2017-09-18_CA_INY_CR2022(1)_FINAL_Geotech_Rpt.pdf

SOUTH LAKE ROAD

CA FLAP INY CR2022(1)

FINAL GEOTECHNICAL REPORT

Report # CA-CX-2022-17-01

Geotechnical Section Technical Services Branch

September, 2017

Table of Contents

SECTION ONE--INTRODUCTION

1.1 SITE CONDITIONS

1.2 PROPOSED CONSTRUCTION

1.3 OBJECTIVE AND SCOPE

SECTION TWO--GEOLOGY AND SEISMICITY

2.1 GEOLOGY

2.2 GEOLOGIC HAZARDS

2.3 SEISMICITY

2.4 SEISMIC DESIGN PARAMETERS

SECTION THREE—FIELD INVESTIGATION

3.1 ROCKFALL OCCURANCE

3.2 SUMMARY OF SUBSURFACE EXPLORATION

3.3 LABORATORY TESTING

SECTION FOUR RCOMMENDATIONS

4.1 ROCKFALL MITIGATION ALTERNATIVES

4.2 ROADWAY REALIGNMENT AND ROCKFALL CATCHMENT DITCHES

4.3 SLOPE SCALING

4.4 SHOULDER STABILIZATION

4.5 CUT SLOPE RECOMMENDATIONS

4.6 SUBEXCAVATION

4.7 UNDERDRAINS

4.7 CORROSION

4.8 SHRINK/SWELL RECOMMENDATIONS

4.9 SPECIFICATIONS

4.10 LIMITATIONS

SECTION FIVE -- REFERENCES

TABLES

TABLE 1: FAULT DATA

TABLE 2: SUMMARY OF SEISMIC PARAMETERS CORRECTED FOR SITE CLASS C

TABLE 3: SUMMARY OF SOIL CLASSIFICATION INDEX TESTS

TABLE 4: RECOMMENDED ROCKFALL MITIGATION ALTERNATIVES

TABLE 5: SUMMARY OF EXISTING PERCENT ROCKFALL CONTAINMENT TO

PROPOSED PERCENT ROCKFALL CONTAINMENT

TABLE 6: ESTIMATED SCALING EFFORT AND QUANTITY

TABLE 7: RECOMMENDED CUT SLOPE RATIOS BY STATION

TABLE 8: RECOMMENDED SUBEXCAVATION BY STATION

TABLE 9: RECOMMENDED UNDERDRAIN BY STATION

FIGURES

FIGURE 1: GENERAL SLOPE GEOMETRY USED IN THE RCAD ANALYSIS

FIGURE 2: PHOTOGRAPH OF TYPICAL EXISTING DITCH CONDITIONS

APPENDICES

APPENDIX A: PROJECT LOCATION AND GEOLOGIC MAP

APPENDIX B: LABORATORY TEST RESULTS

APPENDIX C: PHOTOGRAPHIC DEPICTIONS OF SLOPE SCALING LOCATIONS

SECTION ONE--INTRODUCTION

This report presents the geotechnical engineering study and recommendations pertaining to the rockfall issues, culvert replacement, cut slope recommendations, and roadway underdrain locations on the South Lake Road, CA INY FLAP 2022(1) project. The project limits begin at the junction of South Lake Road and California State Route 168 at an approximate elevation of 7,900 feet and continues south 6.9 miles toward the South Lake up to an approximate elevation of 9,800 feet. The roadway is the primary access route to South Lake, several campgrounds, as well as private residences in the Inyo National Forest. The roadway is managed by Inyo County.

Figure A-1 shows the project location and site map.

1.1 SITE CONDITIONS

1.1.1 SEGMENT 1 STATION 1+00 TO 111+00

From the beginning of the project at station 1+00 at the junction with State Route 168 the roadway ascends up a series of curves confined to an average 22-foot paved section. Significant roadway cut slopes are present in colluvial overburden with 1-3 foot boulders common (boulders up to 5 feet are also present in some locations). Generally, cut slopes in colluvial overburden range from 10 to 50 feet in vertical height with slope angles of 30 to 35 degrees. These unconsolidated cuts and native slopes are generally well vegetated and stable. Evidence of repeated asphalt patching and repair, as well as trees growing in the drainage ditches adjacent to the road are noted between Stations 90+00 and 96+00. Bedrock may be encountered at shallow depths (less than 5 feet) below the pavement surface in some areas as described in the CFLHD Pavements and Materials Memorandum Dated November 2016.

1.1.2 SEGMENTS 2 AND 3 STATION 111+00 TO 365+00.

The roadway passes the Bishop Creek Lodge and begins to climb more steeply. Within these segments, the roadway platform is narrower and curves are tighter. Road cuts in these segments generally consist of granite derived colluvium and talus, and intact granite bedrock. Loose boulders are present in slopes at several locations and Inyo County maintenance personnel note that during the spring runoff season boulders are cleared from the road regularly. The roadway subgrade soils consist mainly of silty sand, gravels, cobbles and up to boulder-sized material as described in the CFLHD Pavements and Materials Report Dated November 2016.

1.2 PROPOSED CONSTRUCTION

The Federal Highway Administration (FHWA) Central Federal Lands Highway Division (CFLHD), in cooperation with the Inyo National Forest and Inyo County is proposing the roadway receive a 3R construction treatment (restoration, resurfacing and rehabilitation) including minor amounts of roadway widening, grading and drainage improvements. The proposed construction will also include minor amounts of scaling, shoulder stabilization, underdrain construction, and alignment corrections identified during the 30 percent field review.

