21-7-8 Ft Bayard Pave Roads Geotechnical Report.pdf

REPORT COVER PAGE

Geotechnical Engineering Report (Revised)

Pave Roads, Repair Storm Drains & Water Utilities Fort Bayard National Cemetery

Fort Bayard, New Mexico July 8, 2021

Terracon Project No. 68205023.Revision1

Prepared for:

Vali Cooper International, LLC

Denver, Colorado

Prepared by:

Terracon Consultants, Inc.

Las Cruces, New Mexico

Terracon Consultants, Inc. 4450 Bataan Memor ia l East Las Cruces, New Mexico 88011 P [575] 527 1700 F [575] 527 1092 www.terracon.com

REPORT COVER LET TER T O SIGN

July 8, 2021

Vali Cooper International, LLC 18300 East 71st Avenue, Suite 130 Denver, Colorado 80249

Attn: Mr. Taqi H. Muhammad, P.E.

Senior Project Manager

Re: Geotechnical Engineering Report (Revised) Pave Roads, Repair Storm Drains & Water Utilities Fort Bayard National Cemetery 200 Cam De Paz Fort Bayard, New Mexico Terracon Project No. 68205023.Revision1

Dear Mr. Muhammad:

Terracon Consultants, Inc. (Terracon) is pleased to submit this Revised Geotechnical Engineering Report for the above referenced project in Fort Bayard, New Mexico. The study was performed in general accordance with Terracon Cost Estimate Document No. P68205023.Revision2, dated September 15, 2020.

We trust that this report is responsive to your project needs, and we appreciate the opportunity to be of service to you on this project. We look forward to the possibility of providing additional construction materials testing services in the near future. If you have any questions concerning this report or if we may be of further service, please contact us.

Sincerely, Terracon Consultants, Inc.

Daniel Castrillo Ivan Avelar, P.E.

Geotechnical Staff Geotechnical Services Manager

Michael E. Anderson, P.E.

Principal / Senior Geotechnical Consultant

Enclosures Copies Submitted: Addressee (1) Electronic https://na3.documents.adobe.com/verifier?tx=CBJCHBCAABAARBSTnCBbwPeyFXOP6uu7U71XYKweFB7_

Geotechnical Engineering Report (Revised) Pave Roads, Repair Storm Drains & Water Utilities ■ Fort Bayard, New Mexico July 8, 2021 ■ Terracon Project No. 68205023.Revision1

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REPORT TOPICS

INTRODUCTION

PROJECT DESCRIPTION

SITE CONDITIONS

GEOTECHNICAL CHARACTERIZATION

GEOTECHNICAL OVERVIEW

EARTHWORK

PAVEMENTS

BURIED UTILITY PIPE RECOMMENDATIONS

STORMWATER DETENTION PONDS

GENERAL COMMENTS

ATTACHMENTS

Note: This report was originally delivered in a web-based format. Orange Bold text in the report indicates a referenced section heading. The PDF version also includes hyperlinks which direct the reader to that section and clicking on the GeoReport logo will bring you back to this page. For more interactive features, please view your project online at client.terracon.com.

ATTACHMENTS

EXPLORATION AND TESTING PROCEDURES

SITE LOCATION AND EXPLORATION PLANS

EXPLORATION RESULTS

FIGURES

SUPPORTING INFORMATION

Note: Refer to each individual Attachment for a listing of contents.

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INTRODUC TION

Geotechnical Engineering Report (Revised) Pave Roads, Repair Storm Drains & Water Utilities

Fort Bayard National Cemetery 200 Cam De Paz

Fort Bayard, New Mexico Terracon Project No. 68205023.Revision1

July 8, 2021

INTRODUCTION

This report presents the results of our subsurface exploration and geotechnical engineering services performed for the proposed roads and drainage improvements at Fort Bayard National Cemetery located at 200 Cam De Paz in Fort Bayard, New Mexico.

The purpose of these services is to provide information and geotechnical engineering recommendations relative to:

■ Site and subgrade preparation.

■ Guidelines for pavement thickness design and construction.

■ Guidelines for buried waterline installation.

■ Construction considerations for on-site storm water detention ponds.

■ Other earthwork-related aspects of construction.

The geotechnical engineering scope of services for this project included the advancement of 16 test borings to depths varying from approximately ½ to 16½ feet below existing site grade.

Maps showing the site and boring locations are shown in the Site Location and Exploration Plan sections, respectively.

The results of the laboratory testing performed on soil samples obtained from the site during the field exploration are included on the boring logs and as separate graphs in the Exploration Results section.

PROJECT DESCRIPTION

Our initial understanding of the project was provided in our proposal and was discussed during project planning. A period of collaboration has transpired since the project was initiated, and our final understanding of the project conditions is as follows:

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Item Description

Information Provided

Statement of work document provided to us by Vali Cooper International, LLC, dated March 30, 2020, received via email on June 1, 2020, and our observations based on a site visit on September 10, 2020 to mark the boring locations.

