which contains different geomaterials.
(g) TBM shall be supplied new and shall be state-of-the-art. The TBM shall be suitable for the ground conditions to be encountered and shall incorporate necessary soil conditioning. They shall be supplied in accordance with all applicable Regulations, and relevant Qatar Construction Specifications, British and European standards. The Contractor shall always use the latest published version of any regulation or standard that relates to health and safety.
4.5.2 Selection of TBM
1. The operation and control features of the TBM shall be designed to minimize sub-surface and ground settlement. Ground loss arising from the TBM boring and tunnel construction operations shall be limited to a maximum value of 1% of the excavated volume, with more stringent limits on maximum ground loss as specified in the Contract Documents. The TBM operating principles shall govern its use in order to meet these requirements.
2. The Contractor is solely responsible for the selection of the TBMs to be used for the tunnelling operations and shall be according to the Project specifications and requirements detailed herein. As a minimum, the following factors shall be taken into account for TBM selection:
(a) The geological, hydrogeological and geotechnical conditions in the zone of influence of the Works;
(b) The geometry of the tunnel section and its alignment;
(c) Manufacture and supply of the machines and their back-up equipment;
(d) Assembly and preliminary tests in the factory, including the grout and soil conditioning system. TBM manufacture shall allow for attendance of the Contractor maintenance and the Engineer during the final assembly and commissioning works;
(e) Technical assistance during assembly at the worksite;
(f) Commissioning and tests at the work site;
(g) Technical assistance during the dismantling operations;
(h) All applicable environmental regulations and licenses;
(i) The stability conditions of the tunnel face and the tunnel section;
(j) The requirements to limit ground and structures deformations below the acceptable levels, as described in the Technical Specification
(k) Any tests to confirm design assumptions;
(l) The time constraints regarding the tunnel construction;
(m) Applicability of supplementary supporting methods if necessary;
(n) Availability of spaces necessary for auxiliary facilities behind the machine and around the access tunnels;
(o) Direction control and measurement system;
(p) The supply and management of spares, consumables and wear parts;
(q) Design of the tunnel boring machine (TBM) and backup equipment and ongoing input during design and manufacture;
(r) Operation and maintenance manuals in English and Arabic, provided electronically together with 4 paper copies;
(s) Technical assistance from the Manufacturer during the tunnel start-up until the specified performance is demonstrated as being achieved, and as necessary thereafter to assist the Contractor in achieving the required performance throughout the tunnel drives as constructed drawings of the TBM, technical documentation and details of planned maintenance requirements prior to commencing TBM and/or Tunnelling Equipment operations including updated operational manuals;
(t) A detailed programme for the design and manufacture of the TBM’s. The Contractor and the TBM Manufacturer shall attend regular meetings with the Engineer to monitor the design and manufacture of the TBM to the Contract schedule.
3. An excavation control system shall be installed necessary for tunnelling operations, orientation and operation of the TBM excavation, backfill grouting and operation of auxiliary facilities. The system will control accurate alignment, excavation control (belt weighers, laser scanner, flow meters and profilers) to ensure stability of the face of the tunnel and minimum disturbance of the surrounding ground and structures.
4. A TBM operational control and monitoring data acquisition system shall be provided. The system shall be compatible with the project-wide underground construction instrumentation and monitoring requirements. The monitoring system shall record and report the key information that will ensure the reliable and safe operation of the TBM. The monitoring system shall also record all necessary parameters to ensure ground movements are kept within the specified limits. The Contractor and Manufacturer shall submit a list of target programmed TBM control parameters to the Engineer for a SONO.
4.5.3 Inspections and tests
1. Prior to commencing any operation with the TBM the Contractor shall submit a programme for the supply, inspection, testing, transfer, assembly and operation of the TBM.
4.5.4 Tunnel Excavation with TBM
1. The bearing positions of the thrust rams shall be designed for the bearing capacity of the geomaterials and the tunnel lining, in order to avoid failures.
