User:Hoskir/Revision Request 4175

REVISION REQUEST 4175 (ON HOLD)

321.2.1.2 Types of Reports

1. The soil survey report touches on foundations by pointing out possible foundation problems. It also contains basic slope recommendations which affect bridge length, soil types and properties for pavement design, depths to rock and type of rock for determining cut quantities, and cut slope recommendations for soil and rock.

2. The preliminary bridge foundation report, which is submitted by the district as an adjunct to the soil survey report, is usually furnished to the Bridge Unit for their guidance in preparing preliminary bridge layouts and to the Materials Engineering Unit for guidance in conducting a more detailed foundation investigation. (Preliminary borings for such reports may be omitted where access problems are especially difficult.)

3. The final foundation investigation report will provide the requested properties from Form A of the Bridge Division Request for Soil Properties in accordance with EPG Sections 320, 321, 700 and other applicable sections. The report will also provide seismic properties as requested on Form B. The Bridge Division or District will provide the preliminary structure layout and location of each foundation location. The Geotechnical Section will determine boring locations and sampling frequency based on guidance in, EPG 321.2 Geotechnical Guidelines, and specific site conditions. The Geotechnical Section may make recommendations for specific foundation types if site conditions require special considerations. The intent is to provide the Bridge Division or District with the information needed to develop designs for the foundation types practical for a particular site. Rules of thumb as to what is practical have been developed jointly by the Geotechnical Section and the Bridge Division. These are discussed in the applicable sections within the EPG.

---

701 Drilled Shafts

Substructure foundations may be designed to transmit loads to foundation strata by concrete columns cast in drilled holes. See EPG 751.37 Drilled Shafts for design guidance and additional information.

This type of foundation is identified in Sec 701 of the Standard Specifications as Drilled Shafts. A drilled shaft is generally considered a deep foundation.

Drilled shafts for bridge structures:

Drilled shafts for bridge structures shall be constructed with a permanent casing and rock socketed. Requirements for plan reporting of steel casing are given in EPG 751.37.1.3 Casing.

The shaft portion of a drilled shaft is founded on rock (limestone, dolomite or other suitable material with q_u ≥ 100 ksf) or weak rock (shale or other suitable material with 5 ksf ≤ q_u ≤ 100 ksf) with a smaller diameter rock socket drilled into same. The inspector should carefully study all general specifications and special provisions pertaining to drilled shafts and become familiar with the designer's intent.

The integrity of the rock socket shall be verified by a foundation inspection hole. This is usually performed after the shaft is drilled. Setting up over a drilled hole can be difficult. The contractor can perform the inspection hole in advance if they submit a procedure that assures the correct location is cored. If the integrity of the cores are questionable the Bridge Division should be contacted to see if the rock socket length should be extended.

Most problems with drilled shafts occur during the concrete pour. The concrete placement requirements in Sec 701 should be reviewed carefully.

An anomaly may be detected on a Cross Hole Sonic log test. If, on further investigation, there is a confirmed defect what are some of the steps needed to remediate the defect?

1. The contractor is responsible for submitting a remediation plan for the repair.

2. The plan should include as a minimum the following:

a) The area of deficient material must be clearly defined using coring or other means.

b) The clean-out process is typically accomplished by flushing the weak material. The access holes needed, water pressure used, and disposal of the soils should be addressed.

c) Confirmation of the deficient material removal must be made. This can be accomplished by camera inspection, CSL, or by other means acceptable to the engineer.

d) The grouting plan should include: grouting type, grout mix design including w/c ratio, complete pressure grouting timeline. The grouting timeline should include placement times, pressure, volume, refusal criteria.

3. A final confirmation of the effectiveness of the grouting should be made. This is typically accomplished by coring. The number of cores required, and depth shall be submitted to the engineer for approval prior to coring. If all the CSL tubes are still usable, a final CSL can be made for acceptance. The engineer of record for the design should be consulted for final acceptance.

Question: Per Sec 701.4.17.2.1 Installation of Pipes, “The pipes shall be filled with water and plugged or capped before shaft concrete is poured.” Why is this necessary?

The water in the tube helps to regulate the temperature of the CSL tube. Without the water, the tube will heat up from the hydrating concrete and cause de-bonding. This de-bonding from the concrete will cause erroneous CSL readings and show up as an anomaly. Typically, de-bonding is more prevalent in the upper 6 ft. of the tube. The water also serves a second purpose: it helps the energy transmission from the wall of the tube to the probes and vice versa.

Drilled shafts for non-bridge structures:

Drilled shafts for non-bridge structures are typically designed and constructed without casing. Permanent casing is not allowed except for special designs.

The shafts may be embedded into rock when soil overburden depth is inadequate for properly anchoring the foundation. If overburden soils are unstable and conduit access is not required in the perimeter of the shaft, temporary casing may be used with an oversized shaft to allow excavation into rock at the required diameter.

---

751.1.2.20 Substructure Type

Once the signed Bridge Memo and the Borings are received, the entire layout folder should be given to the Preliminary Detailer (requested by SPM, assigned by Structural Resource Manager). The Preliminary Detailer will copy the appropriate MicroStation drawings into their own directory. (Do not rename files) Consultants contact Structural Liaison Engineer. The Preliminary Detailer will then draw the proposed bridge on the plat and profile sheets. The bridge should also be drawn on the contracted profile for a perspective of the profile grade relative to the ground line for drainage considerations. The Preliminary Detailer will also generate a draft Design Layout Sheet and then return the layout folder to the Preliminary Designer for review.

The Preliminary Designer will then choose the substructure types for each of the bents. Pile cap bents without concrete encasement are less expensive than column bents but they should not be used at the following locations:

• Where drift has been identified as a problem
• Where the height of the unbraced piling is excessive and kl/r exceeds 120 (kl/r<120 is generally preferred) (take scour into account)
• Where the bent is adjacent to traffic (grade separations)

Encased pile cap bents may be considered if economical. Embed concrete encasement 2 ft. (minimum) below the top of the lowest finished groundline elevation, unless a greater embedment is required for bridge scour. Greater embedment up to 5 or 6 ft. may be considered in situations where anticipated ground line elevation can fluctuate more severely. (Be sure to account for excavation quantities for deeper embedment.) Provision for encasing piles may be considered at the following locations:

• Where drift is a concern and protection is required
• Where larger radius of gyration is necessary and therefore improved buckling resistance for locations where the exposed unbraced column length is large
• Not exclusively where the piles at the pile/wall interface may experience wet/dry cycles and/or excessive periods of ground moisture

For column bents, an economic analysis should be performed to compare drilled shafts to footings. Footings are not recommended for stream crossings where scour potential is identified. For grade separations, assume the top of drilled shaft casing is located at least one foot below the ground line. For shallow rock conditions, consideration should also be given to eliminating the cased portion of the shaft and placing the column directly over an oversized rock socket. Top of drilled shaft casing for stream crossings should consider the following criteria, and with SPM or SLE approval, select the appropriate elevation to balance risk for the anticipated conditions at time of construction:

• 10-year flood elevation
• 1 foot above ordinary high water elevation
• Elevation of nearest overbank
• 3 feet above low water elevation

End Bents are usually pile cap bents; however, if quality rock is abundant at or just below the bottom of beam elevation, a stub end bent on spread footings may be used. If you have any doubt about the suitability and uniformity of the rock, you can still use a pile cap end bent. Just include prebore to get a minimum of 10 ft. of piling. If you have concerns about temperature movements, you can require that the prebore holes be oversized to allow for this movement.