Project Description

We understand that the project is planned to include the following:

n New asphalt surfaced road reconstruction with associated curb & gutter of both cemetery roads and parking areas.

n Replacement of an existing water supply line (4-inch diameter, to be located between the Fort Bayard water tank and the northeast corner of the cemetery property). We understand that the invert elevation of the existing pipeline is about 2 feet below adjacent grades and that the new pipeline will be installed via pipe-bursting methods. Finally, we understand that the existing water line is currently abandoned and was not in use at the time of our field operations.

n We also understand that a new stormwater detention pond will be considered as part of the scope of work for this project.

Grading, Cut/Fill Earthwork and Slopes

We have assumed the finished roadway grade elevations (FGE) will differ from existing grades by no more than about 12 inches.

Pavements We understand that flexible (asphalt) pavement sections will be considered for this project.

Drainage Storm water runoff is planned to be disposed of off-site and into an on-site storm water detention pond located on the southwestern side of the cemetery.

SITE CONDITIONS

The following description of site conditions is derived from our site visit in association with the field exploration and our review of publicly available geologic and topographic maps.

Item Description

Site Location and Parcel Information

The project is located at 200 Cam de Paz in Fort Bayard, Grant County, New Mexico (Latitude: N32.798906, Longitude: W108.154618). See Exhibit D for additional project location information.

Existing Improvements Roads Associated with the Fort Bayard National Cemetery

Current Ground Cover n Existing unpaved aggregate surfaced road: crushed, decomposed granite.

n Other areas: sparse to dense vegetation and native subgrade soils.

Existing Topography The site appears to slope downward from north to south.

Geology

Specific geologic conditions mapped at the location of the project include Mancos Formation and Beartooth Quartzite (Phanerozoic, Mesozoic or Cretaceous), consisting of what was formerly referred to as Colorado Shale which in turn may include equivalents of Tres Hermanos Formation.

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GEOTECHNICAL CHARACTERIZATION

We have developed a general characterization of the subsurface conditions based upon our review of the subsurface exploration, laboratory data, geologic setting and our understanding of the project. This characterization, termed GeoModel, forms the basis of our geotechnical calculations and evaluation of site preparation and pavement options.

Subsurface conditions on the project site can be generalized as loose o very dense sands with varying amounts of silt, clay and gravel. Due to auger refusal conditions encountered during our drilling operations at the location of Boring B-4, material that may be difficult to excavate could be present in the area of said boring location.

Specific details and soil conditions for each of the borings can be found in the individual logs of borings in the Exploration Results section. Stratification boundaries on the boring logs represent the approximate location of changes in soil types. In-situ, the transition between materials may be gradual. A visual side-by-side compilation showing the general subsurface profile observed in our Borings B-1 through B-16 is presented as GeoModel, which can be found in the Figures section of this report.

As part of our analyses, we identified the following model layers within the subsurface profile. For a more detailed view of the model layer depths at each boring location, refer to the GeoModel.

Model Layer Layer Name General Description

1 SC Clayey Sand with Varying Amounts of Gravel (loose to very dense) 2 SC-SM Silty, Clayey Sand with Varying Amounts of Gravel (loose to very dense) 3 SM Silty Sand with Varying Amounts of Gravel (medium dense to very dense)

Groundwater

Borings B-1 through B-8 and B-13 through B-16 were advanced using hollow stem auger drilling techniques to depths of approximately 6½ to 16½ feet below existing grades. Borings B-9 through B-12 were advanced using hand auger methods to depths to approximately ½ to 3 feet below existing grade. Both methods were advanced dry (without water or mud) to evaluate groundwater conditions while drilling, and immediately after completion of our drilling operations. The water levels (or absence thereof) as observed in the boreholes can be found in the individual logs of soil borings in Exploration Results, and they are summarized in the GeoModel figure presented in the Figures section of this report.

Groundwater was not observed in borings B-1 through B-16 during or upon completion of our drilling operations. The absence of groundwater at the time of the field exploration may not be indicative of other times, circumstances (such as perched water conditions), or at other locations.

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Groundwater level fluctuations occur due to seasonal variations in the amount of rainfall, runoff and other factors not evident at the time the borings were performed. Therefore, groundwater levels during construction or at other times in the life of the structure may be higher or lower than the levels indicated on the boring logs. The possibility of groundwater level fluctuations should be considered when developing the design and construction plans for the project, and should be evaluated prior to construction.

GEOTECHNICAL OVERVIEW

Based on the information obtained from our subsurface exploration, the site can be developed for the proposed project. A summary of our findings and recommendations is provided below.

■ Groundwater was not observed at borings B-1 through B-16 during or upon completion of our drilling operations. These observations represent conditions at the time of the field exploration and may not be indicative of other times, circumstances (such as perched conditions), or at other locations.

■ The near surface soils predominantly consist of native, loose to dense sands with varying amounts of silt, clay and gravel material and are suitable for re-use as engineered fill based on soil classification. The on-site soils exhibit low plasticity ranges and are anticipated to present low expansion potential.

