Statement of Work.pdf

Proposed Mitigation of Chalk Cliffs Rockslope, East River Road (MT 540) south of Livingston, MP 4

Background:

On January 20, 2025 a mass rockfall event of approximately 400 CY filled the ditch and spilled across the pavement of East River Road (MT 540) near RP 4 at a large rock cut on the east side of the road. This cut, locally referred to as the Chalk Cliffs, is approximately 170 feet high and 450 feet long (see Figures 1 and 2). The cut is composed of claystone, siltstone, fine-grained sandstone, conglomerate and volcanic tuff. Most of the material is soft and highly erodible, but there is a significant fraction of harder, well-cemented layers that produce blocks and clasts that remain intact after falling and impacting the ground. Figure 7.

East River Road is closed to the public for safety concerns and the existing rock face contains many precarious, large blocks that present an immediate hazard to clean-up efforts. It is recommended that a scaling effort be made to reduce the risk to crews tasked with cleaning out the ditch and clearing the roadway. This scaling effort, accompanied by re-establishing a catchment ditch will reduce (although not entirely eliminate) risk to the travelling public and delay further maintenance once the road is reopened, but only in the short term. The risk will likely rise to its historic level within a year or two as the soft materials continue to erode.

Note that MDT does not appear to own Right-of-Way inclusive of the rock slope. It is likely that an agreement with the landowner will be necessary.

Proposed Scope of work

1: Conduct approximately 270 man-hours of scaling over an approximate area of 9000 square feet above 230 linear feet of roadway. See figures 3 through 6, and the attached Scaling Special Provision: This effort will only remove the most precarious blocks of rock creating an immediate threat to the ditch clean-up and reshaping efforts. Due to the soft and erodible nature of the face, further scaling will yield diminishing return. It is expected that an effort will be made to keep rocks from reaching the adjacent Yellowstone River or damaging the power poles or phone line. MDT Maintenance will place concrete barrier rail along the outboard fog line, which will minimize the risk of rock reaching the river or damaging utilities, however the contractor is expected to provide extra protection if necessary.

2: Remove approximately 1500 CY of scaled material and material that is already present in the ditch and on the road. Reestablish the ditch (approximately 350 linear feet) as shown in Figure

9. Do not undermine the rock face by digging beyond the contact between the in-place rock formation and the adjacent loose material that has accumulated from erosion of the slope above.

Haul all material to the Yankee Jim/Tom Miner Pit and Stockpile Area, which is approximately 8 miles to the south of the site on US 89 at RP 16.5.

3. Clean all equipment and vehicles prior to their transport into the project area. Replace or restore any damaged property to its original condition at Contractor's expense.

S:\PROJECTS\00_ACTIVE\02_BUTTE\00_Misc_D2_rockfall_events\2025\S 540 East River Road\SOW.docx

Figure 1: Oblique View of Slope, Looking East

Figure 2: Overview of Slope with Approximate Width and Height

Figure 3: Oblique View of Slope Showing Proposed Scaling Areas, Looking East

Figure 4: Inset View of Lower Middle Scaling Area

Figure 5: Inset View of Primary Scaling Area on Northern Portion of Slope

Figure 6: : Inset View of Upper Right Scaling Area

Figure 7: Photo of Material from 01-20-25 Event, Depicting Upper Size of Expected Material

Figure 8: Overhead Photo Showing Material and Slope Conditions in and above Primary Area -Note Tension Cracks in Snow Near the Top of the Slope (Photo from 01-21-25)

Figure 9: Idealized Cross Section for Re-establishing Roadside on East Side of Road

ECCB Specials Template Updated 5/20/20

1. SCALING

A. Description. Remove all loose or detached blocks of rock, masses of soil, and other debris that constitute or could constitute a road hazard from the identified areas on the plans or as required by MDT Maintenance.

1) Scaling may be required in the areas above and adjacent to the proposed scaling areas.

2) Make a site assessment and submit a detailed scaling plan.

3) Perform all work in a manner that minimizes exposure of construction personnel and equipment to hazardous conditions. Provide all materials, equipment, and labor necessary to perform this work.

B. Submittals. Submit the following:

1) General Scaling Plan.

a) Submit this plan for approval by the designated MDT representative at least 10 working days prior to beginning any work. The General Scaling Plan must include:

b) A detailed Work Plan for scaling. The Work Plan must include, but is not limited to, the following:

(1) The proposed construction/scaling sequence and schedule.

(2) The types of equipment and tools to be used in the work.

(3) The number of scaling crews to be employed on the project and their anticipated work schedule. Each scaling crew must consist of a minimum of one working foreman and two scalers. Always maintain the minimum crew size(s).

The designated MDT representative will approve or reject the Submittals within 10 working days after receipt of a complete submission. Do not begin scaling work until the submittal requirements are satisfied and accepted by the MDT representative in writing.

Deviations from the approved submittals must be re-submitted for approval. No adjustment in contract time will be allowed due to incomplete submittals.

C. Construction Requirements.

1) Do not begin scaling until all submittals have been approved and the provisions of the submitted plans have been implemented.

2) Conduct scaling in accordance with the approved General Scaling Plan.

3) Provide a working foreman to oversee the crew of scalers during all scaling work.

4) Do not perform scaling without the scaling foreman on-site.

5) MDT Maintenance will provide approximately 400 linear feet of jersey barrier placed prior to construction along the western edge of the PTW. If scaling activities have the potential for damaging the roadway and/or adjacent facilities, provide additional appropriate protective devices as required.

6) Perform scaling using standard hand scaling bars, hand drills, “boulder busters,” portable hydraulic wedges, jacks, air pillows, or other mechanical means. The use of power equipment, such as walking excavators, slushers, drag scaling systems, etc. must be approved by the MDT representative prior to use.

7) Remove all scaling debris produced during scaling operations from the site and dispose of the material in accordance with the Disposal of Scaled Material Special Provision or as directed by the MDT representative.

D. Method of Measurement. Scaling is measured by the man hour. Measurement will occur from the time a scaler or scaling foreman is equipped and begins ascending the slope until the scaler or scaling foremen has descended the slope. Measurement is also made for the scaling foreman for time spent at the base of the slope when it is necessary for him to act as a spotter for a crew of at least two scalers working on the slope. Work conducted by additional scaling foremen may be measured with prior approval by the MDT representative. Scaling hours over the allotted hours shown in the plans will not be measured unless approved by the MDT representative.

S540_scaling