Landslides are frightening and an example of one more way\u00a0nature has her way with us when conditions are right.\u00a0 Such a large mass of soil and rock sweeping away everything in its path must be terrifying to see, and terrifying to be in.\u00a0 I’ve seen the aftermath of large landslides and earthwork failures and investigated some.\u00a0 They are\u00a0a humbling\u00a0experience.<\/p>\n
The recent landslides in B.C. at\u00a0Fairmont Hot Springs Resort\u00a0and\u00a0Johnsons Landing on\u00a0Kootenay Lake\u00a0certainly fall in that frightening category.\u00a0 Others in B.C. and elsewhere in Canada, including the Atlantic provinces, are smaller but still serious in causing injury and financial loss.<\/p>\n
News reports indicated that geotechnical engineers and geological speciallsts were on the disaster sites within hours of the landslide.\u00a0 A good thing quickly getting knowledgeable technical\u00a0people there.\u00a0 Landslides are engineering failures, particularly when they affect people\u00a0 The investigations they do and the data they collect\u00a0are certain to assume the\u00a0status of forensic engineering investigations.<\/p>\n
(Geotechnical engineers are civil engineers who have specialised in the investigation and study of the physical properties of soil and rock as engineering materials)<\/p>\n
These large landslides appear to have occurred after smaller\u00a0landslides along streams\u00a0– like Fairmont Creek, created dams\u00a0causing water levels to rise.\u00a0 Eventually the rising water would overtop the dam and wash it away and downstream.\u00a0 The mixture of\u00a0stream water and dam material would\u00a0pick up other material along the stream bed to create\u00a0the mass of soil that swept over the inhabited areas as a large landslide.<\/p>\n
It’s certain more landslides are occurring in B.C. as I write, both large and small.\u00a0 If not in or near inhabited areas then in remote areas for sure.<\/p>\n
Landslides are natural geological events.\u00a0 They occur when conditions are right – the strength of the soil on a sliding surface is not great enough to hold back the mass of soil.<\/p>\n
The physics principle involved is the same as that underlying the reason we\u00a0slip on ice in winter and fall and are able to ski on snow and have fun.<\/p>\n
Sometimes the strength of the soil is just great enough that the mass of soil stays in place.\u00a0 Until something comes along to reduce the strength that little bit so it’s no longer adequate.\u00a0 Or increase the weight of the mass of soil.\u00a0 That something can be water – rainwater.\u00a0 The water is said to “trigger” the landslide, a term used by geotechnical engineers\u00a0and sometimes the general public.<\/p>\n
Once the mass of soil starts to move – the land starts to\u00a0slide, it takes the easiest path like flowing water.\u00a0 Simply downhill – down a slope, or down\u00a0a natural channel in the terrain, for example, a water course or stream bed.\u00a0 The mass of soil\u00a0in a\u00a0landslide\u00a0can be quite “liquid”.<\/p>\n
Geotechnical engineers can investigate, analyse, and\u00a0predict with considerable\u00a0accuracy that a landslide will occur.\u00a0 They cannot really say when.\u00a0 Except perhaps when it’s imminent if they are able to examine the\u00a0terrain for the signs.\u00a0 For example, signs like fissures in the ground surface – “tension” cracks to engineers, leaning trees, and muddy water like\u00a0that seen at Fairmont Hot Springs Resort.<\/p>\n
They can also advise with some confidence on\u00a0the stability of a sliding mass of\u00a0soil that has come to rest like the geotechnicians did\u00a0at the Resort.\u00a0 Their degree of confidence would likely be greater than that possible by structural engineers at the site of a collapsed building like the one\u00a0at Elliot Lake.<\/p>\n
Engineering Investigation<\/span><\/em><\/p>\n A geotechnical engineering investigation of a landslide – either before the event to predict the likelihood of its occurrence or afterwards to\u00a0determine the\u00a0cause – would have the fundamental components\u00a0of an\u00a0engineering failure investigation:<\/p>\n Data\u00a0would be\u00a0gathered in two basic stages:<\/p>\n These basic stages are\u00a0likely underway at present at the Fairmont Hot Springs Resort\u00a0and Johnsons Landing.<\/p>\n Existing data is often concerned with conditions at the ground surface and new data with conditions below the surface.<\/p>\n Existing\u00a0Data<\/span><\/em><\/p>\n Existing data\u00a0might consist of:<\/p>\n Reviewing and studying existing\u00a0data like this, an experienced\u00a0geotechnical engineer could offer a quite informed and fairly confident statement on the susceptibility of an existing hillside to landslides, or the cause\u00a0of an existing landslide.<\/p>\n Statements like these have likely already been made about the landslides in British Columbia.<\/p>\n New Data<\/span><\/em><\/p>\n New data that would increase the confidence of the geotechnical engineer\u00a0in his opinions would consist of:<\/p>\n Analysis <\/em><\/span><\/p>\n Investigative tasks like the above provide a lot of data to be\u00a0analysed.\u00a0 But the results of the analysis enable\u00a0well-founded\u00a0opinions to be formed on the cause of the landslide and remedial work to begin.\u00a0 The\u00a0analysis\u00a0also enables areas prone to landslides to be avoided when building new structures or to\u00a0be stabilized before building.<\/p>\n","protected":false},"excerpt":{"rendered":" Landslides are frightening and an example of one more way\u00a0nature has her way with us when conditions are right.\u00a0 Such a large mass of soil and rock sweeping away everything in its path must be terrifying to see, and terrifying … Continue reading \n
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