Exhibit A Geologic Subsurface Investigations

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EFH Notice 210-WI-145 May 2020

Exhibit A

Geologic Subsurface Investigations

Scope This exhibit provides guidelines for subsurface investigations performed by NRCS and partner staff and establishes the basic expectations for a functional review of consultant designs. It follows the policy in the National Engineering Manual , Part 531, Geology, for Group B structures, and complements the investigation guidelines presented in National Engineering Handbook, Part 631, Geology. Marking Work limits of the geologic subsurface investigation, including ingress and egress, should be shown on a plan view map, marked by stakes, flags, tree markings, or other suitable methods, and approved by the landowner. Equipment A soil bucket auger or hand probe (e.g. back saver probe) can be used to investigate soils to a depth of about 6 feet. A backhoe or excavator can be used to excavate a test pit to a depth of about 20 feet. A drill rig should be used to investigate soils to a depth greater than 20 feet. A drill rig can retrieve disturbed or undisturbed samples by drilling down to the designated sampling depth with a solid stem or hollow stem auger. A disturbed sample can be obtained by pressing a split-spoon sampler into the soil. Some silty or sandy soils will not stay in the split spoon as it is drawn up. A core catcher can be attached to the end which allows soil to enter but not fall out. An undisturbed sample can be obtained by pressing a thin-walled, Shelby tube into the soil. Some drill rigs are equipped to perform standard penetration tests (SPT) to determine relative density of the soil during the sampling process. SPT blow counts (N-value) are the number of blows per foot to drive the split spoon sampler. Empirical correlations can be made between SPT blow counts and the mechanical properties of soil, such as shear strength, which is used to determine the bearing capacity for structures. A backhoe can retrieve disturbed samples at designated depths. Soil descriptions can be performed on soil chunks removed from the test pit. Under safe conditions, undisturbed samples can be obtained by pressing a thin-walled Shelby tube into the trench wall. A Munsell Soil Color Book is used to describe soils using color properties of hue, value (lightness), and chroma (color purity). A water level meter is a battery-operated resistivity sensor on the end of a reel that is used to measure water depth in a test hole. If the water level is less than 25 feet, a cloth tape with a metal weight on the end can be used to plunk the water surface to identify the depth by sound. A Torvane apparatus is a hand-held instrument used for the rapid determination of in-situ, undrained shear strength (tons/sq. ft.) in relative layers of fully saturated, cohesive soils varying in consistency from very soft to stiff. Fine-grained soils with low porosity often appear moist but are in fact saturated. Shear strength values would be overstated for moist soils using this instrument.

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A pocket penetrometer is a hand-held instrument used for the rapid determination of in-situ, unconfined compressive strength (tons/sq. ft) in relative layers of fine-grained soils. The compressive strength is multiplied by a factor of two to get undrained shear strength (tons/sq. ft.) in saturated, cohesive soils. Fine-grained soils with low porosity often appear moist but are in fact saturated. Shear strength values would be overstated for moist soils using this instrument. A cone penetrometer is an instrumented probe with a conical tip, hydraulically pushed into the soil at a constant rate. A basic cone penetrometer reports tip resistance and shear resistance along the cylindrical barrel. The resistance is correlated to shear strength of saturated cohesive soil. A dynamic cone penetrometer is an apparatus in which a weight is manually lifted and dropped on a cone which penetrates the ground. The number of inches per hit is recorded and penetration is loosely correlated to relative density and shear strength in saturated cohesive soils. Safety Soil test pits shall be excavated to meet U.S. Department of Labor, Occupational Safety and Health Administration (OSHA) regulations with adequate size, depth and slopes to enable a person to safely enter and exit the pit, if required. Excavation requirements are contained in OSHA Standards-29 CFR 1926.651 and 1926.652. References for Soil Profile Descriptions Soil profile descriptions should be logged in accordance with the descriptive procedures, terminology, and interpretations found in:

• ASTM D 2488 Standard Practice for Description and Identification of Soils (Visual-Manual Procedure), or

• NRCS National Engineering Handbook, Part 650, Engineering Field Handbook, Chapter 4 Elementary Soil Engineering, “Field Identification and Description of Soils.”