■ Based on our findings during the field phase of this project, we think the possibility of encountering relatively dense gravels, high lateral soil pressure resistance and high friction resistance to pipe-jacking will be present at this site. Additionally, since the existing pipe appeared to have a limited soil cover ranging between 2 and 3 feet, the contractor should use appropriate means and methods to prevent the heaving of the surface during pipe-jacking operations. Finally, the contractor should design and properly size the thrust blocks at the end of the excavated pit(s) to reduce the risk of exceeding the passive lateral resistance of the soil during pipe-jacking.

■ Relatively dense clayey sands with some gravel were observed at various depths within the proposed water line alignment, which may present difficulties during the trench excavation. Extra effort or heavy duty equipment may be required for utility trench excavations.

■ Effective drainage should be completed early in the construction sequence and maintained after construction. Additional site preparation recommendations, including subgrade improvement, fill placement, and excavations are provided in the Earthwork section of this report.

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■ Based on our experience with similar projects in similar site conditions, a flexible (asphaltic concrete) pavement system may be considered for this site. The Pavements section addresses design of pavement systems.

This summary should be used in conjunction with the entire report for design purposes. Details were not included or fully developed in this section, and the report must be read in its entirely for a comprehensive understanding of the items contained herein. The section titled General Comments should be read for an understanding of the report limitations.

EARTHWORK

The following sections present recommendations for site preparation, excavation, subgrade preparation and placement of engineered fill (if applicable) on the project. Earthwork on the project should be evaluated by Terracon, which should include observation and testing of those tasks and materials, and of other geotechnical conditions exposed during the construction of the project.

The recommendations presented for design and construction of earth-supported elements, such as pavements, are contingent upon following the recommendations outlined herein.

Site Preparation

Road reconstruction areas should be first stripped and grubbed (including the existing crushed/decomposed granite material) to a sufficient depth to remove visual remains of vegetation, organic material and other debris/unsuitable surface material) at the start of the earthwork operations. The crushed/decomposed granite material may be reused as fill material if it meets the requirements shown in the Fill Material Classifications and Requirements subheading of this report section.

The site should be properly prepared and regraded to create a relatively level surface to receive fill and to provide for a relatively uniform thickness of fill beneath the proposed pavements (if applicable). Proper site drainage should be maintained during construction so that ponding of surface runoff does not occur and cause construction delays and/or inhibit site access.

Once final subgrade elevations have been achieved the exposed subgrade should be carefully proofrolled with a 20-ton pneumatic roller or equivalent equipment, such as a fully loaded dump truck, to detect weak zones in the subgrade. Weak areas detected during proofrolling, or zones of fill containing organic matter and/or debris, should be removed and replaced with soils exhibiting similar classification, moisture content, and density as the adjacent in-situ soils.

Relatively dense clayey sands with some gravel were observed at various depths within our hand-augered borings and extended to the boring termination depths (from about 6 inches to about 3 feet below existing grades) in Borings B-9 through B-12. The subsurface within the proposed water line may be underlain by shallow rock in the area of the alignment which may be difficult to

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Subsequent to proofrolling, and just prior to placement of engineered fill (if applicable), the exposed subgrade within the construction areas should be evaluated for moisture and density. If the moisture and/or density do not meet the criteria described in the Compaction Requirements subsection below, the subgrade should be scarified to a minimum depth of 8 inches, moisture conditioned, and recompacted according to the Compaction Requirements subsection below.

Additional subgrade preparation for pavement areas is presented in the Pavements section of this report.

Fill Material Classification and Requirements

On-site, imported, structural, engineered, processed and/or recompacted soil, fill and backfill used for this site should be free of visual remains of vegetation and organic debris, and free of particles larger than 4 inches in nominal diameter.

The classification and physical property requirements of fill material are presented in the table below along with the acceptable locations for placement:

Fill Type 1 USCS Classification Suitable for use at these locations

On-Site Soils 2 SM, SC, SC-SM (or combinations thereof)

■ General site grading and fill, including scarified surfaces.

■ As engineered fill (if applicable) under pavement.

Imported SM, SC, SC-SM 4

(or combinations thereof)

■ General site grading and fill.

■ As replacement for high plasticity clay subgrade.

■ As engineered fill (if applicable) under pavement

■ Small utility service line and drain trench backfill.

1. Controlled, compacted fill should consist of approved materials that are visually free of organic matter, debris and particles larger than 4 inches. Frozen material should not be used, and fill should not be placed on a frozen subgrade. A sample of each proposed fill source should be submitted to the geotechnical engineer for evaluation.

2. On-site soils classified as SM, SC, SC-SM are considered suitable for use as fill material.

3. Imported clayey sands, silty sands, or combinations thereof; the fill material should have a liquid limit (LL) not exceeding 35, and a plasticity index (PI) not exceeding 15.

Prior to filling operations, or over-excavation and recompaction operations (if any), samples of the proposed borrow and on-site materials should be obtained for laboratory moisture-density testing and suitability of placement guidelines as stated above. The tests will provide a basis for evaluation of fill compaction by in-place density testing.

