Taiyaba rashid jmi


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Taiyaba rashid jmi

  2. 2. 2 RETAINING WALLS • Retaining walls are used to retain earth or other materials which have the tendency to slide and repose at a particular inclination. • They provide lateral support to the earthfill, embankment or other materials in order to hold them in a vertical position. • Types: Gravity retaining wall Cantilever retaining wall Counterfort retaining wall Buttress retaining wall Basement/foundation wall Bridge abutment
  3. 3. 3 GRAVITY RETAINING WALL • Made of plain concrete or brick masonry. • Stability of wall is maintained by its weight. • Generally made up to a height of 3m of wall.
  4. 4. 4 CANTILEVER RETAINING WALL • Consists of a vertical wall, heal slab & toe slab which act as cantilever beams. • Stability maintained by weight of retaining wall & weight of earth on the base of retaining wall. • Height ranges from 3m to 8m.
  5. 5. 5 COUNTERFORT RETAINING WALL • Height ranges from 6m to 8m. • More economical to tie the vertical wall with the heel slab by counterforts at some spacing. • Acts as tension member to support vertical wall & reduces bending moment. • Supports the heel slab & reduces bending moment. • Spacing: 1/3rd the height of wall. • Stability maintained by weight of earth on base & by self-weight. • More widely used as it is hidden beneath the retained materials. • Has a clean, uncluttered face for more efficient use of space in front of wall.
  7. 7. 7 BUTTRESS RETAINING WALL • Similar to the counterfort wall. • Vertical wall is tied with toe of retaining wall at some spacing. • Acts as compression member to support vertical wall & reduces its bending moment. • Supports toe slab & reduces its bending moment. • Spacing: 1/3rd the height of the wall. • Buttress as compression member is more economical than a tension counterfort.
  9. 9. 9 BASEMENT/FOUNDATION WALL • Restrained at the bottom by basement floor slab & at the top by the first floor slab. • Subjected to: Lateral earth pressure exerted by earth fill Vertical load from superstructure. • Lateral support is provided by basement floor & first floor slabs.
  10. 10. 10 BRIDGE ABUTMENT • Behaviour similar to basement or foundation wall. • Superstructure induces horizontal & vertical loads that alter the normal cantilever behaviour.
  12. 12. 12 FORCES ON RETAINING WALLS • Self-weight • Weight of soil above foundation base • Earth pressure • Surcharge i.e., forces due to loads on earth surface • Soil reactions on footing • Friction on footing due to sliding
  13. 13. 13 CONSTRUCTION METHODS • A concrete retaining wall • An interlocking block retaining wall • A Wood retaining wall • An Insulated Concrete Form retaining wall or ICF retaining wall
  14. 14. 14 SLOPE STABILITY • The field of slope stability encompasses the analysis of static and dynamic stability of slopes of earth and rock-fill dams, slopes of other types of embankments, excavated slopes, and natural slopes in soil and soft rock. SIMPLE SLOPE SLIP SECTION SLOPE WITH ERODING RIVER & SWIMMING POOL
  15. 15. 15 SLOPE STABILITY • If the forces available to resist movement are greater than the forces driving movement, the slope is considered stable. • Factor of safety=Forces resisting movement /Forces driving movement. • In earthquake-prone areas, the analysis is typically run for static conditions and pseudo-static conditions, where the seismic forces from an earthquake are assumed to add static loads to the analysis. • METHOD OF SLICES • BISHOP’S METHOD • SARMA METHOD • LORIMER'S METHOD
  16. 16. 16 METHOD OF SLICES SLOPE STABILITY-ANALYSIS METHODS • Method for analysing the stability of a slope in two dimensions. • The sliding mass above the failure surface is divided into a number of slices. • The forces acting on each slice are obtained by considering the mechanical equilibrium for the slices.
