CEEN 341 - Lecture 18 - Settlement Beneath Footing

[@mettecharlottejensen6947]

as a former teacher - and now as an engineer in soil mechanics and geotechnical design - I have to say, that your teaching skills are absolutely fantastic. After being away from soil mechanics for a year, I am now watching all of you lectures CEEN 341to recap before starting a new position in a department for Soil mechanics and Geotechnical design from the beginning of 2023. It is clear that you really have a passion for the field as well as for teaching. You make it fun, interesting and VERY useful - though I am practicing in Denmark - and as you know there are few deviations in the way we practice geotechnical design depending on country. But the physics (gravity) and the behaviour of the soil don't care about borders;-)) THANKS🤗😀

[@ChinthanieMahanama]

Awesome explanation. Been stuck on an assignment and this video helped me understand it.

[@NapalmNewt]

Excellent videos and lectures. I encourage you to keep them up!

[@Neo-qp8iy]

it is very easy to learn the soil mechanics from these videos, thank you dr.

[@aaronsanjuan6342]

Thank you so much, Dr. Franke!

[@abbas2294]

Great lecture. Btw I have a question that is it necessary to compute settlements at 100% consolidation? For example: I have to construct a building and the design life period of a building we know is 50 years. Lets say the degree of consolidation of soil at age of 50 years is 60% then how much degree of consolidation should be taken for computing settlements?

[@abduljabbarkhan9107]

Say, we have two sand layers below the footing with one clay layer sandwiched in between. Let us assume that all three layers are within B depth below footing. How can we calculate immediate settlement of these two layers of sand using the Meyerhof formula?

[@john9076]

One question, If it is case 2, where the pre consoldiation pressure is still higher than the po + delta p. Could we omit the secondary settlement as it is insignificant?

[@yousefhamdan4337]

Why do we ignore immediate settlement of clay

[@xualan5403]

Hi Sir. Why when it comes to effective stress for consolidation settlement the point of interest is always the center of clay layer?

[@kanchanomshanti1163]

Because that is layer which consolidates at the last....

[@mehulkatakiya4892]

no, not in case of single drainage condition. It is because we consider the average settlement of strata. At a top of layer, a settlement will be less and at the bottom of the layer, a settlement will be more.

[@mehulkatakiya4892]

at 32:17, shape of settlement vs time is wrong because most of the settlement will occur in earlier time.

[@officehours4028]

Sorry, but it’s not wrong. The rate of consolidation will always match the shape of the plot for average degree of consolidation. You are correct that most of the settlement will indeed occur in the initial stages of consolidation, but the remainder of the settlement can take a long time to occur.

[@mehulkatakiya4892]

thats why i am saying..it should be concave upward not convex upward..because it is settlement vs time plot for consolidation not DEGREE OF CONSOLIDATION vs time...because what u have drawn simply indicate after few years, settlement will increase drastically..!!

[@officehours4028]

My friend, average degree of consolidation relates directly to the amount of total consolidation that has occurred, so the shapes of the plots should be the same. For example, in my plot, 50% of the predicted primary consolidation settlement occurs in about 10% of the total time for consolidation to complete (ie., about 0.2 year). The other remaining 50% of primary consolidation settlement occurs over the remaining 2 years!

[@mehulkatakiya4892]

@@officehours4028 yes sir..but if this explanation is for settlement vs time plot, it doesn't match with what u are showing at 32:30.

[@mehulkatakiya4892]

i think time must be on vertical axis and settlement on horizontal for the curve at 32:17.

[@mehulkatakiya4892]

Sir, can you tell me how to calculate the coefficient of secondary consolidation?

[@officehours4028]

It is the slope of the void ratio vs time or strain versus time curve AFTER primary consolidation has finished, and it is taken from time-rate of settlement readings during a loading cycle in a consolidation test.

[@mehulkatakiya4892]

so, can we calculate it from any load cycle of test? ..as secondary consolidation is independent of stress..

[@officehours4028]

Yes.

[@officehours4028]

But understand that the coefficient will change depending on whether the soil is overconsolidated or normally consolidated. So if you anticipate that your soil will be normally consolidated in the field, then you should use time-rate curves from a similar load.

[@mehulkatakiya4892]

@@officehours4028 ohh...then is its value considerable or negligible for over consolidated soil also? i am asking this because even if we talk about primary consolidation, then Cc is much higher than Cr.