Phase IV Geotechnical Report 050106.pdf

Veterans Affairs Medical Center May 1, 2006

Project No. 301699005

TABLE OF CONTENTS

Page

1. INTRODUCTION

2. SCOPE OF SERVICES

3. PROJECT DESCRIPTION

4. GENERAL SITE CONDITIONS

5. FIELD EXPLORATION AND LABORATORY TESTING

6. GEOLOGY AND SUBSURFACE CONDITIONS

6.1. Geologic Setting

6.2. Potential Geologic Hazards

6.3. Ground Motion

6.4. Subsurface Unit Encountered

6.5. Soil Percolation

6.6. Groundwater

6.7. Liquefaction

7. FINDINGS AND CONCLUSIONS

8. RECOMMENDATIONS

8.1. Earthwork

8.1.1. Site Grading

8.1.2. Structural Fill and Backfill

8.1.3. Import Soil

8.1.4. Temporary Excavations

8.2. Structure Foundations

8.3. Lateral Earth Pressures

8.4. Concrete Slab-On-Grade Floors

8.5. Settlement

8.6. Geotechnical Parameters for the Tunnel Design and Construction

8.7. Exterior Concrete Flatwork and Curbs and Gutters

8.8. Pavement Sections

8.8.1. On-Site Parking and Access Areas

8.8.2. Preliminary Pavement Sections for Pecos Road

8.8.3. Preliminary Pavement Sections for Deer Springs Way and Walnut Road

8.9. Concrete and Corrosion Considerations

8.9.1. Concrete

8.9.2. Buried Metal Pipes

8.10. Moisture Infiltration Reduction and Surface Drainage

8.11. Observation and Testing

8.12. Plan Review

8.13. Pre-Construction Meeting

9. LIMITATIONS

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10. SELECTED REFERENCES

Tables

Table 1 – Faults in Site Vicinity

Table 2 – Seismic Design Parameters

Table 3 – Caliche Layers Encountered

Table 4 – Summary of Laboratory Test Results

Table 5 – Soil Percolation Test Results

Table 6 – Flexible Pavement Section Thickness for On-Site Parking and Access Areas

Table 7 – Preliminary Pavement Sections for Pecos Road

Table 8 – Preliminary Pavement Sections for Deer Springs Way and Walnut Road

Table 9 – Requirements for Concrete Exposed to Sulfate-Containing Soil

Figures

Figure 1 – Site Location Map

Figure 2 – Boring Location Map

Figure 3 – Lateral Earth Pressures for Yielding Retaining Walls

Figure 4 – Lateral Earth Pressures for Restrained Retaining Walls

Figure 5 – Retaining Wall Drainage Detail

Appendices

Appendix A – Field Sampling Procedures and Exploratory Boring Logs

Appendix B – Laboratory Testing Procedures and Results

Appendix C – Chemical and Solubility Test Results

Appendix D – Boring Logs from Previous Evaluation

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1. INTRODUCTION

In accordance with your request, Ninyo & Moore has performed a geotechnical evaluation for the proposed Veterans Affairs Medical Center to be located southeast of the intersection of Pecos Road and Clark County Beltway 215 (CC-215) in North Las Vegas, Nevada. The location of the site is indicated on Figure 1. The purposes of our geotechnical study were to evaluate the subsurface soil conditions at the site and to provide design and construction recommendations regarding geotech-nical aspects of the project. This report presents the findings of our subsurface exploration, results of our laboratory testing, conclusions regarding the subsurface conditions at the subject site, and geotechnical recommendations for the design and construction of this project.

Ninyo & Moore also previously performed a preliminary geotechnical evaluation for the project.

This earlier study included preparation of the referenced report (Ninyo & Moore, 2005).

2. SCOPE OF SERVICES

The scope of our services included the following:

Review of pertinent background data listed in the Selected References section of this report.

The data reviewed included a site plan, design codes and manuals, aerial photographs, in-house geotechnical and soils data, referred geotechnical report, and published geologic maps and literature.

Coordination and mobilization for subsurface exploration, including clearance of existing utilities at the site conducted through Underground Service Alert (USA).

Drilling, logging, and sampling of 30 exploratory soil borings to depths ranging from ap-proximately 4.4 to 74.0 feet to evaluate subsurface soil conditions and to obtain soil samples for laboratory testing.

Performance of six soil percolation tests to evaluate the rate of water infiltration into the sub-surface soils in proposed parking lot areas.

Performance of laboratory tests on selected soil samples obtained from the exploratory exca-vations to evaluate mechanical and engineering properties, including in-place moisture con-tent and dry density, gradation, plasticity, consolidation characteristics, expansion potential, R-value, solubility potential, resistivity, sulfate content, sodium content, and sodium sulfate content.

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Compilation and analysis of the accumulated data.

Preparation of this geotechnical evaluation report presenting our findings, conclusions, and recommendations, including geotechnical recommendations regarding earthwork, structure foundations, lateral earth pressures, concrete slab-on-grade floors, exterior concrete flatwork and curbs and gutters, preliminary pavement sections for the dedicated streets, pavement sec-tions for parking and access areas, concrete and corrosion considerations, and moisture infil-tration reduction and surface drainage.

