## Pore pressure increase in slope analysis

## Pore pressure increase in slope analysis

(OP)

Hi, I am reading Professor Duncan's book ("Soil strength and slope stability") and it is indicated that undrained and drained conditions depend on the time of application of the load. For example, undrained conditions are related to rapid loading (in this case the application of the load is too fast so it does not give time for water to dissipate thru the soil) and drained conditions are related to slow loading (loading is slow enough so it lets the water to dissipate).

My question is: I have a slope as a result of cut operations. The slope is quite above groundwater table. 5m height 1:1 slope. Overconsolidated clay. Su approx. 35 to 50 kPa. Not loading is planned for this slope. However it failed after several days of consecutive heavy rain. I understand that shear strength (effective stress) decreased since pore water pressures increased. Is the buildup of water pressure from the heavy rain considered as a rapid loading case, so undrained conditions (total stress) govern the analysis in this case?

If it is not considered as a rapid loading case, so I will need to check under drained conditions (effective stress), I understand that I will need pore pressure information for the slope which is not easy to obtain...

Thanks for your advice in advance.

My question is: I have a slope as a result of cut operations. The slope is quite above groundwater table. 5m height 1:1 slope. Overconsolidated clay. Su approx. 35 to 50 kPa. Not loading is planned for this slope. However it failed after several days of consecutive heavy rain. I understand that shear strength (effective stress) decreased since pore water pressures increased. Is the buildup of water pressure from the heavy rain considered as a rapid loading case, so undrained conditions (total stress) govern the analysis in this case?

If it is not considered as a rapid loading case, so I will need to check under drained conditions (effective stress), I understand that I will need pore pressure information for the slope which is not easy to obtain...

Thanks for your advice in advance.

## RE: Pore pressure increase in slope analysis

## RE: Pore pressure increase in slope analysis

## RE: Pore pressure increase in slope analysis

## RE: Pore pressure increase in slope analysis

## RE: Pore pressure increase in slope analysis

f-d

ípapß gordo ainÆt no madre flaca!

## RE: Pore pressure increase in slope analysis

## RE: Pore pressure increase in slope analysis

## RE: Pore pressure increase in slope analysis

Please recall that we are designing earthwork to be weatherproof. So, if the in-situ saturation (i.e., from a July exploration) is below 80 percent, it may not be there in January.

f-d

ípapß gordo ainÆt no madre flaca!

## RE: Pore pressure increase in slope analysis

## RE: Pore pressure increase in slope analysis

f-d

ípapß gordo ainÆt no madre flaca!

## RE: Pore pressure increase in slope analysis

## RE: Pore pressure increase in slope analysis

some OC clays tend to revert back to its mud like state NC when subjected to many cycles of watering and dehydration , hell i even had a marly shale destroyed in 10 min in pure water . So you should add those in mind , plus Terzaghi and al suggest using the same OC clays and adding water to it to convert it into a slurry provided the amount of water added does not reach the liquid limit . Then , a DSS test is performed , or you could use their formula that inject a OCR to the power of 1-m in the Mohr-Coulomb shear strength formula . with care that is .

## RE: Pore pressure increase in slope analysis

## RE: Pore pressure increase in slope analysis

## RE: Pore pressure increase in slope analysis