CONSTRUCTION OF CONCRETE LINING IN TUNNELS

Prepared byHimanshu Batra

ENGG(QSS)

Sr. No. Activity

1 Survey Of the Tunnel

2 Construction of Kicker / Kerb

3 Fixing of protective felt and waterproofing membrane

4 Fixing of reinforcement

5 Survey

6 Construction of Overt lining

Stages

Sr. No Responsibilities Responsible Person

1

Execution of work at Site as per drawings and specifications i.e. cutting and fixing of reinforcement, movement of shutter, fixing of shutter, concrete pouring and maintaining quality work.

LINING INCHARGE

(CONTRACTOR) / Tunnel Engineer

from CLIENT

2Maintenance of Gantry including hydraulic and electrical component servicing, lubrication

Site CPE Engineer

3Alignment of Gantry including setting and positioning of gantry as per the approved drawing

Survey Engineer

4Checking quality of materials and quality of end product as per the specification. QA QC Engineer

5Checking safety aspects for safe execution of the work Safety Officer

Responsibilities

Sr. No. Equipment Capacity Quantity1 Concrete Batching plant 60 cum/Hr 012 Concrete pump 30 cum/Hr 043 Transit Mixers 6 cum 044 Mai Pump 025 Main Tunnel Lining gantry 12.5 m 016 Escape Tunnel Lining gantry 10 m 017 Lay By Lining gantry 10 m 018 Cross Passage Lining gantry 6 m 019 Kerb Lining Gantry for Main Tunnel 12.5 m 0110 Kerb Lining Gantry for Escape Tunnel 12 m 01

11 Needle Vibrators 6 nos. 12 Movable Jumbo for fixing of Geo Textile

and Reinforcement 02

13 Diesel Generator for tunnel lighting & construction power

As per requirement

14 Welding Machine 0215 Dewatering Pump As per requirement16 Grouting pump As per requirement17 Tunnel dumpers 20T As per requirement

Machinery, Instruments & Material

FORM WORK Generally for tunnel lining steel forms are used in the interest of speed and economy due to their multiple use. There are various types of form work used for tunnel lining, such as :-•Rib and Plates,/Rib and Laggings, (Where the Concrete is to be hand placed, tunnel 5m diameter)•Travelling Shutters with or without Telescoping. The use of a particular type for a job depends on the size, shape and the length of tunnel.Travelling Non-telescoping Form Work - •The whole form work is preassembled and mounted on a travelling frame fixed with wheels running on a track and screw jacks are provided for collapsing .•In all types or travelling forms the sections are hinged to permit collapsing. J ac k s are required for bracing and aligning the forms.• This type is easy and economical to move. Travelling Telescoping Form Work - •This is so designed that the back unit can be collapsed and moved forward through the front unit without disturbing it. •The side plates are hinged to the arch plate so that it is possible to collapse them. The traveller is equipped with jacks and other accessories for this purpose.

•As per requirement of construction, two separate formworks are provided for construction of Kerb and overt lining. The formwork shall be movable and hydraulically operated. Hydraulic mobile form work move on rails.

•Survey work of the Kerb should be the first activity. All levels and alignment should be as per working drawing and recording to be done. Before erection of Shutter survey team should fix the level and outer finish of concrete lining.

•Tunnel floor shall be thoroughly cleaned before commencement of construction activity. All loose material, dirt shall be removed by using water jet and wire brush.

•Shear Dowels 32mm @1m spacing .The cover of reinforcement shall be 50 mm. Lap length of bar shall be 55D.

•Kerb shutter shall be moved to the position. The shutter shall be well cleaned and oiled before every pour following the technical specifications.

•M30 is to be batched and mixed in a batching plant., Slump 100 – 150 mm. GI Earthing strips of size 40 x 4 mm

•Setting time for Kerb concrete shall be 10 hours. After 10 hours the shuttering shall be removed. Curing shall be done 28 days after concreting.

KERB/KICKER

Preparation for substrate

•All surfaces to which waterproofing is to be applied shall be sufficiently clean, smooth and free from deleterious materials and projections.

• For fixing of the protective felt and the waterproofing membrane, a minimum shotcrete cover of 50 mm to rock is required.

• Irregularities of the shotcrete lining surface shall be eliminated by means of additional shotcrete, which is called as smoothening shotcrete(thickness 0.2m). The ratio of the diameter to depth of irregularities shall be not less than 5:1.

GEOTEXTILE & PVC

•The protective felt shall be attached to the shotcrete using suitable fixings specified by the manufacturer.

