Principles of Geotechnical Engineering (MindTap Course List)
9th Edition
ISBN: 9781305970939
Author: Braja M. Das, Khaled Sobhan
Publisher: Cengage Learning
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Chapter 9, Problem 9.7P
To determine
Find the safe depth of excavation before the bottom heaves.
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An exploratory drill hole was made in a stiff saturated clay (Gs = 2.72, and w = 35%). The sand layer underlying the clay was observed to be under artesian pressure. Water in the drill hole rose to a height of 12 ft above the top of the sand layer. If an open excavation is to be made in the clay, how deep can the excavation proceed before the bottom heaves?
A hole was made in a stiff saturated soil having a Gs = 2.71 and moisture content of 0.30. The sand layer underlying
the clay was observed to be under artesian pressure. Water in the drill hole rose to a height of 6.30 meters above the
top of the sand layer
%3D
Exploratory drill hole
10 m
6.3 m
4.5 m
Saturated clay L Sand
a. If an open excavation is to be made in the clay, determine the safe depth of excavation before the bottom
heaves. Round your final answer to three significant figures.
b. How much is the pressure at the interface of the clay and sand?
c. f a factor of safety of 2.0 is to be ensured, how deep should be the excavation from the ground surface?
Note: Draw Free Body Digram and show full solution
Topic: Soil Stresses (Soil Mechanics_
9.7 An exploratory drill hole was made in a stiff saturated clay having a moisture
content of 29% and G, = 2.68 (Figure 9.27). The sand layer underlying the clay
was observed to be under artesian pressure. Water in the drill hole rose to a
height of 6 m above the top of the sand layer. If an open excavation is to be made
in the clay, determine the safe depth of excavation before the bottom heaves.
Exploratory drill hole
10 m
45 m
Saturated clay Sand
Figure 9.27
Chapter 9 Solutions
Principles of Geotechnical Engineering (MindTap Course List)
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- 4.An exploratory drill hole was made in a stiff saturated clay having a moisture content of 22% and Gs = 2.82 as shown in Figure 1.3. The sand layer underlying the clay was observed to be under artesian pressure. Water in the drill hole rose to a height of 8 m above the top of sand layer. If an open excavation is to be made in the clay, determine: a. The maximum depth of excavation before the bottom heaves. b. What would be the required height of water inside the cut in order to ensure a factor of safety of 2? Exploratory drill hole 12m 8m 4.5 m Saturated clay O Sand Figure 1.3.arrow_forwardAn exploratory drill hole was made in a stiff saturated clay, as shown in Figure 1, having a moisture content of 25% and Gs = 2.56. The sand layer underlying the clay was observed to be under artesian pressure. Water in the drill hole rose to a height of 3 m above the top of sand layer. If an open excavation is to be made in the clay. a.What is the maximum depth of excavation before the bottom heaves? b.What would be the required height of water inside the cut in order to ensure a factor of safety of 1.5?arrow_forwardAn exploratory drill hole was made in a stiff saturated clay (see Figure 9.9). The sand layer underlying the clay was observed to be under artesian pressure. Water in the drill hole rose to a height of 4 m above the top of the sand layer. If an open excavation is to be made in the clay, how deep can the excavation proceed before the bottom heaves? Exploratory drill hole G,= 2.72 Moisture content =w= 35% 6.1 m 4. 4 m Saturated clay Sandarrow_forward
- Exploratory drill hole 12m 8m 4.5 m An exploratory drill hole was made in a stiff saturated clay having a moisture content of 22% and Gs = 2.16 as shown in Figure. The sand layer underlying the clay was observed to be under artesian pressure. Water in the drill hole rose to a height of 8 m above the top of sand layer. If an open excavation is to be made in the clay, determine: a. The maximum depth of excavation before the bottom heaves. b. What would be the required height of water inside the cut in order to ensure a factor of safety of 2.1?arrow_forward8. An exploratory drill hole was made in a saturated stiff clay having a water content of 32%. It was observed that the sand layer underlying the clay was under artesian pressure water in the drill hole rose to a height of 4 m. above the top of the sand layer. If an open excavation is to be made in the clay. (See picture below) Determine the void ratio of clay. (Answer: 0.864) Determine the saturated unit weight of clay. (Answer: 18.76 kN/m3) How deep can the excavation proceed before the bottom of the saturated clay heaves or when its effective stress is zero. (Answer: 5.91 m)arrow_forwardAn oedometer test on a 1" thick, doubly-drained sample from the clay stratum (shown below) attained 50% consolidation in 6.5 minutes. Find: (a) The total differential settlement of the fully loaded tank. (b) The time required for 75% consolidation in the field. (c) The depth of excavation for minimal settlement. = 35° Y-120 pcf = 10 ° c = 250 psf Ysat 110 pcf - Ca 1.27 Ce=0.40 40 ft 10 ft 57 ft D = 150 ft Steel Oil Tank Flexible steel foundation Sand Clay A You = 60 pcf Sand B Uniform, normally consolidated clay W.T.arrow_forward
- Soil mechanicsarrow_forwardShow solution. The answer must be 8.22 x10^-10 ft/secarrow_forwardA large building is to be built on a thick layer of normally consolidated clay shown in the figure below. The building is to be placed at the bottom of a 4 m deep excavation, which will correspond to 1 level of parking garages. The water table remains 4 m below the ground surface during the entire process. Find the OCR in the middle of the clay layer at Point A, a long time after excavation and before construction of the building. (Answer tolerance = 2%).arrow_forward
- Q6: A saturated clay sample was consolidated in the triaxial cell under a cell pressure of 150 kN/m². The drainage valve was then closed and the deviator stress was quickly increased to 200 kN/m when failure occurred. If c' = 15 kN/m2 and O = 20 °, find the pore water pressure and Skempton's pore pressure coefficient A at failure.arrow_forwardPlease solve fully. Thanksarrow_forwardb. If c, = 2.05 × 10-3 in./sec, determine k in ft/sec corresponding to the average void ratio within the pressure range. 11.17 The time for 75% consolidation of a 25-mm clay specimen (drained at top and bottom) in the laboratory is 22 minutes. How long will it take for a 6-m thick clay layer in the field to undergo 55% consolidation under the same pressure increment? In the field, there is a rock layer at the bottom of the clay.arrow_forward
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