{"id":1111,"date":"2013-02-09T17:47:05","date_gmt":"2013-02-09T17:47:05","guid":{"rendered":"http:\/\/www.ericjorden.com\/blog\/?p=1111"},"modified":"2013-02-09T17:47:05","modified_gmt":"2013-02-09T17:47:05","slug":"gabion-retaining-wall-collapse-results-in-litigation","status":"publish","type":"post","link":"http:\/\/www.ericjorden.com\/blog\/2013\/02\/09\/gabion-retaining-wall-collapse-results-in-litigation\/","title":{"rendered":"Gabion retaining wall collapse results in litigation"},"content":{"rendered":"<p>(The following is one in a series of cases I have investigated that illustrate the different <strong>forensic engineering methods\u00a0I\u00a0use to investigate<\/strong> <strong>the cause of failures<\/strong> and <strong>accidents<\/strong> that <strong>result in civil litigation.\u00a0 <\/strong>The methods are described in\u00a0some detail)<\/p>\n<p>The investigation of the wall collapse is reported under the following main headings with several sub-headings:<\/p>\n<ul>\n<li>The case (a description of the\u00a0collapsed gabion wall, the legal\/technical issues, and my client)<\/li>\n<li>Forensic engineering investigation of the failure and the methods used<\/li>\n<li>Cause (of the collapse)<\/li>\n<li>Post mortem (<strong>an engineering &#8220;rule of thumb&#8221; might have prevented the collapse<\/strong>)<\/li>\n<\/ul>\n<h1><span style=\"color: #3366ff;\"><strong>The case<\/strong><\/span><\/h1>\n<p><strong>Description of collapse<\/strong><\/p>\n<p>The gabion wall was on\u00a0the shore of a\u00a0harbour in eastern Canada.\u00a0\u00a0The wall\u00a0was 10 feet high and more than 100 feet long.\u00a0 There were short wing walls to the main wall aligned shoreward.\u00a0 A &#8220;gabion&#8221; is a wire basket\u00a0about 3 feet\u00a0by 3 feet in section and 10 feet long\u00a0filled with course stone several inches in size.<\/p>\n<p>The wall was being constructed to reclaim land on the seaward side of a\u00a0quite large\u00a0townhouse property.\u00a0 The wall\u00a0fell over just before construction was complete.\u00a0 It was rebuilt before I was retained.<\/p>\n<p><strong>Legal\/Technical issue<\/strong><\/p>\n<p>At issue was the cause of the\u00a0wall\u2019s failure.\u00a0 This was in connection\u00a0with a claim of damages against the designer and his insurance company.<\/p>\n<p><strong>Client<\/strong><\/p>\n<p>I was asked by the plaintiff,\u00a0a property manager who was acting on behalf of a contractor, to\u00a0determine\u00a0the\u00a0cause of the collapse.<\/p>\n<h1><span style=\"color: #3366ff;\">Forensic engineering investigation<\/span><\/h1>\n<p>My forensic engineering investigation relied on the\u00a0following methods.\u00a0 The methods\u00a0are described in\u00a0more detail below:<\/p>\n<ol>\n<li>Examining\u00a0the site of the rebuilt wall<\/li>\n<li>Studying\u00a0photographs taken of the collapsed wall<\/li>\n<li>Studying\u00a0a design sketch of the wall<\/li>\n<li>Interviewing\u00a0two workers who were on the wall at the time it failed, including one who slid\u00a0down with the wall on a piece of construction equipment as it fell over<\/li>\n<li>Interviewing\u00a0the design engineer<\/li>\n<li>Reviewing\u00a0design principles for coastal and marine structures<\/li>\n<li>Reviewing\u00a0weather and sea conditions at the time of the failure<\/li>\n<\/ol>\n<p><strong>Description of methods of forensic engineering investigation<\/strong><\/p>\n<p><strong>1. Examining the site of the rebuilt wall<\/strong><\/p>\n<p>This initial site visit and visual assessment is standard in an engineering investigation and an important initial task by a forensic engineer (Ref. 1).\u00a0 Drawings and photographs are fine but picking up a concrete impression is important.\u00a0 It&#8217;s well recognized that, &#8220;A picture is worth a\u00a01,000 words&#8221;.\u00a0 However, a\u00a0visual assessment is invaluable.