B08__A17_Geotechnical_Data_Report_Lateral_73.pdf

Prepared for:

Prepared by:

August 2023

CRIP LATERAL 73-36

CHECK STRUCTURE

GEOTECHNICAL REPORT

CRIP Lateral 73-36 Check Structure

Geotechnical Report

Prepared For:

Bureau of Indian Affairs

Office of Trust Services

Division of Water and Power

Task Order No. 140A1622F0021

Prepared By:

DOWL

1300 Cedar Street

Helena, MT 59601

August 30, 2023 \\dowl.com\j\Projects\26\12494-01\50Geo\73-36 Report\Lat73-36_GeotechnicalReport.docx

Geotechnical Report: August 2023

Page i

TABLE OF CONTENTS

Executive Summary

1.0 Introduction

2.0 Project Understanding

3.0 Investigation

4.0 Subsurface Conditions

5.0 Engineering Analysis & Recommendations

6.0 Geotechnical Design Continuity

7.0 Limitations

8.0 References

LIST OF TABLES

Table 1: Exploration Summary

Table 2: Laboratory Tests

Table 3: Sodium Adsorption Ratio (SAR) Results

Table 4: Total Dissolved Salt (TDS) Results

Table 5: Groundwater Depths During Drilling

Table 6: Documented Faults

Table 7: Seismic Design Parameters for Site Class E

Table 8: Foundation Design Parameters

Table 9: Lateral Earth Pressures

Table 10: Estimated Engineering Properties

Table 11: Slope Stability Results

Table 12: Minimum Geotextile Properties

Table 13: Fill Specifications

Table 14: Compaction Specifications

Table 15: Soil Chemistry

LIST OF FIGURES

Figure 1: Vicinity and Location Map

Figure 2: Surficial Geologic Map

Figure 3: Exploration Locations

Figure 4: TDS Dispersion Results

LIST OF APPENDICES

Appendix A: Exploration Logs

Appendix B: Photograph Log

Appendix C: Laboratory Test Results

Appendix D: Calculations

EXECUTIVE SUMMARY

DOWL prepared this geotechnical report for the U.S. Bureau of Indian Affairs. This report addresses the recommendations for the sublateral 73-36 Check Structure 1 of the Colorado River Irrigation Project.

Based on the information obtained from our subsurface exploration and testing, the site is suitable for reconstructing the check structure. Through the course of our evaluation, we identified the following geotechnical considerations:

• Generally, subsurface soils consist of silty sand and poorly graded sand with silt to the depth explored (11.2 feet).

• Based on our evaluation, the new check structure and head gate can be constructed on a conventional mat foundation.

• On-site soils appear to be suitable for use as general fill (e.g., for embankment construction and structure backfill) but not as structural fill below foundations.

• Based on the slope stability analysis, the inside slope of the canal has a factor of safety of 1.4, which is slightly below the standard minimum value. To increase the factor of safety to 1.5, we recommend placing a geotextile in the upper two feet of the canal embankment.

• Loose sands at the project sites are likely liquefiable under seismic events, which would likely result in differential settlement of the structure. Mitigation is possible to prevent liquefaction-induced settlement; however, this mitigation is costly, and even if select structures are mitigated, the remainder of the canal system would still likely be susceptible to settlement, damage, or failures, possibly requiring the system to be taken out of service for repairs. If the Bureau of Indian Affairs wishes to pursue liquefaction mitigation alternatives further, additional exploration is warranted to determine the depth and nature of the liquefiable horizons.

• Due to the likely presence of liquefiable soil, the site likely classifies as Site Class F; ASCE 7 recommends a site-specific seismic response analysis, which is beyond our scope.

1.0 INTRODUCTION

DOWL completed a geotechnical investigation for the 73-36 Check 1 structure replacement on the Colorado River Irrigation Project (CRIP) near Parker, Arizona. The structure was near failure, and this work was performed under exigent (i.e., near emergency) conditions. The scope of geotechnical services involved reviewing existing geotechnical and geological information, field observations, subsurface exploration, laboratory testing, engineering analyses, and preparing this Geotechnical Report. The purpose of these services is to provide geotechnical-related recommendations for project planning and design. We conducted this referencing our work plan dated July 26, 2023.

Our geotechnical engineering scope of work for this project included excavating two test pits to depths of about 11 feet below existing site grades, limited lab testing for soil engineering properties, and engineering analyses to provide foundation recommendations.

In 2017, DOWL performed a geotechnical study for four bridges across the length of the CRIP irrigated area. The closest bridge was the Peterson Road Bridge (#H024), about 3.5 miles west of the site (DOWL 2017). In 2022, DOWL performed a geotechnical study for three check structures on the CRIP Main Canal, located approximately 11 miles north of this project (DOWL 2022). We used information from those studies in the evaluation of the current project.

2.0 PROJECT UNDERSTANDING

2.1 EXISTING SITE CONDITIONS

The project is located south-southwest of Parker, Arizona. The project area is east of the Colorado River.

The canal is part of CRIP, operated and maintained by the Bureau of Indian Affairs (BIA). We illustrate the project Location in Figure 1. The check structure is located within the 73-36 CRIP Sublateral Canal. The canal was constructed of two earth embankments. The canal may be accessed by a gravel-surfaced operations and maintenance roadway on top of the embankments on both sides. The canal is in a relatively flat topographic area with a gentle slope down to the south-southwest. The surrounding area is agricultural land and is predominately used for the production of hay and other forage crops. The check structure provides a controlled, near-constant upstream water surface, allowing the diversion of water into CRIP sublateral 73-36-7. The existing check structure is in poor repair, and recently, a void developed below the existing structure (see Photograph 1 and Photograph 2). The structure underwent significant settlement (particularly on the east side), with displacement of joints and the development of large cracks in the walls. The structure is not considered salvageable; rather, complete replacement is necessary. To keep the structure and adjacent sublateral 73-36-7 ditch in operation, CRIP made an emergency repair to address undermining. This emergency repair included excavation and placing grout on the upstream side of the structure to fill voids and arrest undermining and piping. CRIP also installed a fabric-wrapped gravel layer at the downstream end of the slab to help prevent loss of additional soil from underneath the structure if the upstream grouting was only partially effective. Since the efficacy of these repairs is unknown, BIA directed DOWL to develop plans for the complete replacement of the check and headworks facilities.