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A qualified soil technician should perform sufficient in-place density tests during the filling operations to evaluate that proper levels of compaction, including dry unit weight and moisture content, are being attained.

Compaction Requirements

Exposed subgrade and fill should be properly moisture-conditioned and compacted according to the following requirements:

Material Type and Location 1

Compaction Parameters 2

Min. Compaction Requirement

(ASTM D1557)

Range of Moisture Contents for Compaction (from Optimum)

Minimum Maximum Proofroll and subgrade scarification 95% -2% +2%

Acceptable on-site or engineered fill:

Beneath pavements 95% -2% +2%

Pipe Backfill 3 See the Buried Utility Pipe Recommendations section.

Miscellaneous backfill (sidewalk, landscaping, other) 92% -2% +2%

1. Horizontal, level lifts (no sloping lifts) should be placed. Loose fill layers 8-inches thick or less may be placed when heavy, self-propelled compaction equipment is used. Loose fill layers not exceeding 4-inches or less in thickness should be placed when hand-guided equipment (i.e. jumping jack or plate compactor) is used.

2. The moisture content and percent compaction should be measured against the results of a Proctor sample per the corresponding ASTM standard, for each lift of engineered fill (if applicable) during placement via the nuclear density method (ASTM D6938). Should the results of the in-place density tests indicate the specified moisture or compaction limits have not been met, the area represented by the test should be reworked and retested as required until the specified moisture and compaction requirements are achieved.

3. See the Buried Utility Pipe Recommendations section for pipe trench backfill recommendations.

Fill Construction Observation and Testing

The exposed subgrade and each lift of compacted fill (if applicable) should be tested, evaluated, and reworked, as necessary, until approved by the geotechnical engineer’s representative prior to placement of additional lifts. We recommend that each lift of fill be tested for density and moisture content at a frequency of at least:

■ One test for every 5,000 square feet in pavement areas;

■ A minimum of one test for every fill layer in any area, or;

■ A minimum of one test for every 200 linear feet of compacted utility trench backfill.

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Grading and Drainage

Grades must provide effective drainage during and after construction. Infiltration of water into utility trenches should be prevented during construction. After construction is finalize, we recommend verifying final grades to document that effective drainage has been achieved.

Earthwork Considerations

We anticipate that shallow excavations for the proposed construction can be accomplished with conventional earthmoving equipment. However, near surface very dense soils were encountered at the site and may require additional effort or heavy-duty equipment to advance excavations.

Upon completion of filling and grading, the contractor should avoid equipment or foot traffic over prepared subgrade surfaces to a practical extent and should maintain a proper subgrade moisture content prior to construction of concrete or pavement elements.

Relatively dense clayey sands with some gravel were observed at various depths within our hand-augered borings and extended to the boring termination depths (from about 6 inches to about 3 feet below existing grades) in Borings B-9 through B-12. Based on our borings and general observations of the conditions of the project site, the subsurface within the proposed water line may be underlain by shallow, partially weathered rock or heavily fractured rock, and may therefore be difficult to excavate. Partially weathered rock or heavily fractured rock typically requires loosening by blasting in confined (trench) excavations. Therefore, extra effort or heavy-duty earth-moving equipment may be required for trench excavations. Excavations for utility trenches may require a hoe ram, a heavy dozer equipped with a mechanical ripper, a rock saw, rock trenchers, jack hammer or similar trenching equipment. Please note that a rippability study has not been conducted for this project, and hence an experienced contractor should evaluate the required excavation means based on the geotechnical findings provided in this report.

Surface water should not be allowed to pond on the site and soak into the soil during or after construction. Construction staging should provide drainage of surface water and precipitation away from the construction areas. Water that collects over or adjacent to construction areas should be promptly removed, along with any softened or disturbed soils. Surface water control in the form of sloping surfaces, drainage ditches and trenches, and sump pits and pumps will be important to limit ponding and associated delays due to precipitation and/or seepage. If the subgrade becomes frozen, desiccated, saturated, or disturbed, the affected material should be removed or these materials should be scarified, moisture re-conditioned, and recompacted prior to construction and observed by Terracon.

As a minimum, excavations deeper than 4 feet (if applicable) should be performed in accordance with OSHA 29 CFR, Part 1926, Subpart P, “Excavations” and its appendices, and in accordance with any applicable local, state, and federal safety regulations. The contractor should be aware that slope height, slope inclination, and excavation depth should in no instance exceed those specified by these safety regulations. Flatter slopes than those dictated by these regulations may

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Construction site safety is the sole responsibility of the contractor who controls the means, methods and sequencing of construction operations. Under no circumstances shall the information provided herein be interpreted to mean that Terracon is assuming any responsibility for construction site safety or the contractor's activities; such responsibility shall neither be implied nor inferred.

Terracon should be retained during the construction phase of the project to observe earthwork and to perform necessary tests and observations during subgrade preparation, proofrolling, placement and compaction of engineered fill (if applicable), backfilling of excavations, and just prior to construction of pavements.