For any pile cap bents, where steel piles are to be placed near a fluctuating water line or near a ground line where aggressive soil conditions exist or anticipated to exist in the future, corrosion can result in substantial material loss in pile sections over time, either slowly or rapidly. Galvanized steel piling is required for all new pile cap bents to be used as a deterrent to both accelerated and incidental pile corrosion as commonly seen in the field. Further, conditions like known in corrosive soils, some stream crossings with known history of effects on steel piles and grounds subject to stray currents, these conditions should affect the decision of whether pile cap bents can be effectively utilized. The potential effects of corrosion and the potential deterioration from environmental conditions should always be considered in the determination and selection of the steel pile type and steel pile cross-section (size of HP pile or casing thickness), and in considering the long-term durability of the pile type in service.

Once the substructure type has been determined, re-examine your Preliminary Cost Estimate and notify the district if it needs to be adjusted.

Galvanized Steel Piles

Galvanizing shall be required for all steel piles. Utilizing galvanized steel piles and pile bracing members shall be in addition to the requirements of Standard Specifications Sec 702 except that protective coatings specified in Sec 702 will not be required for galvanized piles or galvanized bracing members.

Where galvanized steel piling is expected to be exposed to severe corrosive conditions, consideration can be given to increased steel pile thickness or consideration of a reduced loaded steel area for bearing, or conditions mitigated to prevent long term corrosivity risk . This equally applies to the potential corrosion and early deterioration of permanent steel casing used for drilled shafts though they are not required to be galvanized. For all cases, further consideration beyond normal practice should be given to investigating corrosion protection, rate of corrosion as it relates to steel thickness design and expected service life including galvanizing losses, corrosion mitigation or different substructure support in order to meet a 75 year or longer design life. For additional information refer to LRFD 10.7.5 and 10.8.1.5. Consult with the Structural Project Manager or Structural Liaison Engineer to determine options and strategy for implementation.

All Bridge and Retaining Wall Piles (For Example, abutment piles, wing wall piles, intermediate pile cap bent piles and pile cap footing piles)

All surfaces of piles shall be galvanized to a minimum galvanized penetration (elevation) or its full length based on the following guidance. The minimum galvanized penetration (elevation) shall be estimated in preliminary design and finalized in final design. The minimum galvanized penetration (elevation) or full length will be shown on the design layout.

Guidance for determining minimum galvanized penetration (elevation):

The designer shall establish the limits of galvanized structural steel pile (i.e., HP pile and CIP pile). All exposed pile plus any required length below ground shall be galvanized. Based on required galvanized pile length determine and show Minimum Galvanized Penetration (Elevation) or Full Length on the Design Layout and on the plans.

When glacial material or other hard material is identified in the geotechnical report discuss with SPM and consider galvanizing full length of pile to avoid the scenario where friction pile may potentially be cut-off once the geotechnical capacity is reached but the depth for galvanization is inadequate.

	Required Pile Galvanizing For Nonscour	Required Pile Galvanizing For Channel Scour	Required Pile Galvanizing For Channel Migration
Estimated Pile Length ≤ 50 feet	Full Length of Pile	Full Length of Pile	Full Length of Pile
Estimated Pile Length > 50 feet	20 feet (in ground)1	20 feet (in ground)1, but not less than 5 feet below max. scour depth.	20 feet (in ground)1, but not less than 5 feet below stream bed elev.
1 “In ground” is measured from finished ground line on intermediate bents, and bottom of beam cap for abutments.

For retaining walls supported on piles, the minimum galvanized penetration (elevation) for piles shall be “Full Length of Pile” for estimated pile length up to 50 feet and 15 feet below bottom of wall for estimated pile length greater than 50 feet.

For bridge end bents on piles with embankments supported by MSE walls, the minimum galvanized penetration (elevation) for piles shall be “Full Length of Pile” for estimated pile length up to 50 feet and 15 feet below top of leveling pad for estimated pile length greater than 50 feet.

Temporary Bridge Piles

Protective coatings are not required in accordance with Sec 718. Galvanized pile is not required. All HP piles driven to rock shall require pile point reinforcement.

---

751.1.2.24 Drilled Shafts

Drilled shafts are to be used when their cost is comparable to that of large cofferdams and footings. Other examples include when there are subsurface items to avoid (culverts, utilities, etc.) or when there are extremely high soil pressures due to slope failures.

Drilled shafts shall be constructed with a permanent casing and rock socketed.

The Final Foundation Investigation Report (or geotechnical report) for drilled shafts should supply you with the anticipated tip of casing, nominal tip resistance, nominal tip resistance factor, nominal side resistance, nominal side resistance factor as well as the recommended elevations for which the resistance values are applicable.

The Design Layout Sheet should include the following information:

• Top of Drilled Shaft Elevation
• Anticipated Tip of Casing Elevation
• Anticipated Top of Sound Rock Elevation

Bent	Elevation	Nominal Axial Compressive Resistance (Side Resistance) (ksf)	Side Resistance Factor for Strength Limit State	Nominal Axial Compressive Resistance (Tip Resistance) (ksf)	Tip Resistance Factors for Strength Limit States

---

751.4.1 Reinforced Concrete

Classes of Reinforced Concrete

Below are classes of concrete for each type or portion of structure:

Box Culverts		B-1
Retaining Walls		B or B-1
Superstructure (General)		B-2
	Curbs and Parapets	B-1
	Type A, B, C, D, G and H Barriers	B-1
	Sidewalks	B-2
	Raised Median	B-2
	Slabs	B-2
	Box Girders	B-2
	Deck Girders	B-2
	Prestressed Precast Panels	A-1
	Prestressed I - Girders	A-1
	Prestressed Double -Tee Girders	A-1
	Integral End Bents (Above lower construction joint)	B-2
	Semi-Deep Abutments (Above construction joint under slab)	B-2
Substructure (General)		B
	Integral End Bents (Below lower construction joint)	B
	Non-Integral End Bents	B
	Semi-Deep Abutments (Below construction joint under slab)	B
	Intermediate Bents	B (*)
	Intermediate Bent Columns, End Bents (Below construction joint at bottom of slab in Cont. Conc. Slab Bridges)	B-1
	Footings	B
	Drilled Shafts (except per Standard Plans 903.15)	B-2
	Drilled Shafts (per Standard Plans 903.15)	B
	Cast-In-Place Pile	B-1
(*) In special cases when a stronger concrete is necessary for design, Class B-1 may be considered for intermediate bents (caps, columns, tie beams, web beams, collision walls and/or footings).

