{"id":4240,"date":"2012-02-07T11:48:11","date_gmt":"2012-02-07T11:48:11","guid":{"rendered":"http:\/\/blogs.agu.org\/landslideblog\/?p=4240"},"modified":"2012-02-09T08:13:00","modified_gmt":"2012-02-09T08:13:00","slug":"an-official-report-on-the-tumbi-quarry-landslide","status":"publish","type":"post","link":"https:\/\/blogs.agu.org\/landslideblog\/2012\/02\/07\/an-official-report-on-the-tumbi-quarry-landslide\/","title":{"rendered":"An official report on the Tumbi Quarry landslide"},"content":{"rendered":"

The National Disaster Council of Papua New Guinea has posted online a report<\/a> into the Tumbi Quarry landslide (see previous posts here,<\/a> here<\/a>, and here<\/a>).\u00a0 Presumably this is the “official investigation” that was promised.\u00a0 They should be credited with making this available online, and the document has some useful information on, and images of, the landslide.\u00a0 It is also helpful to get the official view on the landslide event, and there is a management plan for the victims and survivors of the accident.<\/p>\n

However, there are aspects of the report that are perhaps interesting, as follows:<\/p>\n

1. The report only very briefly mentions the quarry<\/strong>.\u00a0 The report states that “naturally high geological weaknesses assisted by abnormally high rain fall combined to cause subsidence to the immediate north west of the quarry triggering a landslide of composite debris.”\u00a0 The image on the front cover clearly shows a part of the quarry, with some of the benches truncated by the lateral margin of the landslide:<\/p>\n

<\/a>\"\"<\/a><\/p>\n

The report is ambiguous as to whether this means that the landslide was associated with the quarry.\u00a0 It maybe that the quarry access \/ haul road also crossed the area now destroyed by the landslide (as per the Esso Highlands plan), and yet this is also not discussed.\u00a0 Clearly at least a part of the quarry was lost in the landslide, so a proper discussion of whether the quarry played a role in activating these weaknesses seems essential to me.<\/p>\n

Note also that these naturally-occurring geological weaknesses are not described or discussed (I assume that this means a set of joints?), and the mechanism of “subsidence” is also quite strange.<\/p>\n

2. The landslide trigger <\/strong>is definitively described as being rainfall, on the basis that there was no recorded seismicity.\u00a0 However, although “continuous heavy rainfall” is described, there is no data to support this, and no eye-witness reports.\u00a0 The next sentence talks about “abnormally high rainfall”, but I can find no other reference to this event.\u00a0 I wonder what evidence there is for this abnormal<\/em> rainfall event, given the high rainfall that this area is likely to receive anyway.<\/p>\n

3. There are odd aspects of the landslide mechanism <\/strong>as described in the report.\u00a0 First, the report notes that pools and seepage on the shear face indicate that the “ground water rose significantly above its historical levels”.\u00a0 I do not understand this logic.\u00a0 Seepage and pools are likely to occur in the aftermath of almost any deep landslide of this type, and I do not see why they indicate that the groundwater levels were abnormally high, or indeed that groundwater even played a substantial role.\u00a0 Second, the report notes that the initial assessment team “saw clear evidence of liquefaction of the rock formation”.\u00a0 This is most surprising.\u00a0 Limestone is not a material that undergoes liquefaction – I have never heard of such a mechanism in any hard (as defined from an engineering behaviour perspective) rock – and so I just cannot understand this purported process.\u00a0 Unfortunately, it is not discussed further.<\/p>\n

So overall, whilst the description of the site is really helpful, though it would be good to see a more detailed consideration of the ways in which the quarry might have been a factor in activating these geological weaknesses.\u00a0 In designing a quarry it is normal practice to ensure that such natural weaknesses are not exposed to the point that they can permit slope failure to occur.<\/p>\n

To my mind this report should not be considered to be the definitive analysis of this landslide.\u00a0 Much more detailed analysis is needed, and lessons need to be learnt in terms of other slopes in Papua New Guinea.<\/p>\n","protected":false},"excerpt":{"rendered":"

An analysis of a report into the Tumbi Quarry landslide in Papua New Guinea. Many questions remain about this event<\/p>\n","protected":false},"author":22,"featured_media":4241,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[3,1],"tags":[469,959,313],"class_list":["post-4240","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-landslide-report","category-uncategorized","tag-featured","tag-landslide-report","tag-papua-new-guinea"],"_links":{"self":[{"href":"https:\/\/blogs.agu.org\/landslideblog\/wp-json\/wp\/v2\/posts\/4240","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/blogs.agu.org\/landslideblog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/blogs.agu.org\/landslideblog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/blogs.agu.org\/landslideblog\/wp-json\/wp\/v2\/users\/22"}],"replies":[{"embeddable":true,"href":"https:\/\/blogs.agu.org\/landslideblog\/wp-json\/wp\/v2\/comments?post=4240"}],"version-history":[{"count":0,"href":"https:\/\/blogs.agu.org\/landslideblog\/wp-json\/wp\/v2\/posts\/4240\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/blogs.agu.org\/landslideblog\/wp-json\/wp\/v2\/media\/4241"}],"wp:attachment":[{"href":"https:\/\/blogs.agu.org\/landslideblog\/wp-json\/wp\/v2\/media?parent=4240"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/blogs.agu.org\/landslideblog\/wp-json\/wp\/v2\/categories?post=4240"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/blogs.agu.org\/landslideblog\/wp-json\/wp\/v2\/tags?post=4240"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}