Published: July 15, 2022
Geotechnical exploration and testing programs should be planned together and should specifically characterize the geotechnical conditions for anticipated project needs. As such, prior to planning the exploration and testing programs for a specific project, the anticipated engineering parameters necessary for design and construction should be identified to the fullest extent practicable, and the scope of exploration, sampling, and testing should be estimated. During the exploration and testing programs, the resulting information should be compared for consistency with those conditions previously speculated and reconciled. If subsequent exploration and testing results are not consistent with the developing model of subsurface conditions, then further exploration and testing will be needed to reconcile those differences and adjust the model of subsurface conditions accordingly. The reliability of the parameters and resolution of subsurface conditions will be directly influenced by the exploration, sampling and testing methods employed, quality of workmanship, and the frequency, locations, and depths explored. Please refer to Figure 300-1.
The reconnaissance consists of studying the visible site conditions, site history, and the soil and geologic conditions for the design of the proposed work and establishing tentative types, locations and depths of exploratory methods for the subsurface exploration, with respect to project needs. Additional reconnaissance may be needed as unknown geologic and geotechnical conditions are encountered during the project development.
Review all available design plans for the project. Projects are planned in steps, recognizing that unknown geologic and geotechnical conditions will be encountered and defined during planning level site reconnaissance and exploration. Maintain a close liaison with the transportation system planners, dealing with developing findings. Begin coordination during concept development and continue through the Project Development Process. Plans necessary prior to commencement of the subsurface exploration reconnaissance are as follows:
Plans for the roadway showing:
- Topography of the site
- the proposed alignment
- Centerline or baseline ground profile
- Proposed grade
- Typical sections
- General cross sections in sidehill areas and critical foundation areas
- General location map of the project referenced to existing roads and streets
- Proposed drainage features (e.g. culverts, channels/ditches, drop inlets/outlets, etc.)
Figure 300-1. Soil and rock property selection flowchart (FHWA-IF-02-034, page 5)
Plans for bridges, retaining walls, and other structures showing:
- Topography of the site
- Plan view of structure showing proposed alignment and the location of proposed foundations
- A general location map showing the structure location with respect to existing roads and streets
Plans for remediation of geohazards, including landslides, rockfall, mines, and karst, are typically developed after the subsurface exploration. Perform a complete survey of the site, including topography and location of roadway and geohazard features, as soon in the planning process as possible. Depict this survey on a stationed plan view and closely spaced cross sections.
302.2 Office Reconnaissance
Review the Project Initiation Package (PIP) prepared for the project. In addition, consider all of the resources listed in Section 302.2.1 as part of the office reconnaissance. The level of effort expended on this review is established by the size and complexity of the project. However, regardless of the size of a project, some review must take place prior to the field reconnaissance.
302.2.1 Literature Search
Conduct a literature search of the soil and geologic conditions of the project. Provide a comprehensive review of all existing information available for the study area. Much of this information is available electronically, and can be readily incorporated into base mapping for presentation. It is assumed, based on the project type, that not all reference materials listed herein may be applicable for use. Consider the following resources, but do not limit the search to only these:
- Information from ODOT
- Plan views, profiles, and cross-sections of previous projects
- Construction diaries and inspection reports
- Documented changes to the plans during construction activities (e.g., slope, spring drains)
- Maintenance records
- Boring logs, geotechnical profiles, structure foundation exploration plans or other project related documents on file with the Office of Geotechnical Engineering (can be obtained at https://gis.dot.state.oh.us/tims/Map/Geotech) or the District
- Environmental subsurface explorations on record with the Office of Environmental Engineering or the District
- History and occurrence of landslides
- History and occurrence of rockfalls
- Pile driving records from the respective District or from the Office of Geotechnical Engineering
- ODNR Division of Geological Survey
- Boring logs on file
- Measured geologic sections
- Bedrock Geology Maps
- Bedrock Topography Maps
- Bedrock Structure Maps
- Geologic Map of Ohio
- Quaternary Geology of Ohio
- Known and Probable Karst in Ohio
- Information Circulars
- Report of Investigations
- Location and information on underground mines
- Location and characteristics of karst features
- Landslide Maps
- ODNR Division of Mineral Resource Management
- Applications and permits files for surface mines (coal & industrial mineral)
- Active, reclaimed or abandoned surface mines
- Abandoned Mine Land (AML) sites
- Emergency Projects
- ODNR Division of Water Resources
- Water well logs
- Ohio Wetland Inventory Maps
- Maps Identifying the presence of lake bed sediments, organic soils or peat deposits
- Other Sources
- Aerial photographs
- National Wetland Inventory Maps (USFWS)
- Satellite imagery
- Soil Surveys (USDA NRCS)
- USGS quadrangles
- USGS publications and files
- City and County Engineers
- Academia with engineering or geology programs
- USGS Open File Map Series #78-1057 “Landslides and Related Features”
302.3 Field Reconnaissance
Observe the following features during the field reconnaissance. Record GPS coordinates of all notable features – see Section 303.2.