1.3 OBJECTIVE AND SCOPE

The objectives of this study are specifically to develop recommendations concerning rockfall-prone slopes, shoulder stabilization, cut slope recommendations, culvert headwall and wingwall design, and underdrain areas identified during the 30 percent field review. In accomplishing these objectives, the scope of work included field exploration and sampling, correlation of available data, engineering analysis, and recommendations. The field exploration included visual site reconnaissance, surface hand sampling and lab testing.

SECTION TWO--GEOLOGY AND SEISMICITY

2.1 GEOLOGY

2.1.1 REGIONAL GEOLOGY

South Lake Road is located on the eastern edge of the Sierra Nevada geologic province near the transitional zone with the Basin and Range geologic province to the east. The Sierra Nevada is comprised of a single large westward tilted granitic batholith, predominantly of Jurassic and Cretaceous age characterized by steep slopes and granitic rock. A batholith is an intrusive igneous rock that is formed by magma cooling slowly at depth. This is the result of a subduction zone along California’s coast wherein the Pacific plate sank under the less dense North American plate, heating the subducted plate at depth and producing magma that ascended through the overlying lithosphere. These granitic rocks are primarily granite, granodiorite, quartz diorite and monzonite of various degrees of weathering.

During the last 10 million years, at least four periods of glacial advance have coated the mountains in a thick mantle of ice. Today, a few small glaciers remain representing the southern-most glaciers in North America. The extensive history of glaciation within the range coupled with the erosion resistant nature of the granitic rocks that make up most of the Sierra Nevada have created a landscape of hanging valleys, towering waterfalls, craggy peaks, alpine lakes and gigantic glacial canyons.

The Sierra Nevada Range is still growing today gaining height during earthquakes near Bishop and Lone Pine. Rain and winter snows combined with the steep character of the landscape create an environment that includes massive movements of sediment and rapid erosion. The mountains are being removed by erosion almost as quickly as they grow. This erosion has created and deposited sediments thousands of feet thick on the floor of the nearby valleys.

2.1.2 SITE GEOLOGY

From the beginning of the project at Station 1+00 the roadway traverses steep terrain comprised predominantly of Quaternary-aged alluvial, colluvial, and glacial till deposits of small to large boulders in a silty to clayey sand and gravel matrix overlying Cretaceous-aged Lamarck Granodiorite to approximate station 247+80. Here at station 247+80 the road climbs above the highest reach of the alluvial and glacial deposits and granodiorite is exposed at the surface.

Isolated pockets of Devonian to Orodovician metasediments and Cretaceous quartz monzonite are exposed near the road alignment throughout the project. Figure A-2 shows the proposed alignment superimposed on the USGS Geologic Maps of the region.

2.2 GEOLOGIC HAZARDS

Geologic hazards exist from both the natural environment of the project sites and from existing and proposed construction of the roadway. The main geologic hazards that may exist within the vicinity of the project limits include: rockfall, erodible granular soils, seismic events, and debris flows. Rockfall, in particular is likely to be encountered during construction along the route.

Section 3 discusses the rockfall along the route and Section 4 of this report discusses short-term and long-term rockfall mitigation alternatives.

2.3 SEISMICITY

The South Lake Road Project area is located in an active seismic region. The closest active faults to the project site are listed in Table 1, Fault Data. The major fault zones within a 40-mile range to the project location are the Round Valley Fault, Owens Valley / Keough Hot Springs Fault, Independence Fault, Owens Valley Fault, Unamed Faults of the Volcanic Tablelands, White Mountains Fault, and Fish Slough Fault. These faults are strike-slip to normal with slip-rates of

0.01 to 0.10 inches per year, (0.25 to 2.5 millimeters per year) and vary in length from 13 miles, as seen in the Owens Valley / Keough Hot Springs faults, to 73 miles in the Owens Valley Fault.

The overall trend of the faults within 40 miles of the project location is North by South with dips both east and west. Table 1 displays the fault data and the Maximum Moment Magnitude of each of these faults.

TABLE 1: – Fault Data

Fault Name Fault Zone Maximum Moment

Magnitude (Mmax)

Distance From center of project

(Miles)

Fault Parallel Slip Rate (INCH/Year)

Length (Miles)

Age (years)

Round Valley Round Valley 7.0 4.5 0.10 22 < 15,000 Owens Valley/

Keough Hot Springs

Owens Valley 7.2 10.8 0.08 13 < 15,000

Independence Sierra

Nevada Frontal

7.1 11.3 0.01 44 < 15,000

Owens Valley Owens Valley 7.2 13.3 0.06 73 < 15,000

Unnamed Faults Volcanic Tablelands 6.7 9.6 0.04 25 < 15,000

White Mountains Inyo-White Mountains 7.4 17.1 0.01 23 < 15,000

Fish Slough Fish Slough 6.7 14.7 0.04 14 < 15,000

2.4 SEISMIC DESIGN PARAMETERS

Recommended seismic response parameters for the South Lake Road Project design are based on the (AASHTO) LRFD Bridge Design Specifications, 7th edition, 2015, and represents horizontal peak ground acceleration (PGA) with 7 percent probability of exceedance in 75 years (approximately 1000-year return period). The 1000-year return period uniform hazard spectrum for the South Lake Road Project site was taken near the middle of the project at 37.22057º N latitude and 118.56704º W longitudinal, was obtained in accordance with the AASHTO ground motion maps for the probabilistic horizontal acceleration values corresponding to specific peak ground acceleration (PGA) and the spectral coefficients, namely the short- and long- period ground acceleration (Ss and S1 respectively) and corrected for the soil profile at the end project.

