Published: July 15, 2022
Perform the work in a manner to promote the greatest accuracy in results, efficiency in execution, safety of life, protection of property, and according to the directions and to the satisfaction of ODOT and the Consultant. Refer to “Geotechnical Engineering Circular No. 5, Geotechnical Site Characterization,” FHWA NHI-16-072, for state of the practice information regarding boring, sampling, and field testing. This publication is available on the FHWA website.
401.1 Schedule of Borings
Prepare a complete boring schedule prior to proceeding with the borings. For each boring, provide a reference to centerline or baseline, planned depth, sampling frequency, and any planned in-situ testing – subject to approval by the District Geotechnical Engineer. Schedule borings so as to minimize delays and moving of drilling equipment.
401.2 Inspection and Supervision
The Consultant is responsible for the inspection and supervision of the boring and sampling as it is being performed. The use of faulty equipment or improper procedures is not permitted. Failure to correct faulty equipment or improper procedures is cause for stopping the work.
401.3 Field Location of Test Borings
The Consultant is responsible for placing necessary staking on a project site. Identify the location of test borings for roadway, bridges, retaining walls, or other purposes on the ground by a stake showing boring exploration identification number.
Access to the project site will be as stipulated in the ODOT Specifications for Consulting Services. Prior to entry on private property, coordinate right of entry with the District. If access to private property is denied, notify the District Production Administrator.
Obtain all necessary permits from government and private agencies. For work performed within ODOT right-of-way, complete Form MR 505 and submit to the District Permit Department.
401.6 Underground Installations
Determine the location of all underground installations such as gas lines, water lines, sewers, electrical cables, telephone cables, highway lighting, or other structures prior to performing the borings. Notify the appropriate owners of such installations of the work to be performed. Most utility owners can be contacted through the Ohio Utilities Protection Service (1-800-362-2764) and usually require at least two business days’ notice prior to commencing the work. Local municipalities or the ODOT District that own or maintain utilities may need to be contacted directly. Exercise caution to avoid damage to underground installations.
401.7 Operation on Navigable Waters
In cases where borings are to be performed within the limits of navigable waters, notify the authority having jurisdiction over such waters (the District Engineer of the U.S. Army Corps of Engineers; the United States Coast Guard; the port, river, or harbor authority; or any other applicable authority) of the proposed work. Obtain approval for entry on such waters and conform to any regulations of the governing authority.
401.8 Stream Gauges
At sites where borings are made from a barge, boat, or other piece of floating equipment, install an adequate stream level gauge and keep records of water surface elevations for determining accurate boring elevations. Furnish a reference elevation point necessary for proper setting of the gauge. Establish this point in accordance with the latest ODOT Survey Manual, as defined for low order spot elevations.
401.9 False Starts
If a boring cannot be completed due to encountering underground utilities, structures, or hazardous materials, the existence and location of which were not previously known, the boring will be considered a false start, for which payment will be made.
401.10 Abandoned Borings
Advance borings to the depths specified through whatever material is encountered, including boulders, fill, and other types of obstructions. No measurement or payment will be made for borings abandoned or lost before reaching the specified depth, except as provided for by false starts. Do not abandon any boring without first obtaining the approval of the District Geotechnical Engineer.
401.11 Cave-ins and Voids
If, while drilling borings, cave-ins or voids are encountered in the soil or bedrock, including at a possible mine or karst location supporting existing roadways, contact the District Geotechnical Engineer. Take care to prevent cross-hole communication, artesian flow of groundwater from the void, or any other potential dewatering.
401.12 Hazardous and Toxic Materials
If during drilling operations, 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.
401.13 Damage to Property
Perform the operations in such a manner to minimize damage. Repair any damage and restore the premises to the conditions initially encountered as much as practical.
Report property damage within one week of completing all work on the property. Use the property damage report in Appendix B to report damage and submit to the District Production Administrator. ODOT is not liable for damage to property when such damage is a result of negligence in the performance of the work.
401.14 Traffic Maintenance
Provide traffic control according to the Ohio Manual of Uniform Traffic Control Devices for the appropriate Typical Application Number for the site. This publication is available online.
401.15 Groundwater Determination
Measure and record the groundwater level in all borings drilled on land prior to adding drilling fluid, at the completion of drilling, and at other times as necessary. If more than one day is required to complete a boring, measure and record the depth of the boring at the end of each day and the groundwater level at the beginning and end of each day. No additional compensation will be made for groundwater determinations except when required for instrumentation.
402 Methods of Advanced Borings
402.1 Hand Operated Equipment
These types of equipment are portable, relatively easy to move, and can sample to relatively shallow depths either individually or in conjunction with multiple pieces of equipment. General types of hand operated equipment include, but are not limited to, hand augers, mechanical soil augers, and peat samplers. Refer to ASTM D 1452 for guidance on equipment and procedures for the use of earth augers in shallow geotechnical explorations.