3. PROJECT DESCRIPTION

We understand that the subject project will include designing and constructing a medical facility on a site that is approximately 144.7 acres in size, of which approximately 120 acres is antici-pated to be utilized. Based on our review of the referenced plan (RTKL, 2006), the project will include a series of structures ranging from a two-story for the Business Administration and Edu-cation Departments, three-story Ambulatory, Outpatient Care Area, six-story Patient Tower, two-story Mental Health wing and three-story Nursing Care Units building. The project also includes a warehouse area, loading dock area, and central plant east of the main facility, and a partial basement below the Diagnostic and Treatment building. Footings for the basement are antici-pated to be at a depth of up to 21.5 feet below finished grade. A tunnel or a partial tunnel is being considered between the main facility and the central plant. Structural loads for the structures are anticipated to be low to high. The structures are anticipated to be of steel-frame or masonry con-struction with slab-on-grade floors. We also understand that the northern portion of the site will be cut down up to approximately 10 feet and the southern portion will be filled up to approxi-mately 10 feet.

We also understand that the project will include half-street improvements for Pecos Road, Deer

Springs Way, and Walnut Road (dedicated streets). Pecos Road improvements are proposed from

Deer Springs to CC-215, and will consist of removing a 32-foot wide existing temporary asphalt concrete roadway and replace with half street improvements. Deer Springs Way is proposed to be constructed from Pecos Road to Walnut Road. Walnut Road is proposed to be constructed from Deer Springs Way to the CC-215 right-of-way (ROW). Exterior flatwork, paved parking and access road areas, and retaining walls are also anticipated for the project. Off-site utilities, such as water and sewer lines were not a part of our evaluation.

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Consideration is being given to utilizing planter areas in parking lots to handle surface runoff during rainstorms by constructing percolation basins. This method will be used if the percolation rates at the site are adequate.

4. GENERAL SITE CONDITIONS

The subject site is located adjacent to Pecos Road between Centennial Parkway and CC-215 in

North Las Vegas, Nevada. The approximately 144.7-acre site is contained within a portion of

Clark County Assessor’s Parcel No. 123-19-000-001 designated as Government Lots 2 and 3.

The site is bordered generally by Pecos Road on the west, and undeveloped portions of Parcel

No. 123-19-000-001 on the north, south, and east (Figure 2).

At the time of our field activities, the site was undeveloped. The ground surface was generally undisturbed although a few vehicular trails were observed extending across the site. A few spoils piles (fill) were observed in the northern portion and along the eastern boundary of the site.

Some scattered trash and areas of dumped construction debris were also observed.

The topography at the site is slightly undulatory and it slopes downward to the south. Numerous ephemeral drainage washes, up to a few feet wide and deep, were observed. The washes were dry at the time of our field activities.

301699005R Color.doc 3 long Pecos Road.

Indications of underground utilities were not observed at the site during our field activities.

However, the Williams-Kern River high-pressure gas transmission underground pipeline and underground fiber optic utility easement was observed extending in a general northeast-southwest direction in the southern portion of the parcel located south of the subject site.

Additional underground utilities may also be present in the site vicinity. Overhead utilities observed included high-voltage electric lines extending a

5. FIELD EXPLORATION AND LABORATORY TESTING

Ninyo & Moore’s subsurface exploration of the project site was performed between February 24, 2006, through March 02, 2006. This exploration consisted of drilling, logging, and sampling 30 small-diameter exploratory borings (B-1 through B-30). The borings were advanced to depths ranging from approximately 4.4 to 74.0 feet with truck-mounted CME 85 and Mobile B-60 drill rigs utilizing 8-inch outside diameter hollow-stem augers and the boreholes were backfilled with drill cuttings after drilling operations.

The purposes of the exploratory borings were to evaluate subsurface soil and groundwater conditions at the project site and to obtain soil samples for laboratory testing. The approximate locations of the borings are shown on Figure 2. The approximate ground surface elevations are also presented on the boring logs. Logs of the borings and a description of sampling procedures utilized are presented in Appendix A.

Laboratory tests were performed on representative soil samples collected from the borings to evaluate mechanical and engineering properties, including in-place moisture content and dry density, gradation, plasticity, consolidation characteristics, expansion potential, R-value, solubility potential, resistivity, sulfate content, sodium content, and sodium-sulfate content. In-place moisture content and dry density test results are indicated on the boring logs in

Appendix A. The other laboratory test results and descriptions of the testing procedures utilized are presented in Appendix B and Appendix C (Chemical and Solubility Test Results).

Six percolation test holes were excavated on March 30, 2006 within proposed parking lot areas.

Percolation tests were performed in approximately 8-inch diameter holes which had been excavated through the upper approximate 1 foot of soil. The locations of the percolation tests are also shown on Figure 2.

Ninyo & Moore previously performed 12 borings during the preliminary geotechnical evaluation for the project. The borings were drilled to depths ranging from 14.4 feet to 39.4 feet. The location of the previous borings are indicated on Figure 2. The boring logs from the preliminary evaluation are presented in Appendix D.

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6. GEOLOGY AND SUBSURFACE CONDITIONS

Based on the findings of our limited subsurface exploration and review of referenced geologic and soils information, the site is underlain by Quaternary-age alluvium (native soil). Near-surface undisturbed native soils at the site have been previously mapped as the Weiser unit, which consists of silty gravel and poorly graded gravel with silt and clay. Ninyo & Moore’s findings regarding the geologic setting, geologic hazards, ground motion, site seismic class, subsurface unit encountered, groundwater, and liquefaction at the site are provided in the following sections.

6.1. Geologic Setting

The site is located in the northern portion of the Las Vegas Valley, which lies in the southwestern portion of the Great Basin, within the Basin and Range physiographic province.

