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BLUM THEORY

BLUM THEORY

BLUM THEORY

(OP)
I would also appreciate if one can share a typical example of a steel sheet pile design using BLUM theory.

RE: BLUM THEORY

Steel manufacturer, TradeArbed,Inc., had a sheet pile design manual titled, Practical Design of Sheet Pile Bulkheads, 2nd Edition.  Pages 27 to 29 have an explanation of Blum's method.  They contacting Arcelor or Skyline Steel for a copy of the manual or its successor.

RE: BLUM THEORY

(OP)
Thank you so much, but I already have that manual, besides my main concern is I tried using PROSHEET for calculating the stresses on the Sheet pile, and when compared with my own excel sheet ( simple basics applied to calculate stresses using principles of soil mechanics) they somehow do not seem to tally.

Besides while dealing with BLUM i am trying to compare its main working priciple with design of sheet pile using some other theory.

RE: BLUM THEORY

I believe that ProSheet checks moment equilibrium when solving for the sheet pile length. The user then adds the extra embedment as desired.   Or the user can input a reduced Kp to give embedment with the desired safety factor.  The input safety factor in ProSheet addresses only the bending stress of the sheet pile.

If you apply a safety factor to Kp, you will need a bigger sheet pile section than if you use full Kp, solve for moment equilibrium, and then increase the embedment length by about 20%.

Certain text books add extra sheet pile embedment in order to get force equilibrium in the x direction.  This seems like baloney to me.  For a cantilevered wall, the passive resistance is a reaction, not a force.  Due to its shorter moment arm in checking moment equilibrium, the total passive pressure will always be greater than the total active pressure.  Even though the total passive presure is greater than the total active pressure, the wall cannot move backwards.  If it could, the active side would become passive and the passive side would become active.  The process would then keep repeating.  Makes no sense.  For cantilevered sheet pile walls, I solve for moment equilibrium only, get the required embedment depth, then add at least 20% to the embedment length.  Then, I'm done.

Good luck in trying to match your Excel calcs with the ProSheet results.

RE: BLUM THEORY

(OP)
Ok I appreciate your comment, fully agree to it, neverthless I have a question for you and will kindly appreciate if you let me know.

 In Prosheet, when you enter the value for Ka and Kp and similarly the Densities submerged, for example U have a elevation of 6 m and 7m. the soil profile changes at 6 m and at 7 m. ( which means diff densities and different Ka values at 6 and 7 M). I want to know when Prosheet calculates the pressure /  stress does it take the soil properties below 6 m for its calculation or above 6 m for its calculation ( for calculating stress at 6 m).


I guess my question cud be a bit confusing, but I know this understanding when applied to my excel calculation solves the problem.

RE: BLUM THEORY

It uses the appropriate soil valuse for each soil layer.  Look at the earth pressure diagram printout to see how the pressures change at the layers.

You may want to call an engineer from Skyline Steel in New Jersey who can answer your questions.  Try calling 973-428-6100.  Ask for David Borger in engineering.

RE: BLUM THEORY

(OP)
Thank you for your Kind Reference. I will call him and talk to him. But I somehow do not quite agree with PROSHEET considering the appropiate soil value for each layer. neverthless will think upon it more.

I will aslo ask Mr Borger regarding further information dealing with Corrosion,and the difficulties a Design engineer faces for encountering corrosion allowance for sheet piles, as that per EUROCODE is NOT based upon the semi-probabilistic approach.

once again appreciate your best reply.

RE: BLUM THEORY

(OP)
While calling Mr. David borger what reference shud I give him, if I may ask you?

Thank You.

RE: BLUM THEORY

Just tell him you have questions about ProSheet and how it addresses multiple soil layers.

RE: BLUM THEORY

(OP)
in PROSHEET, it calculates the CROSS FORCE, I suppose that it is done from the total pressure diagram. If I am right, the cross force is calculated by the area of the total pressure diagram, AT THE RESPECTIVE ELEVATION.
BTW to Note PROSHEET DOES NOT GIVE THE RIGHT BOUSSINESQS FORMULA BUT ON CORRECTING IT THEN THE TOTAL PRESSURE DO MATCH.

IN THAT CASE FROM THIS PRESSURE DIAGRAM HOW DO U CANCULATE THE CROSS FORCE?

APPRECIATE YOUR REPLY,

RE: BLUM THEORY

The cross force is the shear force in the sheet pile wall.  It is calculated just like it would be for any beam design.

