05. DL Appendix A - Geotech Report.pdf

Geotechnical Evaluation

FOR

Devils Lake Substation Devils Lake, North Dakota

Western Area Power Administration (WAPA)

FMG Project No. 190781.00

October 11, 2019

Prepared For:

Western Area Power Administration 200 4th Street SW Huron, SD 57350

FMG ENGINEERING 3700 Sturgis Road • Rapid City, SD 55702 • fmgengineering.com • 605-342-4105

Civil Engineering Geotechnical Engineering Materials Testing Laboratory i Land Surveying Environmental Services Water Resources

October 11, 2019

Mr. Travis Maas Western Power Administration 200 4th Street SW Huron, SD 57350

Re: Geotechnical Evaluation for Devils Lake Substation Devils Lake, ND

Dear Mr. Maas:

As requested, we have performed a geotechnical evaluation for the referenced project. The purpose of this evaluation was to identify the subsurface characteristics, suggest suitable foundation systems for the substation structures and provide the geotechnical design parameters.

The findings and recommendations of this report were prepared in accordance with generally accepted professional engineering principles and practices. We make no other warranty, either expressed or implied.

We trust this information to be sufficient. If you have any questions or desire any additional information, please do not hesitate to contact us.

Respectfully submitted, FMG Engineering

Alex Fisher, P.E.

Enclosures c: Z:\190781 WAPA - Devils Lake Substation\Geotech ii

TABLE OF CONTENTS

SECTION PAGE

TRANSMITTAL LETTER .......................................................................................................................................... i

TABLE OF CONTENTS & LIST OF FIGURES .................................................................................................. iii & iii

1. INTRODUCTION

2. FIELD SAMPLING AND TESTING PROCEDURES

3. LABORATORY ANALYSIS

3.1 ATTERBERG LIMITS

3.2 GRAIN SIZE ANALYSIS DATA

3.5 SOIL CHEMICAL ANALYSIS

3.6 SAMPLE STORAGE

4. SITE CONDITIONS

4.1 MATERIALS PRESENT

4.1.1 Material Descriptions

4.2 GROUNDWATER TABLE

4.3 GEOLOGIC CONDITIONS

5. CONCLUSIONS AND RECOMMENDATIONS

5.1 FOUNDATION SELECTION

5.1.1 Cast-in-Place Drilled Pier Foundation System

5.1.2 Shallow Foundation Systems

5.2 ACCESS ROADS AND VEHICLE TRAFFIC AREAS

5.3 SOIL CORROSIVITY

5.4 SITE SEISMICITY

5.5 GENERAL MATERIAL PLACEMENT REQUIREMENTS

5.5.1 Fill Materials

5.5.2 Fill Placement

5.6 EXCAVATIONS, SHORING AND SITE GRADING

5.6.1 Excavations and Shoring

5.6.2 Site Grading

6. PROJECT OBSERVATION AND CONSTRUCTION QUALITY ASSURANCE

iii

7. CONCLUDING STATEMENT

TABLES, FIGURES AND APPENDICES

TABLE 1 - CAST-IN-PLACE DRILLED PIER DESIGN CRITERIA

TABLE 2 – SHALLOW FOUNDATION DESIGN CRITERIA

TABLE 3 - SOIL CORROSIVITY RATINGS (ROBERGE, 2013)

TABLE 4 - SEISMIC DESIGN CRITERIA

TABLE 5 - SOIL COMPACTION CRITERIA

FIGURE 1 ............................................................................................................ BOREHOLE LOCATIONS

FIGURE 2 ......................................................... CLASSIFICATION OF SOILS FOR ENGINEERING PURPOSES

APPENDIX A .................................................................................................................. GEOLOGIC LOGS

APPENDIX B ....................................................................................................... LABORATORY TESTING

APPENDIX C ........................................................................................... SOIL ELECTRICAL RESISTIVITY

APPENDIX D ........................................................................................................................ REFERENCES

FMG Geotechnical Evaluation

1. INTRODUCTION

Western Area Power Administration (WAPA) plans to construct an addition to the existing Devils Lake Substation in Devils Lake, North Dakota. The existing Devils Lake Substation is located on the south side of the City of Devils Lake, south of the intersection of Highway 2 and Highway 20. Specifically, the substation is located within the SE ¼ of Section 3, T153N, R64W. We understand that the new substation addition will include a service building, transformer, steel poles and frames on reinforced concrete foundations.

FMG Engineering was retained by WAPA to perform a geotechnical evaluation of the proposed substation site to identify the subsurface conditions, suggest suitable foundation systems for the substation structures, and provide geotechnical design parameters.

We understand that cast-in-place drilled pier foundation systems are preferred for frame structures and structures with overturning moments. Other lightly loaded equipment/structures are commonly supported by shallow foundations or slabs-on-grade. If proposed construction or locations differ significantly from that described above or elsewhere described in this report, our office should be contacted to re-evaluate the recommendations contained in this report.

Figure 1 illustrates the specific locations of our field explorations. This report presents our geotechnical evaluation of the substation site. Our evaluation included the following general scope of activities:

1. A general review of the regional geology, and related site characteristics.

2. Field exploratory borings, sampling, and testing at representative locations to determine the depth, thickness, orientation, engineering characteristics, and composition of the subsurface conditions.

3. Field soil electrical resistivity testing in support of electrical grounding system design by others.

4. Laboratory tests to identify the soil types, classifications, and engineering properties of the subsurface materials encountered at the site.

5. An analysis of the data obtained, and determination of suitable geotechnical design parameters and other such recommendations as considered applicable to satisfactory design and performance.

Field and laboratory tests were generally accomplished in accordance with current

ASTM, AASHTO and IEEE procedures, where applicable. The evaluation was accomplished under the direction of a registered professional engineer. This report presents the geotechnical engineering evaluation with recommendations for foundation design. We have also included a discussion of our field sampling and testing procedures, laboratory analyses, and site conditions.

2. FIELD SAMPLING AND TESTING PROCEDURES

A total of five boreholes were drilled at the locations shown on Figure 1 to identify the subsurface characteristics and obtain soil samples for laboratory testing. The boreholes were observed by the FMG Engineering field geologist.

