Plasticity index (PI) of 15 or greater, determined in accordance with ASTM D 4318This chapter contains provisions to building and foundation systems in areas that are not subject to scour or water pressure by the actions of wind or wave action.
In this chapter there are allowable bearing pressures, stresses, and design formulas that are used with allowable stress design load combination specifications. When looking at the quality and design of materials used structurally in excavations, footings, and foundations, one must also look at all the requirements that the quality and design materials used for excavations, footings, and foundations must conform to. Excavations and fills must also comply with code requirements.
If the foundation is proportioned using the load combinations allowed, and the computation of the seismic overturning moment is by the equivalent lateral-force method, the proportioning must be in accordance with Section 12.13.4 of ASCE 7.
This section contains provisions for foundation and soil investigations. Classification and investigation of the soil must be made by a registered design professional where required by the building official. If such investigation is required, it is the owner’s or applicant’s responsibility to submit the foundation and soil investigation to the building official where required in this section.
There are many reasons why a building official may require a foundation and soil investigation. Any soils where the classification, strength, or compressibility are in doubt or where a load-bearing value greater than that specified in this code is claimed, the building official will require the necessary investigation.
There are four provisions that a soil must meet to be considered expansive. Tests that show compliance with the first three bullets will not be required if bullet 4 is conducted.
Plasticity index (PI) of 15 or greater, determined in accordance with ASTM D 4318
More than 10 percent of the soil particles pass through a no. 2 sieve, determined in accordance with ASTM D 422
More than 10 percent of the soil particles are less than 5 micrometers in size, also determined in accordance with ASTM D 422
Expansion index greater than 20, determined in accordance with ASTM D 4829.
A subsurface soil investigation will be performed to find out if the ground-water table is above or within 5 feet below the elevation of the lowest floor level where floors are located below the finished ground level adjacent to the foundation. A subsurface soil investigation is not required where you can provide waterproofing that is in accordance with this chapter.
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Soils that swell when subjected to moisture are classified as expansive soils and contain clay materials that attract and absorb water. If the building official suspects that you may have this type of soil, you can bet that a soil test will be required. |
Another reason for foundation and soils investigations is for buildings and structures with a Seismic Design Category C, D, E, or F. The investigation for category C differs from D, E, and F and includes an evaluation of the potential hazards that result from earthquake motions such as slope instability, liquefaction, and surface rupture due to faulting or lateral spreading. Categories D, E, and F must meet the same investigation as Category C, in addition to the following:
To determine the lateral pressures that are made by earthquake motions and the affect they have on basement and retaining walls
An assessment of potential consequences of any liquefaction and loss of soil strength, including estimation of differential settlement, lateral movement, or reduction in foundation and must address mitigation measures. You may use these measures for consideration in the design of the structure and can include ground stabilization and selection of appropriate foundation types.
An evaluation for liquefaction and soil strength loss for site peak ground acceleration must be done as well. An exception to this is a site-specific study where peak ground acceleration is determined in accordance with Section 21.2.1 of ASCE 7.
Foundation and soils investigations include soil classification where soils are grouped according to their general behavior under given physical conditions. It is important that you understand such classifications.
Necessary tests of materials from borings, test pits, or other subsurface exploration and observation are used to determine soil classification. If required, additional studies must be made to evaluate the following:
Slope stability
Soil strength
Position and adequacy of load-bearing soils
The effect of moisture variation
Compressibility
Liquefaction and expansiveness.
The soil classification and design load-bearing capacity must be put on the construction document. The building official may request a written report of the investigation and must be submitted. The following list contains information that is contained in the report. Take note that this list is not limited and there could be more specific information that the building official is requesting.
A plot showing the location of test borings and/or excavations
A complete record of the soil samples
A record of the soil profile
Elevation of the water table, if encountered
Recommendations for foundation type and design criteria
Expected total and differential settlement
Pole and pier foundation information
Special design and construction provisions for footings or foundations founded on expansive soils, as necessary
Compacted fill material properties and testing.