Photograph 1. 73-36 Check Structure Looking Upstream

Photograph 2. Void under Slab and Cracked Wing Wall

CRIP 73-36 CHECK 1 REPLACEMENT

GEOTECHNICAL INVESTIGATION

WWW.DOWL.COM VICINITY AND LOCATION MAP FIGURE 1

LA PAZ COUNTY, ARIZONA

VICINITY MAP

NOT TO SCALE

LOCATION MAP

PARKER

73-36 LOCATION

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2.2 PROPOSED CONSTRUCTION

The BIA plans to replace the 73-36 Check 1 structure. The existing structure is in poor condition and is failing. Based on preliminary drawings1, the new structure will be about 50 feet wide and 48 feet long, with 8.5-foot-tall walls. The water depth upstream of the check structure will be about six feet. The new structure will support a long-crested weir with a total weir length of approximately 85 feet. The replacement structure will be located downstream of the existing check and in the vicinity of test pit TP-

2. Based on preliminary drawings, the floor elevation of the canal at the structure will be at an elevation of 313.7 feet. The top of the structure and canal embankments will be at an approximate elevation of

322.2 feet. Based on preliminary information from DOWL’s structural engineers, we anticipate a bearing pressure of up to 1,600 pounds per square foot (psf) at the base of the slab, including the water column.

All elevations included in this report reference the North American Vertical Datum of 1988 (NAVD88).

A new headgate structure will replace the existing gate in the same location in the vicinity of Test Pit TP-

1. The new concrete structure will be about nine feet tall, have a one-foot-thick footing that is four to five feet wide. The structure will have a gravel filter and drain on the embankment side and the forebay will have either a concrete slab or riprap and filter material. We anticipate a bearing pressure of less than 1,500 psf at the base of the footing, including the water column.

2.3 SITE GEOLOGY

A surficial geologic map of the project area (Wilson 1960) is presented in Figure 2. The project is located in southwest Arizona in the Parker Valley, part of the Lower Colorado River Valley region. Based on the geologic map, the subsurface soil in the valley consists of sand, silt, and gravel deposited in the Holocene and late Pleistocene epochs. The soil was likely deposited from stream channels and floodplains of the Colorado River. East of the project area, older river terrace deposits are mapped. Bedrock in the project area generally appears to consist of intrusive and extrusive volcanic rocks such as basalt, rhyolite, andesite, and granite.

1 Refer to DOWL deliverable E3-1: Long-crested Weir Design Considerations Memorandum. August 18, 2023.

CRIP 73-36 CHECK 1 REPLACEMENT

WWW.DOWL.COM SURFICIAL GEOLOGY MAP FIGURE 2

PROJECT LOCATION

Wilson, E.D., 1960, Geologic map of Yuma County, Arizona, Arizona Bureau of Mines, County Geologic Map Series M-3-11, 1:375,000.

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3.0 INVESTIGATION

3.1 FIELD INVESTIGATION

DOWL performed fieldwork on August 4, 2023. Fieldwork consisted of site observations, excavating, and logging two test pits. We illustrate boring locations in Figure 3. The BIA excavated the test pits to about 11 feet below the existing ground. During the topographic survey, DOWL surveyed the test pit locations relative to the project datum (Arizona State Plans – South).

Table 1: Exploration Summary

Test Pit Depth (feet)

Approximate

Surface

Elevation (feet)

Northing (feet)

Easting (feet)

Location

TP-1 11.2 316.7 1,059,910 505,765 Near existing check structure and proposed headgate structure

TP-2 11.2 316.1 1,059,569 505,762 Near proposed check structure

The BIA excavated the test pits under the direction of a DOWL engineer using a GRADALL XL4100. We provide exploration logs in Appendix A, which include soil and groundwater conditions. Stratification boundaries on the boring logs represent the approximate location of changes in soil types; in situ, the transition between materials may be gradual and may vary. In Appendix B, we present photographs of the test pit excavations.

We based the soil descriptions shown on the boring logs on field and laboratory testing referencing ASTM Standards2 D2487 or D2488. The soil and groundwater conditions depicted are only for the specific dates and locations reported and may not necessarily represent other locations and times.

2 ASTM D2487 is “Standard Practice for Classification of Soils for Engineering Purposes (Unified Soil Classification System)” and ASTM D2488 is “Standard Practice for Description and Identification of Soils (Visual-Manual Procedures).

SU

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EXISTING CHECK STRUCTURE

73-36 CRIP CHECK 1 REPLACEMENT

GEOTECHNICAL INVESTIGATION

WWW.DOWL.COM EXPLORATION LOCATIONS FIGURE 3

LEGEND

GEOTECHNICAL TEST PIT LOCATIONS

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TP-1

3.2 LABORATORY TESTING

DOWL transported samples to laboratories for testing after selecting representative field samples for testing based on visual examination of the soil and consideration of the design criteria. DOWL performed tests for index and engineering soil properties in Billings, Montana. Energy Labs of Billings, Montana, completed corrosion testing of select soil samples. Laboratory testing included:

Table 2: Laboratory Tests

Test Purpose

Natural Moisture Content

ASTM D 2216

Provides a measure of natural (in-situ) water content.

Moisture Density Relationship (Standard Proctor)

ASTM D 698

Provides a measure of the relationship of water content to the density of a soil during compaction.

Atterberg Limits

ASTM D 4318

Provides an indicator of the consistency and swell potential of fine-grained soils.

Particle-Size Distribution

ASTM D 421

Provides a measure of grain sizes of the soils to classify and identify physical characteristics.