The number of boreholes and the location were selected by WAPA with respect to proposed substation equipment and were adjusted by FMG in the field as necessary to avoid existing utilities. If, during subsequent planning, the substation locations change significantly from those described in this report and shown on Figure 1, we recommend drilling additional boreholes to verify soil conditions in unexplored areas.

Field testing consisted of obtaining standard penetration test (SPT) and relatively undisturbed Shelby Tube samples from various depths in the boreholes. The SPT testing was performed to identify the relative field strengths of the subsurface materials and to obtain samples for laboratory analyses; the Shelby Tube samples were obtained for laboratory analyses.

Geologic logs of the boreholes were maintained by a field geologist and the materials were classified in accordance with ASTM: D 2487-90 and D 2488-90 (Unified Soil Classification System), Figure 2. The geologic logs include the general drilling method data, depths of major changes in the character of the subsurface materials, visual description of the materials, sample locations, standard penetration data and locations, and groundwater data.

In addition, the geologic logs also include the data from certain laboratory classification and physical property analyses. The geologic logs are presented as Appendix A.

The geologic logs and related information depict only the conditions and materials encountered at the specific borehole location and at the particular time designated on the logs.

Soil conditions at other locations may be different from those encountered at the borehole locations. Also, the passage of time may produce a changed soil condition. We have extrapolated the data obtained from the boreholes and our conclusions and recommendations are based on the assumption that the materials encountered are representative of the soils that exist over the site. Anomalies may be present around the boreholes.

In addition to the boreholes drilled at the site, a field soil electrical resistivity survey was performed. The field resistivity survey was performed in general accordance with IEEE Standard 81 and ASTM G57 using the Wenner Four-Electrode Method with an IRIS R1 Plus resistivity meter. The results of the resistivity survey are presented as Appendix B.

3. LABORATORY ANALYSIS

The laboratory analysis was directed towards the determination of soil types drilled on the site and their engineering properties. The laboratory testing was performed in general conformance with current ASTM and AASHTO procedures, where applicable. The laboratory testing results are provided in Appendix C, and on the geologic logs where applicable.

3.1 ATTERBERG LIMITS

The Atterberg limits were determined for multiple samples. These tests allow for more detailed classification of soils, and provide information relative to the expected engineering characteristics and properties. (ASTM D4318-05)

3.2 GRAIN SIZE ANALYSIS DATA

Multiple standard grain size analysis determinations were performed to determine the grain size distribution and assist in the determination of the physical characteristics and engineering properties of the subsurface materials. (ASTM D422-63(2007))

3.3 UNCONFINED COMPRESSION TESTS

In order to determine the strength characteristics of the on-site materials, unconfined compression testing was performed on select samples. The unconfined compression test results provide indications of the soil's cohesive shear strength (undrained shear strength) in pounds per square foot (psf). (ASTM D2166)

3.4 CONSOLIDATION ANALYSES

Consolidation/swell tests were performed on relatively undisturbed samples that were obtained from the soil encountered at the site. The consolidation/swell test allows determination of the soil's swell pressure, percentage of swell, collapse potential, and approximate volume change potential with varying moisture conditions. The data from the consolidation/swell test can be used to develop potential uplift pressures or consolidation characteristics which may affect the performance of the foundation. (ASTM D2435)

3.5 SOIL CHEMICAL ANALYSIS

To assess corrosivity to concrete and steel, select soil samples were tested for pH, Chloride content and Sulfate content. The results of the chemical analysis are presented in Appendix F and discussed in Section 5.3.

3.6 SAMPLE STORAGE

The soil samples obtained during this evaluation will not be stored. If the client wishes to receive the samples, arrangements should be made; otherwise the samples will be discarded.

4. SITE CONDITIONS

The existing Devils Lake Substation is located on the south end of the City of Devils

Lake, North Dakota. The substation is constructed immediately southwest of, and contiguous with, a large, WAPA maintenance and storage yard facility. The new substation addition will be constructed to the southeast of the existing substation and to the south of the maintenance and storage yard facility and will be contiguous with both. A combination of open space, light commercial and multifamily residential property surround the site to the west, south and east.

The proposed substation site is currently undeveloped and is vegetated only by short grass. Site grades slope slightly to the northwest; no manmade or natural drainage features were noted at the site. At the time of our field exploration, the surface of the site was quite soft and wet, although no standing water was present. Several overhead transmission lines transect the site.

4.1 MATERIALS PRESENT

The stratigraphy of the project site generally consists of generally unstratified sands silts and clays to the total depths explored.

4.1.1 Material Descriptions

Clay and silt soils were encountered to the total depths explored in BH19-1, in the northern portions of the site, and locally as minor lenses throughout the other boreholes drilled at the site. The silt and clay soils were found to be dark gray to black, moist to wet, medium to highly plastic and stiff to hard in consistency. The clays were found to be stiff in the shallow subsurface, becoming very stiff to hard below 10 feet. Where encountered, the silt soils were found to be brown, moist, low plasticity and medium stiff in consistency. The near-surface clays were found to be non-expansive as indicated by laboratory testing.

The sand soils were to be generally well-graded with a variable silt fraction. The sands were brown to gray in color, moist to saturated, non-plastic, and loose to hard in density. The sands were generally found to be dense in the shallow subsurface, becoming very dense to hard below 10 feet. However, loose sands were encountered at a depth of 5 feet in BH19-2.

The geologic logs indicate the specific soil characteristics observed throughout the profiles in each of the boreholes advanced at the site.

4.2 GROUNDWATER TABLE

Groundwater was encountered throughout the site at depths ranging from 7 to 10 feet below existing grades. However, groundwater presence and levels should be anticipated to vary in response to seasonal changes in precipitation, bedrock fracture patterns, high precipitation events, and snow melt, and may not be accurately delineated within the normal scope of a geotechnical evaluation.