302.3.1 Existing Pavements
Identify and document the condition of existing pavements, noting the locations of wet or pumping subgrade or poorly performing pavement.
302.3.2 Existing Structures
Identify and document the condition of existing structures, noting signs of distress and the impact of any existing structure on the exploration or the proposed construction.
Identify and document the condition of existing embankments, noting evidence of either general or differential settlement, erosion, localized sags, or slope failures.
Identify and document the general drainage capability of soils, the location of springs and seeps, and the extent of poorly drained areas, wetlands, swamps, bogs, and ponds. Identify and document the condition and functionality of existing drainage features and systems relative to performance of geotechnical structures and earthwork.
Identify and document evidence of dormant or active landslides, their locations and limits, and landslide topography in general. Note all surface cracks, scarps, toe bulges, and other indications of landslide activity.
302.3.6 Bedrock Exposures
Identify and document the limits of bedrock exposures and the types and vertical intervals of bedrock exposed. If possible, note the strike and dip of the bedrock. Note rock fall hazards along existing alignments.
Identify and document the limits and general composition of rubbish, debris, and other waste fills or waste pits. If during reconnaissance, any materials such as, but not limited to, drums, tanks, or stained earth or any unusual odors are encountered, discontinue geotechnical exploration work and notify the District Geotechnical Engineer immediately. The site will be considered to contain hazardous or toxic material and must be handled in accordance with ODOT policy.
Identify and document the limits and status of surface or underground mining, quarrying, reclaimed areas, or other excavation operations. Note any evidence of mining operations, spoil piles, mine water discharge, and possible mine subsidence features. Refer to the ODOT Manual for Abandoned Underground Mine Inventory and Risk Assessment for additional guidance.
302.3.9 Soft Soils
Identify and document the limits of compressible or low strength soil, such as peat or soft clay that will affect settlement, embankment stability or foundation support.
302.3.10 Water Crossings
Identify and document the condition of foundations of existing structures, noting any settlement, scour, streambed and bank composition, and channel migration (erosion or sedimentation). Contact the District Bridge Engineer for bridge inspection information.
302.3.11 Land Usage
Identify and document the current land usage. Categories of land usage include but are not limited to agricultural, wooded, residential, rural residential, commercial, and industrial.
Identify and document ground surface features that may be related to karst formations, for karst prone areas.
For ODOT projects, a typical geotechnical exploration includes drilled borings. Therefore, references made in this specification for the development of a geotechnical exploration program are for a drilled boring program, except as noted. Other methods of subsurface exploration are available, as discussed in Section 400, and may provide useful and efficient design data in conjunction with or in place of borings. Contact the District Geotechnical Engineer for review and approval of any geotechnical exploration program that utilizes a method other than borings.
Planning of a geotechnical exploration program cannot be prescribed by simple guidelines to fit all conditions. However, follow the guidelines given in this section whenever practical. Evaluate a project considering its specific geological conditions, the proposed work, and existing subsurface information. Selectively locate borings for development of maximum subsurface information, using a minimum number of borings to achieve that end. Also consider topography, geologic origin of materials, surface manifestation of soil conditions, and any special design considerations when determining the spacing and depth of the borings. Locate the borings to provide adequate overhead clearance for equipment, adequate clearance of underground utilities, minimum damage to private property, and minimum disruption of traffic, without compromising the quality of the geotechnical data.
