St.
Edward’s State Park Logging Road Report
Ben Carlson, Aaron Clements, Amelia Hawkridge, Benjamin McColl,
Anny Schmidt, Mark Williamson
FE 346 Design of Low Volume Roads
University of Washington
June 4, 2004
Table of Contents
Sedimentation
Modeling Results
A. Slope Class Map of St. Edward’s Park
B. Cross Section Views from Road Eng
C. Road Profile View from Road Eng
D. Road Plan View from Road Eng
E. Mass Haul Diagram from Road Eng
G. Runoff and Sediment Yield from USDA
WEPP Model
H. Average Annual Sediment Yield (lb)
from USDA X-Drain Model
K. Minimum Lane Width for a Log Truck
Overview
Location
The area under consideration is located in St. Edward’s Park at T 26 N, R4E, and spans the E 1/2 of section 23 and the W 1/3 of section 24
Objective and Criteria
A road is needed from a timber landing to one of two roads A or B, as shown in the slope class map in Appendix A. This road must meet the following criteria:
- maximum grade = 10% adverse, 15% favorable
- minimum curve radius = 60'
- switchback on < 35% sideslopes only
- 12' running surface
- total length of road, which runs parallel to a creek within 150 ft, cannot exceed 500 ft.
- stay within the Park boundary
Design Approach
The road was originally pegged on a 10 foot interval contour topographic and slope class map with three slope classifications: low (0-30%), medium (30-50%), and high (>50%). The road was laid out such that its side-slopes were mainly within the low to medium range.
In the field the grade line and then the P-line was laid out while topographic variables were also measured.
In the office Road Eng was used based on measurements made in the field and the following tasks were completed automatically to design the road:
- Adjusted the road cross sections vertically based on the best fit grade line and then adjusted based on the profile view of the road (see final cross sections in Appendix B and profile view in Appendix C)
- Adjusted the cross sections horizontally based on cut and fill
- Observed the plan view: balance new road location with planned location (see the plan view in Appendix D)
- Adjusted the road position based on the mass haul diagram (see the mass haul diagram Appendix E)
- Checked cross sections for proper fill height and slopes
- Added curve widening, turnouts, and culverts
- Performed road costing and sedimentation analysis
The road is 2347.2 feet in length. A standard logging truck was the design vehicle for this road, and a lowboy configuration was used as the critical vehicle in the planning of this road. The final design approach was to build the most economic road meeting the mandatory.
Mass Diagram
The final mass haul volume of this road is 2109.0 cubic yards. (see the mass haul diagram Appendix E)
The mass diagram begins with an approximate balance of excavation and fill volume, but at about station 6+74.4 there begins an accumulation of surplus of excavation. Some of this surplus was used for fill from station 11+92.8 until station 14+87.3 where there is more surplus due to full cuts. At station 16+87.2 fill material is borrowed so the mass haul volume drops until station 18+00.3 where a surplus begins that continues for the duration of the road.
Design Speed
The design speed is governed by the grade because most of the road is above 10% grade. The primary critical points are the switchback and the large curve after the switchback, although neither of which necessarily govern or effect vehicle speed. Because of this, little effort is given to curve smoothing, with the main concern being road width/curve widening, not speed. In other words, more effort is put into grading the road and maintaining a grade less than or equal to 16%.
Road Description
The following is a summary of the road parameters. The complete details can be found in Appendix I.
The road-grade ranges from -8% to 15%, starting at 1% for the first 160 feet off the landing. There are six minor curves in the first section of the road, before the switchback; the switchback itself; a major curve; and three more minor curves toward the end of the road.[1]
Maximum curve radius is 60 feet; minimum is 51 feet (minor curve #2). The maximum curve grade excluding the switchback is 15%, minimum is 3%. Switchback grade ranges from -8% to 11%.[2] Curve widening was based on a typical low-boy configuration and ranged from 1 foot added to our 16 foot road template design, to 10.3 feet at the turnout located between stations 10+93.2 to 11+62.3. Typical curve widening was approximately 4 feet.
Side slopes of 50% or more required a full bench cut. Side slopes less than 50% are have fill slopes designed with a 1.5:1 fill ratio, and are limited to 20 feet in vertical height at a maximum, unless fill lands on an out-sloped bench like at station 12+16.2. Cut slopes use a 1:1 slope ratio. Cut and fill were originally balanced, however balance was often skewed as grade requirements needed to be met and mass haul volumes were kept to a minimum. A full through cut is needed from L-Stations 14+84.8 to 15+45.3; and a full fill is needed from L-stations 12+16.2 to 13+38.2 and 17+33.3 to 17.65.0.
The road is designed with 12 inches of ballast with a slope of 2:1 and a V-shaped ditch that is 3 feet wide and 2 feet deep.
A total of 9 cross-drain culverts are placed along the length of the road. Each one is at a 90 degree angle to the center line of the road on a -2 % gradient. In compliance with standard forest practices, one culvert is placed for every 40 feet of elevation gain. Six of the culverts are 18 inches in diameter with 3 larger, 24 inch diameter culverts strategically placed to compensate for sediment overflow and buildup from up-slope cross-drains. Length of each culvert varies depending on road width at that location.
