KNOWLEDGE · TUNNELS AND UNDERGROUND STRUCTURES

Tunnels: joint sealing and section monitoring

Water may travel along a joint and emerge far from the defect. Divide the repair by treatment zone: in the joint, in the segment or behind the lining.

Assessment Procedure and options Selection and next step

EXPLORE THE METHOD

Segment joint: needle access and injection control

First see the objective in the full cross-section, then follow drilling, assembly and installation of the equipment, injection and observation of successive points. The sequence concerns the segment connection shown; other lining zones require separate assessment.

Segment joint cross-section: the black profile represents the gasket zone, yellow represents injection material beside the connection, and the thin element is the material delivery needle.

01 · Objective and geometry

Assess the joint sealing zone

The detail shown aims to deliver material to the leaking zone beside the segment connection. The diagram shows the target material path and the needle left in place; subsequent illustrations explain preparation and installation.

Assess actual joint geometry, gasket position and water conditions. This is one tunnel detail. Repairing a segment crack, filling a void behind the lining and ground stabilisation have different objectives and require separate access and material selection.

Distinguish the joint from a crack and a void behind the lining.
Establish gasket position before drilling.

Material and tunnel zone selection →

A drill bit from inside the structure reaches the connection zone beside the black gasket profile.

02 · Access preparation

Create access to the assessed zone

Plan the hole using the segment and gasket detail. The path shown is an access diagram for a specific zone, not permission to drill arbitrarily through the gasket, reinforcement or the entire lining.

Monitor direction and depth. Stopping a hole short of the target or extending it beyond the intended zone may cause entirely different material spread. Adapt hole preparation to the selected needle and material.

Check connection documentation.
Confirm depth and clear passage.

Application trial →

Two assembly components before connection: tube and thin needle. The green arrow shows assembly direction.

03 · Assembly

Connect the needle to the injection tube

Select a compatible needle and tube set so that, after installation, the tip delivers material to the planned location. Check the connection method for the specific model.

Before assembly, assess component condition and clear passage along the injection path. Assembly length follows the connection cross-section; visual similarity to the drawing alone does not confirm interchangeability.

Check component compatibility.
Do not install a damaged or blocked needle.

Socket and assembled needle with tube; the arrow shows their interaction during installation.

04 · Assembly

Prepare the correct installation socket

The option shown requires a socket matched to the assembly. It must transmit installation movement according to the instructions and allow controlled installation.

Do not select tightening force from the illustration's appearance. Installation method depends on the specific accessories and prepared hole.

Use a compatible socket.
Check the ability to control installation depth.

The assembly has been inserted into the hole; the needle tip reaches the connection zone and the tool is used for installation.

05 · Assembly

Install the assembly in the prepared hole

Insert and install the assembly according to the model's instructions, retaining the planned tip position. The tool aids installation but does not replace checking that the target is reached.

Before injecting material, check stability, connection and the ability to deliver injection material. Do not start pumping if there is doubt that the tip lies in the target zone.

Confirm position and stability.
Check connection tightness.

The pump hose is connected to the assembly; yellow injection material enters the leaking zone beside the joint.

06 · Injection and observation

Inject material into the zone beside the gasket

Select material for water, movement, geometry and the ability to retain it in the connection. With strong inflow, a separate flow-reduction stage may be needed before actual sealing.

During the trial, observe pressure, uptake and nearby discharges. Do not equate filling shown in the drawing with proven filling of the actual connection. Uncontrolled migration behind the lining requires assessment and adjustment.

Monitor material in the target zone.
Respond to unusual uptake or discharge.

Materials for tunnels →Pressure and observation →

Two injection points in the connection. Material appearing at the next point shows communication between them.

07 · Injection and acceptance

Observe successive points and complete the work

Material reaching the next needle is an observation of spread within the zone. Base continuation on the trial and section behaviour, not merely the first drop appearing. Record quantity, pressure and discharge locations.

In the detail shown, the needle remains in the structure. Complete the connection and acceptance according to the system and repair design. Assess watertightness and joint behaviour after completion; material contact between points alone does not replace this inspection.

Keep documentation for individual points.
Check watertightness after completion.

Cleaning the delivery system →

Mark the location before naming the method

Assign observations to a tunnel ring or section and a position around the perimeter. Distinguish joint leakage, segment cracks, cavities, penetrations and suspected voids behind the lining. For each zone, record water conditions, previous interventions and repair access.