402.1.1 Hand Auger
Hand augers are acceptable for obtaining disturbed samples of fine grained soils, free of larger gravels, cobbles, boulders, large rock fragments, or construction debris. This equipment can also be used in granular soils or saturated fine grained soils, but with limited effectiveness.
The equipment should be of a type that will retain the soil as it is cut with a minimum 2-inch (50 mm) diameter cutting head. The cutting head may be a bucket style, which retains the sample within the cutting head, or a screw style, which retains the sample on the auger flight.
402.1.2 Mechanical Auger
A mechanical auger is acceptable for obtaining disturbed samples of fine grained soils, free of larger gravels, cobbles, boulders, large rock fragments, or construction debris, above the piezometric surface. This equipment can also be used in granular soils or saturated fine grained soils, but with limited effectiveness.
The equipment is advanced using a continuous flight auger, with a power source at the end of the shaft. Power sources include, but are not limited to, hand-held drill, small hand- operated combustion or electric engine, or a portable drilling platform.
402.1.3 Peat Sampler
A peat sampler is acceptable for obtaining disturbed samples of saturated or very soft, fine grained soils or peat, free of larger gravels, cobbles, boulders, large rock fragments, or construction debris. The peat sampler can be used in conjunction with a hand auger or a mechanical soil auger to reach the desired sample depth prior to use.
The equipment consists of an open plate sampling head which is pushed into the undisturbed soils for the length of the sampling head. The sampler is then twisted 180º clockwise, cutting a sample core which is then retracted to the ground surface.
Other forms of hand operated equipment such as, but not limited to, tripod with portable motorized cathead, probing rods, or retractable plug sampler, may be used with prior authorization from the District Geotechnical Engineer.
402.2 Rotary Drilling
This type of equipment employs either mechanical or hydraulic power from an integral motor or power take-off from the carrier vehicle. Rotary drills are equipped with an automatic hammer for drive sampling, hydraulic head, and a chain or cable pulldown for press sampling and coring. These drill rigs are available in truck-mounted, track-mounted, rubber-tired ATV-mounted, skid-mounted, or trailer-mounted. Use a calibrated automatic hammer, except for portable drilling equipment such as a skid rig. Other exceptions require prior authorization from the District Geotechnical Engineer. Air or water rotary drilling is permissible as long as the operation minimizes adverse impact to the surrounding formation. General types of rotary drilling are: continuous flight solid stem auger, hollow-stem auger, cased (concentric), and rotary wash (mud) drilling.
402.2.1 Continuous Flight Solid Stem Augers
This method is acceptable to determine the vertical sequence of fine grained soils relatively free of cobbles and boulders, and for obtaining disturbed or undisturbed samples. This method should not be used in soil formations where the boring walls become unstable when not supported.
402.2.2 Hollow Stem Augers
This method is acceptable to determine the vertical sequence of subsurface strata in materials relatively free of cobbles and boulders, and for obtaining disturbed or undisturbed samples. This method of drilling is acceptable for advancing the boring and recovering undisturbed samples, provided the inside diameter of the auger stem is large enough to permit recovery of 3-inch (75-millimeter) diameter or larger undisturbed samples.
Except in saturated sand, use a center plug when advancing the augers between sample intervals to limit soil cuttings from entering the hollow stem augers.
402.2.3 Cased (Concentric) Boring
This method is acceptable for all borings in soil and rock. Casings maintain an open drill hole, ensure maximum circulation of drilling fluid, and prevent foreign materials from falling into the hole. Use flush-joint casing for drilling or driving. Use commercial pipe with couplings only for driving. Telescoping casing may be used as long as the minimum size does not restrict sampling. Perform all sampling in advance of the casing shoe.
402.2.4 Rotary Wash (Mud) Drilling
This method is acceptable for advancing the boring, maintaining an open hole, and obtaining either disturbed or undisturbed samples, especially below the piezometric surface. Maintain a head of drilling fluid above the piezometric surface when advancing the boring.
Use and dispose of drilling fluids and muds properly and according to all manufacturer recommendations and applicable state and federal regulations.
402.3 Other Boring Methods
Other forms of boring methods such as bucket augers, sonic drilling, direct push, and angle hole drilling, may be used with prior authorization from the District Geotechnical Engineer.