Ground motions caused by earthquakes are influenced not only by the distance from the fault planes, but also by the geology and soils found at the site. Subsurface profiles similar to the ones within the project, with soil layers overlaying bedrock that significantly differ in stiffness and density, will have amplified ground motions and a resonant period governed by the layer thickness and shear wave velocity of the materials. The damage potential of strong ground motions with respect to a structure is typically affected by the period of the strong earthquake motion and the resonant period of both the soil and the structure. Based on the material within the project area, the average time-weighted shear wave velocity for the top 100 feet (VS100) of subsurface materials was estimated between 1,200 and 2,500 feet per second. Therefore, the site is classified as Class C according to the site class definitions specified in Table 3.10.3.1-1 of

AASHTO.

The recommended spectral acceleration coefficient values for probabilistic design with a return period of 1000 years were calculated using the program provided with the AASHTO LRFD Bridge Design Manual developed by the USGS (2008) entitled “Seismic Design Parameters”, version 2.10 and are summarized in Table 2, Summary of Seismic Parameters Corrected for Site Class C.

TABLE 2: – Summary of Seismic Parameters Corrected for Site Class C.

Seismic Parameters Horizontal Peak Ground Acceleration, (As) 0.407g

Horizontal Response Spectral Acceleration at Period of 0.2 sec, (SDs) 0.991g Horizontal Response Spectral Acceleration at Period of 1.0 sec, (SD1) 0.489g

Site Factor at Zero-Period of Acceleration Spectrum, (Fpga) 1.00 Site Factor at Short-Period Range of Acceleration Spectrum, (Fa) 1.01 Site Factor at Long-Period Range of Acceleration Spectrum, (Fv) 1.47

Based on the long acceleration coefficient SD1 value of 0.457 calculated as Fv.S1, the alignment is assigned to seismic hazard Zone 3 according to Table 3.10.6-1 in AASHTO. Seismic hazard zones reflect the variation in seismic risk in different regions needing different requirements for design as depicted in Table 4.7.4.3.1-1 in AASHTO.

SECTION THREE—FIELD INVESTIGATION

A visual investigation of the slope and roadway conditions was performed during the 30 percent design site visit on October 25th and 26th, 2016. The investigation involved a visual inspection of the existing roadway elements (rockfall-prone slopes, embankments, and roadway surface) as well as the proposed construction’s cut and fill slopes. Hand samples of the soil were taken at various locations during the visual investigation; one sample was tested in the laboratory as discussed in below.

3.1 ROCKFALL OCCURANCE

Visual field investigations revealed that rockfall events occurring along the South Lake Road corridor originate from following two sources:

1. Fractured or jointed rock outcrops where rockfall events can result from freeze-thaw weathering and levering of boulders and blocks from the rock, and the general systematic process of weathering within joints and cracks lead to the eventual movement of slope material. Rockfall produced from these slopes are principally a natural occurrence, emanating higher up on the slopes beyond the original road cuts.

2. Largely unconsolidated slopes deposited from glacial moraines or colluvial slopes where erosion of the soil around boulders contained in a colluvial mass creates rockfall events. In contrast to the rockfall from the fractured or jointed rock outcrops, rockfall produced from the unconsolidated slopes is primarily from within the man-made roadway cuts. During original construction of the alignment these slopes were cut steeper than the angle of repose.

The unconsolidated slopes were identified as the main sources of rockfall within the approved program and scope with the funding available and will be the focus of this study. Some minor areas of rock outcrops are also discussed.

3.2 SUMMARY OF SUBSURFACE EXPLORATION

A geotechnical subsurface investigation was not performed as there are no proposed structures or significant cuts or fills planed as part of this project. However subsurface data was obtained in July of 2016 as part of CFLHD pavements investigation which consisted of 14 borings excavated to a maximum depth of 13.5 feet. Neglecting the cobble and boulder fraction, the pavements investigation revealed the subgrade and embankment materials to be classified as non-plastic silty SAND with gravel (SM to SW-SM in USCS). The investigation also reached auger refusal in 6 of the 14 borings within 4 feet of the pavement surface likely due to the presence of cobbles, boulders or near-surface bedrock comprising the subgrade or embankment. Please refer to the Pavements and Materials Report Dated August, 2017 including the test results obtained.

During the site visit in October of 2016 a near-surface hand sample was collected to classify existing material near the existing culverts planned for replacement at Station 216+66. The sample was collected within a foot of the existing ground surface.

3.3 LABORATORY TESTING

Laboratory testing was conducted on the soil sample obtained during the field visit to estimate the material parameters. Laboratory test procedures and results, along with grain size curves are presented in Appendix B, Laboratory Test Results and summarized in Table 3, Summary of Soil Classification Index Tests. However due to the nature of the sampling and testing performed, it was impracticable or impossible to incorporate the larger sized material into the sample obtained and it should be made clear that these slopes do contain an estimated abundance of cobbles and boulders (up to 30 percent of the total material) that are not represented in the laboratory summary.

