NM ERFO FS SNTFE 2022-1(1)_Geotech Report_Sealed_Flat.pdf

Geotechnical Investigation Report

El Porvenir Bridge Replacement

Montezuma, New Mexico

Yeh Project No.: 223-295 July 1, 2024

Prepared for:

Mr. Wes Sennett, P.E., S.E.

MGE Engineering, Inc.

7415 Greenhaven Drive, Suite 100 Sacramento, CA 95831

Prepared by:

Yeh and Associates, Inc.

2000 Clay Street, Suite 200

Denver, Colorado 80211

Phone: 303-781-9590

Geotechnical Investigation Report

El Porvenir Bridge Replacement

Montezuma, New Mexico

Yeh Project No.: 223-295 July 1, 2024

Prepared by:

Matt Kelly E.I.T., G.I.T. Samantha C. Sherwood, P.E.

Staff Engineer Sr. Project Manager

Reviewed by:

I-Ping Chen, P.E.

Project Manager I-IIII Ping Chen, PPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPP EE.E.

Samantha Sherwood

Digitally signed by Samantha Sherwood Date: 2024.08.09 11:43:26 -06'00' i

Table of Contents

1 PURPOSE AND SCOPE OF WORK

2 SITE CONDITIONS

3 PROPOSED CONSTRUCTION

4 GEOLOGIC SETTING

5 SUBSURFACE INVESTIGATION

5.1 SURFACE AND SUBSURFACE CONDITIONS

5.2 LABORATORY TESTING

6 GEOLOGIC CONSIDERATIONS

6.1 SEISMICITY

6.2 SULFATE ATTACK AND CORROSION

7 CONSTRUCTION RECOMMENDATIONS

7.1 SITE GRADING CONSIDERATIONS

7.2 FILL MATERIALS AND PLACEMENT

7.3 EXCAVATION AND TRENCH CONSTRUCTION

7.4 DRAINAGE CONSIDERATIONS

8 FOUNDATION RECOMMENDATIONS

8.1 DRILLED SHAFTS

8.2 BRIDGE FOUNDATION LATERAL RESISTANCE

9 ABUTMENT RECOMMENDATIONS

10 LIMITATIONS

11 REFERENCES

List of Tables

TABLE 5-1. SUMMARY OF BEDROCK AND GROUNDWATER CONDITIONS

TABLE 6-1. SEISMIC DESIGN PARAMETERS

TABLE 6-2. ANALYTICAL TEST RESULTS

TABLE 8-1. NOMINAL DRILLED SHAFT AXIAL RESISTANCES

TABLE 8-2. LPILE PARAMETERS

TABLE 8-3. ESTIMATED LPILE SOIL PROFILES

List of Figures

FIGURE 1. PROJECT LOCATION

FIGURE 2. GEOLOGIC MAP OF THE PROJECT SITE, FROM GEOLOGIC MAP AND CROSS SECTIONS OF THE GALLINAS CREEK

AND SANGRE DE CRISTO MOUNTAINS, SAN MIGUEL COUNTY, NEW MEXICO

FIGURE 3. BORING YA-B1

ii

FIGURE 4. BORING YA-B2

FIGURE 5. BEDROCK CORE FROM 20 TO 30 FEET IN YA-B1

FIGURE 6. BEDROCK CORE FROM 20 TO 30 FEET IN YA-B2

List of Appendices

APPENDIX A – BORING LOCATION PLAN

APPENDIX B – BORING LOGS

APPENDIX C – LABORATORY TEST RESULTS

Geotechnical Report Project No. 223-295A El Porvenir Bridge Replacement July 1, 2024

1 PURPOSE AND SCOPE OF WORK

This report presents the results of Yeh and Associates, Inc.’s (Yeh) geotechnical engineering investigation for the replacement of the prior bridge near Montezuma, New Mexico. The previous bridge over Beaver

Creek near El Porvenir Campground bridge was destroyed during the Calf Canyon/Hermits Peak wildfire in 2022. The purpose of this report is to provide geotechnical investigation and recommendations for use by MGE Engineering, Inc. (MGE) to redesign the bridge.

Our scope of services included the following:

Conduct a subsurface investigation, consisting of two borings with a truck-mounted ODEX and rock coring drill rig.

