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HomeMy WebLinkAbout01.05 Geologic & Geotechnical Feasibility 09.15.19951 HEPWORTH-PAWLAK GEOTECHNICAL, INC. 5020 Road 154 Glenwood Springs, CO 81601 Fax 970 945-8454 Phone 970 945-7988 GEOLOGIC AND GEOTECHNICAL ENGINEERING FEASIBILITY REVIEW PROPOSED LOGGING ROADS ,' IN THE TEPEE PARK FOREST MANAGEN ENT AREA GARFIELD COUNTY, COLORA O .JOB NO. 195 392 SEPTEMBER 15, 1995 PREPARED FOR: DAVID A. LEVY FORESTRY SERVICES ATTENTION: MR. DAVID A. LEVY P.O. BOX 1797 NEVADA CITY, CALIFORNIA 95959 HEPWORTH-PAWLAK GEOTECHNICAL, INC. September, 15, 1995 David A. Levy Forestry Services Attention: Mr. David A. Levy P.O. Box 1797 Nevada City, California 95959 5020 Road 154 Glenwood Springs, CO 81601 Fax 970 945-8454 Phone 970 945-7988 Job No. 195 392 Subject: Geologic and Geotechnical Engineering Feasibility Review for Proposed Logging Roads in the Tepee Park Forest Management Area, Garfield County, Colorado. Gentlemen: As requested we have conducted a feasibility review for the proposed new logging roads in the Tepee Park Forest Management Area. The purpose of the review was to evaluate the feasibility of the proposed road construction based on the anticipated geologic and geotechnical conditions along the proposed road alignments. It should be feasible to construct narrow logging roads along the proposed road alignments. Constraints to road construction are (1) where cross -slopes are steep, (2) where the alignment crosses the dormant landslide complex on U.S. Forest Service land, and (3) A. the alignment crosses the slump block complex in the western mesa segment. Geotechnical guidelines have been developed to reduce the potential for local construction related slope instability. Possible local road instability, if it were to occur, should not be extensive and should not result in environmental problems to the watershed which cannot be remediatecl. The report which follows describes our review and presents our findings. If there are questions, please call. Respecthilly submitted, HEPWORTH - PAWLAK GEOTECHNICAL, INC. Ralph G. Mock Engineering Geologist Rev. by: SLP RGM/ro cc: High Country Engineering - Attn: Roger Neal PURPOSE AND SCOPE OF STUDY This report presents the findings of a geologic and geotechnical engineering feasibility review for proposed logging roads in the Tepee Park Forest Management Area, Garfield County, Colorado. The management area and vicinity are shown on Fig. 1. The purpose of the review was to evaluate the feasibility of the proposed road construction based on the anticipated geologic and geotechnical conditions along the proposed road alignments. The work was performed in accordance with our March 24, 1995 proposal to David A. Levy Forestry Services. The anticipated geologic and geotechnical conditions in the management area were evaluated based on published regional geologic mapping and reports, aerial photograph interpretations, and a field reconnaissance. The field reconnaissance covered the proposed alignments on U.S. Forest Service land and part of the new road proposed in the eastern part of the management area. We were accompanied by Roger Neal of High Country Engineering on August 17, 1993 during our reconnaissance of the project. An assessment of road construction feasibility and constraints was made based on our field observation and information reviewed. Geotechnical guidelines have been developed to assist in road design and construction. This report summarizes the data obtained during the review and presents our conclusions and recommendations. PROPOSED CONSTRUCTION Logging operations in the management area will require construction of several new roads in addition to the existing roads. Road planning and Layout were in progress at the time of this study. The new road alignments proposed at the time of this review are shown on Fig. 1. Most of the roads will be on private land with about one mile on U.S. Forest Service land. The roads will be seasonal and not surfaced, except that a gravel surfacing will be provided for 35 feet on either side of culverts in the section on U.S. Forest Service land. The roads will be single lane with turnouts. Typical road widths will be between 12 to 14 feet. The cut and fill slopes will be protected from erosion by seeding and mulching. Where necessary erosion stabilization matting will be used. SITE CONDITIONS The Tepee Creek Forest Management area is located