Sedimentation
Local Soil and Road Drainage
According to the US Department of Agriculture, the St. Edward’s Park area is characterized primarily by Kitsap and Alderwood soil series. As can be seen in the map in Figure 1 below, the ridge where this road will be constructed is a classified as an Akf soil (Alderwood/Kitsap soil on very steep slopes).
Figure 1: USDA soil series map of St. Edward's State Park[3]
This type of soil is a mixture of sandy and silty loam known for a rapid to very rapid runoff potential and severe to very severe erosion and slippage hazard[4]. Please see Appendix F for more details about this soil type.
Cross Drain Spacing
This road was designed following standard culvert placement practices. Standard practice is to place an 18” culvert every forty feet of elevation change, with every third culvert being 24” to accommodate additional flow from a larger storm event and as a backup if a smaller culvert becomes blocked. This road also contains additional culverts where draws present in the topography indicate that an intermittent stream may be present.
Sedimentation Modeling Results
The runoff and sediment yield from this road was modeled using the USDA model WEPP[5]. These values can be used to make an estimate of the soil erosion from this road. The results from this model are in the table below. The complete results, including the parameters used to generate these numbers, can be found in Appendix G.
Table 1: Runoff and sediment yield from the road based on the USDA WEPP model
|
Rain runoff |
Snow runoff |
Sed road |
Sed profile |
|
18.47 in |
0.48 in |
38681 lb |
19973 lb |
The USDA model X-DRAIN[6] was also used to estimate average annual sediment yield in pounds. This can be used to determine the optimum cross drain spacing based on the road grade. The model shows that for a road grade of 8 – 16% a culvert spacing of 40 ft, just as the road has been designed, will be close to optimum. The complete results can be found in Appendix H.
Curve Widening Accommodations
Mule Train Truck Dimensions
The road was designed to accommodate access by a standard pole truck, as shown in the figure below.
Figure 2: Standard mule train configuration, typical for Canada
The details of the legal dimensions required of any logging truck can be found in Appendix J. In Appendix K can be found a figure illustrating the minimum lane width for a log truck with a 20-ft tractor, 10-ft stinger, and 30 ft bunk to bunk.
Curve Widening:
Existing curve parameters would not accommodate the extraction of 90 foot length poles. In order to meet proper operation limits of pole hauling the existing curve radius would have to be increased from the current 60 feet to at least 100 to 120 feet, also requiring an additional 16 feet of curve widening. Because of the switchbacks position in relation to an adjacent property line, such an increase in curve radius would not be feasible. In addition to this, without further information pertaining to the number of marketable poles on the harvesting site, it is not possible to justify the increased cost of constructing such a switchback. There would be a large increase in excavation costs involved in the discussed road adjustment.
Road Costing
The total cost of the road is estimated to be $28,239.71. The cost per station is estimated to be $1,325.37. Please see the complete details in Appendix L.
Appendix
A. Slope Class Map of St. Edward’s Park
Slope Class Key: 0 – 30 %, 30 – 50 %, 50 + %
Contour interval: 10 ft
B. Cross Section Views from Road Eng
See attached.
C. Road Profile View from Road Eng
See attached.
D. Road Plan View from Road Eng
See attached.
E. Mass Haul Diagram from Road Eng
See attached.
F. Alderwood and Kitsap soils
Mapping
Symbol: AkF
This
mapping unit is about 50 percent Alderwood gravelly sandy loam and 25 Kitsap silt
loam.
Slopes are 25 to 70 percent. Distribution of the soils varies greatly within
short
distances.
An area mapped with this soil may have only one of these soils or both of
them.
Typical
Profile: Alderwood Portion
Depth
from Surface:
0
to 27 inches: Very dark brown, dark brown, and grayish brown gravelly
sandy
loam
27
to 60 inches: Grayish brown, weakly to strongly consolidated
glacial
till (hardpan)
Typical
Profile: Kitsap Portion
Depth
from Surface:
0
to 24 inches: Very dark brown and yellowish brown silt loam
24
to 60 inches: Olive gray silty clay loam
Permeability:
Moderate
to moderately rapid above the hardpan (if present) and very slow
within
it.
Rooting
Depth:
Roots
penetrate easily to the hardpan (if present) . Roots have difficulty
penetrating
into the hardpan.
Depth
to Seasonal High Water Table: 2 to 3˝ feet
Available
Water Holding Capacity:
Seasonally
low (Summer) to seasonally high (Winter) in Alderwood portion
moderate
to moderately high in Kitsap portion.
Runoff
Potential:
Rapid
to very rapid
Erosion
and Slippage Hazard:
Severe
to very severe
USE
AND MANAGEMENT:
Primary
use is for timber production. Douglas-fir, Western Red Cedar, Western
Hemlock,
Red Alder, and Bigleaf Maple are important tree species for use on these soils.
These
soils have severe limitations on equipment use for site preparation and timber
harvest.
Adequate vegetation must always be left on these slopes if logged.
These
soils have severe limitations for engineering and recreational uses.
These
soils are not recommended for use for cropping, pasture, or livestock grazing
purposes.