4.3 GEOLOGIC CONDITIONS

The geologic conditions of the project site can be generally described as Quaternary shoreline and nearshore sediments associated with Devils Lake. These sediments typically consist of sands and gravels and thinly-laminated silt and clay. Although not encountered in our boreholes, these lake sediments overlie glacial sediments at depth. (Manz, 2004)

Available geologic mapping of the area does not indicted faulting or significant geologic structures which may impact siting, design or performance of the proposed substation. (Manz, 2004)

5. CONCLUSIONS AND RECOMMENDATIONS

From our subsurface exploration and engineering analysis, we have arrived at the following conclusions and have the following recommendations with regard to foundation design for the proposed construction. The conclusions and recommendations presented in this report do not reflect variations in subsurface conditions that are likely to exist in unexplored areas. Should such variations be revealed during construction, it may be necessary to re-evaluate our recommendations based upon on-site observation of the variations. Also, we should be retained to review the foundation plans, as well as applicable portions of the specifications when they become available.

5.1 FOUNDATION SELECTION

We understand that cast-in-place drilled pier foundation systems are preferred for frame structures and structures with overturning moments. Other lightly loaded structures that can tolerate some minor post-construction movement could be supported on shallow foundations and slabs-on-grade. The design and construction criteria presented below should be observed for cast-in-place drilled pier foundation systems and shallow foundations systems.

5.1.1 Cast-in-Place Drilled Pier Foundation System

Table 1 - Cast-in-Place Drilled Pier Design Criteria

Note: -Significant variations in the stratigraphy below the structures should be expected both in terms of depth to and composition of soil layers.

-Upper 2 feet of soil and any fill materials should be neglected for analysis.

-Skin friction should be neglected at bottom of pier for a length equal to one (1) pier diameter.

-Uplift Skin Friction (psf) = 0.75*Compression Skin Friction

*Depth intervals are from existing grades at the borehole locations and are based on the average depths to strata as encountered in the boreholes. Foundation analysis and design should consider the site cuts and fills and the resulting changes to site subsurface stratigraphy.

**We recommend the drilled piers end bear a minimum of 15 feet below existing grades in the Lower Clays and Sands.

5.1.1.1 Design and Construction Criteria

1. We recommend that the drilled piers be designed with an allowable load pressure developed through the combination of end bearing and skin friction. We also recommend a minimum pier length of 15 feet, a minimum pier diameter of 18 inches, and a minimum center-to-center pier spacing of at least 3 pier diameters.

Soil Layer

Depth

Interval, (feet)*

L-Pile

Soil

Type

Effective

Unit

Weight, γ

(pcf)

Friction

Angle, Φ (deg)

Cohesion, c (psf) ε50, (in/in) p-y

Modulus, k, (pci)

Ultimate

Passive

Equivalent

Fluid

Pressure, (pcf)

Ultimate

Compression

Skin

Friction, (psf)

Ultimate

End

Bearing

Capacity, (ksf)

Depth to

Water

Table

(ft)

1, Upper

Clays and

Sands

2-10 Sand

(Reese) 100 27 - - 20 250 140 N/A**

8 2, Lower

Clays and

Sands

10-40 Sand

(Reese) 118 35 - - 125 435 530 60,000**

2. Casing may be required to keep the holes from collapsing, particularly during installation of large diameter foundations, even in the absence of groundwater.

Groundwater will likely enter the pier excavations. The concrete should be placed as soon after drilling as practical and provisions should be made to remove any water that enters the excavations prior to concrete placement. A pump will likely be required. If the water cannot be removed, then it may be necessary to “tremmie” or “pump” the concrete beneath the water.

3. We suggest continuous observation during the drilling operation to observe that loose soils and debris are not left in the holes, that the concrete is placed without segregation, that reinforcing steel is placed in accordance with specifications, and that the tops of holes are not mushroomed.

4. The concrete used for pier construction should have a slump of five to seven (5 to 7) inches. The concrete should have a maximum aggregate size that is smaller than one fifth (1/5th) of the space between the rebar. We suggest that the concrete be dropped the full pier depth provided the concrete does not hit the pier sides or any obstructions. Also, we recommend that the concrete not be vibrated.

5. The drilled piers should be reinforced their full length. We suggest, after placement of the concrete, that the reinforcing steel be placed in the drilled piers.

If pre-tied cages are preferred, a chute or "tremmie" should be used to properly control concrete placement. We recommend implementing construction techniques that limit concrete segregation resulting from the concrete hitting the steel reinforcement as it falls into the excavation.

6. Cobble or boulder sized material, debris, or cemented bedrock may be encountered during pier installation. These materials may require additional effort to excavate.

7. Settlements of cast-in-place drilled piers at the site are expected to be on the order of ½ inch or less.

5.1.2 Shallow Foundation Systems

Lightly loaded structures or equipment relatively tolerable of foundation movement could be supported on shallow foundations. However, loose sands and soft to medium stiff silts and clays were encountered locally in the shallow subsurface. Due to the compressible nature of these low-density soils, subgrade improvements will be necessary to mitigate movements of shallow foundations. Without subgrade improvements, shallow foundation movements on the order of 2 inches may occur as the soils respond to the foundation loads.

To mitigate shallow foundation movements, we recommend that an engineered fill section be constructed below all shallow foundation elements and slabs-on-grade which support equipment. The engineered fill section should be a minimum of 2 feet in thickness for frost depth foundations and 4 feet in thickness for slab-on-grade foundations. If constructed in accordance with the recommendations of this report, shallow foundation movements are anticipated to be on the order of 1 inch or less. The shallow foundation design and construction criteria are presented below in Table 2 and Section 5.1.2.1.

It should be noted that the settlement and heave values obtained from these analyses and presented herein are subject to the inherent variability of the soil profile and idealized methods used in the analysis. It is not uncommon for actual movements to vary from estimates. The actual magnitude of movement that will occur beneath the foundation or floor system will depend on the inherent variability of soil mineralogy and profile, the actual in-service loading conditions, the extent to which the subgrade soils are exposed to moisture variations, and the quality of the earthwork and foundation preparation procedures.

Table 2 – Shallow Foundation Design Criteria

Parameter Value

Subgrade Preparation Overexcavation and installation of 2-foot engineered fill section for frost-depth foundations and 4-feet for slabs-on-grade.