I also believe that ProSheet, when calculating the Boussinesq surcharge pressure, multiplies the classical Boussinesq lateral pressure by Ka because sheeting is not a rigid wall as is the basis for the Boussinesq analysis.  Therefore, ProSheet should be giving a lateral force that is less than what you would expect from the regular, classical, Boussinesq equation.

You should confirm my above statements with Skyline or Arcelor.

RE: BLUM THEORY

Bousinesq does not depend on Ka, but uses u which is similar. Most lateral pressure calculations that are a variation of bosinesq do not have a lateral pressure coefficent. The difference betweena sheeted wall and a rigid wall is a factor of 2, with the rigid wall having the higher pressure. The deformation of the flexible wall allows for a reduced lateral pressure.
Blum theroy is detailed in the old pile buck manual and possibly in the old US Steel sheetpile manual, which is availble on sliderule era's website. Blum theroy assume embedment is sufficient to develop full cantilevr capacity in the lower portin of an ancored sheet. With one row of anchors the system is determinate. this is done by assuming a shear hinge at the point of zero pressure below the dredge line. It is then broken into 2 detrminate beams and solved. The Blum method (also called equivelent beem or fixed earth) uses deeper sheets than the free earth, but sheeting size and anchor loads are less.

RE: BLUM THEORY

(OP)
I once again appreciate this knowledge of BLUM, but now I am more inclined on the name of the software which I can use or rely upon which exactly follows the BLUM THEORY OF DESIGN. I completely agree with your statement of Boussinesq is completely INDEPENDENT ON Ka.

I also agree with in Blum it develops enough embedment depth in order to achieve fully rigidity at base. I tried using a software SPW 2006 for a simple example of SPW length = 11 m. This example requires excavation on the left of the SPw = 6.5 m NOW WITH THIS EXCAVATION DEPTH, using SPW 2006 it says no equiliubiurm is achieved. Now inspite of using depth of Sheet pile as 100 m ( that is impossible ) yet for the sake of input it still says no equilibrium is achieved. hence I NEED ONE SOFTWARE WHICH I CAN FULLY RELY ON WHICH FOLLOWS THE BLUM APPROACH. AND IF THAT IS PROSHEET THEN I STILL HAVE A PROBLEM OF SHEAR FORCE CALCULATION.

RE: BLUM THEORY

(OP)
Just to add to my above thread, while using SPW the software decides the level of phgreatic level for achieving equilibrium of the sheet pile, this seems a bit bizarre to me, because everytime to decide the length of SPW having the desired phreatic level is not in our hands.

RE: BLUM THEORY

(OP)
Another Interesting point observed in PROSHEET

1) The surcharge Load if entered in the initial stage of INput as Caqout Surcharge = Value (kN/ m2) . And if the same is entered in Boussinesqs then it will calculate the Surcharge twice ( in its calculation of Total Pressure). So basically the point is in calculation of Simnple Earth Pressure it consideres ( asks) if there is any Caquot Surcharge ( to either right or left) and then besides this if u enter in Boussinesq's. The final pressure diagram will have considered Surcharge twice.
PLEASE CORRECT ME IF I AM WRONG!!!

RE: BLUM THEORY

I believe you are correct.  But, why enter it twice?

RE: BLUM THEORY

(OP)
Why is it asked twice?

secondly while checking the same results using SPWALL 2006 and also MSHEET, the same profile of sheet pile fails due to high phreatic level which is unidentifiable using PROSHEET.
All I am trying to say is PROSHEET is not at all a conclusive software! for an analysis of SPW

RE: BLUM THEORY

I have never used PROSHEET I have downloaded it to fool around with it. I think you are right about the software. T he website contains the following diclaimer:

 "The following software will be useful in a preliminary design but should in no way be used for final design. The technical and marketing department of ARCELOR COMMERCIAL RPS will provide you the necessary technical assistance to lead your project to a great success and will help you if you encounter problems using the software."

On the other hand, Blum theory is fairly easy to do by hand. So you could simply do the calculations with out the software.
 

RE: BLUM THEORY

ProSheet is free.  You get what you pay for.  Be careful with SPW911.  Compared to hand calcs and CT Shoring, I have found that SPW911 gives much higher moments and brace loads when using multiple soil layers where at least one layer is a significantly weaker soil.

RE: BLUM THEORY

I second PEinc's caution about SPW911.  I like the program and use it alot.  I think the user interface is very well done. But I have also had problems with it when the wall supports multiple soil layers.  I always carefully check the results and make sure that they make sense.