Unit Stresses of Reinforced Concrete

Class of Concrete	Aggregate Maximumsize (Inches)	Cement Factor (barrels percubic yard)	$f^{\prime }c$ (psi)	$fc$ (psi)	$n$ (*)	$E_c$ (ksi)
A-1	3/4	1.6 (Min.)	5,000	2,000	6	4074
B	1	1.4 (Min.)	3,000	1,200	10	3156
B-1	1	1.6 (Min.)	4,000	1,600	8	3644
B-2	1	1.875 (Min.)	4,000	1,600	8	3644

(*) Values of n for computations of strength only.

Reinforcing Steel
Reinforcing Steel (Grade 60)	$F_y$ = 60 ksi

---

751.37.1.2 Materials

Commentary for EPG 751.37.1.2 Materials

Concrete used for drilled shaft for traffic structures in accordance with standard plan 903.15 shall be Class B concrete with minimum compressive strength, f’_c = 3 ksi. For all other drilled shaft construction concrete shall be Class B-2 with minimum compressive strength, f’_c = 4 ksi.

---

751.37.1.3 Casing

Commentary for EPG 751.37.1.3 Casing

Drilled shafts for bridge structures:

All drilled shafts shall have permanent casing installed through overburden soils to prevent caving of these soils during construction. Drilled shafts shall be socketed into bedrock. Welded or seamless steel permanent casing shall be in accordance with Sec 701.

Rock sockets shall be uncased.

Permanent Casing Thickness Design and Plan Reporting:

Any drilled shaft for a major bridge over a river or lake or any drilled shaft longer than 80 feet or any drilled shaft greater than 6 feet in diameter shall have a minimum casing thickness of 1/2 inch specified unless a greater thickness is required by design for strength. The thickness of casing in either case shall be shown on the bridge plans and noted as a minimum.

All other drilled shafts shall not have a minimum casing thickness specified unless a specific thickness is required by design for strength. The minimum thickness in the latter case shall be shown on the bridge plans and noted as a minimum.

For drilled shaft stiffness computations and load distribution analysis, use the minimum casing thickness required. When a minimum casing thickness is not required, assume a casing thickness of 3/8” for the analysis.

---

751.37.1.5 Related Provisions

Commentary for EPG 751.37.1.5 Related Provisions

The provisions of these guidelines were developed presuming that design parameters required to apply the provisions are established following current MoDOT site characterization protocols as described in EPG 321. Specific attention is drawn to EPG 321.3 Procedures for Estimation of Geotechnical Parameter Values and Coefficients of Variation. The provisions provided in these guidelines presume that parameter variability, as generally represented by the coefficient of variation (COV), is established following procedures in EPG 321.3.

Sign structure drilled shaft supports are the exception. Sign structure standard drilled shafts are developed using assumed soil properties and following AASHTO LRFD Bridge Design Specifications 9^th Edition for design. Site specific designs for drilled shafts for sign structure support may also follow AASHTO LRFD Bridge Design Specifications 9^th Edition if there is not enough geotechnical information available to establish the COV.

---

751.37.1.6 Drilled Shaft General Detail Considerations

For Seismic detail requirements for seismic design category, SDC B, C and D, See EPG 751.9.1.2 LRFD Seismic Details.

Pay items shown in above table are for example only, show actual pay items and quantities in plan details for specific project.

Notes:

(1) Number of pipes (equally spaced) for Sonic Logging Testing (for bridge structures only):

Diameter ≤ 2.5 ft: 2 pipes

Diameter >2.5 ft but ≤ 3.5 ft: 3 pipes

Diameter >3.5 ft but ≤ 5.0 ft: 4 pipes

Diameter >5.0 ft but ≤ 8.0 ft: 5 pipes

Diameter >8.0 ft: 6 pipes

Single diameter reinforcing cage is typically used. Modify details based on design for single or multiple-diameter cages and splice location(s).

See EPG 751.37.1.3 for casing requirements for bridge structures and non-bridge structures.

When determining P bar diameter for barbill, assume 3/8” casing unless otherwise specified.

See EPG 751.50, G8, for notes to include for drilled shafts and rock sockets (starting at G8.1).

(2) See EPG 751.37.1.1 Dimensions and Nomenclature for Design Aid: Minimum Rock Socket Length.

(3) When difference between drilled shaft and column diameter is 6" a single reinforcement cage is typically used for the socket and shaft and the vertical reinforcement extends into the column. A separate column steel cage is then placed around the protruding shaft reinforcement without requiring an adjustment to minimum cover for rock socket or column reinforcement. When difference between drilled shaft and column diameter is 12” either the vertical column steel or dowels will need to be extended into the shaft or the cover in the socket and shaft will need to be increased to allow the shaft reinforcement to extend into the column. In the former scenario an optional construction joint is recommended as discussed in note 4 for oversized shafts. In the latter scenario the same number of vertical bars should be used in the shaft and column to allow the shaft bars to be tied to the column cage. Any reduction in cage diameter required for fit-up shall be considered in design.

(4) When difference between drilled shaft and column diameter is greater than 12" (oversized shaft generally 18" to 24" larger than column), show "Optional construction joint" at bottom of column/dowel reinforcement in the drilled shaft and use EPG 751.50 Standard Detailing Notes G8.8 and G8.9 in plan details.

Bridge Standard Drawings (Drilled Shafts - DSS → As Built Drilled Shaft Data [DSS_01])

As Built Drilled Shaft Data (PDF)

---

751.37.2 General Design Procedure and Limit States

Commentary for EPG 751.37.2 General Design Procedure and Limit States

Drilled shafts should be sized (diameter and length) to support the required factored loads in the most cost effective manner possible without excessive deflections. The initial diameter and length of drilled shafts are generally established considering vertical loading at the strength limit state(s) according to EPG 751.37.3. The resulting shaft should then be evaluated at the axial and lateral serviceability limit states (settlement and lateral deflection) according to EPG 751.37.4 and EPG 751.37.5, where the shaft dimensions shall be adjusted if serviceability requirements are not satisfied.

The Strength Limit State and applicable Extreme Event Limit States shall be investigated when calculating the soil and structural resistance of the drilled shaft. The Service I Limit State shall be used when evaluating lateral deflection and settlement.

Guidance

There is one type of drilled shaft construction for bridge structures. There are three types of drilled shaft construction for non-bridge structures, but only two types need be considered for design. See EPG 751.37.1.3 Casing.

Drilled shafts for bridge structures:

Permanently cased shaft through soil and socketed into rock. A reduced shaft diameter for rock socket is required. This case shall be used for all MoDOT bridge structures. For axial loading and settlement computations substitute D with D_s and L with L_s which are equal to the diameter and length of the rock socket since the required resistance to loading and settlement are computed for segment of the shaft in rock only (Rock sockets to be installed through casing shall have diameters 6” less than the inside diameter of the casing to allow for clearance and insertion of rock excavation re-tooling equipment).