Allowable Bearing Capacity 2,000 psf

Modulus of Subgrade Reaction 75 pci

Frost Depth (Bowels, 1988) 6 feet

Sliding Friction Coefficient 0.40

Passive Earth Pressure 250 psf

5.1.2.1 Design and Construction Criteria

1. We recommend that the materials beneath all footings be excavated, or fill materials placed, to allow a minimum depth of 2 feet of engineered fill below designed frost-depth footing elevations and 4 feet below slab-on-grade foundations. The foundation excavations should be oversized 1 foot laterally beyond each side of the footing for every 1 vertical foot of overexcavation.

The engineered fill should meet the requirements outlined in Section 5.5 of this report and be compacted in accordance with the soil compaction criteria provided in Table 5.

2. In the event that soft conditions are encountered at the base of the foundation excavations, the foundation excavation should be overexcavated to stable conditions as directed by the Geotechnical Engineer. As directed by the Geotechnical Engineer, the overexcavation should be replaced with properly compacted native soils, engineered fill or stabilization rock meeting the requirements outlined in Section 5.5.1 of this report. The engineered fill should be compacted in accordance with Table 5.

3. Compacted fill placed against the sides of the footings to resist lateral loads may be moisture-conditioned, on-site soil. The fill should be placed in accordance with the fill and soil compaction criteria provided in Table 5.

Sliding friction at the bottom of the footing can be taken at 0.40 times the vertical dead load for foundations placed directly on properly compacted engineered fill. The passive resistance of the soil may be calculated on the basis of an equivalent fluid unit weight of 250 pcf for the properly compacted on-site sand soils used as backfill.

4. Precipitation events or fluctuations in groundwater levels could cause the base of the foundation excavations to be within the range of possible groundwater fluctuations. Therefore, it may be necessary to install sump pits and dewater the excavations to allow proper subgrade preparation and foundation construction. We recommend that the contractor obtain the necessary permits for the dewatering operations and that the dewatering be performed in accordance with local, county, state, and federal regulations.

5. Care should be exercised during foundation excavation as to not disturb the excavation subgrade. We recommend that an excavator with a smooth cutting edge be utilized as excavations near designed depths. Should the excavation subgrade be disturbed, we recommend that the excavation subgrade be scarified to a depth of 8 inches and recompacted in accordance with the criteria provided in Table 5 of this report prior to placement of concrete, reinforcing steel or engineered fill to provide a uniform subgrade.

6. The natural soils may pump or deform excessively under the wheel loads of heavy construction vehicles as the excavations approach footing levels.

Construction equipment should be as light as possible to avoid this difficulty.

The movement of vehicles over proposed foundation areas should be restricted. Any areas disturbed by construction traffic should be stabilized or over-excavated and replaced with stabilization rock or compacted engineered fill.

7. Post construction movements of shallow foundation and slab systems constructed in accordance with the recommendations of this report are expected to be on the order of 1 inch.

A qualified Geotechnical Engineer should observe all footing excavations prior to concrete placement, as well as perform compaction testing during any moisture-conditioned fill placement.

5.2 ACCESS ROADS AND VEHICLE TRAFFIC AREAS

After stripping of topsoil and organic materials and/or the placement of fill materials, any access road or vehicle traffic area subgrade within the substation yard should be scarified to a minimum depth of 8 inches, moisture conditioned and recompacted in accordance with the compaction criteria provided in Table 5 prior to placement of any gravel surfacing.

Due to the generally soft subgrade conditions of the site, we recommend a minimum of 12 inches of aggregate subbase and aggregate surfacing be placed in all areas of the substation yard that will experience vehicle traffic of any kind. Unless installation sequencing can be coordinated, we do not recommend the use of a geogrid material to reduce the aggregate thickness because future foundation, grounding system or conduit installation will compromise the geogrid and may result in subgrade failures.

5.3 SOIL CORROSIVITY

The near surface site soils can be considered extremely corrosive to buried steel. This corrosivity rating is based on the electrical resistivity of the site soils in the upper 5 feet (~500 Ω-cm), and generally adopted corrosion severity ratings (see Table 3 below). The results of the soil electrical resistivity testing are presented in Appendix C.

Table 3 - Soil Corrosivity Ratings (Roberge, 2013)

Soil Resistivity, Ω-cm Corrosivity Rating

>20,000 Essentially Non-Corrosive

10,000 – 20,000 Mildly Corrosive

5,000 – 10,000 Moderately Corrosive

3,000 – 5,000 Corrosive

1,000 – 3,000 Highly Corrosive

<1,000 Extremely Corrosive

Based on the results of laboratory reactivity testing of representative samples, concrete in contact with the on-site soils will have a severe exposure (up to 3,000 ppm) to sulfate-containing soils (ACI 318, Table 4.3.1). To provide protection against sulfate related corrosion and in accordance with the referenced ACI document, we recommend a Type V cement, or a Type I/II cement with sulfate resistance equivalent to Type V cement, be utilized for concrete exposed to soils at the site, a maximum water-cement ratio of 0.45 (by weight, normal weight concrete), and a minimum compressive strength (f’c) of 4,500 psi be specified for all concrete exposed to the site soils. The results of the laboratory reactivity testing are presented in Appendix B.

5.4 SITE SEISMICITY

Seismic design should be in accordance with the ASCE 7-16 seismic design parameters provided below. The Seismic Site Class indicated below in Table 4 assumes the soil conditions encountered at the bottom of the borings continue to a depth of 100 feet. A more detailed and accurate Site Class evaluation may be achieved by performing geophysical seismic surveys to develop the shear wave velocity profile for the site to a depth of 100 feet.

Table 4 - Seismic Design Criteria

ASCE 7-16 Seismic Design Parameters

Seismic Category A

Site Class D

MCE Spectral Response Accelerations

Short Period, Ss 0.043 g

1-second, S1 0.018 g

Site Coefficients, Fa 1.6

Site Coefficient, Fv 2.4

Design Spectral Response Accelerations

Short Period, SDS 0.046 g

1-second, SD1 0.028 g

5.5 GENERAL MATERIAL PLACEMENT REQUIREMENTS

5.5.1 Fill Materials

The on-site materials, segregated from any oversized material greater that 6-inches in maximum dimension, will be suitable for use as foundation backfill and general site fill, but will not be suitable for use as engineered fill or gravel surfacing. It should be noted that some processing, drying or sorting of the on-site materials may be required prior to placement as fill, as in-situ moisture contents may be above optimum moisture contents.

