CE-802-B Foundation Engineering - May 2024 Question Paper

Under each question, How to answer lists the points an answer should cover, outlined by CampusPrep from the syllabus. Check the details against your textbook.

1. 7 Marks
   aWhat is meant by N value? Why should we apply correction for the N value obtained from the field? Briefly explain the corrections.
   How to answer

   • Define SPT N-value as blows for 30 cm penetration after seating drive
   • Explain need for correction due to overburden, dilatancy, hammer energy etc.
   • Briefly explain overburden correction and water-table/dilatancy correction
   • Mention corrected N-value use in bearing capacity and liquefaction
2. 7 Marks
   bWhat are the factors affecting the selection of type of foundations?
   How to answer

   • List soil, structural, groundwater and environmental factors
   • Explain bearing capacity, settlement, and economic considerations
   • Mention type of structure, loads, and site constraints
   • Conclude selection criteria for shallow vs deep foundation
3. 7 Marks
   aExplain any two boring methods with a neat sketch.
   How to answer

   • Select any two methods e.g. auger, wash, rotary, percussion boring
   • Describe procedure and equipment with neat labelled sketch
   • Mention suitability and soil conditions
   • Mention sampling and limitations
4. 7 Marks
   bDetermine net ultimate bearing capacity of the circular footing of size 2.5 m located at 1.5 m depth below ground level in pure clay soil for the following cases: When water table is at Consider the following soil characteristics, cohesion $= 50\,kPa$ and unit weight of soil is $18\,kN/m^3$. Use Terzaghi's theory.

   1. i)far below from foundation base
   2. ii)Ground level.
   How to answer

   • Write Terzaghi net ultimate formula for circular footing in pure clay ($\phi=0$)
   • Select bearing capacity factors $N_c, N_q, N_\gamma$ and shape factors
   • Compute case i with water table far below using $\gamma=18\,kN/m^3$
   • Compute case ii with water table at ground level using submerged unit weight
5. 7 Marks
   aWhat are the Factors affecting bearing capacity of the soil?
   How to answer

   • Define bearing capacity and its types
   • List factors: soil strength, footing size, depth, water table, loading
   • Explain effect of each factor briefly
   • Mention bearing capacity equations relevance
6. 7 Marks
   bThe plate load test was conducted on a clayey soil strata by using a plate of 0.3 m wide square and the ultimate load per unit area for the plate was found to be 180 kPa. what would be The ultimate bearing capacity (in kPa) of a 2m wide square footing.
   How to answer

   • State plate load test principle for clayey soil
   • Use that ultimate bearing capacity in clay is independent of width
   • Equate plate ultimate to footing ultimate $q_{uf}=q_{up}$
   • Report $180\,kPa$ as ultimate for 2 m footing
7. 7 Marks
   aWhat are the various approaches available to estimate the load carrying capacity of a single pile? Discuss the static formulae for pile capacity.
   How to answer

   • List dynamic, static, pile load test approaches
   • Write static formulae for skin friction and end bearing in clay and sand
   • Explain parameters $c, \phi, \alpha, K, \delta$
   • Mention limitations and choice of method
8. 7 Marks
   bA group of 16 piles of 45cm diameter is arranged with a centre to centre spacing of 1.0m. The piles are 12m long and are embedded in soft clay with cohesion 20 kN/ m$^2$. Bearing resistance may be neglected for the piles. Adhesion factor is 0.7. Estimate the ultimate load capacity of the pile group.
   How to answer

   • Compute block size from 16 piles at 1.0 m spacing
   • Compute block skin friction $Q_{bg}=2(B+L)D c$ neglecting end bearing
   • Compute single pile sum vs block capacity for comparison
   • Report minimum as ultimate group capacity
9. 7 Marks
   aA drop hammer weighing 60 kN and having an effective fall of 0.75 m drives an RCC pile weighing 30 kN. The average settlement per blow is 1.4 cm. The total elastic compression is 1.8 cm. Assume the coefficient of restitution as 0.3 and a factor of safety is 3, determine the allowable load on pile.
   How to answer