Crumb Dispersion

ASTM D6572

Provides an estimate of the dispersion potential of soil.

We present laboratory test results in the summary table and figures in Appendix C.

3.2.1 Dispersion

Crumb dispersion tests were performed on a sample from each test pit, and neither were dispersive.

Chemical tests were performed on the soil samples to coincide with the dispersive physical property tests (double hydrometer, crumb, and pinhole) for the borings along the outlet conduit. The cation chemical tests are used to determine the individual amounts of sodium (Na), magnesium (Mg), potassium (K), and calcium (Ca), total dissolved salts (TDS), and the sodium adsorption ratio (SAR). Based on research by the NRCS and others, calcium or magnesium cations dominate in nondispersive clay, and sodium cations are dominant in dispersive clay. Additionally, one of the most common units to express the presence of sodium is the sodium adsorption ratio (SAR = Na/(½(Ca+Mg)½). SAR results are summarized in Table 3 and TDS results are summarized in Table 4 and Figure 4 along with NRCS guidelines for a soil’s dispersive characteristics.

Table 3: Sodium Adsorption Ratio (SAR) Results

Sample Location Sodium

Absorption Ratio *NRCS Dispersion Characterization

TP 1 (3 ft) 7.4 Nondispersive

TP 2 (7 ft) 4.0 Nondispersive *Characterization guidelines based on Table 13-3 in NRCS NEH 633, Ch. 13, June 2013 Draft (USDA 2013).

Table 4: Total Dissolved Salt (TDS) Results

Sample Location Total Dissolved Salts (meq/L)

Sodium

*Dispersion Characterization

TP 1 (3 ft) 41.6 54.4 Transitional

TP 2 (7 ft) 22.4 44.0 Transitional

* (Sherard, Dunnigan and Decker 1977).

Figure 4: TDS Dispersion Results

4.0 SUBSURFACE CONDITIONS

4.1 OBSERVED SOIL CONDITIONS

The generalized soil profile encountered at the check structure site consists of silty sand in Test Pit TP-1 and poorly graded sand with silt in TP-2 to the depths explored. Appendix A presents the exploration logs with lithology descriptions and other engineering properties. In the following paragraphs, we provide a general description of the soil strata.

4.2 GROUNDWATER

Groundwater was encountered at depths of eight feet below the ground surface in Test Pit TP-2 and was not encountered in TP-1 at the time of field exploration. These observations represent groundwater conditions only at the time of the observations and may not necessarily be representative of other times or locations. Groundwater conditions can change with varying seasonal and weather conditions and other factors (e.g., adjacent irrigation practices, canal water levels, and drain conditions).

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

0 1 10 100 1000

P ec en t

So d iu m

Total Dissolved Salts, meq/liter

TP 1 (3 ft)

TP 2 (7 ft)

Dispersive

Non-dispersive

Transitional

Table 5: Groundwater Depths During Drilling

Boring Depth (ft) Elevation (ft)

TP-1 NE NE

TP-2 8.0 308.1

4.3 SEISMICITY

4.3.1 Faulting

The proposed project is located in an area of Quaternary faulting. Based on the USGS Quaternary Fault Fold Database (USGS, 2018), two Quaternary faults exist in the project vicinity:

Table 6: Documented Faults

Fault Name Distance from

Project Site (mi) Recent

Earthquake Published Slip Rate (mm/yr)

Fault Length

(mi)

Average Strike

Blythe Graben 43 Late

Quaternary Unspecified 4 Unspecified

Chemehuevi Graben 47 Late

Quaternary Unspecified 3 Unspecified

Available publications do not include documentation that these faults have offset during the Holocene (last 15,000 years). Based on the fault locations, the site's surface rupture risk is low.

4.3.2 Seismic Loading

DOWL utilized site soil and geologic data, our knowledge of local geology, the project location, Minimum Design Loads and Associated Criteria for Buildings and Other Structures (ASCE 2016), and the National Earthquake Hazards Reduction Program (NEHRP) to estimate Seismic Site Classification of "F" at the project sites. The site is classified as Site Class F because the soil is liquefiable. ASCE 7 recommends a site-specific site response for Site Class F. If the soil at the site were not liquefiable, it would classify as Site Class E. Based on ASCE 7, a site-specific seismic hazard analysis is necessary to determine seismic loading.

Based on a meeting with BIA personnel on August 29, 2023, and because this is a low-risk structure, BIA has chosen to use Site Class E. We queried the ASCE 7 Hazard tool website (ASCE 2021) for seismic design parameters provided in Table 7.

Table 7: Seismic Design Parameters for Site Class E

Peak Acceleration, PGA

Short Period Acceleration, SDS

Long Period Acceleration, SD1

0.19 0.47 0.43

4.3.3 Liquefaction

Liquefaction is the partial or total loss of soil shear strength that can occur during strong earthquake motion of significant duration. Liquefaction is a process where high shear deformations result in a progressive build-up of pore water pressure. Because the seismic loading occurs rapidly, the excess pore pressures cannot dissipate, and the effective stress is reduced, resulting in a temporary loss of shear strength. Earthquake-induced liquefaction typically occurs only in loose, wet, granular soils during strong, long-duration ground motion. However, liquefaction can occur in low-plasticity silts and clays. Typically, liquefaction occurs within soil horizons less than 50 feet deep where groundwater is shallow (i.e., less than 20 feet deep).

Based on the geologic mapping and the boring logs in the 2017 and 2022 DOWL reports, loose (potentially liquefiable) sand extends below the groundwater in most of the project area. It is our opinion that the soil at this site is likely liquefiable and may settle under seismic loading.

To reduce the liquefaction potential, the loose granular soil could be densified. For potential mitigation alternatives, DOWL would recommend consideration of either stone columns or compaction grouting.

Stone columns are installed and compacted in large-diameter borings drilled into (or through) the liquefiable layer. Compaction grouting involves pumping a low slump grout into the liquefiable soil layers.

