Design of Retaining Wall Ribbed / Shelf Type ?

[Sanjeee]

I have to design a reinforced concrete retaining wall which has aprox. 7 mt in height, on backfilled soil side I don't have much space for foundaiton protrusion which normally we use to take the balancing overturning moment from backfilled soil, active soil effect, I can create max 2mt protrusion for foundaiton cause I'm hitting the property line limt, on the other side there will be no soil back fill and is totally inside of plot and can be used as road I can extended that to any length that I want for the image shown below I have 2mt at the soil side and 3 mt on the other side, that is totally 5mt rafter foundaiton.

Soil characteristics :
Sandy Clay and Sandy Clay
Cohesion = 67kN/m2
Friction angle = 4,58
density 17 kN/m3 ( saturated 19kN/m3)


I modeled the system as shown below, I even considered to create the vertical ribs in order to increase rigidity, for now slope stability safety factor is SF = 2.8, max settlment in ULS is 3,2cm a and I don't experience and failure in RC design up to now. So as per caclualtion everything seems doable, but that short leg on soil side makes me uneasy.

I will appreciated your comments on that.

 

[HTURKAK]

.......for now slope stability safety factor is SF = 2.8, max settlment in ULS is 3,2cm a and...........

The factor of safeties against overturning and sliding should be the first step rather than settlement calculation. 7 m is substantial height and tilting of the wall could be problem.

 

[XR250]

but that short leg on soil side makes me uneasy.

I will appreciated your comments on that.

As long as the sliding and overturning calcs workout, what is your concern? Are you using retaining wall software? Honestly, with a 3 meter toe, I can't imagine settlement will be an issue.

 

[CJLCivilStruct]

I think others have mentioned in threads similar before - and I agree - that for walls of this height it's a good idea to batter the front face of the wall back such that minor settlement rotations and deflections of the stem don't make it look like the leaning tower of pisa.

Just a thought.

 

[Sanjeee]

@HTURKAK 7 m is substantial height and tilting of the wall could be problem.

yes that thing wories me, overturning seems to be major issue ( if I take the farthest point as moment arm for moment balancing then it comes to acceptable limits ) sliding seems minor, because one way or the other I'm planing to connect toe side with road concrete which will be at least 8~10mt wide ( 25cm thick)

As long as the sliding and overturning calcs workout, what is your concern?

Most probably the hardest and most important question , even though I can judge with technical datas and calulations (which I believe is heavily on theoritcal basis) experience showed me in past diffrent results, cantilevered walls tend to deflect over time, I didn't see any of them collapse up to now but they became like snake gradually. So my ultimate goal here is, to be as efficient as possible w/o sacrificing safety.

and I agree - that for walls of this height it's a good idea to batter the front face of the wall back such that minor settlement rotations and deflections of the stem don't make it look like the leaning tower of pisa.

Plaxis software, yes I created the batter on the back side instead of front, That way it will have more slick view, furthermore batter ribs can be extended to foundation edge as well for more staiblity, please see image below

If I create horizontal shelf at the middle height will be counter conducive to balance the tilting effect of wall ?




For all of you, what kind of soil do you think that I have to use for backfilling cohesive soil ( natural soil will serve that purpose ) or granular material like gravel, sand etc. ? I think that cohesive soil will be better.

What is your opinion?