Supplementary answer
Dear Dr. Fakharian
Amir Kabir University
Answer 1: Theoretical issues and consequences of flooding
As a result of foundation flooding, depending on the type of soil and the speed of water flow, the soil may suffer from any of the following factors: erosion, swelling, divergence, reduction of resistance, increase in settlement potential, instability due to rotational sliding of sloping land.
Answer 2: Survey and field identifications
– It should be determined whether the floodwater is under the condition of rising water without horizontal flow or with high-speed flow. An example is the rapid flow of land adjacent to Karkheh in Pol Dekhter and similar.
– In a flood without flow, the probability of water breaking and diverging is less. In this situation, the reduction of soil resistance in the upper thin layer (because there is no tension on the soil yet and it swells easily) and the swelling in susceptible clay soils due to high water absorption should be evaluated.
– In the condition of flow: the effects of water washing and the amount of damage caused by it should be checked carefully. Especially if the soil contains a lot of sand and silt and is easily washed by water flow (scouring).
– Swelling clay soils containing montmorillonite have greater dispersion in flow conditions. With the tests of Etterberg limit, crumb test, pinhole, it is possible to evaluate the tendency of divergence with acceptable accuracy.
– Conducting a plate loading test on the soil adjacent to the foundation that has been under the same flow or absorption conditions to evaluate the resistance loss and settlement potential in the current conditions.
– Visual inspection and surface sounding of the condition of the soil next to and under the foundation
– If the footing is on the slope or adjacent to the slope, evaluating the potential of sliding and ground movement
– If the concrete pouring of the foundation has just been done, the amount of damage and even its washing should be evaluated.
Answer 3: solution and solution
If concrete is not poured:
– Effects of swelling, scouring and any adversities observed in the identification stage, mold and reinforcement should be collected, proper improvement should be done and re-implemented.
– Depending on the type of soil, improvement can be rolling and compacting the local soil (if it is granular) or removing 30 to 60 cm and replacing it with quality materials and compacting it.
– If there is a problem of water washing, it is better to increase the depth of the foundation to avoid the risk of water breaking. A complementary or alternative solution can be collecting the soil and replacing it with soil-cement or lime-cement mixture depending on the type of local soil.
– If the foundation concrete has been poured, the decision to continue the implementation, destroy the foundation or improve the soil is a more sensitive matter and should be done with more care and measures.
In any situation in flooded areas:
– Conducting drainage around the building to deal with future water inundation and keep it dry or prevent flooding again.
– Sealing the floor and surrounding walls of the building up to one meter is essential.
– Slope ground or foundation adjacent to the slope: if cracks, movement or sliding are observed upstream, downstream and around the foundation, strengthening and stabilization must be done first. Depending on the case, it may be necessary to use soil amendment methods for stabilization.
– If the foundation is near the river bed: the probability of front (or rear) landslides going towards the foundation in the future should be evaluated.
– Note 1: Of course, it is not possible to provide the answer to all cases in flooded areas with a simple prescription. Each case should be reviewed and evaluated by a geotechnical expert and a suitable solution should be provided based on the results and observations.
– Note 2: The above solutions are for foundations on which columns and structures have not yet been built. Regarding the foundation damage of the existing buildings and the foundations on which the skeleton has been implemented, naturally, more detailed discussions will be discussed in the identification stage and remedial solutions. As a rule, in the event of erosion, subsidence, or soil erosion, various soil modification methods can be used.
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