2. The thrust rams shall operate either individually or together in any possible combination.
3. Access must be given to all working or maintenance areas of the TBM. Provision shall be made for emergency exits.
4. All necessary measures to prevent the risk of water ingress shall be taken before commencement of the Works.
5. Immediately upon any work stoppage, the stability of all TBM excavations and the safe condition of the tunnel (including regular inspections) shall be ensured.
6. All lighting used by the Contractor shall ensure uniformly distributed lighting in all working areas.
4.5.5 Operation of TBM
1. All information relevant to the control of the TBM operation shall be accessible to the Engineer in real time.
2. Operation and maintenance of the TBM, shall be according to the guidelines of the manufacturer and the operation and maintenance manuals, which shall always be up to date and available for inspection of the Engineer.
3. An air-conditioned control cabin shall be provided at the front end of the back-up system from which the TBM will be driven. This shall contain all the remote controls and visual displays as necessary for the safe operation of the TBM and its environment.
4. A separate above-ground monitoring facility shall be provided for each TBM that will duplicate all the remote controls and visual displays within the respective (sub-surface) Control Cabin.
5. The cutting tools shall regularly be inspected.
6. The TBM bearing shall be regularly inspected. The bearing shall be removable rearward from the front bulkhead with the minimum of disturbance to the other components, in the event of the need for replacement. A replacement main bearing should be available within 12 weeks should the replacement be required.
7. The cutter head shall be a substantial structure, which provides the necessary mechanical support to the tunnel face. It shall incorporate the necessary abrasion protection features to enable the shield to be able to complete excavation of the tunnels through all the expected geological conditions.
8. The cutter head structure and bearing with its support system shall be rated to absorb the maximum forces envisaged in operation. This shall include normal operation and ultimate load condition where full power may need to be used in the event the TBM becomes stuck, resulting in maximum shove loading and maximum torque.
4.5.6 Tunnel Excavation Data Reports, Shift Reports
1. Detailed data for all TBM excavations shall be kept.
4.5.7 As-built Details
1. The Contractor shall keep records of as-built details of the tunnelling works, including ring erection and soil conditions encountered during boring.
4.5.8 Safety Regulations
1. The design and manufacture of the TBM and back-up systems shall comply with all applicable laws and regulations, relevant Codes of Practice relating to safety and relevant Qatar Construction Specifications, British and European standards including, but not limited to, those described below. The Contractor shall always use the latest published version of any regulation or standard that relates to health and safety.
(a) EN 12336: 2005 Tunnelling Machines – Safety Requirements.
(b) EN 12110: 2002 Tunnelling Machines – Air Locks-Safety Requirements.
(c) BS 6164: 2001 Code of practice for safety in tunnelling in the construction industry.
(d) The Work in compressed Air Regulations 1996.
(e) HSE L96 A Guide to the Working in Compressed Air regulations (1996).
(f) EN ISO 9000 and 9001 Quality management and quality assurance standards.
(g) EN 60079 Electrical apparatus for potentially explosive atmospheres.
(h) EN 50402: 2005: Electrical apparatus for the detection and measurement of combustible or toxic gases or vapours or of oxygen. Requirements on the functional safety of fixed gas detection systems.
(i) EN 981: 1997 Safety of machinery. System of auditory and visual danger and information signals.
(j) EN 60034-9 Rotating Electrical Machines – Noise Limits.
(k) EN ISO/IEC 17050 – 1:2004 Conformity assessment. Suppliers declaration of conformity. General requirements.
(l) EN 981Safety of machinery-System of Danger and Non Danger signals with sound and light.
(m) EN 61310-1 Safety of Machinery-Indicating, marking and actuating principles; part 1 Visual, audible and tactile signals.
(n) EN 1012 Compressors and vacuum pumps; Safety requirements.
(o) EN ISO11688; Parts 1 & 2: Recommended Practice for the design of low noise machinery and equipment.