PAVEMENTS

Proper subgrade preparation, as well as the proper selection and placement of the aggregate base and surface source materials is crucial to the long-term performance of the pavement layers.

Subgrade Preparation

Subgrade materials at this site will consist of sands with varying amounts of silt, clay and gravel.

The top of the subgrade soils for the pavement areas should be exposed and prepared as recommended in the Earthwork section of this report.

Due to the relatively low blow-counts (below 10 blows per foot) observed at the surface in Borings B-1, B-2, B-5, or B-8, the top 12 inches of the subgrade soils should be over-excavated and recompacted within the planned pavement areas at or near the location of Borings B-1, B-2, B-5, or B-8, and the exposed subgrade at the bottom of the over-excavation should be proof-rolled per the Site Preparation heading of the Earthwork section of this report.

Site grading is generally accomplished early in the construction phase. The subgrade should be carefully evaluated at the time of pavement construction for signs of disturbance or excessive rutting. If disturbance occurred, subgrade should be reworked prior to paving. Imported fill material may be used if it meets the selection requirements previously stated.

Vehicular Traffic Loading Conditions

Traffic patterns and anticipated loading conditions were not made available to Terracon at the time of this report. Based upon our experience with similar projects, tabulated below are the assumed traffic frequencies and loads used to design pavement sections for this project. When actual traffic conditions have been determined Terracon should be contacted to review the information to consider a need for revision of the pavement designs and related recommendations.

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Pavement Area

Traffic Level Description

Automobile Parking Areas Light Duty

Light traffic (Few vehicles heavier than passenger cars, no regular use by heavily loaded two axle trucks.) (ESAL 1 < 5)

Vehicle Access Driveways and Drive-Thru Areas

Medium Duty

Medium traffic (Similar to Light Duty, including not over 50 loaded two-axle trucks or lightly loaded larger vehicles per day.

No regular use by heavily loaded trucks with three or more axles.) (ESAL = 6-25)

1. Equivalent daily 18-kip single-axle load applications.

If the pavements are subject to heavier loading and higher traffic frequencies than assumed, this office should be notified and provided with the information, so that we may review these pavement sections and make revisions, if necessary.

Pavement Design Considerations

Pavement design methods are intended to provide structural sections with adequate thickness over the subgrade such that wheel loads are reduced to a level the subgrade can support. Design of Asphaltic Concrete (AC) pavements are based on the procedures outlined in the National Asphalt Pavement Association (NAPA) Information Series 109 (IS-109). Design of Portland Cement Concrete (PCC) pavements are based upon American Concrete Institute (ACI) 330R-08;

Guide for Design and Construction of Concrete Parking Lots.

Listed below are pavement component thicknesses, which may be used as a guide for pavement systems at the site for the traffic classifications stated herein. The following minimum thickness recommendations were based on our estimated traffic loading, the requirements of the pavement design guidelines, the laboratory test results of the sampled soils, and our experience with similar projects and soil conditions.

California Bearing Ratio (CBR) tests were performed for this project to evaluate the support and characteristics of the subgrade. A CBR value of 21 was use for our analysis based on laboratory testing, soil classification, and our observations of the soil conditions at the site.

Flexible Pavement System (Hot Mix Asphalt)

Component Material Thickness, Inches

Light Duty Medium Duty Hot Mix Asphalt 2.0 3.0

Aggregate Base Material 6.0 6.0

Rigid pavements will perform better than asphaltic pavements in areas where short-radii turning and braking are expected (i.e. entrance/exit aprons, trash pads) and under heavy duty traffic due

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Rigid Pavement System (Portland Cement Concrete)

Component Material Thickness, Inches

Light Duty Medium Duty Heavy Duty

Concrete 5.0 5.5 6.0

1. Heavy duty sections are intended only for dumpster pad areas.

Aggregate base layers are not required under rigid pavement sections for structural purposes.

For drainage purposes (especially near landscaping areas), a 4-inch aggregate layer may be used. The aggregate layer may consist of Base Material as described in the following report subheading.

Waste dumpster areas should be constructed as heavy-duty concrete pavement with the thickness provided above. The concrete pad areas should be designed so that the vehicle wheels of the collection truck are supported on the concrete while the dumpster is being lifted to support the large wheel loading imposed during waste collection.

Please note that flexible pavement is not recommended for heavy duty traffic. Exposed subgrade should be properly prepared and compacted prior to sub-base or flexible base placement per our recommendations presented at the beginning of the Pavements section of this report.

Pavement Material Recommendations

Presented below are our recommended material requirements for the various pavement sections.

Hot Mix Asphalt Surface Course: The hot mix asphalt surface course should be plant mixed, hot laid, meeting the requirements in the New Mexico Department of Transportation (NMDOT) 2019 Standard Specifications for Highway and Bridge Construction, Section 423. Criteria for the job specifications should include compaction to within an air void range of 3 to 5 percent. The asphalt cement content by percent of total mixture weight should be within ± 0.5 percent asphalt cement from the job mix design.

