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Earthwork Operations 

·         Interpretation of meaning of “phase” and “isolated compaction (or mixing) operations” 

This is not specifically a difference between Districts, but more often than not a difference from project to project or from one CEI/Department inspection staff  to another. Below are the specification sections involved, followed by a discussion of several situations I have seen or have heard about on various projects since CQC began. 

This resolution or clarification of this issue requires careful consideration as the definitions should be consistent between all of the following specification sections. If an “isolated compaction operation” is considered a day’s production for pipe backfill, then it should also be a day’s production for MSE wall backfill. Any clarification will ultimately affect the number of samples/density tests required. This may affect the number of QC and VT technicians required to adequately staff a project and thusly the cost of QC/QA. As cost of QC must be included in the contractor’s bid, the clarification may affect future prices.

·         Specification sections: 

In 120-8.1 General it states “A LOT is defined as a single lift of finished embankment not to exceed 500 feet. Isolated compaction operations will be considered as separate LOTs.  For multiple phase construction, a LOT shall not extend beyond the limits of the phase.” 

In 125-8.1.1 General it states “A LOT is defined as one lift of backfill material placement, not to exceed 500 feet in length or a single run of pipe connecting two successive structures, whichever is less. Backfill around structures compacted separately from the pipe will be considered as separate LOTs. Backfill on each side of the pipe for the first lift will be considered a separate LOT. Backfill on opposite sides of the pipe for the remaining lifts will be considered separate LOTs, unless the same compactive effort is applied. For multiple phase backfill, a LOT shall not extend beyond the limits of the phase. When placing backfill within a trench box each lift of backfill is considered a LOT. Placement of backfill within trench box limits will be considered a complete operation before trench box is moved for next backfill operation. When the trench box is moved for next backfill operation this will start new LOTs for each lift.” 

In 160-5.1 General it states “A LOT is defined as a single lift of finished Subgrade, not to exceed 500 feet. Isolated mixing operations will be considered as separate LOTs. Curbpads and shoulders compacted separately shall be considered separate LOTs. Isolated compaction operations will be considered as separate LOTs.” 

In 200-6.1 General it states “A LOT is defined as a single lift of finished base not to exceed 500 feet. Shoulders compacted separately shall be considered separate LOTs. Isolated compaction operations will be considered as separate LOTs. For multiple phase construction, a LOT shall not extend beyond the limits of the phase.” 

·         Situations: 

Pipe backfill - 

1.     What constitutes a phase? Is it an MOT phase? For example: A run of pipe goes across a 4 lane roadway between 2 structures, one on each side of the roadway. During one MOT phase the pipe is installed across the right roadway from one structure to the median. During the second phase the pipe is installed from the median across the left roadway to the next structure. Additionally during each phase the work takes 2 nights (crossing 1 lane a night). I  am aware of the following interpretations that have been utilized on projects:

a.     The total run of pipe was less than 500 feet so only 1 test per lift was required (except bottom lift) across the full width of the roadway.

b.    “Phase” was interpreted as MOT phase. As long as there was 1 test for each lift across the right roadway and the same across the left roadway, the specifications were met.

c.     Each night’s operation was considered a “phase” or “isolated compaction operation”, therefore testing of each lift was required each night. 

ECI: Option “C” is the ECI Group’s interpretation of the above scenario.  However the group was hesitant to commit to one answer because the phase of construction is dependent on several issues such as maintenance of traffic, contractors execution of work, etc.

LOTs are defined in the specification.  The length of the LOT may be reduced by phased construction or the Contractor’s execution of work. 

2.     What constitutes a “phase” or “isolated compaction operation”? For example – A 200’ run of pipe is being installed between 2 structures along one side of the road. If this is shallow small diameter pipe with no factors limiting production, the pipe could be installed in 1 day. One test would be required per lift (except the bottom) between the 2 structures. If this was in an urban area where driveways had to be maintained, installation may take several days, as pipe must be installed and backfilled to maintain a driveway before the next driveway can be closed to install the next piece of pipe.  

a.     I have seen this tested as if it was all installed in 1 day with one test/lift between the structures.

ECI: This is correct for a typical pipe placement without any driveway

b.     I have seen it tested as each day being considered a “phase” with one test required per lift placed each day

ECI: This is correct for pipe placement with a driveway interruption_(Explanation:  The situation where construction is phased to keep a driveway open.)

c.     If this was deep pipe and a trench box was used, densities would be run on each lift for every 10-20’ of pipe (depending on length of trench box). What makes this any different than crossing a driveway and backfilling it to the top before proceeding with the next section of pipe?