When office reconnaissance discloses historic geotechnical exploration(s), utilize this information to the fullest extent possible. As subsurface information becomes available during progression of the boring and sampling program or if the alignment or locations of the roadway or structures change during the project development, review the locations of the borings; consider increasing or decreasing the number of borings initially considered or moving borings to more strategic locations.
If during the planning stage, any materials such as, but not limited to, drums, tanks, or stained earth or any unusual odors are encountered, discontinue geotechnical exploration work and notify the District Geotechnical Engineer immediately. The site will be considered to contain hazardous or toxic material and must be handled in accordance with ODOT policy.
All references to blow counts for determination of boring depths refer to the N60 value – see Section 404.
All boring plans must be submitted to the District Geotechnical Engineer and approved before beginning the boring, sampling, and field testing task. Submit a scaled boring plan, showing all project and historic borings, and a schedule of borings in tabular format. In the schedule of borings, present the following information for each boring:
- exploration identification number
- location by station and offset
- estimated amount of rock and soil. Also show the total of each for the entire program.
303.2 Exploration Identification Number
Survey and record all exploration (borings, probes, test pits, etc.) locations according to the ODOT Survey & Mapping Specifications. See Survey & Mapping Specifications Section 300 for Datum and Coordinate Systems and Section 400 for precision requirements. Determine the station and offset of all explorations. For geotechnical documents and reports, report exploration locations in geographic coordinates (Latitude and Longitude) shown as decimal degrees to six decimal places. Report all stations and offsets to the whole foot and elevations to one decimal place.
Assign each exploration with an identification number, unique within a project, according to the following format:
“X” designates the method of geotechnical exploration, using:
B – Drilled boring
C – Static cone
D – Dynamic cone T – Test pit
H – Hand auger
X – Other (use for pavement cores)
A pavement core by itself is not a subsurface exploration method, and therefore, do not number borings and pavement cores consecutively such as B-001-0-20, X-002-0-20, B-003-0-20, etc. Use a completely separate numbering sequence for pavement cores only.
Use “ZZZ” and “W” to identify an exploration location within a particular geotechnical exploration program. The primary set of numbers, “ZZZ”, begins at 001 for each project and continues consecutively in the cardinal direction. Show all three digits, including leading zeroes. The secondary number, “W”, designates explorations located between, or offset from, consecutively numbered explorations. For the first exploration with a particular primary number, assign the number zero for “W.” Use the numbers 1 through 9 for “W” for additional explorations offset from the first or located between consecutively number explorations. For example, explorations located between B-005-0 and B-006-0 are designated B-005-1, B-005-2, etc.
Use “YY” to designate the year that the geotechnical exploration program began. Note that this is not necessarily the year that the exploration was performed. A boring planned in 2007 but drilled in 2008 will use “07”, such as B-005-0-07. The numbers “YY” may be used to distinguish between different phases of geotechnical exploration performed several years apart.
Do not repeat primary and secondary combinations. For example, B-005-0-07 and C-005-0-07 should not exist on the same project. Instead use B-005-0-07 and C-005-1-07 or C-006-0-07. For another example, B-004-0-11 and B-004-0-13, drilled as part of different phases of geotechnical exploration, should not exist on the same project. Instead use B-004-0-11 and B-004-1-13 (if the latter boring was drilled between explorations 4 and 5).
Either “W” or “YY” or both may be omitted in references to the explorations, such as in reports or drawings, so long as the omission will not cause any confusion. If omitted, “W” is assumed to be zero and “YY” is assumed to be the year of the current geotechnical exploration program.
Exploration Identification Number: B-014-1-07
A drilled boring located between explorations 14 and 15. Part of a geotechnical exploration program planned in 2007.
Exploration Identification Number: T-004
A test pit that was performed as part of the current geotechnical exploration program.
When referring to historic explorations that did not use the above identification scheme, assign an exploration identification number that is similar to the original identification number, using the following guidelines and examples.