Provide laboratory testing to determine engineering characteristics of the existing soils and rock.

Analyze the field data and laboratory test results and provide a geotechnical investigation report that includes the following:

Description and results of subsurface investigation.

Boring Location plan.

Summary of the general site geological and geotechnical conditions.

Earthwork recommendations for maximum recommended stable soil slopes, foundation preparations and excavation requirements Geotechnical design and construction recommendations for proposed structures based on the results of the geotechnical investigation.

2 SITE CONDITIONS

At the time of our investigation, a low water crossing was used to cross Beaver Creek and provide access to the camp on the north side of the creek. A timber bridge on spread footings previously provided access, prior to the Calf Canyon and Hermits Peak wildfires. Evidence of post fire debris flows, and sediment laden runoff were visible in the area.

3 PROPOSED CONSTRUCTION

The project consists of the replacement of the former timber bridge over Beaver Creek, near the El

Porvenir campground. The project area is shown in Figure 1.

Figure 1. Project Location.

4 GEOLOGIC SETTING

The project site is in Sangre De Cristo Mountains of northern New Mexico. According to the USGS

Geologic Map and Cross Sections of the Gallinas Creek and Sangre De Cristo Mountains, San Miguel

County, New Mexico the investigation site is adjacent to several faults (Figure 2) including the El

Porvenir Fault and unnamed faults. These faults were active during the Laramide Orogeny

(approximately 80 to 35 million years ago) when the Sangre de Cristo Mountains were formed. The surface deposits at the project location have been mapped as Alluvium (Qal). The bedrock directly below the site has been mapped as pegmatites and metamorphic rocks (pCm). Outcrops of conglomerate sandstone, Sandia formation (Ps), and sandy clastic limestone, Tererro and Espiritu Santo formations

(MDte), run southwest to northeast. Limestone and Shale (Pml) are present to the south and west. The formations shown on the map in Figure 2 were also identified in the field by the investigation team.

Bridge Site

Figure 2. Geologic Map of the Project Site, from Geologic Map and Cross Sections of the Gallinas Creek and

Sangre De Cristo Mountains, San Miguel County, New Mexico.

5 SUBSURFACE INVESTIGATION

The geotechnical exploration included two bridge borings. The boring spacing, termination depth and locations at a minimum meet the requirements as specified in the AASHTO Load Resistance Factor

Design (LRFD) Bridge Design Specifications, 8th edition, 2017 (AASHTO, 2017). The boring locations are shown on the Boring Location Plan in Appendix A. Boring logs are presented in Appendix B.

The borings were drilled on December 5th through December 8th, 2023, with a CME-75 truck-mounted drill rig by Enviro-Drill. The borings were advanced with ODEX then rock cored once competent bedrock was encountered in the boreholes. Subsurface conditions encountered in the borings were logged by a representative of Yeh. Samples were taken at approximately 5-foot intervals. Rock samples were collected with NQ coring equipment.

The boring locations were determined by site accessibility relative to the proposed replacement bridge location. The latitude and longitude of the boring locations were recorded in the field using a handheld device providing accuracy to within about 10 feet. Elevations were interpolated from civil plans provided by MGE. Location coordinates and interpolated elevations are presented on the boring logs.

Photos of the boring locations during drilling are shown in Figures 3 and 4.

Penetration resistance measurements were taken by driving standard split-spoon (SPT) samplers into subsurface materials at approximate 5-foot intervals. The SPT sampler has an O.D. of 2.0 inches and I.D.

of 1.375 inches. The SPT sampler was driven 18 inches, per ASTM D1586. The SPT samplers were advanced by an automatic-hammer of 140-pounds falling 30 inches.

The number of blows required to drive the SPT sampler the last two 6-inch intervals, or fractions thereof, constitutes the penetration resistance value as shown on the boring logs. The penetration resistance value is a useful index to evaluate the consistency and relative density, or hardness of the subsurface materials encountered. The bedrock recovered by coring was classified with a rock quality designation (RQD). RQD is the measurement of all intact specimens over 4 inches in length and is used to estimate the degree of jointing or fracturing of a rock mass.

Figure 3. Boring YA-B1.

