Reso 2005-825 - Laserfiche WebLink

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Based on the field investigation, the general subsurface soil profile was found to consist of clean sand, organic sand, silty sand and silt to a depth of 5 to 6 feet below ground surface, where a. layer of dark brown peat was encountered. The peat typically extended to a depth of 7 to 8 feet.. In boring B-5 the peat was only encountered from depths of 5.7 to 6.0 feet below the ground surface. Below the peat we encountered sand and silty sand that extended to the bottom of the shallow borings at 10 feet below grade. In boring B-5 silty sand and silt continued from the bottom of the peat to a depth of 16 feet below ground surface where a weathered limestone layer was encountered that extended to the bottom of the boring at 40 feet below ground surface. In boring B-6 the peat was underlain by sand and silty sand that extended to a depth of 14.5 feet where a second layer of peat was encountered that extended to a depth of 16 feet below ground surface. At 16 feet we again encountered a weathered limestone layer that extended to the bottom of the boring at 40 feet. Detailed information pertaining to the borings is included in the Standard Penetration Test boring records within the appendix. A Dade County Exfiltration Test was also performed as part of the field investigation to determine subsurface drainage conditions. The test indicated a hydraulic conductivity value of 1.22 x 10-4 CFS/SEC-FT HEAD. It should be noted that the upper 5 feet of soil at the site was extremely variable and that a 4 feet thick layer of peat was encountered at a depth of 5 feet at the ex filtration test location. Below the peat, grey sand with shell was encountered. At other locations on the site we encountered silt and silty sand in this same depth range (9 to 15 feet below ground surface), which could result in significantly lower hydraulic conductivity. It appears from the subsurface investigation that reliable drainage conditions can be found in the limestone layer that begins 16 feet below grade. The groundwater table was encountered at depths ranging from 3.5 feet to 5.0 feet below the existing ground surface at the time of the borings. Fluctuations in the groundwater table can be expected due to changes in ground surface elevation, seasonal rainfall, surface runoff, construction operations, and other site-specific occurrences. Please note that the subsurface conditions may vary outside ofthe boring locations. In the event subsurface conditions other than those presented in this report are encountered during construction, please contact our office so that our evaluation may be reviewed. Engineering Evaluation Once the samples obtained in the field investigation were returned to the laboratory, a geotechnical engineer visually classified the samples. Based on our visual classification, the site subsurface soils may be classified as SP (poorly graded sand), OP (poorly graded gravel), SP-SM (silty sand), ML (low plasticity silt) and PT (peat). The relative density ofthe soils encountered above the limestone was very loose in all of the borings except B-1 with Standard Penetration "N" values ranging from 1 to 3 blows per foot. In boring B-1 the relative density of the soil above the limestone was loose with Standard Penetration ''N' values of 7 blows per foot. The relative density of the limestone layer that was encountered below 16 feet depth was typically medium dense with some areas that were loose or very dense. This variation of relative density within the 1 imestone layer is common in weathered 1 imestone formations. The variations are 555 Sawgrass Corporate Parkway' Sunrise, Florida 33325. (954) 835-9055' FAX (954) 835-9044 n LJ n (u~ n LJ n u n u n u n LJ n LJ II u h u n LJ n u n L-J II LJ n u n LJ n ~. n ~~ LJ