CEEN 641 - Lecture 14 - Shear Strength of Clays

[@oscarmoyles6363]

Hi there, How can I conceptualize suction in heavily over-consolidated clays? (@13:00 mins) What would it feel like if I were to hold the material/try to manipulate it? Thank-you Oscar

[@abrarullah4132]

Please make a video on the effects of earthquake on slopes and embankments. Also please start tutorials on some geotech softwares. Really so many people are benefiting from your work. Thanks alot for such nice video.

[@muhamadaminalsalamat9608]

Thank you for wonderful explanation ! however regarding the CU test how do you draw the line in spite of that you just have one point ? are the all three samples in CU test consolidated to the same SIGMA3. and during the vertical loading phase you were changing the cell pressure. ?

[@geoturista]

Very good video. Could you recommend some papers that support this idea of using c'=0 kPa in compacted clay embankments in some cases, please?

[@irinaperepelitsa4810]

Love your lectures! Do you have anything on shear strength of sand?

[@alexchasewilliams]

Thank you for the videos. I'm a Mechanical Engineer by training but am trying to learn about soil mechanics to gain a better understanding of vehicle performance in soils. I'm struggling with the definition of "drained soil" though. Does that mean there is no moisture whatsoever in the soil or it is just not saturated? If there is some moisture wouldn't there be some cohesion from the surface tension between the particles?

[@fedup0012]

Thr r 2 kind of water depending upon how they r associated wd soil..1 is gravitational water which can be drained under gravitational force if drainage is permitted in soil/by soil..2nd is adsorbed water by soil particles..if soil is partially saturated,this adsorbed water produces apparent cohesion due to surface tension,however when soil is fully saturated (i.e all voids r filled wd water) the meniscus of surface tension gets destroyed(becomes flat) thus no apparent cohesion will be there..

[@bikx32]

Not understanding one thing- you prefer CU over UU, why CU is quicker/easier? (True?) Su underestimates shear strength 15%, figure is showing higher value of Su.

[@c4fishfood]

It was not super clear, but he is stating that TxUU is easier/faster than TxCU, not the other way around. I’m not sure why he thinks that Tx-UU would underestimate the strength- the figure given at 36min is a bit mixed up- you would not in my experience plot a UU circle in a CU or CD diagram, and it would be pure coincidence if your UU circle happed to be tangent to failure envelope as shown. Also, I’m curious why he states that rate of strain and saturation on a UU test could lead to lower values... I need to re-read the ASTM but I believe that saturation and rate of loading is no different between TxUU and TxCU.

[@tangosierra2288]

The figure is a little erroneous, the circle is not comparing the circles of two tests but showing where on the failure circle you would be looking in the case of the two tests. The reason the UU is easier is it does not have a consolidation phase before you test the sample. The CU test requires a consolidation phase so therefore has an extra step and is more costly/ takes longer. As you don't have the consolidation phase the UU test tends to fail at a lower stress because of various factors listed within the video (saturation, strain rate, not quite getting the effective stress right). So the UU test gives a conservative evaluation that takes less time. The question often will come down to how much budget do you have for testing and do you / the engineer of record want to sharpen the pencil for a higher value.