403 Types and Methods of Sampling
In general, there are three types of samples obtained in a subsurface exploration: disturbed samples, undisturbed samples, and rock cores. Obtain samples that are representative of the in situ soil and rock. During the advancement of the boring, inspect the cuttings generated at the surface for signs of strata changes. Refer to ASTM D 4700 for guidance on both disturbed and undisturbed sampling of soils from the vadose zone. As a minimum, obtain a soil sample at each strata change and at intervals not to exceed 5 feet. Obtain soil samples at more frequent intervals as required in Section
300. When encountered, obtain continuous samples of bedrock as required in Section 300.
403.1 Disturbed Samples
Disturbed samples of soil are samples obtained in a manner that does not cause alteration in the composition of the material, but may cause a major disturbance in the soil structure. Disturbed samples are commonly used for visual description, water content determination, and soil classification. The most common and accepted method of obtaining disturbed samples in soils free of cobbles and boulders is split-spoon sampling performed during the Standard Penetration Test. Perform the Standard Penetration Test as outlined in AASHTO T 206 or ASTM D 1586 and as directed in Section 300, except as noted here. If the sampler sinks under the weight of the rods or under both the weight of the rods and hammer, note the length of travel to the nearest inch (25 mm) and drive the sampler through the remainder of the test interval. If the sampler sinks for a complete 6-inch increment, record 0 blows for that increment. Do not drive the sampler more than 18 inches. Use a calibrated automatic hammer, except for portable drill rig(s) utilized for difficult access. Other exceptions require prior authorization from the District Geotechnical Engineer.
Disturbed samples may also be obtained with hand operated or rotary drilling equipment (auger samples), in test pits (bulk samples), and auger tube sampler.
403.2 Undisturbed Samples
Undisturbed samples of soil are samples obtained in a manner that causes minimum disturbance to both the structure and composition of the soil. Undisturbed soil samples are obtained primarily with thin-walled tube samplers and piston samplers.
403.2.1 Thin-walled (Shelby) Tube Sampler
This type of sampler consists of an open tube constructed from steel, galvanized steel, or brass. Collect thin-walled tube samples according to AASHTO T 207 or ASTM D 1587.
403.2.2 Piston Sampler
For very soft or highly saturated soils, where poor recovery from a thin-walled tube sampler occurs, a piston sampler can be used. The piston sampler is very similar to the thin-walled tube sampler, except that a piston is used to create a vacuum within the tube which holds the sample in place, reducing the potential for the sample loss.
403.2.3 Other Undisturbed Samplers
Other types of undisturbed samplers such as Denison sampler, pitcher sampler, and WES sampler, can be used with prior authorization from the District Geotechnical Engineer.
403.3 Coring of Rock
During drilling operations, exercise extreme care in determining the top of bedrock. Upon encountering top of bedrock, take a continuous cylindrical core to disclose the sequence of rock strata and for laboratory analysis as necessary. Perform coring in accordance with AASHTO T225, except a single tube barrel is not permitted. As a minimum, use a double tube core barrel, swivel type.
Water, air and slurry drilling methods are all acceptable. Select a method that minimizes loss or breakage of the core and minimizes the impact to the in-place formations.
Use a size and type of core barrel and bit in the coring of rock, concrete, or boulders that permits maximum recovery of the penetrated interval. A Type N series core barrel (NX or NQ) is preferred. Smaller sizes than Type N are not permitted. Adjust drill fluid or air pressure and rate of flow, speed of bit rotation, and pressure on the bit as necessary to try to achieve 100 percent recovery. Do not exceed 5 feet in the initial coring run below top of rock. Do not exceed 5 feet in a coring run in fractured or highly fractured rock. After achieving 90 percent recovery in rock that is moderately fractured or better, increase core run lengths to a maximum of 10 feet.
Angle hole core drilling or scribe knife core drilling may be used to better define the bedding planes and fracture orientations with prior authorization from the District Geotechnical Engineer.
404 Standard Penetration Testing (SPT) Calibration
Standard Penetration Testing (SPT) has well-documented variation in the energy delivered to the split-spoon sampler from the hammer. The SPT hammer efficiency variation results in SPT blow counts that may not be representative of the actual subsurface conditions. Some items affecting the energy delivered to the split-spoon sampler include the drill rig type, hammer type, drill rod, and hammer operating system. In an effort to normalize Standard Penetration Testing, calibration of each SPT hammer utilized on ODOT projects is required such that an N60 value, penetration resistance normalized to 60 percent drill rod energy ratio, can be determined for each split-spoon sample. Details of the calibration requirements are presented below.
404.2 Calibration Testing
Calibrate each hammer system by energy testing in accordance with ASTM D 4633 and calculate a drill rod energy ratio, ER. Perform the calibration under the supervision of a Registered Engineer.
Perform the SPT energy calibration for each hammer system at least once every two years and after any hammer system change or repair. Keep a copy of the latest calibration records for the hammer system being used with the drill rig. Provide a copy of each calibration to the Office of Geotechnical Engineering, Attn: Field Exploration and Lab Section Head.