on the northern side of Battlement Mesa near the headwaters of Beaver and Tepee Creeks. Other drainages in the area are Porcupine Creek and West Mamm Creek, see Fig.1. All of these streams drain to the north to the Colorado River. Road access to the area is along Beaver Creek valley which separates the mesa into eastern and western segments. Elevations along the Beaver Creek valley range form 8,800 to 9,600 feet. The ridge lines on the top of the mesa are at elevations of 10,400 to 10,600 feet. The top of the mesa in the western segment is a strongly rolling upland with slopes in the range of 10% to 25%. The eastern mesa segment is a relatively narrow north tending ridge which is the divide between Beaver and West Mamm Creeks. All of the drainages have cut deep valleys below the mesa top. Slopes alone the valley sides in areas underlain by the Green River Formation are steep in the range of 40% to 100%. Valley side slopes in the range of 30% to 50% are typical of areas underlain by the Uinta and Wasatch Formations. Cliff amphitheaters, the result of accelerated erosion along the mesa rim, have locally developed at the heads of Porcupine and West Mamm Creeks. In places relief along the cliff is as much as 800 feet. Vegetation in the management area consists of aspen and conifer forests with some open grass lands at the higher elevations. Oak brush is present in places in the lower elevations in the northern part of the management area. Marshy, poorly drained ground is present along most of the perennial streams, in the vicinity of the upland ponds and locally in the vicinity of springs and seeps. MANAGEMENT AREA GEOLOGY Our interpretation of the major geologic feature in the management area are shown on Fig.1. The geologic map is based on our field observations, aerial photograph interpretations, and regional geologic maps (Donnell and Others, 1989 and Yeend and Others, 1988). The area is on the northern side of Battlement Mesa which is the erosional remnant of a large Miocene -age, basalt plain which has been dissected and eroded by the Colorado River and its tributaries. Relief between the mesa top and the Colorado River valley to the north is about 5,300 feet. The lava flows which formed the original basalt 3 plain at the crest of Battlement Mesa have been extensively modified by frost breakup and large rotational slumps in the slump block complex (Qsb) in the southwestern part of the management area. SEDIMENTARY FORMATION ROCK Several sedimentary rock formations which range in age from Eocene to Miocene underlie the basalt flows at the top of the mesa. In descending stratigraphic order the formations are (1) unnamed rocks of Miocene- and Oligocene(?) -age, (2) the Uinta Formation, (3) the Parachute Creek Member of the Green River Formation, (4) the Anvil Points Member of the Green River Formation, and (5) the Shire Member of the Wasatch Formation. All five of these formations are present along the proposed road alignments. Outcrops are not common and the formations are usually covered by colluvium. Regional mapping and deep subsurface exploration show that the sedimentary rocks in Battlement Mesa are nearly flat -lying. A regional dip of about 2° to the west is indicated by structural contours on top of the Wasatch Formation (Donnell and Others. 1989). Some variation in the regional dip should be expected in road cuts because of minor folding. Bedding dips measured.at rock outcrops in the eastern mesa segment were between 8° and 13°. Major faults are not known to be present in the region (Donnell and Others, 1989; Tweto and Others, 1978; and Yeend and Others 1988). Unnamed Miocene- and Oligocene(?) Rocks: The unnamed Miocene- and Oligocene(?) -age rocks (Tsr) are present in the southwestern part of the management area and are inferred to underlie the slump block complex (Qsb) to the south. They consist of a sequence of varied -colored claystone, mudstone, and fine- to medium -grained sandstone. The rocks are poorly cemented and relatively week. Uinta Formation: The Uinta Formation (Tu) is present below the rolling upland which forms the northern part of the western mesa se`gnlent and near the top of the ridge which forms the eastern mesa segment. The Uinta is a light -brown to gray, fine-grained to medium -grained sandstone and light -gray medium grained marlstone and siltstone. The rock is poorly cemented but fine to hard. 4 Parachute Creek Member of Green River