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Rockfall Protection - Wookey Hole Catch Net 2015

Wookey Hole Catch Net

Rockfall Protection - Wookey Hole Catch Net 2015

Rope Access Contractor placing bolts prior to the installation. The clock to be caught is to the left of the contractor.

Rockfall Protection - Wookey Hole Catch Net 2015

Installation of the transmission ropes.

Rockfall Protection - Wookey Hole Catch Net 2015

Four anchors drawn together and connected to U-brake

Rockfall Protection - Wookey Hole Catch Net 2015

Catch net during construction

 

System length

6 m - 15 m

 

Year of installation

2015

Initial situation

Frederick Sherrell Ltd Consulting Engineers approached us to ask, “is it possible to create a horizontal catch net to catch and hold a potentially unstable 10 ton boulder?” The client is Wookey Hole Show caves, they were planning to bore a tunnel from an existing cave to a cave that previously was only accessible to divers. There was a small risk that the vibration from the works could dislodge a 10 ton block in the roof of the currently accessible cave.

To carry out the works all tools, equipment, anchors and all components of the catch net had to be carried into the cave system by hand. A specialty rope access contractor with extensive experience in caves was engaged to assist with installation of the upper and lower access ropes. They first had install bolts for the rope access, before installing the anchors and the catch net. The anchors had to be drilled and installed using hand held equipment so the anchors had to be short enough for easy handling. To add to the complication of using short anchors the bedrock in the cave is a Dolomitic Conglomerate with a mean strength of only 35-40MN/m2. Following pull out tests we discovered that we would be required to design for a max load of 40kN per anchor.

Description

Geobrugg engineers designed a solution using our ROCCO 12/3/350 ring net to catch the block. Given the requirement to hand-carry and manually winch the net to the roof, we customized the ring net panels to allow for easy maneuverability and easy installation based on the location of the ropes. To take load from any impact Geobrugg installed five transmission ropes across the width of the cave. Geobrugg installed a U300 brake at each end of the ropes. Perimeter ropes were installed to give shape to the net.

Collaborating with the designers at Frederick Sherrell we designed a novel solution for installing suitably safe anchors given the weakness of the rock. In total 14 sets of anchors were installed. The anchors were paired together using wire rope. Two pairs were then attached to the U300 brake at each anchor point.

Upon project completion the contractor commented that the system drawings were clear, Geobrugg's engineer was accessible if there were questions, and the installation was extremely straightforward and far less complicated and time consuming than he had expected. He was impressed with this level of service and drawings that were provided for a custom designed product.

Customer

Wookey Hole Caves

Engineering

Frederick Sherrell Ltd Consulting Engineers

Your local contact

Kevin H. Coyle
 

Kevin H. Coyle

Regional Manager Northeast

Natural Hazards
Hydraulic Engineering
Geobrugg North America, LLC,3 Beaudet Terr,Columbia CT 06237 / United States Regional Manager Northeast

E-Mail

Saleh Feidi
 

Saleh Feidi

Regional Manager California

Natural Hazards
Hydraulic Engineering
Geobrugg North America, LLC,8921 Emperor Ave.,San Gabriel, California 91775 / United States Regional Manager California

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John Kalejta
 

John Kalejta

Regional Manager Central US

Natural Hazards
Hydraulic Engineering
Geobrugg North America, LLC,3215 67th Avenue Pl,Greeley CO 80634 / United States Regional Manager Central US

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Bob Lyne
 

Bob Lyne

Regional Manager Southeast

Natural Hazards
Hydraulic Engineering
Geobrugg North America, LLC,8004 Windspray Drive,Summerfield NC 27358 / United States Regional Manager Southeast

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Pierce Runnels, Civil Engineer
   

Pierce Runnels

General Manager Geobrugg North America

Natural Hazards
Geobrugg North America, LLC,22 Centro Algodones , Civil Engineer General Manager Geobrugg North America

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Tim Shevlin
 

Tim Shevlin

Sales Director

Natural Hazards
Geobrugg North America, LLC,Salem OR 97302 / United States Sales Director

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