Figure 4. Boring YA-B2.

5.1 Surface and Subsurface Conditions

Two bridge borings, YA-B1 and YA-B2 were drilled by Yeh adjacent to the low water crossing on the west side of Beaver Creek . The approximate boring locations are shown on the boring location plan in

Appendix A. The legend and boring logs are included in Appendix B. Laboratory test results are provided in Appendix C and are shown on the boring logs.

The bridge borings encountered well graded sands with gravel in the top 5 feet with river cobbles and boulders present at the surface. Surface boulders are commonly about one to three feet in diameter, with larger outliers. Between depths of 5 feet and the bedrock was a mixture of poorly graded gravels with sand, clayey sand with clay lenses, boulders, and cobbles. Photos of the bedrock core are shown in

Figures 5 and 6.

Figure 5. Bedrock core from 20 to 30 feet in YA-B1.

Figure 6. Bedrock core from 20 to 30 feet in YA-B2.

Groundwater measurements were performed at the time of drilling. Groundwater was measured in borings YA-B1 and YA-B2 during drilling at a depth of 8 feet below grade. Groundwater observations represent groundwater conditions at the time of the field exploration and may not be indicative of other times or at nearby locations. Variations in groundwater conditions may occur seasonally. The magnitude of the variation will be largely dependent upon the amount of spring snowmelt, duration and intensity of precipitation, site grading changes, and the surface and subsurface drainage characteristics of the surrounding area.

Table 5-1 provides a summary of the bedrock and groundwater conditions for the bridge borings. The surface elevations, approximate bedrock depths/elevations, and approximate groundwater depths/elevations are estimated to the nearest foot. The groundwater depths and elevations are based on observations during drilling.

Table 5-1. Summary of Bedrock and Groundwater Conditions

Boring ID

Ground Surface

Elevation at Time of

Drilling1 (feet)

Approx.

Depth to Top of Bedrock1

(feet)

Approx.

Elevation to

Top of Bedrock1

(feet)

Approx.

Groundwater

Depth1

(feet)

Approx.

Groundwater

Elevation1

(feet)

YA-B1 7513 17 7496 8 7505

YA-B2 7517 14 7503 8 7509

1Borings not surveyed. Depths and elevations are approximate and based on handheld GPS coordinates and civil plans provided by MGE.

5.2 Laboratory Testing

Selected soil and bedrock samples were tested in the laboratory to determine the classification and engineering properties of the materials encountered in the borings. The testing was conducted in general accordance with locally recognized test procedures, primarily those of the American Society for

Testing and Materials (ASTM) and American Association of State Highway and Transportation Officials

(AASHTO). The following tests were performed:

Sieve analysis Soil classification Natural moisture content determination

Atterberg limits Unconfined compressive strength of rock Water-soluble sulfate content Water-soluble chloride content Resistivity pH

The material descriptions and laboratory test results were used for the geotechnical engineering analyses and the development of pavement and structure recommendations. Details of laboratory test results are presented in Appendix C and are integrated with the boring logs in Appendix B.

6 GEOLOGIC CONSIDERATIONS

Geologic and geotechnical engineering concerns encountered on this site include seismicity and corrosion potential. Seismic design parameters and the corrosion test results are presented below.

6.1 Seismicity

Based on the site class definitions provided in Table 3.10.3.1-1 of AASHTO, 2017, the site is categorized as a Site Class D. Based on the recommendations in Table 3.10.6-1 of AASHTO, 2017, the site classifies as Seismic Zone 1.

The peak ground acceleration (PGA) and the short- and long-period spectral acceleration coefficients (SS and S1, respectively) for reference Site Class B were determined using the USGS seismic hazard design tool. The site is designated as Site Class D and site-specific adjustments were determined. The PGA, SS, S1 and seismic design parameters adjusted to Site Class D are shown in Table 6-1 below. These values may be used to construct the Design Response Spectrum for use in seismic design.

Table 6-1. Seismic Design Parameters Site Class

(Reference) PGA (0.0 sec) SS (0.2 sec) S1 (1.0 sec)

B 0.083 g 0.194 g 0.061 g Site Class AS (0.0 sec) SDS (0.2 sec) SD1 (1.0 sec)

D

0.133 g 0.310 g 0.146 g

FPGA Fa Fv

1.6 1.6 2.4

* The site class was based on the conditions encountered in our shallow exploratory soil borings and our knowledge of the soil conditions in the site vicinity. The soil characteristics extending beyond the depth of our borings were assumed for the purposes of providing this site classification.