Each method acts to densify the soils within the areas treated.

Two other potential alternatives, dynamic compaction and vibro-compaction are likely not feasible due to the relatively high fines content of the soils. A final potential alternative involves retrofitting the structures with deep foundation elements, such as driven piles, that extend through the liquefiable zones.

However, based on other structures DOWL has been involved with in the project vicinity, pilings may extend to 100 feet or more below the ground surface.

In summary, the liquefaction potential of the soil can be reduced, but the mitigation costs will likely be high. Further, if earthquake-induced liquefaction occurs at the project location, the event may also induce liquefaction failures throughout much of the canal system. While the improved structures (if mitigated for liquefaction-induced settlement) would be stable, the canal system would likely suffer damage in other areas through the system and may still need to be taken out of service to address failures at other locations. Based on a meeting with BIA personnel on August 29, 2023, and because this is a low-risk structure and much of the irrigation system may fail in an earthquake, BIA has chosen not to pursue exploration and liquefaction mitigation.

5.0 ENGINEERING ANALYSIS &

RECOMMENDATIONS

5.1 FOUNDATIONS

Based on information from the subsurface exploration, laboratory testing results, and our analysis, it is our opinion that the proposed 73-36 check structure and headgate structure can be supported on a conventional mat/footing foundation system bearing on engineered fill over native soil. If encountered below the foundations, any undocumented fill should be removed. We provide specific recommendations in the following sections.

5.1.1 Conventional Foundation

The hydraulic structure may be founded on a conventional foundation according to the parameters listed below.

• Prior to placement of structural fill, compact the exposed subgrade (see Section 5.4.1).

• A DOWL geotechnical engineer should observe the finished subgrade prior to placing fill or concrete to verify that foundation conditions are similar to those encountered in the test pits.

• Remove and replace soft or loose zones or zones of unsuitable material, if encountered, with structural fill.

• Place a stabilization geotextile (see Section 5.4.8)

• Place a minimum of 12 inches of structural fill and then 12 inches of drain gravel. Where drain gravel is not specified, place 24 inches of structural fill.

Note that there is potential for liquefaction settlement during/after an earthquake, as discussed in Section

4.3.3. Settlement calculations are presented in Appendix D.

Table 8: Foundation Design Parameters

Footing Design Criteria Recommendations Notes

Mat Foundation Maximum Allowable Bearing Pressure

Static Loads (Dead & Sustained Live):

2,000 psf

Transient Loads (Wind & Seismic):

3,500 psf

Subgrade Modulus, k 150 psi/in

Maximum Estimated Settlement

Total (in) Differential (in) Based on 1,600 psf foundation pressure.

1 inch

0.5 inch over 25 feet

Subgrade Preparation and Structural Fill

Compact structural fill to 98% standard Proctor

Overexcavate 24 inches of soil below the foundation, lay stabilization geotextile, place 12 inches of structural fill, then 12 inches of drain gravel.

Design uplift of shallow foundations from wind and seismic events using the weight of the foundation and soil above the footing. You can include soil resistance in the shape of a truncated pyramid above the foundation. The pyramid edges are defined by straight lines extending from the top of the footing on either side at a 1H:2V (horizontal: vertical) slope.

DOWL used SIGMA/W software to evaluate the settlement of the structure and the proposed embankments. We estimated soil parameters from SPT values and consolidation testing. We assumed a load of 1,600 psf applied to the foundation (see Appendix D).

5.2 LATERAL EARTH PRESSURES

Design below-grade walls for retaining walls and any structure retaining soil to resist lateral earth pressures from the retained soil adjacent to the structure and hydrostatic pressures from retaining water (if undrained, not recommended). Also, account for lateral surcharge loads from equipment, slopes, or vehicles adjacent to the walls in the structural wall design. We provide recommended lateral earth pressures for below-grade wall design in Table 9.

Table 9: Lateral Earth Pressures

Lateral Earth Pressure Case Equivalent Fluid

Pressure (pcf)

Above Water

At-rest (no wall movement) 61

Active (wall moves away from soil mass) 36

Passive (wall moves into soil mass) 390

Below Water

At-rest (no wall movement) 93

Active (wall moves away from soil mass) 80

Passive (wall moves into soil mass) 259 Based on a unit weight of 125 pcf, effective unit weight of 65 pcf below the water table, and friction angle of 31 degrees.

• Construct below-grade walls, retaining walls, or other retaining structures with adequate drainage as specified by the structural engineer to reduce the potential for instability or leakage.

• The retaining walls move away from or toward the soil to develop active and passive resistance, respectively. For walls that cannot tolerate movement, structurally design walls utilizing at-rest equivalent earth pressures.

• We based the above equivalent fluid pressures on the assumption that the surface of the backfill is level adjacent to the walls.

• Lateral surcharge pressures due to equipment (e.g., the control building, construction equipment, and equipment necessary for installation of bulkheads or future gate repairs), slopes, storage loads, etc., are not included in the above lateral earth pressure recommendations. Include these loads in the design of the walls.

5.2.1 Seismic Earth Pressure

We recommend using the Mononobe-Okabe approach to determine the additional earth pressures due to earthquakes. Using the assumed unit weight of the retained soil at this project (125 pcf) and the design peak horizontal ground acceleration (0.19g), we estimate the equivalent additional fluid (active) earth pressure acting on the wall is 8 pcf. We calculated this value using ½ the peak ground acceleration in the horizontal direction.

5.2.2 Coefficient of Friction

We recommend using a coefficient of friction of 0.45 between cast-in-place concrete and structural fill or granular native soil. The friction value may be combined with the passive pressure to resist horizontal loads.

5.3 EMBANKMENT SLOPE STABILITY

DOWL performed slope stability analyses of the proposed canal embankments upstream of the 73-36 Check Structure. DOWL evaluated the slope stability of the embankments using Geostudio's Slope/W and the soil properties shown in Table 10. The inside and outside slopes of the canal will be 2H:1V. The tops of the embankments will be 16 feet wide. We summarize the slope stability results in Table 11 and the stability outputs in Appendix D.

