{"id":55794,"date":"2025-09-29T23:00:03","date_gmt":"2025-09-29T14:00:03","guid":{"rendered":"https:\/\/norimen.net\/wordpress\/%e6%b3%95%e9%9d%a2%e5%b1%8b%e3%81%af%e7%9f%a5%e3%81%a3%e3%81%a6%e3%81%84%e3%81%a6%e6%ac%b2%e3%81%97%e3%81%84%e3%80%81%e7%8f%be%e5%a0%b4%e3%81%a7%e3%82%88%e3%81%8f%e4%bd%bf%e3%81%86%e7%b2%98%e7%9d%80-3\/"},"modified":"2026-05-16T17:05:20","modified_gmt":"2026-05-16T08:05:20","slug":"cohesion-phi-3","status":"publish","type":"post","link":"https:\/\/norimen.net\/en\/cohesion-phi-3\/","title":{"rendered":"What Slope Engineers Should Know: A Discussion of Cohesion (c) and Angle of Internal Friction (\u03c6), Commonly Used on Construction Sites (Part 3)"},"content":{"rendered":"<p>Hello, everyone.<\/p>\n<p>This is Enta.<\/p>\n<p><a title=\"What Slope Engineers Should Know: A Discussion of Cohesion (c) and Angle of Internal Friction (\u03c6), Commonly Used on Construction Sites (Part 1)\" href=\"https:\/\/norimen.net\/en\/cohesion-phi-1\/\" target=\"_blank\" rel=\"noopener\">What Slope Engineers Should Know: A Discussion of Cohesion (c) and Angle of Internal Friction (\u03c6), Commonly Used on Construction Sites (Part 1)<\/a><\/p>\n<p><a title=\"What Slope Engineers Should Know: A Discussion of Cohesion (c) and Angle of Internal Friction (\u03c6), Commonly Used on Construction Sites (Part 1)\" href=\"https:\/\/norimen.net\/en\/cohesion-phi-1\/\" target=\"_blank\" rel=\"noopener\">What Slope Engineers Should Know: A Discussion of Cohesion (c) and Angle of Internal Friction (\u03c6), Commonly Used on Construction Sites (Part 1)<\/a><\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone size-full wp-image-55509\" src=\"https:\/\/norimen.net\/wordpress\/wp-content\/uploads\/2025\/09\/4d6e1912684e7edf660e5f589c892258-2.jpg\" alt=\"Internal friction angle \u03c6 and cohesion C\" width=\"500\" height=\"500\" \/><\/p>\n<p>In my last post, I wrote about the strength of soil.<\/p>\n<p>&nbsp;<\/p>\n<p>So, this time...<span id=\"toc2\">We will take a closer look at the adhesion c (kN\/m\u00b2).<\/span><\/p>\n<h2>Definition of Adhesive Strength<\/h2>\n<p>Cohesion (symbol: c) is a numerical measure of the force with which soil particles tend to stick to one another.<\/p>\n<p>It is expressed in kN\/m\u00b2 and is an essential indicator for evaluating the strength characteristics of soil.<\/p>\n<p>If this \u201ccohesion\u201d is high, slopes and excavated surfaces are less likely to collapse; conversely, if it is low, the soil cannot support itself and is more prone to collapse.<\/p>\n<p>&nbsp;<\/p>\n<h3>An Illustration of Adhesive Force<\/h3>\n<p>Sandy soil (dry sand) \u2192 Cohesion \u2248 0; loose and crumbly.<\/p>\n<p>Cohesive soil (clayey) \u2192 High cohesion; the wall surface tends to stand on its own.<\/p>\n<p>&nbsp;<\/p>\n<p>For example, when making \u201csandballs\u201d in a sandbox, dry sand won\u2019t hold its shape, but sand that contains moisture or clay will harden.<\/p>\n<p>So this \u201cproperty of solidifying\u201d is what we call adhesive force, right?<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone size-full wp-image-55601\" src=\"https:\/\/norimen.net\/wordpress\/wp-content\/uploads\/2025\/09\/cc634649826a11b81863d7a2a521592c-1.jpg\" alt=\"Sandballs\" width=\"600\" height=\"399\" \/><\/p>\n<h3>Meaning of the Numbers<\/h3>\n<p>For example, if c = 20 kN\/m\u00b2,<\/p>\n<p>This means that the soil is being held in place by a force of 20 kN (approximately 2 metric tons) per square meter of shear surface area, preventing it from collapsing.