The General Limit Equilibrium (GLE) method was used to estimate the need for additional seismic lateral earth pressures for retaining wall design using the methodology described in FHWA (2011) LRFD Seismic

Analysis and Design of Transportation Features and Structural Foundations Reference Manual and the

AASHTO (2017) LRFD Bridge Design Specifications. A horizontal pseudostatic coefficient (kh) of 0.09 was estimated using procedures described in FHWA (2011) and referenced in Section A11.5.2 of AASHTO

(2017). The procedures presented in FHWA (2011) consider the design earthquake, duration, and a displacement of up to 2 inches for the abutments. The seismic data used to estimate the horizontal pseudostatic coefficient (kh) are presented in Section 5.1.

The GLE analysis performed using SLIDE2 (Rocscience 2024) for the proposed abutment wall height up to 14 feet resulted in factors of safety greater than 1.0 under static design conditions (with an earth pressure load factor of 1.5 used in the design of abutments) and seismic loading from the design earthquake. Therefore, abutments designed for static conditions are considered sufficient to resist loading from the design earthquake, and an additional seismic earth pressure increment is not needed for design of the proposed abutments.

6.2 Sulfate Attack and Corrosion

Representative soil samples were selected for chemical testing including water-soluble sulfate and chloride content, pH, and electrical resistivity. The test results are presented in Appendix C and summarized in Table 6-2. This concentration of water-soluble sulfates represents a Class 0 degree of sulfate attack on concrete exposed to these geologic materials. The degree of attack is based on a range of Class 0 (negligible) to Class 3 (very severe) as described in the American Concrete Institute (ACI)

Standard 201.2R, “Guide to Durable Concrete”.

A qualified corrosion engineer should review the laboratory data and boring logs to determine the appropriate level of corrosion protection for materials in contact with these soils.

Table 6-2. Analytical Test Results Boring

ID

Depth

(ft) Material Water Soluble Sulfates, %

Water Soluble Chlorides, % pH Resistivity, ohm-cm

YA-B1 0-5 Sand with Silt and Gravel 0.005 0.0420 7.6 7950

YA-B1 5.5-6.4 Clayey Sand 0.005 0.0660 6.8 5230

Boring

ID

Depth

(ft) Material Water Soluble

Sulfates, % Water Soluble Chlorides, % pH Resistivity, ohm-cm

YA-B2 0-5 Sand with Silt and Gravel 0.013 0.0600 7.6 4760

YA-B2 5-6 Sand 0.001 0.0630 7.1 9100

YA-B2 6-6.5 Sand with Organic Silt 0.069 0.0660 6.9 3240

7 CONSTRUCTION RECOMMENDATIONS

The following sections present recommendations for site preparation, ground improvement, excavation, subgrade preparation, fill placement, and surface drainage on the project. Site preparation and earthwork operations should be performed in accordance with FHWA Standard Specifications for

Construction of Roads and Bridges on Federal Highway Projects (FP-14). Earthwork should be observed and evaluated by a qualified representative of the geotechnical engineer. The evaluation of earthwork should include observation and testing of engineered fills, ground improvement, subgrade preparation, foundation bearing soils, and other geotechnical conditions exposed during the construction of the project.

7.1 Site Grading Considerations

Initial site work should consist of stripping vegetation, organics, debris, and other deleterious materials from the proposed structure areas and any other areas to receive fill. All exposed surfaces should be free of mounds and depressions, which could prevent uniform compaction. Stripped materials consisting of vegetation and organic materials should be wasted from the site or used to revegetate landscaped areas after completion of grading operations. Once properly cleared, all exposed areas which will receive fill should be scarified and compacted as required by FP-14.

Based upon the subsurface conditions encountered, near surface subgrade soils exposed during construction may be unstable. The stability of the subgrade may be affected by precipitation, repetitive construction traffic, and other factors.