Table 3: Summary of Soil Classification Index Tests

Station Offset Sample Depth (feet) Percent Passing 200 LL PI USCS AASHTO

216+66 25 FT RT of Centerline 0-1 4.3 NV NP GP-GM A-1-a (0)

Notes: NV = No Value, NP = Non-Plastic

SECTION FOUR RCOMMENDATIONS

This section provides mitigation alternatives and recommendations pertaining to the rockfall-prone slopes, shoulder stabilization, cut slopes, roadway subexcavation and soil corrosion potential.

4.1 ROCKFALL MITIGATION ALTERNATIVES

The following three alternatives can be considered to mitigate rockfall along the route:

1. Alignment shifts to maximize the distance from the rockfall source slope to the edge of the traveled way.

2. Engineered rockfall ditch to increase the percent of retained rockfall thereby decreasing the likelihood of fallen rock reaching the traveled way.

3. Slope scaling to remove the loose rock that presents a hazard as a future potential rockfall.

The most practical recommended alternative is a combination of one or more of the aforementioned items on any given slope and/or adjacent roadway elements. Coupling the alternatives of ditch improvements and slope scaling, which utilizes the similar equipment and crews, may greatly reduce rockfall frequency and consequences. As there is a direct relationship between roadway alignment and available ditch width these two mitigation alternatives will be discussed simultaneously. This report will address slope scaling individually.

As discussed in Section 3, unconsolidated slopes were selected to receive rockfall mitigation as they are the main source of rockfall that can be mitigated within the scope and budget of this project. The selection of specific slopes for rockfall mitigation was based on several factors including, but not limited to:

• Input from Inyo County on frequently maintained rockfall areas. Meaning, where the county has frequent issues clearing the roadway of fallen rocks or where ditches must be cleared of fallen rock often.

• Existing roadway condition. Often areas susceptible to rockfall can be determined by the condition of adjacent roadway features. Along the route, rockfall impacts have resulted in divots and damage to the existing pavement surface.

• Experience with similar slopes with rockfall potential hazard.

Table 4 presents the five selected slopes and their recommended rockfall mitigation alternatives.

Table 4: Recommended Rockfall Mitigation Alternatives

Station to Station Rockfall Mitigation Alternative

1) Roadway Realignment

2) Engineered Rockfall Ditch 3) Slope Scaling

294+90 - 298+40 X X X

351+60 - 352+60 -- -- X

353+40 - 354+00 -- -- X

354+80 - 355+50 -- -- X

356+20 - 359+60 -- -- X

Alignment shifts and engineered rockfall ditches from Station 351+60 to 359+60 were not pursued due to limited existing bench width and project budget. However, clearing of existing ditches should be carried out following scaling operations.

4.2 ROADWAY REALIGNMENT AND ROCKFALL CATCHMENT DITCHES

4.2.1 ALIGNMENT SHIFTS

At all rockfall locations the ditch widths are limited or non-existent, resulting in rockfall reaching the paved surface. To increase ditch width and thereby rockfall catchment capacity; two measures can be implemented. The first is performing cut slope excavation to move the slope further from the roadway, or shifting the roadway further from the existing cutslope.

Excavation of the unconsolidated slopes to produce sufficient ditch width in addition to laying the slope back to a lesser angle to reduce long-term rockfall is not considered feasible or within the original scope of the project because it would require a vast amount of material be excavated and moved off-site. From station 294+90 to 298+40 it is feasible to shift the roadway away from the cutslope to create the maximum possible inboard ditch catchment area without requiring an outboard retaining structure for additional roadway bench width.

4.2.2 ENGINEERED CATCHMENT DITCHES

Engineered catchment ditches are recommended from station 294+90 to 298+40 to reduce the amount of falling rock that reaches the roadway. In this section, the road will be realigned to make use of the outboard shoulder and a catchment ditch will be added on the inboard side of the road. This represents a relatively inexpensive mitigation option, due to the existing bench width in this area.

State-of-the-practice catchment ditch design currently follows the guidance provided in the 2001 Oregon Dept. of Transportation (ODOT) manual, entitled “Rockfall Catchment Area Design Guide” (RCAD). In the ODOT study, over 11,000 rocks ranging 1-3 ft in diameter, were rolled from slopes of various heights and slope ratios to catchment ditches of varying width and inclinations of 1V:4H, 1V:6H and Flat (0V:1H) to determine rockfall retention percentages.

Figure 3 below displays the geometry conditions used in the RCAD rockfall criteria. The 1V:4H foreslope ratio proved to be the most effective foreslope configuration tested to retain rockfall and was the ratio used in percent retained analysis in the following discussion.

Figure 1: General slope geometry used in the RCAD analysis

Traditionally the RCAD is used to achieve a targeted percentage of retained rockfall. For example if an objective to catch 50 percent of the rockfall originating from the top of a 70 foot high, 53 degree cutslope was set then according to design criteria presented in the RCAD manual a 13-foot wide ditch with a 1V:4H foreslope must be constructed (RCAD Figure 5.19).

