 So wrth y argylchedd y teis o ddau cofniriaid, er byw'n ddau sydd yn olygu ar y hwyl a'r drosfyn Cymru, ac mae'n cael ei wneud ar yr oed y bocs, mae'r oed bach yn agai'n ddau cael ei gweld arcofniriaid mewn bach. Mae yr hyn, wrth g adjustment, yn ei clywed, mae'r pob ddweud o hyd ac mae'r hoffodd a'r hyffodd a'r hoffodd rai chyfodd a'r oed yn gweithio, yn gweithio hir o'r hoffodd i'r hoffodd, a'r hoffodd yn elu. Felly allan'ch meddwl is this, prysw celebrwl hynny, daodd Non Cymru緊ed Mae'r fyddechrau yn ymwneud bod lle mae'n meddwl iawn y cyflogion y troi'r prysgol yn rhan o'r cyflogion iawn, so mae'n meddwl i chi'n meddwl i chi'n meddwl i chi'r trefiach bydd y brifwyr, y brifwyr ei fod yn ymwneud yn y brifwyr yn y brifwyr yn y brifwyr. A oedden nhw'n llunio'r ffordd yma, y bwysig lle o'r bwysig o'r triaxiol. A mae'n fyddwch ar y bwysig o'r triaxiol. Fe ydy bach yn dweud, byddwn ar y consider o mynd. Byddau'r newydd yng Ngharor Nŵr,'r%d yr argynnu'r tŵr, a byddwn ar yijo o mynd yn boblungu, omswm yn y bram honno yw. Mae'n material yw rhydd. Rwy'n credu unrhyw lle'r hyn ar y mynd. Mae'n ddiddordeb am y mynd yng Ngharor Nŵr, ac yma'n ddiddordeb arall. ond ond dŵa, a dŵa tan jei ar y hwnny yw i'r blynedd ac ydych yn bach. Wrth i'n gweld sut ar y fyddiad a ddweud. Oherwydd mae'r penderfyniadau yma yn ystirledig gynhyrchu gwahanol yn y ddelhau. Ystod y penderfyniadau digestion erbyn yn gwneud hynny'r sefyll ynnghwys yn hanesydd. Bw, ond yma yma'r lleid ar y swydd gyntaf gyda'r cyndrygu, yma'r lleid ar unrhyw o'r fwyllt. ac mae gennym ni'n cael y cyfnod yn y cael y cael. Ac mae gwybod ni'n cael cyfrifau Cyfrifol 3 ac Cyfrifol 2. Yn y gallu gwneud yn y test ymlaen, mae'n cael Cyfrifol 3 ac Cyfrifol 2, oedd y cyfrifol yw gwirio cyfrifol, ac mae'n cael y cyfrifol yw'r axial, fel mae gennym ni yn cael eu gwirio. Yn y test, y cyfrifol yw'n cael y cyfrifol yw'r cyfrifol yw'r cyfrifol. Ydy answer ychydig cael y teamfyrdd y cyfrifol a gyfrifol y nwell yn y мнigoedd. på beth fe eich cyfrifol effeithio yeliau hyffordicaethau triaxial ddiweddlu gwyddarion y Cyfrifol yw cyfrifol yw gyfrifol yw overlifol. Ac bennan rifles y seemsolved cyfrifol yw Cyfrifol 1 a Cyfrifol 3, sawn bod hynny sefydlu cyfrifol compliance y Byrydure. Felly, sgwm 1 effektif stress is equal to sgwm 1 minus the pore water pressure and sgwm 3 effektif stress is equal to sgwm 3 minus the pore water pressure. So, we take the pore water pressure away from both of the normal stresses. Another thing that we can measure in the triaxial test is the vertical displacement of the sample. If we take the vertical displacement and divide it by the initial soil height, what we derive is what's called the axial strain. So, changing H over H0 equals axial strain. We also monitor the change in volume of the water within the cell. So, if the sample increased in volume, it would push some of this water out of the cell and we'd measure it out here. And if we take the change in volume and we divide it by the initial volume, what we get is the volumetric strain. So, these are the things that we monitor in a triaxial test, but how do we interpret them? So, what happens in a drained triaxial test is that we usually start the sgwm 1 and sgwm 3 at around the same value, the same pressure. So, we'd start the test off at the same point on the y axis, on the x axis. And what we do is real increase, so this is sgwm 3 and sgwm 1 will start at the same point. In a triaxial test, you'd keep sgwm 3 constant and increase sgwm 1 up the x axis until you got to the point of failure. So, at the point of failure, you'd record the axial stress, that's sgwm 1. Effective stress I should say for both of those. And what you can do is then draw the top half of the Mohr circle, drawing them together through Mohr's circle. And from that, you'd be able to get the maximum shear stress during the test. But if you recognise the axis, we can draw a Mohr Coulomb failure envelope on this axis. But to do that, we need to do more than one test, we need to do several tests. So, what we do is then increase the conditions at which we'd start the second test. So, we'd start sgwm 3 at a larger value, these different colours. So, let's say we'd start the next test here at sgwm 3 and increase sgwm 1 again until we got to the point of failure. And let's say that was here. And again, we can connect those up through the top half of a Mohr's circle. And finally, we'll do it again for another test. So, we might start it here and make material might fail here. So, once we've got our three test results here, what we can do is join the curves together with a line that touches all three curves. And that would be our Mohr Coulomb failure envelope. So, if we took the tan of the gradient of that line, we would find phi. And the intercept would be cohesion. So, we can use the triaxial test, like the shear box test, to derive shear strength parameters of angle of friction and cohesion. This also helps demonstrate what would happen if you increased your pore water pressure, or the effects of changing pore water pressure, in that, if you increased your pore water pressure, both the sgwm 1 and sgwm 3 would change by the same amount or decrease by the same amount. And the whole circle would shift to the left for increasing pore water pressure until the point where you are... So, let's say we had stress conditions in the soil that created a Mohr's circle over here. And it was... So, our maximum shear stress would be known. But what about if we increased pore water pressure? Well, the whole circle would shift down until it passed the failure envelope, and at which point the material would fail. And that's why the pore water pressure is really important to understand, as well as the difference between these two principle stresses. So, there's a number of different tests that we can do in a triaxial test. The first one I mentioned was a drained triaxial test. And that means that we let the water flow out of the material during the test. We can also do an undrained test, in which case the pore water pressures are the... We can also do a drain test. We can also do an undrained test, and that's when we stop the water flowing out of the soil and let the pore water pressures build up. And that's really useful for telling us things about the short-term behaviour of the soil. For instance, when we're loading the material. And what the results of an undrained test would look like would be something like this, where no matter where you started your test, or what stress range you did it under, you would only ever reach the same maximum shear stress. So the consequences of doing an undrained triaxial test would be this. So maybe multiple more circles of stress, but all reaching the same maximum shear stress. And that's called the undrained shear strength of the material. And there are also variants on this between consolidated and unconsolidated. And that means whether we allow the material to consolidate before the test when we're ramping up the load. And I've put a matrix of these different tests on my website.