• NRCS National Engineering Handbook (NEH), Part 631, Geology, Chapter 2-Engineering Geology Investigations; Chapter 3-Engineering Classification of Earth Materials; Chapter 4- Engineering Classification of Rock Materials; and Chapter, 5-Engineering Geology, Logging, and Testing.

Depth Soil profile descriptions should extend below the ground surface to the minimum depth required to identify critical soil properties, bedrock, or subsurface water regimes that will affect the practice design and construction. Location and Elevation Conservation practice standards often specify the minimum number, depth, and distribution of test holes. The number, depth, and distribution of test holes performed in the investigation should be sufficient to characterize the subsurface conditions. The existing, undisturbed ground surface at a test hole location should be tied to a vertical benchmark elevation and a horizontal reference point or baseline.

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Bedrock Where possible, the type of bedrock, such as sandstone, limestone, dolomite, shale, or granite, should be recorded on the soil log. The soil log should also include the top elevation of the bedrock surface, a description of weathered or unweathered condition, and the potential for excavation (rippability). Water Table Water levels fluctuate within the soil. The highest level can be identified by redoximorphic features (mottles) within the soil matrix. Redoximorphic features are characterized by redox concentrations (ferric iron accumulations), redox depletions (areas of depleted mineral oxides), and reduced matrices. Soil color descriptions using the Munsell Soil Color Book should be performed under natural light conditions to give the most accurate color determinations. Changes in soil color due to air exposure should be noted. Frozen soil should be thawed prior to evaluating soil color, texture, structure, and consistency. Identification of redoximorphic features may be difficult in sand and gravel, and soils with low amounts of organic matter and iron. These sites should be investigated during the wettest time of the year (i.e. spring or late fall) to maximize the potential of observing the highest water level. In dense soils with a high clay content, water can take up to 48 hours to equalize in a test hole. The test hole should not be filled until the end of the investigation to maximize the time for seepage into the hole. Record the water depth and time of day at the end of excavation and immediately prior to backfill to estimate equalization. The hole can be left open and fenced off, or a monitoring well can be installed, in order to observe fluctuating water elevations over time. A monitoring well typically consists of a 1.5-2” diameter PVC pipe with a slotted screen. Observed water or lack of water should be recorded on the soil log. The investigation should determine if a water-bearing stratum is a regional water table, or a localized zone of saturation perched on low permeability soil (e.g. clay pans, glacial till). A localized zone of saturation can also perch in an isolated lens of sand/gravel within a fine-grained soil unit. Perched water levels can be seasonally charged by stream or ditch flows. The engineering perspective is that a drainage system may not be effective in controlling a regional water table. The regulatory perspective is that a regional water table should not be lowered for the purposes of installing agricultural waste storage practices. Wisconsin Conservation Practice Standard 313, Waste Storage Facility, contains criteria for identifying subsurface saturation which is not to be drained. Soil Index and Engineering Properties Soil index and engineering properties are determined from disturbed and undisturbed soil samples obtained from test holes (e.g. backhoe pit or soil boring) or natural escarpments such as a raw streambank. The required sample sizes are presented in NEH, Part 631, Chapter 5, Engineering Geology, Logging, Sampling, and Testing, and ASTM D 1140-17. Index properties are qualitative properties used for the identification and classification of soils for engineering applications. Index properties include moisture content, specific gravity, grain size distribution, plasticity or Atterberg limits (liquid limit, plastic limit, and shrinkage limit), in-place dry density, and relative density. Engineering properties are used to quantify the behavior of soils subjected to various types of loads. They include shear strength (cohesion and angle of internal friction), compaction (optimum moisture content and maximum dry unit weight), permeability, compressibility, and swell/collapse potential. Engineering