Constructing a 13-foot catchment ditch along the route in many cases would dictate that the alignment be shifted so far to the outboard side that a retaining structure must be constructed to acquire the necessary bench width. However, given the scope of the project, it was not feasible to assign a desired percent catchment to each existing cutslope and design the alignment to meet the catchment criteria. Instead, the design goal is to provide the maximum possible percent retained by maximizing the ditch width with a 1V:8H foreslope while maintaining the paved road on the existing roadway bench. Quantification in the percent retained of the existing conditions verses the proposed percent retained was performed to verify that alignment shifts and engineered catchment ditches improved the rockfall catchment. A summary of this data is presented in Table 5 below.

Varies

Varies 10 ft to 80 ft

Slope Angle Varies 1V:1H to near vertical

Table 5: Summary of Existing Percent Rockfall Containment to Proposed Percent Rockfall Containment

Station to Station

Slope Geometry Existing Alignment Proposed Alignment

Improvement In Percent

Containment Maximum

Slope Angle

Maximum Height Of Potential Rockfall

Average Ditch Width

(ft)

Foreslope Estimated

Percent Containment

Average Ditch Width

(ft)

Foreslope Estimated

Percent Containment

293+00 - 294+50 1V:0.55H 75 2.5 1V:10H 2% 4 1V:8H 10% 8%

294+50 - 295+10 1V:0.15H 10 4.5 1V:10H 27% 9.5 1V:8H 78% 51%

295+10 - 297+00 1V:0.75H 75 2.5 Flat 2% 9.0 1V:8H 12% 10%

297+00 - 299+50 1V:1H 80 3.0 Flat 2% 8.0 1V:8H 11% 9%

The ODOT design guidance provides a good index for catchment ditch design and expected performance. However, factors such as rock shape and density, slope roughness, slope hardness, and slope profile configuration (e.g., linear, benched) will also affect ditch catchment performance.

Figure 2: Photograph of typical existing ditch conditions. Removing debris and duff and reestablishing all ditches along the route will improve the overall rockfall catchment.

Outside of the area identified for engineering rockfall catchment ditches, we recommend to reestablish ditch widths, depths and profiles wherever possible and that an item be added to the contract to cover all the ditch rehabilitation throughout the South Lake Road. This will improve the retention of minor rockfall-prone areas with minimal required effort. Performing regular maintenance of the ditches after construction will also provide some degree of effective rockfall mitigation for all the slopes along the roadway.

4.3 SLOPE SCALING

Slope scaling is the removal of loose, broken, or partially detached rock from the slope using manual methods, or excavation equipment. Manual, or “hand-scaling”, methods commonly involve 3 man crews consisting of experienced scalers skilled at systematically removing loose, isolated rockfall hazards with a variety of specialized hand tools, manual and pneumatic jacks.

Scaling crews typically work off ropes, but may occasionally work from crane baskets or lifts, and always require spotters on the roadway to continually survey the slope for unsafe working conditions. Slope excavation, or “machine-scaling”, methods commonly involve excavators using buckets to pry rock from the slope, hydraulic hammers to bring down larger unstable rock masses, and/or heavy chains to brush large quantities of loose debris from the slope. Machine scaling uses similar crew sizes and clean-up/haul equipment as hand-scaling, and also relies on roadway spotters to ensure operation safety. Hand-scaling and machine-scaling may be done in tandem on raveling slopes where high, localized rockfall exists outside the reach of common excavators (30-40 ft). For high slopes with substantial rockfall hazard, long-reach excavators are available that extend to well over 70 ft.

As previously stated five locations have been identified for rockfall scaling treatment. Table 6 specifically addresses the estimated crew hours and volume of material the scaling operation will produce within each station range. The table also provides an approximate location where the scaling will be performed on each slope and the anticipated effort (“Light” to “Moderate”) of scaling the operation. Appendix C photographically depicts the areas of scaling interest or specific rocks that the scaling operation should address. The highlighted areas may be adjusted as they are general locations of the proposed scaling operation. All proposed scaling locations should be discussed on-site during the scaling pre-work meeting with a member of the CFLHD Geotechnical team.

It is recommended that the scaling operation be accomplished by means of hand tools only.

Unless the contractor can successfully demonstrate the use of machinery (long-reach excavators) to the satisfaction of the CFLHD Geotechnical engineer, scaling should not incorporate machinery as their use could easily loosen additional rock within the colluvial slopes that was not intended to be removed. Equipment used during the scaling operation and ditch clean-up work should be sufficiently armored for the operator’s safety. As with any construction operation, it is the contractor’s responsibility to independently access the safety of the scaling operation and provide necessary measures to protect all construction personal, traveling public and roadway elements from harm.

Table 6: Estimated Scaling Effort and Quantity (1)

Station to Station Side Crew Hours

Estimated Scaling Volume (CUYD) Anticipated Scaling Effort & Particular Location on Each Slope (2)

For info only

294+90 - 295+20 RT 2 10

Light scaling of loose rock up to approximately 20 vertical feet on the slope. Ditch clearing.

295+20 - 296+60 RT 8 30

Moderate scaling up to rock outcrop approximately 50 to 60 vertical feet on slope. Ditch clearing.

296+60 - 298+40 RT 8 30

Light to moderate scaling to remove loose material throughout the lower 30 to 40 feet of slope. Ditch clearing. Do not remove stacked rock at toe of slope.

351+60 - 352+60 LT 6 10

Light scaling to approximately 5 to 10 vertical feet on slope. Ditch clearing. Do not disturb talus field above road cut.

