Lateral earth pressure is very important in the the estimation of retaining structures stability. Three main conditions may apear: At rest, active earth pressure and passive case. How could we determine in real field if soil is in the at rest condition?
Hello,
I've two interpretations of your question. Do you mean:
- in a natural field without any stuctures, how assess the value of Ko ?
or
- when building a retaining structure, how knowing what's the earth pressure ?
Assessing the value of ko is not a problem. I want to know the best procedure to find out if the soil condition is at rest case in the field (with or without a structure in place)?
If you have level ground conditions it's always at rest. In order to have active earth pressure somewhere, the earth should be moving (e.g. a landslide). In the free-field (without buildings) you can't have passive earth pressure.
The lateral earth pressure coefficients at rest (K0) can be measured by KSB (K0 stepped blade)
K0 condition is a idealised state with zero lateral strain. In the field, you can measure the actual stress and strain with specific facilities, thus you don't need to identify whether it is at K0 condition.
The best and most accurate way to measure and find out lateral earth pressure at rest is to perform a self boring pressuremeter test at site. But this costs a lot sometimes, menard pressuremeter is also beneficial tool for this purpose, however the result of the test can be inaccurate according to person who performs it and soil type etc.
It can be measured using stepped blade or self-boring pressuremeter. Although these techniques are the best available ones, yet the insertion of these tools change the state of lateral stresses in the soil.
Another approach is to use the correlations of DMT, CPT and SPT to determine it or the OCR.
There are also some correlations that links the OCR to the index properties in clays that were developed by Prof. Mayne. Using the OCR, the K0 coefficient can be determined.
There are also correlations that can determine K0 or the OCR using the combined results of CPT and DMT together.
Other approaches include correlations of the OCR or K0 with the shear wave velocity.
I believe that the best way is use all possible approaches and reach a concluded profile of K0 based on the results of the different methods.
The coefficient of lateral earth pressure can be determined as a function of the lift-off pressure obtained from the PMT stress-strain curve. Also, it can be empirically computed using the data of SPT, CPT and DMT tests.
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