The Las Vegas Valley is a naturally formed structural basin as a result of block faulting, a fundamental characteristic of the Basin and Range physiographic province.

The Las Vegas Valley extends in a northwest-southeast direction and it drains generally toward the southeast through the Las Vegas Wash into Lake Mead. Surrounding the alluvium-filled

Valley are relatively steep mountain ranges. These ranges are the Spring Mountains to the west; the Desert, Sheep, and Las Vegas ranges to the north; the McCullough Range to the south; and Sunrise Mountain and Frenchman Mountain to the east.

Based on our review of the referenced geologic data, the Las Vegas Valley is underlain by

Proterozoic igneous and metamorphic basement rock, which is overlain by thick Paleozoic and Mesozoic sedimentary rock, and Tertiary volcanic rock. The floor of the Las Vegas

Valley is underlain by Tertiary and Quaternary alluvial, aeolian, and playa deposits surrounded by more steeply sloping alluvial aprons, or fans, of poorly sorted gravel and sand deposits. These sediments can be up to approximately 5,000 feet thick in some parts of the Las Vegas Valley.

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6.2. Potential Geologic Hazards

Ninyo & Moore’s geotechnical study of the project site included an evaluation of the possi-ble presence of geologic hazards, such as faults and ground fissures in the site area. This evaluation included visual observation of the site for indications of adverse geologic fea-tures and review of published geologic and soils maps and literature, and other data listed in the Selected References section of this report. Referenced geologic data were also reviewed to evaluate seismic activity levels, and associated potential earthquake hazards, for faults in the site vicinity. It should be noted that the fault seismic activity levels provided in this sec-tion were obtained/interpreted primarily from United States Geological Survey (USGS, 2006) data.

Based on our field observations and review of referenced data, no faults extend through the project site. Review of referenced geologic data indicates that the nearest active fault (i.e., a fault that has experienced ground surface rupture within the past 11,000 years) to the site is the Black Hills fault. The Frenchman Mountain fault and the Eglington fault, which are con-sidered potentially active (i.e., faults that have been experienced ground surface rupture within the past 1.6 million years) are also located in the site vicinity. The distances from the site to these active and potentially active faults are provided in the following Table.

Review of referenced geologic data also indicates that the site is located near an unnamed

Las Vegas Valley fault. The distance from the site to this fault is provided in the following

Table. Referenced USGS data indicate that this fault is of uncertain origin and that its seis-mic activity level has not been established. Further, there is some controversy among geolo-gists as to the origin of this geologic feature, and other similar features in Las Vegas Valley, which have been previously referred to as “compaction faults”. Differing proposed origins for these faults include:

Differential consolidation or compaction over time of the thick alluvial and lakebed sedi-ments in Las Vegas Valley.

Tectonic factors associated with faults that may extend into the basement bedrock be-neath the Valley’s sediment.

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A combination of differential consolidation and tectonic factors.

Table 1 – Faults in Site Vicinity

Fault Name Seismic Activity Level *

Approximate Distance

From Project Site to

Fault (miles)

Black Hills fault Active 26.0

Eglington fault Potentially Active 2.4

Frenchman Mountain fault Potentially Active 6.2

Las Vegas Valley faults (unnamed fault) Not Established 2.3

* From United States Geological Survey (USGS, 2006) data.

Ground fissures, generally believed to be caused by erosion, and differential stress resulting from regional subsidence due primarily to withdrawal of groundwater, are known to occur near faults in Las Vegas Valley. Review of referenced geologic data does not indicate the presence of ground fissures at the project site and no ground fissures were observed during our field activities.

As part of this study, Ninyo & Moore evaluated whether the project site is located in a Spe-cial Geotechnical Considerations Area, as shown on the referenced Clark County Soil

Guidelines Map (CCBD and NBMG, 1998). This map indicates important aspects of near-surface soils in Las Vegas Valley. Review of the referenced Clark County Soil Guidelines

Map indicates that a portion of the site is located within a Special Geotechnical Considera-tion Area described as “Potential Drainage Areas or Recent Sediment Deposits.” Soils in such a Special Geotechnical Consideration Area may have solubility, clay swell, corrosion, gypsum salt, and expansive or hydro-collapse potential.

6.3. Ground Motion

Ninyo & Moore performed a ReMi survey during the course of our preliminary geotechnical evaluation (Ninyo & Moore, 2005) in the central portion of the site to evaluate the seismic

Site Class, as described in the referenced International Building Code (ICC, 2003). Data was collected to a depth of approximately 100 feet using a geophone array (line) using a Ge-

301699005R Color.doc 7 ometrics 24 channel SmartSeis SE with 20 4.5-Hz P-wave geophones spaced approximately

20 feet apart. The approximate location and orientation of the array is indicated on Figure 2.

Ambient noise (microtremors) was recorded for a total period length of 16.38 seconds with a sampling interval of 2,000 microseconds. The one-dimensional shear wave velocity struc-ture and average shear wave velocity to approximately 100 feet deep was evaluated using

Optim Software’s SeisOpt ReMi v.20 software.

The calculated average shear wave velocity to a depth of 100 feet at the location of the geo-phone array was approximately 3,022 feet per second. Based on this finding and the findings of our limited subsurface exploration, a Site Class C is characteristic of the site for design purposes.

