PE Exam Preparation for Geotechnical Engineers
This blog intends to help anyone preparing for PE exam or practicing in the area of geotechnical engineering. You are welcome to post your questions related to soil mechanics and I'll try to solve them. I am a senior-level professional geotechnical engineer currently based in Houston, TX. I started this blog in order to help anyone who is preparing for PE and/or has questions related to geotechnical engineering. I took my PE exam on April 2009 (and passed!).
Thursday, February 12, 2015
Monday, June 23, 2014
Wednesday, October 21, 2009
Lateral Earth Pressure
My inability to be able to steal some time out of my schedule leaves me no option but to provide you with some links that might help you. I'll, however, post my take on lateral earth pressure in near future which may be too late for the candidates taking their exam day after tomorrow but may help those who are taking their exams next year or later. I really apologize for the inconvenience and wish all the examinees the very best!
The following link provides a pretty good (and brief) lesson on lateral earth pressure.
http://www.pdhonline.org/courses/c155/c155content.pdf
For any questions, feel free to ask me.
The following link provides a pretty good (and brief) lesson on lateral earth pressure.
http://www.pdhonline.org/courses/c155/c155content.pdf
For any questions, feel free to ask me.
Wednesday, October 14, 2009
A question by a visitor
Anonymous said...
I'm confused in calculating the effective vertical stress in a sandy gravel soil layer below the graound water level and it is between a sand layer on the top and a clay layer on the bottom.
What unit weight i have to consider the sand unit waight or I need the porosity(n)of the sandy gravel to get the unit waight?
Thanks
What unit weight i have to consider the sand unit waight or I need the porosity(n)of the sandy gravel to get the unit waight?
Thanks
geotechie said...
suppose we have a situation like the following:
_____________________________________________
Sand wet unit weight = Ys,w
layer thickness = d1
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
water table @ depth dw, unit weight of water = Yw
Sand saturated unit weight = Ys,sat
______________________________________________
Sandy Gravel
saturated unit weight = Ysg
layer thickness = d2
______________________________________________
Clay
saturated unit weight = Yc
layer thickness = d3
______________________________________________
Effective Stress = Total Stress - Pore Water Pressure
Total Stress at the bottom of clay layer = (Ys,w)(dw) + (Ys,sat)(d1-dw)+ (Ysg)(d2) + (Yc)(d3)
Pore water pressure = (Yw)(d1-dw) + (Yw)(d2) + (Yw)(d3)
Therefore, Effective Stress =
(Ys,w)(dw) + (Ys,sat)(d1-dw)+ (Ysg)(d2) + (Yc)(d3) - (Yw)(d1-dw) - (Yw)(d2) - (Yw)(d3)
= (Ys,w)(dw) + (Ys,sat-Yw)(d1-Yw) + (Ysg-Yw)(d2) + (Yc-Yw)(d3)
Let me know if it helps (or if it does not).
Sand wet unit weight = Ys,w
layer thickness = d1
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
water table @ depth dw, unit weight of water = Yw
Sand saturated unit weight = Ys,sat
______________________________________________
Sandy Gravel
saturated unit weight = Ysg
layer thickness = d2
______________________________________________
Clay
saturated unit weight = Yc
layer thickness = d3
______________________________________________
Effective Stress = Total Stress - Pore Water Pressure
Total Stress at the bottom of clay layer = (Ys,w)(dw) + (Ys,sat)(d1-dw)+ (Ysg)(d2) + (Yc)(d3)
Pore water pressure = (Yw)(d1-dw) + (Yw)(d2) + (Yw)(d3)
Therefore, Effective Stress =
(Ys,w)(dw) + (Ys,sat)(d1-dw)+ (Ysg)(d2) + (Yc)(d3) - (Yw)(d1-dw) - (Yw)(d2) - (Yw)(d3)
= (Ys,w)(dw) + (Ys,sat-Yw)(d1-Yw) + (Ysg-Yw)(d2) + (Yc-Yw)(d3)
Let me know if it helps (or if it does not).
Sorry guys...
I am extremely sorry guys...its been a very busy several weeks...I'll try to post something on retaining walls before the PE exam.
Saturday, October 3, 2009
Shear Strength - Problem #3
A Consolidated Undrained (CU) triaxial test is conducted on silt. The effective cell pressure is 4.32 ksf. The deviator stress is 3.45 ksf. The total pore pressure for this test is 2.88 ksf. Draw Mohr's circle of the initial and final condition. Also, show circles that represent total and effective stresses.
Thursday, October 1, 2009
Shear Strength-Triaxial Test
Advantages:
1. Suitable for cohesive soils as well
2. Samples can be saturated
3. Principal planes do not rotate
4. Failure will seek the weakest plane
Three permissible drainage cases:
UU or Unconsolidated Undrained
CD or Consolidated Drained
CU or Consolidated Undrained
Think of practical situations where these tests would be appropriate.
1. Suitable for cohesive soils as well
2. Samples can be saturated
3. Principal planes do not rotate
4. Failure will seek the weakest plane
Three permissible drainage cases:
UU or Unconsolidated Undrained
CD or Consolidated Drained
CU or Consolidated Undrained
Think of practical situations where these tests would be appropriate.
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