<\/p>\n<p>&nbsp;<\/p>\n<p>To get a concrete idea, consider a shear cross-section of 1 m\u00b2,<\/p>\n<p>It possesses \u201cadditional strength\u201d that allows it to withstand a load of 20 kN \u2252 2,000 kgf (approximately 2 metric tons) without collapsing.<\/p>\n<p>This strength manifests as a \u2019cohesive component\u201c that exists even when the \u201deffective stress (\u03c3\u2019)\u201d and \u201cfriction angle (\u03c6)\u201d are zero.<\/p>\n<p>&nbsp;<\/p>\n<p>Shear strength equation:<strong><span style=\"font-size: 150%;\">=+\u03c3\u2032\u00b7tan<\/span><\/strong><\/p>\n<p>Even when \u03c3\u2019 = 0 here, \u03c4 = c, and a resistance of 20 kN\/m\u00b2 is generated.<\/p>\n<p>&nbsp;<\/p>\n<p>In terms of design, based on the Mohr-Coulomb failure criterion,<\/p>\n<p>Shear strength is evaluated as \u03c4 = c + \u03c3\u2019\u30fbtan\u03c6 (where \u03c3\u2019 is the effective stress and \u03c6 is the angle of internal friction), and c is treated as the \u201cconstant cohesion component\u201d within this equation.<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone size-full wp-image-55522\" src=\"https:\/\/norimen.net\/wordpress\/wp-content\/uploads\/2025\/09\/12cfd044c5d61fe14475b3e4a6a3d5f9-2.png\" alt=\"Clone Destruction Test\" width=\"600\" height=\"400\" \/><\/p>\n<p>&nbsp;<\/p>\n<p>Why is this important?<\/p>\n<p>&nbsp;<\/p>\n<p>Slope Stability Analysis: The higher the cohesion, the greater the stability.<\/p>\n<p>Feasibility of drilling: Required for estimating the self-supporting time.<\/p>\n<p>Foundation Design: Essential for determining bearing capacity and slip failure.<\/p>\n<p>In particular, determining whether the soil at the site is sandy soil with near-zero cohesion or cohesive soil with high cohesion is a key consideration during the construction phase.<\/p>\n<p>&nbsp;<\/p>\n<p>Adhesion c [kN\/m\u00b2] = The adhesive force exerted by the soil.<\/p>\n<p>It is nearly zero in sandy soil, but high in clay.<\/p>\n<p>In mathematics, it is a constant in the \"Mole-Coulomb equation.\"<\/p>\n<p>This is a required item in slope stability calculations.<\/p>\n<p>&nbsp;<\/p>\n<p>And as an engineer, it\u2019s important to keep in mind that c varies significantly depending on the type of soil and its moisture content.<\/p>\n<p>That\u2019s exactly why you can see how important it is to drain the water, right?<\/p>\n<p>&nbsp;<\/p>\n<p>See you later.<\/p>","protected":false},"excerpt":{"rendered":"<p>Hello, everyone. This is Enta. What Slope Engineers Need to Know: A Discussion of Adhesion (c) and Angle of Internal Friction (\u03c6), Commonly Used on Construction Sites (Part 1) What Slope Engineers Need to Know: A Discussion of Adhesion (c) and Angle of Internal Friction (\u03c6), Commonly Used on Construction Sites (Part 1) In my previous post, I wrote about soil strength.  \u2026<\/p>","protected":false},"author":2,"featured_media":55791,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"_bbp_topic_count":0,"_bbp_reply_count":0,"_bbp_total_topic_count":0,"_bbp_total_reply_count":0,"_bbp_voice_count":0,"_bbp_anonymous_reply_count":0,"_bbp_topic_count_hidden":0,"_bbp_reply_count_hidden":0,"_bbp_forum_subforum_count":0,"footnotes":"","jetpack_post_was_ever_published":false},"categories":[34,38],"tags":[2095,6989,6990,7013,7014,7015],"class_list":["post-55794","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-slope-work","category-construction-management","tag-2095","tag-6989","tag-6990","tag-c","tag-7014","tag-7015"],"acf":[],"yoast_head":"<!-- This site is optimized with the Yoast SEO Premium plugin v28.2 (Yoast SEO v28.2) - https:\/\/yoast.com\/product\/yoast-seo-premium-wordpress\/ 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