Geotech_Report.pdf

To: Pat Flynn, Project Manager, CFLHD, Lakewood CO

From: Charlie Martinez, Engineering Geologist, CFLHD, Lakewood CO

Through: Matthew J. DeMarco, Lead Geotechnical Engineer, CFLHD, Lakewood, CO

Subject: Engineering Geology for the CA PRA DEVA 11(1), Bonnie Clare Road

1.0 Introduction

Cutslopes are proposed along a 7.6 mile segment of the Bonnie Clare Road that runs through Grapevine Canyon from the Park boundary at the Nevada state line past Scotty’s Castle to the junction of the Ubehebe Crater Road.

In December 2010 a station by station analysis of the proposed cutslopes were made based on visual observations of the existing slopes. These recommendations were fine-tuned during a field review in April 2011. The existing cutslopes vary considerably from alluvial and colluvial soils to a complex sequence of sedimentary and volcanic rocks. A Summary of Soil Survey with a description of the soil or rock type and the associated slope ratio recommendations and shrink/swell factors are included in the appendix. The recommended cutslope ratios for soil are based on many factors including the performance of the existing slopes, the angle of repose, cementation, cohesion, grain size and soil shape. The recommended cutslope ratios for rock are based primarily on the rock structure, degree of weathering and cementation. The shrink/swell factors for each material type are also presented. The shrink factors in soils along the route range from 0 to -10% and the swell or bulk in the rock range from 0 to +20% based primarily on degree of weathering, structure and grain size. These recommendations are derived from past projects in the area. Note: Negative percentages indicate a decrease in volume or shrink and positive percentages indicate an increase in volume or swell (bulk).

2.0 Regional Geology

Death Valley National Park lies within the Basin and Range geologic province. As the name implies, the Basin and Range Province is characterized by numerous mountain ranges with basins between them. The ranges are generally jagged with bold faces and cliffs essentially devoid of vegetation. The basins occupy much more area than the ranges and with time, because of the interior drainage, these ranges will be buried in their own waste material. The landscapes are typical of an arid region and the dominant landforms are alluvial fans, pediments and playas.

Vegetation is generally sparse and wind erosion is active. Although in the desert regions the landforms are clearly the result of wind activity and glaciations, the dominant erosional process is by water. Most of the streams are dry much of the year. When intense storms do occur, with

Technical Memorandum

Date: October 28, 2011 little or no vegetation to slow run-off, flash floods develop which have the capacity to erode and transport large quantities of materials and quickly alter the landscape. Rocks representing all geologic eras are found in this province. Precambrian granites and metamorphic rocks in present in some of the ranges; however, Paleozoic limestones and sandstones are the dominant rock type.

The basins are blanketed by thick deposits of Quaternary age sediments and thinner deposits of Tertiary volcanics.

3.0 Local Geology

The local geology of the Bonnie Clare Road and Grapevine Canyon is a complex sequence of sedimentary rocks consisting of interbedded chert, limestone, sandstone (graywacke) and conglomerate that is draped by younger volcanic tuffs, breccias and basalt. There are also some metamorphic rocks consisting of quartzite produced by local metamorphism as a result of the volcanic activity. The sedimentary sequence of rocks was deposited in both marine and fluvial environments that have undergone severe tectonic activity resulting in normal faults and folds.

This has resulted in numerous tilted fault blocks dissected by alluvial fans created during flash flooding and debris flows during torrential rain events. This debris finds its way down the steep cliffs and slopes until it reaches the canyon bottom. As it emerges onto the valley floor and loses energy, the coarsest debris accumulates first with the finer material deposited below. There is an excellent example of an alluvial fan from station 258+00 to 264+50, LT. Mechanical erosion caused by water and wind has produced many oversteepened slopes consisting clastic or granular soils made up primarily of silty sands, gravels, cobbles and boulders. Some of these slopes have gravel and large cobble size rock fragments nested above finer more erodible soils and during rain events create a rockfall hazard onto the travel lane. The best example of this is from station 283+50 to 284+50, LT.

4.0 Recommendations

Generally, most of the soil slopes are stable at a 1:1.5 (V:H) ratio and some that have calcium sulphate (gypsum/anhydrite) or calcium carbonate (calcite) cementation are stable at a 1:1 ratio.

There is one slope from station 283+50 to 284+50 that it is recommend not to cut due to the loose nature of the gravel and cobble size rock fragments above finer more erodible soils. It is recommended that wherever practical these soil slopes (not the rock slopes) be laid back as flat as possible to promote any vegetation and reduce erosion. The recommended slope ratios for the rock range from 1:1 to 4:1. Generally, the conglomerate, limestone and weaker volcanic rock (tuff and breccias) should be laid back to 1:1 or flatter and the stronger volcanic rock, chert and quartzite should be laid back to 4:1 slope or flatter. These ratios are controlled by the slope height, rock structure, strength (cementation) and degree of weathering. Unlike the soil slopes, rockfall is not a problem along the route. There is one short basalt outcrop from station 363+75 to 364+25, LT that may require blasting. If we can minimize the impact to the cut we can excavate this by using a hydraulic hammer. It may be possible to eliminate this cut completely.

Rock scaling requirement is non-existent to very minimal as most of the loose material is removed during rainstorm events. Revegetation of the slopes is not practical as the climate is extremely arid and topsoil is not available.