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properties can be obtained from either undisturbed or remolded, disturbed samples depending on whether the loads will be applied on undisturbed or disturbed soils (e.g. borrow material). Lab tests include triaxial shear, standard or modified Proctor, unconfined compression strength (Qu), consolidation, and permeability. A variety of field tests are available to estimate soil index and engineering properties. In-place shear strength in relative layers of saturated cohesive soils can be determined with a Torvane, pocket penetrometer, or other generally accepted methods. These tools can be used along the backhoe pit wall, or natural escarpment, or from soil chunks removed from the pit. They can also be used on the ends of Shelby tubes or split spoon samples. Other common field tests include in-place density, permeability, and moisture content. Soil Profile Descriptions (Logging) Soil profile descriptions should contain the following information for each soil horizon or layer. Additional criteria can be included as described in ASTM D 2488. Example soil logs are presented in Appendix 1.

• Layer thickness (e.g. 2.3 ft) as defined by changes in moisture, color, geologic material, or texture • USCS group symbol (i.e. CL, ML) • USCS group name and modifiers (i.e. ML with sand) • Gradation by volume: percent boulders (>12 inches) and percent cobbles (3 inch to 12 inches). • Gradation by dry weight: percent gravel (3 inch to #4 sieve), percent sand (#4 to #200 sieve), and

percent fines (Passing #200 sieve). • Plasticity of fines: non-plastic, slightly plastic, low, medium, high • Munsell color(s) (e.g. – Matrix - 70%, 10 YR 5/4; Redox. Depletions - 15%, 10 YR 6/1; Redox.

Concentrations - 15%, 10 YR 5/8) o Percent of matrix and matrix Munsell color (in moist condition) o Percent of redoximorphic features defined by matrix color, redox concentration, redox

depletions, gleyed matrix, depleted matrix, or reduced matrix color, and/or manganese concentrations with the associated Munsell color

• In-situ moisture content: dry, slightly moist, moist, very moist, wet • Consistency: very soft, soft, medium stiff, stiff, very stiff, hard • Structure: stratified, laminated, fissured, slicken-sided, blocky, prismatic, lensed, homogeneous

(massive • Local geologic parent material (e.g. – alluvium, slope alluvium, colluvium, glacial till, glacial

lake sediment, outwash, residuum, loess, bedrock) • Additional observations or descriptions as needed:

o Seepage or water table depth o Depth of caving or sloughing of auger hole or investigation pit sides o Lenses or mixed materials o Ribboning length o Thread length and type of break o Dilatancy (none, slow, rapid) o Presence of roots or root holes, o Presence of mica, gypsum, etc., o Surface coatings on coarse-grained particles, o Difficulty in boring, probing or excavating, etc. should be noted.

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Hole Closure Test holes should be backfilled to the ground surface. When the investigation is complete, excavated soil used as backfill should be replaced in layers and density similar or greater than the surrounding undisturbed soils. Drill holes shall be abandoned in accordance with WI Administrative Code, Chapter NR 141, and are typically backfilled with bentonite chips or pellets. Test holes excavated within the footprint of structures create the potential for leakage or differential settlement. Careful attention should be given to test hole location or the selection and compaction of backfill material. Soils and Geology Report The geology or soils report is part of the design folder for the practice and should contain the following information, as applicable to the site:

1. A narrative discussion (soil mechanics report) a. The narrative discusses the limiting design factors and conclusions that can be drawn

from an analysis of all the soil profile descriptions, sampling, and lab testing for the project.

b. It includes the siting engineer’s evaluation of the foundation issues of structural integrity (e.g. bearing capacity, consolidation (settlement), lateral earth pressures, and slope stability) for above ground tanks.

2. Legible site map, drawn to scale, no smaller than 8.5 inches by 11 inches, showing the following: a) Vertical and horizontal reference points (TBMs) b) Geophysical baselines, if any c) Test hole locations

3. Geologic profile (see Figure 1 and 2, details will vary). 4. Soil profile descriptions for each test hole. Each log sheet should contain the project name and

practice, test hole location and elevations, investigator’s name, investigation date, equipment used, depth of collected samples, soil map unit and landscape position. The log should note limiting features such as the depth to bedrock, observed water elevations, and other subsurface water regimes found during the investigation. Also include identification of collected samples, including sampling methods, intervals, recovery lengths, and blow counts as demonstrated in Appendix 2 as applicable.