Use the first letter of the original exploration identification for “X” and the original number for “ZZZ”. If the original exploration identification number includes a secondary letter after the primary number, such as B-3A, use the secondary letter for “W” (for example, B-003-A), otherwise use zero for “W”. Use the year of the geotechnical exploration program for “YY”. The year the exploration was performed may be used for “YY” if the year the project was planned is not known. When assigning exploration identification numbers to historic explorations, duplicate numbers are acceptable, so long as the first letter, “X”, is different. For example, R-003-0-69 and S-003-0-69 may exist on the same project.
Table 300-1. Examples of Exploration Identification Numbers For Historic Explorations.
Original Boring Identification
Year of Original Boring
New Exploration Identification Number
303.3 Borings for Evaluation of Existing Pavement Subgrade (Type A)
For projects involving rehabilitation or widening of existing pavement, and where the proposed subgrade will not vary from existing subgrade by more than 3.0 feet, locate borings based on the proposed pavement work as follows:
- If the proposed pavement work consists of replacing or rubblizing the existing pavement only, drill 100 percent of the borings through the existing pavement.
- If the proposed pavement work involves adding a lane, along with replacing or rubblizing the existing pavement, drill 50 percent of the borings through the existing pavement and 50 percent of the borings in the planned widened area.
- If the proposed pavement work involves adding a lane without replacing or rubblizing the existing pavement, drill 100 percent of the borings in the planned widened area.
Where subsurface conditions are considered uniform, space the borings a maximum of 400 feet apart, including one boring at the beginning of the project and one boring at the end of the project. Place borings closer than 400 feet as necessary to identify non-uniform or problematic conditions. Offset borings from the centerline or baseline as needed to obtain representative samples of the subgrade that will be encountered during construction. Locate borings to explore poorly performing pavements and the presence of wet or soft subgrade conditions when field reconnaissance indicates their potential existence. Do not rely solely on historic borings to evaluate subgrade conditions.
Extend borings 6 feet below proposed top of subgrade or below existing grade, whichever is lower in elevation. Extend borings through any soft or loose soil into stiff or medium dense soil.
Perform continuous Standard Penetration Test sampling for the 6-foot (2-meter) interval immediately below proposed top of subgrade.
Mainline borings drilled through the pavement may be used to represent the shoulder subgrade when evaluating shoulders for maintenance of traffic.
303.4 Roadway Borings (Type B)
For projects involving a new horizontal alignment or where the existing vertical alignment will change by more than 3.0 feet, locate borings as near as practical to the centerline or baseline of the proposed roadway except where surface or subsurface conditions disclose variable conditions. Locate borings to disclose the nature of subsurface materials at the deepest points of cuts, areas of transition from cut to fill, and foundation areas beneath the points of highest embankment.
Where subsurface conditions are considered uniform, space the borings a maximum of 400 feet apart, including one boring at the beginning of the project and one boring at the end of the project. Place borings closer than 400 feet as necessary to identify non-uniform or problematic conditions. Consider all the proposed routes and ramps of the project, utilizing boring locations that contribute to more than one alignment whenever possible.
Extend borings to a depth of 10 feet below proposed grade or existing ground surface, whichever is lower in elevation, unless bedrock is encountered at a shallower depth or unless noted otherwise. In areas where soft or loose soils are encountered, extend the borings 5 feet into stiff or medium dense soils, with a minimum boring depth of 10 feet, or to bedrock, whichever is encountered first.
Perform Standard Penetration Test sampling at 2.5-foot intervals unless noted otherwise. Obtain representative undisturbed samples when appropriate.
303.4.1 Embankment Foundations (Type B1)
Determine the maximum height of embankment by measuring vertically from the existing ground line to the proposed ground line. Locate borings to disclose the nature of subsurface materials beneath the points of highest embankment. Where weak or compressible soils are encountered and stability or settlement problems are anticipated, locate borings transverse to centerline or baseline, as required to establish the lateral extent of such conditions beneath the full width of the proposed embankment. Obtain additional borings along the alignment to define the problem limits as necessary. At bridges, the abutment borings may be used to explore the approach embankment foundations.
Extend borings to a minimum depth equal to the height of the embankment or 10 feet, whichever is greater, of which the last 10 feet must be in stiff or medium dense soils. Terminate the boring if bedrock is encountered.
Obtain samples at maximum 5-foot intervals below 20 feet.