Formation: The Parachute Creek Member (Tgp) underlies the lower valley sides of Beaver Creek in the Tepee Park area and crops out near the tops of the erosional amphitheaters at the head of Porcupine and West Tamm Creeks. The Parachute Creek is a gray, black, and brown (gray weathering) marlstone which includes oil shale with minor light -gray siltstone; light -Wray and brown, fine -to medium grained sandstone; and numerous very thin tuff beds. The Parachute Creek Member is usually cemented, relatively resistant to erosion, and locally formes cliffs. Anvil Points Member of Green River Formation: The Anvil Points Member (Tga) underlies the Beaver Creek valley sides in the norther part of the management area. It is also present in the Porcupine and West Mamm drainages. The Anvil Points is a brown to buff, massive fine- to coarse grained sandstone with minor light -gray siltstone and- marlstone beds and a few, thin tan low-grade oil -shale beds. Like the Parachute Creek Member, the Anvil Points is usually cemented, relatively resistant to erosion. and locally formes conspicuous ledges. Shire Member of Wasatch Formation: Except for a small area in the northwestern part of the management area, the Shire Member is not present in the management area. The Shire Member probably underlies much of the dormant landslide complex along the western side of the Beaver Creek valley along the propose road alignment on U.S. Forest Service land. The Shire Member is a purple, lavender, red, gray and brown claystone with some local lenticular, fine- to coarse-grained sandstone and conglomerate beds and thin limestone beds. The sandstone, conglomerate, and limestone beds are commonly cemented and hard. The claystone is non-cemented and relatively week. Most of the landslides in the area are underlain by the Shire Member. SURFICIAL DEPOSITS A variety of surficial deposits are present in the management area and vicinity. These include old alluvium (Qoal) and old pediment deposits (Qop) in the uplands. Geologically young alluvium (Qat) consisting of alluvial fans and valley floor alluvium is present in the Tepee Park area and along Beaver Creek to the north. Colluvium (Qc) usually covers the sedimentary rock formations on the valley sides and in the upland 5 areas. Only the alluvium and colluvium will be encountered along the proposed road alignments. Alluvium: The alluvium consists of angular to rounded rock fragment from gravel to boulder size in a stratified sandy clay matrix. In many places basalt boulders up to several feet in size are present in the alluvium. It is expected that the depth of the alluvium in most area will be deeper than the road cuts. Marshy, poorly drained ground is present along most of the perennial streams, in the vicinity of the upland ponds and locally in the vicinity of springs and seeps. Colluvium: The colluvium consist of angular sedimentary rock fragments and locally basalt boulders in a sandy clay to clay matrix. The colluvium is poorly sorted and in most areas the rock fragments are supported by the soil matrix. Depth of the colluvium is expected to be variable, ranging from a few feet to deeper than the propose road cuts. In general the colluvium is expected to be relatively shallow on the steeper slopes, but deep colluvium may be present in these areas. In most areas the colluvium appears to be well drained, but locally poorly drained colluvium should be expected. Likely areas of poorly drained colluvium are along the first order ephemeral stream channels. LANDSLIDE FEATURES There are several landslide features in the management area and vicinity. They include a slump block complex (Qsb), dormant landslide complexes (Qls(d)), active debris flow complexes (Qdf(a)) and active landslide complexes (Q1s(a)), see Fig. 1. The currently proposed road alignments do not cross active landslide complexes or active debris Clow complexes. The existing road and the proposed new road alignment on the U.S. Forest Service land crosses a dormant landslide complex. About one mile of the proposed road alignment in the western mesa segment crosses the slump block complex. Slump Block Complex: The top of Battlement Mesa in the southwestern part of the management area is characterized by broken, irregular topography which results from the breakup of the original basalt plain by large rotational slump blocks, solifluction, and frost 6 breakup. The numerous lakes and ponds in the slump