Appendix A Photographs

Photo 1 Station 110, Unconsolidated to weakly cemented material

Photo 2 STA 119+50, Light gray to tan conglomerate

Photo3 STA 121+50, Gray welded tuff and breccia, recommend 4:1 cutslope

Photo 4 STA 188+75, Gray and brown interbedded chert and quartzite

Photo 5 STA 195+25, Colluvium overlying brown yellow tuff

Photo 6, STA 207 Gray and brown interbedded chert and quartzite

Photo 7, STA 237+75 Colluvium overlying sandstone

Photo 8, STA 252+50 Gray to yellow brown layered chert and limestone

Photo 9, STA 283+50 Colluvium. Recommend do not cut.

Photo 10, STA 301 Light brown sand, gravel and cobbles, loose.

Photo 11, STA 310 Tan conglomerate, weakly cemented

Photo 12, STA 364 Dark brown basalt

Appendix B Summary of Soil Survey

Summary of Soil Survey

Project: GCA PRA DEVA 11(1), Bonnie Clare Road Date Performed: December 2010 Beginning Reference Location: Begin Project STA 0+00 @ Park Boundary Performed by: C. Martinez

Station to

Station Description of Soil or Rock Recommended

Max. Slope Ratios (V:H)

Shrink(-)/ Swell(+) Factor

Water Problem Area

(Yes/No)

Recommendations

110+00 to 111+00

Sand, gravel, cobbles and boulders, unconsolidated to weakly cemented, draped over gray crystalline rock. Brown moderately weathered schist.

1:1 0 No

Recommend 1:1 or flatter

119+50 to 120+50

Light gray to tan conglomerate (gravels and cobbles), moderately to well cemented.

4:1 okay. See remarks

0 No 2:1 better, will produce less rockfall

121+50 to 122+00

Gray welded tuff and breccia, gravel to boulder size rock fragments.

4:1 okay +5% No

135+50 to 135+75

Light brown yellow welded tuff, sand to gravel size

4:1 okay +5% No

188+75 to 189+90

Gray and brown interbedded chert and quartzite with silica nodules

4:1 okay +10% No

189+90 to 192+50

Light brown silty sand and gravel, loose, unconsolidated

1:1.5 okay -10% No Recommend 1:2

195+25 to 195+75

Light brown yellow welded tuff 4:1 okay +5% No

Description of Soil or Rock Recommended Max. Slope

Ratios

Shrink/ Swell

Factor

Water Problem Area

(Yes/No)

Recommendations

200+25 to 204+25

Colluvium consisting of brown silty sand, gravels, cobbles and boulders, unconsolidated

1:1.5 -10% No 2:1 better

204+75 to 206+25

Weakly cemented conglomerate consisting of sand, gravels and cobbles

1:1.5 0 No

206+25to 207+00

Gray and brown interbedded chert and quartzite

4:1 okay +10% No

222+50 to 223+00

Brown weakly cemented to unconsolidated sand and gravel overlying light yellow brown very weak tuff

1:1 okay -10% No 1:1.5 better

223+00 to 224+00

Brown sand and gravel, some cobbles and boulders, very weakly cemented

1:1.5 -10% No

235+25 to 236+25

Light brown to tan conglomerate, weakly cemented

1:1 0 No 1:1.5 better

236+50 to 237+75

Brown silty sand, rounded cobbles and boulders

1:1 -10% No

237+75 to 240+00

Unconsolidated colluvium over light yellow brown to tan sandstone (graywacke), gravels, cobbles and some boulders

1:1.5 -10% No

240+00 to 242+00

Light brown silty sand, gravels and cobbles

1:1.5 -10% No

242+00 to 243+00

Gray brown layered chert

4:1 okay +10% No

Description of Soil or Rock Recommended Max. Slope

Ratios

Shrink/ Swell

Factor

Water Problem Area

(Yes/No)

Recommendations

243+00 to 243+25

Gray conglomerate (sand and gravels) 1:1 okay 0 No

246+25 to 246+50

Gray to yellow brown layered chert and limestone

4:1 okay +10% No

251+00 to 251+75

Gray to yellow brown layered chert and limestone

4:1 okay +10% No

252+25 to 252+75

Gray to yellow brown layered chert and limestone

4:1 okay +10% No

255+00 to 255+25

Gray to yellow brown layered chert and limestone

4:1 okay +10% No

256+25 to 256+75

Light brown conglomerate, weakly cemented 1.3:1 okay 0 No

257+25 to 264+50

Gray to yellow brown limestone 1:1 okay +10% No

258+00 to 264+50

Alluvial fan, loose unconsolidated sand, gravel and cobbles

1:1.5 -10% No

283+50 to 284+50

Colluvium (sand, gravel and cobbles) overlying interbedded light brown sandstone and conglomerate

See remarks -10% No Recommend DO NOT CUT

Description of Soil or Rock Recommended Max. Slope

Ratios

Shrink/ Swell

Factor

Water Problem Area

(Yes/No)

Recommendations

284+50 to 284+75 interbedded light brown sandstone and conglomerate

1:1 0 No

289+00 to 289+50

White tuff, coarse sand to small gravels 1:1 +5% No

291+50 to 291+75

Light brown conglomerate, weakly cemented 1:1 okay 0 No

300+00 to 300+75

White brown chert, fractured 1.3:1 okay +10% No

300+75 to 301+75

Light brown sand, gravel and cobbles, loose 1:1.5 -10% No

301+75 to 302+00

Chert 1:1 +10% No

307+75 to 308+00

Light brown conglomerate, weakly cemented 1:1 or flatter 0 No

308+25 to 309+25

White brown chert 4:1 okay +10% No

309+25 to 310+25

Tan conglomerate, weakly cemented 1:1 0 No

312+75 to 313+75

Tan conglomerate, weakly cemented 1:1 0 No

363+75 to 364+25

Dark brown basalt 4:1 +20% No Will require blasting

Recommendations