In general, permanent cut slope angles in overburden materials should not exceed 3H:1V, however, flatter slope angles may be necessary for revegetation.

7.2 Fill Materials and Placement

All embankment fills should conform to the FHWA Standards. Prior to receiving fill, the exposed subgrade materials should be scarified to a minimum depth of six inches and the scarified materials appropriately processed and compacted to meet the requirements of FP-14.

All compaction should be performed in horizontal lifts that are 12 inches or less in compacted thickness, using equipment and procedures that will produce a uniform fill with the required moisture contents and densities throughout the lift. The required percent of relative compaction and moisture content for the embankment materials are presented in the FP-14, Section 204.10.

Backfill materials should have a Class 0 severity of sulfate exposure. Backfill materials should be tested for severity of sulfate exposure prior to placement. We recommend that the subgrade preparation process including soil excavation, the placement and compaction of materials, proof rolling, and visual inspection of foundation soils be observed and evaluated by the geotechnical engineer of record or the engineer’s representative.

7.3 Excavation and Trench Construction

Excavations into the on-site soils will encounter a variety of conditions. All excavations must comply with the applicable local, State, and Federal safety regulations, and particularly with the excavation standards of the Occupational Safety and Health Administration (OSHA). Construction site safety, including excavation safety, is the sole responsibility of the contractor as part of its overall responsibility for the means, methods, and sequencing of construction operations. Yeh’s recommendations for excavation support are provided for the Client’s sole use in planning the project. In no way do they relieve the contractor of its responsibility to construct, support, and maintain safe slopes. Under no circumstances should the following recommendations be interpreted to mean that Yeh is assuming responsibility for either construction site safety or the contractor’s activities.

We believe the bedrock material at this site will classify as Type A material using OSHA criteria. Due to the presence of fluctuating ground water levels all other material will classify as Type C material using

OSHA criteria. OSHA requires that unsupported cuts be no steeper than ¾H:1V for Type A material, 1H:1V for Type B material, and 1½H:1V for Type C for unbraced temporary excavations in dry conditions.

Flatter slopes will be required below groundwater or if seepage is present. A Registered Professional

Engineer should design any excavations greater than 20 feet. Please note that the contractor’s OSHA-defined “competent person” must make the actual determination of soil type and allowable sloping in the field. The soils encountered by the proposed excavations may vary significantly across the site. The preliminary classifications presented above are based solely on the materials encountered in widely spaced exploratory test borings. The contractor should verify that similar conditions exist throughout the proposed area of excavation.

As a safety measure, we recommend that all vehicles and stockpiles be kept to a lateral distance equal to at least the depth of the excavation from the crest of the slope. The exposed slope face should be protected against the elements and monitored by the contractor on at least a daily basis.

7.4 Drainage Considerations

Moisture conditions in the subgrade soils influence the performance of pavements, foundations, and other improvements. The risk of wetting these subgrade soils can be reduced by proper planning and maintenance of surface grades and drainage. Excessive wetting of the subsurface before, during, and after construction can cause movement of pavements and foundations. Precautions should be taken to avoid wetting or drying of open excavations for foundations and other earthwork.

Positive drainage away from the structures should be provided. Proper design of drainage should include preventing the ponding of water on or immediately adjacent to structures and pavements.

Surface features that could retain water in areas adjacent to the roadway or structures should be graded to drain.

8 FOUNDATION RECOMMENDATIONS

Due to constructability and resiliency concerns, drilled shafts were selected for design. The soil and bedrock properties were estimated from penetration resistance, material descriptions and laboratory test data. The subsurface conditions are suitable for construction of a bridge on drilled shaft foundations.

The design and construction of the foundation elements should comply with all applicable requirements and guidelines listed in AASHTO, 2017 and FHWA specifications.

8.1 Drilled Shafts

Drilled shafts can be installed into bedrock to obtain support below the scour limits. The estimated bearing resistance should be developed from tip resistance in the underlying bedrock. The resistance from the overburden soil should be neglected.

