HomeMy WebLinkAboutCDP 12-04; ARMY NAVY ATHLETIC FIELD; FINAL SOILS REPORT; 2018-09-13September 13, 2018
Army and Navy Academy
2605 Carlsbad Boulevard
Carlsbad, California 92008
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CHRJSTIAN WHEELER_
ENGINEER_ING
Attention: James C. Callaghan, Constmction Manager
Subject: NCTD Storm Drain Compaction Report
CWE 2180204.01
Athletic Facility, Army Navy Academy, 2605 Carlsbad Boulevard, Carlsbad, CA
Reference: Cluistian Wheeler Engineering, "As-Graded Geotechnical Report", Proposed Athletic Field
Improvements (Report 2120311.17), dated October 4, 2013.
Ladies & Gentlemen:
In accordance with your request, Cluistian Wheeler Engineering has prepared tlus report to summarize tl1e
results of tests conducted in the areas to support a catch basin and culver on the northern side of tl1e athletic
field and tl1e clean out area located at the southern end of tl1e storm drain line at the subject site. The backfill
associated with tlus storm drain line connecting these components was previously obse1ved and tested, and
was summarized under separate cover (C\v'E 2120311.17). Our geotechnical se1vices were coordinated by
Turner Construction, and were provided on April 12, August 31 and September 6, 2018.
In order to assist in our understanding of the designed configuration of the storm drain trench line, our firm
was provided witl1 grading and erosion control plan for the site area prepared by Hofman Planning &
Engineering, bearing an approval date from the City of Carlsbad of March 26, 2013. Plate Nos. 1 and 2 of
tlus report are a reproduction of sheets 7 and 8, modified to show tl1e approximate locations of our field
tests.
FIELD OBSERVATIONS
Our field observations began on April 12, 2018 with a representative from our firm on-site to observe tl1e
bottom of tl1e excavations in the areas to support the catch basin and culver on the northern side of tl1e
athletic field. Due to saturated soil conditions, Mirafi HP570 stabilization fabric was placed at the bottom of
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CWE 2180204.01 September 13, 2018 Page 2
the excavation and cmshed rock was placed above the fabric to bottom of pipe elevation. Prior to placing the
stabilization fabric, the saturated soils were removed. Soils exposed at the bottom of the excavations
consisted of competent old paralic deposits.
Subsequently, backfills soils were placed in the areas to support the catch basin and culver on tl1e nortl1ern
side of the atliletic field and the clean out area located at the southern end of the stonn drain line. Our firm
was not contacted to provided observations and testing se1vices during tl1e placement of tl1e backfills.
During our site visit on August 31, 2018, testing was performed at the finished grade elevation in these areas.
The testing in the clean out area located at tl1e soutl1ern end of the storm drain line indicated least 90 percent
relative compaction. However, tests performed in the area of tl1e catch basin and tl1e storm drain box,
indicated relative compaction less than 90 percent and ve1y low moisture content. It was recommended that
the backfill soils to be removed and replaced as properly compacted fill.
The previously placed backfills in the area of the catch basin and tl1e storm drain box were removed down to
about 2 to 3 feet below existing surface, which left about 8 to 12 inches of soil in place. These soils exposed
at tl1e bottom of the excavation were moisture conditioned and compacted. Backfills were typically placed by
the skidsteer in relatively tliin, uniform lifts. Moisture-conditioning was applied as needed and compactive
efforts were tl1en performed by means of a manually operated reciprocating compactor to attain at least 90
percent of ma..ximum d1y density. The locations of our field testing are shown on Plate Nos. 1 and 2.
LABORATORY AND FIELD TESTING
The maximum d1y density and optimum moisture content of the soils predominantly encountered in the
earthwork were determined in our laborato1y in accordance witl1 ASTM D1557, "Test Method for
Laborat01y Compaction Characteristics of Soil Using Modified Effort." The tests were conducted in
accordance with the methodology prescribed for the grain-size distribution of the soils tested. The results of
tl1ese tests are presented on Table I in Appendix A.
Field tests to measure tl1e in-place density and moisture content of tl1e storm drain backfills were conducted
' in accordance with ASTM D6938, "Standard Test Metl1ods for Density of Soil and Soil-Aggregate in Place by
Nuclear Methods." The locations of the field tests were selected by our technician in areas discerned to
exhibit compaction tliat was generally representative of tl1at attained in tl1e fill. The results and approximate
locations of the field tests are shown on Table II in Appendix A.
Appendix A
Test Results
CWE 2180204.01 September 13, 2018 .Appendix A, Page A-1
TABLE I: SUMMARY OF OPTIMUM MOISTURE & MAXIMUM DENSITY TEST RESULTS (ASTM D1557)
Soil Description Optimum Moisture MaximUD1D.ty
Type (%) Density (pcf)
1 Dark Brown, Silty Sand with Gravel 9.6 126.4
TABLE II: SUMMARY OF FIELD IN-PLACE DENSITY TEST RESULTS (ASTM D6938) -STORM DRAIN
Field Field Max. Rel Test Date Location Elev. Soil Moisture Dry Density Comp. No. (feet) Type (%) Density (pcf) (%) (pcf)
SD1 8/31/2018 Storm Drain, Clean Out 39.0 1 10.2 114.9 126.4 90.9
SD2 8/31/2018 Storm Drain, Catch Basin & Culvert 33.0 1 3.0 107.1 126.4 84.7
SD3 9/6/2018 Storm Drain, Catch Basin & Culvert 31.0 1 12.2 114.8 126.4 90.8
SD4 9/6/2018 Retest SD2 33.0 1 10.7 114.5 126.4 90.6