NOTE: If a trench box is used and the procedure outlined in the specifications is followed for density testing, a single run of pipe can easily have in excess of 100 density tests performed between 2 structures (depending on the length of the trench box and the depth of the pipe). Yet the if the same run of pipe can be installed with sloped trench walls so a box is not required, less than 10 densities may be required. Is this not excessive testing with a trench box, especially if the same compaction procedure is used throughout?

Industry suggests that the earthwork task team look at the trench box LOT definitions.  Industry would like FDOT to consider process control sampling/testing for density testing for trench backfilling. 

ECI: A “phase” or “isolated compaction operation” depends on whether the contractor’s method of construction is a continuous rolling operation or not.  In above scenario a & b each lift requires one density test because each lift (up to 500 feet) is constructed as a separate compaction operation.  In scenario c each lift in the trench box is constructed as separate compaction operations.

Specification 125-8.1.1 states  “When the trench box is moved for next backfill operation this will start new LOTs for each lift.” However, the July 2007 specifications allow reduced frequency in pipe backfill after 6 passing LOTs.  This specification can be used to reduce density testing in trench boxes.

 

Embankment-

1.     How is “isolated compaction operations” defined? Typically embankment is placed in large areas in a single operation, although construction of an area may occur over several days. In all cases I am aware of only 1 density is required per lift per 500’ interval even though it may be constructed over several days. This is especially true in the construction of MSE walls and wire walls. Often construction and backfill of an MSE wall occurs over a period of several weeks with only 1 density required per lift for every 500’ section in each area to be tested (1 within 3’ of wall, 1 from 3’ to end of straps, 1 in embankment beyond straps). If operations on different days are not considered “isolated operations”, how does this differ from pipe backfill? 

ECI: Density testing is based on LOT size and not based on compaction operation time. 

Stabilized subgrade-

1.     Definition of LOTS for mixing operations and sampling for LBR and proctor: typically during mixing operations the full width of a roadway section (mainline and shoulders) are mixed in a single operation. Additionally the mixing is performed to a deeper depth to produce additional stabilized material to be used to build curb pads, build up shoulder pads, etc. In District 5 a LOT is considered 500’ of area mixed. A sample obtained for LBR and proctor value represents the mainline, the shoulder and the extra thickness material rolled over to produce curb or shoulder pads. On some projects in District 1/7 the Department has adopted the opinion that 3 samples of the material are required; 1LOT is mainline, 1 LOT is the bottom stabilized material on the shoulder/curb pads, and 1 LOT is the material rolled over to bring the shoulders/curb pads to grade in a single 500’ section. 

ECI: Use one Proctor and LBR result for both mainline and shoulder when mixed in one operation. 

2.     When the stabilized subgrade is compacted, often the bottom stabilized material under shoulders and curb pads is compacted with the mainline subgrade. On some projects this is considered a single operation (shoulder compacted with mainline) and no densities are performed on this bottom lift under the shoulders/curb pads. On other projects a density is required on the mainline and on the bottom lift under the shoulder/curb pad. As the upper portion of the stabilized subgrade for shoulders and curb pads is usually compacted in a totally separate operation it is usually tested for density as a separate LOT. It is only that bottom lift that seems to be tested inconsistently. 

ECI: Consider the roadway and shoulder/curb as one LOT for the purpose of Maximum Density Determination when mixed in the same operation.  Meet the frequencies in specification 160-7.2.4 

Base Course- (this does not apply to asphalt base course)

1.     As with stabilized subgrade, base course for shoulders is often constructed with mainline pavement. Base course material from an approved source is delivered to the project and placed on both mainline roadway and shoulders. The material delivered is consistent, but the problem exists in that the pay item for the base on shoulders is different from the pay item for the mainline (different base groups).

a.     When sampling for proctors, on some projects one sample is obtained and entered into LIMS under the mainline base course pay item number with a remark that it represents the shoulder pay item number also. On other projects a separate sample is obtained from the base material placed on the shoulder which is entered into LIMS with the shoulder pay item number. I have seen both methods used on different projects within the same District. 

ECI: If the Contractor places rock base for both shoulder and roadway in one operation, consider it as one LOT for the purpose of obtaining a proctor sample. 

b.    When performing density testing, often the bottom lift of base course is placed and compacted in one operation with density tests performed. The base course for the shoulder (if 8” or less) is usually placed and compacted with the top lift of the mainline base course. This is often done in one operation. On some projects a note is made in the logbook that the shoulder and mainline were compacted in one operation and 1 density test is performed representing both. On other projects a density test is performed on the mainline AND a test is performed on the shoulder. 

