Week 7 Challenge

1)How to fix no. of piles in the deep foundations in a flyover in Delhi, listing all the loads acting on it and making all the combinations as per IRC 6.

• Piles are the most preferred type of foundation for supporting the piers of overhead bridges. They offer greater resistance to vertical and horizontal actions from the bridge deck than shallow foundations. Furthermore, they extend the foundation of piers beyond scouring zones so that there will be no loss of bearing capacity.
• For calculating the no. of piles it depend on pile capacity. For determining the pile capacity it also depends on various parameters of soil along with its pile size, type, length and soil quality.
• So first of all the load coming from the super structure is need to be determined.
• Then the ultimate bearing capacity of single pile is determined by emperically as
  • Qup = qb*Ab + qs*As
    • Where, Qup = Ultimate load on pile qb = End bearing resistance of unit area
    • qb = Skin Friction resistance of unit area

Ab = Bearing Area

As = Surface Area

Then the Safe bearing capacity of the pile is determined by dividing the factor of safety.

• Combinations

Comb.	DL (G)	SIDL (CB)	Surfacing (WC)	LL(Q)	Longitudinal forces (Ff)	Longitudinal forces (Fb)	Longitudinal forces (Fcf)	Wind Load (W)	Seismic force (Feq)	Wave Current (Fwc)	Buoyancy (Gb)
I	1.35	1.35	1.75	1.5	1.5	1.5	1.5			1.0	1.0
IA	1	1	1	1.3	1.3	1.3	1.3			1.0	1.0
II	1.35	1.35	1.75	1.5	1.5	1.5	1.5	1.5		1.0	1.0
IIA	1	1	1	1.3	1.3	1.3	1.3	1.3		1.0	1.0
IIB	1.35	1.35	1.75						1.5	1.0	1.0
III	1.35	1.35	1.75		1.5			1.5		1.0	1.0
IIIA	1.0	1.0	1.0		1.3			1.3		1.0	1.0
IIIB	1.35	1.35	1.0						1.5	1.0	1.0

• What are the different factors that can impact the number of piles and its depth. how it is different in wall type abutment .
  • Basically the factors that can impact the piles and its depth is the type of loading that has to be applied on the structure.
  • Also for determining the depth of the depth, soil investigation report plays a major rolr in this. Because if any hard starta presents then the bearing capacity of piles has been determined by bearing action of piles and if very weak soil presents up to greater depth then the bearing capacity has been determined by friction only or in some cases the capacity can be determined by both the action which is mainly depends upon the soil starta.
  • For determing the loads on the struture we have to consider all the types of loads that is coming on to it. Like described in IRC codes
    • Constant Structural Loads
    • DL
    • SIDL
    • Surfacing load
    • prestressing loads
    • Varriyng Loads
      • Vehicular loads
      • Braking Load
      • Wind Load
      • Seismic Load
      • Temp. load
      • Impact/ Accidental load
      • Centrifugal load
  • In case of wall type abutment some extra forces has to be considered at the time of designing /analysis. Like Live load surcharge on the abutment, horizontal force due to water current, seismic effect etc. and for these loads the partial safety factors considered is also different as per described in IRC 112.
• Free Pier and Fixed Pier
  • Based on the type of forces the pier is subjected to, bridge piers are classified as Fixed and Free piers.
  • The piers supporting only on the piles and transmitting the load to the foundation without pile cap are called free piers. Free piers transfer only axial forces from the bearing to the foundations.
  • The piers supporting on the pile cap and transmitting the load to the foundation through pile cap are called fixed piers. Fixed piers transmits axial as well as moments to the foundations.

2)How to fix the diameter of well in the deep foundation in a river bridge in Delhi, listing all the loads acting on it and making all the combinations as per IRC 6.

• Well foundations are the most preferred important and critical type of foundation for supporting the piers and abutments of overhead bridges. They offer greater resistance to vertical and horizontal actions from the bridge deck than pile foundations. Further more, they extend the foundation beyond scouring zones so that there will be no loss of bearing capacity with greater stability.
• For calculating the no. of piles it depend on the capacity. For determining the well capacity it also depends on various parameters of soil along with the well size, type, length and soil quality.
• So first of all the load coming from the super structure is need to be determined.
• Then the ultimate bearing capacity of well is determined by emperically or by load test.Then the Safe bearing capacity of the well is determined by dividing the factor of safety.