Estimated maximum considered earthquake ground motions across the United States are provided in the referenced ICC 2003 International Building Code (IBC). The mapped ground motions are at 0.2-second and 1.0-second periods with 5 percent critical damping.

According to the IBC, the parameters in the following table are characteristic of the site for design purposes.

Table 2 – Seismic Design Parameters

Value

Parameter Short

Period

Long

Period

2003 IBC Reference

Mapped Maximum Considered Earthquake Spectral Re-sponse Acceleration, SS and S1

0.57g 0.18g Figure 1615

Site Coefficient, Fa and Fv 1.17 1.62 Table 1615.1.2

Maximum Considered Earthquake Spectral Response

Acceleration Adjusted for Site Class Effects, SMS and SM1

0.67g 0.29g Equation 16-38 and 16-39

Design Spectral Response Acceleration, SDS and SD1 0.45g 0.19g Equation 16-40 and 16-41

6.4. Subsurface Unit Encountered

Alluvium was encountered in the exploratory borings to the total depths explored (up to ap-proximately 74.0 feet). The alluvium consisted predominantly of an upper layer of loose to very dense, silty gravel with sand overlying layers of very stiff, slightly cemented sandy lean clay with gravel. Slightly to highly gypsiferous and slightly porous zones were also encoun-

301699005R Color.doc 8 tered. The slightly porous clay soils were encountered at depths of approximately 7.5 feet or deeper.

Slightly cemented soils and a few layers of moderately hard to hard, moderately to strongly cemented soils (caliche) were encountered in seven of the borings. Caliche is a naturally oc-curring cemented soil with rock-like characteristics. The following describes typical proper-ties of caliche encountered in southern Nevada.

Caliche generally occurs in layers a few inches to several feet thick.

Caliche layers can vary significantly in the thickness, degree of cementation, and harness over short distances, and it can be discontinuous.

Caliche varies in composition from primarily fine-grained material to primarily coarse-grained material.

Moderately hard, moderately cemented caliche can generally be gouged with a knife with difficulty and can be broken with a few hammer blows.

Hard to very hard, strongly cemented caliche is difficult to scratch with a knife and breaks with difficulty with repeated hammer blows.

Considerable difficulties may be encountered in caliche removal. Rock excavation meth-ods may be needed.

The following table presents the approximate depth of, thickness of, and hardness and degree of cementation of the caliche layers encountered in the borings.

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Table 3 – Caliche Layers Encountered

Boring

Location

Approximate

Depth of Caliche

Layer

(feet)

Approximate

Thickness of

Caliche Layer

(feet)

Hardness and Degree of

Cementation of Caliche Layer

B-19 35 14.0** Moderately hard, moderately cemented

18.5 2.5 Moderately hard, moderately cemented B-20

23.0 16.3** Moderately hard , moderately cemented

27.0 2.0 Moderately hard, moderately cemented B-21

33.0 16.2** Moderately hard to hard, moderately ce-mented to strongly cemented

45.0 2.0 Moderately hard, moderately cemented B-22

54.0 20.0** Moderately hard to hard, moderately ce-mented to strongly cemented

B-24 33.5 15.5** Moderately hard, moderately cemented

B-26 19.5 9.9** Moderately hard to hard, moderately ce-mented to strongly cemented

B-29 26.0 3.4** Moderately hard, moderately cemented

* Depth measured from ground surface at time of drilling.

** Boring terminated in caliche.

Laboratory tests were performed on selected samples of alluvium obtained from the bor-ings. The results of these tests are summarized in the following table. The results of in-place moisture content and dry density tests are also presented on the boring logs in Ap-pendix A. Additional information regarding the laboratory test procedures and results are provided in Appendix B and Appendix C.

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Table 4 – Summary of Laboratory Test Results

Test Type Test Results Test Result Classification

In-Place Moisture Content 0.7 to 19.6 percent --

In-Place Dry Density 76.6 to 128.3 pcf Low to moderate dry densities

Atterberg Limits

Liquid Limit

Plastic Limit

No value to 65

No value to 26

R-Value 70 to 79 --

Swell potential -0.15 to -1.19 percent --

Resistivity

In-situ moisture content

Saturated

9,300 to >30,000 ohm-cm

310 to 9,800 ohm-cm

Very severely corrosive to buried metal

Sodium Content 0.00 to 0.06 percent --

Sulfate Content 0.00 to 0.23 percent Negligibly to severely deleterious to concrete

Sodium Sulfate Content 0.00 to 0.14 Negligible chemical (salt) heave potential

Total Salts (Solubility) 0.05 to 1.35 percent very low to moderate solubility potential

6.5. Soil Percolation

Our evaluation also included performing six soil percolation tests (PT-1 through PT-6) in proposed parking lot areas. The percolation tests were performed in approximately 8-inch diameter holes excavated through the upper approximate 1 foot of soil. The purpose of the soil percolation tests was to evaluate the rate of water infiltration into the subsurface soils.

The approximate locations of the soil percolation test holes are shown on Figure 2.

The test holes were excavated and then filled with water prior to testing. The water in the test holes was subsequently adjusted to a depth of approximately 6 inches and percolation rate measurements were made. Results of these tests are provided in the following table.