303.4.2 Cut Sections (Type B2)
Determine the maximum depth of cut by measuring vertically from the existing ground line to the proposed ground line. Locate borings to disclose the nature of subsurface materials at the deepest points of cuts. Locate a minimum of one boring on centerline or baseline where the depth of cut is relatively uniform in the cross section. Obtain offset borings if soft, loose, or wet soils are encountered and stability of the cut slopes is a concern.
Extend borings in stiff or medium dense soil to a minimum depth of 10 feet below the proposed grade.
In cut sections involving bedrock, core bedrock to a depth of 10 feet below the proposed excavation at maximum intervals of 1000 feet. These borings will typically be located at the back of the ditch line at the points of deepest cut. Where major changes in the geology or lithology occur, reduce the interval to establish the limits of these changes. Keep in mind that more severely weathered and deteriorated rock conditions are typically encountered on the sides and ends of a hill as compared to the middle. Keep the amount of rock core utilized in developing the stratigraphic column of bedrock to a minimum. Supplement borings that core bedrock with soil borings that extend to the top of bedrock spaced a maximum of 400 feet apart, in order to develop the elevation of the bedrock surface and the nature of the soil overburden throughout the cut. Complete mapping of all bedrock exposures within the project limits to augment the proposed boring plan.
303.4.3 Sidehill Cut Sections (Type B3)
Where the slope and the thickness of soil overburden are relatively uniform in the cross section, and the depth of cut is significantly greater on one side of centerline or baseline than on the other, locate borings as follows:
- Locate one boring in the back of the proposed ditch line area on the uphill side. Locate an additional boring on the uphill side, at a point where it is anticipated the backslope will intersect the ground line. If the horizontal distance between borings is inadequate to define subsurface conditions, or in the case where irregular slope, talus, or residual cover is encountered, obtain one or more intermediate borings as necessary.
Extend upper borings to depths sufficient to vertically overlap the adjacent lower boring by at least 10 feet. Where the depth of cut exceeds 35 feet with at least half the interval anticipated being through bedrock, extend the upper borings to depths sufficient to provide at least 10 feet of vertical overlap in bedrock between adjacent borings.
- Where the slope is irregular or the overburden is estimated to be non-uniform in thickness, obtain additional borings on the downhill side in the proposed ditch line area.
- Obtain additional borings as necessary to determine the profile of top of bedrock or variability of soil type.
Figure 300-2. Example boring layout in cross section for sidehill cut section.
303.4.4 Sidehill Cut-Fill Sections (Type B4)
Where the slope and the thickness of soil overburden are relatively uniform in the cross section, and where one side of the centerline or baseline requires excavation and the other side requires fill, locate borings as follows:
- Where the depth of cut exceeds 10 feet, regardless of the embankment height, locate and drill borings according to Section 303.4.3 to explore the cut.
- Where the maximum height of embankment at the outer edge of shoulder is 5 feet or less, obtain one boring on the centerline or baseline, in addition to any borings drilled in the cut section.
- Where the maximum height of embankment is between 5 and 10 feet, obtain one boring at the outer edge of shoulder in the embankment section, in addition to any borings drilled in the cut section.
- Where the maximum height of embankment exceeds 10 feet, locate the borings in the embankment section according to Section 303.4.5, in addition to any borings drilled in the cut section.
303.4.5 Sidehill Fill Sections on Unstable Slopes (Type B5)
Where embankment fill will be placed on slopes with signs of sloughing or sliding, obtain a minimum of two borings on the downhill side. Locate one boring at the point where a 1:1 slope from the proposed pavement edge intercepts the ground line and locate the other where the proposed embankment slope intercepts the ground line. If the horizontal distance between borings is inadequate to define subsurface conditions, or in the case where irregular slope, talus, or residual cover is encountered, obtain one or more intermediate borings.
Extend borings 10 feet into stiff or medium dense soils below what is considered to be unstable material. Where bedrock is at a shallow depth, extend the lower borings to a depth of 10 feet into bedrock and extend the upper borings to depths as required to define a complete stratigraphic column continuous with the bedrock penetrated by the lower boring.