   • Write Hiley / Engineering News pile driving formula
   • Substitute hammer weight, fall, set and elastic compression
   • Apply coefficient of restitution and factor of safety
   • Compute ultimate then allowable load
10. 7 Marks
    bWhat are the characteristics of expansive and collapsible soils?
    How to answer

    • Define expansive and collapsible soils
    • List mineralogical and index characteristics
    • Explain swelling, shrinkage and collapse behaviour
    • Give examples e.g. black cotton soil, loess
11. 7 Marks
    aWhat are the problems and preventive measures of foundations on collapsible soils ?
    How to answer

    • Describe collapse settlement problems and structural damage
    • Explain preventive measures: compaction, pre-wetting, piles
    • Mention drainage and chemical stabilization
    • Conclude suitable foundation choice
12. 7 Marks
    bA singly under-reamed, 8 m long RCC pile weighing 20 kN with 350 mm shaft diameter and 750 mm under-ream diameter is installed within the stiff, saturated silty clay (undrained shear strength is 50 kPa, adhesion factor is 0.3, and the applicable bearing capacity factor is 9) to counteract the impact of soil swelling on a structure constructed above. Neglecting suction and the contribution of the under-ream to the adhesion shaft capacity, what would be the estimated ultimate tensile capacity of the pile?
    How to answer

    • Write ultimate uplift formula for under-reamed pile in clay
    • Compute shaft adhesion $\pi d L \alpha c_u$ and bulb bearing $\pi/4(D^2-d^2)N_c c_u$
    • Add pile weight consideration and neglect suction as stated
    • Report sum as ultimate tensile capacity
13. 7 Marks
    aA 5m high rigid retaining wall has to retain a backfill of dry, cohesionless soil having the following properties: Angle of internal friction $= 30^\circ$, void ratio $= 0.74$, specific gravity $= 2.68$. Plot the distribution of Rankine active earth pressure on the wall and determine the magnitude and point of application of the resultant thrust.
    How to answer

    • Compute dry unit weight from $e, G$
    • Compute Rankine $K_a$ for $\phi=30^\circ$ and pressure $p_a=K_a\gamma z$
    • Plot triangular distribution to 5 m depth
    • Compute total thrust $P_a=0.5 K_a\gamma H^2$ at $H/3$ from base
14. 7 Marks
    bA retaining wall of height 5 m retains a sand fill, whose angle of internal friction, $\phi =30^\circ$ and unit weight is 118 kN/m$^3$. Estimate the active earth pressure force and its position from bottom of wall.
    How to answer

    • Write Rankine $K_a=(1-\sin\phi)/(1+\sin\phi)$ for $\phi=30^\circ$
    • Compute $P_a=0.5 K_a \gamma H^2$ with given unit weight
    • Locate resultant at $H/3$ above base
    • Report force and position
15. 7 Marks
    aExplain about the Culmann's graphical method.
    How to answer

    • State principle of Culmann construction for earth pressure
    • Describe steps to draw failure wedge and force polygon
    • Explain determination of maximum thrust
    • Mention application to non-uniform backfill
16. 7 Marks
    bA square footing $1.6\,m \times 1.6\,m$ is placed over sand of density $17\,kN/m^3$ and at a depth of 0.8 m. The angle of shearing resistance is $20^\circ$. The bearing capacity factors are $N_c = 17.7, N_q = 7.4$ and $N_\gamma = 5.0$. Determine the total load that can be carried by the footing.
    How to answer

    • Write Terzaghi bearing capacity for square footing
    • Substitute $c=0, \gamma, D_f, B$ with $N_q, N_\gamma$
    • Compute ultimate bearing capacity $q_u$
    • Multiply by area $1.6\times1.6$ for total load