• Depending on the location 2 to 4 No’s fixing elements shall be used per square meter.

•Adjacent sections of felt shall be overlapped by 100 mm and joined by point welding (skilled operator) or similar suitable method

•Along the bottom of the tunnel side walls the felt shall extend sufficiently to cover the lateral drainages.

•The layer is made up of a geo textile material of nonwoven polypropylene felt of weight 500 grams / sqm, with roll size of 3 meter to 5 meter wide and up to 30 meter long. The roll shall be lifted by hoist over the membrane carrier and unroll on the either side of the crown of tunnel.

FIXING OF PROTECTIVE FELT

• Laying shall be carried Out in Dry Conditions with a minimum overlap of 10 cm.

•Along the vertical surface the geo textile felt shall be anchored (grounded) to the substrate of shotcrete below, through fitting washers fixed with nails/screws by impact tool or rotary hammer drill machine.

•The geo textile felt shall be fixed to the shotcrete through PVC with a minimum number of 2 to 4 washers each sqm at corners.

• The geo textile felt shall be set transversally to the longitudinal axis of the tunnel and, in order to avoid any possible contact between the waterproof liner and the shotcrete.

•Geotextile felt shall also be wrapped on No-fines porous concrete at drainage assembly.

(No-Fines Concrete is a method of producing light concrete by omitting the fines from conventional concrete. No-fines concrete as the term implies, is a kind of concrete from which the fine aggregate fraction has been omitted. This concrete is made up of only coarse aggregate, cement and water)

FIXING OF PROTECTIVE FELT

•The lining element i.e. waterproofing membrane shall be PVC synthetic waterproofing membrane of 2.00 mm thick and it will be laid by overlapping the adjacent membrane sheet edges of 80mm to 100mm by hot air welding. •The waterproofing membrane is made up of two coextruded layers of contrasting colors but forming a homogeneous body.

•In this way the visible layer will come out with a color contrasting with the one of the layer underneath so that it will be easier to spot possible damage to the membrane.

•The membrane sheets shall be welded to the PVC rondells by Manual hand held welding machine tool.

WATERPROOFING

Seam Test with Compressed Air

•For seams between adjacent sheets of waterproofing membrane the testing for tightness shall be carried out by means of compressed air pumped into the test channel which is formed by the double welded joint. Initial test pressure shall be 2 bars for a test period of 5 minutes or 1.5 bar for a test period of 10 minutes.

• The joint shall be considered waterproof if the loss of air pressure in both cases is not more than 20%.

TESTING OF WELDS

•Construction of overt lining forms second part of concrete lining structure.

• Lining concrete shall be as per IS 456:2000. It should be started after completion of 100 m of Kerb Lining. •False work/staging for fixing rebar shall be erected in position along with templates for controlling the rebar position.

•Then the fabricated rebar's shall be placed in position and tied with each other to maintain its position. Then the cover blocks shall be fixed to the rebar to maintain the cover to the reinforcement.

•The final alignment of the rebar shall be checked with reference to the templates and any errors in the same shall be rectified.

•Reinforcement to be free from dust. Lap 55d,cover 50mm.

OVERT LINING

•Invert PCC or wooden block is to be provided for lying rail @3.6m centers. The rail shall fixed firmly . Items to be checked : -

•Nut & Bolts of shutters & Trolley.

•Hinge Pin, Thruster Pin, Bottom Thruster Pin.

•Thruster screw jack to be completely in contact with shutters at both the upper thruster and the bottom thruster

• Shutter vibrators and electric lines should be connected and checked for earth leakage.

•Hydraulic piping and fitting accessories to be checked for leaks and pressure tested•.•All hinges should be examined.

•Bulk head fitting.

•Telescopic cylinder & the shuttering cylinder.

•Hydraulic pipe and hydraulic seals as well as ram are to be periodically checked.

•Vibrator mounting system is to be in fixed condition and regularly tightening of bolts to be done.

NECESSARY CHECKS

• The shutters are provided with windows at various levels for concreting and inspection approximately at 2 to 3m height differences.

•Concreting differential on two walls should not exceed 0.75m.This means that both walls must be filled simultaneously. •Jacks for vertical loads during concreting. The trolley is made free after the alignment of the formwork at a given spot is completed.

•During concreting a certain amount of side thrust develops due to hydrostatic concrete pressure. To counter the hydrostatic pressure at the bottom, thruster is provided. They are referred to as spuds.

•Shutter vibrators should be used with the Overt Formwork Provision has been made in the shutters for fixing the vibrators.

SHALL ALSO INCLUDE..

CONCRETING•Inform Government Officials.