• Combinations

Comb.	DL (G)	SIDL (CB)	Surfacing (WC)	LL(Q)	Longitudinal forces (Ff)	Longitudinal forces (Fb)	Longitudinal forces (Fcf)	Wind Load (W)	Seismic force (Feq)	Wave Current (Fwc)	Buoyancy (Gb)
I	1.35	1.35	1.75	1.5	1.5	1.5	1.5			1.0	1.0
IA	1	1	1	1.3	1.3	1.3	1.3			1.0	1.0
II	1.35	1.35	1.75	1.5	1.5	1.5	1.5	1.5		1.0	1.0
IIA	1	1	1	1.3	1.3	1.3	1.3	1.3		1.0	1.0
IIB	1.35	1.35	1.75						1.5	1.0	1.0
III	1.35	1.35	1.75		1.5			1.5		1.0	1.0
IIIA	1.0	1.0	1.0		1.3			1.3		1.0	1.0
IIIB	1.35	1.35	1.0						1.5	1.0	1.0

• What are the different factors that can impact the number of wells and its depth.
  • Basically the factors that can impact the wells and its depth is the type of loading that has to be applied on the structure.
  • Also for determining the depth of the well, soil investigation report plays a major role in this. Well foundation can be of PCC or RCC.
  • For determing the loads on the struture we have to consider all the types of loads that is coming on to it. Like described in IRC codes
    • Constant Structural Loads
    • DL
    • SIDL
    • Surfacing load
    • prestressing loads
    • Varriyng Loads
      • Vehicular loads
      • Braking Load
      • Wind Load
      • Seismic Load
      • Temp. load
      • Impact/ Accidental load
      • Centrifugal load
  • In case of wall type abutment some extra forces has to be considered at the time of designing /analysis. Like Live load surcharge on the abutment, horizontal force due to water current, seismic effect etc. and for these loads the partial safety factors considered is also different as per described in IRC 112.
  • fixed and free pier

    • The piers supporting a free bearing are called fixed piers.free piers transfer only axial forces from the bearing to the foundations.

    • The piers supporting a fixed bearing are called fixed piers. Fixed piers are subject to transverse and longitudinal forces.

1)What is free standing length in a pile system and how to determine this. Also list all the applicable code clauses from IRC and IS codes.

• A pile system having pile cap standing cleary above the ground is known as free standing pile system. This free standing length of pile is calculated by calculating the scouring depth. For calculating the bearing capacity of a pile the pile length below the scouring is being considered and the length of the pile above scouring level is considered as non-effective which is also known as free standing length of pile.
• For determining the scouring depth, it is being described in the clause no 708.4.3.1 of IRC 78.

If the free standing length of the pile is equal to the full length of the pile then there is complete failure of the pile structure. There will be settelmemt failure, buckling failure of the pile will occur. In this type of case there will be no soil around the pile so there will not be any resistance/capacity due to frictional resistance of pile.

Roughly determine no. of piles on abutment of height 5 m and width of 12 m. Vertical capacity – 250 tonnes. Horizontal capacity-35 tonnes

• Consider the width of abutment = 2m

DL = 12 x 5 x 2 x 2.5 = 300 t

Consider LL = 150 t

Earth Load = 150 t

Total vertical load = 600 t

vertical capacity of pile = 250 t

considering FOS = 3

Allowable bearing pressure = 250/3 = 84 t

So no. of pile required = 600/84 = 7.14 → 8 No.s

c)List out failures in deep foundations and their remedies as per the codal provisions. What all construction parameters need to be taken care of before planning a deep foundation

• The failure of pile foundation
  • Lack of adequate boring
  • Inaccurate soil classification
  • Soft strata under tip of pile
  • Inadequate driving formula (wrong data)
  • Improper size of hammer cause insufficient penetration, too light or damaged if too heavy
  • Misinterpretation of load
  • Damaged of encased piles
  • Buckling of piles
  • Breaking of piles
  • Vibration that cause lateral or vertical movement
  • Flowing strata caused by adjacent excavation or bank sloughing
  • Tension failure of concrete pile for lack of reinforcement
  • Eccentricity due to bowing or falling out of plumb
  • Decay due to lower ground water level
  • Insect and marine borer attack and corrosion
• Remedis to prevent failure in pile foundation
  • Early repair such as encasement or replacement
  • Removal of partial load
  • Underpinning
• The failure of Well foundation
  • Due to sinking
  • Due to tilting and shifting
• Remedis to prevent failure in well foundation
  • Eccentric grabbing
  • Eccentric loading
  • water jetting
  • Arresting the cutting edge