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Aktu Btech Quantum Notes will help you be more prepared for the Geotechnical Engineering test. Your route to success lies in these vital, in-depth resources that address the most frequently asked issues. Improve your knowledge right now! **Unit-2 Soil Hydraulics**

Dudes 🤔.. You want more useful details regarding this subject. Please keep in mind this as well.Important Questions For Geotechnical Engineering:*Quantum*B.tech-Syllabus**CircularsB.tech*AKTU RESULTBtech 3rd Year*Aktu Solved Question Paper

**Q1. A granular soil deposit is 7 m deep over an impermeable layer. The ground water table is 4 m below the ground surface. The deposit has a zone of capillary rise of 1.2 m with a saturation of 50 %. Plot the variation of total stress, pore water pressure and effective stress with the depth of deposit, e = 0.6 and G = 2.65.**

**Ans. Given:** Depth of soil deposit 7m, Depth of water table = 4 m, Specific gravity, G= 2.65, Degree of saturation, S = 50 * Void ratio, e = 0.6, Capillary rise = 1.2 m

**To Find:** Plot the variation of

with the depth of deposit.

1. Bulk unit weight,

**4. At Level A-A : **

**5. At Level B-B (Upper Side):**

**6. At Level B-B (Bottom Side): **

**7. At Level C-C: **

**8. At Level D-D: **

**Q2. Describe Darcy’s law and give its validity.**

**Ans. Darcy’s Law:**

- i. Darcy’s law states that there is a linear relationship between flow velocity (v) and hydraulic gradient (i) for any given saturated soil under steady laminar flow conditions.

ii. If the rate of flow is q (volume/time) through cross-sectional area (A) of the soil mass, Darcy’s Law can be expressed as:

**Validity of Darey’s Law: **

- 1. If the flow through soils is laminar, Darcy’s law is true.
- 2. It is applicable to the flow of silts, clays, and fine sands. The flow may be turbulent in coarse sands, gravels, and boulders, making Darcy’s law inapplicable.
- 3. The relationship between velocity (v) and hydraulic gradient I must be linear for Darcy’s law to be true.
- 4. The interstices are exceedingly narrow in soils with extremely fine-grained particles, such as colloidal clay. As a result, the velocity is relatively low. The Darcy’s law is invalid on such soils.

**Q3. What are different methods for determination of the coefficient of permeability in a laboratory ? Discuss their limitations.**

**Ans. A. Permeability:** It is a characteristic of a porous media that free or gravitational water (or other fluids) can travel slowly through its interconnecting spaces.

**B. Laboratory Methods:** The coefficient of permeability of a soil can be determined by using the following methods :

**1. Constant Head Permeability Test:**

- i. For determining the coefficient of permeability of coarse-grained soils with high permeability, such as clean sands and gravel, constant-head experiments are used.
- ii. Fig. shows the arrangement in which the flow is one-dimensional and in downward direction.
- iii. The figure also indicates the head loss (h
_{1}) and the corresponding length of soil, L, over which the head loss occurs. - iv. The experimental data consist of a measured quantitý of discharge Q during a time interval t, under steady state conditions of flow. The head loss h
_{l}is also noted. - v. k can be computed from the formula,

**Limitations: **Following are the limitations of constant head permeability test:

- i. Equipment expensive.
- ii. Complicated to set up and to use.
- iii. Not suitable for most sites.
- iv. Test duration long.

**2. Falling or Variable Head Permeability Test: **

- i. Falling-head test are used for fine-grained soils with low permeability, such as silty or clayey fine sand, silts, and clays.
- ii. A typical set-up for falling head permeability test is shown in Fig. The water level in the stand pipe is observed from time to time.
- iii. Let A be the area of soil sample, a the area of stand pipe and L the length of soil sample.
- iv. If the head difference at time t
_{1}is h_{1}and at time t_{2}is h_{2}, then coefficient of permeability is calculated from the expression.

**Limitations:** Test specimen cannot be consolidated to expected in-situ effective stress.

**Q4. Discuss the factors that influence permeability of soil.**

**Ans. **Following are the factors affecting the permeability of soils:

**1. Properties of Pore Fluid:**- i. Fluids that fill pores in soil or rock are known as pore fluids.
- ii. Pore fluid viscosity and the unit weight of the pore fluid are inversely correlated with permeability.

**2. Void Ratio:**The area accessible for low thus increases with an increase in the void ratio, increasing permeability for crucial situations.**3. Entrapped Air and Organic Impurities:**The flow is obstructed by organic contaminants and trapped air, and as a result, the coefficient of permeability is lessened.**4. Adsorbed Water:**- i. Adsorbed water refers to the microscopic water layer that envelops each soil particle.
- ii. Because this water cannot travel freely, it limits the effective pore space, which lowers the coefficient of permeability.

**5. Shape of Particles:**While angular soil has a greater specific surface area than round soil, it is less permeable than soil with rounded particles. Permeability is inversely proportional to specific surface area.

**Q5. Explain flownet. Describe its properties and its applications.**

**Ans. A. Flownet:** Flownet is a type of grid created by drawing several equipotential and stream lines.

**B. Characteristics / Properties of Flownet:** Following are the characteristics of a flownet:

- 1. In a flownet, equipotential lines and stream lines cross one another orthogonally.
- 2. Flow cannot cross a flow line, and flow velocity always runs perpendicular to the equipotential line.
- 3. Equipotential drop is the name given to the loss of head between two equipotential lines, which is always the same.
- 4. Flow fields are the area between two equipotential lines and flow lines, and in an isotropic media, they are roughly square; in an anisotropic medium, they are roughly rectangular.

**C. Application:** Flownet is used to:

- 1. Estimation of seepage losses from reservoir.
- 2. Determination of seepage pressure.
- 3. Uplift pressure below dams.
- 4. To check against the possibility of piping and many others.

**Q6. What are the assumption and limitations of Dupuits’s theory ?**

**Ans. A. Assumptions: **Following are the assumptions of Dupuits’s theory:

- 1. Darcy’s law is true because the flow is laminar.
- 2. The soil bulk is homogeneous and isotropic.
- 3. The well reaches all the way down into the aquifer.
- 4. The stream is constant.
- 5. Throughout, the permeability coefficient is constant.
- 6. The flow is horizontal and radial as it approaches the well.
- 7. The normal groundwater cycle is unaffected.

**B. Limitations:** Various assumptions have been made in the Dupuits theory formulae. n actual practice, however, none of these conditions may get fulfilled; say for example:

- 1. Aquifers are not entirely homogeneous, for one.
- 2. The aquifer may have been only partially penetrated by the well.
- 3. There may be variations in permeability.
- 4. The base of the cone might not be a circular because the ground water table could be sloped.
- 5. It’s possible that the equilibrium conditions weren’t entirely attained.

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