Test 6 - Seepage, Flow Nets and Piping

Question 1 ప్రశ్న 1

Which statement correctly describes a conventional flow net for steady two-dimensional seepage through a homogeneous, isotropic, saturated soil?

A Flow lines and equipotential lines coincide because both represent constant total hydraulic head. B Flow lines and equipotential lines intersect orthogonally, and the fields are drawn approximately as curvilinear squares. C Equipotential lines represent paths along which groundwater particles move continuously. D Every flow channel must have a different total head loss between the same upstream and downstream boundaries.

Question 2 ప్రశ్న 2

For seepage beneath a hydraulic structure founded on homogeneous isotropic soil, how should a perfectly impermeable foundation boundary and a boundary maintained at constant total hydraulic head be represented in a flow net?

A Both boundaries must be represented as flow lines. B Both boundaries must be represented as equipotential lines. C The impermeable boundary is an equipotential line, and the constant-head boundary is a flow line. D The impermeable boundary is a flow line, while the constant-head boundary is an equipotential line.

Question 3 ప్రశ్న 3

A saturated soil has coefficient of permeability 4.0 × 10^-5 m/s and hydraulic gradient 0.25. Water flows steadily through a gross cross-sectional area of 5.0 m². Using Darcy's law, calculate the seepage discharge.

A 5.0 × 10^-5 m³/s. B 2.0 × 10^-4 m³/s. C 1.0 × 10^-5 m³/s. D 5.0 × 10^-4 m³/s.

Question 4 ప్రశ్న 4

For an ideal flow net representing steady two-dimensional seepage through homogeneous isotropic soil, which expression gives the discharge per unit width perpendicular to the section?

A q = kH(Nd/Nf), where Nd is the number of potential drops and Nf is the number of flow channels. B q = kH(Nf + Nd), irrespective of the shape of the flow fields. C q = kH(Nf/Nd), where H is the overall head difference. D q = H(Nf/Nd)/k, with permeability appearing in the denominator.

Question 5 ప్రశ్న 5

An ideal flow net beneath a weir has 4 flow channels and 12 potential drops. The total hydraulic head difference is 6 m, and the foundation soil has k = 2.0 × 10^-5 m/s. What is the seepage discharge per metre length of the weir?

A 1.0 × 10^-5 m³/s per metre. B 4.0 × 10^-5 m³/s per metre. C 2.4 × 10^-4 m³/s per metre. D 3.6 × 10^-4 m³/s per metre.

Question 6 ప్రశ్న 6

Two valid idealized flow-net cases have identical hydraulic conductivity, total head difference and number of flow channels. Case P has 10 potential drops, while Case Q has 20 potential drops. According to the standard flow-net discharge expression, how does the computed discharge in Case Q compare with Case P?

A It is twice that of Case P. B It is four times that of Case P. C It is equal to that of Case P. D It is half that of Case P.

Question 7 ప్రశ్న 7

A flow net represents a total hydraulic head loss of 6 m distributed over 12 equal potential drops. What is the head loss between two successive equipotential lines?

A 0.50 m. B 2.00 m. C 6.00 m. D 72.00 m.

Question 8 ప్రశ్న 8

The upstream and downstream total hydraulic heads are 12 m and 3 m, respectively, relative to a common datum. A flow net has 9 equal potential drops. At a point reached after 4 potential drops from the upstream boundary, the elevation head is 2 m. If gamma_w = 10 kN/m³, what is the gauge pore-water pressure at that point?

A 20 kPa. B 40 kPa. C 60 kPa. D 80 kPa.

Question 9 ప్రశ్న 9

At a point beneath the impervious floor of a hydraulic structure, the total hydraulic head is 5 m above a specified datum and the point itself has an elevation head of 1 m. If gamma_w = 10 kN/m³, what is the local uplift pressure magnitude?

A 10 kPa. B 40 kPa. C 50 kPa. D 60 kPa.

Question 10 ప్రశ్న 10

A flow net has an overall head difference of 8 m and 10 equal potential drops. At the downstream exit, the last potential drop occurs over an approximate flow-path distance of 0.40 m. What is the average exit hydraulic gradient over this interval?

A 0.20. B 0.50. C 0.80. D 2.00.

Question 11 ప్రశ్న 11

Two points on a seepage flow path have total hydraulic heads of 13.2 m and 9.6 m. Their separation along that path is 2.4 m. What is the magnitude of the average hydraulic gradient between the points?

A 1.50. B 0.67. C 3.60. D 5.50.

Question 12 ప్రశ్న 12

A saturated soil experiences a uniform hydraulic gradient of magnitude 0.35. If the unit weight of water is 10 kN/m³, what is the seepage force per unit volume of soil?

A 0.35 kN/m³. B 10.35 kN/m³. C 3.50 kN/m³. D 35.00 kN/m³.

Question 13 ప్రశ్న 13

A saturated soil element has a total volume of 4 m³ and experiences a uniform seepage gradient of magnitude 0.25. Taking gamma_w = 10 kN/m³, calculate the magnitude of the total seepage force acting on this element.

A 2.5 kN. B 10.0 kN. C 25.0 kN. D 40.0 kN.