Before digging any trenches, pits, tunnels, or other excavations, precautions must be taken so that lateral support from any footing or foundation is not disturbed or removed without unpinning or protecting the footing or foundation against settlement or lateral translation.
Backfill is the refilling of an excavated space with soil free of organic material, construction debris, lumps that are larger than a pebble and boulders, or with a controlled low-strength material (CLSM). Backfill must be compacted in a manner that does not damage the foundation or the water/dampproofing materials.
In areas where footings will bear on compacted fill areas you must make sure that the compacted fill complies with the provisions of an approved report. Below is a list of the seven items that must be contained in such approved report:
Specifications for the preparation of the site prior to placement of the compacted fill material
Specifications for material to be used as compacted fill
Test method to be used to determine the maximum dry density and optimum moisture content of the material to be used as compacted fill
Maximum allowable thickness of each lift of compacted fill material
Field test methods for determining the in-place dry density of the compacted fill
Minimum acceptable in-place dry density expressed as a percentage of the maximum dry density determined in accordance with bullet three of this list
Number or frequency of field tests required to determine compliance with bullet six of this list
The provisions for controlled low-strength material (CLSM) on which footings will bear must follow similar rules. There is an approved report in which specific provisions must be followed, including:
Specifications for the preparation of the site prior to placement of CLSM
Specifications for the CLSM
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Compacted fill material that is less than 12 inches in depth does not need to comply with an approved report, provided it has been compacted to a minimum of 90 percent Modified Proctor. See ASTM D 1557 for more information regarding this exception. Also note that controlled low-strength materials do not need to be compacted. |
Laboratory or field test method(s) to be used to determine the compressive strength or bearing capacity of the CLSM
Test methods for determining the acceptance CLSM in the field
Number and frequency of field tests required to determine compliance with bullet 4 of this list.
Immediately adjacent to the foundation is where site grading takes place. The slope cannot be any less than one unit vertical for every 20 units horizontal for a minimum distance of 10 feet measured perpendicular to the face of the wall. You must provide a 5-percent slope for an approved alternative if physical obstructions or lot lines prohibit the original 10 feet requirement. When using swales, they must be sloped for a minimum of 2 percent where located within 10 feet of the building foundation.
Resistant surfaces that are within 10 feet of the building foundation must be sloped for a minimum of 2 percent away from the building. One exception to this is for climatic or soil conditions. If such conditions exist, the slope of the ground away from the building foundation is allowed to be reduced, but no less than one unit vertical in 48 units horizontal (2 percent slope). The procedure that you use to establish the final ground level will account for additional settlement of the backfill. Grading and fill for flood hazard areas will not be approved unless the following is true:
Fill is placed, compacted, and sloped to minimum shifting, slumping, and erosion during the rise and fall of flood water and, if applicable, wave action
Demonstration through hydrologic and hydraulic analyses performed by a registered design professional and done in accordance with standard engineering practice that the proposed grading or fill will not result in any increased flood levels
Fill is conducted and/or placed to avoid diversion of water and waves toward any building or structure
Demonstration that the cumulative effect of the proposed flood hazard area encroachment, when combined with all other existing and anticipated flood hazard area encroachment, will not increase the design flood elevation more than 1 foot at any point.
There are maximum allowances that you must adhere to for foundation pressure, lateral pressure, or lateral sliding-resistance values. These must not exceed the values allowed by code unless you have data to verify the use of a higher value. Any higher values must be submitted and approved for use.
Do not assume that mud, organic silt, organic clays, peat, or unprepared fill have an acceptable load-bearing capacity unless you have the data to back that up. I believe we all know what happens when we assume something to be true. And it would be a great deal of time, money, and energy wasted if you assume that the use of a material is acceptable without the data to back it up. That being said, there is however, an exception to this. An acceptable load-bearing capacity is permitted to be used if the building official considers the load-bearing capacity of mud, organic silt, or unprepared fill to be adequate for the support of lightweight and temporary structures.
To determine the resistance of structural walls to lateral sliding, calculate by combining the values from the lateral bearing and sliding resistance. Remember you have to submit the reasons or data for this and obtain approval.