5. Lab results and lab reports on soil tests, such as soil classification, specific gravity, in-place density, moisture content, shear strength, Atterberg limits, P200, compaction, etc. Field soil profile descriptions should be red-lined with this information.

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Additional Guidance for Specific Cases Investigation in Karst Areas Bedrock profiles should be investigated for the following conservation practices if they are located within 1,000 feet of a karst feature (e.g. sinkhole):

• Embankments designed to maintain a permanent pool of water. • Embankments ≥ 25 feet in total height. • Waste treatment or storage facilities.

Geophysical tools can complement the investigation, particularly if the cost of physical investigation is prohibitive. Field data should be collected by the NRCS geologist, private consultant, or field staff trained in the use of sounding equipment. Bedrock soundings can be used to evaluate soil-filled joints, discontinuities, voids, or other indications that may warrant further investigation or design limitations. The geology or soils report for Karst areas should include the following content:

1. Bedrock profile on a site map. 2. Geophysical imaging or sounding data. 3. Interpretations, design limitations, and recommendations.

Investigation for Above Ground Tanks The foundation for an above ground tank requires additional investigation to determine bearing capacity and potential for total and differential settlement. Tanks under consideration are vertical wall structures that contain more than 50,000 gallons or exceed a footprint of 800 square feet. They are considered “above ground” if the footings or floor sets on earthfill, or 50% or more of the tank height is above the original ground surface. The level of investigation is divided into four cases (shown below). Example soil logs are presented in Appendix 2. A planning investigation may need to be followed by a more detailed design investigation to collect all the necessary information. Case I: The tank is set entirely on an excavated surface of glacial till, over-consolidated clay, or dense

coarse-grained soils.

• Consult with a soil scientist or staff experienced in soil mechanics to verify the presence of glacial till or over-consolidated clay. Over-consolidated clay can be estimated using undrained shear strength and plasticity index.

• Excavate at least two test holes to a depth of 15 feet below the tank footings or refusal. Test holes should be evenly spaced around the tank perimeter.

• Log the soil profile description. • Measure and record the relative shear strength of soil layers in the test hole or on intact soil

chunks removed from the test hole using a Torvane or pocket penetrometer. Thicker layers may need multiple readings down the test hole to detect changes in strength due to higher confining pressures. If the in-place, fine-grained soils are not firm enough to test for consistency or retrieve samples, the foundation is probably not suitable for a structure.

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• If one of the following criterion apply to the strength of soil layers, lab samples are not required. If these tests are inconclusive, an undisturbed sample can be obtained for an unconfined compression (Qu) test.

o Field tests indicate native soils have adequate bearing capacity. Adequate bearing capacity for structures, such as pre-engineered tanks and walls, is typically 2,000 psf. This correlates to a Torvane reading of 0.5 ton/sf or pocket penetrometer reading of 1.0 ton/sf.

o USCS soil description and consistency correlate to a presumptive allowable bearing capacity that exceeds the tank load. Presumptive allowable bearing capacity values can be obtained from the International Building Code (IBC) or International Code Council (ICC) or Conservation Practice Standard 313, Table 3.

Case II: The tank is set entirely on an excavated surface of alluvium, colluvium, or loess.

• Drill at least three test holes below the tank footings to a depth of 30 feet, or 1.5 times the least plan view dimension of the tank, or refusal. The test holes should be evenly spaced around the tank perimeter. Hollow stem augers, borehole casing, or drilling fluid may be needed in sands or saturated silts to keep the hole from caving in.

• Concurrently perform Standard Penetration Testing (blow counts) and Split Barrel Sampling (ASTM D 1586) at 2.5-foot intervals to a depth of 15 feet and 5-foot intervals thereafter.

• Soil logs should indicate the blow counts, sampling interval and recovery lengths. Obtain undisturbed samples of representative soil strata in each hole by pressing thin-wall, (Shelby) tubes. Seal the tubes to preserve the moisture content. Ship the samples to a lab with a testing request for specific gravity, in-place moisture content, in-place dry density, consolidation, and unconfined compression strength (Qu).