353+40 - 354+00 LT 4 10 Light scaling up to rock outcrop at approximately 10 vertical feet on slope.

354+80 - 355+50 LT 6 10

Light scaling to rock outcrop at approximately 10 vertical feet on slope.

Ditch clearing

356+15 - 359+60 LT 6 20

Moderate scaling on slope brow at approximately 20 to 30 vertical feet, light to moderate scaling below. Ditch clearing.

Notes:

(1): Stations, quantities and measurements presented are approximate and may be adjusted during the pre-scaling meeting and/or during scaling operations after mutual agreements between the contractor and the FHWA.

(2): Vertical distance is measured from top of existing pavement on the in-board ditch side and projected onto slope. Slope distance is not presented in the above table but will be greater than vertical distance.

Assumptions of the slope scaling recommendations include:

• For slopes with moderate to low volumes of loose rock, scaling crews can quickly dress slopes with minimal delays to traffic. For slopes with large rockfall volumes, large localized rock masses to be removed, dangerous rockfall exposures high on the slope, or requiring slope crest excavation, roadway closures may be required.

• Scaling cannot be expected to remove the entire loose rock hazard from the slope. Hand-scalers will generally do a better job of removing small, loose rock to ensure safe overhead conditions as work progresses downslope. Machine-scaling operations typically remove larger volumes of larger rock from the slope, but tend to leave small slope debris behind.

“Chaining” or “brushing” by dragging chains over the slope can be effective in removing small rock debris.

• Hand scaling should not progress downslope if stable conditions cannot be obtained within the upper reaches of the slope. If unstable conditions cannot be remedied, the scaling operation should be abandoned or machine scaled after discussions with a member of the CFLHD Geotechnical staff.

• Scaling results are proportional to the skill and experience of the scalers. Experienced crews cost more, but typically work faster and produce higher quality results (buying years of slope performance in many cases).

• Unsupervised scaling may result in substantial over-excavation and significant overruns in scaling quantities if expected results are not well communicated and closely monitored.

• Scaling is not a permanent solution to rockfall. Scaling frequency is dependent on many factors, including the erosional/weathering durability of the slope, extent and persistence of structural features producing loose rock, and presence of other effective mitigation measures such as catchment ditches or barriers.

Effective scaling programs require clearly communicated expectations during contracting (pre-bid on-site meetings and special contact specifications), and supervised operations by knowledgeable construction management staff. Scaling measures for each slope identified should be evaluated early in the scaling program for continuity of work products.

4.4 SHOULDER STABILIZATION

Two shoulder embankment stabilization methods were developed to repair and protect the roadway embankment lost from surface drainage erosion.

Stabilization Method 1- Constructed of mechanically placed boulders according to Section 252 of the SCR’s and 705.04(a) of the FP-14. The rock should be placed to match the surrounding slopes but should not exceed a 1V:1.5H slope face. The rock should bench into the slope with vertical steps not to exceed 4 feet and minimum bench widths of 4 feet to 8 feet, depending on the height of the proposed repair.

Stabilization Method 2 – Used when a slope steeper than a 1V:1.5H is needed to match existing topography. Use mechanically placed boulders in concrete or grout according to Section 252 of the SCR’s and 705.04(a) of the FP-14. Place rock at a maximum slope face of 2V:1H and 4-foot maximum height, including a minimum foot of embedment and minimum footing width of 4 feet. To ensure long-term stability of the rock face, at least 15% of the voids within the placed rock mass must be filled with concrete or grout.

4.5 CUT SLOPE RECOMMENDATIONS

In general, the maximum recommended slope ratios for proposed cut slopes is 1V:1.5H for the cut slopes constructed in soil or colluvial slopes (block in matrix). The recommended slope ratio is dependent on the nature of the observed material and the existing stability of the slope. During the excavation of cut slopes on the project large boulders up to 5 feet (or larger) should be expected within the proposed excavation limits. Care should be taken to avoid over excavation by removing (or destabilizing) large boulders found to be crossing the proposed finished slope “neat line”.

A station-by-station recommended cutslope ratio is presented in Table 7. These recommendations are based off of the 30 percent design alignment.

A slope ratio of 1V:1.5H is recommended as the maximum slope ratio for proposed fill slopes.

Table 7: Recommended Cut Slope Ratios by Station

Station to Station Side Slope Type Maximum Recommended Cut Slope Ratio (V:H)

16+00 - 24+50 LT & RT Boulders in matrix of silty sand and gravel. Existing cut slope has sparse to patchy vegetation. 1:2

30+00 - 39+50 LT & RT Boulders in matrix of silty sand and gravel. Existing cut slope is well-vegetated. 1:2

42+00 - 46+00 LT & RT

Boulders in matrix of silty sand and gravel, boulders are mix of granite and meta-sedimentary bedrock. Existing cut slope is well-vegetated.

1:2

48+00 - 50+00 LT & RT

Boulders in matrix of silty sand and gravel, boulders are mix of granite and meta-sedimentary bedrock. Existing cut slope is well-vegetated.

1:2

58+00 - 59+00 RT

Boulders in matrix of silty sand and gravel, boulders are mix of granite and meta-sedimentary bedrock. Existing cut slope is well-vegetated.

1:2

67+00 - 80+00 LT & RT

Silty sand and gravel with cobbles and scarce boulders, cobbles and boulders are predominantly meta-sedimentary bedrock with minor granite. Existing cut slope is well-vegetated.

