October 1, 2013 Dear Prospective Bidders: Re: Contract ID 26.036775A Plans, Proposal, EBS, Questions & Answers October 8, 2013 Letting The Contractor is hereby advised of modifications to the bid documents. The Proposal has been modified: The attached Special Provision dated September 20, 2013 and titled MONITORING OF CONSTRUCTION-RELATED EARTHBORNE VIBRATIONS is hereby added to the Proposal. The following pay item has been added: Item No. Description Unit Quantity MONITORING OF CONSTRUCTION-RELATED 1075001 LS 1 EARTHBORNE VIBRATIONS The Plans have been modified: The following sheet has been revised: Sheet No. Description 2 SUMMARY OF ESTIMATED
Questions and Answers: Will disc bearings be allowed as an alternative to Item No. 7093300: pot bearings (fixed), and Item No. 7093305:pot bearings (guided)? Disc bearings will not be allowed as an alternative for pot bearings for the purposes of bidding. Disc bearings may be offered as a value engineering proposal by the successful bidder with sufficient engineering analysis to demonstrate that the disc bearings meet all design criteria including seismic loadings and movements. Can a manufacture be prequalified to bid on Item No. 7092350: Expansion Dam? Although there are three joint manufacturers listed on the plans, the plan notes and the Expansion Dam Specification do not limit the joint to only the three manufacturers listed. Any manufacturer that supplies a joint that satisfies the design requirements and all requirements included in the plans and Special Provisions may be used. The Plans state to extend the paving width 3.5 ft. in areas of Guard Rail. Will the Traverse baskets need to be extended in this area also? The symbol ## is associated with the 10-foot concrete shoulder as shown in the typical section on plan sheet 3. This symbol identifies the need to mill in rumble strips as noted on the sheet. There is no intent to widen the concrete pavement on the shoulder. The symbol ** indicates that the 2-foot earth shoulder should be widened by 3.5 feet in areas of guardrail as noted on the sheet. Does the 270-day completion time for Enterprise Road include the 45-day waiting period? Yes. The typical cross section for ramp 1 requires CSABC beginning at Sta. 1373+46.13. The typical section starts where the existing ramp is already constructed. Since the ramp is currently in use, how does the Department desire to maintain the flow of traffic? If temporary pavement is required to divert traffic around the construction area, how will this be paid for? It is the intent of the Plans to construct the relocated ramp 1 while maintaining traffic on the existing ramp. It is the intent of the Plans to retain as much of the existing ramp 1 pavement structure as practical in the new ramp 1 where the existing and relocated ramps overlap.
Will the Department add fuel adjustment indices for the following bid items that were not included in the specifications: Cement Stabilized Aggregate Base Course (8 Uniform), Cement Stabilized Aggregate Base Course (10 Uniform), Portland Cement for CSABC, Stone Bridge Lift Material, Granular Bridge Lift Material? No. Will open burning of clearing debris be allowed on this project? Yes, provided all local, county, state, federal and all other applicable rules, regulations, and guidelines are met. What is the method of clearing and grubbing underneath the bridge over the Atlantic Intracoastal Waterway? Clearing and Grubbing of high ground (non-wetlands)under the bridge over the AIWW shall comply with Section 201.4.4 subparagraph 2 of the 2007 SCDOT Standard Specifications for Highway Construction. Clearing under the AIWW bridge within wetlands shall be confined to the impact limits shown in the Department of the Army Permit No. SAC-2000-11889 included in the Permits section of the Proposal. In wetland areas, trees, stumps, etc. shall be cut to within 8 inches of the ground or low water. Stumps may be cut flush with the natural ground if desired by the contractor for his convenience. Grubbing shall consist of removing and disposing of all logs, vegetation, stumps (cut as described above), brush, rubbish, and other objectionable material within the impact limits described in the permit. The stumps and root mass below the ground surface shall be left in place except where directly impacted by the placement of substructure elements. All wetland work must be performed in accordance to the contract documents and approved permits including requirements for access (i.e., from mats, barges, trestles). Logging operations shall not occur without these measures in place. Is there a utility relocation schedule available for review? No. Is there an alternative technical solution for embankment stability that can be used which does not require all fill material to meet the 32 degree internal angle of friction? No, not at this time.