404.3 Determination of N60 Value
Record the blow count (N) values for the Standard Penetration Testing. Correct the measured N value to an equivalent rod energy ratio of 60 percent, N60, by the following equation:
N60 = Nm x (ER/60)
Nm = measured N value = Y+Z
Y = number of blow counts in second 6-inch interval Z = number of blow counts in third 6-inch interval
ER = drill rod energy ratio, expressed as a percent, for the system used
Record the N60 value to the nearest whole number. Utilize the hammer system measured ER value up to a maximum ER value of 90%. It is not necessary to correct refusal blow counts, defined as an SPT drive requiring more than 50 blows with less than 6 inches of penetration.
405 Size, Identification, Preservation, Handling, and Storage of Samples
Clearly and permanently identify all samples with the minimum information: County-Route-Section, Exploration Identification Number, field sample number, and depth from ground surface. Provide suitable facilities for storage, packaging and delivering of samples to guard against theft, loss, damage or breakage. Do not permit samples to freeze under any circumstances prior to visual description and testing.
Retain all untested portions of samples through completion and ODOT approval of Stage 2 plans. Prior to disposing rock cores, contact the District Geotechnical Engineer so that they may take possession if they choose to do so.
405.2 Standard Penetration Samples
Place a representative sample of material in a tightly capped container immediately after collection to prevent loss or gain of moisture. Resealable bags are not acceptable as a sample container. Place material from a single soil stratum in the sample container. If multiple soil strata are encountered in a sample, use a separate container for each stratum sample. Identify each sample by the same sample number, but label as “A”, “B”, “C”, etc. for each stratum encountered in the sample from top to bottom. Record the sample depth at which the strata change occurred.
Do not jam the sample into the container, and take care to minimize damage to the soil structure of the sample. Remove any excess drilling fluid from the sample. Label, preserve and transport the soil samples according to ASTM D 4220, Paragraph 4.1.2.
405.3 Other Disturbed Samples
Collect disturbed samples obtained from test pit or by hand operated equipment in accordance with Section 405.2 Standard Penetration Samples.
Place bulk samples collected in a tightly woven bag, retaining a small portion of the sample in a tightly capped container for moisture determination. When moisture density testing is required, collect at least 20 pounds (9 kilograms) if the sample is fine grained, and relatively free of large gravel, cobbles, boulders, or deleterious materials. If the sample contains a large amount of granular materials, increase the sample size to 40 pounds (18 kilograms).
405.4 Undisturbed Samples
Obtain undisturbed samples that are not less than 3 inches in diameter, and not less than 18 inches nor greater than 24 inches in length, exclusive of any material removed from the ends of the sample prior to sealing. Seal and label samples according to AASHTO T 207 or ASTM D 1587. Transport undisturbed samples according to ASTM D 4220, Paragraph 4.1.4.
405.5 Rock Cores
Submit rock cores in compartmented corrugated cardboard boxes, plastic boxes, or wooden boxes with a cover and prevent accidental opening during handling. The inside of the box should be partitioned into either four or five compartments, each being 2-1/4 inches by 2-1/4 inches in cross- section and hold a total length of no greater than 10 feet of rock core. For quality photographic purposes, the box length will be no greater than 2.5 feet. Identify boxes of rock cores, in addition to the above requirements, by box number and total number of boxes per boring. Additionally, record the core run recovery and run RQD. Place all labeling information on the top of the cover and side of the box. Figure 400-1 illustrates the labeling of the core box.
Place cores in a box in the exact order as removed from the boring. Clearly and permanently mark the top and bottom depths of each coring run and insert and secure dividers between each coring run. Securely block core in a partially filled compartment to prevent shifting and dislocation including where voids or core loss are encountered. Do not divide core from the same core run between boxes. Do not place rock cores from more than one boring in the same box.
If testing is anticipated, protect rock cores during transport and storage until testing can be accomplished. Preserve these rock cores according to ASTM D 5079, Paragraph 7.5.2, excluding the use of microcrystalline wax.
Figure 400-1. Rock Core Labeling.
406 Field Tests
The following field tests are acceptable test methods and explorations and may be used with prior authorization from the District Geotechnical Engineer.
406.1 Test Pits
Perform test pits utilizing excavation equipment. Construct the test pits to the appropriate depth and width to expose the interval to be examined. Comply with applicable regulations regarding trench safety.
Examine the soil and moisture conditions of the test pit sidewalls and bottom of the excavation. Note the soil type, layer thickness, seepage depths, moisture condition, and soil strength measured using a hand penetrometer. Obtain samples for classification and moisture content testing. Record findings and observations on the Field Test Pit Log, which is described in Section 409.3. A sample Field Test Pit Log is presented in Appendix B. Take representative digital photographs of test pit sidewalls.
406.2 Cone Penetration Test
The cone penetration test (CPT) is the hydraulic push of an instrumented steel probe at a constant rate to obtain continuous vertical profiles of stress, pressures, and/or other measurements. No boring, cuttings, or spoil are produced by this test. Testing is conducted according to ASTM D 5778. The cone penetration test can be conducted without the use of a pore pressure measurement (i.e. CPT) or can be conducted using a device to measure penetration pore pressure using a piezocone (i.e. CPTu). Some equipment has the capability to measure the propagation of shear waves using a seismic piezocone (i.e. SCPTu).