Figure 300-3. Example boring layout in cross section for sidehill fill greater than 10 feet and sidehill fill on unstable slope.
303.5 Geohazard Borings (Type C)
Locate borings within the limits of known or suspected geohazards to identify the vertical and lateral extents of the problematic condition(s). Additional borings may be drilled immediately outside the geohazard limits to confirm the lateral extent. Boring locations, spacings, and depths must be determined based on the known or suspected conditions of the geohazard, subsequent to field and office reconnaissance. Consider other exploratory methods as detailed in Section 406, where appropriate.
Perform continuous Standard Penetration Test sampling unless noted otherwise. Obtain representative undisturbed samples where appropriate.
303.5.1 Lakes, Ponds, and Low-Lying Areas (Type C1)
Identify lakes, ponds, and low-lying areas where wet surface soils occur, where wetland or swamp conditions exist, or where no functioning drainage outlet can be observed. Determine the depth of lakes and ponds and the thickness of muck. Determine the thickness of soft surface soils in wetlands and low-lying wet areas. Methods of disturbed sampling other than Standard Penetration Test and undisturbed sampling may be considered. Comply with applicable regulations related to wetlands.
303.5.2 Peat Deposits, Compressible Soils, and Low Strength Soils (Type C2)
Locate borings to identify the vertical and lateral extents of areas of peat deposits, compressible soils, and low strength soils, where significant consolidation or danger of shear failure is considered possible. Consider geophysical or cone penetrometer testing to replace borings to the extent that it is cost effective. See Section 406 for additional information regarding other exploratory methods.
303.5.3 Uncontrolled Fills, Waste Pits, and Reclaimed Surface Mines (Type C3)
Locate borings within the limits of uncontrolled fills, waste pits, and reclaimed surface mines to determine the composition and extent of the fill and character of the underlying natural soils. Locate borings transverse to centerline or baseline as required to establish the lateral extent of such conditions beneath the full width of the proposed embankment. Extend borings through rubbish, debris, scrap, waste materials, clean fill soils, or other artificial fill materials, through underlying soft soils, and into stiff or medium dense soils or bedrock. Comply with all environmental regulations.
303.5.4 Underground Mines (Type C4)
Where the roadway crosses areas of known or possible underground mining, locate borings transverse to centerline or baseline as necessary to establish the lateral extent of mining conditions. Consider surface features, geology, and mine records in determining boring locations. Use geophysical techniques, where appropriate, with drilling, as part of a comprehensive exploration program. Each program exploring underground mines must be tailored for the specific project and site conditions. Contact the District Geotechnical Engineer when mined conditions are anticipated or encountered.
For a preliminary boring program, extend borings to 5 to 20 feet below the lowest known mined interval. Obtain enough information to determine the presence or absence of minable seams and voids, to define the vertical and lateral extent of the seam including its strike and dip, to determine mining impacts, and to determine the phreatic water surface and water quality of each minable seam.
Additional borings may be needed to explore voids or other anomalies encountered in the preliminary borings. For subsequent explorations, extend borings to 5 feet below the lowest known mined interval. Use angled borings, if necessary, when exploring shafts or other slope entries or consider geophysical techniques. Refer to the ODOT Manual for Abandoned Underground Mine Inventory and Risk Assessment for additional guidance.
303.5.5 Landslides (Type C5)
Locate borings within the top, middle and bottom of the landslide area, or as near to these locations as practical. Obtain additional offset and longitudinal borings to define the landslide limits and the bedrock surface as necessary, considering the anticipated remediation. Extend borings through overburden soils and into bedrock. If bedrock is known to be very deep, extend the borings at least 30 feet below the estimated failure surface.
If bedrock is encountered, sample a minimum of 10 feet of bedrock at each boring location. Adjust boring spacing and location, bedrock coring, and boring depth per Section 303.7.3 if the landslide repair will involve a retaining wall.
Figure 300-4. Example boring plan for a landslide exploration.
303.5.6 Rockfall (Type C6)
Refer to Section 303.4.2 with the exception that the mapping of existing bedrock exposures becomes the primary method of exploration with the proposed boring plan used to augment the mapping.
303.5.7 Karst (Type C7)
Subsurface karst features are best explored using both boring and geophysical testing methods. Contact the District Geotechnical Engineer if karst features are suspected.