Table 10: Estimated Engineering Properties

Material Moist Unit

Weight (pcf)

Effective Stress Total Stress

Friction Angle (degrees)

Cohesion (psf)

Friction Angle (degrees)

Cohesion (psf)

Embankment Fill 125 32 0 29 10

Sand 110 28 10 27 20

Table 11: Slope Stability Results

Slope Location and Scenario Calculated Factor of Safety Minimum Factor of Safety*

Inside Slope - Static 1.41 1.5

Inside Slope – Static - Reinforced 1.51 1.5

Outside Slope – Static 1.83 1.5

Inside Slope – Pseudo-Static 1.08 1.0

Outside Slope – Pseudo-Static 1.46 1.0

* Based on (USBR 2011) and (Hynes-Griffin 1984)

The factor of safety for the inside canal slope is 1.41, which is less than the standard minimum of 1.5. A factor of safety of 1.4 has a relatively low probability of failure. To increase the factor of safety to 1.5, we recommend placing a geotextile at the top of the existing slop prior to adding the additional one to two feet of fill necessary to obtain the finished grade elevation. Minimum geotextile properties are provided in Table 12.

Table 12: Minimum Geotextile Properties

Property Test Method Units Requirements

Wide Width Tensile (Ultimate) ASTM D4595 lbs/in 400

Wide Width Tensile (@ 5% Strain) ASTM D4595 lbs/in

200 MD

250 XD

Puncture strength ASTM D6441 lbs 615

Tear Strength ASTM D4533 lbs 100

Apparent opening size ASTM D4751 Sieve size

(mm) No. 40 (<0.43)

Ultraviolet Stability (retained strength ASTM D4355 % >70 after 500 hrs of exposure

5.4 EARTHWORK

5.4.1 Subgrade Preparation

• Soil containing vegetation and organics (topsoil) is generally not present. However, if topsoil or other organic soil is encountered, remove and replace it with structural fill.

• Remove uncontrolled fill below planned improvements or structures.

• Scarify, moisture condition, and compact upper subgrade soil as specified in Table 14.

• Grade the exposed subgrade surfaces to remove mounds and depressions, which could prevent uniform compaction. If unexpected fills or obstructions are encountered during site clearing or excavation, remove such features and clean the excavation before placing backfill and construction.

• Soil disturbance negatively impacts the soil's performance. Disturbed soil is not allowed below any structure or pavement, especially at footing or slab subgrades.

• Moisture condition and compact disturbed soil or fill placed to achieve site grades to the requirements in Table 14: Compaction Specifications.

• Remove pumping or rutting subgrade areas to depths between 12 and 18 inches or as directed by

DOWL.

• Replace over excavations with granular structural fill. Contact DOWL's geotechnical engineer to review and approve the exposed subgrade.

• Once DOWL approves the contractor’s prepared subgrades, it is the contractor's sole responsibility to protect subgrades from degradation.

5.4.2 Excavation

Based on the materials encountered in the test pits, conventional earthmoving equipment should be capable of excavating the site soils.

5.4.3 Temporary Slopes

Excavations must conform to OSHA Standards for Excavations, 29 CFR Part 1926.652 Appendix B to Subpart P. Based on field observations and laboratory tests, the soils at the site are classified as OSHA Type C. OSHA requires that Type C soil excavation slope angles do not exceed 1.5H:1V. The nature and extent of subsurface variations and groundwater conditions between the boring locations may not become evident until construction. Evaluate soil conditions during construction by the contractor's responsible person to comply with OSHA requirements. Temporary excavation slopes may be required for soil improvement excavations and utility trenches. Conduct excavations and shoring following OSHA standards. Do not allow surcharges within a horizontal distance equal to half the excavation depth.

Construction vibrations can cause excavations to slough or cave. The contractor is solely responsible for site safety and excavation configurations.

Groundwater may be expected during excavations. If site soil excavations are not backfilled quickly, they may degrade when exposed to runoff and require over-excavation and replacement with structural fill.

We recommend construction activities, particularly earthwork, be performed as rapidly as possible or during drier conditions to reduce the potential for remedial earthwork.

5.4.4 Structural Fill

Fill placed below the structure must be structural fill. The sandy soil is suitable for canal embankment, retaining wall backfill, or below exterior concrete flatwork. However, the on-site silt and sand are not suitable for placement below the proposed structure, and we recommend structural fill as specified in Table 13.

Table 13: Fill Specifications

Soil/Fill Product Allowable Use Material Specifications

Non-Structural Fill

(Landscape Fill)

Any area that will not have structures or embankments (typically landscape areas)

• Soil classified as GM, GW, SM, SW, SC, CL, or ML according to the USCS.

• Soil may not contain particles larger than 8 inches in median diameter.

• The soil must contain less than 3% (by weight) of organics, vegetation, wood, metal, plastic, or other deleterious substances.

General Fill

Site grading outside the structure footprints, utility backfill areas, canal embankment, non-structural fill, foundation backfill

• Soil classified as SM, SC, CL, or ML according to the

USCS.

• Site soil must have less than three percent vegetation, organics, and debris.

• Soil may not contain particles larger than 6 inches in diameter.

• The soil must contain less than 3% (by weight) of organics, vegetation, wood, metal, plastic, or other deleterious substances.

Structural Fill

Over-excavations and soil improvements.

• Soil classified as GP, GM, GW, SP, SM, or SP, with at least 30 percent retained on a number 4 sieve and less than 15 percent passing a number 200 sieve.

• Soil may not contain particles larger than 2 inches in diameter.

• The soil must contain less than 3% (by weight) of organics, vegetation, wood, metal, plastic, or other deleterious substances.

Unsatisfactory Soil

NONE

• Soil classified as MH, OH, CH, OL, or PT may not be used at the project site.

