Microporous Loess soils
Microporous Loess soils
(OP)
We propose to excavate in microporous Loess soil around the city of Galati in Romania. The proposed structure is a combined sewage storage tank 25m diameter 15m below ground level.
Does anyone have any experience in excavating in this type of soil and the associated geotechnical hazards.
Also typical soil strength parameters (total stress) would be much appreciated.
Thanks in advance.
Does anyone have any experience in excavating in this type of soil and the associated geotechnical hazards.
Also typical soil strength parameters (total stress) would be much appreciated.
Thanks in advance.





RE: Microporous Loess soils
RE: Microporous Loess soils
RE: Microporous Loess soils
RE: Microporous Loess soils
I seem to be getting confilting reports about this material. Some papers say that Loess can cause a number of problems associated with its sudden settlement upon wetting. Problems result because Loess undergoes structural collapse when wetted. This happens when the initial dry density is low and the initial water content is low.
However as you say - you can excavate a vertical face in the same material.
The construction method is not a problem, however I would appreciate some typical shear strength and dry density parametets if any has any.
Cheers
RE: Microporous Loess soils
RE: Microporous Loess soils
The most critical problem with loess, as already discussed, is collapse (hydro collapse). Because they are wind-deposited, loess soils will usually have a low dry density and high void ratio. There are many rules of thumb to use in evaluating collapse potential. The easiest rule of thumb is dry unit weight - if the dry unit weight is less than 85 pcf, you are likely looking at some collapse potential (unless you are already below the water table). Dry unit weights down to about 72 pcf are pretty common in this area. If you have collapse potential, then take a hard look at potential sources of moisture and leakage.
Considering a sewage storage tank, I would be looking at providing 2-3 feet of compacted cohesive material beneath the tank, and anywhere you might have leaks, if you have determined that collapse could be a problem. This will provide a low-permeability zone and help protect your collapse-sensitive materials.
Notes for sampling loess: Loess is very sensitive to disturbance. SPT won't tell you much - get some Shelby tubes. Use 3" tubes, and only do 1-foot pushes. Dry loess will compress a lot when pushing a tube if you are not careful, which will throw your density through the roof.
Hope this helps...
RE: Microporous Loess soils
RGds,
Myoho