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Table 5 – Soil Percolation Test Results

Percolation Test Hole Percolation Rate

(minutes per inch)

PT-1 4.1

PT-2 4.9

PT-3 5.0

PT-4 7.5

PT-5 5.5

PT-6 5.0

6.6. Groundwater

Groundwater was not encountered in the exploratory borings, which were advanced to depths of up to approximately 74.0 feet. Based on review of the referenced State of Nevada Division of

Water Resources well log database, the depth to groundwater in the vicinity of the site may be deeper than approximately 115 feet below grade. Seasonal fluctuations in groundwater levels and surface water flow may occur. These fluctuations may be due to variations in ground surface topography, subsurface geologic conditions, rainfall, irrigation, and other factors.

Evaluation of factors associated with groundwater fluctuations was beyond the scope of this study.

6.7. Liquefaction

Liquefaction is a phenomenon in which loose, saturated soils lose shear strength under short-term (dynamic) loading conditions. Ground shaking of sufficient duration results in the loss of grain-to-grain contact in potentially liquefiable soils due to a rapid increase in pore water pressure, causing the soil to behave as a fluid for a short period of time. To be potentially liquefiable, a soil is typically cohesionless with a grain-size distribution generally consisting of sand and silt. It is generally loose to medium dense, saturated, and subjected to sufficient magnitude and duration of ground shaking.

Soils encountered in the exploratory borings at the site consisted primarily of loose to very dense, silty gravel with sand, and slightly cemented, very stiff clays, with layers of moderately hard and hard, moderately cemented and strongly cemented caliche layers.

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Review of the referenced State of Nevada Division of Water Resources well log database indicates that the depth to groundwater in the vicinity of the site may be deeper than approximately 115 feet below grade.

7. FINDINGS AND CONCLUSIONS

Based on the findings of this study, there are no known geotechnical or geologic conditions that would preclude the proposed development of the site, provided the recommendations presented herein are implemented and appropriate construction practices are followed. Geotechnical design and construction considerations for the proposed project include the following:

Structure foundations that are shallower than 6 feet below existing grade may be founded on medium dense to very dense native soils or on adequately placed and compacted structural fill. Foundations for the proposed basement that are anticipated to be deeper than 6 feet below existing grade should be founded on zone of 2.5 feet of adequately placed and com-pacted structural fill (reworked on-site or imported soil) as discussed in section 8.1.1.

Recommendations regarding design of foundations are provided in Section 8.2.

Laboratory test results and field observations indicated that the native clay soils encountered at depths deeper than approximately 7.5 feet were dry, porous, and prone to slight to moder-ate consolidation if inundated with water. It is anticipated that there will be cuts at the site up to approximately 10 feet during site grading. The geotechnical consultant should observe footing excavation bottoms to evaluate the exposed soils and if removal and replacement of the existing soils with structural fill is needed. In addition, measures should be taken to re-duce moisture infiltration into the soils underlying structures, as discussed in Section 8.10.

Layers of caliche were encountered at depth in the exploratory borings. These cemented lay-ers were up to approximately 20 feet thick in some of the borings. Due to the variable nature of caliche, additional more shallow caliche layers may exist at the site. If caliche is encoun-tered, rock-excavation techniques, including use of heavy-duty backhoe and/or trenchers, headache ball, hoe-ram, and/or rock-saw, or other excavation methods should be anticipated for the project.

Findings of our study indicate that the non-cemented native soil encountered in the borings is generally suitable for use as structural fill and backfill. However, layers of moderately hard to hard, moderately to strongly cemented soils (caliche) were also encountered in the bor-ings. Oversize materials should be anticipated from caliche excavation. Oversize materials should be processed as described in Section 8.1.1 to meet the recommendations for structural fill and backfill, or be removed from the site. Excavated on-site native soils may be used as

301699005R Color.doc 13 structural fill and backfill provided they meet the recommendations presented in Sections

8.1.2.

Results of laboratory tests indicate that the non-cemented native soils generally do not meet

USSPWC requirements for Type I and Type II Aggregate Base. However, based on the labo-ratory R-value test results, the granular native soils at the site have an R-value higher than

60, which indicates that they may be used as Type I Aggregate Base in roadways.

Some shrinkage should be anticipated when on-site non-cemented soils are excavated, proc-essed, and compacted. For planning purposes, approximately 25 percent shrinkage may be anticipated.

Due to the presence of cemented soils at the site, bulking of this material should be antici-pated when this material is excavated, processed/crushed, and compacted. For planning pur-poses, up to approximately 10 percent bulking should be anticipated.

Exterior or interior foundation perimeter drains should be installed below basement floor ele-vations.

Review of published geologic data and our field observations, do not indicate the presence of adverse on-site geologic hazards, such as faults and ground fissures, which may affect the proposed site development.

Findings of our study indicate that a seismic Site Class of C and parameters provided in Ta-ble 1 are characteristic of the site and should be considered in the design of the proposed structures, where appropriate.

Due to soil conditions encountered in the exploratory borings and anticipated depth to groundwater, it is our opinion that there is a low potential for liquefaction of the subsurface soils at the site.

Groundwater was not encountered in our explorations, which were excavated to depths of up to approximately 74.0 feet. Therefore, groundwater is not anticipated to adversely affect con-struction of the proposed improvements.

8. RECOMMENDATIONS

The following recommendations are intended for incorporation into the design and construction of the proposed buildings and exterior site improvements.

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8.1. Earthwork

The following sections provide recommendations for earthwork, including site grading, structural fill and backfill, import soil, and temporary excavations at the site.

8.1.1. Site Grading

Prior to grading, the areas of proposed site improvements should be cleared of any sur-face obstructions, debris, organics (including vegetation), and other deleterious materi-als. Such materials generated from clearing operations should be removed from the project site and disposed of at a legal landfill site.