• Any soil type not maintaining moisture content within 5% of optimum during compaction is unsatisfactory soil that must be disposed of and replaced.

• Any soil containing more than 3% (by weight) of organics, vegetation, wood, metal, plastic, or other deleterious substances

5.4.5 Compaction Requirements

Place fill material in lifts not exceeding 12 inches in uncompacted thickness. Moisture condition and compact fill according to Table 14.

Table 14: Compaction Specifications

Application Moisture Content (% of optimum)

Minimum Compaction

Subgrade ±4 95% ASTM D698

Below Foundations ±4 98% ASTM D698

Base and Subbase Courses ±4 97% ASTM D698

Utility Trenches ±4 95% ASTM D698

Site Grading Fill ±4 95% ASTM D698

Canal Embankment ±4 95% ASTM D698

Foundation Backfill ±4 95% ASTM D698

5.4.6 Testing and Observations

We recommend the following compaction testing frequencies:

• Structural Fill below Footing and Subgrade - One compaction test every 2,500 square feet (SF) of fill, or 2 tests per lift, whichever results in the greater number of tests per each 1-foot lift of fill.

• Foundation/Retaining Wall Backfill - One compaction test every 100 linear feet (LF) of the wall or 2 tests per wall line, whichever results in the greater number of tests per each 1-foot lift of backfill.

• Trenches - One compaction test every 400 linear feet or 2 per trench, whichever results in the greater number of tests per each 1-foot lift of backfill.

• To verify construction conforms to the intent of the specifications, we recommend DOWL be retained to observe and record the following:

○ Site preparation, including grubbing, stripping, excavating, and proof-rolling;

○ Removal of topsoil and root zone beneath structures.

○ Excavations and subexcavations before placing backfill/fill materials or before construction of foundations; and

○ Approval of additional excavation, replacement, or stabilization if unsuitable soil is identified by the geotechnical engineer during excavation or proof-rolling operations.

5.4.7 Wet Weather/Soil Construction

• Ideally, perform earthwork construction when the soil moisture content is less than two percent above optimum.

• If possible, do not perform earthwork after rainfall when the soil is wet. Allow the soil to dry sufficiently to allow construction traffic without disturbing the subgrade.

• If the subgrade soil becomes wet, it may be necessary to perform earthwork with track-mounted equipment that reduces vehicular pressure applied to the soil if construction commences in wet areas or before the soil can dry enough to support wheeled vehicles.

• If the subgrade is soft and does not provide a stable construction platform, the contractor may place an initial 16-inch lift of structural fill over a stabilization geotextile (see Section 5.4.8) to help reduce the compaction energy on the unstable subgrade. Thicker structural fill lifts may only be installed over sensitive subgrades and with DOWL's approval during construction. Initial thicker fill lifts and over-excavations to remove soft, wet soil can only be placed after the contractor has unsuccessfully attempted to moisture condition and recompact the native soil.

5.4.8 Stabilization Geosynthetics

Stabilization geosynthetic fabrics are applicable in the following instances:

• when constructing on soft, wet soil;

• for foundations soil improvement applications; and

• as separation fabrics between drainage aggregate, below the construction access road surfacing, and at the base of over-excavations.

Where required, apply geosynthetics directly on approved subgrades, taut, without wrinkles, over-lapped at least 12 inches, and in accordance with the manufacturer’s recommendations. Consult DOWL to review geosynthetic applications or other subgrade improvement alternatives. Geotextile fabric placed at the bottom of the footing excavation must meet the requirements for stabilization fabric in Section 1014, Geosynthetics, of the Arizona Department of Transportation Standard Specifications for Road and Bridge Construction (ADOT 2021).

5.5 SOIL CORROSION POTENTIAL

Soil chemistry (pH, soluble sulfates, and resistivity) tests were performed on two samples (Table 15).

Based on the results shown in the table below, concrete in contact with the on-site soil classifies as exposure class S1 according to ACI 318 table 19.3.1.1 (ACI, 2014). To achieve the required protection against sulfate related corrosion, we recommend specifying Type II cement or increase the amount of Type II cement in the concrete to achieve a maximum water-to-cement ratio of 0.50 (by weight, normal weight concrete) and a minimum compressive strength, f'c, of 4,000 pounds per square inch (psi). Details can be found in the above ACI reference and in the Portland Cement Association publication "Design and Control of Concrete Mixtures."

According to Corrosion/Degradation of Soil Reinforcement for Mechanically Stabilized Earth Walls (FWHA, 2009) the soil at the site is “moderately corrosive” to “corrosive” to steel. Based on that publication and the tests results below, we estimate a corrosion rate of 0.85 ounce per square foot per year for carbon steel and 0.25 ounce per square foot per year for galvanized steel .

Table 15: Soil Chemistry

Sample Location Material Type Soluble

Sulfates (ppm) pH

Resistivity (ohm-cm)

TP-1 @ 3 feet SM 431 8.4 1220

TP-2 @ 7 ft SP/SM 167 8.7 2910

6.0 GEOTECHNICAL DESIGN CONTINUITY

Geotechnical design continuity will be an essential aspect of the successful completion of this project. In DOWL’s opinion, geotechnical continuity can occur in three stages: planning, design, and construction.

Specifically, we recommend that DOWL maintain the geotechnical design continuity in the following aspects:

• Geotechnical Design Confirmation: The potential soil variation may significantly impact foundation construction. As such, we recommend the BIA retain DOWL to provide geotechnical engineering oversight during site grading and foundation excavation to observe the potential variability in the soil conditions and provide consultation regarding potential impacts on foundation construction.

• Construction Observation and Testing: We recommend the BIA retain DOWL to review observation and testing performed by an accredited laboratory (AASHTO or the Corps of Engineers) during site preparation, grading, structural fill placement, and backfilling to verify compliance with the recommendations presented in this report. Being involved in inspection and oversight during this process will reduce the potential for an unforeseen construction error that may ultimately impact the project.

