5b_Repair Roof_B3010_Design Analysis_Final.pdf

COPYRIGHT 2016 BY CH2M HILL, INC. • COMPANY CONFIDENTIAL

Des ign Ana l ys i s

100% Design Roof Repair Munitions Storage Facility 3010

Design Contract No: FA4897-14-D-3002 Project No: QYZH 12-0066

Prepared for Mountain Home AFB

Mountain Home, ID

October 21, 2016

1 100% DESIGN ANALYSIS ROOF REPAIR MUNITIONS STORAGE FACILITY 3010

Project Description Overview This project will provide a new roof system to Facility 3010, an existing earth covered magazine (ECM) storage facility. The structure has a curved concrete roof and the existing cover consists of an existing waterproofing system containing layers of tar, sand, plastic and geotextile, as well as a sloped earthen cover, and gunite cap. The gunite has cracked significantly and caused erosion of the earthen cover beneath it. This project will remove the existing roof cover system (waterproofing system, earth, and gunite) and replace it with a new roof cover system. The new roof system will consist of a waterproof membrane, sloped earth cover, separation geotextile, and geogrid/geocell filled with crushed rock, similar to a recently modified facility (B3005). The project will also provide a new perimeter footing drain and infiltration gallery to prohibit groundwater from reaching the foundation.

Existing Conditions In addition to the conditions described above, one metal ventilation cap and lightning protection system exist on the current roofline. The ventilation cap and concrete shaft will be retained and protected. The catenary lightning protection system (LPS) consists of three posts and a continuous wire connected to the electrical grounding system, which will remain in place during construction. The contractor will be required to coordinate with the Government for a Government test of the system prior to beginning construction. If a repair of the system is deemed necessary, the contractor will not begin construction activities until the system is repaired. The contractor will be required to periodically verify that the system is intact and undamaged throughout construction.

A portion of the existing gunite cap was will be removed to expose the layers underneath it for sampling purposes. The dirt cover has been tested for pesticides (Chlordane), the membrane tested for asbestos, and paint on the ventilation cap tested for lead. The results of the tests indicated the presence of lead in the paint on the vent. The contractor shall abate the containments and repaint the vent.

A draft geotechnical engineering report indicates the existing site is comprised of native dry to moist, firm to very stiff, non‐ to low‐plasticity silts with varying amounts of fine‐grained sand. Bedrock exists below the native soil at a depth of 3 to 5 feet. The recommended design infiltration rate is 0.6 inches per hour.

Civil and Architectural Design Site demolition will consist of removing the gunite cap, geotextile, earth cover, and waterproof membrane. The lightning protection system will be retained and protected. The ventilation cap sits atop a concrete shaft. Per the as‐built drawings, the shaft appears to be open to the ECM below. The cap will be removed and the shaft protected during construction. After construction, the cap will be reinstalled and painted. The existing perimeter drain system (perforated pipe and aggregate fill) will also be demolished. Existing earth fill will be stockpiled on‐site for reuse and imported fill will be provided if required to meet minimum cover requirements. All other demolished materials will be disposed of off‐ site.

The concrete structure will be exposed to allow the removal of the existing waterproof membrane and construction of a new waterproofing system; a fluid applied (roll‐on or spray‐on) water based high build polymer modified asphalt emulsion system with reinforced sheet flashing. Earth fill will be placed to a minimum depth of 2‐feet 4‐inches over the structure, resulting in finished side slopes similar to existing, 2 100% DESIGN ANALYSIS ROOF REPAIR MUNITIONS STORAGE FACILITY 3010 and compacted to ensure structural integrity. The minimum depth of cover was provided by the user. A heavy duty separation geotextile will be placed over the earth fill to prevent infiltration of surface runoff and the section will be topped with a 3‐inch deep geogrid / geocell filled with 4‐inches of 1‐inch minus crushed rock. The geotextile is designed to handle the foot traffic anticipated over the rock surface without puncture or damage, based on conversations with the manufacturers.

