Week 2 Challenge

Aim: To Define all loads to be applied in the abutment of the bridge as per IRC 6 and the clauses.

Check for overturning and sliding of 4 m height of Abutment (from ground level), embedded 2 m in ground.

Theory: A bridge abutment is a structure which connects the deck of a bridge to the ground, at the ends of a bridge span, helping support its weight both horizontally and vertically. It resists the lateral movement from the earth fill of the bridge approach.

Loads acting on the Abutment are:

Dead load – It is the weight of the structural components like deck slab, girders, Pier, abutment cap, pier shaft/abutment stem in a structure. It acts in vertically downward direction. Clause 203 of IRC: 06-2017.

Super imposed dead load - It is the weight of Crash barrier, wearing coat, Light pole over the deck of the superstructure. It acts in vertically downward direction. Clause 206 of IRC: 06-2017.

Earth pressure – the weight of soil resisted by the pier shaft or abutment stem. It acts in horizontal direction. Clause 214 of IRC: 06-2017.

Live load – It is the load of the traffic above the deck due to movement of vehicles. It acts in vertically downward direction. Clause 204 of IRC: 06-2017.

Braking load - It is a load induced sudden or when brakes are applied in a vehicle. It acts in horizontal direction. Clause 211 of IRC: 06-2017.

Temperature load – This load is considered due to fluctuation in temperature of the location where the bridge is built. It acts in horizontal direction. Clause 215 of IRC: 06-2017.

Wind load – It is a load exerted by the wind at that particular location where the bridge is built in horizontal direction & vertical direction. Force in vertical direction tends to lift the structure and force in horizontal direction tends to push the structure. Clause 209 of IRC: 06-2017.

Seismic load – A force due to earthquake acting in horizontal direction and vertical direction. Force in vertical direction tends to lift the structure and force in horizontal direction tends to push the structure.

Water pressure – It is a force exerted by the water in a stream or river to pier shaft or Abutment stem in lateral direction. Clause 210 of IRC: 06-2017.

Check for overturning and sliding:

Input Data:

Dimensions

Top width of the retaining wall = 300mm

Bottom width of Retaining wall = 450mm

Size of foundation = 1000 x 2950 x 600 mm

Width of toe = 1000mm

Width of heel = 1500mm

Length of Retaining wall = 1m

Concrete & Steel Data

Grade of Concrete = M30

Grade of Steel = Fe500

Unit Weight of Concrete = 25kN/m3

Soil Data

Unit Weight of Soil = 20kN/m3

Angle of internal friction of Soil = 30°

Surcharge angle = 0°

Angle of inclination of wall from vertical face = 90°

Angle of friction between wall & soil = 20°

Safe Bearing Capacity of Soil = 200kN/m2

Load Calculations

Description	Shape	L	B	D	Lever arm	Vertical load	Horizontal load	Vertical moment	Horizontal moment
Footing	Rectangle	1	2.95	0.6	1.475	44.25	-	65.27	-
Wall	Rectangle	1	0.45	4.0	1.225	45.00	-	55.13	-
	Triangle	1	0.00	4.0	1.45	0.00	-	0.00	-
soil	Rectangle	1	1.5	4.0	2.2	120.00	-	264.00	-
	Triangle	1	0.0	4.0	1.45	0.00	-	0.00	-
Active EP	Triangle	1	-	4.0	1.68	-	53.37	-	89.7
	Triangle	1	-	1.4	0.59	-	6.54	-	3.8
					Total	209.25	46.83	384.39	85.81

Factor of safety against sliding = 0.5 x (W/H ) = 0.5 x ( 209.25/46.83 ) = 2.23 >1.5 Hence OK

Factor of safety against overturning = Mv/Mh = 384.39/85.81 = 4.48 > 2 Hence OK

2. Aim: To decide the boreholes location and its depth of exploration in case of shallow foundation and the parameters to get from the site/geotechnical investigations for design of the foundation. To List different type of soils/rock (minimum 5) and the criteria to be followed for the shallow foundations for selecting the foundation level, their characteristics with pictures and to draw a typical borehole showing all the data.