Drilled shafts for non-bridge structures:

1. Uncased shaft through soil and not socketed into rock. For axial loading and settlement computations use D = diameter of shaft.

2. Uncased shaft through soil and rock. Similar to (1) because the shaft diameter is assumed to be constant between soil and rock.

3. Temporarily cased shaft through soil with an uncased and reduced or same shaft diameter in rock. This method is optional for the contractor in limited scenarios and requires the shaft in soil to be oversized by six inches with respect to the shaft diameter shown on the plans.

Permanently cased shafts shall not be allowed to use frictional resistance of the soil for either a drilled shaft with or without a rock socket.

Temporarily cased shafts may use the frictional resistance of the soil only for the case where a rock socket is not used (see the Geotechnical Section).

Note on Definitions:

1. Where L_,i is defined, L_i shall mean the length of the shaft segment through soil or through rock.

2. Where L is defined, L shall mean overall shaft length including the length of the rock socket.

---

751.37.3 Design for Axial Loading at Strength Limit State

Commentary for EPG 751.37.3 Design for Axial Loading at Strength Limit State

Geotechnical resistance to axial loading at the relevant strength limit state shall be computed as the sum of tip resistance and side resistance unless conditions are present that may prevent reliable mobilization of tip resistance (e.g. karst conditions with known or likely voids that cannot be specifically identified or characterized). Shafts should be sized such that the factored geotechnical resistance to axial loads exceeds the factored axial loads:

$R_R=R_{sR}+R_{pR}\ge \gamma Q$

(consistent units of force)

Equation 751.37.3.1

where:

R_R = factored axial shaft resistance (consistent units of force),

R_sR = factored side resistance (consistent units of force),

R_pR = factored tip resistance (consistent units of force) and

$\mathit{\gamma }Q$ = factored load for the appropriate strength limit state (consistent units of force).

Tip resistance and side resistance shall be computed according to the provisions of EPG 751.37.3 for the material type(s) encountered. The Structural Project Manager or Structural Liaison Engineer shall be consulted before utilizing design methods other than those provided in EPG 751.37.3 for calculating the geotechnical resistance of drilled shafts.

The factored side resistance for drilled shafts shall be established from factored unit side resistance values for the relevant soil/rock conditions as provided in this article. For stratified ground conditions or where the shaft dimensions change (e.g. at tip of temporary casing for non-bridge structure, or at top of rock socket for bridge structure), the shaft shall be divided into segments with practically uniform shaft geometry and soil/rock properties and unit side resistance values determined for each shaft segment. The total factored side resistance shall then be computed as the sum of the factored resistance values for each shaft segment:

$R_{sR}=\sum _{i=1}^n(q_{sR-i}\cdot A_{s-i})=\sum _{i=1}^n({\varphi }_{qs-i}\cdot q_{s-i}\cdot \pi \cdot D_i\cdot L_i)$

(consistent units of force)

Equation 751.37.3.2

where:

n = number of shaft segments,

$q_{sR-i}={\varphi }_{qs-i}\cdot q_{s-i}$ = factored unit side resistance for shaft segment i (consistent units of stress),

$A_{s-i}=\pi \cdot D_i\cdot L_i$ = perimeter interface area for shaft segment i (consistent units of area),

${\mathit{\varphi }}_{qs-i}$ = resistance factor for unit side resistance along shaft segment i (dimensionless),

${\mathbf{q}}_{s-i}$ = nominal unit side resistance along shaft segment i (consistent units of stress),

D_i = shaft diameter for shaft segment i (consistent units of length), and

L_i = length of shaft segment i (consistent units of length).

${\mathit{\varphi }}_{qs-i}$ and ${\mathbf{q}}_{s-i}$ shall be determined in accordance with the provisions of this article, based on the material type present along the respective shaft segment.

Side resistance shall generally be neglected or reduced, as recommended by the Geotechnical Section, over shaft segments with permanent casing and over any length of rock socket that is deemed unusable.

The factored tip resistance for drilled shafts shall be established from factored unit tip resistance values for the relevant soil/rock conditions as provided in this article. The appropriate tip resistance shall be established for the soil/rock located between the tip of the shaft and two diameters below the tip of the shaft. The factored tip resistance shall be computed as

$R_{pR}=q_{pR}\cdot A_p={\varphi }_{qp}\cdot q_p\cdot \pi \cdot \frac{D^2}{4}$

(consistent units of force)

Equation 751.37.3.3

where:

$q_{pR}={\varphi }_{qp}\cdot q_p$ = factored unit tip resistance (consistent units of stress),

$A_p=\pi \cdot \frac{D^2}{4}$ = cross-sectional area of the shaft at the tip (consistent units of area),

${\mathit{\varphi }}_{qp}$ = resistance factor for unit tip resistance (dimensionless),

${\mathbf{q}}_p$= nominal unit tip resistance (consistent units of stress), and

D = shaft diameter at the tip of the shaft (consistent units of length).

${\mathit{\varphi }}_{qp}$ and ${\mathbf{q}}_p$ shall be determined in accordance with the provisions of this article, based on the material type present within a depth of 2D below the tip of the shaft.

Tip resistance shall be neglected, as recommended by the Geotechnical Section, when the shaft tip is located within karstic rock or other conditions where tip resistance cannot be reliably determined.

The specific methods and resistance factors for determining nominal and factored side and tip resistance shall be selected based on the material type(s) present along the sides and beneath the tip of the shaft:

• EPG 751.37.3.1 shall generally be followed to estimate resistance for shafts in rock from results of uniaxial compression tests on intact rock core with uniaxial compressive strengths (q_u ) greater than 100 ksf;

• EPG 751.37.3.2 shall generally be followed to estimate resistance for shafts in weak rock from results of uniaxial compression tests on rock core with uniaxial compressive strengths (q_u ) greater than 5 ksf but less than 100 ksf;

• EPG 751.37.3.3 shall generally be followed to estimate resistance for shafts in weak rock from results of Standard Penetration Tests with equivalent N-values (N_eq ) less than 400 blows/foot;

• EPG 751.37.3.4 shall generally be followed to estimate resistance for shafts in weak rock from results of Texas Cone Penetration Tests with measured penetrations (TCP) greater than 1 inch/100 blows but less than 10 inches/100 blows;

• EPG 751.37.3.5 shall generally be followed to estimate resistance for shafts in weak rock from results of Point Load Index Tests with Point Load Indices (I_s(50) ) less than 40 ksf;

• EPG 751.37.3.6 shall generally be followed to estimate resistance for shafts in cohesive soils with undrained shear strengths (s_u ) less than 5 ksf; and

• EPG 751.37.3.7 shall generally be followed to estimate resistance for shafts in cohesionless soils.

Additional guidance on selection of specific methods and resistance factors based on the material types encountered is provided in the commentary to these guidelines.