Case III: All or a portion of the tank is set on less than 3 feet of earthfill above the stripping elevation.

• Follow the protocol for Case I or II on the in-place soils, as applicable. • Estimate the area and depth of required excavation in the borrow area. Log the soil profile

description and obtain a disturbed, composite sample from at least two test holes in the borrow area. A composite sample is a representative blend of soil materials that will removed from the borrow area and used as earthfill under the structure. Ship the sample to a lab for a compaction test to develop a performance specification.

• Course-grained material used as fill may require a relative density test of the borrow material for a performance specification. A leveling course (< 12 inches) of dumped clean gravel, or sand under vibratory compaction, may be installed below the tank floor with no additional sampling or testing.

Case IV: All or a portion of the tank is set on 3 feet or more of earthfill above the stripping elevation.

• Test holes, sampling, and testing protocol under the tank and in the borrow area should be determined on a case-by-case basis in consultation with the State Conservation Engineer. This case typically involves bearing capacity and settlement computations based on consolidation and shear tests on undisturbed samples in the foundation, and consolidation, unconfined compression strength (Qu) and shear tests on remolded samples from the borrow area.

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Investigation of Post or Pier Foundations for Roof Structures Post and pier foundations are embedded structural columns that provide vertical and lateral support for buildings. They are placed in pre-excavated holes and then backfilled. Recommendations for foundation investigation are taken from ASAE EP 486.3 Shallow Post and Pier Foundation Design. The minimum site investigation typically includes 5 test holes, one at each corner and one in the center of the structure. Additional test holes along the walls depend on soil variability, and the size and importance of the structure.

• The depth of exploration should exceed the footing depth by two feet. If the footing depth is unknown at the time of investigation, use the frost depth in local codes.

• If the USCS soil description is dense coarse-grained soil to the bottom of the test hole, lab samples are not required.

• Measure and record the relative shear strength of soil layers in the test hole or on intact soil chunks removed from the test hole using a Torvane and pocket penetrometer. Thicker layers may need multiple readings to detect changes in strength due to higher confining pressures. If in-place, fine-grained soils are not firm enough to test for consistency or retrieve samples, the foundation is probably not suitable for a structure.


o Field tests indicate native soils have adequate bearing capacity. Adequate bearing capacity is typically 2,000 psf. This correlates to a Torvane reading of 0.5 ton/sq. ft. or pocket penetrometer reading of 1.0 ton/sq. ft.

o USCS soil description and consistency correlate to a presumptive allowable bearing capacity that exceed the tank load. Presumptive allowable bearing capacity values can be obtained from the International Building Code (IBC) or International Code Council (ICC) or Conservation Practice Standard 313, Table 3.

• As a substitution for test holes, an initial investigation or additional investigation for bearing capacity can be conducted with a cone penetrometer or dynamic cone penetrometer. Measure and record the relative shear strength of the soil profile about every 12 inches.

Earthfill that is used to level up a building foundation can have a significant impact on post and pier behavior. Earthfill can reduce the bearing capacity for posts/piers. The lateral sidewall strength of pre-excavated holes in earthfill can affect the stability of posts/piers that experience shear and bending moments.

• If earthfill above the stripping elevation is less than 4 feet under all or a portion of the building footprint, estimate the area and depth of required excavation in the borrow area. Log the soil profile description in the borrow area and obtain a disturbed, composite sample from at least two test holes. A composite sample is a representative blend of soil materials that will removed from the borrow area and used as earthfill under the structure. Ship the samples to a lab for compaction tests to develop a performance specification. Note: Earthfill less than 4 feet suggests posts/piers are setting on native material at the bottom of the hole.

• If earthfill above the stripping elevation is 4 feet or more under all or a portion of the building footprint, the test hole distribution, sampling, and testing protocol for the foundation and borrow pit should be determined on a case-by-case basis in consultation with the State Conservation Engineer.