In the case of clays, such as sandy, silty, or clayey silt, under no circumstance can the lateral sliding resistance be more than one-half of the dead load. It is possible for increases to be allowed for lateral sliding resistance. For each additional foot of depth to a maximum of 15 times the tabular value.
Footings and foundations are crucial to the success of a building. When properly designed, footings and foundations withstand the forces of a building. Footings and foundations are built directly on undisturbed soil, compacted fill material, or CLSM, with a minimum depth of footings below the undisturbed surface of 12 inches. While the top surface of footings has to be level, the bottom surface is not. The bottom surface of footings is allowed to have a slope not to exceed one unit vertical in 10 units horizontal.
There are times when it is necessary to change the elevation of the top surface; this is when footings must be stepped. Another important element regarding footings and foundations is frost protection. Foundation walls, piers, and other permanent supports of buildings and structures must be protected, by either extending below the frost line, erecting on solid rock, or constructing in accordance with ASCE 32. If your building is free-standing and all of the following conditions are met, frost protection is not required.
Buildings classified in Occupancy Category I include areas of 600 feet or less for light-frame construction or 400 square feet or less for other than light-frame construction with an eave height of 10 feet or less.
Footings that are on granular soils (soils consisting mainly of sands and gravels), must be located so that the line drawn between the lower edge of adjoining footings will not have a steeper slope more than 30 degrees with the horizontal, unless the material supporting the higher footing is braced or retained or otherwise laterally supported in an approved manner. For the most part, buildings that are below slopes are set apart from the slope at an acceptable distance from the slope for protection from slope drainage.
In cases where the existing slope is steeper than one unit vertical in one unit horizontal, the toe of the slope is to be assumed to be at the foundation.
Most wet basements are caused by surface water which is not adequately drained from the foundation wall. On graded sites, the top of the exterior foundation is to extend above the elevation of the street gutter from an approved drainage device. Alternate elevations are allowed with permission of the building official if you can demonstrate that required drainage to the point of discharge and away from the structure is provided at all locations.
An alternate setback and clearance are also allowed, but, once again, with the building official’s permission. The official has the authority to request an investigation and recommendation of a registered design professional to demonstrate that the intent has been satisfied. Any investigation of this request includes the consideration of material, height of the slope and slope gradient, load intensity, and erosion characteristics of any materials used for the slope.
Footings are to have a minimum width of 12 inches. Structural Design, contains provisions for unfavorable effects due to the combinations of load and footings. The dead load is permitted to include the weight of foundations, footings, and overlying fill. Reduced live loads are allowed to be used in the design of footings.
When machinery operations or other vibrations are sent through the foundation, you must give consideration in the footing design to prevent detrimental disturbances of the soil. There is much to learn and understand about vibratory loads to concrete footings. Design, materials, and construction of concrete footings not only have to comply with this chapter, but to concrete requirements as well. Please be aware though, that in instances where a specific design is not provided, concrete footings that support walls that are made of light-frame construction can be designed in accordance with the code, and all concrete in footings must have a specified compressive strength of no less than 2500 pounds per square inch at 28 days.
It is important that you do not place concrete footings through water. You may seek permission from the building official if you are using a funnel or some other method. The key is to get the building official to give you approval to use a funnel to place concrete. You must be sure to protect concrete from freezing during the time that you are placing it and for a total of no less than five days thereafter. Under no circumstance is water allowed to flow through concrete that has been laid in the ground. Next we will examine foundation walls.
When you have a difference in height between the exterior finish ground level and the lower of the top of the concrete footing that supports the foundation you end up with an unbalanced backfill height. There are instances when an unbalanced backfill height is permitted, such as where an interior concrete slab on grade is provided and is in contact with the interior surface of the foundation wall. And foundation walls of rough or random rubble stone cannot be less than 16 inches thick and rubble stone cannot be used for foundations for structures in Seismic Design Category C, D, E, or F.
