Pages F-28 through F-29.pdf

F-28 DIVISION 200

recent three years. Provide the proposed template for presenting monitoring results, including the date, time, temperature and name of the individual taking the measurement. Include methods for assuring the quality of data readings.

(c) Mitigation. Submit proposed ground control measures intended to arrest ground movement. Include methods, materials and a review of how the proposed ground control measures will interact with the ground support elements identified in Section 206.

210.04 General. Furnish, install and monitor convergence points in accordance with the procedures outlined in this Section, and at the approved plan required by Subsection 210.03.

locations and configurations indicated in the Plans. Provide convergence arrays at 18 approved locations, determined by existing ground conditions encountered in the main tunnel adjacent to window adits; within window adits; and in the main tunnel adjacent to and within shear zones.

Provide convergence arrays consisting of three fixed survey monitoring points (one at the crown, and two at opposing sidewalls near springline).

Conform to the following:

Revised by Amendment A002

Special Contract Requirements Project: OR DOT CRGNSA 100(4), Historic Columbia River Highway State Trail, Mitchell Point Crossing

(a) Action trigger levels.

(1) Level I – increased monitoring. The Level I action trigger level is reached when a change in relative ground movement or behavior is identified between a previous sequence of readings and the most recent reading. Required actions include the following:

(a) Take a confirmation reading as soon as practicable;

(b) Submit a notification to the CO, including the results of the initial reading and the confirmation reading, along with a summary of activities that may have caused the change in ground movement or behavior; and

(c) Increase monitoring frequency to double the typical monitoring frequency or no less than once per week, whichever is more frequent, until the readings have stabilized for at least three consecutive readings.

(2) Level II – corrective action(s). The Level II action trigger level is reached when an observed ground movement exceeds the associated ground movement threshold as provided in Table 210-1. Required actions include the following:

(a) Take a confirmation reading as soon as practicable;

(b) Submit a notification to the CO, including the results of the initial reading and the confirmation reading, along with a summary of activities that may have caused the change in ground movement or behavior;

(c) Install ground control measures in conformance with the instrumentation, monitoring and mitigation plan (refer to Subsection 210.03); and

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F-29 DIVISION 200

(d) Increase monitoring frequency to double the typical monitoring frequency or no less than twice per week, whichever is more frequent, until the readings have stabilized for at least five consecutive readings.

Table 210-1 Summary of Action Trigger Levels

Action Trigger Level Type Ground Movement Threshold

Level I Increased monitoring Not applicable – change after stable readings Level II Corrective action(s) 0.25% of initial reading Level III Maximum allowable 0.50% of initial reading

(b) Monitoring frequency. Obtain readings in accordance with the schedule provided in Table 210-2.

Revised by Amendment A002

Special Contract Requirements Project: OR DOT CRGNSA 100(4), Historic Columbia River Highway State Trail, Mitchell Point Crossing

(3) Level III – maximum allowable. The Level III action trigger level is reached when an observed ground movement exceeds the associated ground movement threshold as provided in Table 210-1. Required actions include the following:

(a) Unless it is unsafe to do so, immediately halt other work activities and take a confirmation reading;

(b) Submit a notification to the CO, including the results of the reading and the confirmation reading, along with a summary of activities that may have caused the change in ground movement or behavior;

(c) Unless it is unsafe to do so, conduct a visual inspection of the ground support elements with the CO;

(d) Prepare a corrective measures plan that amends the instrumentation, monitoring and mitigation plan and details additional or modified ground control measures intended to arrest ground movement;

(e) Install ground control measures in conformance with the corrective measures plan (refer to Subsection 210.04(a)(3)(d));

(f) Install arrays of convergence points upstation and downstation, at a distance of 2 times the tunnel diameter, from the location where the Level III threshold was reached; and

(g) Increase monitoring frequency to no less than daily at the location where the Level III threshold was reached and at the newly installed convergence point arrays immediately upstation and downstation. Maintain the daily monitoring frequency until readings have stabilized for at least ten consecutive readings after ground control measures have been installed. Maintain a weekly monitoring frequency during the duration of all tunnel excavation and ground support activities.

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