{"id":1461,"date":"2019-07-16T15:28:05","date_gmt":"2019-07-16T07:28:05","guid":{"rendered":"http:\/\/people.utm.my\/snorafida\/?p=1461"},"modified":"2019-07-18T10:24:44","modified_gmt":"2019-07-18T02:24:44","slug":"drained-undrained-which-one-modelling","status":"publish","type":"post","link":"https:\/\/people.utm.my\/snorafida\/drained-undrained-which-one-modelling\/","title":{"rendered":"Drained, Undrained; which one? (modelling)"},"content":{"rendered":"

In geotechnical engineering, sometimes it is tricky how to model a problem.<\/p>\n

Should it be an effective soil stiffness?<\/p>\n

Should it be total stress?<\/p>\n

All of this relates to a bigger issue which is; the drained or undrained modelling condition (soil permeability condition).<\/p>\n

To understand, first, one has to knew what type of soil involve in the problem, and either is it the problem analyse for a short term or long term (stability)condition?<\/p>\n

Drained condition<\/strong><\/em><\/p>\n

Drained condition almost always exists for coarse-grained material<\/em> such as gravels and sands under static\/monotonic loading. In this condition, it is assumed that material have large permeability so that the pore water can quickly drain out.<\/p>\n

Eg. of the conditions can be:<\/p>\n

    \n
  1. Soil with seismic loading condition due to the quick rate of loading saturated loose sands can experience undrained loading condition resulting in liquefaction.<\/li>\n
  2. In case of liquefaction where unloading condition exists, the common approach is to either use residual strength parameters of liquefied soil per Idriss<\/a> and Boulanger (2008)<\/a>\u00a0guidelines or adopt advanced constitutive models for which the input parameters are drained parameters.<\/li>\n<\/ol>\n

    Drained parameters (E’, \\nu’, \\<\/u>phi’<\/u>E<\/i><\/u>\u2032,<\/u>\u03bd<\/i><\/u>\u2032,<\/u>\u03d5<\/i><\/u>\u2032)<\/u> must be always used for the analysis of\u00a0coarse-grained materials<\/u>\u00a0(i.e., gravels, sands).<\/p>\n

     <\/p>\n

    Undrained condition<\/strong><\/em><\/p>\n

    On the other hand, due to the low material permeability, undrained condition almost always exist for clays and silts<\/em> when subjected to quick static loads and earthquake loads.<\/p>\n

     <\/p>\n

    For more;<\/p>\n

    http:\/\/geotechsimulation.com\/2018\/05\/18\/soil-drained-undrained-behavior\/<\/a><\/p>\n

     <\/p>\n

     <\/p>\n

    Speed Notes:<\/p>\n

    Slope stability analysis<\/b><\/p>\n

    Short-term condition<\/u>: undrained parameters\u00a0(E_u, \\nu_u, S_uEu<\/i>\u200b,\u03bd<\/i>u<\/i>\u200b,Su<\/i>\u200b)*<\/p>\n

    Long-term condition<\/u>: drained parameters\u00a0(E’, \\nu’, c’, \\phi’E<\/i>\u2032,\u03bd<\/i>\u2032,c<\/i>\u2032,\u03d5<\/i>\u2032)<\/p>\n

    Pseudo-static condition<\/u>: undrained parameters\u00a0(E_u, \\nu_u, S_uEu<\/i>\u200b,\u03bd<\/i>u<\/i>\u200b,Su<\/i>\u200b)*<\/p>\n

    *\u00a0 If generation of pore water pressure is simulated in the analysis, drained stiffness parameter (E’, \\<\/i>nu’E<\/i>\u2032,<\/i>\u03bd\u2032) <\/i>must be used instead of\u00a0<\/i>E_u<\/i>, \\<\/i>nu_uEu<\/i>\u200b,<\/i>\u03bd<\/i>u\u200b. This is because the analysis accounts for the pore water stiffness\u00a0(<\/i>K_wKw<\/i>\u200b) in the calculation of soil volume stiffness.<\/i><\/p>\n

