210 - Foundations

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210.2 - DEFINITIONS

SPECIFICATIONS COMMENTARY
The following shall supplement A10.2:

FHWA DCDPF – NHI 05-042 Design and Construction of Driven Pile Foundations

FHWA DCMSEFHWA NHI-10-025/ FHWA GEC 011 – Vol II, Design and Construction of Mechanically Stabilized Earth Walls and Reinforced Soil Slopes – Volume II

FHWA NGCAW – FHWA NHI-07-071 Earth Retaining Structures

FHWA RBOC – FHWA-HI-92-001 Rock Blasting and Overbreak Control

FHWA SF – FHWA-NHI-06-088 Soils and Foundations

FHWA TMDCRT – FHWA NHI-09-010 Technical Manual for Design and Construction of Road Tunnels Civil Elements

210.4 - SOIL AND ROCK PROPERTIES

210.4.2 - Subsurface Exploration

SPECIFICATIONS COMMENTARY
The following shall supplement A10.4.2:

Conduct subsurface investigation in accordance with Section 105 – Geotechnical Investigations.

The number of borings per substructure and boring depths shall be determined in accordance with Section 105 – Geotechnical Investigations.

210.4.3 - Laboratory Test

SPECIFICATIONS COMMENTARY
The following shall supplement A10.4.3:

Prepare laboratory test programs in accordance with Section 105 – Geotechnical Investigations.\

210.4.6 - Selection of Design Properties

210.4.6.3 - Soil Deformation

SPECIFICATIONS COMMENTARY
The following shall supplement A10.4.6.3:

Consolidation settlement shall be considered for very soft to medium-stiff fine-grained soils, such as clays and silts. Elastic settlement should be considered for granular soils and stiff fine-grained soils.

210.4.7D - Running Sands

SPECIFICATIONS COMMENTARY
The term “running sands” typically refers to loosely packed granular deposits that become fluidized by water passing through them. They flow due to lack of confinement and excess pore water pressure. Although these materials are also prone to soil liquefaction, the term running sands is commonly applied for fluidization during soil excavation, and it is not related to application of seismic forces. As a result of soil excavation, a hydraulic gradient is induced, resulting in water flowing towards the bottom of the excavation. Running sands are typically observed as fluidized soils coming out of the bottom of the excavation (sand boils).

The following are typical indications of the potential for running sands. These criteria are based on previous experience by the Department and accepted practices (FHWA TMDCRT). Only soils satisfying all of the criteria listed below should be considered as potential running sands:

  • Granular soils with very loose to medium-dense relative density.
  • Soils classified as AASHTO A-1-b with less than 10 percent of fines (material passing the No. 200 sieve) regardless of relative density.
  • Soils that are in-situ saturated or will be saturated as a result of construction activities (excavation below the water table or below a stream, pond, or another body of water).

The potential for a soil to become running sand should be assessed depending on the encountered subsurface conditions and the planned construction activities, such as the depth of excavation and changes on the groundwater table (anticipated hydraulic gradient).

Previous experience, flow nets, or other analytical techniques can also be used to estimate this potential. Depending on the expected potential of soil to become running sand, the following steps should be considered during construction:

  • For soil with a low potential, create a firm base at the excavation by adding stone material. Undercut or overexcavate poor materials as necessary.
  • For soil with a moderate potential, increase resistance to water flow by increasing the embedment depth of sheeting/shoring. See FHWA NGCAW for recommended embedment values.
  • For soil with a high potential, add well points, sumps, or deep wells to lower the water table in the vicinity of the excavation. This can be done in addition to increasing the shoring embedment depth, depending on the conditions.

For moderate and high potential sites, underground utilities, relocations, and similar obstructions may preclude the use of sheeting/shoring. Underground relocations should be avoided at these work areas, if possible, or directed around the work area instead of under it.

The potential for running sands and corrective measures should be identified during the design phase. The proposed corrective measures should also be included as bid items. Not identifying the potential for running sands could result in unnecessary additional costs and time delays.

C210.4.7D

If soils are identified as potential running sands based on the criteria provided in this section (soil classification, content of fines, relative density, saturation), the level of potential for fluidization could be assessed based on the following criteria:

Low potential:

   -‎ Top of the stratum located below the bottom of the excavation.

   ‎- ‎Groundwater table expected to be at or slightly below the bottom of the excavation.

Moderate potential:

‎   - ‎Top of the stratum located at or above the bottom of the excavation.

   - ‎Groundwater table expected to be slightly above the bottom of the excavation.

   - ‎Expected hydraulic gradient of approximately 0.3 or less (see FHWA NGCAW and A11.6.3.4).

High potential:

   ‎- ‎Top of the stratum located at or above the bottom of the excavation.

‎   - ‎Groundwater table expected to be significantly above the bottom of the excavation.