•Surface to be thoroughly cleaned by the use of high velocity water jet or steel brooms, picks or other effective means, satisfactory to the Engineer.

•Cement slurry is to be poured from top spout at crown to avoid tendency for steel reinforcement to extract cement paste from new concrete and honey combing at Kerb-Overt junction.

•Concrete placement will be started from the bottom level windows and proceed to the concrete spout at the shutter crown.

•Concreting should be planned for completion in 8-9 hours. Pouring height of Concrete shall not exceed 1.0 m to prevent segregation of concrete.

•When pouring is completed at Top Level Windows on both side but before concrete is started at Crown Level through spouts, keep the Bulkhead open in center minimum 600mm x 300mm near the rock face for inspection and pressure relief.

•Placing temperature of concrete for underground works shall be maintained between 100-250C. (Placing of concrete in accordance with the procedure set out in the IS:7861 (Part II) 1981.)

•The concrete grade of M30 is required in the lining concrete. Concrete mix as per approved mix design shall be prepared. The concrete produced in 60m3 /hr.

•Slump of concrete shall be checked at batching plant as well as at site and it should be as specified by mix design, (160 cm at our site)

•Pouring of concrete shall be done by concrete pump through various windows & pipes in layer by layer as mentioned in below –

•Left side window no. 1, 2 & 3•Right side window no. 4, 5 & 6•Left side window no. 7, 8 & 9•Right side window no. 10, 11 & 12•From Top Pipe no. 1, 2 & 3 pipe.

•The best vibration time is 15 to 20 seconds. Over vibration shall be avoided.

•Setting time for Overt concrete setting time shall be 15 hours. After that the shutter shall be removed. Any honeycombing or air bubbles shall be repaired.

CONCRETING

Contact grouting involves the injection of fluid grout to provide positive contact between a structure and an adjacent face.Sequence of activities is as follows:

a)MS pipe 1.5” to be fixed at the positions as directed by the Engineer before concreting of the overt lining. b)The pipe shall be 3 cm away from membrane. 3 no’s of pipes above SPL to be installed to facilitate the grouting. c)The pattern of the pipes shall be staggered and interval of the holes @ 5 m along the tunnel axis. Grease is applied on circumference of the pipe and the pipe is removed before initial setting of the concrete.d)Prior to grouting, proper workability of grout shall be checked in association with the grouting equipment ,slump range between 15 to 40.e)Cement shall be OPC 53 grade or PPCf)Temperature of water should be such as so that at the time of grouting temperature of grout shall not be less than 200 C.g)Grouting is completed when the required pressure can be kept constant over a period of 10 min.

CONTACT GROUTING

•Approved hydrophilic swelling joints will be fixed along the longitudinal joints between kerb and overt lining.

• Same process will be repeated for circumferential joints between kerb and overt lining also.

Hydrophilic swelling joint placement

Concrete lining in Main tunnelHeight of crown from Ground m 7.5Length of Shutter m 12.5Concrete Quantity per shutter Cum / Shutter 96 ApproxCapacity of concrete pump cum / hr 30Output of pump @ 75% efficiency cum / hr 22.5Time Cycle for Concreting

1 Returning of completed transits mixer after pouring of last pour @ 10 KM/Hr for lead 1.5 Km

min 9

2 Locating of new transit mixer min 53 Actual capacity of transit mixer cum 54 Empting duration of one transit mixer min 185 Total time for one emptying min 416 Capacity of pouring cum / hr 8.787 Concrete time as per Pump hr 9.62

Time cycle for 1 Shutter1 Removal of ducting hr 22 Release of shutter, cleaning of shutter plates, moving of formwork to

next locationhr 1.5

3 Cleaning of shutter with wire brush, Oiling of shutter plates hr 14 Fixing of bulkheads hr 1.55 Reinforcement Fixing, wherever is required - In Parallel hr Parallel6 Alignment of the shutter hr 1.57 Cleaning of Kerb with fresh water and spreading of Mortar hr Parallel8 Arrangement of Concrete Pump and Pipes hr Parallel9 Pouring Overt Concrete hr 9.9

10 Initial Set and retention of Stopper/ Bulkhead/traveler in place hr 7

TIME CYCLE- MT

11 Total Time Cycle hr 24.4

Effective time

Working hrs/ day hrs/ day 22

No’s of cycles per day nos/ day 0.90

Working days/ month days/ month 27

Shutter length m 12.5

Lining concreting length to be completed per day m / day 11.27

Lining concreting length to be completed per month m / month 304.3

ANY QUESTIONS???