(p) EN620:2002 Specification for mechanical and spliced joints in conveyor belting for use underground.
4.5.9 Fire Prevention
1. A fire hazard assessment which will identify and mitigate all potential fire sources shall be carried out by the Contractor jointly with the TBM Manufacturer and submitted to the Engineer for a SONO.
2. Subject to the conclusions of the hazard assessment, the TBM and back-up systems shall be provided with:
(a) The fire suppression system which shall be suitable to mitigate the risks identified in the hazard assessment.
(b) Emergency plunger buttons at suitable locations to activate a fire alarm.
(c) Hand held extinguishers provided with colour coded covers in suitable locations.
(d) A means of rapidly shutting off fresh air ventilation to the tunnel face, after the area has been evacuated.
(e) Operators and training manuals for use by the Contractor.
(f) Conveyor belting, rubber covered rollers and other similar parts to be manufactured in materials that reduce the fire risk, fire load, spread of flame and toxic fume risk.
(g) Hydraulic hoses shall comply with BS EN 853/ISO 1436. The hose covers to be flame retardant and to conform to the requirements of MSHA. All hydraulic hoses shall be fitted with swaged end connections, re-usable fittings are not permitted.
(h) Gas monitoring for oxygen deficiency, CO2, CO, H2S, NO2, SO2 and CH14.
(i) Smoke detection and rate of temperature rise.
(j) Water mist screen to be positioned at the rear of the back-up System.
(k) Low density foam generators to be sited at high fire risk areas with either automatic or manual operation in the event of fire.
(l) Spraying nozzles to be installed at the last sledge to create an anti-smoke curtain in case of fire in the tunnel.
(m) Essential services shall be protected so that they remain operable during all tunnelling operations for a period of 1 hour. The essential services are:
(i) Emergency power supplies
(ii) All fire suppression systems
(iii) TBM emergency lighting
(iv) Environmental monitoring systems
(v) All controls and tunnel communications
(vi) The security of the air supply and control systems to the man lock shall remain operable in all emergencies, particularly in the case of fire
(vii) Emergency evacuation chambers
4.5.10 Electrical Specification
1. All TBM electrical installations shall comply with all relevant regulations and with all relevant British, European and Qatar standards. The Contractor shall always use the latest published version of any regulation or standard that relates to health and safety.
2. The following list of relevant regulations and standards in non-exhaustive:
(a) BS 6164 Code of Practice tunnelling
(b) EN 12336:2005 Tunnelling Machines Safety Requirements
(c) Electricity at Work Regulations 1989
(d) BS 7671:2008 Requirements for Electrical Installations
(e) IEE Wiring Regulations 16th Edition
(f) BS5304 and EN292 Safety of Machinery
(g) BS 7430:1988. Earthing
(h) EN 60204 Safety of Machinery
(i) BS7375:1996 Distribution of Electricity on Construction sites
(j) EN 60529 1992 Degrees of Protection of Enclosures
(k) BS 6724:1997 armoured cables for low emissions
(l) BS 5000-3:2006 Rotary Electrical Machines for Particular applications
(m) EN 60898 1991 Moulded case and miniature circuit breakers
4.5.11 Environmental Conditions
1. Control and monitoring of environmental conditions to include but not limited to:
(a) Fire protection systems
(b) CCTV monitoring of work areas
(c) Electrical power
(d) Humidity
(e) Dust monitoring
(f) Inundation of the cutter head chamber
(g) Ventilation air supply (including failure)
(h) Gas detection system for oxygen deficiency, CO2, CO, H2S, NO2, SO2 and CH4. The data acquisition unit shall include provision for the monitoring of tunnel gas alarms throughout the tunnel to provide early warning to the TBM operator of potential gas danger
4.6 TUNNEL EXCAVATION WITH CONVENTIONAL MEANS
4.6.1 General
1. This Specification applies to all tunnel excavation Works using conventional mechanical means and the implementation of the tunnel’s primary support. All tunnel excavation Works shall be in accordance with Contractor’s design which has received a SONO.
