Soils, Foundation and Basement Construction

1. Soils, Foundation and Basement Construction Chapter 21

2. Rocks & Soil • Rocks • Mineral particles are firmly bonded together • Located beneath layer(s) of soil • Soil • Unconsolidated mineral particles or conglomerates located at the top layer of the earth’s crust • Most foundations are supported on soil, except when the soil strength is not adequate

3. Soil classification • Particle size • Coarse grained (gravel & sand) • Fine grained (silt & clay) • Particle shape • Spherical or ellipsoidal, shaped by mechanical weathering • Gravel, sand & silt • Flat, plate-like, large surface area to volume ratio • Behavior influenced by electrostatic forces and presence of water • Cohesion • Cohesive soils are fine grained and particles are attracted to each other in the presence of water. • Non-cohesive soils are course grained and are not attracted to each other • Organic soils consist of fully or partially decayed plant matter, compressive and unsuitable for foundations

4. Soil characteristics by particle size

5. Soil properties and foundation design • Engineering properties • Soil bearing capacity • Particle size distribution • Stability & drainage • Nature of excavation • Depth of water table • Drainage and dewatering • Compressivity • Foundation settlement

6. Soil sampling and testing • Soil sampling • Test pit method • Test boring method • Also allows for standard penetration test on site • Laboratory testing • Sieve analysis • Determines particle size distribution • Soil classification • Moisture content • Dry density • Liquid limit, plastic limit • Compressive strength • Shear strength

7. Test boring equipment

8. Soil sample

9. Sieves used to determine particle size

10. Test boring log

11. Site preparation prior to construction • Fencing site • Locate and mark utility lines • Demolish unneeded structures and utility lines • Remove trees, brush, topsoil

12. Excavation • The process of removing soil or rock from its original location in preparation for construction • Depth of excavation depends on • Foundation type (deep or shallow) • Soil type • Types of excavations • Open. Large and sometimes deep excavations • Trenches. Linear excavations for utilities or footings • Pits. Excavations for footing of one column, elevator shaft, etc.

13. Self-supporting open excavation for basement

14. Uniform slope & stepped excavations. Used when adequate space is available on site

15. Supports for deep excavations • Sheet piles • Interlocking vertical steel sheets driven into soil prior to excavation • Lower part of sheet remains buried, providing cantilever • Deep excavations braced (> 15 ft.) • Bracing • Cross-bracing • Diagonal bracing • Tieback

16. Profile of steel sheet piles

17. Sheet piles driven into soil with diesel hammer

18. Types of bracing for sheet piles

19. Section through excavation with soldier piles and lagging

20. View of excavation: cut faces braced with soldier piles and lagging

21. Section: soil nailed excavation support

22. View of soil nailed excavation

23. Controlling groundwater • Prevent surface water from entering excavation • Draining soil around the foundation • Sumps • Well points

24. Sumps collect and pumps discharge groundwater after it enters the excavation

25. Wellpont system prevents water from entering excavation

26. Foundation systems • Superstructure • Portion of structure located above ground • Substructure • Basements if provided • Foundation • Shallow foundations bear directly on upper level of soil • Slab on ground • Footings • Deep foundations when soil of adequate strength is not available close enough to surface for shallow foundations

27. Perimeter foundation walls and isolated piers with footings

28. Stiffened concrete slab on ground

29. Foundation walls and footing

30. Columns and footings

31. Footing types

32. Design parameters of a footing

33. Steel reinforcement in isolated reinforced concrete column footing

34. Steel reinforcement large footing for central crane

35. Uniform and differential settlement

36. Presumptive allowable bearing capacity of soils

37. Reinforced masonry perimeter foundation for wood light framing

38. Reinforced concrete foundation wall and footing for wood light framing

39. Frost-protected shallow foundations (FPSF) • Insulation is used near the slab foundation to keep soil at perimeter warm • Effectively raises the depth of the frost line • Prevents frost-heave and freeze-thaw related soil movement • Conserves energy • Reduces the required depth of the foundation (16 inches) • Rigid insulation placed horizontally and vertically at foundation edge.

40. Diagram of frost-protected concrete slab on ground

41. Commonly used deep foundations

42. Friction and end-bearing piles

43. Pile cap supported by cluster of four piles

44. Piles - generally driven into the ground, but can be site-cast in predrilled holes • Wood • Creosote treated • Limited load capacity • Steel • H-shape • Hollow pipe, filled with concrete after being driven • Steel subject to corrosion • Concrete • Site-cast in predrilled holes • Precast, reinforced concrete solid sections

45. Piers • Pre-drilled holes filled with reinforced concrete • Large diameter, used individually

46. Types of piers

47. Constructing a concrete pier

48. Constructing a concrete pier

49. Diagram: Grade beam and drilled piers

50. Formwork: Grade beam and drilled piers