RE: BLUM THEORY

(OP)
Well I think that using SPW 2006 gives a good sequence regarding wall Construction phase and also helps in distinguishing the importance of phreatic level of water.

RE: BLUM THEORY

My apologies.  We are talking about two different programs. SPW2006 is a free program available here
http://geo.verruijt.net/
SPW911 is a commercial software program available from PileBuck.

I didn't know about SPW2006, so thanks for the tip.

RE: BLUM THEORY

(OP)
There sure is a problem regarding high bending moment using SPW 2006. There is another problem encountered is, while following the construciton sequence ( say for example in 5 loading stages) It then while running says equilibirum is not achieved as results do not converge, but on repeated analysis it still gives a bending moment chart. Now I feel this is some sort of an error.
If the software cannot converge to any resultsa it should conclude saying floating point error. But instead it does give the bending moments whioch are exhorbitant ( 6000 kNm) as against MSHEET for the same giving around 3000. can any one explain the SPW error ?

I think I ahve followed the exact sequence of staged construction!

RE: BLUM THEORY

The Fixed Earth method for analysing anchored sheet pile walls is discussed in Sheet Pile Design by Pile Buck, which also discusses application of SPW 911.

I use the term "Fixed Earth method" because, although Hermann Blum came up with the method in the early 1930's, there are many variations in its application.  Blum's original idea was to create an equivalent, simply supported beam with two supports: one at the anchor and the other at the point of contraflexure, which generally appears at a distance just below the excavation line.  The variations and simplifications begin with estimating that point of contraflexure.  The rest of the pile--including the computation of the embedment below the excavation line--is handled separately.

Part of the problem here perhaps is that "Blum's method" should be referred to in the plural.  If you look at the literature over the years (Tschebotarioff, ARBED, Pile Buck manuals, etc.) you will see the variations.

The ultimate objective of all of the variations in Blum's method is a pile toe with a) no slope (thus the "fixed end" and b) no moment.  There will be a reaction, and that is usually dealt with with the 20% of embedment extension beyond the computed embedment length (although I have seen a variation on that too.)

As far a matching a sheet pile program with Blum's original method, given the variations this can be difficult.  Complicating the issue is the lack of user friendliness amongst some of the programs, which can translate into GIGO very quickly.

RE: BLUM THEORY

Hello PEinc, i knew that you have delt with sheet piles design. I have i question.

In my case, i am analyzing a cantilever sheet pile.

According to the references i have read, i can do moment about the tip (sum of moments about the tip = 0), in order to find my depth value.

ok, now i get my depth, it;s a reasonable value. But my question is, when i try to check with my Sum of horizontal forces (Passive Vs active forces), they are not ZERO using that value of depth, in order to get them ZERO, i need to find OTHER value of depth.

When i get this new value, then i try to check with my sum of moments (about the tip), but in this case it is not zero,

i think it sounds a little by weird, (they should be zero both at the same value of depth), my question is, what approach should i use, the moments? or the Sum of forces?

in my case, i get a very very low value when i use the sum of forces approach ( 0.5ft Vs 12ft). With moments, makes sense.

am i going to have always an unequilibrium?

Please, reply, thanks

RE: BLUM THEORY

The first step in the cantilevered sheeting design is to find an embedment deppth that gives moment equilibrium.  Then, I increase the embedment by at least 20%  to provide a safety factor for overturning.  (Remember, it is just as common to increase the embedment depth to provide a safety factor after calculating the embedment depth as it is to initially divide the passive earth pressure coefficient by a safety factor and then calculate the embedment.  The former method will result in a more economical sheet pile size than the latter while giving somewhat similar embedment depths.)  Next, references will say to check horizontal force equilibrium.  This is where I disagree with the references.

In checking moment equilibrium, because the passive pressure moment arm is much less than the active pressure moment arm, the total passive force must be much greater than the total active force.  Therefore, you can never really increase the embedment in an effort to equilize the horizontal forces.  The deeper you make the sheeting, the more you increase both the active and passive forces.  In addition, as you increase the embedment, you also increase the safety factor for overturning.

Remember, passive earth pressure is not an applied force.  It is a reaction.  For cantilevered sheeting walls, only enough passive force builds up as necessary to resist overturning.  Since the total passive force will always be greater than the total active force, you will automatically have a safety factor against sliding.  If a cantilevered sheeting wall wanted to slide backwards toward the higher side, then the lower side would become the active side and the higher side would become the passive side.  Then, following that line of thinking, the process would have to reverse and then keep repeating.  However, this is impossible.

