Boundary Conditions

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Tausifilyas
Posts: 8
Joined: Mon Sep 23, 2019 6:57 pm
Location: Pakistan

Boundary Conditions

Post by Tausifilyas » Wed Sep 25, 2019 4:42 am

Dear Sir/Madam,
I am doing a project to design a cover system for vault type landfill disposal facility. Cover system consists of multilayered profile having concrete lid/slab beneath it.
Cover Profile: (From Top to Bottom)
0-20 cm Sandy Clay as Vegetation Layer
20-120 cm Silty Loam as Evapo-transpiration Layer
120-150 cm Sand as conductive layer
150-250 cm Clay as barrier layer
250-280 cm Sand as Conductive layer
280-310 cm Concrete Slab (Disposal Vault lid)
I want some guidance regarding upper and lower boundary conditions.
I have taken atmospherics BC as upper and but confused about lower boundary condition, whether it should be free drainage or seepage BC. Kindly Guide about that. Also guide me about BC on sides of profile to accommodate Lateral Flow.

Jirka
Posts: 4980
Joined: Sat Mar 16, 2002 3:47 pm
Location: USA
Location: Riverside, CA

Re: Boundary Conditions

Post by Jirka » Wed Sep 25, 2019 6:44 pm

That will depend on your conditions. It is usually a Free Drainage BC, if you allow gravitational draining of the profile. If the bottom of the profile is open to the atmosphere (e.g., some lysimeters), you can use a Seepage Face BC.

Based on the information you provided, I do not see why you would have lateral flow. If the profile is on a slope, you can use a Gradient BC.

J.

Tausifilyas
Posts: 8
Joined: Mon Sep 23, 2019 6:57 pm
Location: Pakistan

Re: Boundary Conditions

Post by Tausifilyas » Thu Sep 26, 2019 6:06 am

Dear Jirka,
Thank you for your responding back!
On the basis of my understanding, it may be incorrect, Free drainage BC is applied in such conditions where bottom most material (in my case concrete slab) is continuing up to saturated zone. In my case, beneath the concrete slab there is host rock, therefore i cant applied Free drainage here. Also cant apply seepage face BC because there is no contact to atmosphere here.
Its very challenging to select suitable BC for my system.
Cover system is applied to protect water ingress into landfill disposal facility, that's why sand layer is used to drain percolating water laterally.
Kindly guide me about what type of BC will be applied at the bottom of concrete slab and on the side of cover profile.
Thank you.

Jirka
Posts: 4980
Joined: Sat Mar 16, 2002 3:47 pm
Location: USA
Location: Riverside, CA

Re: Boundary Conditions

Post by Jirka » Thu Sep 26, 2019 2:05 pm

Is you can choose any of the standard BCs for the bottom of your profile, why don't you extend the profile all the way to the groundwater level and then fix the pressure head there to keep GWT constant or use no flow to allow water to accumulate there? J.

Tausifilyas
Posts: 8
Joined: Mon Sep 23, 2019 6:57 pm
Location: Pakistan

Re: Boundary Conditions

Post by Tausifilyas » Sun Sep 29, 2019 6:10 am

I am doing a project to design a cover system for vault type landfill disposal facility.
Presentation2.jpg
Presentation2.jpg (79.84 KiB) Viewed 1457 times
Cover Profile: (From Top to Bottom)
0-20 cm Soil; 20-120 cm Clay; 120-150 cm Sand; 150-250 cm Clay; 250-280 cm Concrete
Red Color box is my domain which has to be modelled. I want some guidance regarding upper and lower boundary conditions. I have taken atmospherics BC as upper and but confused about lower boundary condition, whether it should be free drainage or seepage BC and BC on sides of profile to accommodate Lateral Flow (in sand Layer).
The purpose of this cover is to protect the toxic waste from water ingress. So that I used sand as lateral drainage.
Output I needed is the bottom flux that will be used in further calculation.

Tausifilyas
Posts: 8
Joined: Mon Sep 23, 2019 6:57 pm
Location: Pakistan

Re: Boundary Conditions

Post by Tausifilyas » Sun Sep 29, 2019 6:12 am

PS: water table is 60 meter deep.

Tausifilyas
Posts: 8
Joined: Mon Sep 23, 2019 6:57 pm
Location: Pakistan

Re: Boundary Conditions

Post by Tausifilyas » Tue Oct 29, 2019 5:36 am

need guidance please.

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