2. Chapter 2 a Soils & Excavation

3. Building Foundations The purpose of foundations is to provide stability and to safely transfer building loads to the earth. The purpose of foundations is to provide stability and to safely transfer building loads to the earth. Three load considerations occur: Three load considerations occur: Vertical weight of the building Vertical weight of the building Horizontal forces above ground such as wind Horizontal forces below ground as in earthquakes.

4. Foundation Loads Dead Load Dead Load Weights of building material due to gravity Weights of building material due to gravity Live Load Live Load Those type loads that can change, such as weight of furniture, people, wind, snow, ice, and in certain areas of the world, horizontal forces below grade, such as movement caused by earthquakes. Those type loads that can change, such as weight of furniture, people, wind, snow, ice, and in certain areas of the world, horizontal forces below grade, such as movement caused by earthquakes.

5. Foundation Requirements Foundations Must Be: Foundations Must Be: Safe From Structural Failure Safe From Structural Failure Free of Settlement that does not impair Function, such as unsightly cracks and damage to the building that would allow deterioration due to weather. Free of Settlement that does not impair Function, such as unsightly cracks and damage to the building that would allow deterioration due to weather. Foundations Must Be Technically & Economically Feasible Foundations Must Be Technically & Economically Feasible

6. Types of Settlement No SettlementUniformDifferential

7. Of the two types of settlement, Differential Settlement is the worst, as structural failure often occurs when one part of a structure moves and another part doesn’t. Of the two types of settlement, Differential Settlement is the worst, as structural failure often occurs when one part of a structure moves and another part doesn’t. Differential settlement is due basically to two conditions: Differential settlement is due basically to two conditions: Poor bearing capacity of soil in differing areas of the building. Shrinking and swelling of the soil which allows one part of a building to sink due to load – or forces of swelling soil causing an upward movement in parts of a building.

8. The Leaning Tower of Pisa One of the Most Famous Examples of Differential Settlement

9. Between an Areaway & Sidewalk

10. Differential Settlement Next to A Building Column

11. Differential Settlement happens when one part of a building changes elevation relative to another part of the building. Differential Settlement happens when one part of a building changes elevation relative to another part of the building. Differential settlement is usually caused by an inconsistency in the soil bearing, or a change in the soil volume. Differential settlement is usually caused by an inconsistency in the soil bearing, or a change in the soil volume. Types of soil range from the most stable -- from hard granular particles -- to clay - - - to somewhere in between – which may contain sound, structural particles and some that are not. Types of soil range from the most stable -- from hard granular particles -- to clay - - - to somewhere in between – which may contain sound, structural particles and some that are not.

12. Types of Soil Soil types are identified by analysis in a laboratory by Geotechnical Engineers. Soil types are identified by analysis in a laboratory by Geotechnical Engineers. Soil that is basically stable are comprised of hard particles that touch and do not move when subjected to loads or inclusion of water. Soil that is basically stable are comprised of hard particles that touch and do not move when subjected to loads or inclusion of water. Soil that is mostly clay has extremely small particles. Water will force the particles apart, causing the mass to swell – in all directions. When water migrates out of the mass, the soil will shrink. Soil that is mostly clay has extremely small particles. Water will force the particles apart, causing the mass to swell – in all directions. When water migrates out of the mass, the soil will shrink.

13. ClaysPorous (sandy)

14. Soil Particle Distribution  Soil is rarely one type - but a mixture of different particles due to years of migration of particles, caused by wind and water.  Distribution of soil type, particle size, and particle strength is important in Predicting: –Load Bearing Capacity –Stability –Drainage Characteristics

15. A type of soil that is available in nearly all locations is called loam, which is a rather generic name for common, ordinary soil that does not have characteristics of unstability in some form. A type of soil that is available in nearly all locations is called loam, which is a rather generic name for common, ordinary soil that does not have characteristics of unstability in some form. Loam is very good farm type soil, as it contains sand, some clay, silt, and organic matter. Since it does not contain an overbalance of clay or silt it is a stable foundation soil when compacted to a dense formation. Two types of soil unique to the West Texas area have varying characteristics: Two types of soil unique to the West Texas area have varying characteristics:

16. Caliche – actually is soil with a high content of calcium carbonate. Is strong when dry but unstable when wet. Good for a sub layer for concrete and asphalt roads when protected from absorbing moisture. Not a good base for bearing capacity under buildings. Caliche – actually is soil with a high content of calcium carbonate. Is strong when dry but unstable when wet. Good for a sub layer for concrete and asphalt roads when protected from absorbing moisture. Not a good base for bearing capacity under buildings. Playa Lakes – Soil found in playa lakes has extremely small particles, structurally unsound, and very unstable. It is composed of drainage silt over years of washing downhill from someplace else moving to lower levels until it ends at a playa lake. Playa Lakes – Soil found in playa lakes has extremely small particles, structurally unsound, and very unstable. It is composed of drainage silt over years of washing downhill from someplace else moving to lower levels until it ends at a playa lake.

17. Soil Investigation Who needs to know soil characteristics? Who needs to know soil characteristics? When do they need to know them? When do they need to know them? How is that knowledge obtained? How is that knowledge obtained?

18. SOIL BEARING CAPACITY SOIL BEARING CAPACITY Since the weight of a building ultimately must rest on the earth, the capacity for the soil to resist loads – forever - is of major concern before any appreciable advancement is made to formulate a design. Since the weight of a building ultimately must rest on the earth, the capacity for the soil to resist loads – forever - is of major concern before any appreciable advancement is made to formulate a design. Geotechnical Testing laboratories take soil samples at construction sites at varying depths and test the soil composition for strength and stability. Generally, the engineers will recommend a type of foundation design for a specific type of building. Geotechnical Testing laboratories take soil samples at construction sites at varying depths and test the soil composition for strength and stability. Generally, the engineers will recommend a type of foundation design for a specific type of building.

19. Pictured here Is a geotech drilling team making a test boring. As the auger extends into the ground, the hollow tube gathers soil at all depths.

20. oMultistory buildings will require deep footings that extend to a rock strata for support. oMedium height (2 to 4 story) buildings may be built on soil with spread type footings, but must be protected from adverse conditions, such as inclusion of water and freezing. oLight load buildings (1 & 2 story) generally have foundations near the ground surface. These also must be protected from adverse conditions.

21. PRIMARY ADVERSE CONDITIONS PRIMARY ADVERSE CONDITIONS  For low to medium height buildings, sufficient bearing capacity can generally be found within the soil structure, without the need for rock bearing.  But even with sufficient bearing capacity, unstable soil can be a detriment to buildings due to uneven settlement.  Shallow footings spread to areas required for bearing capacity work against bearing design when clay soil absorbs moisture and swells, causing upheaval in varying parts of the building. Cracks occur and increase the potential for structural stress.

22. SOLUTIONS TO DIFFERENTIAL SETTLEMENT IN SINGLE STORY BUILDINGS 1 Remove the soil in the immediate building area to a satisfactory depth (usually around 4 feet) and install stable, compacted soil. 1 Remove the soil in the immediate building area to a satisfactory depth (usually around 4 feet) and install stable, compacted soil. 2 Stabilize the soil: 2 Stabilize the soil: Mix stabilizing ingredient into the soil such as cement or fly ash. Mix stabilizing ingredient into the soil such as cement or fly ash. Inject lime slurry under pressure into the soil Inject lime slurry under pressure into the soil 3 Where concrete floors are to be placed, expand the soil to maximum volume by saturating it with water, then seal with a moisture barrier such as plastic sheeting. 3 Where concrete floors are to be placed, expand the soil to maximum volume by saturating it with water, then seal with a moisture barrier such as plastic sheeting.