303.6 Proposed Underground Utilities (Type D)
Locate borings as near as practical to the centerline of proposed underground utilities to disclose the nature of subsurface materials and determine whether the required excavation will be in soil or bedrock.
Where subsurface conditions are considered uniform, space the borings a maximum of 600 feet apart, including one boring at the beginning of the excavation and one boring at the end of the excavation. Place borings closer than 600 feet as necessary to identify non-uniform or problematic conditions.
Extend borings to a depth of 3 feet below the depth of any proposed underground utilities. Drill borings deeper if significant sheeting or shoring is required.
Perform Standard Penetration Test sampling at maximum 5.0-foot intervals. Obtain representative undisturbed samples when appropriate.
303.7 Structure Borings (Type E)
Locate borings within the limits of the proposed substructure elements. Locate borings initially to provide adequate information for the design of the complete substructure unit. If the initial data does not reveal sufficient information to define the subsurface conditions relative to structural support and performance, or if the structure location or concept is changed, obtain additional borings.
Exceptions to the boring depths specified in this section may be made if the size and type of structure or subsurface conditions warrant. Extend borings through any unsuitable or questionable foundation materials into stiff or medium dense soil or into bedrock to sufficient depth where the loads imposed by the structure do not significantly affect settlement. As a general rule, carry borings to such depths that the net increase in soil stress under the load of the structure is less than 10 percent of the effective soil stress at that depth, unless hard or dense soils or bedrock are encountered first.
Unless noted otherwise, obtain samples in structure borings at 2.5-foot intervals to a depth 20 feet below the proposed footing elevation. Obtain samples below this depth at maximum 5-foot intervals. For foundation elements subject to scour, obtain continuous samples for particle-size analysis from the approximate elevation of the channel bottom to a depth 6 feet below the channel bottom, and perform a complete classification in accordance with Section 603 on each sample.
Where bedrock is exposed within or near the limits of the proposed structure, determine the bedrock surface elevation and the horizontal and vertical limits of the exposed bedrock by survey methods. Determine the type of bedrock by visual inspection at the site of the exposure.
303.7.1 Bridges (Type E1)
Obtain a minimum of one boring for each substructure unit. For substructure units over 100 feet in width, obtain a minimum of two borings. Consider twin parallel structures as one structure, unless site conditions dictate that they should be considered as individual structures. If the initial data does not reveal sufficient information to define the subsurface conditions, obtain additional borings. Where the bedrock surface varies significantly, additional borings may be required to adequately define the subsurface conditions.
Extend borings for bridges in soil through soft or loose soil and 30 feet into hard or dense soils requiring not less than 30 blows per foot. Extend borings in soil to depths not less than 30 feet but no greater than 100 feet below the proposed footing elevation.
Where bedrock is encountered above the proposed footing elevation, core bedrock to a depth of 5 feet below the proposed footing elevation. Where bedrock is encountered below the proposed footing elevation, core a minimum of 10 feet of bedrock. Core additional (deeper) bedrock if drilled shafts are being considered.
303.7.2 Culverts (Type E2)
- (Type E2a) For three-sided culverts, and pipe culverts or box culverts with a planned diameter or span greater than 10 feet , obtain two borings at opposite corners, one each near the proposed inlet and outlet. Extend borings through soft or loose soil and 20 feet into soils requiring not less than 20 blows per foot . Extend borings in soil to a minimum depth of 30 feet below the bottom of the culvert, or 5 feet into bedrock, whichever is less. Scour sampling and testing are not required for pipe culverts and box culverts.
- (Type E2b) For pipe culverts or box culverts with a planned diameter or span less than or equal to 10 feet and planned full height headwalls, locate embankment borings at the proposed culvert to define the subsurface conditions. No additional borings are required. If no embankment borings are planned, such as for a culvert replacement, obtain two borings at opposite corners, one each near the proposed inlet and outlet, each to a depth of 20 feet below the invert elevation of the culvert or to auger refusal on bedrock, whichever is shallower. If auger refusal is encountered above the stream bed, core bedrock to the elevation of the stream bed. Scour sampling and testing are not required for pipe culverts and box culverts. Do not drill borings for a culvert with planned half-height headwalls or a pipe culvert with a planned diameter less than 5 feet.