After the previously described removals have been performed, the full depth of any existing on-site fill and loose and/or disturbed native soils should be removed/ excavated from proposed building and exterior site improvement areas, including block screen/retaining wall, pavement, and concrete flatwork areas, processed, and stockpiled for later use as structural fill at the site. Prior to placement and compaction of structural fill, the geotechnical consultant should observe footing excavation bottoms to evaluate the exposed soils and if removal and replacement of the existing soils with structural fill is needed. Scarification may terminate where moderately hard to very hard caliche is encountered, as evaluated in the field by the geotechnical consultant.

Some shrinkage should be anticipated when the native non/slightly cemented soils are excavated, processed, and compacted. For planning purposes, an estimated shrinkage factor of approximately 25 percent may be used for soils within approximately 5 feet of the existing ground surface. Depending on finished grade elevations for the project, some importation of soils may be needed.

As previously indicated, layers of caliche were encountered in the borings. Therefore, rock excavation techniques should be anticipated for utility trench excavations and dur-ing grading operations, particularly in areas of cut. Use of heavy-duty ripping equip-ment, heavy-duty backhoe, headache ball, hoe-ram, and/or rock saw should be

301699005R Color.doc 15 anticipated. The contractor should be aware of the potential for (and take adequate pre-cautions to reduce the potential for) vibrational damage to adjacent or nearby structures, and take appropriate precautions, when using heavy impact equipment during removal of caliche. Oversize materials will likely be generated during excavation of the ce-mented soils at the site. These materials will need to be crushed prior to use as structural fill and backfill, or removed from the site and disposed of in a suitable manner. Bulking of this material should be anticipated when it is excavated, processed/crushed, and compacted. For planning purposes, up to approximately 10 percent bulking should be anticipated.

It is anticipated that there will be cuts at the northern end of the site up to approximately

10 feet during site grading. If grading operations expose relatively porous, hydro-collapsible, native clay soils at footing bottom elevations, the encountered soils should be overexcavated to approximately 2.5 feet below the foundation bottom and replaced with adequately compacted structural fill.

Ninyo & Moore’s field observations and laboratory test results indicated that the native soils encountered in our exploratory borings should generally be suitable for use as structural fill and backfill material. The excavated on-site soils may be used as struc-tural fill and backfill provided they meet the recommendations presented in the follow-ing section.

8.1.2. Structural Fill and Backfill

Soils used as structural fill and backfill should be placed and compacted in uniform horizontal lifts to a relative compaction of 90 percent (95 percent in paved parking ac-cess and roadway areas), as evaluated by ASTM D 1557. Structural fill placed lower than 5 feet below finished grade should be compacted to 95 percent. Retaining wall and utility trench backfill should be similarly placed and compacted to a relative compac-tion of 90 percent (ASTM D 1557).

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Structural fill and backfill soils should be placed and compacted at a moisture content within approximately 2 percent of optimum for granular soils and approximately

2 percent above optimum for cohesive soil. The actual optimal lift thickness of fill dur-ing grading will depend on the type of soil and compaction equipment used, but should generally not exceed approximately 8 inches in loose thickness.

Structural fill and backfill soils should not contain organic matter, debris, other deleteri-ous matter or rocks or hard chunks larger than approximately 6 inches nominal diame-ter. These soils should have a low solubility potential (3 percent or less) and a very low to low expansion potential (EI less than 50), as evaluated by ASTM D 4829 (Expansion

Index Test).

Placement and compaction of structural fill should be performed in accordance with

Uniform Standard Specifications for Public Works' Construction, Off-Site

Improvements (USSPWC), Clark County Area, Nevada, Third Edition (Clark County, 2001a). Grading and earthwork should be observed and the geotechnical consultant should test compaction of structural fill and backfill materials prior to placing subsequent lifts.

8.1.3. Import Soil

We recommend that any import soil consist of coarse-grained (50 percent or more retained on No. 200 sieve) material with a low solubility potential (1.0 percent or less), as evaluated by the referenced Clark County Department of Building Inspection

Services, Technical Guideline (TG) TG-19-2001, a low sulfate content (less than

0.1 percent), and a very low to low expansion potential (EI less than 50) as evaluated by the latest version of American Society for Testing and Materials (ASTM) D 4829. We further recommend that proposed import material be evaluated by Ninyo & Moore at the borrow site for its suitability prior to importation to the project site. Import soil to be used as structural fill and backfill should be placed and compacted in accordance with the recommendations set forth in the previous sections.

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8.1.4. Temporary Excavations

Temporary excavations should be performed in accordance with the referenced Occupa-tional Safety and Health Administration (OSHA) Construction Industry Regulations

(OSHA, 2005) requirements and recommendations. Excavations deeper than 5 feet should be benched or laid back at a slope no steeper than 1:1 (horizontal to vertical), measured from the bottom elevation of the excavation, or the excavation should be ap-propriately shored. Temporary earth-retaining systems will be subjected to lateral loads resulting from earth pressures. A structural engineer experienced in retaining systems for temporary excavation should be consulted by the contractor during the design of the shoring system. On-site safety of personnel is the responsibility of the contractor.

Spoils from excavations should not be placed near the edges of the excavations. For open-cut trenches or unbraced excavations, spoil piles should be placed away from the edge of the excavation at a distance equivalent to the excavation depth. In addition, sur-face drainage should be directed away from the top edge of trench excavations and traf-fic should be routed as far away from the excavation as practical during construction.