406.3 Dynamic Cone Penetration Test
The dynamic cone penetration (DCP) test is performed using a steel rod with a steel cone attached to one end, driven into the soil by dropping a sliding, calibrated hammer from a standard height. Testing is conducted according to ASTM D 6951. The material strength is measured by the penetration in inches (millimeters) per hammer blow. Although the procedure is typically used to evaluate the strength of pavement and subgrade materials, it can also be used to evaluate the compaction of fill and characteristics of deeper soils. The results of the DCP test can be correlated with CBR, unconfined compressive strength, resilient modulus, and shear strengths.
406.4 Pressuremeter Test
The pressuremeter test (PMT) involves inflating a cylindrical probe against the sidewalls of a boring. In general, the instrument is placed in a pre-bored hole prior to expansion, although it is possible to self-bore the instrument to the test location. The pressuremeter can be used to obtain specific strength and deformation properties of the subsurface soils and rock.
Testing is performed according to ASTM D 4719. A pseudoelastic modulus can be calculated from the pressuremeter readings.
406.5 Vane Shear Test
The vane shear test (VST) is the use of a simple rotated blade to evaluate the undrained shear strength in soft clays and silts. The use of the VST should be limited to soils in which slow (6 degrees per minute) rotation of the blade will lead to undrained shearing. Testing is performed according to ASTM D 2573.
406.6 Flat Plate Dilatometer Test
The flat plate dilatometer test (DMT) involves pushing an instrumented steel blade into the subsurface soils and periodically stopping the penetration to obtain specific pressure measurements at the selected depth. No boring cuttings or spoil are generally produced by this test, although it is possible to advance a conventional soil boring and then perform the DMT downhole within the boring.
Testing is performed according to ASTM D 6635. The pressure measurements, combined with the hydrostatic water pressure, produce three index parameters related to soil classification, compressibility, and horizontal stress.
406.7 Geophysical Testing
Geophysical testing methods are often non-invasive and the results can be used to establish the stratification of subsurface materials, the profile of the top of bedrock, depth to groundwater, limits of types of soil deposits, rippability of hard soil and rock, and the presence of voids, buried pipes, and depths of existing foundations. In general, geophysical testing can cover a relatively large area with few tests. Results are interpreted qualitatively and best when correlated with information obtained from borings, test pits, and other direct methods of exploration. Major types of geophysical testing include seismic (seismic refraction and spectral-analysis-of-surface waves (SASW)), electrical (DC resistivity, electromagnetics, and ground penetrating radar (GPR)), gravity, and magnetic methods. Refer to “Application of Geophysical Methods to Highway Related Problems” FHWA-IF-04-021 dated August 2004 for more information regarding applicability of methods. This publication is also available online.
FHWA has developed a companion web tool to aid in the selection of appropriate geophysical methods which is available here: Application of Geophysical Methods to Highway Related Problems.
406.8 Subsurface Void Imaging
Methods that have been used to image or map subsurface voids include boring cameras, boring LIDAR, and sonar. These methods can provide more information about the condition, size, and orientation of voids when that information is needed.
407 Sealing or Backfilling of Borings
Backfill or seal all borings in accordance with these specifications and in a manner which ensures against subsequent damage or injury to persons, animals, or equipment. The Consultant will be liable for claims and any regulatory violation resulting from borings which are not properly backfilled or sealed, except when the borings are performed by ODOT. Refer to Section 500 for abandonment of instrumented borings.
These requirements are not intended to be used if known contamination exists at a site, or where borings encounter contamination during the exploration. Seal borings completed at sites where contamination is known or thought to exist in accordance with the applicable oversight agency’s requirements.
407.1 Backfilling Borings
Not all borings require sealing. Backfilling a boring is a semi-uncontrolled process of placing a mixture of natural soil and bentonite pellets or chips into the boring following completion of the drilling. Backfill a boring if it meets any of the following conditions; otherwise, seal it:
- Drilled to a depth of 10.0 feet or less
- Encountered predominantly granular soils (more than 75% of the profile)
- Did not encounter static groundwater level considered to be hydraulically connected with the groundwater table (naturally occurring static water). Prior knowledge of geology and groundwater conditions in the area will be necessary.
Backfill a boring to a maximum depth of 40 feet. If a boring extends deeper than 40 feet, seal the portion of the boring below 40 feet in accordance with the requirements of Section 407.2, regardless of the conditions encountered. When predominantly granular soils are encountered pull the augers or casing to allow the natural formation to collapse. Backfill the remaining borehole which has remained open to the ground surface. It is the responsibility of the Consultant to avoid any negative impact to the environment and settlement of the backfill material.