On-site sources of engineered fill were not identified. These materials will have to be imported to the site. We recommend that all engineered fill materials consist of non-expansive, well-graded natural or crushed gravel with 100% passing the 3-inch sieve and between 8% and 20% passing the #200 sieve. The engineered fill material should also have a liquid limit less than 30. The engineered fill material must be approved by FMG prior to transport to the site.

On-site sources of stabilization rock were not identified. These materials will have to be imported to the site, if necessary. The stabilization rock should be a clean rock with 100% passing the 3-inch sieve, 0 to 15% passing the 1-inch sieve, and 0 to 8% passing the #4 sieve. The stabilization rock must be approved by FMG prior to transport to the site.

5.5.2 Fill Placement

We suggest that sufficient density tests be taken by qualified personnel to indicate the degree of compaction being attained. We recommend controlling scarification, fill and backfill operations using the moisture content and dry density relationship as determined by ASTM D 1557 (Modified Proctor Density). The fill materials should be placed in 6-12 inch loose lifts and compacted to the densities and moisture contents outlined in Table 5 below.

Any additional moisture required to achieve compaction in a layer should be added and the entire lift mixed to obtain uniform moisture content.

We suggest that final testing of the footing subgrade and other fills in "structural areas" be performed (in addition to testing during placement) immediately before concrete placement to determine the integrity of the materials. Severe changes in the condition of these materials can occur after initial preparation as the result of rain, snow, drying, freezing, excessive heat, and construction activities. Any subgrade or foundation material that becomes disturbed desiccated, or does not conform to the moisture content and compaction requirements indicated in Table 5 should either be removed and replaced or reworked to meet these recommendations.

Table 5 - Soil Compaction Criteria

Placement Location Soil Type Moisture Content Compaction

Degree

Scarification of Subgrade

Utility Trench Backfill

Foundation Subgrade

Foundation/Retaining Wall

Backfill

Vehicle Traffic Areas

Free-Draining Materials

(Sand and Gravels - Less

Than 8% Fines)

Workable 95%

(ASTM D-4253)

Cohesive Materials

(Clays and Silts)

+3% of Optimum 92%

(ASTM D-1557)

Cohesionless Materials

(Sands and Gravels –

More Than 8% Fines)

Workable 95%

(ASTM D-1557)

Site Grading Approx. 15 Feet

Away from Structures and

Vehicle Traffic Areas

Cohesive Materials

(Clays and Silts)

+3% of Optimum 85%

(ASTM D-1557)

Cohesionless Materials

(Sands and Gravels –

More Than 8% Fines)

Workable 90%

(ASTM D-1557)

The earthen site construction materials should not be placed on frozen ground and compaction operations should not be performed during periods when temperatures are below 25 degrees Fahrenheit. Placement of earthen site construction materials at temperatures below 35 degrees Fahrenheit may result in frost entering the soils and making placement at the required specifications difficult. Therefore, we suggest when temperatures are below 40 degrees Fahrenheit and earthen materials are being placed below structures, that the earthen site construction materials be continuously observed and tested. If frozen materials are observed being placed below structures then we suggest that they be removed and replaced with unfrozen materials as directed by the geotechnical engineer or testing personnel.

Soils having relatively high silt or fine sand contents, such as those encountered on-site, are often difficult to compact to the desired specifications although they may be compacted well enough to suit the intended purpose. If great difficulty is encountered during construction in regard to meeting the compaction specifications, a qualified geotechnical engineer should be consulted to determine if the placement of the soils at lower densities could still provide suitable characteristics.

5.6 EXCAVATIONS, SHORING AND SITE GRADING

5.6.1 Excavations and Shoring

Excavations at the site will likely encounter sands, clays and silts. We do not anticipate excavation difficulties for properly sized equipment in good working order.

However, it is possible that cobbles or boulder sized material or debris exist in the subsurface and may require additional effort if encountered.

Regarding excavations at the sites, we recommend that they be sloped or shored in accordance with OSHA regulations, and to generally maintain adequate safety provisions on the job-site. The near surface soils can be considered OSHA Type B soils. It is the contractor's responsibility to maintain job-site safety, and the occasional or longer term presence of an FMG, Inc. representative at the site does not constitute a review or a responsibility regarding safety aspects.

5.6.2 Site Grading

Only minor site grading is anticipated to prepare the site for desired site drainage and substation yard elevations. We have the following recommendations with regard to site grading.

1. All fill materials placed within the substation yard shall be considered structural subgrade and compacted accordingly.

2. We recommend that all topsoil, root zones, organics, etc. be stripped in areas to receive fill or from foundation footprints.

3. The substation pad should be designed with sufficient slope to provide positive drainage from the pad in general, and positively away from all foundation elements. Protection of shallow foundation subgrade from moisture ingression is critical to satisfactory foundation performance at this site. Additional post-construction movements of foundations will occur if the foundation subgrade is subjected to moisture variations.

4. Due to the relatively soft subgrade conditions at the site, positive drainage from the substation yard surface will be critical to short- and long-term subgrade stability and performance as a driving surface. We recommend that particular care be exercised when grading the subgrade surface to ensure the designed slopes are attained. After installation of conduits, grounding systems or other trenches or below grade items which disturb the temporary aggregate surface or subgrade, all disturbed areas and interruptions of the designed site slopes should be repaired prior to the installation of any additional aggregate subbase or surfacing. Subgrade repair should include the backfill and proper recompaction of all trenches and the re-establishment of desired site grades and slopes. Compaction should be in accordance with Section 5.5.2 of this report. The site subgrade should be inspected by the Civil Engineer or Geotechnical Engineer and any necessary repairs to the subgrade should be made prior to placement of any additional aggregate base or surfacing.

5. Soft conditions may be encountered during site grading. Construction equipment with low contract pressures should be considered. If soft conditions are encountered during site grading, stabilization may be necessary to allow proper construction. Stabilization efforts should be as directed by the Geotechnical Engineer based upon site observations.