1:2

88+00 - 111+00 LT & RT

Silty sand and gravel with cobbles and scarce boulders, cobbles and boulders are predominantly meta-sedimentary bedrock with minor granite. Existing cut slope is well-vegetated. Seepage noted at toe of existing cut slope near

Sta. 96+00.

DO NOT CUT,

LIMITED RIGHT-OF-WAY

4.6 SUBEXCAVATION

Subexcavation may be required in several areas along the roadway. These areas can be identified by wheel rutting and alligator cracking in the pavement surface. A minimum of 1 foot of subexcavation is recommended for the station ranges presented in Table 8. This will entail excavation and re-compaction or complete replacement (at the discretion of the CO) of a minimum of 1 foot of material below the pavement structural section. The bottom of the excavation should be lined with separation geotextile. It is recommended that the contract provide a provisional subexcavation quantity (in addition to the station ranges in Table 8) to be used at the CO’s discretion in event that additional subexcavation locations arise during construction.

Table 8: Recommended Subexcavation by Station

Station to Station Side

96+00 - 96+70 LT & RT

209+50 - 213+00 LT & RT

217+00 - 217+10 LT & RT

243+10 - 243+50 LT

247+00 - 247+55 LT

290+20 - 290+40 RT

359+10 - 359+50 LT & RT

4.7 UNDERDRAINS

Representatives of Inyo County noted that seasonal seepage is observed at several locations within the proposed project alignment. In addition, seepage areas were noted during the field visit. Underdrains are recommended in these areas to improve performance of the roadway subgrade and embankment and cut slopes. Underdrains are recommended for the station ranges presented in Table 9.

Table 9: Recommended Underdrain by Station

Station to Station Side

90+50 - 96+70 LT & RT

209+50 - 213+00 LT & RT

332+50 - 333+50 LT

346+90 - 351+50 LT

349+25 - 362+00 LT

4.7 CORROSION

Corrosion tests were conducted as part of the Pavements and Materials investigation. Refer to the Pavements and Materials Report Dated November 2016 detailing the recommendations for corrosion mitigation and supporting laboratory testing.

4.8 SHRINK/SWELL RECOMMENDATIONS

The proposed South Lake Road will require cuts in slopes comprised of sands and gravels with cobbles and boulders. Many of the fill slopes are overlain with a veneer of loose, uncompacted granular side-cast material with cobbles and boulders up to several feet thick.

For the purpose of estimating shrink/swell values, sands and gravels with cobbles and boulders are assumed to be the predominate material located in permanent cuts. The recommended shrink/swell factors are based on a combination of standard tabled values for common materials in the FLH Technical Guidance Manual (2006) and experience with other CFLHD projects in similar materials.

The estimated shrink/swell values for the sands and gravels with cobbles and boulders of the cut slopes are assumed to Shrink 5 percent (Shrink Factor 0.95) if reused as embankment.

4.9 SPECIFICATIONS

Special provisions were developed to be consistent with geotechnical recommendations stated above and should be incorporated into the special contract requirements (SCR). The following SCR’s were added for this project:

Section 252 – Special Rock Embankment Section 623 – Special Labor Slope Scaling

4.10 LIMITATIONS

The recommendations in this report are based on the data obtained from visual investigations, field review, and laboratory test results. The results of these explorations and tests represent conditions at the specific locations indicated. Subsurface variations across the site are likely and may not become evident until excavation is performed. The Analysis and Recommendations sections in this report include interpretations and recommendations developed by the Government in the process of preparing the design. These interpretations are not intended as a substitute for the personal investigation, independent interpretation, and judgment of the Contractor.

SECTION FIVE -- REFERENCES

American Association of State Highway and Transportation Officials (AASHTO), 2015, LRFD

Bridge Design Specifications, 7th Edition with 2015 interim revisions.

Federal Lands Highway (FLH), Project Development and Design Manual (PDDM), FHWA, 2008, dated March.

Federal Lands Highways (FLH), 2006, Technical Guidance Manual (TGM), A geotechnical supplement to the FLH Project Development and Design Manual.

Pierson, L.A., C.F. Gullixson, and R.G. Chassie, 2001, Rockfall Catchment Area Design Guide – Final Report, Oregon Dept. of Transportation Research Group pub. No. SPR-3(032), November 2001, pp.92.

United States Geological Survey (USGS) 2008 National Seismic Hazard Maps http://geohazards.usgs.gov/cfusion/hazfaults_search/hf_search_main.cfm

APPENDIX A

FIGURES

FIGURE A-1- PROJECT LOCATION AND SITE MAP

FIGURE A-2- GEOLOGIC MAP OF THE SOUTH LAKE ROAD PROJECT AND SURROUNDING

REGION WITH DESCRIPTION OF GEOLOGIC UNITS

APPENDIX B

LABORATORY TESTING

APPENDIX B

LABORATORY TEST RESULTS

B.1 INTRODUCTION

Laboratory tests were completed on a select soil sample recovered for the field exploration program in general accordance with the American Association of State Highway and Transportation Officials (AASHTO) and American Society for Testing and Materials (ASTM) testing methods. The laboratory testing program was completed to provide data for engineering studies and to classify the materials into similar geologic groups. The testing program included soil physical properties. Individual test results are summarized in Table B-1, and a gradation plot of the sample is presented in Figure B-1.