ECI: The construction operation dictates the number of nuclear density test required.  Typically the contractor “boxes out” to construct the curb pad.  Nuclear density tests need be taken on the lower lift of curb pad, the upper lift of curb pad and the mainline roadway after the upper lift of curb pad is constructed.  Review other construction operations on a case by case to determine the necessary testing protocol. 

Verification testing frequency-

1.     The method used to number LOTS is up to the contractor. Various methods are utilized. Although typically on subgrade and base the frequency of 1 VT test per 4 QC tests along the length of the roadway is maintained. On Earthwork operations for embankment and pipe backfill the method of what 1 per 4 means has differed. For example: a contractor has pipe being installed in 4 separate areas by 4 different crews. The QC technician is performing tests for all 4 crews. The LOT numbers are running sequentially irrespective of where they were run. Lot 140 may be a test for the 1^st crew, 141 for the 3^rd crew, 142 for the 4^th crew and 143 for the 2nd crew. If the VT technician is performing 1 test per 4 consecutive LOTS, it will be performed on 1 of these crews. On the next four consecutive LOTS the random VT test might be performed on the same or a different crew. I have seen this method used with the end result being that occasionally there will be runs of pipe where there is only 1 VT test for 5 – 8 QC tests. On other projects I have seen the 1 VT per 4QC frequency based upon each run of pipe. I believe the later is the desire of the Department, but it is not the way it is always performed. 

ECI: VT should verify QC test based on each operation. 

Stockpiled materials-

1.     On many urban projects phasing, MOT, and limited room often dictates working in isolated areas. Often materials such as stabilized subgrade and base course are stockpiled in a convenient area and moved to these isolated areas as needed. Set procedures have not been established to deal with sampling of stockpiled materials. If base course from a stockpile is used to construct several crossovers and a some turn lanes, how often does it need to be sampled for a proctor value. Same applies to an LBR value and proctor on stabilized subgrade. I have seen projects where a sample is obtained and the test results used for several isolated areas. On other projects a sample has been obtained in each isolated area after the material is in place. 

ECI: For each isolated area to be constructed the contractor will be allowed to create one stockpile to construct the area.  QC will be required to collect enough material from the stockpile to create and split into three separate samples and retain for verification and resolution. 

 

·         RECOMMENDATIONS: 

The issues above may  become even more convoluted when we consider the possibly of specifications for traffic and non-traffic areas. When considering this issue (with respect to density testing), we recommend consideration of the concept of “process control” and “independent verification”. “Process control” tests are part of the contractor’s QC in asphalt operations. Additionally the CEI/Department has the option of performing IV testing at any time in asphalt, concrete, and earthwork operations.

I have almost never seen IV testing performed on earthwork. The CEI/Department performs their required VT testing (1 per 4) and that is all. At the start of the project the contractor performs test sections to develop and document the successfulness of a specified compaction operation. If there is no faith put into accepting that this documented compaction method yields satisfactory results, then why is it required? If the same effort/method is used on every lift backfilling pipe within a trench box and satisfactory results are being obtained, then why all the testing each time the trench box is moved? If at ANY time during compaction operations the VT technician feels that the specifications are not being met, they have the authority to perform an Independent Verification test. Is the true purpose of QC and VT testing to have documented test results which meet the specifications or is it to control a process to achieve a quality product?

 If it takes several days for a contractor to install the pipe between structures and QC acceptance tests and Verification tests are randomly performed at 1 test per lift between the structures, “Process control tests” can be performed on a daily basis to insure the continued effectiveness of the compaction method established. This does not mean testing every lift, but throughout the day running a few random tests. If desired by the Department, these tests could be recorded in the density logbook as process control. The use of IV tests would insure the effectiveness of the PC testing. If it is found that there are a number of PC tests which are not meeting the specifications, then the contractor should adjust the compaction process and increase the frequency of PC testing until consistent satisfactory results are being achieved. Additionally the frequency of IV testing should also be increased until the CEI/Department is satisfied that the specifications are being met. 

It is also recommended that the Department clarify their intent with respect to QC/VT testing frequency when multiple crews are working in several areas.  

The Department should also clarify how to handle the sampling of stockpiled materials for isolated area construction. As there is little variability in consistency in a well maintained stockpile, the test data from a single sample should be applicable for several isolated areas. For example: If in a roadway section consisting of 3 lanes with two 10’ shoulders is stabilized full width in a single operation, the area represented by a single proctor/LBR sample is 3111 SY per 500’ LOT. Therefore if  3111 SY of turn lanes or other isolated areas are constructed with material from a stockpile, 1 sample should be sufficient for all these areas.