4.6.2 Working Conditions
1. Safe and continuous access to all tunnels, as well as the required safety conditions shall be ensured throughout the execution of Works.
2. All lighting used by the Contractor shall ensure uniformly distributed lighting in all working areas.
3. Pumping, drainage and mud and water removal equipment shall be installed, operated and maintained, in order to ensure that all Permanent Works shall be constructed in dry conditions and shall be protected against water.
4.6.3 Working Interruptions
1. Upon any work stoppage the stability of all tunnel excavations and the safe condition of the tunnel (including regular inspections) shall be ensured.
4.6.4 Safety Measures and Systems
1. An emergency power supply shall be available on site to provide power for all electrical installations, which are considered essential for the safety of the tunnel and the working personnel.
2. An emergency evacuation procedure shall be prepared which is also approved by local authorities.
4.6.5 Work Execution
1. Pre-excavation Works
(a) Prior to the commencement of the tunnel excavation Works, all necessary measures shall be taken to locate, fill and seal any voids from all investigation boreholes that may be encountered during excavation.
(b) If required by the design and/or method statement, and prior to commencing any tunnel excavation works, ground improvement works shall be performed.
2. Monitoring
(a) Prior to the commencement and throughout the tunnel excavation Works, as well as after their completion, it shall be ensured that all monitoring instruments that have been installed are fully functional, regularly calibrated and monitored.
(b) The Engineer may instruct the stoppage of the works, when the instruments are not completely installed, or the Contract requirements are not fulfilled.
3. Geological mapping of the excavation surfaces
(a) Geological mapping of the excavation surfaces shall be performed upon completion of each heading/bench advance, except for where the immediate sealing of the excavation face using shotcrete is required.
(b) The geological mapping shall be performed concurrently with the excavation. The tunnel’s faces shall be cleaned to the extent possible so as to enable collection of the necessary data for the complete geological mapping and the classification of the geomaterial at the tunnel face.
4. Probe drillings
(a) Investigation drillings through the tunnel face and/or through the ground surface for further investigation of ground and groundwater conditions and of possible weak zones, voids wells or any other disturbances shall be carried out.
(b) The number, location and orientation of probe drillings shall be designed in a manner to collect the maximum possible amount of data, depending on the type and the inclination of strata, the presence of water, the geometry and the tunnel alignment. All drilling logs shall be made available to the Engineer.
5. Emergency Conditions in the Tunnel
(a) When wells or other voids are encountered during excavation Works, the area shall immediately be protected against collapse, to ensure the safety of the Works and all persons.
(b) Any damage to the Works or the structures, including local failure of the primary support, shall be reinstated immediately.
6. Surveys
(a) The correct construction, orientation and shape of the tunnel, based on the design (such as, alignment data, structural tolerances, convergence tolerances) shall be verified. Measurements of excavated cross sections shall be performed.
(b) The minimum thickness of the primary support shall always be greater than or equal to the relevant thickness in the design.
7. Tunnel Excavation Shift Reports
(a) A Shift Report for all underground excavations shall be maintained. This report shall include sufficient data for the full recording of the cycle of Works. The report shall be available to the Engineer at all times.
4.7 PRECAST CONCRETE TUNNEL LINING SEGMENTS
4.7.1 General
1. This Specification concerns the supply of materials and equipment as well as execution of Work for the production and installation of precast concrete segments to be used as the lining of all TBM.
2. The segmental precast concrete lining shall consist of a number of precast segments to form rings.
3. Radial joints in adjacent rings shall be staggered so that there are no continuous joints. The circumferential joints between adjacent rings shall be continuous.
