CR4® - The Engineer's Place for News and Discussion®

 Previous in Forum: A question Next in Forum: How Many Washers Must Be Included in Bolted Connection for Steel Construction
Active Contributor

Join Date: Mar 2011
Posts: 17

# Soil Friction Angle and Pressure at Retaining Walls

03/30/2011 4:44 AM

Hi every body

If I have two soil (A&B) have identical in place wnit weights. Soil A has angle of friction=42 degree and B has angle of friction =36 degree. Under active condition which soil woul exert more pressure on a retaining wall?

Pathfinder Tags: soil friction
Interested in this topic? By joining CR4 you can "subscribe" to

Guru

Join Date: Nov 2007
Posts: 1226
#1

### Re: Soil Friction Angle and Pressure at Retaining Walls

03/30/2011 5:18 PM

Check it out with a calculator and let us know your findings.

pv = γ.z (vertical pressure)

ph = ka.pv = ka.γ.z (horizontal pressure)

By Rankine theory, active pressure coefficient,

ka = (1-sinφ)/(1+sinφ).

__________________
Bruce
Active Contributor

Join Date: Mar 2011
Posts: 17
#2

### Re: Soil Friction Angle and Pressure at Retaining Walls

03/31/2011 4:32 AM

I found te following:

In active pressure I found the pressure at retaining wall is increasing when the angle of friction increase

Guru

Join Date: Nov 2007
Posts: 1226
#3

### Re: Soil Friction Angle and Pressure at Retaining Walls

03/31/2011 11:28 AM

__________________
Bruce
Active Contributor

Join Date: Mar 2011
Posts: 17
#4

### Re: Soil Friction Angle and Pressure at Retaining Walls

03/31/2011 2:50 PM

I read it , and iI understanding it, but when I write my pervious replaying error in typing , thanks alot

Active Contributor

Join Date: Mar 2011
Posts: 17
#5

### Re: Soil Friction Angle and Pressure at Retaining Walls

03/31/2011 2:59 PM

that mean when the angle friction increase the lateral pressure will decrease in active case,

but in my study i found

Ka= tan (45 - Φ/2)², for rankine method so which way is correct

2
Guru

Join Date: Nov 2007
Posts: 1226
#6

### Re: Soil Friction Angle and Pressure at Retaining Walls

03/31/2011 7:04 PM

Read it again. It should read Ka= tan2(45 - Φ/2) which is equivalent to the formula I gave you earlier. It is simply a trig identity.

If φ = 30, Ka = tan2(45 - 30/2) = 0.3333

Alternatively, Ka = (1 - sinφ)/(1 + sinφ) = 0.3333 so they are both correct.

If φ = 40, Ka = 0.217, so it is decreasing with increasing friction angle.

__________________
Bruce
Active Contributor

Join Date: Mar 2011
Posts: 17
#7

### Re: Soil Friction Angle and Pressure at Retaining Walls

04/01/2011 10:08 AM

I have read it again, and i want just thank you alot for that explanation, I understood it, so may be can i ask you in other topic ?

Guru

Join Date: Dec 2007
Location: California
Posts: 2365
#8

### Re: Soil Friction Angle and Pressure at Retaining Walls

05/11/2011 1:18 PM

Why does this sound like a home work problem in a introductory geotech class.

Interested in this topic? By joining CR4 you can "subscribe" to