Sign in to follow this  
Followers 0
passpepasspe

Geotech Problem

5 posts in this topic

A moist soil consists of 10 ft of sand resting on bedrock, with the groundwater table 4 ft below the surface. The unit weight of the saturated soil is 130 lbf/ft3, and the moist soil has a unit weight of 125 lbf/ft3. The earth pressure coefficient for both the saturated and moist soil is 0.40. What is most nearly the total vertical stress at a depth of 10 ft? The given answer is 1280 lbf/ft^2 but i get 1654 lbf/ft^2.

Here is how I am solving this:

Total Vertiical Stress = Effective STress + Pore Water Pressure

PORE water pressure = 6 * 62.4 = 374.4

Effective Stress: 125 (4) + 130( 6) = 1280

total vertiiclal stress: 374+ 1280 = 1654 lbf/ft^2

Not sure how the solution gives 1280 lbf/ft^2

let me know what I am doing wrong.

Share this post


Link to post
Share on other sites
A moist soil consists of 10 ft of sand resting on bedrock, with the groundwater table 4 ft below the surface. The unit weight of the saturated soil is 130 lbf/ft3, and the moist soil has a unit weight of 125 lbf/ft3. The earth pressure coefficient for both the saturated and moist soil is 0.40. What is most nearly the total vertical stress at a depth of 10 ft? The given answer is 1280 lbf/ft^2 but i get 1654 lbf/ft^2.

Here is how I am solving this:

Total Vertiical Stress = Effective STress + Pore Water Pressure

PORE water pressure = 6 * 62.4 = 374.4

Effective Stress: 125 (4) + 130( 6) = 1280

total vertiiclal stress: 374+ 1280 = 1654 lbf/ft^2

Not sure how the solution gives 1280 lbf/ft^2

let me know what I am doing wrong.

Typical problem where more information is given than what is necessary to solve it.

You have 4 feet of moist soil sitting on top of 6 feet of saturated soil. The total vertical stress (not effective) at the bottom of the layer is the sum of the two vertical stresses above and below the water table:

125 x 4 = 500

130 x 6 = 780

Total = 1280

Share this post


Link to post
Share on other sites
A moist soil consists of 10 ft of sand resting on bedrock, with the groundwater table 4 ft below the surface. The unit weight of the saturated soil is 130 lbf/ft3, and the moist soil has a unit weight of 125 lbf/ft3. The earth pressure coefficient for both the saturated and moist soil is 0.40. What is most nearly the total vertical stress at a depth of 10 ft? The given answer is 1280 lbf/ft^2 but i get 1654 lbf/ft^2.

Here is how I am solving this:

Total Vertiical Stress = Effective STress + Pore Water Pressure

PORE water pressure = 6 * 62.4 = 374.4

Effective Stress: 125 (4) + 130( 6) = 1280

total vertiiclal stress: 374+ 1280 = 1654 lbf/ft^2

Not sure how the solution gives 1280 lbf/ft^2

let me know what I am doing wrong.

Typical problem where more information is given than what is necessary to solve it.

You have 4 feet of moist soil sitting on top of 6 feet of saturated soil. The total vertical stress (not effective) at the bottom of the layer is the sum of the two vertical stresses above and below the water table:

125 x 4 = 500

130 x 6 = 780

Total = 1280

given this probelm, isnt there also pore pressure on the 6 ft of saturated soil coz there is water present? maybe i am not reading the problem correcty.. have I drawn the chart below correctly?

___________________

125 unit weight

_________V________4 ft (groundwater)

130 unit weight

__________________ 10

bedrock

Share this post


Link to post
Share on other sites
A moist soil consists of 10 ft of sand resting on bedrock, with the groundwater table 4 ft below the surface. The unit weight of the saturated soil is 130 lbf/ft3, and the moist soil has a unit weight of 125 lbf/ft3. The earth pressure coefficient for both the saturated and moist soil is 0.40. What is most nearly the total vertical stress at a depth of 10 ft? The given answer is 1280 lbf/ft^2 but i get 1654 lbf/ft^2.

Here is how I am solving this:

Total Vertiical Stress = Effective STress + Pore Water Pressure

PORE water pressure = 6 * 62.4 = 374.4

Effective Stress: 125 (4) + 130( 6) = 1280

total vertiiclal stress: 374+ 1280 = 1654 lbf/ft^2

Not sure how the solution gives 1280 lbf/ft^2

let me know what I am doing wrong.

Typical problem where more information is given than what is necessary to solve it.

You have 4 feet of moist soil sitting on top of 6 feet of saturated soil. The total vertical stress (not effective) at the bottom of the layer is the sum of the two vertical stresses above and below the water table:

125 x 4 = 500

130 x 6 = 780

Total = 1280

given this probelm, isnt there also pore pressure on the 6 ft of saturated soil coz there is water present? maybe i am not reading the problem correcty.. have I drawn the chart below correctly?

___________________

125 unit weight

_________V________4 ft (groundwater)

130 unit weight

__________________ 10

bedrock

The question asked for total pressure and not for effective pressure. The water water pressure is not considered in this case so the answer is 1280.

Share this post


Link to post
Share on other sites
A moist soil consists of 10 ft of sand resting on bedrock, with the groundwater table 4 ft below the surface. The unit weight of the saturated soil is 130 lbf/ft3, and the moist soil has a unit weight of 125 lbf/ft3. The earth pressure coefficient for both the saturated and moist soil is 0.40. What is most nearly the total vertical stress at a depth of 10 ft? The given answer is 1280 lbf/ft^2 but i get 1654 lbf/ft^2.

Here is how I am solving this:

Total Vertiical Stress = Effective STress + Pore Water Pressure

PORE water pressure = 6 * 62.4 = 374.4

Effective Stress: 125 (4) + 130( 6) = 1280

total vertiiclal stress: 374+ 1280 = 1654 lbf/ft^2

Not sure how the solution gives 1280 lbf/ft^2

let me know what I am doing wrong.

Typical problem where more information is given than what is necessary to solve it.

You have 4 feet of moist soil sitting on top of 6 feet of saturated soil. The total vertical stress (not effective) at the bottom of the layer is the sum of the two vertical stresses above and below the water table:

125 x 4 = 500

130 x 6 = 780

Total = 1280

given this probelm, isnt there also pore pressure on the 6 ft of saturated soil coz there is water present? maybe i am not reading the problem correcty.. have I drawn the chart below correctly?

___________________

125 unit weight

_________V________4 ft (groundwater)

130 unit weight

__________________ 10

bedrock

The question asked for total pressure and not for effective pressure. The water water pressure is not considered in this case so the answer is 1280.

130 #/cubicft is the weight of saturated soil. That includes the water weight.

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!


Register a new account

Sign in

Already have an account? Sign in here.


Sign In Now
Sign in to follow this  
Followers 0