The tunnel's lower part collects both local water and water running down from the sides and crown. A wet point near the invert need not be the original leakage location. Compare observations along the joint and on adjacent rings, including after surface cleaning.

Three zones mean three tasks

In the segment joint

The objective is to seal the assessed space beside the connection while preserving its function. Select needle or borehole access for the actual cross-section, gasket position and permissible intervention.

Within the segment itself

A crack, damaged edge and cavity are different defects. Establish whether flexible sealing, void filling or force-transferring repair is needed. The latter is defined by the structural design.

Behind the lining

Material may reach an unfilled space or the ground. This requires a different scope of assessment, displacement monitoring and quantity calculation from local joint sealing.

Access for future repair

Before closing layers, permanent injection and observation points can be designed. Their presence provides application access; it does not itself confirm lining support or watertightness.

The needle is part of planned access

The cross-section shows injection into the segment connection zone. Needle geometry, depth and tip position must relate to joint documentation. Do not treat the needle as a tool for randomly puncturing the gasket. Joint cleaning and clear points allow water to be distinguished from arriving material.

Choose a short reference section. One point serves for injection, with subsequent points for controlled observation and further injection. Plan their closure without disconnecting a pressurised system. Where zones require discharge restriction, select a seal that retains observation access and does not block connection movement.

The joint may communicate with space behind the lining

Material appearing at an adjacent point confirms a connected flow path. If quantity increases without progress, material emerges in a distant section or water carries soil particles, reassess the treatment zone. Communication with space outside the joint is possible. No sand in the small needle channel does not exclude such a connection.

Switching to injection behind the lining changes the task. Assessment is needed of available space, pressure limits, possible escape paths and how structural response will be measured. Increasing the material limit in the existing procedure is insufficient.

Combine cleaning, reaction and observation

Contamination in the joint zone may weaken adhesion and conceal discharge paths. After preparation, conduct a reaction-time trial at the working temperature. Select it for path length, water flow and material retention. With intense inflow, the leak-stopping stage must create conditions for the selected main seal.

Inject gradually, recording pressure, quantity, time and communication sequence. Controlled re-injection means topping up an accessible zone within the working window; it is not synonymous with high pressure. In a ventilated area, finish selection should include protection of materials sensitive to drying.

A void beneath the lining requires displacement monitoring

If the objective is filling or support stabilisation, the design specifies material, stages and lining monitoring. Expanding resin may affect the structure after pumping ends. Levelling readings must be compared with uptake and material communication.

Unintended lifting, a sudden pressure rise or lack of expected communication require stopping and reassessing the section. See the difference between stabilisation, filling and lifting. A hose or packer rating is not the permissible pressure for the lining.

Inspect the section under its service conditions

Plan a work window allowing time for preparation, reaction, cleaning and inspection. In section documentation, record the target zone, points, formulation, consumption and unintended discharge locations. Do not apply one section's result to the entire lining where conditions vary.

Sealing acceptance includes adjacent water paths and section connections. Stabilisation acceptance also includes required support and displacement measurements. Inspection after water conditions change allows assessment of locations inactive during the works.

RESINBAU SELECTION

Site conditions determine the material

ResinBau AcrylGel + Polymer →

For flexible sealing of assessed joints; select reaction time and protection against drying.

HydroGum →

For zones with water needed for reaction and connection sealing; control the material path and conditions confining expansion.

WaterStopper →

A stage stopping strong inflow to enable further controlled repair.

CrackFlex →

Flexible sealing of cracks or selected connections where water flow allows material to remain in the zone.

GeoPolymer.350 →

For designed void filling and stabilisation. Selection requires monitoring expansion effects on the lining; it does not replace flexible material in a moving joint.

InjectGrout →

Mineral filling of suitable voids, including those containing water. The TDS requires no flow during injection and for 12 hours afterwards; relate conditions to the element temperature.

Calculate what you know

CALCULATORBatch preparation →

Match the product and variant to the approved method for the section.

CALCULATORMaterial quantities →

Record quantities for each zone and formulation; conversion does not determine coverage behind the lining.

Next step

Discuss your project conditions

Prepare a cross-section, a description of water and movement, and results of previous trials. ResinBau helps select the material and application method.

Discuss your project / technical selection ↗