---

751.37.3.7 Axial Resistance for Individual Drilled Shafts in Cohesionless Soils

Commentary for EPG 751.37.3.7 Axial Resistance for Individual Drilled Shafts in Cohesionless Soils

Side Resistance for Drilled Shafts in Cohesionless Soils

The nominal unit side resistance for shaft segments located in cohesionless soils shall be computed using the “β-method” as

$q_s=\beta \cdot {\sigma }_v^{\text{'}}$

(consistent units of stress)

Equation 751.37.3.21

where:

q_s = nominal unit side resistance for the shaft segment (consistent units of stress),

β = an empirical correlation factor (dimensionless) and

σ'_v = average vertical effective stress for the soil along the shaft segment (consistent units of stress).

The value for β shall be taken as (O’Neill and Reese, 1999)

$\beta =1.5-0.135\sqrt{z}$	(for N60 ≥ 15)	Equation 751.37.3.22a
$\beta =\frac{N_{60}}{15}\cdot (1.5-0.135\sqrt{z})$	(for N60 < 15)	Equation 751.37.3.22b

where 0.25 ≤ β ≤ 1.2 and

z = depth below ground surface to center of shaft segment (ft.) and

N₆₀ = average SPT N-value corrected for hammer efficiency (blows/ft).

If permanent casing is used, the side resistance shall be ignored for the cased portion.

The resistance factor ${\mathit{\varphi }}_{qs}$ to be applied to the nominal unit side resistance shall be taken as 0.55 (LRFD Table 10.5.5.2.4-1).

Tip Resistance for Drilled Shafts in Cohesionless Soils

The nominal unit tip resistance for shafts founded on cohesionless soils shall be computed from corrected SPT N-values, N₆₀ (O’Neill and Reese, 1999).

For N_60≤50:

$q_p=1.2\cdot N_{60}\le 60ksf$

(ksf)

Equation 751.37.3.23

where:

q_p = nominal unit tip resistance for the shaft (ksf) and

N₆₀ = average SPT N-value corrected for hammer efficiency (blows/ft).

For N₆₀ ≥ 50:

$q_p=0.59\cdot {\sigma }_v^{\text{'}}\cdot \left(N_{60}\right(\frac{p_a}{{\sigma }_v^{\text{'}}}){)}^{0.8}$

(ksf)

Equation 751.37.3.24

where:

q_p = nominal unit tip resistance for the shaft (ksf),

N₆₀ = average SPT N-value corrected for hammer efficiency (blows/foot),

p_a = 2.12 ksf = atmospheric pressure (ksf).

${\sigma }_v^{\text{'}}$ = vertical effective stress for the soil at the tip of the shaft (ksf).

Note that these expressions are dimensional so values must be entered in the units specified.

The resistance factor ${\mathit{\varphi }}_{qp}$ shall be taken as 0.50 for Equation 751.37.3.23 and as 0.55 for Equation 751.37.3.24.

---

751.37.4.1 Settlement of Individual Drilled Shafts using Approximate Method

Commentary on EPG 751.37.4.1 Settlement of Individual Drilled Shafts using Approximate Method

Prediction of factored settlement due to factored service loads shall be determined as follows depending on the magnitude of factored loads relative to the magnitude of factored side and tip resistance:

If $\gamma Q\le R_{sR}+0.1R_{pR}$:

${\delta }_R=0.005\cdot D\cdot \frac{\gamma Q}{R_{sR}+0.1R_{pR}}+{\delta }_{eR}$

(consistent units of lengths)

Equation 751.37.4.3

where:

$\mathit{\gamma }Q$ = factored load for the appropriate serviceability limit state (consistent units of force),

R_sR = total factored side resistance determined according to the provisions of this article (consistent units of force),

R_pR = factored tip resistance determined according to the provisions of this article (consistent units of force),

δ_R = factored total settlement of shaft due to factored service loads (consistent units of length),

D = shaft diameter (consistent units of length) and

δ_eR = factored elastic compression of the unsupported length of the shaft (consistent units of length).

If $R_{sR}+0.1R_{pR}\le \gamma Q\le R_{sR}+R_{pR}$ :

${\delta }_R=0.005\cdot D+0.045\cdot D\cdot \left(\frac{\gamma Q-R_{sR}-0.1R_{pR}}{0.9\cdot R_{pR}}\right)+{\delta }_{eR}$

(consistent units of lengths)

Equation 751.37.4.4

where:

$\mathit{\gamma }Q$ = factored load for the appropriate serviceability limit state (consistent units of force),

R_sR = total factored side resistance determined according to the provisions of this article (consistent units of force),

R_pR = factored tip resistance determined according to the provisions of this article (consistent units of force),

δ_R = factored total settlement of shaft due to factored service load (consistent units of length),

D = shaft diameter (consistent units of length) and

δ_eR = factored elastic compression of the unsupported length of the shaft (consistent units of length).

Note that if $\gamma Q\ge R_{sR}+R_{pR}$, the factored service load exceeds the maximum factored resistance of the shaft and the limit state cannot be satisfied without increasing the dimensions of the shaft.

The factored side resistance in Equations 751.37.4.3 and 751.37.4.4 shall be established from factored unit side resistance values for the relevant soil/rock conditions as provided in this article. For stratified ground conditions or where the shaft dimensions change, the shaft shall be divided into segments with practically uniform shaft geometry and soil/rock properties and unit side resistance values determined for each shaft segment. The total factored side resistance shall then be computed as the sum of the factored resistance values for each shaft segment:

$R_{sR}=\sum _{i=1}^n(q_{sR-1}\cdot A_{s-i})=\sum _{i-1}^n({\varphi }_{\delta s-i}\cdot q_{s-i}\cdot \pi \cdot D_i\cdot L_i)$

(consistent units of force)

Equation 751.37.4.5

where:

n = number of shaft segments,

$q_{sR-i}={\varphi }_{\delta s-i}\cdot q_{s-i}$ = factored unit side resistance for shaft segment i (consistent units of stress),

$A_{s-i}=\pi \cdot D_i\cdot L_i$ = perimeter interface area for shaft segment i (consistent units of area),

${\mathit{\varphi }}_{\delta s-i}$ = settlement resistance factor for side resistance along shaft segment i (dimensionless),

q_s-i = nominal unit side resistance along shaft segment i (consistent units of stress),

D_i = shaft diameter for shaft segment i (consistent units of length) and

L_i = length of shaft segment i (consistent units of length).

Values for q_s-i shall be determined in accordance with the provisions of EPG 751.37.3, based on the material type present along the respective shaft segments. Values for ${\mathit{\varphi }}_{\delta s-i}$ shall be established as provided subsequently in this article. Side resistance shall generally be neglected or reduced, as recommended by the Geotechnical Section, over shaft segments with permanent casing and over any length of rock socket that is deemed unusable for consistency with evaluations performed for strength limit states.