23. SOIL FILL and EXCAVATION SOIL FILL and EXCAVATION After sufficient information is known regarding foundation type due to soil, and preliminary corrections are made; After sufficient information is known regarding foundation type due to soil, and preliminary corrections are made; –Soil fill is added to or taken away from the site as necessary to establish proper levels of surface elevation for drainage and general terrain design. –Soil fill is made and compacted in the area of the building to establish finish soil grade before preparations for installation of concrete foundation. –Soil fill is always made in “lifts” – layers of not more than 8” to 12” at a time, then compacted to assure that all soil is sufficiently dense.

24. The compaction of soil is done in order to reduce the space between particles of soil as much as possible so the density of the soil will resist subsequent movement. The compaction of soil is done in order to reduce the space between particles of soil as much as possible so the density of the soil will resist subsequent movement. Water is added to the soil as compaction is done in careful amounts in order to densify the soil to a percentage of maximum, with optimum water content. Water is added to the soil as compaction is done in careful amounts in order to densify the soil to a percentage of maximum, with optimum water content. Compaction is done with a variety of equipment specific for the soil types, including pronged ‘sheep’s foot’ rollers, flat rollers, rubber-tired rollers, and vibrating rollers. Hand-held compactors are used in small areas. Compaction is done with a variety of equipment specific for the soil types, including pronged ‘sheep’s foot’ rollers, flat rollers, rubber-tired rollers, and vibrating rollers. Hand-held compactors are used in small areas.

25. Vibrator compactor for small areas

26. Backfilling in “Lifts” – Compacted & Tested Soil Placement & Compaction

27. Vibratory Roller Sheeps Foot Compactor Compactor - Dozer Water Wagon SheepsfootVibratory Roller

28. PlateTamperTrench Sheeps Foot Walk - Behind Roller Compaction Equipment

29. oPreparatory requirements by the Architect of a project will determine how construction procedures develop. The Architect will state in the General Conditions and Specifications how results of construction processes are verified. For instance: After placement and compaction of the soil, compaction tests will be made by the Geotechnical Laboratory that did the soil analysis. After placement and compaction of the soil, compaction tests will be made by the Geotechnical Laboratory that did the soil analysis. Engineers will take samples of the soil after compaction is complete, then make tests in the lab to determine compaction percentage results. Engineers will take samples of the soil after compaction is complete, then make tests in the lab to determine compaction percentage results. Reports of the compaction tests are delivered to the Architect, stating the moisture content and the percentage of compaction. Reports of the compaction tests are delivered to the Architect, stating the moisture content and the percentage of compaction.

30. Sample Location Selected Sample Removed & sent to the testing ‘Lab’ Sand Replaces Sample ‘Material ’ ‘In Place’ Volume of Sample Determined

31. Maximum Density Of soil with the Optimum moisture Content

32. Density test results for three soil samples.

33. EXCAVATION FOR FOUNDATION  After all dirt work is done, trenches are cut for under floor piping such as plumbing, electrical, fire sprinkler pipes etc., for installations that must be made before concrete is placed.  Then trenches are cut for foundation grade beams, spread footings, and areas where the floor slab will be made thicker for load bearing walls.  The surface of excavations that will form concrete are sprayed with a material that will not allow the dry soil to draw water from the concrete.

34. o Required reinforcing steel is then installed at the proper places and secured. o Concrete is then placed in the excavation under and around the reinforcing steel and tamped to eliminate voids in the structural concrete. o In areas where the soil is not stiff enough to form the sides of beams & footings, and in areas where appearance and finish of concrete is essential, wood or steel forms will be set to determine the limits of the finish concrete structure.

35. OPEN TRENCH FOR STRUCTURAL GRADE BEAM

36. GRADE BEAMS AFTER CONCRETE HAS BEEN PLACED

37. EXCAVATION FOR A SWIMMING POOL AND INTEGRAL HOT TUB