Properties of Over/Underconsolidated clays
Properties of Over/Underconsolidated clays
(OP)
hi all,
just a quick question, how do I know if the clay is overconsolidated or underconsolidated based on the following information...
12m of saturated soft-firm clay overlying permeable rock. A consolidation test taken from a depth of 6m gave the following results: Cc = 0.35; Cr = 0.08; Calpha = 0.01; Cv = 3x10-7 m2/sec (for pressures 10 to 100kPa); e0 = 0.95; sigma dash p = 42kPa. Triaxial shear tests provided the following information: Su = 50kPa; c dash = 3 kPa and phi dash = 25 degrees.?????
I understand the policies so if you cannot help thats ok, but if someone could point me in the right direction as to where I could obtain such information that would be great
Thanks
just a quick question, how do I know if the clay is overconsolidated or underconsolidated based on the following information...
12m of saturated soft-firm clay overlying permeable rock. A consolidation test taken from a depth of 6m gave the following results: Cc = 0.35; Cr = 0.08; Calpha = 0.01; Cv = 3x10-7 m2/sec (for pressures 10 to 100kPa); e0 = 0.95; sigma dash p = 42kPa. Triaxial shear tests provided the following information: Su = 50kPa; c dash = 3 kPa and phi dash = 25 degrees.?????
I understand the policies so if you cannot help thats ok, but if someone could point me in the right direction as to where I could obtain such information that would be great
Thanks





RE: Properties of Over/Underconsolidated clays
Assuming a total density of 116 lb/ft^3 or 1840 kg/m^3 (based on e0=0.95 and all assumed approx. saturated), the total overburden stress is 9.81 m/s^2 * 1860 kg/m^3 * 6m = 109,500 Pa = 109 kPa.
Assuming the water table is 2 m down, the effective stress is 109 kPa - 4 m * 1000 kg/m^3 * 9.81 m/s^2 = 70 kPa. If the WT is at the surface, it would be 51 kPa.
Hmmm. Either way, that's more than what I surmise is the preconsolidation stress, 42 kPa. That would suggest that it is underconsolidated, but does that make sense geologically? Only if an embankment fill was constructed over it recently or if the clay is in an active tailings pond.
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Check:
116 * 6 m * 3.28 ft/m = 2300 lb/ft^2 = 110 kPa
62.4 * 4 * 3.28 = 819 lb/ft^2 = 39 kPa
110-39 = 71 kPa
RE: Properties of Over/Underconsolidated clays
f-d
¡papá gordo ain't no madre flaca!
RE: Properties of Over/Underconsolidated clays
If they measured Su = 50 kPa, I would guess that the sample was consolidated in the triax cell to something higher than in situ stress. That's 70 percent to 100 percent of my sigma'v estimate, which implies a mighty high strength ratio. Intial void ratio e0 = 0.95 --> gamma-dry ~86 lb/ft^3 and saturated water content ~ 35%. Sounds pretty soft to me.
hemipower - Can you give us a bit more detail when you get in - triax test conditions, suite of three samples, site description, Atterberg limits, other?
Your use of "phi dash" instead of "phi prime" makes me think you don't live in my time zone. You're in (or from) UK, NZ, or Australia, right?
(PS - Does your handle refer to your Dodge truck?)
RE: Properties of Over/Underconsolidated clays
RE: Properties of Over/Underconsolidated clays
It's very rare for shallow soils not to be overconsolidated because of dessication.
Sorry to shout, but you really should consult with a soils engineer rather than try to figure these things out for yoursel. You seem like you're smart enough to do the calculations but it doesn't appear that you have enough experience (no shame in that) to know if your results make sense.