lateral load from drilled shaft on mse walls

[mudman54]

can anyone advise me on the best procedure to take the results from LPILE or COM624 and convert it to soil pressures that could be transmitted to a mechanically stabilized earth wall?

 

[dcarr82775]

You could look at the shear in the drilled pier. As the shear in the pier decreases, that load must be transferred to the soil. If you take the load on that leaves the pier per foot of depth and divide it by the pier diameter that would give you a pressure.

 

[FixedEarth]

What is the origin of the lateral load? Do you have a sketch to help in visualizing?

 

[mudman54]

the MSE wall is a wrap around bridge abutment; lateral loading comes though the piles which support the bridge abutment. actually, i found out that COM624 has a result called "soil resist" which i never appreciated for 20 years until just now. it is the interaction of the pile structure and the soil, the "p" in the famous "p-y" curves where "y" is the deflection of the pile. in effect, p is like a little spring constant, so from there one can get the force in the soil at various depths along the pile.

 

[six06]

actually Lpile and COM624 give you the soil reactions with depth. The soil reaction is in units of Force per unit length of the pile. That number is the resultant force and is calculated as the integration of the stress bulb around the pile (including the active and passive stresses). So theoretically, that would be the resultant force per unit length that the soil would fell when the pile is laterally loaded.

 

[mudman54]

great, six06; so if i have regularly spaced soil reactions i can integrate them along the pile within the zone of interest and get a lateral force?

 

[six06]

not really, the number that lpile gives you is already the resultant soil reaction (distributed force). So, i would see what those reactions are, see if their values are reasonable, and come with an approximate force on the wall. You have to consider that the way these forces are calculated are a little bit tricky and could lead on values way over (or under) the reality.

 

[FixedEarth]

There are many ways to get your lateral loads. I never use the spring anology method. In real life the soils are surrounding the pier or pile continuously. There is no gap in lateral soil support.

The best I have seen is the method proposed by Budhu and Davis 1986 and 1987 and before that Teng.

The following equation works for granular soils. You can compute your lateral load by equating it to the area of a triangle. The embedded length minus the "ignore passive resistance" height is L, pier diameter is B, and the base of the triangle is 3*Gamma*B*Kp*L. The area would give you your lateral load directly.

However if you have a Moment in addition to the lateral load, then it may be faster to compute the required embedment by obtaining the following Teng paper:

"Tapered Steel Poles - Caisson Foundation Design" Prepared by Teng and Associates, July 1969

To get the Budhu and Davis method look at Amazon for "Foundations and Earth Retaining Structures" book by Budhu. It comes with APILES program that is very useful.