we know that in Alfa method computing nominal side friction capacity in cohesive soils for drilled shafts is possible with Multiplication of Adhesion Factor and undrained shear strength, therefore the Reese and O'Neill (1989) approach as modified by Brown, et al.(2010) suggests that alfa is zero from the ground surface to depth of 1.5m (5 ft) or depth of seasonal moisture change (whichever is greater).
So let me ask:
how to compute depth of seasonal moisture change? Obviously, there is some in-situ measurements but what are they? by the way i saw some articles dedicated to validate surface soil moisture with an infrared thermometer, i also know thats limited to depth of 5cm.
appreciate your time.
If you had long-term EMC depth data for a specific location that would provide a seasonal moisture change depth value. Otherwise crude approximations can be estimated from aridity measures like TMI, if meteorological data is available.
Dear Milad,
The effect of seasonal change in soil moisture depths is mainly depends on rainfall data and its frequency of occurrence. The other factors like surface water during rainy season also influencing the soil moistures depth. The ground water depth is usually measured by metrological department and its data are maintained by central water board..ok all the best..
Dear Milad
I understand that you need that information (depth of seasonal moisture changes) for the purpose of pile capacity computation. Well, I do not have a worldwide experience, but for Polish climate conditions I find it negligible. But if you ask :-)
Cyclic changes of cohesive soil moisture may be related to groundwater level changes in neighboring saturated grounds. But that takes time depending on the cohesive soil plasticity. And the change range is reduced by inertia proportional to cohesive level thickness.
The most important factor is the influence of roots of trees. It can go up to 4-5 meter or deeper and, depending of the season, it causes large moisture changes and may induce large volume changes in swelling soil.
To sum up.
Please refer to local conditions. Even similar soils may behave differently depending on their origin and local conditions. If you have any doubts just take samples from boring holes and check it throughout a year or two (once a month lets say).
Best regards
The active zone, or the depth of occurring periodical moisture changes in soil, is varied from site to site. In some countries, the depth of the active zone may reach fifteen meters. To determine this depth, the liquid limit, plastic limit, and natural moisture content are required. From these soil properties, the liquidity Index can be determined, and by plotting the liquidity Index against the depth of the soil profile over several seasons, the active zone depth can easily be determined.
Follow this link please:
https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/soil-moisture
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