Theory and Explanation:

Soil investigation is required for the following purposes:

To know the allowable bearing capacity of foundation for proposed building.

To know the depth and type of foundation for the proposed building.

To know the allowable passive resistance for the foundation of proposed building.

To know the type, grading and nature of soil.

To know the ground water level.

Subsurface exploration in shallow foundation depends on the following parameters:

Nature of the soil

Selection of depth suitable for the structure

Based on SPT: Standard penetration test is designed to provide the geotechnical information of the soil. It provides a measure of penetration resistance.

Determining bearing capacity of the soil

Determining settlement of soil

Location of water table

Bore Hole: Bore hole is a deep vertical hole with smaller diameter drilled into the ground to obtain the soil samples for the purpose of testing the soil for geotechnical report and for the design of the foundation. Bore holes are drilled to find the bearing capacity of the soil, nature of the soil strata, liquefaction in the soil. Bore holes should be done at the proposed location of abutment and pier.

The depth generally depends on the width of the foundation as per the loadings, bearing capacity multiplied by 1.5 ( IRC 78). The samples obtained are utilized to get necessary information about the soil characteristics by means of laboratory tests.

Depth of exploration = 1.5 x Width of foundation

Bore log are done in the pier location. Under every foundation we need to have one bore log to assess the soil criteria.

The Results give details of ground conditions, previous use of site, present conditions, groundwater and drainage pattern. The tests must give adequate information to determine:

The soil’s bearing capacity

Settlement characteristics

Fig: Typical bore log showing bore hole data

Types of soil are :

Sandy soil : It is brittle and gritty when touched and this is because of the huge spaces present between the particles. Also, it has low water holding capacity. The draining of water is so quick that water even does not reach the root of the plants. As there is a quick running of water plant does not get the chance to get the nutrients efficiently.

Silty soil : If compared to sandy soil, silty soil is usually smaller in size and so they are smoother and it becomes soapy slick when moistened. It also has rock and other mineral fragments. Its water-holding capacity is better than sand because of its fine texture. It is also good for agricultural activities because of its characteristics.

Clay soil : this has the smallest particle composition of the other types of soil and it has fair water storage qualities. The space between the particles of clay soil does not allow the air to pass and their tendency to settle together. Plant nutrients will be tightly held due to its slow draining tendency and so this soil is rich in plant food for better growth. Clay soil is good for growing ornamental plants and fruit trees. Aster, Helen's flower, Flowering quince, and other shrubs and perennials thrive in this soil. It feels sticky, rolls up easily, and forms into a sausage-like Shape if moistened.

Loamy soil : this is said to be the perfect type of soil as the gardens and gardeners just love it. Loamy soil is composed of a mixture of sand, silt, and clay. Because of its previous organic matter content, this soil has higher calcium and pH level. The texture of this soil is dark. The particles have airspaces between them which help them to take nutrition to travel to the roots. Loamy soil is the greatest soil and framers friendly. This soil is good for bamboos, climbers, perennials, tubers, and shrubs like Dog's tooth violets, Wisteria, Rubus, and others thrive.

Peaty soil : This soil is commonly called Black Soil because of the color of the peaty soil is black or dark brown in color. Black soil has rich organic content and feels soft when touched. This soil helps to regulate the pH level of the soil. The soil is spongy in nature. Peaty soil is good for the production of rice crops when drained and fertilized properly.

Types of rock are :

Igneous rock : It is one of the three main rock types. Igneous rock is formed by magma or lava cooling and solidifying. In either the mantle or crust of a planet, the magma can be derived from partial melts of existing rocks.

Metamorphic rocks : The arise from the transformation of existing rock types, in a process called metamorphism, which means change in form. The original rock (protolith) is subjected to heat and pressure causing profound physical and/or chemical change. The protolith may be a sedimentary rock, an igneous rock or another older metamorphic rock.

Sedimentary rock: It is one of the three main rock groups (along with igneous and metamorphic rocks) and is formed in four main ways: by the deposition of the weathered remains of other rocks (known as ‘clastic’ sedimentary rocks); by the accumulation and the consolidation of sediments; by the deposition of the results of biogenic activity; and by precipitation from solution.