Backfill material shall consist of a mixture of natural soil and a minimum of 20% bentonite chips or pellets, by volume. A general estimate is one 50-pound bag of bentonite chips for every 15.0 feet of boring in a 6.5-inch diameter hole. Thoroughly mix the chips or pellets and the natural soil utilizing a shovel at the ground surface and ensure that the material is sized to enable placement down the hole without bridging. Where isolated seams, layers, or pockets of water seepage are encountered, increase the amount of bentonite at those depths.
Compact the upper 10.0 feet of backfill material. Backfill to a depth of 2.0 feet below the top of the boring. For the upper 2.0 feet, place the same material as encountered in the upper 2.0 feet of the boring, matching any pavement.
407.2 Sealing Borings
Sealing a boring is a controlled process of constructing a permanent hydraulic barrier in a hole using knowledgeable seal selection and conscientious seal placement. For a boring that requires sealing, refer to Table F.1 in Appendix F for sealant material selection, depending on boring diameter and depth. The placement of the sealant material within the boring is an essential function for the sealing performance. Improper placement of a seal can result in voids and internal erosion of the seal.
If the boring is advanced into bedrock more than 10 feet, the core hole should be sealed.
Seal borings using either bentonite chips or pellets (BCP) or grout to a depth of two feet below the ground surface. For the upper 2.0 feet, place the same material as encountered in the upper 2.0 feet of the boring, matching any pavement. Acceptable use of BCP and grout mixtures are presented below.
407.2.1 Bentonite Chips or Pellets (BCP)
BCP may be used to seal a boring to a maximum depth of 40 feet.
When chips are added to water they generally hydrate and swell quickly. If chips are added to a boring too quickly they can wedge and block the hole, referred to as bridging. When fully hydrated, the bentonite forms a solid low hydraulic conductive layer which seals against the boring walls. However, hydrated bentonite has low strength and provides little bearing support.
Bentonite pellets typically hydrate at a slower rate than the chips. If the pellets are coated, then the onset of hydration is retarded until the coating has dissolved. This allows for the pellets to reach the bottom of a water filled boring prior to creating the seal.
Refer to Table F.2 for recommended sizes of bentonite chips and pellets, depending on the boring depth and diameter, based on NCHRP’s “Guide for Sealing Geotechnical Exploratory Holes”.
BCP are typically placed by “pouring” into an open boring from the surface. When placing this way, the rate of pouring is critical. Too quick of a rate of placement can result in bridging. Periodically sound the boring to determine if bridging is occurring. If bridging occurs, use a tamper to break the blockage, allowing the bentonite to fall to the bottom of the boring. Typical rate of placement of bentonite chips is 20 lbs/min.
When the boring contains a water column, bentonite pellets settle through the water column at a rate of approximately 1 ft/sec. To avoid bridging, the pellets should be placed at a rate no greater than one 50 pound bag in 2 minutes.
407.2.2 High Solids Content Bentonite Grout (HSB)
HSB is relatively thick with high viscosity. Generally, this type of grout has at least 20% solids content. The percentage of solids is determined based on the solids content, by dry weight of dry powdered bentonite and mixing water. For a solids content of 30% or more, a positive displacement pump will be necessary for pumping. Powdered bentonite and commercial one-sack grouts are readily available which only require water and means of mixing.
407.2.3 Neat Portland Cement Grout (PC)
PC consists of ASTM C150 Type I Portland Cement mixed with clean water. Typically, 5 to 7 gallons of water are mixed with 94 pounds of cement. The mixing proportions can be expressed in terms of the water:cement ratio (w/c) which is based on the weight of water being mixed to the weight of dry cement. The unit weight of water is assumed to be 8.34 pounds per gallon. Additives are typically not utilized in this grout. Typical PC mixture designs are presented in Table F.3.
407.2.4 Cement Bentonite Grout (C/B)
C/B typically contains the same volumes of materials utilized in PC, but with the addition of bentonite. Mix proportions for a 5% C/B are presented in Table F.3.
407.2.5 Grout Placement
Mix the selected grout in accordance with industry standard practices and manufacturer’s specifications. Place all grout by tremie method. The tremie pipe can either be inserted through the hollow stem augers or casing prior to removal, or within the open boring after removal of tooling. Insert the tremie pipe to just above the bottom of the open boring making sure the tip of the tremie pipe is not inserted into loose materials. After insertion of the tremie pipe, begin grout placement either by gravity or pressure (pumped). Once grouting starts, keep the discharge end of the tremie pipe in the grout column until grouting operations are completed.
After completing the grouting operations, wait to place the top two feet of material to determine if any settlement of the grout occurs. If grout settlement occurs, add additional grout as needed before placing the upper two feet of in kind material.