User based procedures dictate quarterly inspection to ensure compliance with minimum cover (2‐feet 4‐ inches) on ECMs. In an effort to protect the new geotextile and waterproof membrane features, four integral gauges will be constructed along the top of the roof to assist users in evaluating roof cover.

They will consist of capped galvanized pipes attached to the roof by flanges. The pipe will be etched with tick marks (in inches) with 0” beginning at the top of the existing concrete roof and continuing to the exposed pipe cap and painted red from 0”‐24”, yellow from 24” to 32” and green from 32” to top of pipe.

Site Grading and Drainage The site is relatively flat with very little distinguishable drop across the site. The top of the roof elevation will be established by the 2‐feet 4‐inch minimum earth fill plus the thickness of the waterproofing system and geotextile, geogrid, aggregate cover. The top and side slopes of the new roof system will be 3:1 from the centerline of the roof to the outer edge of the ECM vertical wall and 2:1 beyond to meet existing grade. Any surface water that percolates through the 1‐inch crushed rock will be collected and conveyed along the geotextile surface to the toe of the slope. Per conversations with manufacturers of the geotextile and geogrid, it is possible to successfully utilize these products on 1.5:1 slopes.

Any groundwater will be collected in the footing drain and discharged to the infiltration gallery as described below. The site will be graded at 2% away from the toe of the slope for a minimum of 10‐feet.

The concrete apron on the west side of the building will be retained and protected. There is no existing stormwater collection system in this area. Stormwater runoff from this site is intended to infiltrate into the ground per existing conditions. All disturbed surfaces will be restored.

A new footing drain will be constructed at the outside perimeter of the existing concrete footing. The drain will be approximately 3‐feet wide by 2‐feet deep and comprised of a 6‐inch perforated pipe backfilled with clean aggregate contained within a geotextile fabric. The pipe will slope away from the high points at the existing headwall at approximately 0.5% to the low point of the site. It will continue away from the building to an underground infiltration gallery. The gallery will be comprised of aggregate material with sufficient void space to provide storage of the minimal amount of groundwater anticipated at the site and collected by the footing drain while providing infiltration into the surrounding ground. A monitoring well will be constructed in the infiltration gallery to facilitate periodic visual inspection of the water level in the gallery.

All soil disturbed by construction, not receiving a surface treatment, shall have a tackifier applied to reduce dust emissions from the site.

Electrical Design The electrical system and intrusion detection system for the facility will not be modified by this project.

The existing catenary lightning protection system (LPS) will be retained, extended, and reconnected to the existing LPS ground electrode system. The extension is necessary to provide proper protection of the ECM. See the Existing Conditions paragraph for more information.

REPAIR-ROOF_B3010_100PER_DESIGN-ANALYSIS.DOCX 3

Design Guidance, Codes, and Standards Design will comply with the following standards:

Unified Facilities Criteria (UFC) as applicable, including:

UFC 1‐200‐01. General Building Requirements

UFC 3‐340‐02. Structures to Resist the Effects of Accidental Explosions

UFC 4‐420‐01. Ammunition and Explosives Storage Magazines

DoD 6055.09‐M. DoD Ammunition and Explosives Safety Standards

DoD 5100.76‐M. Physical Security of Sensitive Conventional Arms. Ammunition and Explosives

DDESB Memorandum. DDESB‐PD. Minimum Requirements to Validate Explosives Safety Protective Construction

DDESB Technical Paper (TP 15). Approved Protective Construction

Engineering Technical Letters (ETLs), Air Force Instructions (AFIs), and manuals:

ETL 02‐12. Communications/Information System Criteria for Air Force Facilities

AFMAN 91‐201. Explosives Safety Standards

Installation Development and Design (ID2) for MHAFB

NFPA 70 ‐ National Electrical Code (NEC)

NFPA 780 – Standard for the Installation of Lightning Protection Systems