The factored tip resistance in Equations 751.37.4.3 and 751.37.4.4 shall be established from factored unit tip resistance values for the relevant soil/rock conditions as provided in this article. The appropriate tip resistance shall be established for the soil/rock located between the tip of the shaft and a distance of 2D below the tip of the shaft. The factored tip resistance shall be computed as

$R_{pR}=q_{pR}\cdot A_p={\varphi }_{\delta p}\cdot q_p\cdot \pi \cdot \frac{D^2}{4}$

(consistent units of force)

Equation 751.37.4.6

where:

$q_{pR}={\varphi }_{\delta p}\cdot q_p$ = factored unit tip resistance (consistent units of stress),

$A_p=\pi \cdot \frac{D^2}{4}$ = cross-sectional area of the shaft at the tip (consistent units of area),

${\mathit{\varphi }}_{\delta p}$ = settlement resistance factor for tip resistance (dimensionless),

q_p = nominal unit tip resistance (consistent units of stress) and

D = shaft diameter at the tip of the shaft (consistent units of length).

The value for q_p shall be determined in accordance with the provisions of EPG 751.37.3, based on the material type present within a depth of 2D below the tip of the shaft. The value for ${\mathit{\varphi }}_{\delta p}$ shall be established as provided subsequently in this article. For consistency with evaluations for strength limit states, tip resistance shall be neglected, as recommended by the Geotechnical Section, when the shaft tip is located within karstic rock or other conditions where tip resistance cannot be reliably determined.

The factored elastic compression of the unsupported length of the shaft shall be determined as

${\delta }_{eR}=\frac{\gamma Q(L-L_s)}{{\varphi }_{\delta e}\cdot E_p{A}_p}$

(consistent units of length)

Equation 751.37.4.7

where:

δ_eR = factored elastic compression of the unsupported length of the shaft (consistent units of length),

$\mathit{\gamma }Q$ = factored load for the appropriate serviceability limit state (consistent units of force),

L = overall shaft length (consistent units of length),

L_s = length of the rock socket (consistent units of length),

E_p = nominal modulus of elasticity for the shaft (consistent units of stress),

A_p = nominal shaft area (consistent units of area) and

${\mathit{\varphi }}_{\mathit{\delta }e}$ = settlement resistance factor for elastic compression of the shaft.

Values for the settlement resistance factor for elastic compression of the shaft shall be taken from Table 751.37.4.1 according to the operational importance of the structure.

Table 751.37.4.1 Settlement resistance factors for elastic compression of drilled shafts

Operational Importance	Settlement Resistance Factor, Φδe
Minor or Low Volume Route	0.68
Major Route	0.64
Major Bridge <$100 million	0.61
Major Bridge >$100 million	0.60

Settlement Resistance Factors for Approximate Method for Drilled Shafts in Rock

Settlement resistance factors to be applied to side resistance for shaft segments through rock shall be determined from Figure 751.37.4.1.1 based on the coefficient of variation of the mean uniaxial compressive strength, $CO{V}_{\overline{q_u}}$. Values for $CO{V}_{\overline{q_u}}$ shall be determined in accordance with EPG 321.3 Procedures for Estimation of Geotechnical Parameter Values and Coefficients of Variation to reflect the variability of the mean uniaxial compressive strength for the rock over the shaft segment. Settlement resistance factors to be applied to tip resistance for shafts founded on rock shall similarly be determined from Figure 751.37.4.1.2 based on values for $CO{V}_{\overline{q_u}}$ that reflect the variability of the mean uniaxial compressive strength for the rock over the distance 2D_s below the tip of the shaft.

Fig. 751.37.4.1.1 Settlement resistance factors for side resistance of drilled shafts in rock from uniaxial compression test measurements using approximate method.

Fig. 751.37.4.1.2 Settlement resistance factors for tip resistance of drilled shafts in rock from uniaxial compression test measurements using approximate method.

Settlement Resistance Factors for Approximate Method for Drilled Shafts in Weak Rock from Uniaxial Compression Tests on Rock Core

Settlement resistance factors to be applied to side resistance for shaft segments through weak rock shall be determined from Figure 751.37.4.1.3 based on the coefficient of variation of the mean uniaxial compressive strength, $CO{V}_{\overline{q_u}}$. Values for $CO{V}_{\overline{q_u}}$ shall be determined in accordance with EPG 321.3 Procedures for Estimation of Geotechnical Parameter Values and Coefficients of Variation to reflect the variability of the mean uniaxial compressive strength for the rock over the shaft segment. Settlement resistance factors to be applied to tip resistance for shafts founded on weak rock shall similarly be determined from Figure 751.37.4.1.4 based on values for $CO{V}_{\overline{q_u}}$ that reflect the variability of the mean uniaxial compressive strength for the rock over the distance 2D_s below the tip of the shaft.

Fig. 751.37.4.1.3 Settlement resistance factors for side resistance of drilled shafts in weak rock from uniaxial compression test measurements using approximate method.

Fig. 751.37.4.1.4 Settlement resistance factors for tip resistance of drilled shafts in weak rock from uniaxial compression test measurements using approximate method.

Settlement Resistance Factors for Approximate Method for Drilled Shafts in Weak Rock from Standard Penetration Test Measurements

Settlement resistance factors to be applied to side resistance for shaft segments through weak rock shall be determined from Figure 751.37.4.1.5 based on the coefficient of variation of the mean equivalent SPT N-value, $CO{V}_{\overline{N_{eq}}}$. Values for $CO{V}_{\overline{N_{eq}}}$ shall be determined in accordance with EPG 321.3 Procedures for Estimation of Geotechnical Parameter Values and Coefficients of Variation to reflect the variability of the mean equivalent N-value over the shaft segment. Settlement resistance factors to be applied to tip resistance for shafts founded on weak rock shall similarly be determined from Figure 751.37.4.1.6 based on values for $CO{V}_{\overline{N_{eq}}}$ that reflect the variability of the mean equivalent N-value over the distance 2D_s below the tip of the shaft.

Fig. 751.37.4.1.5 Settlement resistance factors for side resistance of drilled shafts in weak rock from Standard Penetration Test measurements using approximate method.

Fig. 751.37.4.1.6 Settlement resistance factors for tip resistance of drilled shafts in weak rock from Standard Penetration Test measurements using approximate method.

Settlement Resistance Factors for Approximate Method for Drilled Shafts in Weak Rock from Texas Cone Penetration Test Measurements

Settlement resistance factors to be applied to side resistance for shaft segments through weak rock shall be determined from Figure 751.37.4.1.7 based on the coefficient of variation of the mean TCP-value, $CO{V}_{\overline{TCP}}$. Values for $CO{V}_{\overline{TCP}}$ shall be determined in accordance with EPG 321.3 Procedures for Estimation of Geotechnical Parameter Values and Coefficients of Variation to reflect the variability of the mean TCP-value over the shaft segment. Settlement resistance factors to be applied to tip resistance for shafts founded on weak rock shall similarly be determined from Figure 751.37.4.1.8 based on values for $CO{V}_{\overline{TCP}}$ that reflect the variability of the mean TCP-value over the distance 2D_s below the tip of the shaft.

Fig. 751.37.4.1.7 Settlement resistance factors for side resistance of drilled shafts in weak rock from Texas Cone Penetration Test measurements using approximate method.