\u00a0 This is\u00a0so even if the collapsed structure has been rebuilt as was the case\u00a0with the gabion wall.<\/p>\n<p>I was able to see\u00a0how the toe of the gabion wall was constructed where it was exposed to the\u00a0scour and erosive forces of wave action in the harbour.<\/p>\n<p>I also saw the location of the\u00a0townhouse with respect\u00a0to the wall.\u00a0 The contractor had expressed concern that construction of the wall as designed would undermine the townhouse.\u00a0 A simple rule of thumb ruled this out.<\/p>\n<p><strong>2. Studying photographs taken of the collapsed wall<\/strong><\/p>\n<p>Photographs are important, and sometimes all we have.\u00a0 They are particularly important when detailed photographs are taken during construction.\u00a0 They are also important when taken of the failed structure\u00a0that is subsequently\u00a0removed before the forensic engineer gets there.\u00a0\u00a0The latter was the\u00a0case in this\u00a0instance.<\/p>\n<p>The\u00a0photographs\u00a0showed the actual wall construction and that it failed in a quite classic manner &#8211; it just tipped, tilted, leaned\u00a0over along most of its length.\u00a0 The exception was where the wall was tied in and anchored to the wing wall at one end.\u00a0 It\u00a0remained upright there.<\/p>\n<p><strong>3. Studying a design sketch of the wall<\/strong><\/p>\n<p>It goes without saying that a professional engineer investigating a failure would want to know how the\u00a0failed structure was designed and intended to be built.\u00a0 This is a standard\u00a0task in\u00a0a forensic investigaion.<\/p>\n<p>The sketch showed how the design engineer originally wanted the base of the wall constructed\u00a0and the toe of the wall protected against scour and erosion.\u00a0 Simple rules of thumb suggested the base design was adequate.\u00a0 The toe protection was less so.<\/p>\n<p><strong>4. Interviewing workers<\/strong><\/p>\n<p>Interviewing workers is a\u00a0standard task in a forensic investigation.\u00a0 The interviews sometimes\u00a0provide quite valuable\u00a0information on conditions at the moment of failure.<\/p>\n<p>I interviewed two workers who were on the wall at the time it failed, including one, an equipment operator,\u00a0who slid down with the wall on a piece of construction equipment as\u00a0the wall collapsed.<\/p>\n<p>In\u00a0engineering analysis we\u00a0speak at times about a &#8220;trigger&#8221; in a failure.\u00a0 All conditions are present &#8211; or\u00a0nearly so, for\u00a0a structure, a wall, an earth slope, etc.,\u00a0to collapse.\u00a0 The trigger pushes the structure over the edge\u00a0in a sense.\u00a0 Sometimes there is heavy rain &#8211; the trigger,\u00a0just before a landslide.<\/p>\n<p>The construction equipment\u00a0just back of\u00a0the gabion wall at the time was the trigger in this case, an extra surcharge\/weight on the wall.<\/p>\n<p><strong>5. Interviewing the design engineer<\/strong><\/p>\n<p>We always want to\u00a0talk with the design engineer\u00a0when investigating a failure but often don&#8217;t have the opportunity during the investigative stage.\u00a0 This lack of opportunity is particularly the case when the\u00a0design engineer is\u00a0the defendant in\u00a0a civil action.<\/p>\n<p>In this case, however, the design engineer was quite professional in agreeing to talk with me.\u00a0\u00a0His design was okay\u00a0in the\u00a0short term.\u00a0 It turned out that\u00a0a change he approved during construction caused the problem.<\/p>\n<p>The change involved reducing the width of the base from about six feet &#8211; 2\/3 the height of the wall, to three feet &#8211; 1\/3 the height of the wall.\u00a0 The change was made because the contractor said he couldn&#8217;t build a six foot\u00a0base.\u00a0 He also expressed concern that the townhouse would be undermined.