A reader in the U.K., Len Threadgold,\u00a0(see profile below) commented on\u00a0last week’s\u00a0blog. (Ref. 1)\u00a0\u00a0Len speaks with some authority when he notes that the problems with water can be grouped under\u00a0the following three headings.\u00a0 He also notes that separating problems into neat categories is useful but sometimes the categories work in association with each other – see examples below.<\/p>\n
This classification is good<\/em><\/strong>:\u00a0A way of understanding natural events and environmental processes.\u00a0 In a sense, a way of measuring things.\u00a0 Engineers like that.\u00a0 It helps us solve problems and explain causes and technical issues\u00a0to the justice system.\u00a0 As such, it’s a forensic engineering method:<\/p>\n 1. The problems that the presence of water causes<\/strong><\/p>\n We don\u2019t like flooding or working under water –\u00a0so\u00a0this problem\u00a0concerns water level.<\/p>\n Examples would be your\u00a0flooded basement, also the water pooling in your back garden that has drained from the land above\u00a0– sorry to bring\u00a0these examples up.\u00a0 And the recent flooding that occurred in Truro, N.S., and in the U.K., and forecast for the Saint John River, New Brunswick.\u00a0 Water pressure would also be a factor in a wet basement; see #3\u00a0below.<\/p>\n 2. The problems that the flow of water causes<\/strong><\/p>\n These problems\u00a0are about\u00a0erosion, the removal of soil as a result of water flow,\u00a0the speed of the water.<\/p>\n For example, coastal erosion such as that occurring around the entire coast line of Prince Edward Island and also\u00a0at Red Head, on the Bay of Fundy near Saint John, New Brunswick.\u00a0\u00a0The flowing water on the coast is\u00a0wave\u00a0action and long shore currents.<\/p>\n I investigated one landslide at Red Head some time ago that destroyed a home at the top of\u00a0a sea cliff.\u00a0 I learned two weeks ago that erosion of the bottom of the cliff continues\u00a0to remove\u00a0the buttressing effect of the soil there.<\/p>\n Rain triggered the landslide at Red Head that I investigated – after erosion of the toe\u00a0set the stage.\u00a0 Rain did this by increasing the pressure in the\u00a0ground water behind the cliff; see #3 below.<\/p>\n 3.\u00a0The problems\u00a0that the pressure of water causes<\/strong><\/p>\n These problems arise because water pressure affects\u00a0soil strength.\u00a0 You know this when your boots sink into the mud – clay in engineering – after a rain storm.<\/p>\n The problems are bigger than sinking, muddy boots though.<\/p>\n Water pressure – what we call pore water\u00a0pressure<\/em> in\u00a0engineering –\u00a0is often a factor in landslides as\u00a0it was\u00a0for the landslide at Red Head.\u00a0 At times water pressure is the principal cause in changing an adequately stable slope to an unstable one.\u00a0 Its effect is to\u00a0reduce the frictional strength of the soil.<\/p>\n Water pressure was certain to have been a factor in the recent landslide in Washington State, U.S.\u00a0 This landslide\u00a0took more than a dozen lives\u00a0with others still missing.\u00a0\u00a0I saw early reports that there was a known risk of a landslide at this location.\u00a0 The assessment leading to that conclusion is certain to have considered pore water pressure and its potential to change.<\/p>\n Len has investigated the potential for landslide problems in Hong Kong.\u00a0 These would\u00a0 be slopes that were susceptible to increases in pore water pressure.\u00a0 Simple drains often fixed the problems but sometimes more in-depth water interception was necessary.<\/p>\n Water pressure is a factor in\u00a0our\u00a0wet basements.\u00a0 And, believe or not, in many slip and fall accidents.\u00a0\u00a0It’s\u00a0the reason signs in a swimming pool caution us not\u00a0to run on the pool deck.<\/p>\n In some slip and fall accidents, a person’s weight is momentarily applied to water on the floor\u00a0surface.\u00a0 The frictional or skid resistance of water is much lower than the material forming the floor surface – almost negligible by comparison.\u00a0 So low in fact that the person slips and falls.<\/p>\n Len’s classification is a good one, an aid to those of us investigating problems with water and needing to explain the cause of\u00a0a problem to the justice system.<\/p>\n Many of the forensic engineering problems I investigate\u00a0– not just a few, and not just the obvious drainage and flooding problems –\u00a0can be traced back to water and fall under one or more of\u00a0the headings Len has identified.<\/p>\n Reference<\/strong><\/p>\n 1. Image credits and why forensic engineers like wet weather, the heavier the rain the better,\u00a0posted April 9, 2014 http:\/\/www.ericjorden.com\/blog\/2014\/04\/09\/image-credits-and-why-forensic-engineers-like-wet-weather-the-heavier-the-rain-the-better\/<\/a><\/span><\/p>\n Len Threadgold’s Profile<\/strong><\/p>\n Len is a civil engineer in the U.K. specializing in soil, rock, and ground engineering – geotechnical engineering.\u00a0 We were colleagues when I practiced\u00a0there.\u00a0\u00a0Len’s firm, Geotechnics Ltd, provides consulting services to an international clientele including\u00a0dealing with\u00a0slope stability problems in Hong Kong and the U.K. – problems that would fall under #3 above.\u00a0\u00a0The U.K. had their share of severe flooding problems this past year, problems with the mere presence of water; #1 above.\u00a0 Len read a draft of this blog because it’s his classification system and some of the examples and comments are his.<\/p>\n <\/p>\n <\/p>\n \u00a0<\/span><\/p>\n \u00a0<\/span><\/p>\n","protected":false},"excerpt":{"rendered":" A reader in the U.K., Len Threadgold,\u00a0(see profile below) commented on\u00a0last week’s\u00a0blog. (Ref. 1)\u00a0\u00a0Len speaks with some authority when he notes that the problems with water can be grouped under\u00a0the following three headings.\u00a0 He also notes that separating problems into … Continue reading