Dear Fayrouz,

Due to the limited number of soil tests and the measurements errors, there are some uncertainties in the determined Kv and Kh. According to the reported data in literature, the CoV of these two properties could be very big, so multiplying them by 10 is acceptable.

If you work in saturated steady state flow conditions, the Kv and Kh are indeed the most important properties for the PWP. The following ideas are maybe useful for you:

1. Use some empirical equations to predict the Hydraulic Conductivity so that you can have a range for respectively Kh and Kv

2. Modify the ratio of Kh/Kv. Since embankments are usually constructed by layers, Kh is normally significantly lager than Kv, and the ratio is related to the compaction, consolidation etc .

3. Consider the spatial variation of these two properties inside the embankment

Best regards,

Xiangfeng

Thank you so much, this was really helpful knowing that it's not a sharp decision,

If i can, ihave some more inquires:

1- you say " According to the reported data in literature, the CoV of these two properties could be very big, so multiplying them by 10 is acceptable. "

do you mean by "Cov" the coefficient of consolidation? also if there's some reference to state regarding this point in my work, i'd be grateful, cuz if i did multiply by 10 i need some support as i'm not using the oedometer test data.

2- regarding your 2nd suggestion, you mean those of the soft soil beneath embankment or the embankment itself?

Dear Fayrouz,

We can't vary the vertical and horizontal permeability with out any reference..I feel if kv and kh used in the analysis is purely based on field permeability test results, then in this case you don't have an option to vary permeability, since permeability value is measured in the field. If you don't have any field data then it is better to get data from literature. You are requested to check other parameters also like material properties of soil and stone column used to accelerate the pore water pressure. Also, verify the dimension of the mesh, density of the mesh and type of element. ok all the best..

Thanks a lot for your interest, the Kv is measured from oedometer test, and i found that some researches stated that permeability in field is much higher than lab.

Also my material parameters are the ones that are measured and mentioned in the work.

would u kindly state some parameters that would affect pore pressure?

Mr.Fayrouz,

As i mentioned the material properties of stone column which includes density, angle of internal friction and permeability. Also, check density of the soil and other properties like cohesion and angle of internal friction. ok all the best in your research..

Thank you very much, good luck to you too.

Dear Fayrouz,

1. The CoV in my previous answer refers to ‘Coefficient of Variation’. You can have a look on the TABLE 3 in this article (Duncan, J., 2000. Factors of safety and reliability in geotechnical engineering. J. Geotech. Geoenvironmental Eng. 126, 307–316). As I said in my previous answer, the number of performed oedometer tests is limited and there are some errors in the tests and measurements, so the determined permeability value sometimes cannot represent well the entire embankment. Please do not forget that there is also a characteristic of spatial variation for soil properties. As you will find from the mentioned-article, the permeability’s CoV is significantly larger than the ones of other soil properties (density and friction etc.), which means that there are many uncertainties in the permeability. As a result, for me, multiplying Kh and Kv by 10 is acceptable if you assume the soil is homogeneous.

2. I suggested also to vary the ratio of Kh/Kv for the embankment. Embankments were usually constructed with horizontal layers and compacted vertically, the Kh is normally larger than Kv. The ratio is also a parameter with uncertainties since it depends on many factors (compaction during construction and consolidation after construction).

Best regards,

Xiangfeng

Dear Xiangfeng Guo

1- Thanks a lot i 'll check it, and you guided me to look further for the uncertainty in lab permeability tests and i found interesting data to cite, so am grateful!

2- I just want to clarify that my main issue deals with the soft soil beneath the embankment load, not the seepage in the embankment itself, so i'm a little confused if changing the embankment permeability will affect the pore pressure in the underlying soft soil ?

Dear Fayrouz Yasser ,

For the second point: well, I didn’t notice that the water flow takes place inside the soft soil from the questons. Ok, then, it is also allowed to modify the ratio of Kh/Kv for the soil. Due to complex geology process, upper loads from embankment and settlement, the soil is not perfectly isotropic but anisotropic. Probably, Kh>Kv remains valid for the soft soil. Maybe you can find more discussions about this issue in literature.

Best regards,

Xiangfeng