Week 4 Challenge
Bridge is structure build over physical obstacles. Bridge mainly divided into three components 1) Sub-structure 2) Superstructure 3)foundation . Foundation is structure use to transfer sub structure and super structure load into hard strata or to soil having sufficient bearing stratum. There are mainly two types of foundation in bridges 1) Shallow foundation 2) Deep foundation.
1) Shallow foundation- When depth is less than or equal to width is known as shallow foundation. Soil having sufficient bearing capacity and hard strata is easily available we preferred shallow foundation. When soil data not available we generally go with minimum depth of 2m in case of shallow foundation as per IRC-78( Code for foundation and substructure).there are various types of shallow foundation - a) Isolated footing b)Combined footing c) Strip footing d) Mat footing e) Cantilever footing.
Design checks for shallow foundation- Sliding, overturing, base pressure, scour , SLS & ULS check.
Design and construction parameter- a) minimum reinforcement is 250mm2/m should be provided in both direction. b) No tension should be provided in bottom c) Spacing should not be more than 300mm. d) generally depth is 2m from EGL.
f) Excavation, protection cover using shoring and other , PCC, Reinforcement fixing and concreting.
2) Deep foundation- When depth is greater than or equal to width is known as deep foundation. Soil does not having sufficient bearing stratum and hard strata is not easily available we preferred deep foundation. There are various types of deep foundation a) Pile foundation b) well foundation c) cassion foundation.
Pile is vertical structural member used to transfer sup & super structure load into hard strata. Friction, anchor, end bearing, composite pile. Mostly pile foundation are used in bridge/metro structure.
Piling is done through rig machine. Castin situ and precast pile are available. As per codel IRC -78 cover for reinforcement in pile is 75mm. Tolerance in pile is 75mm is allowed. Minimum bulb area between two end bearing pile is 2.5m. offset from face of pile is minimum is 150mm. pile consist of group 2 pile,3 pile, 4 four pile etc.
Pile bored cast in situ construction activity- Pile coordinate marking using suvey machine i.e. Total station with as per drawing coordinate. Using rig machine start boring as per required depth as mention in drawing. Lowering of reinforcement cage using rig machine with cover block of 75mm. concreting with minimum M35 using tremie cone and then CHSL & PIT test to get whether homogeneity , voids, honey comb is present or not. Use vibrater machine to prevent all these cavities.
Foundation failure in bridge – Due to design failure, due to scour failure, due to material failure, due to faulty geotechnical data.
Requirement of foundation- Structural stability, constructibilty, durability, economy, should not impair function of structure.