 The charge nature of clay minerals creates some interesting and unique physical properties of soils that are rich in them. It means some clay-rich soils over a certain range of water content can exhibit a plastic behaviour. Plasticity is when a material can change shape, can deform at constant volume with little additional change in stress. Bydd y cyfan, byddwn ni'n gwybod gyda soelau, mae o'r tynnu o'r plustiadau soelau. Rydyn ni'n gweld i ddechrau'r soelau, oedden nhw'n gweld am y gallu gwyfaint ac oedden nhw'n gweld ni'n gweld eich cyfantol oesolid, oedden nhw oesolid, oedden nhw oedden nhw oedden nhw. Ac ydych chi'n gweld eich cyfaint, mae yna gwyfaint. Ydw i'n gweld eich cyfaint, a fyddwch chi'n gweld i'r cyfaint, felly mae'n ddweud yn gweithio'r llwyddiad. Ond ydy'r rhaid i'r llwyddiad yma yn ymlaen i'r cyfnoddau, sydd yn cyfnoddau'r cyfnoddau. Mae'n ddefnyddio'r cyfnoddau, mae'n ddefnyddio'r cyfnoddau. Mae'n ddefnyddio'r cyfnoddau yn ddefnyddio'r cyfnoddau a'r cyfnoddau. Ond mae'n ddefnyddio'r cyfnoddau yn ymgyrchol. The transition between a solid state and a plastic state is called the plastic limit. The transition between the plastic and the liquid state is called the liquid limit. These are both waterfall contents so they'r waterfall content at that limit. The reason why this is important, is that soils at the plastic limit can have almost 70 times more strength than the soils at the liquid limit. Understanding where a soil is within the range, and understanding what it is for the soil is really quite important. A we can define the range at which soils behave plastic through something called the Plasticity Index. The plasticity index down here is equal to, so plasticity index is IP here, is equal to the liquid limit minus the plastic limit. So we can see that soils with a higher plasticity index yng nghylch yw'r rhagwm yn fwy o'r rhan yw'r cyflosid yn ymgwysig. Ym ddweud o'r rhagwm yn cael ei wneud yw'r rhagwm yn ymgwysig yn ddweud. Rwy'n cael ei ddweud, mae'n ddweud y rhagwm yn ddweud. Felly, mae'n ddweud o'r rhagwm yn ddweud gennym i'w rhagwm yn ddweud y rhagwm yn ddweud, for the clay particle size fraction and that defines something called the activity of the clay so if we take this IP, and we divide it by the percentage of the solution that is less than two micrometers in diameter, cyfnod y cyfnod, mae'r cyfnod. Felly, mae'n gwybod y Caelonite, efallai, mae'n cyfnod yma yn amlwg o'r ysgolion 0,5. Ylite mae'r cyfnod yma yn amlwg 0,5 ac 1. Fel y flawn dechrau, mae ei adfranteil wedi 1 a 7. Felly, fel y cyfrwys, mae'n meddwl o leolau hyn wych. Mae'n fflaesio bod yn glas yn y cyfrwys. Mae'n fawr yn y cyfrwys ffordd o gwwr cymwyllu gwahanol. Felly, fel y flawn dechrau, mae'n cyfrwys yn gwyrdd maes ar gyfer y caelau yma. Mae'n ddwy wedi gweld ei bod ni'n meddwl bod y ddw i'n gwelod yn hunain of y cael tario'r ffordd i'w gweithreit, y tario'r ffordd i'w gweithreit. Gofyn i'w gweithreit o'r dnerfod hyn o'r dnyf yn y tario'r ffordd. Y cweinio chi eich limau pleustig ac y limau ffordd? Rhywbeth wedi gweld eich limau. Y cweinio ei limau pleustig i'w ceisio ar y llausfod y Gwyrdd Cymrae a'r llausfod y Gwyrdd Cymrae. So, how do we define this plastic limit and Liquid limit? Well, like I said, we do it experimentally. The Liquid limit is done through something called a cone penetration test. The plastic limit is done through rolling the sample of the material into thread. So, it's a thread rolling. I've put links to videos of these two techniques on the website ...on the link below in the description. So, do take a look at those. You'll probably realise when you're viewing them that... ...in some ways, the techniques are very arbitrary. So a final thing that's useful to know is... ...where on this scale between the plastic limit and the liquid limit... ...does the soil currently reside? So, if you take a sample of soil and you measure the water content... ...whereabouts is that sitting on this scale? And that is defined through the liquidity index. So, if we... ...the liquidity index we write as I L. And that's equal to the current water content... ...or the natural water content of the soil... ...minus the plastic limit... ...divided by the plasticity index. And it really just says whereabouts on this scale... ...is the current natural water content of the soil. And finally, the last thing to point out is that... ...when you start with a solid material and you add water... ...what you find that is that the volume also increases... ...with water content. An alternative way of thinking about that... ...is if you decrease the water content your material will shrink. So there's a limit to that point... ...where the material stops shrinking. And that's called the shrinkage limit. That's usually lower than the... ...well, it's always lower than the plastic limit. And that's called the shrinkage limit. So that's an important characteristic to understand. Especially for soils that might dry out... ...and move past the plastic limit.