Portland Cement Concrete Pavement: The materials and properties of concrete pavement should meet applicable requirements in the ACI Manual of Concrete Practice. The Portland cement concrete mix should have a minimum 28-day compressive strength of 3,500 psi.

Aggregate Base Course Material: Base material should be composed of crushed limestone or crushed concrete meeting the requirements of NMDOT 2019 Standard Specifications for Highway and Bridge Construction, Section 303, Type I or II. The base material should be compacted to at

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Prime Coat Material: Prime coat should be in conformance with NMDOT 2019 Standard Specifications for Highway and Bridge Construction, Section 408, and applied after compaction of aggregate base course layers.

Rigid Pavement Joints and Reinforcement

We recommend Portland cement concrete pavement details for joint spacing, joint reinforcement, and joint sealing be prepared in accordance with American Concrete Institute (ACI) guideline 330R-08, Guide for Design and Construction of Concrete Parking Lots.

Expansion Joints: ACI recommendations indicate that regularly spaced expansion joints may be deleted from concrete pavements. Therefore, the installation of expansion joints is optional and should be evaluated by the design team.

Pavement Drainage

Pavement performance is affected by its surrounding environment and should be sloped to provide rapid drainage of surface water. Water allowed to pond on or adjacent to the pavements could saturate the subgrade and contribute to premature pavement deterioration. Additionally, the pavement subgrade should be graded to provide positive drainage within the granular base section. Appropriate sub-drainage or connection to a suitable daylight outlet should be provided to remove water from the granular bases and subbase layers.

The civil engineer should consider the following recommendations in the design and layout of pavements:

■ Final grade adjacent to paved areas should slope down from edges at a minimum 2%.

■ The subgrade and pavement surface should have a minimum 2% slope to promote proper surface drainage.

■ Install joint sealant and seal cracks promptly.

■ Line the bottom of landscaped areas in or adjacent to pavements with clay soils reduce moisture migration to the pavement subgrade soils or base course.

■ Place properly compacted backfill against the exterior side of curb and gutter.

■ Place curb, gutter and/or sidewalk directly on the prepared subgrade soils rather than on unbound granular base course materials.

Pavement Maintenance

The pavement sections represent minimum recommended thicknesses and, as such, periodic maintenance should be anticipated. Therefore, preventive maintenance should be planned and provided for through an on-going pavement management program. Maintenance activities are intended to slow the rate of pavement deterioration and to preserve the pavement investment.

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Maintenance consists of both localized maintenance (e.g. crack and joint sealing and patching) and global maintenance (e.g. surface sealing). Preventive maintenance is usually the priority when implementing a pavement maintenance program. Additional engineering observation is recommended to determine the type and extent of a cost-effective program. Please note that even with periodic maintenance, some movements and related cracking may still occur, and repairs may be required.

BURIED UTILITY PIPE RECOMMENDATIONS

The following sections provide our recommendations with respect to open trench pipeline installation methods (trench bottom preparation, and our recommendations for bedding and backfill material selection and placement, as well as installation considerations, and guidelines with respect to trench excavation). The sections below also include trenchless pipe installation considerations and tunneling pit excavation recommendations.

We have not been provided specific project data with respect to the utility installation (i.e., plans, profiles, pipe types, sizes, etc.). As such, the following recommendations are general in nature and should be reviewed once detailed project information becomes available. The following recommendations are intended to apply to both gravity (or passive) systems and pressurized (force main) systems unless specifically noted.

Trenching excavations, trench preparation, bedding placement, buried pipe installations, and backfill operations should be performed in accordance with Sections 700 and 800 of the New Mexico Standard Specifications for Public Works Construction and with the following recommendations.

Open Trench Techniques

Our recommendations in this section are based, in part, on the assumption that open-cut techniques will be used for installation (unless otherwise stated), and that invert depths not exceeding those discussed in Project Description are planned for the alignment.

For the purposes of understanding the recommendations presented in this geotechnical report, we will use the following terminology:

■ Trench bottom: the exposed soil surface at the bottom of the trench excavation.

■ Bedding: the soil or fill material between the trench bottom and the bottom of the pipe.

■ Pipe zone: the volume from the bottom of the trench to a quarter-diameter dimension above the top of the pipe.

■ Trench Backfill: the volume between the top of the pipe zone and the ground surface

(or bottom of pavement structure).

Trench Bottom Preparation - The bottom of the trenches should be properly graded to create a relatively smooth and stable surface to receive fill and to provide for a relatively uniform thickness

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Responsive ■ Resourceful ■ Reliable 14 of fill beneath the proposed structures (where applicable). Exposed surfaces should be free of mounds and depressions which could prevent uniform compaction. The bottom of trench excavations should expose competent soils and should be dry and free of loose, soft, or disturbed soil. The exposed subgrade at the bottom of trenches should be evaluated for soil classification, moisture and density.