The following sections describe the laboratory testing procedures.

B.2 SOIL PHYSICAL PROPERTIES TESTS

Physical properties testing included soil identification by visual and manual means, and tests to determine grain size distribution, fines content, and Atterberg limits. When sufficient laboratory testing was completed, a select sample was classified using the Unified Soil Classification System (USCS) and American Association of State Highway and Transportation Officials (AASHTO) soil classification system. Both the visual soil identification system and the referenced soil classification systems are summarized in the Soil Classification Field Reference in Appendix A. Test results are presented in the attached laboratory reports.

The following sections describe the individual physical properties test procedures.

Gradation The grain size distribution of a selected sample was determined in general accordance with the AASHTO T 311 and ASTM D 1140. These tests aid in the classification of soils and provide correlating data with engineering properties of soils, such as permeability, strength, swelling potential, and susceptibility to frost action.

Atterberg Limits Liquid and plastic limit tests were performed on selected fine-grained samples. The tests were completed in general accordance with AASHTO T 89 and T 90 (ASTM D 4318). The Atterberg limits include liquid limit (LL), plastic limit (PL), and plasticity index (PI), which is the plastic limit subtracted from the liquid limit. These limits are generally used to assist in classification of soils, to indicate soil consistency, and to provide correlation to engineering properties.

Table B-1: Summary of Laboratory Test Results

Station Field Number

Offset from

CL (ft)

Depth Interval

(ft)

Grain Size Distribution (%)

Li qu id L im it

Pl as tic ity

In de x Soil Classification

Fi gu re N o.

G ra ve l

Sa nd

Fi ne s

USCS AASHTO

216+50 216+50 25 RT 0 - 1 56 40 4 NP NP GP A-1-a (0) B1

0 14 22 20 12 18 10 4 mm

75.0

37.5 PL= NP LL= NP PI= NP

25.0

19.0

12.5 USCS (D 2487)= GP AASHTO (M 145)= A-1-a (0)

9.5

4.75

2.00 D10= D30= D60= Cu= Cc=

1.18

0.43

0.15 The sample is from road embankment fill near existing culvert.

0.08

PROJECT NUMBER: CA FLAP INY CR2022 (1) Reported by: Darrell Harding PROJECT NAME: South Lake Road Title: CFL Laboratory Manager

PROJECT LOCATION: Inyo National Forest, Inyo County, California Date Tested:

STATION: 216+50, 25 feet from centerline

HOLE NUMBER: -

FIELD NUMBER: 216+50 FIGURE: B-1

SAMPLE DEPTH: 0-1 foot

#100 8

#200 4

11/23/2016

~5.7 ~0.9

#16 25

#40 14 Remarks

3/8 54

#4 44 Coefficients

#10 32 0.09 1.90 15

1 69

3/4 64 Classification

1/2 58 inches %

3 86 Atterberg Limits (ASTM D 4318)

1-1/2 76

TEST RESULTS

Opening Size

Percent Finer

Material Description Poorly Graded Gravel with Silt and Sand

0.0010.010.11101001000

P E

R C

E N

T R

E T

A

IN

E D

B

Y W

E

IG

H T

P E

R C

E N

T P

A S

S

IN

G

B Y

W E

IG

H

T

GRAIN SIZE IN MILLIMETERS

PARTICLE SIZE DISTRIBUTION REPORT

SIEVE ANALYSIS HYDROMETER ANALYSIS

BOULDERS COBBLES

% GRAVEL

COARSE FINE

% SAND

COARSE MEDIUM FINE

% FINES

36" 24" 12" 6" 3" 1 1/2" 3/4" 3/8" #4 #16#8 #30#10 #40 #50 #100 #200

915 610 305 152 75 37.5 19 9.5 4.75 2.36 2 1.18 .6 .425 .3 .15 .075 .037 .019 .009 .005 .002 .001

1 MIN 4 MIN 19 MIN 60 MIN

7 HR-

15 MIN

25 HR-

45 MIN

TIME READINGSSIZE IN INCHES

U.S. STANDARD SIEVE

OPENING IN INCHES

U.S. STANDARD SIEVE

NUMBERS

1"

12.5

1/2"

SILT CLAY

% +3"

U.S. DEPARTMENT OF TRANSPORTATION

FEDERAL HIGHWAY ADMINISTRATION

CENTRAL FEDERAL LANDS HIGHWAY DIVISION

james.arthurs Rectangle

APPENDIX C

SLOPE SCALING

FIGURE C1- STATION 294+90 to 298+40

FIGURE C2- STATION 351+60 to 352+60

FIGURE C3- STATION 353+40 to 354+00

FIGURE C4- STATION 354+80 to 355+50

FIGURE C5- STATION 356+15 to 359+60

Figure C1 - Sta. 294+90 to 298+40

Area of scaling interest (1)

(1) Scaling areas may be adjusted after pre-scaling meeting.

~Sta. 295+20~Sta. 296+60

Figure C2 - Sta. 351+60 to 352+60

(1) Scaling areas may be adjusted after pre-scaling meeting.

Figure C3 - Sta. 353+40 to 354+00

Figure C4 - Sta. 354+80 to 355+50

Figure C5 - Sta. 356+15 to 359+60

SECTION FIVE -- REFERENCES