Question 14 ప్రశ్న 14

For a fully saturated cohesionless soil, the specific gravity of solids is 2.65 and void ratio is 0.65. What is the theoretical critical upward hydraulic gradient?

A 0.65. B 0.85. C 1.65. D 1.00.

Question 15 ప్రశ్న 15

At the downstream exit of a seepage path, the theoretical critical gradient for heave is 0.95 and the calculated upward exit gradient is 0.38. Using FS = i_c/i_exit, what is the factor of safety against the idealized zero-effective-stress condition?

A 2.50. B 0.40. C 0.57. D 1.33.

Question 16 ప్రశ్న 16

Which statement correctly describes the idealized quicksand or boiling condition caused by upward seepage in saturated cohesionless soil?

A It occurs only when soil particles reach the temperature at which water boils. B It occurs whenever any downward seepage exists, regardless of soil properties. C It occurs when upward seepage reduces the effective interparticle stress to approximately zero at the critical hydraulic gradient. D It can occur only in perfectly impermeable clay that permits no groundwater flow.

Question 17 ప్రశ్న 17

A saturated uniform sand layer has its top boundary at atmospheric pore-water pressure and experiences steady upward seepage with hydraulic gradient 0.60. The saturated unit weight is 20 kN/m³ and gamma_w = 10 kN/m³. What is the effective vertical stress at a point 3 m below the top boundary?

A 18 kPa. B 12 kPa. C 30 kPa. D 48 kPa.

Question 18 ప్రశ్న 18

A homogeneous saturated soil column has its top boundary at atmospheric pore-water pressure and experiences steady downward seepage at hydraulic gradient 0.40. Its saturated unit weight is 20 kN/m³ and gamma_w = 10 kN/m³. What is the effective vertical stress at a depth of 2 m?

A 12 kPa. B 20 kPa. C 24 kPa. D 28 kPa.

Question 19 ప్రశ్న 19

A saturated cohesionless soil layer is 2.5 m thick and is subjected to steady upward seepage. Its specific gravity of solids is 2.70 and void ratio is 0.70. What total head loss across the layer would produce the theoretical critical upward hydraulic gradient?

A 2.50 m. B 1.25 m. C 1.70 m. D 4.25 m.

Question 20 ప్రశ్న 20

Which statement most accurately distinguishes backward-erosion piping from the idealized quicksand condition beneath a hydraulic structure?

A Both necessarily require the pore water to evaporate before soil movement begins. B Piping can occur only when the entire foundation has zero porosity. C Piping involves progressive transport and erosion of soil particles along a seepage path, whereas the idealized quick condition concerns loss of effective stress under upward seepage. D A factor of safety greater than one against idealized heave automatically proves that backward-erosion piping cannot occur.

Question 21 ప్రశ్న 21

The pore-water uplift pressure beneath a horizontal impervious floor varies linearly from 70 kPa at the upstream end to 30 kPa at the downstream end. The floor is 8 m long in the seepage direction. What is the resultant upward water force per metre width of the floor?

A 280 kN per metre width. B 400 kN per metre width. C 560 kN per metre width. D 800 kN per metre width.

Question 22 ప్రశ్న 22

For an unchanged homogeneous isotropic seepage domain with fixed hydraulic conductivity and the same valid flow-net shape, the upstream-to-downstream head difference increases from H to 2H. Assuming Darcy flow remains valid, what happens to the seepage discharge?

A It becomes one-half of the original discharge. B It remains unchanged because the number of potential drops is fixed. C It increases by a factor of four. D It becomes twice the original discharge.

Question 23 ప్రశ్న 23

A soil foundation is hydraulically anisotropic, with horizontal and vertical permeabilities differing substantially. Which statement regarding conventional flow-net analysis is most appropriate?

A A suitable transformed-section method may be used; flow lines and equipotentials need not be orthogonal in the original physical coordinates of an anisotropic soil. B The same homogeneous isotropic flow-net construction can always be used unchanged because permeability direction is irrelevant. C Anisotropy causes every equipotential line to become a horizontal straight line regardless of boundary conditions. D Flow-net discharge is always zero if horizontal permeability exceeds vertical permeability.

Question 24 ప్రశ్న 24

What is the principal engineering purpose of placing a properly designed graded filter near the downstream seepage exit of an earth structure?

A To prevent all water movement by making the filter completely impermeable. B To increase the local hydraulic gradient until soil particles are washed out. C To allow controlled drainage while retaining vulnerable soil particles and limiting their migration. D To replace all stability calculations because a filter guarantees zero uplift pressure.

Question 25 ప్రశ్న 25

A hydraulic structure founded on pervious soil shows excessive uplift beneath its floor, a high downstream exit gradient and signs of soil-particle movement at an unfiltered seepage outlet. Which engineering response is most appropriate?

A Reassess the seepage field and adopt appropriately designed measures such as cutoffs, pressure relief or drainage, and graded filter protection, followed by verification of uplift and erosion stability. B Increase the upstream water head because higher seepage pressure will automatically improve effective stress. C Remove downstream filter protection so that the soil particles can leave the foundation freely. D Assume that reducing total seepage discharge alone always eliminates every piping and uplift risk, regardless of the exit gradient.

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