\u00a0\u00a0Consideration of a\u00a0simple rule of thumb would have raised an alarm that the wall would not be stable with a three foot base.\u00a0 Another rule would have demonstrated that the townhouse was not endangered.<\/p>\n<p><strong>6. Reviewing design principles for coastal and marine structures<\/strong><\/p>\n<p>Reviewing the design prinicples applicable to a situation is\u00a0standard fare in a forensic engineeing investigaion and I did this.\u00a0 I was particularly interested in the requirements for protecting the toe of the wall against scour and erosion due to sea conditions.<\/p>\n<p><strong>7. Reviewing weather and sea conditions at the time of the failure<\/strong><\/p>\n<p>This is also standard fare during a forensic investigation and in this case it tied in with reviewing the design principles mentioned above.\u00a0 Sea and weather conditions were calm at the time of the wall collapse.<\/p>\n<h1><span style=\"color: #3366ff;\">Cause<\/span><\/h1>\n<p>I concluded, based on the evidence, that the\u00a0wall failed because of a change in the design of the\u00a0wall during construction.\u00a0 The principle defect was that the base of the 10 foot wall was not wide enough at three feet.\u00a0 I also found that the toe of the wall was not well protected against\u00a0wave action in the harbour.<\/p>\n<h1><span style=\"color: #3366ff;\">Post mortem<\/span><\/h1>\n<p>There is a rule of thumb in the design of conventional gabion retaining walls that the width of the base of the wall must be about\u00a02\/3 the height of the wall &#8211; about 6.5 feet in this case, not 3.0 feet as agreed during construction.\u00a0 A design engineer starts off with this conventional wall\u00a0geometry and then checks that the rule of thumb holds in the particular case.<\/p>\n<p>There are lots of rules of thumbs in engineering,\u00a0 They expedite matters but must always be checked.\u00a0 And they should always be referenced when the pressure is on\u00a0to change things during construction.<\/p>\n<p>The matter was settled out of\u00a0court.<\/p>\n<p><strong>References<\/strong><\/p>\n<p>1. &#8220;Technical&#8221; visual site assessments: Valuable, low cost, forensic engineering method.\u00a0 My blog posted on this site, September 4, 2012<\/p>\n","protected":false},"excerpt":{"rendered":"<p>(The following is one in a series of cases I have investigated that illustrate the different forensic engineering methods\u00a0I\u00a0use to investigate the cause of failures and accidents that result in civil litigation.\u00a0 The methods are described in\u00a0some detail) The investigation &hellip; <a href=\"http:\/\/www.ericjorden.com\/blog\/2013\/02\/09\/gabion-retaining-wall-collapse-results-in-litigation\/\">Continue reading <span class=\"meta-nav\">&rarr;<\/span><\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":[],"categories":[15,16,17],"tags":[],"_links":{"self":[{"href":"http:\/\/www.ericjorden.com\/blog\/wp-json\/wp\/v2\/posts\/1111"}],"collection":[{"href":"http:\/\/www.ericjorden.com\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"http:\/\/www.ericjorden.com\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"http:\/\/www.ericjorden.com\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"http:\/\/www.ericjorden.com\/blog\/wp-json\/wp\/v2\/comments?post=1111"}],"version-history":[{"count":21,"href":"http:\/\/www.ericjorden.com\/blog\/wp-json\/wp\/v2\/posts\/1111\/revisions"}],"predecessor-version":[{"id":1132,"href":"http:\/\/www.ericjorden.com\/blog\/wp-json\/wp\/v2\/posts\/1111\/revisions\/1132"}],"wp:attachment":[{"href":"http:\/\/www.ericjorden.com\/blog\/wp-json\/wp\/v2\/media?parent=1111"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"http:\/\/www.ericjorden.com\/blog\/wp-json\/wp\/v2\/categories?post=1111"},{"taxonomy":"post_tag","embeddable":true,"href":"http:\/\/www.ericjorden.com\/blog\/wp-json\/wp\/v2\/tags?post=1111"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}