Subgrade soils at the trench bottom that classify as those shown in the following Bedding and Backfill Classification Requirements subsection of this report are considered suitable to support bedding material placement, provided the exposed subgrade soils consistently meet classification requirements.

Based on the anticipated invert elevation of the proposed pipeline alignment and the findings from our soil borings, we anticipate the subgrade soils at the bottom of the trench to consist of non-expansive, cohesionless soils classifying as Class III soils (clayey or silty sands) per New Mexico Standard Specifications for Public Works Construction).

If soft, wet, weak, or deleterious materials are exposed at the bottom of the trench, the bottom of the trench should be over-excavated a minimum of 8 inches to expose more competent / suitable soils. The over-excavated material should be removed and replaced with suitable, imported engineered fill, provided the imported material consistently meets the requirements outlined in the Bedding and Backfill Classification Requirements subsection of this report, and compacted according to the Trench Backfill Compaction Requirements subsection of this report.

Similarly, if the moisture and/or density of the on-site subgrade exposed at the bottom of the trench do not meet the criteria described in the Trench Backfill Compaction Requirements subsection of this report, the trench bottom should be scarified to a minimum depth of 8 inches, moisture conditioned, and re-compacted.

Bedding: Bedding is the material used between the bottom of the trench and the pipe that is intended to provide uniform support for the pipe. Bedding may be compacted or uncompacted, depending on the recommendations of the design engineer. Bedding that is uncompacted allows the pipe to sink into the bedding soil allowing for a more uniform distribution of stress on the bottom of the pipe. Under installed conditions, the vertical load on top of a pipe should be distributed over its width and the bedding reaction should be distributed along its contact area with the pipe.

The bedding materials should be selected and placed to provide as much of a uniform contact between the pipe and the material as possible. Bedding material selection should meet the classification requirements of Class I, II or III as described in the New Mexico Standard Specifications for Public Works Construction, as well as the requirements of the Bedding and Backfill Classification Requirements subsection of this report.

Trench Backfill: Trench backfill should not be started until the pipeline is properly bedded in accordance with the above recommendations. The backfill should classify as Class I, II or III soils

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Responsive ■ Resourceful ■ Reliable 15 according to the New Mexico Standard Specifications for Public Works Construction, and as those shown in the Bedding and Backfill Classification Requirements subsection of this report.

On-site or imported engineered backfill used for this site should free of visual remains of vegetation and organic debris, and free of particles larger than 4 inches in nominal diameter. The trench backfill material should then be properly placed, moisture-conditioned and compacted according to the Trench Backfill Compaction Requirements subsection of this report.

Bedding and Backfill Classification Requirements

The classification and physical property requirements of fill material are presented in the table below along with the acceptable locations for placement. Note that trench excavation soil may be re-used as trench backfill if they meet the outlined requirements below:

Trench Bottom, Bedding and Backfill Material Classification Requirements

Installation Portion Suitable Soil Classification Additional Requirements

Trench Bottom or Jacking Pit Bottom

On-Site SC or SM soils per USCS (or combinations thereof)

Either on-site or imported fill meeting Class I, II or III soils according to the New Mexico Standard Specifications for Public Works Construction.

Bedding

On-Site SC or SM soils per USCS (or combinations thereof)

Either on-site or imported fill meeting Class I, II, or III according to the New Mexico Standard Specifications for Public Works Construction.

Imported Poorly Graded Sands (SP) or Pea-Gravel

(GP) per USCS

Either on-site or imported fill meeting Class I, II, or III according to the New Mexico Standard Specifications for Public Works Construction.

Flowable fill Meeting the requirements for flowable backfill outlined in the New Mexico Standard Specifications for Public Works Construction.

Pipe Zone above Bedding

On-Site SC or SM soils per USCS (or combinations thereof)

Either on-site or imported fill meeting Class I, II, or III according to the New Mexico Standard Specifications for Public Works Construction.

Flowable fill Meeting the requirements for flowable backfill outlined in the New Mexico Standard Specifications for Public Works Construction.

Trench above Pipe Zone

On-Site SC or SM soils per USCS (or combinations thereof)

Either on-site or imported fill meeting Class III soils according to the New Mexico Standard Specifications for Public Works Construction.

Flowable fill Meeting the requirements for flowable backfill outlined in the New Mexico Standard Specifications for Public Works Construction.

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Prior to backfilling operations, samples of the proposed borrow and on-site materials should be obtained for laboratory moisture-density testing and suitability of placement guidelines as stated above. The tests will provide a basis for evaluation of fill compaction by in-place density testing.

A qualified soil technician should perform sufficient in-place density tests during the filling operations to evaluate that proper levels of compaction, including dry unit weight and moisture content, are being attained.