407.3 Special Conditions
407.3.1 Body of Water
If a boring is drilled in a body of water and is 12 inches or less in diameter, do not backfill or seal the boring. It is preferred that the boring collapse and fill naturally.
If a void is encountered within the boring, either install casing or plug and seal the boring. Contact the District Geotechnical Engineer to notify them of the void.
If further exploration is necessary, such as borehole camera or downhole mapping, install an open ended solid casing from the ground surface into the void. Install a shale trap immediately above the top of the void. Install a hose clamp on the shale trap to minimize movement after placement. If sufficient annulus exists between the boring wall and the casing place fine aggregate (ODOT CMS Item 703.02) to 5 feet above the shale trap then place C/B grout to the ground surface. If insufficient annulus exists for placement of the fine aggregate, place the C/B grout directly on top of the shale trap.
If no further exploration is necessary, seal the boring. Place a grouting basket or plug in the boring immediately above the top of the void. After placement, install 5 feet of fine aggregate (ODOT CMS Item 703.02) on top of the basket or plug. Seal the remainder of the boring with C/B grout via tremie to ground surface.
If multiple voids are encountered within a single boring, seal using a staged grouting process, tremie method. First, seal from the bottom of the boring to the base of the lowest void with C/B grout. Allow to set for a minimum of 12 hours. Second, install a grouting basket or plug at the top of the lowest void. Seal the section of boring between the lowest void and the next overlying void. Allow to set for a minimum of 12 hours. Repeat as many times as necessary based on number of voids encountered.
407.3.3 Flowing Artesian Conditions
A flowing artesian condition occurs when the hydrostatic head pressure of a water source is greater than the distance from the ground surface to the top of the water-bearing stratum. When the confining layer is penetrated by the boring, water flows from the top of the boring. A head pressure several feet above the ground surface may be encountered. As the boring is advanced, the flow may become restricted. If a flowing artesian condition is encountered at any time during the drilling process, the boring must be sealed in accordance with these requirements.
Capture the artesian head pressure immediately upon encounter and upon drilling completion, if still flowing, by adding a sufficient number of augers or casing to confine the flowing water. Record the height of the water column above the ground surface. Depending on the depth to the top of the water bearing stratum and the measured head pressure above the ground surface, prepare a grout mix to seal the boring that is heavy enough to overcome the hydrostatic pressure (heavy grout). Refer to Table F.4 for design of the heavy grout mix. If a HSB grout is used, the grout will need to be around 30% solids or greater, or include weighting agent drilling additives to overcome the hydrostatic head pressure.
Place the heavy grout using a tremie method within the augers or casing for the full depth of the boring. After initial grout placement, incrementally remove the augers or casing while maintaining a full column of grout and inspecting for water flow at the ground surface. Add grout as necessary to maintain a boring full of grout throughout the removal process. After removal and grout placement, inspect for flowing water at the ground surface. If water flow is observed, reinstall the augers or casing and replace grout with a heavier grout mix. Refer to Table F.4 for design guidance of a heavier grout mix.
When unable to capture the head with the addition of the augers or casing, the use of a disposable or grouting packer may be necessary to restrict the artesian flow to allow for grout placement.
408 Coring and Patching of Bridge Decks
When advancing a boring through a bridge deck, locate the boring to avoid any structural members. If the structure contains prestressed box beams, do not drill through the beams. If a bridge structural member is struck or damaged, immediately contact the District Geotechnical Engineer. When possible, place the boring in the shoulder or in the center of a driving lane to avoid the wheel path of a driving lane.
When coring through a bridge deck, utilize the following procedure unless otherwise directed by the District Geotechnical Engineer or District Bridge Engineer. Step-core the corehole using thin walled core bits. Do not use augers to advance through bridge decks. A step-cored hole consists of two concentric cores, a through core and an over core. The through core consists of a core hole slightly larger in diameter than the outside diameter of the auger or casing to be used in advancing the boring. The through core is advanced the full depth of the bridge deck. The over core will be at least 2 inches larger in diameter than the through core to allow for a minimum 1-inch lip inside the two holes. Advance the over core approximately one-third the depth into the bridge deck.
Upon completion of the boring, place a minimum ¼-inch thick steel plate, cut to the diameter of the over core, on the lip to close off or seal the through core. Fill the over core hole with a high strength quick set concrete flush with the surface of the bridge deck, as shown in Figure 400-2.
Figure 400-2. Typical patch of a bridge deck.
409 Field Boring Logs and Other Records
409.1 Field Boring Logs
Complete a field boring log for each boring hole drilled. The field boring log will contain heading and field data sections which are described in more detail as follows.