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Plain concrete footings that support walls for something other than light-frame construction cannot have an edge thickness of less than 8 inches placed on soil. The exception being that plain concrete footings that support Group R-3 Occupancies can have an edge thickness of only 6 inches, but only when the footing does not extend beyond the thickness of the footing on either side. |
Foundation wall materials such as concrete must be constructed in accordance with the code and with the following list:
The size and spacing of vertical reinforcement is based on the use of reinforcement with minimum yield strength of 60,000 psi, or vertical reinforcement with minimum yield strength of 40,000 psi. 50,000 psi is permitted, provided the same size bar is used and the spacing shown in the table is reduced by multiplying the spacing by 0.67 or 0.83.
Vertical reinforcement, when required, must be placed nearest the inside face of the wall a distance from the outside face of the wall. The distance is equal to the wall thickness, minus 1.25 inches plus one-half the bar diameter. The reinforcement must be placed within a tolerance of 
inch where the distance is less than or equal to 8 inches.
Instead of the support shown in some parts of the code, smaller reinforcing bar sizes with closer spaces can be used if this provides an equal amount of reinforcement.
Any concrete covering used for reinforcement that is measured from the inside face of the wall cannot be less than ½ inch. If measured from the inside face of the wall, the measurement cannot be less than 1.5 inches for no. 5 bars; 2 inches for smaller bars.
Concrete must have a specified compressive strength of not less than 2500 psi at 28 days.
Just like concrete foundation walls, masonry foundation walls must comply with similar standards:
The minimum vertical reinforcement for masonry foundations will have a strength of 60,000 psi.
The specified location of the reinforcement has to be equal or greater to the depth distance as stated in the code.
Masonry units must be installed with Type M or S mortar.
This section starts with some definitions that pertain to the code requirements of the International Building Code book. You will see these words used frequently in this section so it’s good that you have the definitions to refer to when needed.
Flexural length is the length of the pile from the first point of zero lateral deflection to the underside of the pile cap or grade beam.
Micropiles are 12-inch-diameter or less bored, grouted-in-place piles incorporating steel pipe (casing) and/or steel reinforcement.
Pier foundations consist of isolated masonry or cast-in-place concrete structural elements extending into firm materials.
Piers are relatively short in comparison to their width, with lengths less than or equal to 12 times the least horizontal dimension of the pier. Piers derive their load-carrying capacity through skin friction, end bearing, or a combination of both.
Pile foundations consist of concrete, wood, or steel structural elements either driven into the ground or cast in place.
Piles are relatively slender in comparison to their length, with lengths exceeding 12 times the least horizontal dimension.
Piles derive their load-carrying capacity through skin friction, end bearing or a combination of both.
The general requirements for piers and piles must follow the provisions of this section where Group R-3 and U occupancies do not exceed two stories of light-frame construction or where the surrounding foundation materials furnish adequate lateral support for the pile. These are subject to the approval of the building official. You must design and install your pier and pile foundations on the basis of a foundation investigation (this was defined earlier in the chapter), unless you have sufficient data on which to base your design and installation. An investigation and report is expanded for pier and pile foundations to include the following list (keep in mind though that this list is not limited and the building official may require additional information):
Recommended pier or pile types and installed capacities
Recommended center-to-center spacing of piers or piles
Driving criteria
Installation procedures
Field inspection and reporting procedures (to include procedures for verification of the installed bearing capacity where required)
Pier or pile load test requirements
Durability of pier or pile materials
Designation of bearing stratum or strata
Reductions for group action, where necessary.
There are special types of piles that are not specifically mentioned in this code that can be used. However, you must submit acceptable test data, calculations, and other information that relates to the structural properties and load capacity of such piles. It is only after the building official reviews and approves such information that you will be allowed to use the special pile. In any case, the allowable stresses cannot exceed the limitations that have been set.
You must brace all piers and piles to provide lateral stability in all directions. To be considered braced, three or more piles must be connected by a rigid cap, provided that the piles are located in radial directions from the center of mass of the group not less than 60 degrees apart. A two-pile group in a rigid cap is also considered to be braced along the axis connecting the two piles. Any methods that are used to brace piers or piles must be subject to the approval of the building official. Be careful when installing piers and piles.
