3800 RIVERFRONT BLVD Geotech Report 2023-05-04

March 26, 2019 HWA Project No. 2015-061-21 Task 600-7 Ibackfilled, we recommend that all disturbed soil be removed from the roadway alignment. Upon removal of the disturbed soil, the roadway alignment should be proof rolled with a fully loaded dump truck. Observed soft spots should be excavated down to firm soil and backfilled with ICSBC compacted as structural fill. Alternatively, if soft soils extend greater than 12 inches into subgrade soil the upper 12 inches of the soft soil subgrade may be over-excavated with a layer of I Mirafi BX120 placed at the base and 12 inches of CSBC placed as structural above it. Another option is to over-excavate subgrades by at least 12 inches and replace the subgrade materials with at least 12 inches of 2 to 4-inch quarry spalls with a separation fabric above it (Mirafi 140N, or Iequivalent). Once the repair of soft spots is completed these areas should be proof rolled again prior to pavement section placement. I4.5.2 Design Traffic Transportation Engineering Northwest provided current anticipated trip generations, consisting I of an Average Daily Traffic(ADT) count of 11,080 for both directions. Our design is based on a 50% split of traffic on the lanes with 2%of the traffic considered heavy traffic. Each heavy vehicle was considered to provide 0.6 Equivalent Single Axel Load (ESAL). IUsing this data, we calculate approximately 970,900 ESAL for a 20-year design life. I The pavement recommendations presented in this report are based on these traffic calculations. If additional traffic count information is obtained that varies appreciably from these values, the recommendations given in this report should be reviewed and revised as necessary. 4.5.3 Pavement Design I Table 3 provides our HMA design recommendations, assuming the traffic loading, and pavement design parameters described above. These pavement designs are based on the design method given in the 1993 AASHTO Design Guide(AASHTO, 1993) using a required AASHTO IStructural Number(SN) of 4.01, as indicated above. Table 3. I Structure Requirements for New HMA Pavement—20-Year Design Life Material Minimum Layer WSDOT Standard Specification Description Thickness IHMA 3 5-04 & 9-02.1 ATB 5 9-03.9(3) ICSBC 12 9-03.9(3) HMA: Hot Mix Asphalt I ATB: Asphalt Treated Base CSBC: Crushed SurfacingBase Course, compacted as specified. p p 1 Geotechnical Report Revision 3 26 2019.doc 19 HWA GEOSCIENCES INC.