Week 9 Challenge

AIM-: Calculate the forces as per IRC 6 on the foundation and propose the foundation.

In a river of linear waterway 90 m and design discharge as 700 cumec and having silt factor as 1 . Fix the span and type of foundation if HFL is 3 m from the ground.

Velocity of water 1.2m/sec Top road level-100 m Ground level-93.5 m

Vertical pile capacity for 1.2 m dia is 250 tonnes horizontal 35 tonnes

Well having 8 m diameter capacity 70 tonnes/m2 6 m diameter 50 tonnes/m2 7 m diameter 60 tonnes

1. assume simply supported bridges
2. continuous bridge

SOL-:Data Given:

• Linear waterway = 90m
• Design Discharge = 700 Cumec
• Silt Factor= 1
• HFL = 3m
• Velocity = 1.2m/sec
• FRL = 100 m
• OGL = 93.5 m
• Vertical Capacity = 250 tonnes (for 1.2m dia pile)
• Horizontal capacity = 35 tonnes (for 1.2 m dia pile)
• Well capacity - 50 tonnes /m2 (for 6m dia well)
• - 60 tonnes /m2 (for 7m dia well)
• - 70 tonnes /m2 (for 8m dia well)

Scouring in Bridge:

Scouring is defined as the lowering or loss of top bed soil (erosion) around the bridge piers, abutments, etc. due to the water flow currents. Scouring is always a potential threat to bridge stability eventually it can lead to foundation failure

FIRST CALCULATE SCOUR DEPTH BY USING THE EQUATION GIVEN BY LACYS

SCOURING EFFECT

Calculation of scouring Depth.

Db = (1.3XQ/L)

= (1.3X700/90)

= 10.11 m

Ksf = 1

Dsm = 1.34(Db^2/ksF)^2/3

= 1.34(10.11^2)^2/3

= 6.26 m

Maximum depth of scour for design of foundation,

For Abutment,

= 1.27 X dsm

= 1.27 X 6.26

= 8.41

Depth of foundation below foundation.

= 8.41 - HFL

= 8.41 - 3

= 5.41 m

For Pier,

= 2 X dsm

= 2 X 6.26

= 12.52

Depth of foundation below foundation.

= 12.52 - HFL

= 12.52 - 3

= 9.52 m

Calculating the forces as per IRC 6 on the foundation,

General
This design note pertains to the design of abutment . Superstructure consists of Box Girder of 15.00 m c/c of pot cum PTEF bearing. The substructure consists of RCC wall type abutment on pile foundation.

2.What is zero shear point and if there is more scour at region what will be the effect of that on zero shear point?

Answer: The points other than the extreme ends of a beam where B.M. is zero are called points of contraflexure or inflexion. The point at which we get zero shear force we get the maximum bending moment of that section/beam at that point. If Scouring is more, point from where passive earth pressure shall be considered will be different and hence point of zero shear will be lower than normal.

Longitudinal force clause no 211.1 from IRC 6 we need to consider for the bridge in which free bearing and fix bearing concept is taken for design.

3 the Liquefaction and its effects, how it can affect foundation. Also list the remedial measures for the same. How it is different from scouring?

Answer: Liquefaction is a phenomenon in which the strength and stiffness of a soil is reduced by earthquake shaking or other rapid loading. Liquefaction and related phenomena have been responsible for tremendous amounts of damage in historical earthquakes around the world.
Liquefaction occurs in saturated soils, that is, soils in which the space between individual particles is completely filled with water. This water exerts a pressure on the soil particles that influences how tightly the particles themselves are pressed together. Prior to an earthquake, the water pressure is relatively low. However, earthquake shaking can cause the water pressure to increase to the point where the soil particles can readily move with respect to each other.ct

• Effects on the foundation.

The soil liquefication has a disastorus effect on bridges and different structures. The structure built on liquefiable soil may face foundation settlement, crack, tilt, and overturning for the open foundation

For the deep foundation like pile foundation piles may buckle due to seismic force in liquefication soil.

• Remedial measurement for liquefication soil.

Geological studies identify the landfill sediments, and water table in a seismic region. Soil composed of a mix of small and big grains, can safely endure liquefaction, since the smaller grains fill the pores between the larger grains. Thus, the soil strength is maintained. Furthermore, modern buildings are designed to be liquefaction resistant. In a shallow foundation, the foundation constituents are joined to ensure uniform settlement of the foundation. Thus, the induced shear forces are decreased. The soil characteristics may also be enhanced by improving the soil density, strength, and drainage characteristics. Popular mitigation methods to reduce effects of soil liquefaction are:

• Mitigation by deep soil mixing method
• Compaction, Permeation, and Jet Grouting
• Drain Pile technique
• Dynamic compaction and construction of stone columns