block area are caused by disruptions in the surface drainage because of past slumping. Similar slump block topography is common elsewhere on Battlement Mesa and on Grand Mesa to the southwest. The slumping occurs along largge, deep laterally elongated basalt block slumps with the base of the failure surface in the weak unnamed sedimentary rocks between the stronger Green liver Formation and the overlying basalt (Yeend, 1969). Individual slump blocks can be several 1000's of feet long and some may be as deep as 600 feet. The slumping in the region started before the last Pleistocene glacial period (over 25,000 years ago) and may be in part associated with conditions wetter than at present. Most of the slump blocks are probably dormant under current climatic _ conditions but movement has been measured at some slump blocks near the edge of Grand Mesa (Yeend, 1969). These measurements indicate vertical displacement rates of about 3 to 6 inches per year over a two year monitoring period. In addition to the large slump blocks, the slump block complex also has stone fields and ground disturbed by solifluction. These shallow surticial features are associated with past glacial climatic conditions and most are probably inactive under modern environmental conditions. Dormant Landslide Complexes: There are a few areas in the management area and along the western side of the Beaver Creek valley to the north which have topographic features such as ground hummocks, crescent-shaped escarpments, and ponded drainage which appear to be associated with past landslide displacements. Judging from the subdued character of these topographic features the landslide areas have probably been dormant for a long time. However, due to the inherent low stability of some parts of the dormant landslide complexes, grading disturbance or a cycle of unusually wet years could lead to local landslide reactivation. Active Debris Flow Complexes: The large cliff amphitheaters which are locally present along the mesa rim near the headwaters of Porcupine and West Mamm Creeks and the small amphitheater near the head of Tepee Creek result from accelerated erosion and associated debris flows. These processes are active under current environmental 7 conditions as will continue to be active. Roads will not be located in the active debris flow complexes. Active Landslide Complexes: Active landslide complexes are common in areas underlain by the Wasatch Formation. The active landslide complexes typically have numerous small landslide areas with well defined and fresh appearing surface features. Evidence of groundwater seepage is also common in the active landslide complexes. Judging from this, it is reasonable to infer that active landslide creep is occurring or that much of the complex is near a critical stability state. Except for a small area in the northwestern part of the management area, active landslide complexes are not located in the management area or along the proposed road alignment outside the management area. FEASIBILITY EVALUATION It should be feasible to construct narrow logging roads along the proposed road alignments based on the expected geologic and geotechnical conditions. Constraints to road construction are (1) where cross -slopes are steep, (2) where the alignment crosses the dormant landslide complex on U.S. Forest Service land, and (3) where the alignment crosses the slump block complex in the western mesa segment. STEEP CROSS -SLOPES Because of the terrain it will not be possible to avoid all areas with steep cross - slopes, but steep cross -slopes should be avoided when possible. In steep cross -slope areas the potential for local stability problems in road cuts and fills can be reduced by following the geotechnical guidelines present later in this report. Construction on the steeper slopes will, however, involve some risk of causing local instability. Local instability could result in loss of road use while repairs are being made. Possible local road instability, if it were to occur, should not be extensive and should not result in environmental problems to the watershed which can not be remediated. 