409.1.1 Field Boring Log Heading
Record the following information in the heading of the field boring log:
- Project Designation (generally either County-Route-Section or Bridge Number)
- Exploration identification number
- Location; referenced to centerline or baseline or survey stationing, measured to the nearest 1 foot . Include GPS coordinates, see Section 303.2
- Type and make of drilling equipment
- ER and date of last calibration of hammer system
- Method of drilling and sampling employed
- Boring diameter
- Dates of start and completion of the boring
- Names of personnel on site, including crew chief, crew members, and logger
- Ground surface elevation of boring, measured to the nearest 0.1 foot and referenced datum
- Sheet number and total number of log sheets for the boring
- Method and material (including quantity) used for backfilling or sealing, including type of instrument installation, if any
- Any general remarks concerning the drilling operations
409.1.2 Field Boring Log Data
Record the subsurface information relating to the strata conditions and sampling information on the field boring log. Measure depths to the nearest 0.1 foot. Include the following information:
- Thickness of pavement, sod, or topsoil cover at surface
- Depth, length and type of each sample
- Number of blows, in 6-inch increments when standard penetration tests are taken
- Length of each rock core run
- Amount of sample recovered in each sample, measured in inches (millimeters)
- Measurement of the Rock Quality Designation (RQD) of the core run
- Depths of strata changes
- Visual description of each strata encountered, according to Section 600
- Depth where seepage or wet conditions were encountered, including any free water within the sample
- Depth and thickness where obstacles were encountered, such as boulders, squeezing ground, heaving sands, caving materials, or buried structures
- Depth to water level prior to introduction of drilling fluid, for rock core or to wash out heaving sands
- Depth of interval where wash water or air return circulation was lost
- Depth of interval where water gain occurred, and approximate amount of gain
- Color of water and type of cuttings flushed to surface
- Change in resistance or rate of advancement
- Any unusual conditions encountered in advancing the boring and sampling
- Reason for abandoning the boring in the event that the planned depth was not reached
- Depth to water at completion of the drilling operations prior to backfilling
409.2 Rock Core Photograph
Obtain a digital photograph of each core run after placing in the box, looking directly down onto the core. Take a sufficient number of photographs of each box of core to depict the pertinent characteristics of the rock, including any necessary close-up photographs. Wet the rock to enhance the color contrast of the core. Include the project, boring, and rock core run information and a legible scale in each photograph.
409.3 Field Test Pit Log
Complete a field test pit log for each test pit excavated. Complete the heading and field data sections as follows.
409.3.1 Field Test Pit Log Heading
Record the following information in the heading of the field test pit log:
- Project Designation (generally either County-Route-Section or Bridge Number)
- Exploration identification number
- Location; referenced to centerline or baseline or survey stationing, measured to the nearest 1 foot. Include GPS coordinates, see Section 303.2
- Type and make of excavation equipment
- Dates of start and completion of the excavation
- Names of personnel on site, including equipment operator and logger
- Ground surface elevation at test pit, measured to the nearest 0.1 foot and referenced datum
- Sheet number and total number of log sheets for the test pit
- Method of shoring used, if any
- Method of backfilling or sealing
- Any general remarks concerning the excavating operations
409.3.2 Field Test Pit Log Data
Record the subsurface information relating to the strata conditions and sampling information on the field test pit log. Include the following information:
- Thickness of pavement, sod, or topsoil cover at surface
- Depths where bulk samples were taken
- Depths of strata changes
- Visual description of each strata encountered according to Section 600
- Depth where seepage or wet conditions were encountered, including any free water
- Depth and thickness where obstacles were encountered, such as boulders, squeezing ground, heaving sands, caving materials, or buried structures
- Any unusual conditions encountered in excavating the test pit
- Reason for abandoning the test pit in the event that the planned depth was not reached
- Depth to water at completion of the excavation prior to backfilling
410 Method of Payment
Boring, Sampling, and Field Testing 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 for the work involved in Boring, Sampling, and Field Testing, will be on a unit cost basis. The tasks and corresponding units for this work are listed in the Proposal/Invoice form presented in Appendix E. The work includes technical supervision of the agreement and field logging; supplying sample containers, cases, bags, sample tubes and core boxes; delivery and storage of samples; preparation, duplication and delivery of records; backfilling; furnishing all other labor, tools, machinery, materials, supplies, equipment (including floating equipment), and utilities necessary and incidental to completing the work in strict accordance with these specifications. Detailed accounting of direct non-salary expenses will be required in accordance with the Specifications for Consulting Services.
Field coordination and field logging are engineering services to be performed and paid for according to the engineering agreement and the Specifications for Consulting Services. Field coordination includes making arrangements for site access, procuring any necessary permits, clearing utilities, preparing damage reports, and property damage restoration oversight. Field logging includes preparing all records presented in Section 409. The method of compensation for the work involved in field coordination will be actual cost plus a net fee. The method of compensation for the work involved in field logging, if drilling is subcontracted, will be actual cost plus a net fee, otherwise, it will be included in the unit cost of drilling.