After completion of drilling and strengthening of tunnel or underground structure as per NATM method, insulation implementation process shall be started. Before insulation implementation, surface shall be of 5 cm thickness and cavity and bulges shall be minimized by gunned concrete implementation with plane surface. After rough loading through gunned concrete, if necessary, corrections shall be made by finishing coat aggregate and concrete with chemical agents. (Ref:01)

After formation of drainage lines on particularly base on all sections to be covered, Layers shall be formed on lean concrete.
-Geotextile ( in accordance with Highways Technical Specifications, 100% Polypropylene )
-Multiplan Signal Layered PVC Membrane ( Multiplan BA/T )
-Geotextile ( in accordance with Highways Technical Specifications, 100% Polypropylene)

After covering by welding by means of strings used in placement of internal surface of the tunnel with help of Multiplan BAT PVC membrane welding machines, Multiplan BAT 7-10 cm overlap is applied and seam welding process is started using a seam welding fusion robot. After applying seam welding carefully, it is combined with material coming from base and therefore insulation is completed. Covering concrete is applied in sufficient volume by the contractor and tunnel takes its final form. If insulation layer is to be reinforced with spring concrete, it shall consist of double-layer geotextile and one-layer PVC membrane; if not, there may be no need double-layer geotextile in internal surface.


Air conditions;

PVC membrane placement shall be applied when ambient temperature is between +7°C and 40°C.

Pvc Membrane Welding;

Double-seam air welding robots shall be used.

Welding overlap;

Membrane welding overlap shall be minimum 7-10 cm.

Welding Equipment and Accessories;

Equipment approved for field welding shall include double-seam hot air welding robot and the following equipment.
- Double-seam hot air welding robot
- Manometer and small compressor for air pressure test
- Hot air hand welding for patches
- Necessary electrical cables and other tools

Test Welding;

In order to control convenience of welding conditions and welding equipment, field test welding shall be applied. These test shall repeated for all welding equipment used in every beginning of application period and significant air changes. All tests welding machines shall be available in the area where application will be done. Approved welding methods are double-seam hot air welding robot.

Field welding tests;

All test tools and equipment shall be available in the area and ready to be tested.

Air Pressure Test;

The following method shall be used for testing of double-seam hot air welding robot. The required equipment are as follows:

- Air pump with a pressure room which may exert or halt 25–30 (1.75–2.10) psi pressure, assembled on a damper for protection of PVC membrane.
- sharp-pointed, spline needle or another approved pressure feeding tool

Operator shall follow the following steps for test;

- Ending point of welding machine to be test is closed.
- Needle or approved pressure feeding tool is inserted from closed point of channel made by double-seam fusion welding.
- Air is pumped using a pump to determine if air channel is wholly clean.
- Other ending point of the channel is closed.
- Joint welding points made by double-seam welding robots shall be tested for impermeability by pumping pressure air through air channel located in welded joint point. In the beginning test pressure shall be 2 bar for 5 minutes testing or 1.5 bar for 10 minutes testing. In case of air pressure loss more than 20%, joint point is considered as waterproof.


Broken and defective welds shall be welded again as specified in the specification.
Small holes may be repaired using hand welding. If hole is huge, it shall be patched.
Lacerations shall be repaired with patches. If area to be patched is vertical or a stretching area or has sharp edge, this area shall be rounded and accordingly hampered from moving forward. Patches shall be round and oval and faulty part edge shall exceed minimum 10 cm. All patches shall be of same thickness and structure with pvc membrane.

Test Results

All test results shall be documented and kept as important document until they are mutually signed by competent authority preparing delivery record and accepted by building site employees.

PVC membrane implementation acceptance

There are two types of acceptance. Temporal acceptance is performed after implementing company fulfills its responsibilities and makes a record mutually signed by competent authorities. Implementing company bears all responsibilities of pvc membrane implementation until its precise acceptance by competent authorities.
Required conditions for the acceptance of PVC membrane implementation are as follows:
- Implementation should be completed without any problem.
- All tests performed for the implementation should be declared in full and validly.