  ‎ - ‎Expected hydraulic gradient of approximately 0.3 or greater. Note that for a loose soil, a hydraulic gradient of approximately 0.4 to      0.5 will not satisfy a factor of safety of 1.5 when compared to the critical hydraulic gradient (ic = effective unit weight / water unit      weight), and therefore a significant embedment depth of sheeting/shoring will be required. The water table may need to be      lowered in the vicinity of the excavation to reduce the hydraulic gradient.

210.5 - LIMIT STATES AND RESISTANCE FACTORS

210.5.1 - General

SPECIFICATIONS COMMENTARY
The following shall supplement A10.5.1:

The eccentricity of loading for spread footings shall be within the limits defined in Section 210.6.3.3. The eccentricity of loading for deep foundations (driven piles, drilled shafts, micropiles) is controlled by only allowing uplift on extreme event limit states. No uplift is permitted for deep foundation elements under service and strength limit states for regular bridge structures.

210.5.2 - Service Limit States

210.5.2.2 - Tolerable Movements and Movement Criteria

SPECIFICATIONS COMMENTARY
The following shall supplement A10.5.2.2:

Vibration Monitoring and Control

Instrument and monitor vibrations resulting from construction activities such as pile installation, shoring installation, excavation demolition, and rock blasting if the activities take place in close proximity to existing bridge substructures or urban environments (buildings and utilities).

Prior to construction, the Department will review the contractor’s Vibration Monitoring and Control Plan which, for approval, must include at a minimum the following:

  • Preconstruction report documenting the existing conditions of any structure within a radius of approximately 300 feet or as specified by the Department. Inspect and document through photographs, video, sketches, and/or any other applicable means. Document size and extent of any existing cracks or structural deficiencies.
  • Instrumentation program documenting equipment to be used for obtaining vibration measurements (e.g., seismographs) and locations to be monitored. Include anticipated frequency of data collection.
  • Description of procedures to be employed to prevent damage if the expected vibration is higher than the values described herein.

Use the following maximum permissible levels for Peak Particle Velocity (PPV):

  • 0.5 inch/second for normal residential structures, existing bridge substructures, existing pipes and culverts, and any other utilities.
  • 0.2 inch/second for structures already presenting structural deficiencies before construction activities, structures that are extremely sensitive to vibration, or structures on soils susceptible to densification by vibration (i.e., loose fill and running sands).
  • 2.0 inches/second for noncritical structures or structures designed to accommodate vibrations.

See FHWA DCDPF for more information regarding vibration monitoring and control for driven piles, and see FHWA RBOC for more information regarding vibrations during blasting operations. Note these references provide general guidance for estimation of PPV depending on geotechnical conditions and the vibration source.

210.5.5 - Resistance Factors

210.5.5.2 - Strength Limit States

210.5.5.2.3 - Driven Piles
SPECIFICATIONS COMMENTARY
The following shall supplement A10.5.5.2.3:

A minimum of two dynamic tests on production piles shall be provided per substructure. Additional dynamic tests should be considered if site conditions significantly vary on the substructure.

C210.5.5.2.3

For substructures with only one row of piles, this requirement can be waived and only one dynamic test on production piles shall be required. This is intended for smaller projects such as integral abutments where substructures have a single row of piles, typically with five to eight production piles.

210.6 - SPREAD FOOTINGS

210.6.1 - General Considerations

210.6.1.2 - Bearing Depth

SPECIFICATIONS COMMENTARY
The following shall replace A10.6.1.2:

The bottom of spread footings shall be below frost depth as specified in Section 107 – Final Design Considerations – Substructure. Also, the bottom shall satisfy scour requirements on stream environments per Section 107 – Final Design Considerations – Substructure.

210.6.3 - Strength Limit State Design

210.6.3.3 - Eccentric Load Limitations

SPECIFICATIONS COMMENTARY
The following shall replace A10.6.3.3: 

The eccentricity of loading at the strength limit state, evaluated based on factored loads, shall not exceed:

  • One-fourth of the corresponding footing dimension, B or L, for footings on soil (resultant force within the middle one-half of the corresponding footing dimension).
  • One-third of the corresponding footing dimension, B or L, for footings on rock (resultant force within the middle two-thirds of the corresponding footing dimension).

210.6.3.4 - Failure by Sliding

SPECIFICATIONS COMMENTARY
The following shall supplement A10.6.3.4:

Passive pressure resistance in front of regular spread footings shall be neglected for sliding considerations.

C210.6.3.4

The following shall supplement AC10.6.3.4:

Passive pressure developing in front of regular footings is typically neglected because of scour, erosion, or excavation trenches during the design life of the structure.

210.7 - DRIVEN PILES

210.7.1 - General

210.7.1.4 - Batter Piles

SPECIFICATIONS COMMENTARY
The following shall supplement A10.7.1.4:

Batter piles shall have a 1H:4V or 1H:3V batter.