Table 8-1 contains the preliminary recommended values for nominal axial tip resistance and corresponding bedrock elevations for drilled shafts founded in the underlying bedrock. The tip resistance value presented is based on a five-foot minimum rock socket depth. The five-foot socket depth is recommended to increase confinement at the bearing depth considering that fractured and weathered rock is anticipated at the top of the rock surface, to provide lateral stability if scour to bedrock is anticipated and confirm that the shaft is not embedded in a large boulder. To account for axial group effects, the minimum spacing requirements between drilled shafts should be in accordance with Table 10.8.3.6.3-1 in AASHTO, 2017.

Table 8-1. Nominal Drilled Shaft Axial Resistances

Reference Boring

Estimated Top of Bedrock Elevation

(feet)

Nominal Tip Resistance (ksf)

YA-B-1 7496

YA-B-2 7503

Based on Section 10.5.5.2.4-1 in AASHTO, 2017, a resistance factor of 0.50 can be used for the tip resistance.

The following recommendations can be used in the design and construction of the drilled shafts:

Very hard metamorphic bedrock was encountered in the exploratory borings. The contractor should mobilize equipment of sufficient size and operating condition to achieve the required design bedrock penetration.

The drilled shaft recommendations for nominal bearing resistance are applicable for end bearing in bedrock only. The side resistance developed in the overburden soils and rock should be neglected.

Drilled shafts may be designed to resist lateral loads using the recommendations in the Bridge

Foundation Lateral Resistance section of this report. The upper 3 feet of the drilled shaft should be neglected in lateral load resistance calculations.

Drilled shaft construction shall not disturb previously installed drilled shafts. Do not drill additional shafts, allow wheel loads, vibration-inducing equipment, or other construction activities within 15 feet (4.5 meters) or 3 shaft diameters, whichever is greater, of a newly constructed shaft for at least 20 hours.

We estimate individual shaft settlement will be less than ½ inch in bedrock when designed according to the criteria presented in this report.

Groundwater, potentially caving soils, boulders and bedrock should be anticipated during drilling. The contractor should construct the drilled shafts using means and methods that maintain a stable hole without compromising the bedrock to concrete bond providing tip resistance.

Each drilled shaft excavation should be carefully observed by a qualified representative of the

Engineer of Record. The bottom of all drilled shafts should be found in very hard bedrock

(penetration resistance N 100).

8.2 Bridge Foundation Lateral Resistance

The input parameters provided in Table 8-2 are recommended for use with the computer program LPILE to develop the soil models used to evaluate the drilled shaft response to lateral loading. Table 8-3 provides the estimated values associated with the material types encountered in our borings. P-y moduli (kstatic) and initial modulus of rock mass (Erm) values define the initial portion of the material’s resistance during lateral deflection of the foundation element, i.e., P-y curves. The nature and type of loading should be carefully considered.

Individual material layers and their extent can be averaged or distinguished by referring to the boring logs at the locations of proposed foundations. The soil and/or bedrock materials prone to future disturbance, such as utility excavation, frost heave or scour should be neglected in the lateral load analysis to the depth of disturbance, which should be a minimum of 3 feet from ground surface.

Table 8-2. LPILE Parameters

Soil Type LPILE Soil Criteria

Effective Unit Weight [pcf]

Friction Angle, f [deg.]

Undrained Cohesion, c

[psf]

Strain Factor, p-y modulus kstatic [pci]

AGT1 BGT2 AGT1 BGT2

Class 1 Structure

Backfill Sand (Reese) 135 72.5 34 -- -- 90 60

Native Sands and Gravels Sand (Reese) 120 57.5 28 -- 25 20

Cobbles, Boulders in Sand Matrix Sand (Reese) 120 57.5 30 -- -- 90 60

Granitic Gneiss Bedrock

Rock (Vuggy

Limestone Reese)

160 130 -- 8,000 0.001 --

1Above Groundwater Table 2Below Groundwater Table

Table 8-3. Estimated LPILE Soil Profiles

Soil Type

YA-B1

Approx Elevations

YA-B2

Approx

Elevations

Structure Backfill -- --

Native Sands and Gravels above Water Table 7513-7505 7517-7509

Native Sands and Gravels below Water Table 7505-7496 7509-7506

Cobbles, Boulders in Sand Matrix Below Water Table -- 7506-7503

Granitic Gneiss Bedrock 7496 - tip 7503 - tip

Note that groundwater was measured in December, and water levels are likely to fluctuate. Elevations are approximate, based on surface elevations interpolated from the civil survey plans.