4. Tapered rings shall be used to negotiate horizontal and vertical curves and to correct for line and level.
5. All precast concrete lining segments shall have EPDM gaskets inserted into recesses provided in all four mating surfaces of the individual segments. The size and position of the gasket shall be sufficient to take account of all tolerances for the segments and gaskets. Where it is proposed to erect segmental lining without applying shield jacking forces to compress the gaskets it shall be demonstrated that the required watertightness of the segments joints shall still be achieved by adequately compressing the gaskets or by other acceptable means for the SONO from the Engineer.
4.7.2 Materials
1. Concrete
(a) The concrete shall be a minimum strength of class C40/50 as defined under EN 206.
2. Cement
(a) The cement shall comply with the requirements of EN 197.
3. GGBFS
(a) GGBFS intended for use for segments shall comply with EN 15167.
4. Fly Ash
(a) Fly Ash intended for use for both the segments shall comply with EN 450.
5. Microsilica
(a) Microsilica intended for use for segments shall comply with EN 13263.
6. Aggregates
(a) Fine aggregates shall be natural or crushed rock sand in compliance with EN 12620.
(b) Coarse aggregates shall not contain materials which may cause reduction of strength or durability of the concrete. Coarse aggregates shall be crushed aggregate from an approved natural source in compliance with EN 12620.
(c) The potential alkali aggregate reactivity has to be determined and evaluated either by the relevant ASTM standards ASTM C289 and C1260 and ASTM C227.
7. Water
(a) Water shall comply with the requirements of EN 1008. Additionally, to account for the high risk of chloride-induced reinforcement corrosion, the maximum allowable chloride content of the mixing water is 250 mg/l.
8. Admixtures
(a) Admixtures used in the concrete shall conform to EN 934, EN 480 and shall be mutually compatible. They shall be accompanied by full documentation from the manufacturer, which shall be submitted to the Engineer for a SONO. Use and dosage of admixtures shall be in accordance with the manufacturer’s recommendations.
9. Steel
(a) If reinforcement steel for segmental lining is used, it shall be new. The reinforcement shall consist of high ductility bars of B500C category or approved alternative reinforcement.
(b) If steel fibre reinforcement is used for segmental lining it shall comply with EN 14889 and have a minimum tensile strength of 1100 N/mm2.
(c) Manufacturer’s production certificates shall be supplied.
(d) Reinforcement bar welding shall be carried out by certified welders in accordance with Standard EN 17660, EN 15609-01, EN 15614-01 and EN 15614-12. The welding quality shall be certified through EN 287-01/A2.
10. Fasteners, fixings and fittings screws and bits
(a) Specifications for all temporary and permanent fasteners and cast-in fixings shall be provided. All permanent inserts shall be stainless steel.
11. Segment identification
(a) The following information shall be cast in to the internal (concave) surface of all segments or shall be incorporated on a bar code fixed permanently to the inside face of the segment:
(i) QR – followed by the Contract Number
(ii) Date of production
(iii) Mould number
(iv) Ring type e.g. left hand taper or right hand taper
(v) Segment type
(vi) The Contractor shall number the concrete rings in sequential order between the stations, clearly stencilled in clear large durable black numbers on completion of each tunnelled drive.
12. Tests and Checks during Construction
(a) The concrete mixture shall be regularly checked for conformity with the laboratory concrete mix design. The total water-cement ratio shall be in the range prescribed in the laboratory concrete mix design.
(b) In addition, chloride penetration tests shall be performed according to NT Build 492. The tests reports shall be available to the Engineer at all times.
(c) The compressive strength test shall be performed in accordance to EN 45001 and all other tests with EN 206.
13. Tests on the Production Line
(a) Prior to the beginning of the full-scale production of lining rings, three trial rings shall be built and assembled to check that the required tolerances have been met.
(b) At least 1 in every 20 segments produced from each mould shall be checked for compliance with the casting tolerances. Checks shall continue throughout the production period and shall be performed on segments selected at random by the Engineer for the control of the production of segments to the required tolerances.
(c) All segments shall be systematically checked for surface defects and repaired if required.
(d) Dimensional control of segments shall be made on a daily basis to meet the tolerance ranges. The internal diameter of the completed ring, during tunnel lining construction, will be checked on Site.