Trench Backfill Compaction Requirements - Exposed subgrade and fill should be properly moisture-conditioned and compacted according to the New Mexico Standard Specifications for Public Works Construction, and the following requirements:

Trench Backfill Material Compaction Requirements (On-Site or Imported Soils)

Installation Portion 1

Compaction Parameters 2

Min. Compaction Requirement

(per ASTM D1557)

Range of Moisture Contents for Compaction (from Optimum)

Minimum Maximum

Trench Bottom or Jacking Pit Bottom 2 95% -3% +3%

Bedding 90% -3% +3%

Pipe Zone above Bedding 90% -3% +3%

Trench above Pipe Zone 90% -3% +3%

1. Horizontal, level lifts (no sloping lifts) should be placed. Loose fill layers 8-inches thick or less may be placed when heavy, self-propelled compaction equipment is used. Loose fill layers not exceeding 4-inches or less in thickness should be placed when hand-guided equipment (i.e. jumping jack or plate compactor) is used.

2. In accordance with the New Mexico Standard Specifications for Public Works Construction. The moisture content and percent compaction should be measured against the results of a Proctor sample per the corresponding ASTM standard, for each lift of engineered fill during placement via the nuclear density method (ASTM D6938). Should the results of the in-place density tests indicate the specified moisture or compaction limits have not been met, the area represented by the test should be reworked and retested as required until the specified moisture and compaction requirements are achieved.

The exposed subgrade and each lift of compacted fill should be tested and evaluated (or reworked as necessary), until approved by the geotechnical engineer’s representative prior to placement of additional lifts. We recommend that each lift of fill be tested for density and moisture content at a frequency of:

■ A minimum of one test for every fill layer in any area, or;

■ A minimum of one test for every 200 linear feet of compacted utility trench backfill.

Open Excavation and Buried Pipe Installation Considerations

Excavation Process: Our exploratory boring logs are not intended for use in determining construction means and methods and may therefore be misleading if used for that purpose. We recommend that earth-work and utility contractors interested in bidding on the work perform their

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Responsive ■ Resourceful ■ Reliable 17 own tests to determine the quantities of the different materials to be excavated, as well as the preferred excavation methods and equipment for this site.

Upon completion of excavations, the contractor should avoid equipment or foot traffic over compacted subgrade or fill surfaces to a practical extent and should maintain a proper soil or fill moisture content prior to installation of pipe elements or additional backfill.

Surface water should not be allowed to pond on trenches/pits and soak into the soil during or after construction. Construction staging should provide drainage of surface water and precipitation away from the work areas. Water that collects over or adjacent to trench areas should be promptly removed, along with any softened or disturbed soils. Surface water control in the form of sloping surfaces, drainage ditches and trenches, and sump pits and pumps will be important to limit ponding and associated delays due to precipitation and/or seepage.

If the subgrade becomes frozen, desiccated, saturated, or disturbed, the affected material should be removed, or these materials should be scarified, moisture re-conditioned, and recompacted prior to construction and observed by Terracon.

Trenchless Techniques

This section provides our recommendations with respect to trenchless pipe installation considerations and tunneling pit excavation recommendations. Our recommendations are based, in part, on the assumption that trenchless (pipe-bursting) or similar pipe-jacking techniques will be used for installation (unless otherwise stated), and that invert depths not exceeding those discussed in Project Description are planned for the alignment.

We understand that trenchless horizontal directional drilling (HDD) methods are planned to be utilized at this site. Regardless of the methods used by the contractor, we recommend tunnel construction be conducted in accordance with the New Mexico Standard Specifications for Public Works Construction, and applicable sections of the Standard Specification Guidelines by the American Water Works Association (AWWA). Below are general comments regarding geotechnical considerations for trenchless construction techniques.

If excavations exceed 4 feet below the existing ground surface, we recommended that OSHA sloped excavation guidelines or a shoring system be installed to facilitate the excavation of the jacking pit to protect the stability of the excavation walls during the pipeline installation. Temporary shoring should be designed by the contractor’s professional structural engineer. The analysis of pit slope stability system was beyond our scope of work.

The temporary shoring system (if used) should be used in accordance with the manufacturer’s recommendations in accordance with the requirements of a trench safety plan and current OSHA regulations. The system should be monitored daily by a competent person as required by OSHA regulations. Additionally, the soil parameters in the previous table may be used in the design of the shoring systems.

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Pipe-Jacking Installation: We understand that the proposed pipe and/or casing will be installed underneath the existing ground surface using pipe-jacking (pipe-bursting) techniques. Pipe-jacking will require the use of a thrust block in order to advance the tunnel face and casing sections.

For pipe-jacking, a pit is normally excavated to the proposed invert depth of the pipe, and one side of the pit is covered with a plate which is used as the thrust block. The horizontal loads imposed on the thrust block will be resisted by the section of soil directly behind the thrust block.

The thrust restraint design should be performed based upon the American Water Works Association (AWWA) Manual M 9 (2008), Chapter 9, Design of Thrust Restraints. Relatively large soil deformations are necessary to develop full or partial frictional resistance, and the soils surrounding the pipe may be disturbed by future construction, if any. Therefore, a conservative approach should be taken in the design of a thrust restraint.

A total soil unit weight of 110 pcf and a passive earth resistance coefficient (kp) value of 3.2 may be used for the design of the pipe jack thrust block.