it is not about which influence more , it is all about the geometry of both. The bedding plane it is influencing more than the joint if the bedding plane toward the slope face, and vice versa.

Not only the orientation between slope and discontinuity. The poor properties of a discontinuity (roughness, aperture, water, ecc) influence deeply the possible instabilty of a wedge. In fact, in order to analyse slope stabilty, researcher firstly apply BRMR (a rock mass classification) and then Romana classification (use the final rating of BRMR and the same classes).

Yes, That is right , but the most important property and first is: (the orientation) then you need to check the other properties, only if the orientation directed to the slope face.

Thanks

orientation between slope and discontinuity is analysed by Romana classificattion, which consider two instablilty mechanism (sliding and toppling). So instability problems you can have with dip directions opposite (toppling) and not only with similar dip directions between slope and joint.

More over there is wedge failure, which has to be considered with Dips software.

Bedding and joints in sedimentary rocks are both mechanical discontinuity and are of teh same importance  I agree with Devoto S., there is a mutual interactiosn between bedding, joints and slope orientation in determining planar sliding, toppling or wedge sliding (use Dips software). If You apply common geomechanical characterization pay a great attention to rock volume potentially involved, this depending mainly on bedding thickness and joint spacing. Slope intability could be determined by moderate-sized (few cubic meters) rock blocks falling as well as slope-scaled instabilities.

I am thankful to everyone who gave valuable suggestion regarding this question. Whatever I understand from above answer is that bedding and joint plane, both have equal importance according their orientation along the structure. Therefore according to site situation we have to proceed. Am I right?      

Try to find out potential of intersecting planes in addition as wedge failures are very common.

yes, bedding plane is a discontinuity so joint and bedding plane have the same importance. For wedge failure you have to consider two discontinuities.

Bedding plane always prominent in the sandstone than joint plane, hence bedding plane influenced more than joint plane.  Looked in to details including bedding thickness,  orientation, aperture, spacing, persistence, gap etc. and one must see relationship with slope surface. Rock structure rating, frequency of discontinuity also play its role. 

Well, and what happens if You have pluri-metric or decametric-thick bed in sandstones?? In that case, rock slope failures are determined by joints only (if present). Basically, it is all about geometry, respectless the origin of rock discontinuities.

ediluzio

Thanks to everyone for valuable suggestion, as I understand from above discussion, if bedding plane is highly thick, in that case, we looked forward for Joint only as suggested by  prof. Luzio, while in other case we have to consider both, bedding plane as well as joint plane and its orientation, spacing , aperture etc.   

I suggest you read texts written by Prof. Barton (Norway) who had expert in shear strength behavior of rock materials and rock mass.

Fault is one importance of slope stability and lamination and graded bedding.