14. Repair of Segments
(a) A special methodology for the repair of defective segments, addressing all types of repairs shall be provided. The repairs shall include all the methods related to the surface preparation, the work sequence, the appropriate repair materials (depending on the type of defect), the equipment to be used, and the checks to be carried out at each phase of repairing. This methodology shall be submitted to the Engineer for a SONO.
(b) With reference to the repair of segments, two cases of repair are distinguished. The first case relates to the repair of segments located either in the production plant, or the construction Site area before their final placement in the tunnel. The second case relates to segments that have already been incorporated in a ring within the tunnel. A methodology statement for each of these cases shall be prepared for a SONO from the Engineer.
(c) Categories of segment defects are defined as minor, medium and major.
(i) Minor defects on the segments are defined as a broken edge smaller than 25 mm and/or holes due to air bubbles between 5 and 8 mm in diameter. Defects of this category may be repaired.
(ii) Medium defects on the segments are defined by a crack with width less than 0.1 mm or depth less than 20 mm and/or a surface depression with depth less than 20 mm. Where a medium defect occurs prior to the final placement of the relevant segment in the tunnel it shall be rejected.
(iii) Major defects on the segments are defined by a crack with width more than 0.1 mm or depth more than 20 mm and/or a surface depression with depth more than 20 mm and / or a broken edge larger than 25 mm. Where a major defect occurs prior to the final placement of the relevant segment in the tunnel it shall be rejected.
15. Tolerances of Segmentally Lined Tunnels
(a) Tunnels supported with segmental concrete lining, as part of the Permanent Works, shall conform to each of the following tolerances by reference to the axis:
(i) Segment width: +/- 0.5mm;
(ii) Segment thickness: +/- 3.0mm;
(iii) Segment arc length: +/- 0.6mm;
(iv) Inner radius of a single segment: +/- 1.5mm;
(v) Deviation of the ‘AS BUILT’ diameter of the inner face of the segments: 1.0mm and from a perfect circle: 5.0 mm;
(vi) Width of segment grooves: +0.2 mm – 0 mm;
(vii) Depth of segment grooves: +0.2 mm – 0mm;
(viii) Axis of segment grooves: +/-1.0 mm;
(ix) Longitudinal joint evenness: +/- 0.5 mm;
(x) Ring joint evenness: +/- 0.5 mm;
(xi) Unevenness of joints causing stress on the section: not permitted;
(xii) Outer diameter of the constructed ring: +/- 10 mm;
(xiii) Inner diameter of the constructed ring: +/- 10 mm;
(xiv) Outer perimeter of the constructed ring: +/- 30 mm;
(xv) Torsional angle in the longitudinal joint: + 0.04°; and
(xvi) Angle of longitudinal joint conicity: + 0.01°.
4.8 GROUTING FOR SEGMENTAL LINING, CONTACT GROUTING AND FILLING OF VOIDS
4.8.1 General
1. This specification concerns the provision of labour, materials, installations and equipment for filling all voids, including karst voids.
2. This specification applies to tunnels excavated either by TBM or by conventional methods.
3. All voids between the excavation profile and outer limit of the theoretical temporary lining (in sprayed concrete lining (SCL) tunnels) or the segmental lining (in tunnel boring machine (TBM) tunnels) shall be filled with cement grout.
4. Any other voids encountered ahead of the tunnel excavation face shall be filled with cement grout, if their presence prevents or otherwise obstructs the advancement of the excavation face.
5. Grouting for filling karstic voids may require primary and secondary grouting. Primary grouting is the initial grouting which is applied immediately after a unit of lining has been built. Where primary grouting does not completely fill all voids, secondary grouting shall be carried out.
6. Grout shall remain effective for the design life of the tunnel. The grout shall not degrade, shrink or lose strength to an extent that the tunnel would be damaged or become unserviceable as a result.
END OF PART