Concrete Tunnel Closure Solutions

Concrete Tunnel Closure Products from Synthetex

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Concrete Tunnel Closure Products from Synthetex

Get a project estimate today:



Custom cast-in-place (CIP) tunnel closure products from the leading manufacturer of fabric formworks for the casting of concrete.

Sometimes a tunnel closure is required inside a dam facility or around it. Rather than using traditional methods that are difficult to install, rely on a custom-made HYDROCAST armor unit to close the tunnel.

These bags are entirely custom-made to the tunnel’s specifications and can come in different shapes such as cubes, rectangles, or shapes with curves. Unlike normal grout bags, our HYDROCAST armor units have more than two sides, making them an effective tunnel closure tool.

How is HYDROTEX used for spillway protection?

The Problem

Over the lifespan of older infrastructures at power plants, dams, and municipalities, tunnels and pipelines must be closed due to evolving regulatory laws or to prevent collapse that could damage the valuable properties above.

The Solution: HYDROTEX Fabric Forms for the In-Situ Casting of Concrete

Effectively prevent catastrophic collapse by casting a custom-sized concrete bag with HYDROTEX and HYDROCAST fabric formworks. Once filled with concrete, these formworks will create a permanent bulkhead at the ends of tunnels or pipelines. In between the concrete bag bulkheads, the void space can be filled with a flowable fill or grout.

Best HYDROTEX Fabric Forms for Closing Tunnels and Pipelines

HYDROCAST® Armor Units



HYDROTEX® Grout Bags



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Spillway Protection for Dams

A spillway ensures that the dam doesn’t overflow or fail by allowing a controlled amount of water to spill from the dam.

To ensure that the spillway doesn’t experience a loss of soil, dam owners and engineers should factor in a need for an effective erosion control system. A concrete lining such as HYDROTEX fabric-formed concrete will ensure that the spillway continues functioning as it should.

Another solution we offer at dams is embankment protection.

Spillway protection is typically needed for:

Lock and dam

Related Solutions

HYDROTEX® Grout Bags

Grout (Concrete) Bags


Synthetex’s HYDROTEX® Grout (concrete) Bags (GB) and tubes are an economical and convenient choice for applications requiring concrete, grout or sand filling.  Constructed of the high-strength polyester fabrics and using a heavy-duty sewing process, our bags are ready to perform in your most demanding construction or repair installations.  The custom designed bag is available in a variety of materials and a wide assortment of dimensions, porosities, volume capacity, and filling valve types that ensure compatibility with your applications.  Their flexibility and size makes them ideal for installation through confined spaces.

Synthetex provided more than 70 grout bags ranging from a 1.5 m³ to 168 m³ capacity for the repair of an airstrip jetty in the Shetland Islands, Scotland.  The bags were first filled with water and then the water displaced with concrete to permanently fill voids in the rock jetty.

The bags provide the formwork required to cast concrete elements with the mass and stability to withstand the waves and rapidly flowing water.  The concrete grout bags may be placed side-by-side or stacked to form an inherently interlocked concrete structure.  As with our HYDROCAST® formworks, concrete grout bags can be positioned and filled with concrete from the surface in shallow water or by divers in deeper water.

Since they are cast-in-place, they intimately adapt to variations in the subgrade or bottom contours. Installations do not require dewatering, a crucial advantage in emergency repair of scour aprons.  Unlike rock or precast concrete blocks, they do not require placement by heavy lift cranes working from the land or from barges.

Synthetex’s grout bags can be used to help with the following:

  • Breakwater, dike, groin and jetty repair
  • Bridge column repair
  • Culvert aprons
  • Embankment stabilization
  • Grout bag underpinning
  • Seawall and quay wall repairs
  • Scour repairs
  • Vertical drains
  • Void filling

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HYDROCAST® Formworks


HYDROCAST® (HC) Formworks



Synthetex specializes in manufacturing engineered, project-specific fabric formworks for the casting-in-place of concrete armor units and structures for a spectrum of underwater applications.  For more than 25 years, engineering, contractor, and government clients around the world have relied on HYDROCAST® to design and fabricate the special concrete formworks they need for their projects.  They know Synthetex will deliver only the highest quality products, materials, and workmanship—guaranteed.

As leading specialists in the fabrication of fabric formworks for underwater casting of concrete structures, Synthetex offers engineered solutions such as custom armor units for spillway aprons, bulkheads, tunnel and pipe plugs, and more.  Our expertise includes working with nearly every component and material used in concrete formworks today, including high-strength polyester and Kevlar® fabrics and sewing threads, and steel and high tenacity polyester reinforcement cables.  With newly expanded manufacturing capabilities, we’re able to offer end-to-end solutions in-house, delivering finished products that are designed and built to perform.

HYDROCAST® fabric formworks provide low-cost in situ concrete alternatives to natural rock and precast concrete where they are not possible or practical.  Cast-in-place, concrete armor units and structures eliminate the requirement for heavy lift cranes for placement, where rock riprap and precast concrete blocks may require lifts of tens of thousands of pounds.  As with our concrete grout bags, HYDROCAST® can be positioned and filled with concrete from the surface in shallow water or by divers in deeper water.  Since the flexible fabric forms are cast-in-place, they intimately adapt to variations in the subgrade or bottom contours.  Installations do not require dewatering, a crucial advantage in emergency repair of scour aprons.

Synthetex worked closely with the U.S. Army Corps of Engineers and Bergmann Associates for the design of fabric forms for the underwater casting of armor units for the scour aprons of two Ohio River locks and dams. The concrete armor units ranged in sizes, up to 36 ft long x 18 ft wide x 6 ft high, and weights in excess of 10 tons each.  The specification of a fabric formwork that can be deployed underwater and then pumped full with concrete avoided the lifting of the massive armor units.

Heavy-duty, puncture-resistant formworks designed to meet pumped concrete pressures were placed into reusable steel frames and lowered into place in rows and columns.  As the frameworks were lowered they were filled with water to offset buoyancy and to inflate the formwork to its rectangular dimensions.  As concrete was pumped into the formwork an equal volume of water was displaced. The flexible bottom allowed intimate contact with the uneven subgrade. And, all of this is performed entirely under water and constructed on a slope.

HYDROCAST® concrete grout bags meet the requirements for a reliable and economical cast-in-place alternative to traditional rock (riprap) and precast concrete for the armoring of sand-filled geocontainers.

Applications for HYDROCAST® custom fabric formed concrete units:

  • Concrete armor units for dam scour aprons
  • Concrete armor units for the main primary protection of breakwaters, levees, and dikes
  • Artificial concrete reefs
  • Concrete armor units as the protection of sand-filled geocontainers
  • Pipeline and tunnel closures
  • Concrete quay walls and seawalls
  • Concrete sealing of large mineshafts and tubes

Ronald Stive, Director of Projects, Maritime and Waterways at Royall Haskoning DHV, has reported a trend toward using sand packed into geocontainers at the core of a breakwater, a solution that could be ten times cheaper than traditional rock.

“What we have noticed in the past ten years in our port and breakwater projects is that all around the world, people are in a hurry,” he noted. “They don’t accept that these types of structures will take years to design and to construct, so they are always looking for alternative ways to do it faster.

“Secondly, there is a trend to go into deeper water, and into areas where you don’t have quarries nearby and you may have problems where the seabed isn’t stable enough or there’s seismic activity. In these remote areas, you have to look for alternative designs to the traditional rubble mound type of breakwater, because of the fact that the materials are too far away or too costly to bring in.”