Fig. 751.37.4.1.8 Settlement resistance factors for tip resistance of drilled shafts in weak rock from Texas Cone Penetration Test measurements using approximate method.

Settlement Resistance Factors for Approximate Method for Drilled Shafts in Weak Rock from Point Load Index Test Measurements

Settlement resistance factors to be applied to side resistance for shaft segments through weak rock shall be determined from Figure 751.37.4.1.9 based on the coefficient of variation of the mean I_s(50)-value, $CO{V}_{\overline{I_{s(50)}}}$. Values for $CO{V}_{\overline{I_{s(50)}}}$ shall be determined in accordance with EPG 321.3 Procedures for Estimation of Geotechnical Parameter Values and Coefficients of Variation to reflect the variability of the mean I_s(50)-value for the rock over the shaft segment. Settlement resistance factors to be applied to tip resistance for shafts founded on weak rock shall similarly be determined from Figure 751.37.4.1.10 based on values for $CO{V}_{\overline{I_{s(50)}}}$ that reflect the variability of the mean I_s(50)-value for the rock over the distance 2D_s below the tip of the shaft.

Fig. 751.37.4.1.9 Settlement resistance factors for side resistance of drilled shafts in weak rock from Point Load Index Test measurements using approximate method.

Fig. 751.37.4.1.10 Settlement resistance factors for tip resistance of drilled shafts in weak rock from Point Load Index Test measurements using approximate method.

Settlement Resistance Factors for Approximate Method for Drilled Shafts in Cohesive Soils

Settlement resistance factors to be applied to side resistance for shaft segments through cohesive soil shall be determined from Figure 751.37.4.1.11 based on the coefficient of variation of the mean undrained shear strength, $CO{V}_{\overline{s_u}}$. Values for $CO{V}_{\overline{s_u}}$ shall be determined in accordance with EPG 321.3 Procedures for Estimation of Geotechnical Parameter Values and Coefficients of Variation to reflect the variability of the mean undrained shear strength for the soil over the shaft segment. Settlement resistance factors to be applied to tip resistance for shafts founded on cohesive soil shall similarly be determined from Figure 751.37.4.1.12 based on values for $CO{V}_{\overline{s_u}}$ that reflect the variability of the mean undrained shear strength for the soil over the distance 2D below the tip of the shaft.

Fig. 751.37.4.1.11 Settlement resistance factors for side resistance of drilled shafts in cohesive soil from undrained shear strength measurements using approximate method.

Fig. 751.37.4.1.12 Settlement resistance factors for tip resistance of drilled shafts in cohesive soil from undrained shear strength measurements using approximate method.

For shafts founded in soft cohesive soils, consideration shall also be given to including additional settlement induced from time dependent consolidation of the soil.

Settlement Resistance Factors for Approximate Method for Drilled Shafts in Cohesionless Soils

Settlement evaluations for individual drilled shafts in cohesionless soils shall be designed according to applicable sections of the current AASHTO LRFD Bridge Design Specifications.

---

751.37.6.1 Reinforcement Design

Drilled shaft structural resistance shall be designed similarly to reinforced concrete columns. The Strength Limit State and applicable Extreme Event Limit State load combinations shall be used in the reinforcement design.

Longitudinal reinforcing steel shall extend below the point of fixity of the drilled shaft at least 10 ft. in accordance with LRFD 10.8.3.9.3 or the required bar development length whichever is larger.

If permanent casing is used, and the shell consists of a smooth pipe greater than 0.12 in. thick, it may be considered load carrying. An 1/8" shall be subtracted off of the shell thickness to account for corrosion. Casing could also be corrugated metal pipe. If casing is assumed to contribute to the structural resistance, the plans should indicate the minimum thickness of casing required.

Minimum clear spacing between longitudinal bars as well as between transverse bars shall not be less than five times the maximum aggregate size or 5 in. (LRFD 10.8.3.9.3).

For rock sockets use 3” min. clear cover. For drilled shafts for sign structure support, use 3” min. clear cover for all shaft diameters.

For longitudinal reinforcement, splicing shall be in accordance with LRFD 5.10.8.4.

For transverse reinforcement, lap splices for closed circular stirrups/ties shall be provided and staggered in accordance with LRFD 5.10.4.3. Lap length of 1.3 l_d (Class B) for closed stirrups/ties shall be provided in accordance with LRFD 5.10.8.2.6d.

For lap length, see EPG 751.5.9.2.8.1 Development and Lap Splice General.

---

Commentary on EPG 751.37.1.3 Casing

Temporary or permanent casing is commonly required to support the shaft excavation during construction to prevent caving of overburden soils. Use of permanent casing generally simplifies construction by avoiding the need for multiple cranes to simultaneously place concrete and extract the casing and reduces the risk of problems during concrete placement. However, use of either temporary or permanent casing will generally reduce the side resistance of the constructed shaft over the cased length. Alternatives to use of casing for non-bridge structures include use of mineral or polymer slurry to maintain the stability of the excavation during construction, or use of no casing and no slurry when soil/rock conditions will permit the shafts to be constructed without caving of the excavation walls.

Permanent casing may also be required to provide structural resistance, especially when lateral loads are substantial (see EPG 751.37.6). For example, permanent casing may be required to:

• Achieve the required flexural resistance of the drilled shaft
• Resist large lateral loads for bridges located in seismic areas
• Facilitate shaft construction through water
• Support the shaft excavation when there is insufficient head room available for casing recovery

---

751.38.1.1 Dimensions and Nomenclature

Dimensions to be established in design include the bearing depth (depth to footing base) and the footing dimensions shown in Figure 751.38.1.1. Table 751.38.1.1 defines each dimension and provides relevant minimum and/or maximum values for the respective dimension.

Fig. 751.38.1.1 Nomenclature used for spread footings.

Table 751.38.1.1 Summary of footing dimensions with minimum and maximum values

Dimension	Description	Minimum Value	Maximum Value	Comment
D	Column diameter	12”	--	--
B	Footing width	D+24”	--	Min. 3” increments
L	Footing length	D+24”1	--	Min. 3” increments
A	Edge distance in width direction	12”	--	--
A’	Edge distance in length direction	12”	--	--
t	Footing thickness	30” or D2	72”	Min. 3” increments
1 Minimum of 1/6 x distance from top of beam to bottom of footing
2 For column diameters ≥ 48”, use minimum value of 48”. Sign support structures may utilize a minimum thickness of 24”.

The nomenclature used in these guidelines has intentionally been selected to be consistent with that used in the AASHTO LRFD Bridge Design Specifications (AASHTO, 2009) to the extent possible to avoid potential confusion with methods provided in those specifications. By convention, references to other provisions of the MoDOT Engineering Policy Guide are indicated as “EPG XXX.XX” throughout these guidelines where the Xs are replaced with the appropriate article numbers. Similarly, references to provisions within the AASHTO LRFD Bridge Design Specifications are indicated as “LRFD XXX.XX”.