6. PROJECT OBSERVATION AND CONSTRUCTION

QUALITY ASSURANCE

This report completes our current contracted scope of geotechnical services. As the provider of the geotechnical recommendations contained herein, FMG should be retained to provide any necessary pre-construction geotechnical reviews, interpretations, supplemental information and to provide the required construction-period observation and quality assurance program.

If any changes in the nature, design or location of the project are planned, the conclusions and recommendations contained in this report shall not be considered valid unless the changes are reviewed, and conclusions of this report modified or verified in writing.

Frequently, soil conditions vary slightly from those encountered in the borings that were drilled. Therefore, FMG should be retained to review the portions of the plans that pertain to earthwork and foundations and to observe the construction of the foundation and slab system as part of a detailed construction quality assurance program.

Additionally, proper placement of site fill, engineered fill, and other structural elements per our recommendations and per the project specifications is essential to the performance of the foundation and floors of the structure. Failure to properly place the construction materials and structural elements can result in excessive movements potentially leading to failure and significant impact to the structural integrity of the structure.

Our recommendations are based on the necessary assumption that the material and structural element placement will occur as specified and that a detailed construction quality assurance program will be provided that clearly documents the proper placement of materials and structural elements at this site through adequate methods and frequency of testing. In the absence of such quality assurance and documentation performed by FMG, FMG cannot assume responsibility or liability for the performance of any foundation systems, embankments or structural elements of this project. Should another agent perform the construction quality assurance, said agent will necessarily assume the role and responsibilities of project geotechnical engineer of record from FMG.

We are available to observe construction operations, particularly the concrete placement operations, the compaction of the fill materials, and other such field observations as may be necessary. Under no circumstances is it our intent to directly control the physical activities of the contractor or the contractor's workmen. Any field testing or observations performed by FMG would be a part of engineering opinions rendered to the contractor and should not be misconstrued as supervision of the contractor's work or workmen.

File Number:

SEPTEMBER 2019

Location:

Sheet Title:

Date:

Drawn By:

Checked By:

Designed By:

AMF

KJS

Surveyed By:

Number:

Figure

190781

SECTION 3

T153N, R64W, 5TH P.M.

BH#1

DEVIL'S LAKE SUBSTATION

ADMINISTRATION

DEVIL'S LAKE,ND

FMG ENGINEERING

3700 Sturgis Road, Rapid City, SD 57702-0317 fmgengineering.com

(605) 342-4105

WESTERN AREA POWER

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BH19-1

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BH19-2

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BH19-3

afisher Text Box

BH19-4

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BH19-5

afisher Callout Resistivity Survey Alignments afisher Text Box

BH19-X

afisher Stamp

CLASSIFICATION OF SOILS FOR ENGINEERING PURPOSES

ASTM Designation: D 2487-90 and D 2488-90 (Unified Soil Classification System)

Soil Classification Criteria for Assigning Group Symbols and Group NamesA Group Symbol Name

COARSE-GRAINED SOILS Gravels Clean Gravels Cu > 4 and 1 < Cc < 3E GW Well-Graded GravelF More than 50% retained on More than 50% of coarse Less than 5% finesC Cu < 4 and/or 1 > Cc > 3E GP PoorlyGradedGravelF the No. 200 sieve fraction retained on No. 4 sieve Gravels with Fines Fines classify as ML or MH GM Silty GravelF,G,H More than 12% finesC Fines classify as CL or CH GC Clayey GravelF,G,H

Sands Clean Sands Cu > 6 and 1 < Cc < 3E SW Well-Graded SandI 50% or more of coarse Less than 5% finesD Cu < 6 and/or 1 > Cc > 3E SP Poorly Graded SandI fraction passes No. 4 sieve Sands with Fines Fines classify as ML or MH SM Silty SandG,H,J More than 12% finesD Fines classify as CL or CH SC Clayey SandG,H,I

FINE-GRAINED SOILS Silts and Clays inorganic PI>7and on or above "A" lineJ CL Lean ClayK,L,M 50% or more passes the Liquid limit less than 50 soils PI<4 or plots below "A" lineJ ML SiltK,L,M No. 200 sieve organic Liquid limit-oven dried Organic ClayK,L,M,N

----------------------------<.75 OL

soils Liquid limit-not dried Organic SiltK,L,M,O

Silts and Clays inorganic PI plots on or above "A" line CH Fat ClayK,L,M Liquid limit 50 or more soils PI plots below "A" line MH Elastic SiltK,L,M organic Liquid limit-oven dried Organic ClayK,L,M,P

----------------------------<.75 OH

soils Liquid limit-not dried Organic SiltK,L,M,Q

HIGHLY ORGANIC SOILS Primarily organic matter, dark in color, and organic odor PT Peat A. Based on the material passing the 3-in. (75-mm) sieve. G. If fines classify as CL-ML, use dual symbol GC-GM, or SC-SM B. If field sample contained cobbles or boulders, or both, H. If fines are organic, add "with organic fines" to group name.

add "with cobbles and boulders, or both" to group name. I. If soil contains > 15% gravel, add "with gravel" to group name.

C. Gravels with 5% to 12% fines require dual symbols: J. If Atterberg limits plot in hatched area, soil is a CL-ML, silty clay.

GW-GM well-graded gravel with silt K. If soil contains 15% to 29% plus No. 200, add "with sand" or GW-GC well-graded gravel with clay "with gravel," whichever is predominant.

GP-GM poorly graded gravel with silt L. If soil contains > 30% plus No. 200, predominantly sand, add GP-GC poorly graded gravel with clay "sandy" to group name.

D. Sands with 5% to 12% fines require dual symbols: M. If soil contains > 30% plus No. 200, predominantly gravel, add SW-SM well-graded sand with silt "gravely" to group name.

SW-SC well-graded sand with clay N. PI > 4 and plots on or above "A" line.

SP-SM poorly graded sand with silt O. PI < 4 or plots below "A" line.

SP-SC poorly graded sand with clay P. PI plots on or above "A" line.

E. Cu = D60/D10 Cc=(D30)

2/D10xD60 Q. PI plots below "A" line.