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Investigation for Retaining Walls or Continuous Concrete Walls Under Roof Structures Retaining walls or foundation walls provide vertical and lateral support for live loads. The minimum site investigation typically includes 5 test holes, one at each corner and one in the center of the structure, or one test hole every 50 feet for walls. Additional test holes along the walls depend on soil variability, and the size and importance of the structure.

• The depth of exploration should be one and a half times the anticipated base width of the footing. • If the USCS soil description is dense coarse-grained soil to the bottom of the test hole, lab

samples are not required. • Measure and record the relative shear strength of soil layers in the test hole or on intact soil

chunks removed from the test hole using a Torvane and pocket penetrometer. Thicker layers may need multiple readings to detect changes in strength due to higher confining pressures. If in-place, fine-grained soils are not firm enough to test for consistency or retrieve samples, the foundation is probably not suitable for a structure.


o Field tests indicate native soils have adequate bearing capacity. Adequate bearing capacity for walls is typically 2,000 psf. This correlates to a Torvane reading of 0.5 ton/sq. ft. or pocket penetrometer reading of 1.0 ton/sq. ft.

o USCS soil description and consistency correlate to a presumptive allowable bearing capacity that exceed the tank load. Presumptive allowable bearing capacity values can be obtained from the International Building Code (IBC) or International Code Council (ICC) or Conservation Practice Standard 313, Table 3.

• As a substitution for test holes, an initial investigation or additional investigation for bearing capacity can be conducted with a cone penetrometer or dynamic cone penetrometer. Measure and record the relative shear strength of the soil profile about every 12 inches.

• If all or a portion of the walls set on less than 4 feet of earthfill above the stripping elevation, estimate the area and depth of required excavation in the borrow area. Log the soil profile description and obtain a disturbed, composite sample from at least two test holes in the borrow area. A composite sample is a representative blend of soil materials that will removed from the borrow area and used as earthfill under the structure. Ship the samples to a lab for compaction tests to develop a performance specification.

• Course-grained material used as fill may require relative density tests of the borrow material for a performance specification. A leveling course (< 12 inches) of dumped clean gravel, or sand under vibratory compaction, may be installed below the tank floor with no additional sampling or testing.

If all or a portion of the walls set on 4 feet or more of earthfill above the stripping elevation, the test hole distribution, sampling, and testing protocol under the walls and in the borrow pit should be determined on a case-by-case basis in consultation with the State Conservation Engineer.

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Figure 1. Example of Geologic Profiles

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Figure 2. Example of Geologic Profiles

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Appendix 1. Soil logs

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Example narrative discussion of the limiting design factors

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Bedrock is a limiting factor higher on the slope near the barn. (TP 1) The ERI indicates that the bedrock continues to station 2+00 on the geologic profile at a constant depth below the ground surface until it dips deeper in the alluvial valley. (TP 2-4)

Water is perched above the bedrock. Water flow laterally over the bedrock towards the alluvial valley. Tiling is recommended for perched water above the bedrock.

Lower on the slope alluvial soils are the limiting factor with subsurface saturation. All had redoximorphic and reduction indicators with a limiting elevation of 789.8 for subsurface saturation.

Due to clean sands (SP) encountered below the subsurface saturation, it can be assumed that the water table fluctuates in the sands into the CL and ML materials. The redoximorphic features in the CL layer are not from perched water alone. This is partially due to the landscape position of being at the toe of slope. It would take monitoring wells to prove otherwise. If the facility is sited above the subsurface saturation, monitoring wells are not recommended.

Samples 1 and 2 were taken ((TP 4) for testing its suitability for sub-liner material. They meet the requirements for a subliner, CPS-522 table 2A Column B 2 feet thick

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60

75

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Laboratory Testing

Soil Testing Soil Samples Project Number: 313

Sample Number P200 LL PI

TP#4 Sample 1 3-4 feet

75 34 10

TP#4 Sample 1 6-8 feet

60 15 NP

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Appendix 2. Soil logs with sampling data

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Exhibit A Geologic Subsurface Investigations

Documents

Transcript of Exhibit A Geologic Subsurface Investigations