Any disturbance in the required sequence of the required installation can cause distortion and damage and can adversely affect the structural integrity of piles that you are currently installing or ones that are already in place. The International Building Code will allow you to reuse existing piers or piles under certain circumstances and only with the approval of the building official. You will have to submit evidence that the piers or piles are sound and meet all requirements of this code.
All exiting piers and piles have to be load tested or redriven to verify their capabilities as well. The design load applied to such piers or piles must be the lowest allowable load as determined by such tests. There is an approved formula along with load tests or methods of analysis to determine the allowable axial and lateral loads on piers or piles. The allowable compressive load on any pile where determined by the application of an approved driving formula can not be more than 40 tons. You must use the wave equation method of analysis for allowable loads over 40 tons to estimate pile drivability of both driving stresses and net displacement per blow at the ultimate load. To use a follower you must obtain permission from the building official and you cannot use a fresh hammer cushion or pile cushion material just prior to final penetration.
When there is any doubt regarding design load for any pier or pile foundation, testing must be done in accordance with ASTM D 1143 or ASTM D 4945. The following are allowable methods of load test evaluations that are permitted to be used:
Davisson Offset Limit
Brinch-Hansen 90 Percent Criterion
Butler-Hoy Criterion
Other methods approved by the building official.
Piers, individual piles, and group of piles must develop ultimate load capacities of at least twice the design working loads in the designated load-bearing layers. And load-bearing capacities of piers or piles that are discovered to have a sharp or sweeping bend will be determined by an approved method of analysis or by load testing a representative pier or pile. The maximum compressive load on any pier or pile due to mislocation cannot be more than 110 percent of the allowable design load. All piers and piles need proper lateral support to prevent buckling and to allow the design of the pier or pile. This support must be in accordance with accepted engineering practice and provisions of this code.
In addition to learning about allowable pier and pile loads one must be aware of the requirements for seismic design of piers and piles. In the first part of this section you will learn about Seismic Design Category C. (Categories D, E, and F will follow shortly thereafter). Individual pile caps, piers, or piles must be interconnected by ties. These ties must be capable of carrying a force equal to the product of the larger pile cap or column load times the seismic coefficient divided by 10. This can be disregarded only if you can demonstrate that equal restraint is provided with reinforced concrete beams within slabs on grade, reinforced concrete slabs on grade, or very dense granular soils. The code provides an exception to this that states, “Piers supporting foundation walls, isolated interior post detailed so the pier is not subject to lateral loads, lightly loaded exterior decks and patios of Group R-3 and U occupancies not exceeding two stories of light-frame construction, are not subject to interconnection if it can be shown the soils are of adequate stiffness, subject to the approval of the building official.”
Seismic category structures must connect concrete piles and concrete-filled steel pipe piles to the pile cap by embedding the pile reinforcement or field-placed dowels anchored in the concrete pile. This must be embedded for a distance that is equal to the development length. For deformed bars this means the development length is the full development length for a compression or tension. You must be sure that the ends of hoops, spirals, and ties are terminated with seismic hooks.
The American Concrete Institute (ACI) 318, Building Code Requirements for Structural Concrete, Section 21.1 defines this with more clarity and I recommend that you refer to this when terminating these ends. Please note that anchorage of concrete-steel pipe piles is allowed to be done using deformed bars developed into the concrete portion of the pile. Structures that are assigned to Seismic Design Category C must follow design details.
Pier or pile moments, shears, and lateral deflections used for design have to be established considering the nonlinear interaction of the shaft and soil, as recommended by a registered design professional. A pile may be assumed to be rigid if the ratio of the depth of embedment of the pile-to-pile diameter or width is less than or equal to six. You must always include pile group effects from soil on lateral pile nominal strengths where pile center-to-center spacing in the direction of lateral force is less than eight pile diameters. The same is true for vertical pile strength where center-to-center spacing is less than three pile diameters.