- (Type E2c) For culverts of any size that will be bored and jacked or tunneled, obtain a minimum of two borings, one each near the proposed inlet and outlet. Obtain additional borings as needed to define all materials to be penetrated by boring and jacking or tunneling.
- For any culverts with a planned span greater than 20 feet, obtain borings per Section 303.7.1.
303.7.3 Retaining Walls (Type E3)
Obtain borings for retaining walls along the proposed wall alignment. Obtain a minimum of one boring for each retaining wall. For walls over 100 feet in length, obtain a minimum of two borings. For walls over 300 feet in length, space borings a maximum of 150 feet apart. Obtain additional borings as required for stability considerations for walls above or below slopes.
Where two retaining walls will be placed back-to-back within 100 feet of each other, such as an elevated ramp, alternate the boring locations between the two walls and space the borings approximately 150 feet apart.
- (Type E3a) For retaining walls 8 feet high or less, extend the borings below the bottom of the wall face to a depth of twice the height of the wall.
- (Type E3b) For retaining walls more than 8 feet high, extend the borings as follows.
- For borings in soil, extend the borings below the estimated bottom of the wall face through soft or loose strata 20 feet into very stiff or medium dense soils requiring not less than 16 blows per foot, or having an estimated undrained shear strength >2.0 ksf, but not less than 1.5 times the wall height.
- For borings that encounter bedrock above the estimated bottom of the wall face, core bedrock to a depth of 10 feet below the estimated bottom of the wall face.
- For borings that encounter bedrock below the estimated bottom of the wall face, extend the boring 10 feet into bedrock.
For retaining walls which have a drilled-in foundation, such as soldier pile and drilled shaft wall types, extend the borings to a depth below the bottom of the wall face equal to the wall height whether bedrock is encountered or not.
If the proposed wall is to include permanent tiebacks or soil nails, obtain additional borings to determine the subsurface conditions in the anchor zone. Locate borings at a distance 1.0 to
1.5 times the wall height behind the proposed wall (anchor zone may be further behind wall depending on the subsurface conditions and backslope – adjust boring locations accordingly) and at the same spacing as the borings located along the wall alignment. Extend the additional borings to the same elevation as the bottom of the borings located along the wall alignment.
303.7.4 Noise Barrier (Type E4)
Obtain borings for noise barrier foundations along the proposed barrier alignment, or as close as practical without compromising the quality of the geotechnical data. Space the borings approximately 200 feet apart. Extend borings to depths of 25 feet or 5 feet into bedrock, whichever is less. Obtain samples at 2.5-foot intervals for the entire depth of the boring.
303.7.5 CCTV and High Mast Lighting Towers (Type E5)
In most cases, additional borings for light tower foundations are not necessary, as the borings for the nearby roadway and structures are sufficient for the design of lighting foundations. Refer to Section 1140-8 of the ODOT Traffic Engineering Manual for more information regarding light tower foundations. When additional borings are necessary for light towers, extend borings to depths of 25 feet or 5 feet into bedrock, whichever is less. Obtain samples at 2.5-foot intervals for the entire depth of the boring.
303.7.6 Buildings and Salt Domes (Type E6)
Drill a minimum of two borings for each building or salt dome less than 100 feet in length, width, or diameter. Locate borings along the perimeter of the proposed structure. Drill additional borings spaced approximately 100 to 150 feet apart if the dimensions of the proposed structure are greater than or equal to 100 feet. Extend borings a minimum of 10 feet below the anticipated foundation depth for lightly loaded buildings, such as maintenance garages. Extend borings a minimum of 20 feet below the anticipated foundation depth for heavily loaded structures and salt domes. Terminate the boring if bedrock is encountered below the footing elevation. Additional borings or deeper borings may be needed if soft or organic soils, shallow bedrock, or uncontrolled fills are encountered at the site.
304 Method of Payment
Reconnaissance and Planning is an engineering service to be performed and paid for according to the engineering agreement and the Specifications for Consulting Services. The method of compensation will be actual cost plus a net fee.