Cohesion Values in Design
Cohesion Values in Design
(OP)
I am designing a double wall retaining system and I am wondering what values of cohesion I can use for a marine project consisting of soft to firm silty clay, clay, hard clay till and silt till layers. I found a graph in the geotechnical investigation report that plots cohesion against depth from DMT testing. These values varied between 0 near surface and over 125 kPa. However, the contract drawings had a summary table which showed effective cohesion intercept to be 0 kPa for all layers except for the bottom till layer, which showed a value of 5 kPa. Seems like the summary table is very conservative?
I have done a preliminary design for the critical section based on the 5kPa value for the till layer only but also did another design to see how some cohesion (3kPa) for the silty clay layers and found that the cohesion helps significantly. But I am not sure if I can rely on any cohesion. Does anyone have any recommendations? Is it possible to correlate blow counts to cohesion for either clay or silty clay soils? Thank you.
I have done a preliminary design for the critical section based on the 5kPa value for the till layer only but also did another design to see how some cohesion (3kPa) for the silty clay layers and found that the cohesion helps significantly. But I am not sure if I can rely on any cohesion. Does anyone have any recommendations? Is it possible to correlate blow counts to cohesion for either clay or silty clay soils? Thank you.





RE: Cohesion Values in Design
RE: Cohesion Values in Design
RE: Cohesion Values in Design
RE: Cohesion Values in Design
RE: Cohesion Values in Design
f-d
ípapß gordo ainÆt no madre flaca!
RE: Cohesion Values in Design
RE: Cohesion Values in Design
As a side note, earth pressure theory is quite unreliable in reality as soil and soil conditions are highly unpredictable over time (unless using free draining granular backfill and even this can exhibit apparent cohesion properties which initially reduces load). The intent is to come up with a reasonable magnitude of thrust that might be expected over the life of the structure based on reasonable assessment of the retained soil type. This means you take the tested results and compare to expected ranges for similar materials and personal experience then pick a number you are comfortable with based on what the structure is expected to accomplish. It is the "art" part of soil engineering and varies by individual.
RE: Cohesion Values in Design
Boss says, "All we have budgeted for are UC tests so just assume worst case loading, neglect unknowns and use most conservative values".