8 DORMANT LANDSLIDE COMPLEX Road access to the management area will be through U.S. Forest Service land along Beaver Creek. Road access along Beaver Creek will require crossing a dormant landslide complex by the existing road and by a new alignment. The current stability state of the dormant landslide complex is inherently low and could be difficult to evaluate even with subsurface exploration. Extensive cuts and tills through this type of terrain will increase the potential for landslide reactivation. Construction related landslide reactivation could result in loss of road use while repairs are being made. Minor, local landslide reactivation should not result in environmental problems to the watershed which can not be remediated. There may, however, be the possibility of more extensive landslide movements. We consider the likelihood of extensive landslide reactivation related to road construction to be remote provided the guidelines for crossing steep slopes are followed. Considering these constraints there appears to be two options for constructing a narrow lo,iuinu road in this area: (1) use the existing U.S. Forest Service road where possible, and (2) constructing a new road across the landslide which limits grading to the extent practical. The proposed new road alignment will avoid most steep slopes which will required high cuts and tills, but some steep slopes cannot be avoided. Alternative road alignments with more favorable topography, other than the existing road alignment, probably cannot be found. From a landslide stability view point, using the existing road through the entire landslide complex will involve the least disturbance and have the lower potential for landslide reactivations. SLUMP BLOCK COMPLEX The proposed road alignment in the western mesa segment crosses the slump block complex in two areas, see Fig. 1. These areas have not been reviewed in the field. From the aerial photographs, the lower crossing appears to be in an area affected by past solifluction, but the large slump blocks do not appear to be present. Large slump blocks are present in the upper area. Narrow logging road construction in these two areas should not result in environmental problems to the watershed which can not be remediated. Road construction should not have a significant adverse impact on slump block stability because of the large size of the slump blocks in comparison to the grading required for the roads. 9 If creep displacement is occurring alone some of the slump blocks, it should be restricted to narrow zones along the block boundaries and the rate should be comparable to that observed in the Grand Mesa area to the southwest. Considering these creep rates, It should be feasible to maintain a serviceable road across active slump block boundaries. Before finalizing the western mesa segment road alignments, the alignments should be reviewed in the field. GEOTECHNICAL GUIDELINES Based on our current understanding of the geotechnical conditions in the area, the following guidelines have been developed to assist in designing and constructing the proposed new roads. As road construction proceeds it is recommended that the road cuts be observed to evaluated if conditions are similar to those anticipated by our reconnaissance. If actual conditions vary signiticantly, then some modifications in the guidelines may be warranted. The guidelines are for well drained areas free of ground water seepage. If ground water seepage is encountered in cuts, then the potential for instability could be high. Ground water seepage is not expected in most areas of deeper cut sections, but all seepage encountered during construction or which develops after construction should be evaluated to assess the nature of the seepage and need for remedial drainage systems. ROAD CUT SLOPES (1) Road cut slopes in colluvium and weathered formation rock should not be steeper than 1.25:1 (horizontal to vertical) and no higher than 20 feet. In the dormant landslide complex, cuts should be no higher than 10 feet. (2) Roads cuts in unweathered formation rock with bedding dips of less than 20° should be no steeper than 0.5:1 (horizontal to vertical) and no higher than 15 feet. (3) If the cut slope guidelines present in Items 1 and 2 above cannot be achieved, then retaining walls should be considered in soil and weathered rock cut areas. Rock bolting or other forms of slope reinforcement may be needed if bedding is steeper than 20°. The design of retaining walls and rock bolting systems should be evaluated on a site specific basis. 