Scenario The concrete dam in the figure below is to be built on top of a soil whose profile consists of two horizontal layers of soil, each 5 ft thick. The depth to the groundwater table is approx. 6 feet. The dam is anticipated to weigh approx. 8200 psf, and will be 120 feet long (the dimension into and out of the page). The layers of the soil have the following properties: k (ft/s) unit weight (y) (pcf) void ratio (in-situ) top 8.2 × 10-3 122 0.47 bottom 1.9 × 10-7 130 0.33 8 ft Water 10 ft 20 ft Concrete dam 1 1 B 2 ft water
Please answer all questions based on the scenario
Question #1:
Considering the water upstream of the dam,
a) What will be the seepage loss of that water downstream per year?
b) What will the uplift force be on the dam?
Question #2:
What would the stress in the center of the dam be at the middle of the bottom layer? Consider both the overburden pressure and that due to the loading.
Question #3:
A sieve analysis was performed on a sample of the top layer of the soil, with the results shown below:
|
Sieve Size (in.) |
1/2 |
3/8 |
No. 4 |
No. 8 |
No. 16 |
No. 30 |
No. 40 |
No. 50 |
No. 100 |
No. 200 |
pan |
|
Amount retained (g) |
0 |
0 |
21.6 |
39.5 |
77.6 |
102.6 |
89.1 |
95.6 |
90.6 |
60.4 |
33.3 |
Do the following:
a) Calculate the percent retained and percent passing each sieve, and graph the results on a semi-log graph (you may use the attached chart, or graph in Excel and include with your submission). Then, characterize the gradation of the material.
b) Calculate the values of D10, D30, D60, Cu, and Cc .
c) If the LL is 48 and the PL is 26, determine the USCS classification of the soil, and state its suitability for the purpose stated in the scenario.
Question #4:
It has been anticipated that the soil under the proposed dam is contaminated, and needs to be removed and backfilled to a depth of 2.5 feet. A Standard Proctor compaction test was conducted on soil from a borrow pit, with the results shown below right. Based on the results:
a) Plot the Proctor curve for the borrow
b) Find the optimum water content and dry unit weight for the borrow soil.
c) Determine whether the unit weight of the top layer can be met by compacting to 95% of maximum, and what the range of moisture content for that unit weight
d) Suggest a compaction method for this borrow soil (equipment and method) based on the type of soil indicated in Question #1.
e) If we borrow soil from a pit with a void ratio of 0.71, determine how much soil we need to borrow to backfill below the dam to match the in-situ void ratio of the top layer of
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