     <\/p>\n

    Static settlement analysis<\/b><\/p>\n

    Immediate settlement<\/u>:\u00a0undrained parameters\u00a0(E_u, \\nu_u, S_uEu<\/i>\u200b,\u03bd<\/i>u<\/i>\u200b,Su<\/i>\u200b)*<\/p>\n

    Consolidation settlement<\/u>:\u00a0drained parameters\u00a0(E’, \\nu’, c’, \\phi’E<\/i>\u2032,\u03bd<\/i>\u2032,c<\/i>\u2032,\u03d5<\/i>\u2032)<\/p>\n

    *\u00a0 <\/i>If generation of pore water pressure is simulated in the analysis, drained stiffness parameter (E’, \\<\/i>nu’E<\/i>\u2032,<\/i>\u03bd\u2032) <\/i>must be used instead of\u00a0<\/i>E_u<\/i>, \\<\/i>nu_uEu<\/i>\u200b,<\/i>\u03bd<\/i>u\u200b. This is because the analysis accounts for the pore water stiffness\u00a0(<\/i>K_wKw<\/i>\u200b) in calculation of soil volume stiffness.<\/i><\/p>\n

     <\/p>\n

    Seismic time history analysis<\/b><\/p>\n

    Case #1\u00a0\u2013<\/u>\u00a0the analysis is cable of simulating build-up and\/or dissipation of pore water pressure over time:\u00a0 drained parameters\u00a0(E’, \\nu’, c’, \\phi’E<\/i>\u2032,\u03bd<\/i>\u2032,c<\/i>\u2032,\u03d5<\/i>\u2032)<\/p>\n

    Case #2\u00a0\u2013<\/u>\u00a0the analysis is formulated based on fully undrained conditions (in programs like PLAXIS): drained stiffness and undrained strength\u00a0(E’, \\nu’, S_uE<\/i>\u2032,\u03bd<\/i>\u2032,Su<\/i>\u200b)
    \nNote: The undrained analysis accounts for the pore water stiffness\u00a0(<\/i>K_wKw<\/i>\u200b)\u00a0 in calculation of soil volume stiffness.<\/i><\/p>\n

     <\/p>\n

     <\/p>\n","protected":false},"excerpt":{"rendered":"

    In geotechnical engineering, sometimes it is tricky how to model a problem. Should it be an effective soil stiffness? Should it be total stress? All of this relates to a bigger issue which is; the drained or undrained modelling condition (soil permeability condition). To understand, first, one has to knew what type of soil involve […]<\/p>\n","protected":false},"author":7477,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_et_pb_use_builder":"","_et_pb_old_content":"","_et_gb_content_width":"","footnotes":""},"categories":[1],"tags":[],"class_list":["post-1461","post","type-post","status-publish","format-standard","hentry","category-uncategorized"],"jetpack_featured_media_url":"","_links":{"self":[{"href":"https:\/\/people.utm.my\/snorafida\/wp-json\/wp\/v2\/posts\/1461","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/people.utm.my\/snorafida\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/people.utm.my\/snorafida\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/people.utm.my\/snorafida\/wp-json\/wp\/v2\/users\/7477"}],"replies":[{"embeddable":true,"href":"https:\/\/people.utm.my\/snorafida\/wp-json\/wp\/v2\/comments?post=1461"}],"version-history":[{"count":2,"href":"https:\/\/people.utm.my\/snorafida\/wp-json\/wp\/v2\/posts\/1461\/revisions"}],"predecessor-version":[{"id":1463,"href":"https:\/\/people.utm.my\/snorafida\/wp-json\/wp\/v2\/posts\/1461\/revisions\/1463"}],"wp:attachment":[{"href":"https:\/\/people.utm.my\/snorafida\/wp-json\/wp\/v2\/media?parent=1461"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/people.utm.my\/snorafida\/wp-json\/wp\/v2\/categories?post=1461"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/people.utm.my\/snorafida\/wp-json\/wp\/v2\/tags?post=1461"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}