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Unbraced piles in air, water, or in fluid soils have to be designed as columns in accordance with the provisions of this code. Piles that are driven into firm ground are considered to be fixed and laterally supported at 5 feet below the ground surface; in soft material at 10 feet. The building official does have the authority to make any alterations to this after a foundation investigation by an approved agency. |
The second part of seismic design of piers of piles is for those structures that have be assigned to Seismic Design Category D, E, or F. In addition to this section, Seismic Design Categories D, E, or F must adhere to the requirements for Seismic Design Category C too. Provisions of The American Concrete Institute (ACI) 318, Building Code Requirements for Structural Concrete, Section 21.10.4 must apply when not in conflict with this chapter. Concrete for category D, E, or F must have a specified compressive strength of not less than 3000 psi at 28 days. Please see the following list for exceptions to the above:
Group R or U occupancies of light-frame construction and two stories or less in height are allowed to use concrete with a specified compressive strength of not less than 2500 psi at 28 days.
Detached one- and two-family dwellings of light-frame construction and two stories or less in height are not required to comply with the provisions of ACI 318, Section 21.10.4.
Section 21.10.4 of ACI 318 does not apply to concrete piles.
The design details of piers, piles, and grade beams have to be designed and constructed to withstand maximum imposed curvatures from earthquake and ground motions and structure response. Curvatures must include free-field soil strains that have been modified from soil-pile-structure interaction. Site Class E or F sites have to be designed and detailed in accordance with ACI 318, Sections 21.4.4.1, 21.4.4.2 and 21.4.4.3 within seven pile diameters of the pile cap and the interfaces of soft to prestressed concrete piles. ACI 318 dictates many provisions regarding seismic design, including grade beams. However, grade beams that have the capacity to resist the forces from load combinations do not need to conform to ACI 318.
For piles that are required to resist uplift forces or provide rotational restraint, design of anchorage of piles into the pile cap has to be provided considering the combined effect of axial forces. The minimum of 25 percent of the strength of the pile in tension must include anchorage. Anchorage into the pile cap must be capable of developing the following:
In the case of uplift, the lesser of the nominal tensile strength of the longitudinal reinforcement in a concrete pile, or the nominal tensile strength of a steel pile, or the pile uplift soil nominal strength factored by 1.3, or the axial tension force resulting from the load combinations
In the case of rotational restraint, the lesser of the axial and shear forces and moments resulting from the load combinations or development of full axial and shear nominal strength of the pile.
If the vertical lateral-force-resisting elements are columns, the grade beam or pile cap flexural strengths must exceed the column flexural strength. The connections between batter piles and grade beams or pile caps must be designed to resist the nominal strength of the pile acting as a short column. Batter piles and connections must be capable of resisting forces and moments from the load combinations.
Timber is strong, light in weight, and capable of adequate support. Timber piles are round, tapered timbers with the small end embedded into the soil. Timber piles used to support permanent structures are to be treated in accordance with this section and must be designed in accordance with AFPA NDS (American Forest and Paper Association). Round timber piles must conform to ASTM D 25 while sawn timber piles must conform to DOC PS-20 (Department of Congress). Timber piles that are used for support in permanent structures must comply with this section. If it is established that you will be using the tops of the untreated timber piles below the lowest ground-water level assumed to exist during the life of the lowest structure, only then do timber piles not have to comply with this section.
The AWPA U1 (Commodity Specifications E, Use Category 4C) contains very important information to refer to for driven pile foundations. When working with timber piles and suddenly noticing an increase in rate of penetration you must conduct an investigation for possible damage. If the sudden increase in rate of penetration is not related to soil strata, you must remove the pile for inspection, or if non-viable the timber pile must be rejected.
The second type of driven pile foundations that we will review is precast concrete piles. Precast concrete piles have to comply with design and manufacture, must be of a minimum dimension, and must comply with reinforcement and installation requirements.
