Foundation Basics & Surrounding Areas

Foundation Basics & Surrounding Areas

1. Foundations

   • expanded horizontal base of a vertical element such as wall or column in addition to the ground or suboil which supports it
   • Objective is to distribute the weight so it can be carried over a wider, sufficeint area of bearing surface to prevent subsoil from spreading
   • Functional Requirements
     • transmit load imposed by the building safely to the deeper strata
     • must accomplish its function without suffereing excessive differential movement or settlement which might lead to structural damage

2. Building loads

   • Imposed Loads
     • Live loads
       • non-permanent changes due to number of people living in a building
     • Wind/Snow loads
       • load due to the effect of wind/snow/rain and impact on a structural behaviour of a building
   • Dead Loads
     • laod due to the weight of all structural elements (walls, roof, floors) combined weight of these plus effect of gravity

3. Key Features

   • Wall plate
     • As a beam helps to distribute the roofs load evenly along the internal leaf of the perimeter wall which in turn superimposes onto the foundations
   • Internal leaf
     • main load bearing leaf all the way to the foundation
   • External leaf
     • protective cladding/ facing or envelope

4. Total Load

   • imposed on the foundation must be the same magnitude if the building is to remain in equilibirum

5. Gravity

   • natural downward force
     • constant force
       • 9.81 m/s2
   • force= mass x acceleration
   • Newton is the unit of force
     • 1N = 1kg/m/s2

6. Settlement of a building

   • movment in the structure caused by the weight of the building compressing the underlying ground and can manifest in two ways
     • Subsidence
       • movement due to the loss of ground support below foudnation, largely due tio the SHRINKAGE in the void ratio of the founding materials
     • Heave
       • movment caused by loss of ground support resutling from volumetric changes due to EXPANSION in void ratio of founding materials

7. Types of settlement

   • Differential
     • greatest concern in relation to cracking and structural damage in low rise buidlings
   • Total
     • entire structure settles by a uniformed amount
     • always potential of damage to services in ground below
   • Tilt
     • tilts with no angular deformation in the process
     • cracking of surface elements
     • early signs
       • windows misaligning
       • chimney slanting

8. Buidling near trees

   • critical factor is proximity and type of trees
   • different impacts depending on trees mositure intake and shrinkage cabaility
   • High demand
     • If D = H , then FND depth of 1.5m
     • If D = 0.5H, then FND dept 2.3m
   • Low demand
     • If D = H , then FND depth 1m
     • If D -= 0.5H , then FND depth 1.5m

9. Foundation Dimensions

   • Width
     • T =P (or 150mm) whichever is greater
   • Depth
     • avid frost heave
       • 450mm
     • high volume change
       • low potential 750mm
       • high 1000mm
     • trees
       • 10m away
         • 2500mm depth

10. Plasticity Index (PI = LL -PL)

    • Liquid Limit (LL)
      • mositure content at which soil loses its plastic properties and exhibits a liquid
    • Plastic Limit (PL)
      • water content when soil becomes too dry and begins to disintergrate
    • size of the range of water contents where the soil exhibits plastic properties

11. Solutions

    • Crack control movement joints
      • included in every wall
      • wire helps restrain movement
      • also known as bed joint movement control mesh