W911WN-10-B-0006-0004.doc

SECTION SF 30 BLOCK 14 CONTINUATION PAGE

SUMMARY OF CHANGES

SECTION SF 30 - BLOCK 14 CONTINUATION PAGE

The following have been added by full text:

ADDITIONAL QUESTIONS & ANSWERS

ARRA - EMSWORTH BACK CHANNEL LOCKS AND DAM BACK CHANNEL SCOUR PROTECTION AND LFFT ABUTMENT STABILIZATION

W911WN-10-B-0006

CONTRACTOR QUESTIONS

Q1. On Drawing S-5149, Note 6 states that “Permanent casing to have a minimum cross sectional are of 13 in and 5/8” wall thickness. Will the Corps accept a permanent casing meeting the cross sectional area requirements, but with a lesser wall thickness? The reason being is that a 0.625” wall thickness is not a readily made size. However, the cross sectional area requirements can be fulfilled with casing of a standard wall thickness.

A1. 13 sq. in. is the MINIMUM cross-sectional area of the casing. If casing with a wall thickness of 5/8 inches is not readily available with a MINIMUM of 13 sq. in. of cross-sectional area, the contractor should choose a larger size or factor in a special order for the permanent casing.

Q2. Division 31 - Earthwork, Section 31 05 19.19, Geogrid Reinforcement

-2.1.1 - Geogrid Properties, Table 1 lists Allowable Strength (Ta) at 5% strain min. 580 lb/ft in MD and 920 lb/ft in XMD.

Based on the spec reduction factors for calculating Ta at 5% shall be 1.1 for durability for PP and PE materials and 1.15 for PET material. Min. reduction factor for installation damage shall be 1.1 for all. Reduction factor for creep shall be determined by testing.

This means that for a polyester (PET) material the ultimate tensile strength shall be:

580 x 1.1 x 1.15 x 2.86 = 2098 lb/ft ultimate MD 920 x 1.1 x 1.15 x 2.86 = 3328 lb/ft ultimate XMD

For polyethylene (PE)

580 x 1.1 x 1.1 x 4.5* = 3138 lb/ft ultimate tensile strength MD 920 x 1.1 x 1.1 x 4.5* = 5009 lb/ft ultimate tensile strength XMD

For polypropylene (PP)

580 x 1.1 x 1.1 x 7* = 4912 lb/ft ultimate tensile strength MD 920 x 1.1 x 1.1 x 7* = 7792 lb/ft ultimate tensile strength XMD

(* - estimated values).

Is this the values intended by the spec, or are you just looking for a 5% strain strength per ASTM D6637? This would result in very different materials that meet these properties.

Also, the spec calls for UV resistance of 100% after 500 hours. All geosyntheics are suseptible to UV degradation. We typically follow AASHTO M288 specification that calls for geosynthetics to be covered within 14 days of deployment of a roll. If this is followed, 100% of strength can be expected to be maintained in the material.

A2. The specification gives GSI GRI GG4a/GG4b as the guidance for the geogrid reinforcement properties concerning allowable strength. Reviewing the question, it appears that it is understood that the allowable strength needs to be adjusted to determine the ultimate strength but GSI GRI GG4a/GG4b gives different reduction factor maximums than what is shown in your question. Please review GSI GRI GG4a/GG4b for guidance.

As for the UV resistance concern, Amendment 0001 revised the requirement for UV resistance from 100% to 70%.

(End of Summary of Changes)