The M4 tunnel has reopened in both directions between Haberfield and North Strathfield ahead of the peak period on Friday morning.<\/p>\n
The section of the tunnel, which is part of the WestConnex toll network, had been closed in both directions overnight as emergency crews worked on infrastructure repairs.<\/p>\n
So what caused this traffic gridlock in the first place?<\/p>\n
What is shotcrete?<\/p>\n
Shotcrete is a mixture of concrete, water and lots of sand or silt.<\/p>\n
It is shot through a hose with force created by a pump and pressurised air.<\/p>\n
As it moves through the hose, chemicals are added to speed up its setting time and bonding strength.<\/p>\n
The high velocity helps the mixture bond quickly and strongly with the surface it is sprayed onto.<\/p>\n
<\/p>\n
Roof repairs being undertaken on the M4. (Supplied: Transport Management Centre)<\/p>\n
Permanent shotcrete can last 50 to 100 years without additional maintenance, but is still perfectly serviceable indefinitely and can be replaced with a new mix when needed.<\/p>\n
It is used in countries around the world including the US, UK and France.<\/p>\n
What is it used for?<\/p>\n
Shotcrete is commonly used in Australia to help line walls in mines, subways and tunnels such as the one that comprises part of the M4.<\/p>\n
It is also used to construct retaining walls and secure excavations, especially on slopes like the ones on either side of a road cutting through what used to be a hill.<\/p>\n
It can stick to hard surfaces like sandstone or rock, or can be sprayed onto mesh wiring fitted to a more fragile surface.<\/p>\n
The mixture is used instead of normal concrete because it works well on overhead or vertical surfaces due to its quick setting times.<\/p>\n
It does not usually need a mould, can be quicker to cover larger areas, and is helpful for repair work.<\/p>\n
Standard concrete takes more time and resources to spread, level and set.<\/p>\n
<\/p>\n
Some drivers say they were stuck in traffic for more than four hours. (AAP: Bianca De Marchi)<\/p>\n
Is it reliable?<\/p>\n
Geotechnical consultant and owner of Geotechnical Designs, Shaloo Puri, said shotcrete was “very reliable and very strong”.<\/p>\n
She said a set of “rare conditions” were needed for it to start failing and that those geological problems were “such that nobody can predict”.<\/p>\n
“Somebody has designed the wire mesh and shotcrete but [if] the load is coming on that more than what has been designed for, then it will definitely fail,” Ms Puri said.<\/p>\n
“Either there’s a water problem or a rock is loose, putting pressure on the shotcrete.<\/p>\n
“There is so much traffic going over the top and there are lots of vibrations around, so it happens sometimes.”<\/p>\n
She said it was possible for the shotcrete to “crack” and “collapse” given the right circumstances and agreed with the decision to close the motorway.<\/p>\n
What next?<\/p>\n
Mr Collins told the ABC on Friday the tunnel was now fully opened and the area has been deemed safe.<\/p>\n
“Last night the engineers removed the last remaining parts of what they call the shotcrete \u2026 and checked the tunnel, it’s been certified as safe,” he told the ABC.<\/p>\n
“They will go back at some stage to deal with what appears to be a minor water leak and trying to ensure that water doesn’t remove anymore of that shotcrete lining.”<\/p>\n
Mr Collins said shutting down the tunnel was the right thing to do.<\/p>\n
“These tunnels are cut through the same stone, it’s a very stable material\u2026 [but] occasionally there are patches which leak and drip,” he said.<\/p>\n
“It is important to remove the bulges, because they could fall down and that would have been a safety risk.”<\/p>\n
Loading Instagram content<\/p>\n
Transurban, the company which owns the tunnel, issued a statement on Friday morning apologising to customers.\u00a0<\/p>\n
“We apologise for the delays motorists incurred yesterday,” a spokesperson said.<\/p>\n
“Safety is, and continues to be, our number one priority.”<\/p>\n
Motorists affected by the traffic gridlock have been offered a toll refund through the Linkt app or its 133 331 phone line.<\/p>\n","protected":false},"excerpt":{"rendered":"One of Sydney\u2019s main arterial roads has reopened a day after roofing “bulges” shut lanes for emergency maintenance…\n","protected":false},"author":2,"featured_media":328164,"comment_status":"","ping_status":"","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[2],"tags":[43,16388,183991,44,183988,183292,41,39,42,40,183296,183992,183989,183990],"class_list":{"0":"post-328163","1":"post","2":"type-post","3":"status-publish","4":"format-standard","5":"has-post-thumbnail","7":"category-headlines","8":"tag-headlines","9":"tag-m4","10":"tag-m4-closure","11":"tag-news","12":"tag-shotcrete","13":"tag-sydney-traffic","14":"tag-top-news","15":"tag-top-stories","16":"tag-topnews","17":"tag-topstories","18":"tag-westconnex","19":"tag-westconnex-closed","20":"tag-what-is-shotcrete","21":"tag-what-is-shotcrete-used-for"},"_links":{"self":[{"href":"https:\/\/www.newsbeep.com\/au\/wp-json\/wp\/v2\/posts\/328163","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.newsbeep.com\/au\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.newsbeep.com\/au\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/au\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/au\/wp-json\/wp\/v2\/comments?post=328163"}],"version-history":[{"count":0,"href":"https:\/\/www.newsbeep.com\/au\/wp-json\/wp\/v2\/posts\/328163\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/au\/wp-json\/wp\/v2\/media\/328164"}],"wp:attachment":[{"href":"https:\/\/www.newsbeep.com\/au\/wp-json\/wp\/v2\/media?parent=328163"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.newsbeep.com\/au\/wp-json\/wp\/v2\/categories?post=328163"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.newsbeep.com\/au\/wp-json\/wp\/v2\/tags?post=328163"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}