F. If soil contains > 15% sand, add "with sand" to group name.

PLASTICITY CHART

Liquid Limit (LL)

Pl as tic ity

In de x (P

I)

0 10 20 30 40 50 60 70 80 90 100 110

MH or OH

CH or OH

CL or OL

CL-ML ML or OL

"A" Line

Equation of "A" - line: Horizontal at PI = 4 to LL = 25.5, then PI = 0.73(LL-20) (Chart is for general graphic presentation purposes only)

- Figure 2-

Appendix A

Geologic Logs

Appendix B

Laboratory Testing

Tested By: JB/CJ Checked By: JB

LIQUID AND PLASTIC LIMITS TEST REPORT

P

LA

S

TI

C

IT

Y

IN

D

E X

LIQUID LIMIT

0 10 20 30 40 50 60 70 80 90 100 110

CL-ML

CL o r O

L

CH o r O

H

ML or OL MH or OH

Dashed line indicates the approximate upper limit boundary for natural soils

MATERIAL DESCRIPTION LL PL PI %<#40 %<#200 USCS

Project No. Client: Remarks:

Project:

Figure

Source of Sample: BH19-1 Depth: 3.5 Sample Number: S1A

Source of Sample: BH19-2 Depth: 8.5 Sample Number: S2B

Source of Sample: BH19-2 Depth: 20 Sample Number: P2D

Source of Sample: BH19-3 Depth: 3.5 Sample Number: S3A

Source of Sample: BH19-4 Depth: 3.5 Sample Number: S4A

Silty Sand: Very Dark Gray 65 42 23 55 42 SM

Silty Sand: Dark Brown 32 27 5 70 39 SM

Silty Sand with Gravel: Well-graded, Very dark gray, Wet, Non to low plastic, Hard consistency.

42 28 14 65 46 SM

Sandy Silt 32 24 8 77 51 ML

Silty Sand: Very Dark Gray NV NP NP 82 41 SM

190781 WAPA

WAPA - Devils Lake Substation

LIQUID AND PLASTIC LIMITS TEST REPORT

P

LA

S

TI

C

IT

Y

IN

D

E X

LIQUID LIMIT

0 10 20 30 40 50 60 70 80 90 100 110

CL-ML

CL o r O

L

CH o r O

H

ML or OL MH or OH

Dashed line indicates the approximate upper limit boundary for natural soils

MATERIAL DESCRIPTION LL PL PI %<#40 %<#200 USCS

Project No. Client: Remarks:

Project:

Figure

Source of Sample: BH19-5 Depth: 3.5 Sample Number: S5A

Lean Clay with Sand: Brown 35 22 13 80 56 CL

190781 WAPA

WAPA - Devils Lake Substation

Silty Sand: Very Dark Gray

Silty Sand: Dark Brown

Silty Sand with Gravel: Well-graded, Very dark gray, Wet, Non to low plastic, Hard consistency.

inches number size size

0 8 50 42 SM A-7-5(6) 42 65

0 7 54 39 SM A-4(0) 27 32

0 6 48 46 SM A-7-6(4) 28 42

1/2 3/8 100

98 100

#4 #10 #40

#100 #200

0.6453 0.2775 0.2759

Source of Sample: BH19-1 Depth: 3.5 Sample Number: S1A

Source of Sample: BH19-2 Depth: 8.5 Sample Number: S2B

Source of Sample: BH19-2 Depth: 20 Sample Number: P2D

WAPA

WAPA - Devils Lake Substation

190781

+3" % GRAVEL % SAND % SILT % CLAY USCS AASHTO PL LL

SIEVE PERCENT FINER SIEVE PERCENT FINER Material Description

GRAIN SIZE REMARKS:

D60 D30 D10

COEFFICIENTS

Cc Cu

Client:

Project:

Project No.: Figure

P E

R C

E N

T

FI

N E

R

0.1110

1½ in in

¾ in

½ in

3/ in

#4 #1

#2

#3

#4

#6

#1

#1

#2

Particle Size Distribution Report

Sandy Silt

Silty Sand: Very Dark Gray

Lean Clay with Sand: Brown inches number size size

0 7 42 51 ML A-4(2) 24 32

0 1 58 41 SM A-4(0) NP NV

0 4 40 56 CL A-6(5) 22 35

3/4 1/2 3/8

96 100

#4 #10 #40

#100 #200

0.1376 0.1433 0.1041

Source of Sample: BH19-3 Depth: 3.5 Sample Number: S3A

Source of Sample: BH19-4 Depth: 3.5 Sample Number: S4A

Source of Sample: BH19-5 Depth: 3.5 Sample Number: S5A

WAPA

WAPA - Devils Lake Substation

190781

+3" % GRAVEL % SAND % SILT % CLAY USCS AASHTO PL LL

SIEVE PERCENT FINER SIEVE PERCENT FINER Material Description

GRAIN SIZE REMARKS:

D60 D30 D10

COEFFICIENTS

Cc Cu

Client:

Project:

Project No.: Figure

P E

R C

E N

T

FI

N E

R

0.1110

1½ in in

¾ in

½ in

3/ in

#4 #1

#2

#3

#4

#6

#1

#1

#2

Particle Size Distribution Report

Tested By: JB Checked By: JB

UNCONFINED COMPRESSION TEST

Project No.: 190781

Date Sampled: 9-17-19

Remarks:

Figure

Client: WAPA

Project: WAPA - Devils Lake Substation

Source of Sample: BH19-1 Depth: 3.5

Sample Number: S1A

Description: Silty Sand: Very Dark Gray

LL = 65 PI = 23PL = 42 Assumed GS= 2.65 Type: Shelby

Sample No.

Unconfined strength, psf Undrained shear strength, psf Failure strain, % Strain rate, in./min.

Water content, % Wet density, pcf Dry density, pcf Saturation, % Void ratio Specimen diameter, in.

Specimen height, in.

Height/diameter ratio

3.2

0.060

28.8

98.7

76.6

66.0

1.1583

2.83

5.55

1.97

C om pr es si ve

S tre ss , p sf

Axial Strain, %

0 1.5 3 4.5 6

Project No.: 190781

Date Sampled:

Remarks:

Figure

Client: WAPA

Project: WAPA - Devils Lake Substation

Source of Sample: BH19-2 Depth: 8.5

Sample Number: S2B

Description: Silty Sand: Dark Brown

LL = 32 PI = 5PL = 27 Assumed GS= 2.65 Type:

Sample No.