210.7.1.6 - Determination of Pile Loads

210.7.1.6.2 - Downdrag
SPECIFICATIONS COMMENTARY
The following shall supplement A10.7.1.6.2

Downdrag and transient loads such as live loads should not be considered as acting simultaneously on any load combination. For the different load cases, use only the higher of these two factored loads (factored downdrag versus factored transient loads).

C210.7.1.6.2

Downdrag loads are associated with settlement of compressive soils around piles. Soils surrounding the piles experience settlement typically because of additional fill material placed adjacent to the pile foundation (e.g., approach embankments on bridge abutments). Settlement is due to dead loads that have been present for a continuous period of time, such as fill surcharge; it is not due to temporary transient loads. Therefore, transient loads should not be considered at the same time as downdrag loads.

As presented in AC3.11.8, transient loads can actually act to reduce the downdrag loads because they cause a downward movement of the pile, resulting in a temporary reduction or elimination of the downdrag force.

Possible measures to avoid downdrag include preloading of in-situ soils to induce settlement prior to pile installation (with or without wick drains to accelerate consolidation), applying bitumen or another viscous coating to the pile surfaces before installation, and installing piles through casing that isolates them from surrounding settling soil.

210.7.2 - Service Limit State Design

210.7.2.4 - Horizontal Pile Foundation Movement

SPECIFICATIONS COMMENTARY
The following shall supplement A10.7.2.4:

The values presented in Table A10.7.2.4-1 for pile P-multipliers shall only apply for substructures where the expected single-pile deflections are above 1 inch, or where the pile spacing in the direction parallel to the applied load is less than three times the pile diameter.

For substructures where the individual pile deflections are below 1 inch and the spacing of piles in the direction parallel to the load is greater than three times the pile diameter, these multipliers can be omitted (P-multiplier = 1.0).

C210.7.2.4

The multipliers presented in Table A10.7.2.4.1 were developed from FHWA DCDPF. The studies summarized in this document present deflections greater than 1 inch and are expected to represent significant stress overlaps between adjacent piles with displacements close to passive soil failure.

210.7.2.6 - Lateral Squeeze

SPECIFICATIONS COMMENTARY
The following shall supplement A10.7.2.6:

In addition to the reference presented by A10.7.2.6, refer to FHWA SF and FHWA DCMSE for identification of threshold conditions that could potentially result in lateral squeeze, for detailed evaluation of the safety factor against lateral squeeze, and for a means to estimate the horizontal movement due to lateral squeeze. Per FHWA DCMSE, consider a minimum acceptable factor of safety of 1.3 against lateral squeeze. Caution is advised and rigorous analyses (i.e., numerical modeling) shall be performed when the factor of safety against lateral squeeze is less than 2.0.

Lateral squeeze is not limited to pile foundations and fill embankments on top of soft soils. In general, it is a potential problem for soft foundation soil subjected to an unbalanced load at its surface.

Potential solutions to prevent lateral squeeze include but are not limited to:

  • Delayed installation of piles until settlement has stabilized. Consider staged construction and/or preloading.
  • Excavation and replacement of soft soils.
  • Provision of expansion shoes large enough to accommodate movement.
  • Consider lightweight fill to reduce driving forces.
  • Consider ground improvement techniques (e.g., accelerated drainage, reinforced soil, dynamic compaction).

210.7.3 - Strength Limit State Design

210.7.3.4 - Nominal Axial Resistance Change after Pile Driving

SPECIFICATIONS COMMENTARY
The following shall supplement A10.7.3.4:

If soil relaxation or setup is expected to occur during or shortly after pile driving, specify the minimum time for pile restrike of test piles, and if necessary, of production piles.

210.7.3.13 - Pile Structural Resistance

210.7.3.13.4 - Buckling and Lateral Stability
SPECIFICATIONS COMMENTARY
The following shall supplement A10.7.3.13.4:

Equations presented in AC10.7.3.13.4 should be used only for preliminary design. Depth to fixity for final design should be determined using a p-y curve computation.

210.7.5 - Corrosion and Deterioration

SPECIFICATIONS COMMENTARY
The following shall supplement A10.7.5:

See Section 107.3.5.4.1 – Concrete Footings, Piles, and Shafts for measures that shall be taken on all concrete elements used in corrosive environments.

See Section 107.3.5.4.2 – Steel Piles and Casings for measures that shall be taken on all steel piles and casings used in corrosive environments.

See Section 107.3.5.4.3 – Timber Piles for measures that shall be taken on all timber piles used in corrosive environments.

210.7.9 - Probe Piles

SPECIFICATIONS COMMENTARY
The following shall supplement A10.7.9:

A minimum of two test piles with dynamic testing should be performed per substructure bearing on piles (i.e., PDA and CAPWAP testing).

C210.7.9

For substructures with only one row of piles, only one test pile with dynamic testing is required. See Section C210.5.5.2.3.