I know that's not what the books say, but that's how it works.

RE: BLUM THEORY

Hey PEinc

thanks for your reply. I really don;t know if you have read about the rectilinear diagram theory (similar to blum's theory) which deals with how to  find the depth taking into account the passive pressure that is developed behind the wall.

it;s based on a fourth degree equation. But i really don;t know what would be the difference by using that method and the one you use (applying moments about the tip and incresing the depth by 1.2).

Also i have checked the CIRIA report No. 104 which describes the blum's theory (by pathfield and mair 1984) and they do very similar to what you do, but after they get the depth value (d0) they check the new values of passive and active pressures with the increased depth (1.2 do).

The condition is that if the new change in passive pressures - the new change in active pressure, is less than the passsive - active (using d0), (Also they name that R), then is ok.

if not, you gotta increase the depth until this condition satisfies.

But in my case, IT IS NEVER SATIsfied!, Always the R value is very very very high compared to the Change in passice - change in active.

if you have any experience please let me know.

thanks

RE: BLUM THEORY

Sounds like a math exercise.  Why do something harder than something easier that works?

RE: BLUM THEORY

Hey PEinc, thanks for your reply.

now another question about the sheet pile in Cantilever.

Do you think Prosheet is a reliable software to use?/ does it uses the BLum theory to analysis or it only makes moment about the tip and that;s it? or in other words, does it takes into account that at some depth in the active pressure side, it can be developed passive pressures?

bassically i want to compare my calculations with a software to check if i am on the right path.

Mine, is a simple problem, i am not using bussinessq loads neither Caquot parameters, only soils properties and that;s it.

or do you know if is there a more reliable software?/ what about plaxis?

thanks and please reply

RE: BLUM THEORY

The best way to learn how to design is to get a copy of Pile Buck (old or new version) For a cantilever wall, passive pressure forms initally on the front face of the wall, then on the back at a lower depth. Imagine holding a rod with boh hands, on a little higher on the rod than the other. If someone pulls on the rod, you will develop forces in your hands to resist. the forces will be in opposite directions to form an oposing couple.
Although I see many pepole do it, you can not put the active force on the back side and the passive on the front.
Te resulting formula is best solved by trial and error. Again see pile buck for detils. Bowles Foundatin design also reviews it.
Blum theroy is only for walls with on level of bracing. It is not a solution method for cantilevered walls.
There are many other programs besides
plaxis for designing sheets. Civiltech and SPW911 are both fairly easy to use & inexpensive.

RE: BLUM THEORY

I believe that ProSheet lets you choose a cantilevered analysis or, for braced or anchored wall, a fixed earth or free earth analysis method.  I almost always use the free earth method.  While I believe that Pile Buck's Sheet Pile Design Manual (formerly the US Steel heet Pile Design Manual) has a lot of good information in it, I don't think much of its design examples.  At times, they are hard to follow.  I don't remember if Pile Buck ever corrected the errors that were in the US Steel design examples.

ProSheet, I believe, also multiplies a Boussinesq surcharge pressure by Ka, therby giving a lower lateral earth pressure than the formula gives.  The railroads may not accept this lower surcharge.  ProSheet is easy to use for triangular earth loads and sheet piling.  It is not easy to use for soldier beams or earth pressure distributions other than triangular.  I also have gotten some very high (unreasonable?) sheet pile deflections using ProSheet.  The program's strength is that it allows multi-layerd soil profiles and includes cohesion and wall friction.

RE: BLUM THEORY

P.S. Version 8 of CivilTech's Shoring program is good and has fixed the bugs of previous versions.  Although I own both programs, I recommend CivilTech over SPW911.  I never use SPW911 unless I'm checking a design done with it by another engineer.

RE: BLUM THEORY

(OP)
Hi ,

Just to conclude my previous conversation regarding using SPW 2006 by prof arnold verruijt and not SPW 911, I ahve found the exact soultion for simulating the Blum and would like to share it with ya'll. Since that was my key reason for posting this thread.
The SPW program denotes / asks for the Stroke parameter, which is represented as the difference in passive pressures and Spring stiffness, now usually design following sub grade reaction model is used using the spring stiuffness, but SPW uses the concept of follwoing the stroke parameter. If U enter this stroke parameter as a constant minimal value like 0.001 it exactly simulates the Blum condition.

If anyone still disagrees to this, kindly let me know

Danke schön!

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