Unconfined strength, psf Undrained shear strength, psf Failure strain, % Strain rate, in./min.

Water content, % Wet density, pcf Dry density, pcf Saturation, % Void ratio Specimen diameter, in.

Specimen height, in.

Height/diameter ratio

2.0

0.060

22.0

118.7

97.3

83.3

0.6995

2.84

5.41

1.90

C om pr es si ve

S tre ss , p sf

Axial Strain, %

0 1 2 3 4

Project No.: 190781

Date Sampled: 9-17-19

Remarks:

Figure

Client: WAPA

Project: WAPA - Devils Lake Substation

Source of Sample: BH19-3 Depth: 3.5

Sample Number: S3A

Description: Sandy Silt

LL = 32 PI = 8PL = 24 Assumed GS= 2.65 Type: Shelby

Sample No.

Unconfined strength, psf Undrained shear strength, psf Failure strain, % Strain rate, in./min.

Water content, % Wet density, pcf Dry density, pcf Saturation, % Void ratio Specimen diameter, in.

Specimen height, in.

Height/diameter ratio

5.9

0.060

21.6

128.7

105.8

101.5

0.5630

2.87

5.55

1.93

C om pr es si ve

S tre ss , p sf

Axial Strain, %

0 2.5 5 7.5 10

Project No.: 190781

Date Sampled:

Remarks:

Figure

Client: WAPA

Project: WAPA - Devils Lake Substation

Source of Sample: BH19-4 Depth: 3.5

Sample Number: S4A

Description: Silty Sand: Very Dark Gray

LL = NV PI = NPPL = Assumed GS= 2.65 Type: Shelby

Sample No.

Unconfined strength, psf Undrained shear strength, psf Failure strain, % Strain rate, in./min.

Water content, % Wet density, pcf Dry density, pcf Saturation, % Void ratio Specimen diameter, in.

Specimen height, in.

Height/diameter ratio

1.8

0.060

18.7

119.8

100.9

77.7

0.6388

2.85

5.47

1.92

C om pr es si ve

S tre ss , p sf

Axial Strain, %

0 1 2 3 4

Project No.: 190781

Date Sampled: 9/17/19

Remarks:

Figure

Client: WAPA

Project: WAPA - Devils Lake Substation

Source of Sample: BH19-2 Depth: 20

Sample Number: P2D

Description: Silty Sand with Gravel: Well-graded, Very dark gray, Wet, Non to low plastic, Hard consistency.

LL = 42 PI = 14PL = 28 Assumed GS= 2.65 Type: Shelby

Sample No.

Unconfined strength, psf Undrained shear strength, psf Failure strain, % Strain rate, in./min.

Water content, % Wet density, pcf Dry density, pcf Saturation, % Void ratio Specimen diameter, in.

Specimen height, in.

Height/diameter ratio

4.5

0.060

18.8

114.5

96.4

69.5

0.7154

1.58

2.90

1.83

C om pr es si ve

S tre ss , p sf

10000

Axial Strain, %

0 1.5 3 4.5 6

Tested By: JB Checked By: JB

CONSOLIDATION TEST REPORT

V oi d R at io

0.49

0.52

0.55

0.58

0.61

0.64

0.67

0.70

0.73

0.76

0.79

Applied Pressure - ksf

0.1 1 10

Water Added

Natural Dry Dens. LL PI Sp. Overburden Pc Cc Cs Swell Press. Swell

% eoSat. Moist. (pcf) Gr. (ksf) (ksf) (ksf)

83.2 % 23.8 % 94.2 35 13 2.65 500 1.3 0.19 0.02 0.0 0.757

Lean Clay with Sand: Brown CL A-6(5)

190781 WAPA

WAPA - Devils Lake Substation

MATERIAL DESCRIPTION USCS AASHTO

Project No. Client: Remarks:

Project:

Source of Sample: BH19-5 Depth: 3.5 Sample Number: S5A

Figure

MIDCONTINENT

TESTING LABORATORIES, INC.

2381 South Plaza Drive P.O. Box 3388 Rapid City, SD 57709

(605) 348-0111 -- www.thechemistrylab.com

Sample Site: P4A Project Name: Devils Lake Substation

Project Number: 190781

Sampled: 09/17/19 at 12:00 PM by Joe Brown

Sample Matrix: Soil

Lab ID#: 20190920702

Received: 09/19/19 at 09:22 AM by Greg McDougall

Account: W1023 - FMG

ALEX FISHER

FMG

3700 STURGIS RD

RAPID CITY, SD 57702

Parameter Result Units DF MDL PQL Method Analyst/Date

Physical Properties pH 7.50 S.U. 1 EPA SW846 9045C TMN 09/23/19

Non-Metallics

Chloride (Cl-) 92.0 mg/L 5 1.02 2.50 SM 4500-Cl E BLL 09/23/19

Sulfate (SO4) 3090 mg/L 100 29.7 100 SM 4500-SO4 E BLL 09/23/19

Report Approved By:

Report Approved On: 9/25/2019 9:33:43 AM

MIDCONTINENT

TESTING LABORATORIES, INC.

2381 South Plaza Drive P.O. Box 3388 Rapid City, SD 57709

(605) 348-0111 -- www.thechemistrylab.com

Lab Numbers: 20190920702 - 20190920702

QC Sample Report

Parameter Lab#

QC

Value

Smp Value Spike DF Result Limits Method

Spike

Chloride 0923201 7.37 2.57 5.00 1 96.0 % (88.61) - (111.0) SM 4500-Cl E

Sulfate 0923102 1240 873 19.2 20 103.5 % (90.48) - (112.0) SM 4500-SO4 E

Matrix Spike Duplicate

Chloride 0923201 7.33 7.37 1 -0.544% (-7.249) - (6.828) SM 4500-Cl E

Sulfate 0923102 1250 1240 20 1.43% (-4.067) - (6.195) SM 4500-SO4…