8.2. Structure Foundations

Structure foundations should have a width of 12 inches and an embedment depth of

18 inches below adjacent finished grade for buildings and 12 inches below adjacent finished grade for screen/retaining wall foundations. Structure foundations shallower than 6 feet be-low existing grade should be founded on medium dense to very dense and/or very stiff, na-tive soils or a zone of structural fill (reworked native or import soils) or entirely on caliche.

Foundations for the proposed basement and/or tunnel that are anticipated to be deeper than 6 feet below existing grade should be founded on 2.5 feet of adequately placed and compacted structural fill (reworked on-site or imported soil).

An allowable bearing pressure of 2,000 pounds per square foot (psf) may be used for isolated and continuous footings with an embedment of 18 inches below adjacent finished grade and a width of 12 inches. This allowable value may be increased by 800 psf for each

301699005R Color.doc 18 additional 1 foot of width, and 1,500 psf for each additional 1 foot of embedment up to a value of 5,500 psf. These allowable bearing capacities may be increased by one-third for short duration loads, such as wind or seismic. Lateral resistance for footings is presented in the following section. Foundations should be designed and constructed in accordance with recommendations of a qualified structural engineer.

Due to the potential for damaging differential settlement, structure footings (isolated and continuous) should not bear on both caliche and non-cemented or slightly cemented soils. If both cemented and non-cemented/slightly-cemented soils are present at the footing base, the caliche should either be overexcavated approximately 12 inches and replaced with structural fill, or the non/slightly cemented soils should be overexcavated to expose caliche and replaced with lean concrete or Type II Aggregate Base compacted to 95 percent relative compaction, as evaluated by ASTM D 1557.

Footings should be reinforced with two No. 4 or larger steel reinforcing bars, one placed near the top and one near the bottom of the footings, and in accordance with a qualified structural engineer’s recommendations. Increased reinforcement may be recommended by the structural engineer. Seismic parameters for design of foundations for proposed buildings and any retaining walls at the site are provided in Section 6.3.

8.3. Lateral Earth Pressures

Retaining walls, which are not restrained from movement at the top and have level backfill behind the wall, may be designed using an “active” equivalent fluid unit weight of

37 pounds per cubic foot (pcf), as indicated on Figure 3. Retaining walls, which are re-strained from movement at the top and have level backfill behind the wall, may be designed using an “at-rest” equivalent fluid unit weight of 57 pcf, as indicated on Figure 4. These val-ues assume compaction within about 5 feet of the wall will be accomplished with relatively light compaction equipment and that very low to low expansive backfill will be placed be-hind the wall. These values also assume that retaining walls will have a height of less than

10 feet.

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Ninyo & Moore has evaluated “active” seismic earth pressure coefficients based on the

Mononobe-Okabe equation for an active driving wedge. Our analysis considered no groundwater, level backfill, no wall batter, no friction between the wall and backfill soils, and backfill soils with an angle or internal friction of 33 degrees compacted to 130 pcf. Based on our calculations, Ninyo & Moore recommends that retaining walls, which are not restrained from movement at the top, be designed using an additional inverted triangular “active” equivalent fluid unit weight of 8 pcf, as indicated on Figure 3, where appropriate. Retaining walls, which are restrained from movement at the top, be designed using an additional inverted triangular “at-rest” equivalent fluid unit weight of 17 pcf, as indicated on Figure 4.

Retaining walls with level backfill should also be designed to resist “active” and “at-rest” surcharge pressures of 0.29q and 0.45q, respectively. The value for "q" represents the pres-sure induced by adjacent light loads, slab, or traffic loads plus any adjacent footing loads.

Measures should be taken so that moisture does not build up behind retaining walls. Drain-age measures, as indicated on Figure 5, should include free-draining backfill material, and perforated drain pipes or weep holes lined with polyvinyl chloride (PVC) pipe. Drain pipes should outlet away from structures, and retaining walls should be adequately waterproofed in accordance with the recommendations of the project civil engineer or architect.

For passive resistance to lateral loads, we recommend that an equivalent fluid weight of

270 pcf be used up to a value of 3,000 psf. This value assumes that the ground is horizontal for a distance of 10 feet or more, or three times the height generating the passive pressure, whichever is greater. We recommend that the upper 12 inches of soil not protected by pave-ment or a concrete slab be neglected when calculating passive resistance. For frictional re-sistance to lateral loads, we recommend that a coefficient of friction of 0.43 be used between soil and concrete. Passive and frictional resistances may be used in combination, provided the passive resistance does not exceed one-half of the total allowable resistance. The passive resistance may be increased by one-third when considering loads of short duration such as wind or seismic forces.

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8.4. Concrete Slab-On-Grade Floors

Ninyo & Moore recommends that conventional concrete slab-on-grade floors (including supportive base material) be founded on a zone of structural fill (reworked native or import soils), as described in Section 8.1.1. The floor slabs should be 4 inches in thickness. Floor slabs should be designed in accordance with recommendations of a qualified structural engineer. Greater floor slab thickness may be recommended by the structural engineer.

As a means to help reduce shrinkage cracks, we recommend that the slabs be provided with construction joints at spacing intervals of no more than approximately 15 feet, each way and reinforced with No. 3 steel reinforcing bars placed at approximately 18 inches on-center both ways. Reinforcement of the slab should be placed at mid-height. We recommend that

“chairs” be utilized to aid in the placement of the reinforcement. Floor slab reinforcement and joint spacing should also be in accordance with the recommendations provided by a qualified structural engineer. Greater slab thickness and reinforcement and reduced construction joint spacing may be recommended by the structural engineer.