The effects of group interaction should be considered when evaluating pile group horizontal movement.

The reduction in lateral capacity due to group effects are provided in Section 10.7.3.12 of AASHTO, 2017. The values of lateral resistance, P, should be multiplied by P-multiplier values, Pm, to account for group effects (Table 10.7.2.4-1 in AASHTO). The Pm value will depend on the direction of the applied load, center-to-center spacing, and location of the foundation element within the group. Linear extrapolation may be used to estimate the Pm value for a driven pile with center-to-center spacing to diameter ratio of less than 3.

9 ABUTMENT RECOMMENDATIONS

The bridge abutments will be supported on the drilled shaft foundation. The following preliminary design and construction recommendations apply to lateral loading on abutment walls for this project:

Wall backfill materials should meet the requirements of FP-14 for Structure Backfill. Backfill placed adjacent to the structures should be placed and compacted in accordance with FP-14

Specifications.

Walls that can deflect or rotate approximately 0.1 to 0.2 percent of the wall height can be designed for “active” earth pressure conditions. For a rigid wall where negligible deflection can occur, an “at-rest” lateral earth pressure condition should be used.

The lateral earth pressure induced by additional surcharge loads or backslopes above the top of walls should be considered in design, where appropriate and in accordance with AASHTO, 2017

Section 3.11.

Lateral earth pressure for Structure Backfill should be calculated in accordance with Section

3.11.5 of AASHTO, 2017. For Structure Backfill, an effective angle of internal friction of 34 degrees and a unit weight of 135 pounds per cubic foot (pcf) should be used for preliminary design. Friction angles between fill and various wall materials can be found in AASHTO, 2017

Table C3.11.5.3-1.

The equivalent fluid unit weight can be calculated as the lateral earth pressure coefficient times the unit weight. The equivalent fluid unit weight for active earth pressure should not be less than 36 pcf.

A load factor of 1.5 is recommended for active earth pressure and 1.35 for at-rest earth pressure.

Passive earth pressure should be neglected.

Hydrostatic or seepage pressures should not be allowed to develop in the retained soil.

Appropriate drainage elements should be installed near the back and bottom of retaining walls.

10 LIMITATIONS

The findings and recommendations in this report are preliminary and based upon data obtained from field observations, borings, laboratory testing, our present understanding of the proposed construction, and other sources of information referenced in this report. A design-level investigation will be required to provide final design recommendations for the project. It is possible that subsurface conditions may vary between or beyond the locations explored. The nature and extent of such variations may not become evident until construction. If during construction conditions appear to be different from those described herein, Yeh should be advised and provided the opportunity to observe and evaluate those conditions and provide additional recommendations, as necessary. Yeh should also be contacted if the scope of construction changes from that generally described within this report.

Yeh and Associates has prepared this report for the exclusive use of MGE for the proposed bridge over the Beaver Creek in Montezuma, New Mexico. This report was prepared in substantial accordance with the generally accepted geotechnical engineering standards of practice in the site area at the time of our investigation. No warranty is expressed or implied. We recommend on-site observation of excavations and foundation bearing strata by a representative of the geotechnical engineer.

11 REFERENCES

AASHTO, 2017. Load Resistance Factor Design (LRFD) Bridge Design Specifications, Eighth Edition.

Washington, D.C.: American Association of State Highway and Transportation Officials.

Federal Highway Administration, 2011. LRFD Seismic Analysis and Design of Transportation Features and Structural Foundations Reference Manual.

Federal Highway Administration, 2014. Standard Specifications for Construction of Roads and Bridges on Federal Highway Projects.

Baltz, E.H., 1972, USGS Geologic Map and Cross Sections of the Gallinas Creek and Sangre De Cristo Mountains, San Miguel County, New Mexico, United States Geological Survey, scale 1:24,000

United States Geologic Survey Seismic Design Web Service, 2009. AASHTO Guide Specifications at URL:

https://earthquake.usgs.gov/ws/designmaps/aashto-2009.html

Appendix A

BORING LOCATION PLAN

Appendix B

LEGEND AND BORING LOGS

Appendix C

LABORATORY TEST RESULTS