---

751.38.1.2 General Design Considerations

Commentary for EPG 751.38.1.2 General Design Considerations

Footings shall be founded to bear a minimum of 36 in. below the finished elevation of the ground surface. In cases where scour, erosion, or undermining can be reasonably anticipated, footings shall bear a minimum of 36 in. below the maximum anticipated depth of scour, erosion, or undermining.

Footing size shall be proportioned so that stresses under the footing are as uniform as practical at the service limit state.

Long, narrow footings supporting individual columns should be avoided unless space constraints or eccentric loading dictate otherwise, especially on foundation material of low capacity. In general, spread footings should be made as close to square as possible. The length to width ratio of footings supporting individual columns should not exceed 2.0, except on structures where the ratio of longitudinal to transverse loads or site constraints makes use of such a limit impractical. For spread footings supporting overhead sign structures the length to width ratio of footings supporting individual columns may be as high as 4.0.

Footings located near to rock slopes (e.g. rock cuts, river bluffs, etc.) shall be located so that the footing is founded beyond a prohibited region established by a line inclined from the horizontal passing through the toe of the slope as shown in Figure 751.38.1.2. The boundary of the prohibited region shall be established by the Geotechnical Section. For the purposes of this provision, the toe of the slope shall be the point on the slope that produces the most severe location for the active zone. Exceptions to this provision shall only be made with specific approval of the Geotechnical Section and shall only be granted if overall stability can be demonstrated as provided in EPG 751.38.7.

Fig. 751.38.1.2 Prohibited region for spread footings placed near rock slopes unless exception is specifically approved by MoDOT Geotechnical Section.

Footings located near to soil slopes shall be evaluated for overall stability as provided in EPG 751.38.7 unless they are located a minimum distance of 2B beyond the crest of the slope.

---

751.38.1.3 Related Provisions

The provisions in these guidelines were developed presuming that design parameters required to apply the provisions are established following current MoDOT site characterization protocols as described in EPG 321. Specific attention is drawn to EPG 321.3 Procedures for Estimation of Geotechnical Parameter Values and Coefficients of Variation. The provisions provided in this subarticle presume that parameter variability, as generally represented by the coefficient of variation (COV), is established following procedures in EPG 321.3.

Sign structure spread footing supports are the exception. Sign structure standard spread footings are developed using assumed soil properties and following AASHTO LRFD Bridge Design Specifications 9^th Edition for design. Site specific designs for spread footings for sign structure support may also follow AASHTO LRFD Bridge Design Specifications 9^th Edition if there is not enough geotechnical information available to establish the COV.

---

751.38.8.3 Details

Hooks at the end of reinforcement are not required for spread footings supporting sign structures. Include reinforcement near the top of spread footings supporting sign structures as required for uplift and in accordance with design requirements.

---

G8. Drilled Shaft

(G8.1) Include underlined portion when a minimum thickness is required and shown on the plans as minimum.

Thickness of permanent steel casing shall be as shown on the plans and in accordance with Sec 701.

(G8.2) Note may not be required with drilled shafts for high mast tower lighting.

An additional 4 feet has been added to V-bar lengths and additional __-#_-P___ bars have been added in the quantities, if required, for possible change in drilled shaft or rock socket length. The additional V-bar length shall be cut off or included in the reinforcement lap if not required. The additional P bars shall be spaced similarly to that shown in elevation, if required, or to a lesser spacing if not required, but not less than 6-inch centers.

(G8.3) Note not required with drilled shafts for high mast tower lighting.

Sonic logging testing shall be performed on all drilled shafts and rock sockets.

(G8.4) Note to be used only with Drilled Shafts for High Mast Tower Lighting.

Drilling slurry, if used, shall require desanding.

(G8.5) Note to be used only with Drilled Shafts for High Mast Tower Lighting. Drilled shaft diameter is required to be at least 21 in. greater than the largest anticipated anchor bolt circle diameter per the DSP - High Mast Tower Lighting.

The following non-factored base reactions were used to design the drilled shafts for the       ft. high mast lighting towers: overturning moment = * kip-foot, base shear = * kip and axial force = * kip.

 *Values used in the design of the drilled shaft.

(G8.6) Use the following note only when the tops of drilled shafts are ≤ 3'-0" below the ground surface at centerline column / drilled shaft. Otherwise excavation quantity to the top of drilled shafts needs to be figured. Excavation diameter limit will be the 3'-0" larger than the column diameter above the drilled shaft.

The cost of any required excavation to the top of the drilled shafts will be considered completely covered by the contract unit price for other items.

(G8.7)

The tip of casing shall not extend into the rock socket elevation range reported in the Foundation Data table without approval by the engineer.

(G8.8) Use the following note when non-contact or contact lap is required at the top of drilled shaft between column/dowel reinforcement and drilled shaft reinforcement.

Column or dowel reinforcement shall be placed prior to pouring drilled shaft concrete in the area of the lap. Dowel bar or column reinforcement shall not be inserted after drilled shaft pour is complete.

(G8.9) For oversized shafts, use the following note in conjunction with callout for optional construction joint near top of drilled shaft.

Remove sediment laitance and weak concrete to sound concrete prior to setting column/dowel reinforcement if optional construction joint is used.

---

Category:901 Lighting

Nonstandard Lighting Structures

If any lighting installation being considered will use a special or nonstandard structure or with dimensions exceeding those shown in the Standard Plans, Traffic should be consulted early in the project planning regarding the installation’s feasibility and necessary contract provisions. Examples of this situation are high mast lighting and exceeding lengths on the Standard Plans.

Since designing details for nonstandard installations is typically performed by an outside engineer employed by the contractor or producer and is certified to MoDOT, the project contract documents must include appropriate requirements about the design standards used. Since structures beyond MoDOT's standard designs are involved, a performance-based specification of the design signed and sealed by a Missouri Registered Professional Engineer is needed from the contractor. Certification to the current AASHTO Standard Specifications for Structural Supports for Highway Signs, Luminaires and Traffic Signals including the latest fatigue provisions is required. For standard detailing notes regarding drilled shafts for High Mast Tower Lighting, see [[751.50_Standard_Detailing_Notes#G8._Drilled_Shaft|EPG 751.50 Standard Detailing Notes G8.4 and G8.5].

---

901.7.6 High Mast Lighting

High mast lighting is principally used at complex interchanges and lights a large area by a group of luminaires mounted in a fixed orientation at the top of a tall mast, generally 80 ft. or taller. The district must authorize high mast lighting. The request for high mast lighting conceptual approval is to be included with the lighting warrants. Data supporting the selection of pole height, pole location and type of luminaires is to be included with the preliminary lighting plan. Where high mast lighting is used at complex interchanges, adaptation lighting is recommended for each section where vehicles enter and leave the interchange.

The district is responsible for all bid items associated with high mast lighting and to design the foundation and the structure above the foundation for inclusion in the project plans.

For standard detailing notes regarding drilled shafts for High Mast Tower Lighting, see [[751.50_Standard_Detailing_Notes#G8._Drilled_Shaft|EPG 751.50 Standard Detailing Notes G8.4 and G8.5].

---