10 (4) Cut slopes should have adequate surface drainage. Concentrations of surface runoff should not be allowed to flow directly down unprotected cut slopes. (5) Cut slopes should be protected from erosion by re -vegetation or other means. ROAD FILLS (1) Most of the on-site colluvium and formation rock should be suitably for road embankment fills. Exceptions are highly organic topsoil, highly plastic clays and claystones. Rock larger than 12 inches, roots, tree trunks and logs should not be placed in the road fills. (2) Road fill slopes should be no steeper than 1.5:1 (horizontal to vertical) and no higher than 25 feet. Fill slopes in the dormant landslide complex should be no higher than 15 feet. (3) If the fill slope guidelines presented in Item 2 above can not be achieved, then retaining walls or mechanically stabilized earth (MSE) fills should be considered. The design of retaining walls and MSE fills should be evaluated on a site-specific basis. (4) Before fill placement, the subgrade should be prepared by removing all vegetation and highly organic topsoil. Road fill placed on slopes steeper than 20% should be benched into the hillside. The fill should be placed in lifts appropriate for the fill material and compacted to at least 95% of its maximum standard Proctor density at near optimum moisture content. Fill slopes should have adequate surface drainage. Concentrations of surface runoff should not be allowed to flow directly down unprotected slopes. Fill slopes should be protected from erosion by re -vegetation or other means. LIMITATIONS This study was conducted according to generally accepted geologic and geotechnical engineering principles and practices in this area at this time. We make no other warranty either expressed or implied. The conclusions and recommendations submitted in this report are based on a field reconnaissance, review of published geologic maps and reports, aerial photograph interpretations, and our experience in the area. Our 11 findings include interpretations of the data reviewed. Subsurface conditions encountered during construction may differ from those described in this report. If conditions encountered during construction appear different form those described in this report, we should be notified so that re-evaluation of the guidelines and recommendations may be made. This report has been prepared for the exclusive use by our client for feasibility evaluations. We are not responsible for technical interpretations by others of our information. As the project evolves, additional field reviews of the proposed road alignments in the eastern mesa segment should be made. If retaining walls, rock bolts or mechanically stabilized earth fills are needed, then additional studies will be necessary to develop site specific geotechnical recommendations. We recommend on-site observations of the road cuts during construction by a representative of the geotechnical engineer. Respectfully submitted, HEPWORTH - PAWLAK GEOTECHNICAL, INC. Ralph G. Mock Engineering geologist Reviewed by: • • Steven L. Pawlak, RGM/ro • 15222 • A o .017 •• ;� r • LPJ.•gspNAt ENv< 12 REFERENCES Donnell, J.R. and Others, 1989, Geology c1✓1ap of the North Mwnm Peak Quadrangle, Garfield County, Colorado: 11.S. Geological Survey Map MF -2039. Tweto, O. and Others, 1978, Geology Map of the Leadville 1°X2° Quadrangle, Northwestern Colorado: U.S. Geological Survey Map 1-999. Yeend, W.E., 1969, Quaternary Geology cif the Grand and Battlement Mesa Area, Colorado: U.S. Geological Survey Professional Paper 617. Yeend, W.E. and Others, 1988, Geology Map of the Rulison Quadrangle, Garfield County, Colorado: U.S. Geological Survey Map MF -2060. • Qop .0.• ••• • 114-2 i'1\\`tlll 4•7c ) IQc/Tg p arl '1,, `-- -^G __.p` Qc!Tu` 'e 9pT • '•. \"\.\\��� • • \_ Qdf, ,; r( I acfrws% • c • moi. j•- , __ �-- _cc i • )04•-" r SCALE lin. = 2,000 ft. SURFICIAL DEPOSITS: Qal Qc Qoal Qop QIs„) Qsb EXPLANATION Alluvium Colluvium Old Alluvium Old Pediment Deposits LANDSLIDE FEATURES: Active Landslide Complex Active Debris Flow Complex Dormant Landslide Complex Slump Block Complex FORMATION ROCK: Tsr Tu Tgp Tga Tws Unnamed Sedimentary Rocks Uinta Formation GREEN RIVER FORMATION: Parachute Creek Member Anvil Points Member WASATCH FORMATION: Shire Member CONTACT: Approximate boundary between map units. } PROPOSED ROADS: Approximate alignment of proposed roads. NOTES: 1. See report for description of map units. • `•�.r ', �;'�; -. • .,—� /, �; '�= " '%ice : QcJTga //i—• . .�%�` lig /V''::-'*??.: Qsb r • Qcfrgp �1 }'I'f -, 195 392 HEPWORTH-PAWL AK GEOLOGY MAP GEOTECHNICAL, INC. FIG. 1