7.0 LIMITATIONS

DOWL based the conclusions and recommendations presented in this report on the assumption that site conditions are not substantially different than those exposed by the explorations. If, during construction, subsurface conditions are different from those encountered in the explorations, advise DOWL at once to review those conditions and (if necessary) provide alternate recommendations appropriate to the site soils. The geotechnical recommendations herein are based on the premise that an adequate program of tests and observations will be conducted during construction to document compliance with DOWL's recommendations and to confirm conditions exposed during subgrade preparations.

If there is a substantial lapse of time between the submission of this report and the start of work at the site, and especially if conditions have changed due to natural causes or construction operations at or near the site, contact DOWL to review this report and to evaluate the applicability of the conclusions and recommendations presented herein.

DOWL prepared this report for the BIA and for internal use in completing final structure designs. DOWL recommends that the BIA make this report available to prospective contractors only for information and factual data, not as a warranty of subsurface conditions. DOWL prepared this report, including engineering analyses, recommendations, figures, and design details for the CRIP 73-36 check structure and headgate.

These recommendations do not apply to other construction sites. Do not separate the figures from the text for independent use.

DOWL performed these services consistent with the level of care and skill ordinarily exercised by members of the profession currently practicing in this area under similar time and budgetary constraints. No warranty is made or implied.

Any conclusions made by a construction contractor or bidder relating to construction means, methods, techniques, sequences, or costs based upon the information provided in this report are not the responsibility of BIA or DOWL.

8.0 REFERENCES

ADOT. 2021. Standard Specifications for Road and Bridge Construction. Phoenix: Arizona Department of

Transportation.

ASCE. 2021. ASCE 7 Hazard Tool. Accessed August 7, 2020. https://asce7hazardtool.online/.

ASCE. 2016. Minimum Design Loads and Associated Criteria for Buildings and Other Structures. American Socienty of Civil Engineers.

DOWL. 2022. CRIP Main Canal Check Structures Geotechnical Data Report. Billings: DOWL, LLC.

DOWL. 2017. Final Geotechnical Report Bureau of Indian Affairs Colorado River Indian Reservation.

Montrose: DOWL, LLC.

Hynes-Griffin, M.E. and Franklin, A.G. 1984. Rationalizing the Seismic Coefficient Method. Vicksburg: U.S.

Army Corps of Engineers.

Sherard, J. L., L. P. Dunnigan, and R. S. Decker. 1977. Introduction in Dispersive Clays, Related Piping and Erosion in Geotechnical Projects. Chicago: ASTM International.

USBR. 2011. Design Statndards No. 13 Embankment Dams - Chapter 4: Static Stability Analyis.

Washington D.C.: United States Bureau of Reclamation.

USDA. 2013. Part 633 Soils Engineering National Engineering Handbook. National Resource Conservation Service.

USGS. 2020. Earthquake Hazards: Quaternary Fault and Fold Database of the United States. United States Geotechnical Survey. Accessed July 29, 2020. https://www.usgs.gov/natural-hazards/earthquake-hazards/faults?qt-science_support_page_related_con=4#qt-science_support_page_related_con .

Wilson, E D. 1960. Geologic Map of Yuma County, Arizona. County Geologic Map Series M-3-11, Phoenix:

Arizona Bureau of Mines.

Appendix A: Exploration Logs

SOIL CLASSIFICATION/LEGEND

Relat iv e Densi ty or Consistency

Uti l iz ing Standard Penetrat ion T est Values

Cohesionless Soils(a) Cohesive Soils(b)

Density(c) N blows/ft(c)

Relative Density

Consistency N blows/ft(c)

Undrained Shear

Strength(d)

(psf) Very loose 0 to 4 0 - 15 Very soft 0 to 2 <250

Loose 5 to 10 15 - 35 Soft 3 to 4 250 - 500

Med. Dense 11 to 29 35 - 65 Medium Stiff 5 to 8 500 – 1,000

Dense 30 to 49 65 - 85 Stiff 9 to 15 1,000 – 2,000

Very Dense Over 50 >85 Very Stiff 16 to 30 2,000 – 4,000

Hard Over 30 >4,000

(a) Soils consisting of gravel, sand and silt, either separately or in combination, possessing no characteristics of plasticity and exhibiting drained behavior.

(b) Soils possessing the characteristics of plasticity, and exhibiting undrained behavior.

(c) Undrained shear strength = ½ unconfined compressive strength.

(d) Qp - Denotes pocket penetrometer field measurement (tons per square foot) approximation to unconfined compressive strength.

Component Def in i t ions By Gradat ion Component Size Range

Boulders Greater than 12-in.

Cobbles 3-in. to 12-in.

Gravel 3-in. to No. 4 (4.75 mm)

Coarse gravel 3-in. to ¾-in.

Fine gravel ¾-in. to No. 4 (4.75 mm)

Sand No. 4 (4.75 mm) to No. 200 (.075 mm)

Coarse sand No. 4 (4.75 mm) to No. 10 (2.0 mm)

Medium sand No. 10 (2.0 mm) to No. 40 (0.425 mm)

Fine sand No. 40 (0.425 mm) to No. 200 (0.074 mm)

Silt and Clay Smaller than No. 200 (0.075 mm)

Si l t and C lay Descr ipt ions Description Typical Unified Designation

Silt ML (non-plastic) Clayey Silt CL-ML (low plasticity)

Silty Clay, Lean Clay CL Clay, Fat Clay CH

Plastic Silt MH Organic Soils OL, OH, Pt

Descr ipt iv e T erminology Denot ing Components Propor t ions

Descriptive Terms Range of Proportion

Trace or Scattered 0 - 5% Few 5 - 10%

Some or Adjective(a) 15 - 30% And 30 - 50%

(a)Use gravelly, sandy or silty as appropriate.

Unless otherwise noted, drive samples advanced with 140-lb. hammer and 30-in. drop.