  17. 17. 17 BISHOP’S METHOD SLOPE STABILITY-ANALYSIS METHODS • Proposed by Alan W. Bishop. • Method for calculating the stability of slopes. • An extension of the Method of Slices. • By making some simplifying assumptions, the problem becomes statically determinate and suitable for hand calculations. • Forces on the sides of each slice are horizontal • The method has been shown to produce factor of safety values within a few percent of the "correct" values.
  18. 18. 18 BISHOP’S METHOD SLOPE STABILITY-ANALYSIS METHODS • c’= effective cohesion • ’= angle of internal friction • b= width of slice • w= weight of each slice • u= water pressure at base of each slice
  19. 19. 19 SARMA METHOD SLOPE STABILITY-ANALYSIS METHODS • Proposed by Sarawa K. Sarma • A Limit equilibrium technique used to assess the stability of slopes under seismic conditions. • May also be used for static conditions if the value of the horizontal load is taken as zero. • Can analyse a wide range of slope failures as it may accommodate a multiwedge failure mechanism and therefore it is not restricted to planar or circular failure surfaces. • May provide information about the factor of safety or about the critical acceleration required to cause collapse.
  20. 20. 20 LORIMER'S METHOD SLOPE STABILITY-ANALYSIS METHODS • Developed in the 1930s by Gerhardt Lorimer. • A technique for evaluating slope stability in cohesive soils. • Differs from Bishop's Method in that it uses a clothoid slip surface in place of a circle. • This mode of failure was determined experimentally to account for effects of particle cementation. A CLOTHOID OR EULER SPIRAL
  21. 21. 21 REINFORCED EARTH • Also called Mechanically Stabilized Earth or MSE. • Soil constructed with artificial reinforcing. • Can be used for retaining walls, bridge abutments, dams, sea walls, and dikes.
  22. 22. 22 REINFORCED EARTH • MSE walls stabilize unstable slopes and retain the soil on steep slopes and under crest loads. • The wall face is often of precast, segmental blocks, panels or geocells that can tolerate some differential movement. • The walls are infilled with granular soil, with or without reinforcement, while retaining the backfill soil. • Reinforced walls utilize horizontal layers typically of geogrids. • The reinforced soil mass, along with the facing, forms the wall. • In many types of MSE’s, each vertical fascia row is inset, thereby providing individual cells that can be infilled with topsoil and planted with vegetation to create a green wall.
  23. 23. 23 ADVANTAGES REINFORCED EARTH • Ease of installation. • Quick construction. • Do not require formwork or curing and each layer is structurally sound as it is laid, reducing the need for support, scaffolding or cranes. • Do not require additional work on the facing. • Retain sufficient flexibility to withstand large deformations without loss of structural integrity, and have high seismic load resistance.
  24. 24. 24 GEOSYNTHETIC MATERIALS • Polymeric products used to solve civil engineering problems. • Includes eight main product categories: geotextiles, geogrids, geonets, geomembranes, geosynthetic clay liners, geofoam, geocells and geocomposites. • Suitable for use in the ground where high levels of durability are required. • Can also be used in exposed applications. • Available in a wide range of forms and materials, each to suit a slightly different end use. Geocells
  26. 26. 26 GEOGRID • Geosynthetic material used to reinforce soils. • Used to reinforce retaining walls, as well as subbases or subsoils below roads or structures. • Soil pulls apart under tension. Compared to soil, geogrids are strong in tension. • Transfer forces to a larger area of soil. • Made of polymer materials, such as polyester, polyethylene or polyproylene. • Woven or knitted from yarns, heat-welded from strips of material, or produced by punching a regular pattern of holes in sheets of material, then stretched into a grid.
  27. 27. 27 • Also called Cellular Confinement Systems. • Used in construction for erosion control, soil stabilization on flat ground and steep slopes, channel protection, and structural reinforcement for load support and earth retention. • Typically made with ultrasonicallywelded high-density polyethylene (HDPE) or Novel Polymeric Alloy strips that are expanded on-site. • Creates a stiff mattress or slab to distribute the load over a wider area. • Reduces punching of soft soil. • Increases shear resistance and bearing capacity. • Decreases deformation. GEOCELLS
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