Floor slabs should also be underlain by approximately 6 inches of Type II Aggregate Base compacted to 90 percent of the laboratory maximum dry density, as evaluated by ASTM

D 1557. A moisture and mineral migration barrier should be provided by a relatively imper-vious membrane placed beneath slab-on-grade floors. The membrane should consist of visqueen 10 mils in thickness, or equivalent. The membrane may overlie or underlie the pre-viously described approximately 6 inches of compacted base material. If the membrane overlies the base material, it should be covered with approximately 2 inches of moist sand

(not saturated) to help reduce the potential for puncture during construction and to aid in concrete curing. The membrane should be placed in accordance with the manufacturer’s recommendations.

8.5. Settlement

Ninyo & Moore estimates that the proposed buildings, designed and constructed as recommended herein, should undergo total settlement of approximately 2 inches or less.

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Differential settlement is typically limited to one-half the total amount. As discussed, porous soils with a slight to moderate hydroconsolidation potential were encountered in our borings at a depth of approximately 7.5 feet. If these soils become wetted, additional settlement will likely occur. Measures to reduce water infiltration into the subsoils are discussed in

Section 8.10.

8.6. Geotechnical Parameters for the Tunnel Design and Construction

For calculation of overburden loads, Type II Aggregate Base and trench backfill soils, when placed and compacted as specified, may be assumed to have a unit weight of approximately

135 pcf. This value is based on soils being compacted to a relative compaction of 90 per-cent, as evaluated by ASTM D 1557. CLSM used as trench backfill material may be as-sumed to have a unit weight of approximately 120 pcf.

The base of the tunnel should be founded on 8 inches or more of Type II Aggregate Base overlying medium dense to very dense, granular soils or very stiff clay or adequately com-pacted structural fill. If the clay soils at the tunnel bottom elevation are relatively porous , as evaluated by the geotechnical consultant during grading, the porous soils should be over ex-cavated approximately 2.5 feet and replaced with structural fill. Exposed loose or disturbed surficial soil at the base of tunnel excavations should be moisture-conditioned and com-pacted to 90 percent relative compaction, as evaluated by ASTM D 1557. The Type II Ag-gregate Base should be in conformance with Section 704.03.04 of the Uniform Standard

Specifications for Public Works’ Construction (USSPWC) and be compacted to 90 percent relative compaction, as evaluated by ASTM D 1557. An allowable bearing value of 5,500 psf may be used in design of tunnel. This allowable bearing pressure may be increased by one-third for short duration loads, such as seismic. Design parameters for frictional resis-tance to lateral loads have been provided in Section 8.3. A sump pump should be installed at the low point to surface discharge any water collected due to leaks or maintenance opera-tions.

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8.7. Exterior Concrete Flatwork and Curbs and Gutters

Exterior concrete flatwork, such as walkways and entryway slabs, should be approximately

4 inches in thickness and founded on 12 inches structural fill (reworked native or import soils). It is suggested that to reduce the potential for shrinkage cracks, exterior concrete flatwork should be constructed with control joints spaced approximately 5 feet apart for walkways and approximately 10 feet on-center each way for larger slabs. Crack control joint spacing should be in accordance with recommendations of a qualified structural engineer. Reduced joint spacing may be recommended by the structural engineer.

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Formation of shrinkage cracks, and other cracks, due to minor soil movement, may be fur-ther reduced by utilizing steel reinforcement, such as welded wire mesh. However, due to the inherent difficulty in positioning welded wire mesh in the middle of concrete flatwork, other crack control methods should be considered, such as placement of No. 3 steel reinforc-ing bars at approximately 24 inches on-center both ways. Reinforcement of the flatwork should be placed at mid-height. “Chairs” should be utilized to aid in the placement of the reinforcement.

Concrete curbs and gutters should be constructed in accordance with recommendations of the project civil engineer. The referenced Clark County Uniform Standard Drawings for

Public Works Construction Off-Site Improvements (USDPWC), also provides design speci-fications for curbs and gutters. Recommendations regarding concrete utilized in construction of proposed improvements are provided in Section 8.9.1.

8.8. Pavement Sections

The following sections provide pavement sections for on-site parking and access areas, and off-site half-street improvements to Pecos Road, Deer Springs Way, and Walnut Road. The potential sections for the dedicated streets should be considered preliminary. The City of

North Las Vegas will require that the pavement sections be re-evaluated once the roadways are graded to expose native subgrade. Additional reevaluation tests will need to be per-formed and the pavements section recalculated.

8.8.1. On-Site Parking and Access Areas

To form a basis for design of flexible pavement for on-site paved parking and access ar-eas, we have assumed the following:

A design Equivalent Single Axial Load (ESAL) value of 2,960, based on Traffic

Index (TI) = 4.5 for automobile traffic; ESAL value of 15,950, based on TI = 5.5 for delivery truck traffic; and ESAL value of 64,920, based on TI = 6.5 for heavy duty truck and bus traffic areas are applicable.

80 percent reliability.

0.45 standard deviation.

4.2 initial serviceability.

2.5 terminal serviceability.

Resilient Modulus (MR) of 26,300 psi for an R-value of 70 (based on laboratory test results).

Using these values, structural numbers associated with the proposed parking and access…