Unif ied Soi l C lassi f icat ion Sy stem

Criteria for Assigning Group Symbols and Names Soil Classification

Generalized Group Descriptions

COARSE-GRAINED SOILS GRAVELS CLEAN GRAVELS GW Well-graded gravels More than 50% More than 50% of Less than 5% fines GP Poorly-graded gravels retained on coarse fraction GRAVELS w/ FINES GM Gravel and silt No. 200 sieve retained on No. 4 More than 12% fines mixtures sieve GC Gravel & clay mixtures SANDS CLEAN SANDS SW Well-graded sands 50% or more of Less than 5% fines SP Poorly-graded sands coarse faction SANDS with FINES SM Sand and silt mixtures passes No. 4 sieve More than 12% fines SC Sand and clay mixtures

FINE-GRAINED SOILS SILTS & CLAYS CL Low-plasticity clays 50% or more passes Liquid limit INORGANIC ML Non-plastic and low-the No. 200 sieve less than 50 plasticity silts

Non-plastic and low plasticity organic clays

ORGANIC OL

Non-plastic and low-plasticity organic silts

SILTS & CLAYS CH High-plasticity clays Liquid limit INORGANIC MH High-plasticity silts greater than 50

High-plasticity organic clays

ORGANIC OH

High-plasticity organic soils

HIGHLY ORGANIC SOILS Primarily organic matter, dark in color and has an organic odor PT peat

Soi l M oisture

Dry Absence of moisture, dusty, dry to the touch

Slightly Moist Minor existence of moisture, not dusty, but still dry to the touch

Moist Damp but no visible water

Very Moist Zones of visible moisture and usually above the water table

Wet Visible free water, usually soil is below water table

Groundwater Elevat ion

Water Elevation Noted During Drilling

Water Elevation Recorded After Drilling Complete

Samples

Split Spoon Sampler (2.0” OD)

Ring Sampler (3.0” OD)* *Indicates increased blow counts due to sampler size.

Shelby Tube Sampler (3.0” OD)

Bulk Sample (auger cuttings)

Core Barrel

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

MH or OL

ML or OL

C L or O

L

C H o r O

H

"A " L

IN

E "U

LI

N E

Key to Soil Symbols and Terms

Notes

Order of Descriptors

Criteria For Descriptors

- Angularity of coarse grained soils

Consistency of Fine Grained Soils

16 - 30Very Stiff

Apparent Density of Coarse Grained Soils

4 - 10 Loose

31 - 50Dense

-Absence of moisture, dusty, dry to the touch.Dry -Damp, but no visible water.Moist

Moisture Condition

- Other relevant notes

11 - 30Medium Dense tures, little or no fines.

Well-graded gravels, gravel sand mix-

Poorly graded gravels, gravel-sand mix-tures, little or no fines.

Silty gravels, gravel-sand-silt mixtures.

Clayey gravels, gravel-sand-clay mixtures.

Well-graded sands, gravelly sands, little or no fines.

Poorly graded sands, gravelly sands, little or no fines.

Silty sands, sand-silt mixtures.

Clayey sands, sand-clay mixures.

Inorganic silts and very fine sands, rock flour, silty or clayey fine sands or clayey silts with slight plasticity.

Inorganic clays of low to medium plasticity, gravelly clays, sandy clays, silty clays, lean clays.

Organic silts and organic silty clays of low plasticity.

Inorganic silts, micaceous or diatomaceous fine sandy or silty soils, elastic silts.

Inorganic clays of high plasticity, fat clays.

Organic clays of medium to high plasticity, organic silts.

Peat and other highly organic soils.PT

OH

CH

MH

OL

CL

ML

SC

SM

SP

SW

GC

GM

GP

GW

SYMBOLS

GRAPH LETTER

TYPICAL

DESCRIPTIONS

HIGHLY ORGANIC SOILS

NOTE: DUAL SYMBOLS ARE USED TO INDICATE BORDERLINE SOIL CLASSIFICATIONS

SILTS

AND

CLAYS

LIQUID LIMIT

GREATER THAN 50

NO. 200 SIEVE SIZE

SMALLER THAN

OF MATERIAL IS

MORE THAN 50%

LIQUID LIMIT

LESS THAN 50

CLAYS

AND

SILTS

FINE

GRAINED

SOILS

OF FINES)

(APPRECIABLE AMOUNT

FINES

SANDS WITH

(LITTLE OR NO FINES)

CLEAN SANDS

OF FINES)

(APPRECIABLE AMOUNT

FINES

GRAVELS WITH

(LITTLE OR NO FINES)

GRAVELS

SIEVE

PASSING ON NO. 4

FRACTION

OF COARSE

MORE THAN 50%

SOILS

SANDY

AND

SAND

200 SIEVE SIZE

LARGER THAN NO.

OF MATERIAL IS

MORE THAN 50%

4 SIEVE

RETAINED ON NO.

FRACTION

OF COARSE

MORE THAN 50%

SOILS

GRAVELLY

AND

GRAVEL

SOILS

GRAINED

COARSE

SOIL CLASSIFICATION CHART

MAJOR DIVISIONS

CLEAN

Definition of Particle Size Ranges

Boulder Cobble Gravel Sand Silt Clay between silt and clay.

> 12 in (300 mm) 3 in (75 mm) - 12 in (300 mm)

No. 4 Sieve (4.75 mm) to 3 in (75 mm)

No. 200 (0.075 mm) to No. 4 Sieves (4.75 mm)

< No. 200 Sieve (0.075 mm)* < No. 200 Sieve (0.075 mm)* grained soils only)

N-Value (uncorrected)Consistency

Soil Component Size Range

< 4Very Loose

> 50Very Dense

< 2Very Soft 2 - 4Soft 5 - 8Medium Stiff

9 - 15Stiff

> 30Hard

N-Value (uncorrected)Relative Density

- Group Name

- Consistency or Relative Density

- Moisture Condition

- Color

- Particle size descriptor(s) (coarse

Boring Log Descriptive Terminology

-Visible free…