Please go to WWW.BIDX.COM to download the new EBS file for electronic bidding. The revised plans are located on SCDOT s Construction Extranet. The revisions to the Proposal will be incorporated into the Contract. Hard copies are also available from SCDOT s Engineering Publications office upon request. Your usual cooperation will be appreciated. Mark H. Anthony Letting Preparation Engineer MHA:afg Attachment File:PC/MHA
SPECIAL PROVISION September 20, 2013 MONITORING OF CONSTRUCTION-RELATED EARTHBORNE VIBRATIONS DESCRIPTION The project construction will generate vibrations that will travel through the earth, which will subsequently be received or "sensed" by nearby structures and inhabitants. Specific procedures that will generate earthborne vibrations during bridge and roadway construction include (but are not limited to) the installation piles, ground improvement, shoring walls, and vibratory compaction of unclassified or borrow excavation. To mitigate the risk of vibration-related damage to nearby structures, this specification outlines the Contractor's responsibility for performing a program of pre-construction condition assessment and vibration monitoring during construction. This specification is based, in part, on AASHTO R 8-96 (2004) Standard Recommended Practice for Evaluation of Transportation-Related Earthborne Vibrations. As discussed in AASHTO R 8-96 (2004), humans respond to a much broader range of vibration frequencies and intensities than structures. Intrusive vibration levels can annoy humans at much lower intensities than levels considered critical for structures. Thus, occupants of adjacent properties may perceive that the construction-induced vibrations may present risk to their structures. The recommended safe vibration limits are intended to mitigate the risk of structure damage, and more specifically, reduce the development of "threshold cracks" or cosmetic cracking. Such cracks may appear at lower vibration levels than the level at which architectural or minor structural damage would be expected to occur. PRE-CONSTRUCTION CONDITION ASSESSMENT The Contractor shall retain an engineering firm to perform a pre-construction condition assessment to document the conditions of nearby buildings and other sensitive nearby structures prior to the beginning of construction. The Contractor or his representative is responsible for coordinating access with the property owners. The assessment shall be performed on the Sweet Home Free Will Baptist Church and the structures at 6105 and 6115 Sweet Home Church Road. It is estimated that approximately 3 structures will need assessment as directed by the Engineer. The assessment should include video and photographic documentation of all exteriors and interiors, and installation of crack monitors on cracks that might propagate due to construction vibrations. All documentation of existing building conditions and information concerning the type and location of crack monitors shall be presented to the Engineer in a report prior to construction. CRACK MONITORING DURING CONSTRUCTION The Contractor shall perform periodic readings of the crack monitors that were installed during the preconstruction condition assessment when construction is within 400 ft. All readings shall be provided to the Engineer within 48 hours of taking the reading. Provided that the crack readings confirm that vibrations are not contributing to increasing the crack width, the crack monitors may be read once per week. More frequent readings may be directed by the Engineer during activities that are expected to have greater earthborne vibrations (e.g., pile driving). If the crack readings suggest that vibrations from the project site are contributing to crack width, then the Contractor shall immediately notify the Engineer and review those activities that are generating the earthborne vibrations. The Contractor and his or her geotechnical firm shall then submit a detailed plan for repair, perform the repair at no cost to the Department and develop and submit for review a revised construction plan to address the vibration problems and minimize further damage and complaints VIBRATION MONITORING DURING CONSTRUCTION A. Procedure The monitor locations will be selected by the Contractor based on the location of the construction activities and their relative position the structures identified during the pre-construction condition assessment. Prior to construction, a plan of the monitoring locations shall be submitted to the Engineer for acceptance. The plan shall indicate monitoring locations, instruments, and S.C. File No. S.C. File Number 26.036775A.1 Page 1
