354 Final Exam Tutorial Topics 353 review –Consolidation –Settlement (differential) –Weight volume relationships –Excess Pore pressure –Effective/total stress Soil Strength –Peak ultimate and residual –t vs s and Mohr Coulomb –Undrained vs drained –Skempton’s A & B –Loading and unloading Slopes –Wedges and circular failures –Mitchell charts (Ru) –Simple derivations Bearing Capacity –Terzaghi BC equation –Rafts and footings –Undrained and drained –Settlement: elastic - consol –Rocks, and N values –Eccentricity Retaining Walls –Earth pressures –Rankine and Coulomb –Factors of safety
Retaining Walls - Rankine Assumptions 1.Vertical wall 2.No vertical wall friction 3.Failure Active Passive Deviate from Ko ** Active state soils push wall back Wedge is steeper than passive case
Rankine Inclined deviates by: therefore However must still project by horizontalvertical
Rankine Pa First term is soil pressure Second term removes cohesion Third term decreases cohesion to account for tension cracks
Pa acts at H/3 unless…
Example Answer Pa=117.5 Ka=1=0.333 Ka2=0.271 Solve for sliding and Pa c =25 =16
Cohesion What do you do when it is given –Can you trust it –Should it be there Water is bad, can appear even in free- draining materials. Freezing? Uplift pressure?
Active vs Passive According to C.F.M.: –Two times the strain required for K a is needed for full development of K K a use 0.5 K p
Slopes and Sliding Slopes was a big section, but we didn’t have time to quiz you on a lot of it because of time constraints, but on an exam there is lots of time…. Sliding blocks Wedges Bishops long hand Mitchell charts Free body diagrams
Wedgies Force balance drivingresisting Weight Water? Friction Cohesion Water? You need to be able to understand the force systems from a first principles standpoint
Bishop Produces a factor of safety on a given slip circle No inter-slice forces No inter-slice shear Factor of safety for all slices is the same Assumes soil is a rigid plastic Simplified analysis but generally good for Fs>1.2 The circle with the the lowest Fs is the critical circle When the slope angle exceeds 53 degrees the critical circle will pass through the toe Must analyze on a slice by slice basis
Bishop Can you use this method on a wedge? What is angle Why does factor of safety appear twice? Is a drawn slip circle necessarily the lowest factor of safety circle? Where is ground surface?
Crap, don’t I need a bad ass table for this question Yes you do
Mitchell Charts Design charts solved for lowest factor of safety circle Three charts Ru=0.0, 0.3, and 0.6 Calc and use average Ru for slope and linear interpolate factor of safety between charts Remember using it backwards? UseTo get RuRu 00.3 FsFs
Slippery slopes What about water at the toe Excavated slopes? To dewater or not to dewater that is the question Rapid drawdown Tension cracks and slopes –Not out of the question –There are even allowances on Mitchell charts for this Excavated slopes and stress path
Footings, I got your footing right here buddy qfqf qaqa max Take note of the omission of D. Oversight, I think not. Assumptions? What is the physical meaning of each term?
Have I ever told you I hate footings Don’t forget about inclined loading Settlement –Immediate drained –Immediate undrained –Consolidation settlement –Layer model with 1 0 Stress distributions and settlement Fadum is Dr. Knight’s Favourite Could also use table from text if provided Don’t forget RQD but don’t obsess either N values re: q f
Like I need to talk to you about stress. Critical depth = 2B What about Fadum with a point of interest outside of the footing I see another stress distribution approximation for point loadds
Eccentricity! Doesn’t that have something to do with Liberace Use q f from bearing capacity and it terns out that using B’ and L’ in the shape factors is more work than it is worth If e>B/6 then must use B’ and L’ in q max & q min What about strip footings and retaining walls?
Soil Strength M-C Failure Envelope Sample will fail at intersection with envelope ’’ (Failure) ’n’n c’ (Failure) Test 1 Failure Circle failure (1) failure (2) Test 2 Failure Circle NOTE: all stresses are effective Each test is performed at a set void ratio
Skempton Developed “A” parameter for indication of the denseness of a sample Develpoed “B” for a measure of satuation What about negative values of A f
Stress Path of Sample ’’ t = d' + S tan ' s = ( 1 ' + 3 ')/2 Centre of Circle d = c' cos ' tan = sin ' S ( 1 - 3 )/2 = t Radius of Circle d s t sin ’ = tan ’
t vs s space the final frontier
T & S is that anything like S&M? Things to note –Ko line, how do you get it –Loading 1:1 to the right –Unloading 1:1 to the left –Time rate of dissipation of pwp –Stress path line –Better or worse than M-C?
Effective vs Total and Drained vs Undrained Pore pressure is the difference –Effective the what the soil “feels” Can effective exceed total? What does Drained mean. What are the implications of undrained? Bearing capacity and slopes
Consolidation Spring analogy Time rate of consolidation Differential settlement Excess pwp OCR
Weight and Volume Redo the buoyancy question from your first assignment. –Dry density –Saturation –Void ratio –Water content
Jojo’s Network Bearing capacity –Raft or footing –Fs against load, against settlement –Inclined load, eccentric load –Two layer settlement Retaining walls –Rankine –Two layer –Inclined –Passive resistance –Water
Jojo’s Network Stress –Calc and plot stress paths –Convert M-C data to t&s –Peak vs ultimate and c –Dilatency – Slopes –Be prepared for a slice analysis –Draw force diagrams –Water effects –Excavations
Psychic Friends Network Redo the buoyancy question from your first assignment. –Dry density –Saturation –Void ratio –Water content Theory –Assumptions –Coulomb –A f –Total vs Effective –Consolidation –Mitchell vs Bishop
Thought game In central America several ancient structures that rivaled the pyramids existed. Some were destroyed some remain How could you use geotech to determine if you were on the site of a large temple that had been destroyed The panama government has a site that may be of significance to archeologists, but a mining company wants access to subsurface ore deposits. If mining begins al archeological evidence will be destroyed. Can you help determine if the site is important?
Assumptions What would you look for? Calculations?