To resist all stresses brought on by handling, driving, and service loads; piles must be designed and manufactured in accordance with accepted engineering practices. Concrete piles must have a minimum lateral dimension of 8 inches and corners of square piles must be chamfered, which means to have a bevel or groove and the longitudinal reinforcement must be at least 0.8 percent of the concrete section and consist of at least four bars. You must never drive a precast concrete pile before the concrete has attained a compressive strength of at least 75 percent of the 28-day specified compressive strength, but no less than the strength sufficient enough to withstand handling and driving force.
Micropiles are 12-inch-diameter or less bored, grouted-in-place piles incorporating steel pipe (casing) and/or steel reinforcement. There has been a change in the code regarding micropiles and in this section I have covered all of these changes. Keep your eyes open for any details that pertain to your construction or building needs and as always ask your local building official to clarify any questions that you may have regarding this code.
Micropiles must have a grouted section reinforced with steel pipe or steel reinforcing. Micropiles develop their load-carrying capacity through soil, bedrock, or a combination of soil and bedrock. The full length of the micropile must contain either a steel pipe or steel reinforcement. One of the materials used with micropiles is grout.
Grout must have a 28-day specified compressive strength no less than 4,000 psi. As with all piles, micropiles too must be reinforced. For piles or portions of piles grouted inside a temporary or permanent casing or inside a hole drilled into bedrock, the steel pipe or reinforcement must be designed to carry at least 40 percent of the design compression load.
You can use rotary or percussive drilling as a method, with or without casing, to form a hole for the pile. The pile must be grouted using a fluid cement grout and pumped through a tremie pipe that extends to the bottom of the pile until the grout comes back up to the top. There are eight requirements of this code that must be applied to specific installation methods:
For piles grouted inside a temporary casing, the reinforcing steel must be inserted prior to withdrawal of the casing.
The casing must be withdrawn in a controlled manner with the grout level maintained at the top of the pile to ensure that the grout completely fills the drill hole.
Make sure you monitor the grout level inside the casing when you are withdrawing the casing so you can see that there is nothing obstructing the flow of the grout.
You must verify the design diameter of the drill hole for a pile that is grouted in an open drill hole in soil without temporary casing.
By using a suitable means for piles designed for end bearing you will be verifying that the bearing surface is properly cleaned prior to grouting.
Subsequent piles cannot be drilled near piles that have been grouted until the grout has had enough time to harden.
You must grout piles as soon as possible after you have completed drilling.
For piles designed with casing full length, the casing must be pulled back to the top of the bond zone and reinserted to verify grout coverage outside the casing.
Isolated piers used as foundation must comply with minimum dimensions of 2 feet with the height not exceeding 12 times the least horizontal dimension. Reinforcements where required must be assembled and tied together and must be placed in the pier hole as a unit before the reinforced portion of the pier is filled with concrete. This does not apply to steel dowels that have been embedded 5 feet or less in the pier. Please note this exception: Reinforcement is permitted to be wet set and the 2 ½ -inch concrete cover requirements can be reduced to 2 inches for Group R-3 and U occupancies that are not more than two stories of light-frame construction, provided that the construction method can be demonstrated to the satisfaction of the building official.
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Where a steel pipe is used for reinforcement, the portion of the cement grout enclosed within the pipe is permitted to be included at the allowable stress of the grout. The provisions for seismic reinforcement differ from above. Any building or structure that is deemed to be of Seismic Design Category C must have a permanent steel casing from the top of the pile down 120 percent times the flexural length. If a building or structure is of Seismic Design Category D, E, or F, this pile will be considered as an alternative system. |
When placing concrete you have to do so in such a way that any foreign matter is taken out and to secure a full-sized shaft. You may not place concrete through water unless a tremie or other method has been approved. Do not just chute the concrete directly into the pier. Concrete must be poured in a rapid and continuous operation through a funnel hopper that you have placed in the center at the top of the pier. If you find that the pier foundation has belled at the bottom, you must check to see that the edge thickness of the bell is not less than what is required for the edge of footings.
This chapter taught us many things about soils and foundations and the do’s and don’t of piers and pile foundations. It has referred you to other publications which go into greater detail regarding concrete and the provisions that you must follow while building your foundations.