SPECIAL PROVISION frequency of the readings. The vibration monitors shall then be placed at the monitoring locations at a minimum of two weeks prior to construction activities so that background vibrations may be determined. Vibration monitoring shall be performed during installation or removal of bearing piles, sheet piles, and drilled shaft casing and where vibratory construction equipment will be used within 400 ft of structures identified during the pre-construction condition assessment. A monitor should be placed between the vibration inducing activity and the structure and as close to the structure as possible. The locations of the vibration monitors shall be adjusted during construction with acceptance by the Engineer. The sensitivity range of the seismograph shall be selected so that the recording is initiated below the maximum allowable particle velocity shown in Figure 1 and extends above the highest expected intensity. Specific activities of the vibration source shall be indexed in time to allow correlation with the arrivals on the vibration. B. Project Vibration Criteria - The maximum allowable particle velocity is shown in Figure 1. If the data from the monitors indicate that vibrations are exceeding the established criteria, then the Contractor shall immediately notify the Engineer and suspend those activities which are generating the earthborne vibrations, until the Contractor and his or her engineering firm have developed a revised construction plan to resolve the problem. The problem shall be resolved at no additional cost to the Department. C. Instrumentation - The vibration monitors shall consist of digital seismographs that display the particle velocities and associated frequencies plotted against the criteria for this project (i.e., Figure 1). Each seismograph shall contain geophones with response capability in three mutually perpendicular axes or components: one vertical and two horizontal (radial and transverse). The frequency response of the geophones shall be linear from at least 4 Hz to more than 200 Hz. The sensitivity shall range from less than 0.02 in/sec to more than 5.0 in/sec. The BlastMate III by Instantel is one type of seismograph that is suitable for this project. D. Calibration and Instrument Use - The Contractor shall field calibrate the vibration monitors before the start of each recording period. The transducer shall be positioned with the longitudinal axis toward the vibration source. Transducers must be adequately coupled with the ground. Operation of all vibration monitors shall be in accordance with the instrument manufacturer's instructions and recommendations. Vibration records shall be collected in waveform plot or strip chart plot. The peak vector sum of the particle velocity in longitudinal, transverse, and vertical planes shall be shown along with the respective dominant or principle frequencies. The highest recorded particle velocity (i.e., the vector sum of the three orthogonal directions), when indexed to a particle vibration event, shall be reported as the peak particle velocity. The recorded peak particle velocity shall be compared to criteria appropriate for the subject of concern. E. Complaints - In the event of a complaint, the Contractor shall immediately contact the Engineer and review those construction activities that are inducing vibrations into the earth. The contractor shall prepare a report documenting all relevant data such as the time and date presented in the complaint, a description of the construction activities during the subject time/date, data from the monitoring instruments for the subject time/date, complaint information and a description (including photographs, if possible) of the alleged damage. The Contractor and his or her engineering firm shall then submit a detailed plan for repair, perform the repair at no cost to the Department and develop and submit for review a revised construction plan to address the vibration problems and minimize further damage and complaints. METHOD OF MEASUREMENT In addition to the pre-construction condition assessment report, the Contractor shall also provide monthly reports containing the results of the crack monitors and vibration monitors during those activities that generate earthborne vibrations, including (but not limited to) ground improvement and foundation construction. The reports shall document that the Contractor is providing the work described by this specification. S.C. File No. S.C. File Number 26.036775A.1 Page 2
SPECIAL PROVISION BASIS OF PAYMENT Payment shall be made in proportion with the percent of the project that is complete. Final payment of the remaining lump sum balance shall be made when vibration monitoring is complete as approved by the Engineer. Payments shall be made under: Figure 1. Vibration Criteria (adapted from AASHTO R8-96) S.C. File No. S.C. File Number 26.036775A.1 Page 3