liquefaction susceptibility of a soil
liquefaction susceptibility of a soil
(OP)
I am developing a property where part is sloping up by 40% with rock outcroppings showing; the rest is flat and is a small part of the property, on the surface it is a mixture of dark soil and stones of all sizes. On the published California maps of liquefaction hazard the flat area is labeled as liquefaction risk.
I dug a couple of trenches in the area and in both I encountered very dense soil mixed with stones, the soil is dark kind. As I reached the 2 ft depth it was very hard to dug much even by the sharp ax pick I am using. As I went deeper the stones started to get bigger and bigger. The stones I am digging out of the trench as of many sizes. Overnight I thought may be I should fill the trench with water to help me go deeper, when I went to work in the morning I found almost all the water I poured in the trench sitting there nice and clear.
What can be read from the observation? Is the liquefaction hazard just speculative and the real data will confirm or reject the hazard assumption?
I dug a couple of trenches in the area and in both I encountered very dense soil mixed with stones, the soil is dark kind. As I reached the 2 ft depth it was very hard to dug much even by the sharp ax pick I am using. As I went deeper the stones started to get bigger and bigger. The stones I am digging out of the trench as of many sizes. Overnight I thought may be I should fill the trench with water to help me go deeper, when I went to work in the morning I found almost all the water I poured in the trench sitting there nice and clear.
What can be read from the observation? Is the liquefaction hazard just speculative and the real data will confirm or reject the hazard assumption?





RE: liquefaction susceptibility of a soil
Granular soils below the water table
Granular soils above their critical void ratio
Sufficient earthquake magnitude.
You obviously have soils below the water table.
You have granular soil.
You don't provide information on the density of the granular soil.
Not sure about the design earthquake.
A resounding maybe!
f-d
¡papá gordo ain't no madre flaca!
RE: liquefaction susceptibility of a soil
You do mention density, noting it is hard to excavate, "very dense".
The trench did not necessarily extend into the water table, the water you mention is water you poured in yourself. It could be a very "tight" soil.
Regarding your question, yes the mapped hazard is speculative (generalized), need real data to confirm or reject. The data you present indicates (to me) the risk is low, but you probably need borings to 30' to further assess.
RE: liquefaction susceptibility of a soil
here's an example. there are others available
http://earthquake.usgs.gov/regional/nca/alameda/
RE: liquefaction susceptibility of a soil
RE: liquefaction susceptibility of a soil
They most certainly won't accept "These guys I talked to over the internet but have never met didn't think it would be a problem."
RE: liquefaction susceptibility of a soil
Want to ask a question about drilling. What if we encounter rock at 7ft to 12 ft where the drill bit cannot go any further. Can we stop and say we hit a solid bedrock then liquefaction is not a risk or do we have to bring a different kind of drill to go deep to the 30 ft to 40 ft to shed a clear light on liquefaction?
Thanks
RE: liquefaction susceptibility of a soil
RE: liquefaction susceptibility of a soil
RE: liquefaction susceptibility of a soil
RE: liquefaction susceptibility of a soil
RE: liquefaction susceptibility of a soil
RE: liquefaction susceptibility of a soil
RE: liquefaction susceptibility of a soil
RE: liquefaction susceptibility of a soil
RE: liquefaction susceptibility of a soil
http://www.optimsoftware.com/white_papers/
RE: liquefaction susceptibility of a soil
RE: liquefaction susceptibility of a soil
Top 5 ft was as expected tough mixture of stone and top soil.
Then we hit very soft sand for a layer which I believe is almost 7 ft thick.
Then we hit resistance and when looked at the sample it was a pebble like material, like the round shaped little stones that have been running in a river for millions of years. This layer was 3 ft thick
Then came the rock at depth 15 ft. Looks like the serpentine rock is highly weathered for at least two ft when it was exposed in its geological days. we went drilled for 5 ft in the rock, then we added another 5 ft to make sure we were not hitting a local boulder.
In the area people report drilling up to 50 ft to hit rock, I guess I was lucky, this is understandable since my property is far from what geologically could have been a river in past times and at the edge of a hill side.
The above was for the flat part of the property, the next we attempted to drill in few locations on the slop where the house will be sitting in part. The maximum we were able to drill without massive resistance was 7 ft. I also made trench like excavation ranged between 2 to 4 ft to expose the rock; the geologist appreciated it because it was revealing about the rock formation we are dealing with.
RE: liquefaction susceptibility of a soil
f-d
¡papá gordo ain't no madre flaca!