2400 33RD ST GEOTECHNICAL INVESTIGATION 2018-01-02 MF Import

NCE used a 10-ton subtraction piezocone manufactured by the Hogentogler Company, Columbia, Maryland. Thr. serial number of the cone was TC497 and was factory calibrated. The cone measures tip resistance (0 to 1000 tons / square -foot (tsf)), sleeve friction resistance (0 to 10 tsf), pore pressure (0 to 500 pounds / square inch (psi)) and inclination (-I-/- 10 degrees). Stated accuracies for the tip, sleeve, pore and inclination readings are plus or minus 1 tsf, .02 tsf, 5 psi and 2 degrees respectively. In practice, NCE has found the accuracy of the instrument to be much better than the manufacturer's data. The field exploration was performed in the roadway areas and over the non -paved areas of the site. The cone penetrometer probes were advanced or pushed from the ground surface or through a cored hole in the pavement section. 'Thickness of the pavement cores and their locations are presented on Figure A-l. A photo of the cores is presented in Appendix A (photos 4 & 5). The majority of the cone probes were advanced to a depth of 10 feet. In two holes (CPT-1 & 3), the cone was advanced to refusal at the underlying dense glacial soil layer. This depth was 20.5 and 23.6 feet, respectively. In CPT-6, the cone was advanced to 15 feet. At the locations of CPT-10 and CPT-15, the core probe encountered refusal at a shallow depth. At both locations the rig was moved over 5 to 10 feet horizontally and the probe advanced again. This had to be,done three times at the CPT-10 site and only twice at the CPT-15 site. These data are presented in the Appendix as A, B or C probes of their respective number. The printout of the depth reached indictes the obstruction depth. Also, CPT-B was not advanced through the core He deeper then 5 feet due to an obstruction. Since this site was through existing pavement, it could not be moved over. The cone logs are presented in Appendix B for the site and Appendix C for the probes through the pavement core holes. Appendix D presents the data from the pore pressure dissipation test performed in cone probe CPT-E. Conclusions with Comment The following are conclusions with comment based on the new data and analyses. • The results of the probes indicate that the upper 18 to 24 inches of soil at the site is dense and capable of supporting a heavy pavement section. This is also the case beneath the existing pavement sections. • Beneath the upper 18 to 24 inches of firm soil is a softer, weaker fine-grained soil. This is nearly universal over the entire area in question. • The onsite soils do not drain downward. The soft fine-grained material has a low permeability. • The existing pavement sections are performing well based on the current traffic. Smith Avenue has 8 inches of asphalt concrete over. 18 to 24 inches of compacted granular soil. It appears to be performing well. The 4 inches of asphalt observed on the side streets of 32nd and 33"I also appears to be appropriate for the traffic currently operating on them. • To achieve proper grade in design, we understand that the upper 18 to 24 inches of soil or more must be remove. This results in the construction a' - Gcotechnica1, Tunnel and Environmental Engineers Phone (425) 869-5778 nellewe, WA 98005 )'.age 2 ) 3n80 1 Air Fax (425 861-0677