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Rock Anchoring

 
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kvgkrangaraju
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PostPosted: Thu Sep 15, 2022 10:50 am    Post subject: Rock Anchoring Reply with quote

DearSirs,
Is it required to anchor the footing -(an isolated footing of  a multi storeyed building) to the Rock surface when placed over rock even when the said rock is  on a plain surface ?
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vikram.jeet
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PostPosted: Thu Sep 15, 2022 4:19 pm    Post subject: Reply with quote

Foundations on rock are to be provided with Anchors   to bind rcc footings/foundation s with underlying rock.

Though friction between rock and concrete is good/ substantial , but anchoring provides  additional benefits :

(I) It provides extra safety against sliding & Overturning

(ii) It provides safety against upliftment during & after construction  , in case of higher subsoil water conditions

(iii) It not only benefit foundations , but underlying  rock  also get stitched.  Rock is very strong strata but due to presence of discontinuities  , fissures,  joints , shear zones , etc weaken the rock strata .
(Somebody said that  ,Whereas  Soil Mechanics is the study of STRENGTH of soil , Rock Mechanics is the study of WEAKNESSES IN ROCK).

Pl refer BIS Code on foundations on rock .
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es_jayakumar
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PostPosted: Fri Sep 16, 2022 2:09 am    Post subject: Reply with quote

We have once anchored reinforcement bars into the bed rock for a Tower Foundation, for stability against overturning :  https://www.sefindia.org/forum/viewtopic.php?t=12949

E S Jayakumar
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kvgkrangaraju
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PostPosted: Sat Sep 17, 2022 6:48 pm    Post subject: Reply with quote

Dear Sirs,
Thank You  for the prompt reply.
But my doubt was-" is the anchoring  required to be done even when the rock surface is plain and horizontal underneath the footing?" Is there any codal requirement to do so?
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vikram.jeet
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PostPosted: Sun Sep 18, 2022 3:45 am    Post subject: Reply with quote

Dear Er

Yes above response is a generalised one giving benefits of rock anchoring.

Please refer IS 12070 Code for design & Construction of SHALLOW foundations on rock.

Regarding anchoring ,, followingneeds to be kept in view :

As per Code ,

Foundations on rock have UNDESIRABLE EFFECTS OF SEISMIC RESPONSE .

HETEROGENEOUS NATURE OF ROCK

PRECAUTIONARY MEASURES TO BE TAKEN FOR FOUNDATION ON HETEROGENEOUS ROCKS  ON SLOPES . Hence apparently rock  surface appears to be horizontal in small area of this building construction zone , but bed rock profile could be in some grade / Slope .

Also please check up with Geotechnical Consultant who has given Report and foundation Recommendations.
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