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HomeMy WebLinkAboutR-422904A PORTION OF THE NW 1/4 OF SECTION 19, TOWNSHIP 23 NORTH, RANGE 5 EAST, W.M., KING COUNTY, WASHINGTON rn N Nt W w m z J GEOTECHNICAL ENGINEERING NOTES THE FOLLOWING IS EXCERPTED FROM SECTION 4.0 OF THE GEOTECHNICAL ENGINEERING REPORT PREPARED BY MIGIZI GROUP, PROJECT PP2411-T21, DATED 7/8/21 4.0 CONCLUSIONS AND RECOMMENDATIONS IMPROVEMENT PLANS INVOLVE THE CONSTRUCTION OF A NEW 4,560-SF SERVICE BAT EXPANSION TOWARDS THE SOUTHWEST CORNER OF THE EXISTING GMC MASONRY BUILDING, THE CLEARING/STRIPPING/GRADING OF PROPERTIES IMMEDIATELY EAST OF THE BROTHERTON GMC FACILITY, AND THE CONSTRUCTION OF A NEW BROTHERTON CADILLAC COMPLEX, WHICH WILL LARGELY BE OCCUPIED BY A NEW 14,330-SF CADILLAC SHOWROOM/SALES BUILDING, AND ASPHALT PAVEMENTS. SITE PRODUCED STORMWATER WILL BE RETAINED ONSITE IF FEASIBLE. WE OFFER THESE RECOMMENDATIONS: • FEASIBILITY: BASED ON OUR FIELD EXPLORATIONS, RESEARCH, AND EVALUATIONS, THE PROPOSED STRUCTURES AND PAVEMENTS APPEAR FEASIBLE FROM A GEOTECHNICAL STANDPOINT. • FOUNDATION OPTIONS: OVER -EXCAVATION OF SPREAD FOOTING SUBGRADES, TO A DEPTH OF 3 TO 4 FEET, AND THE CONSTRUCTION OF STRUCTURAL FILL BEARING PADS, WILL BE NECESSARY FOR FOUNDATION SUPPORT OF NEW STRUCTURES. IF FOUNDATION CONSTRUCTION OCCURS DURING WET CONDITIONS, IT IS LIKELY THAT A A GEOTEXTILE FABRIC, PLACED BETWEEN BEARING PADS AND NATIVE SOILS, WILL ALSO BE NECESSARY. • FLOOR OPTIONS: WE RECOMMEND OVER -EXCAVATION OF SLAB -ON -GRADE FLOOR SUBGRADES TO A MINIMUM DEPTH OF 1Y2 FEET, THEN PLACEMENT OF PROPERLY COMPACTED STRUCTURAL FILL AS A FLOOR SUBBASE. IF FLOOR CONSTRUCTION OCCURS DURING WET CONDITIONS, IT IS LIKELY THAT A GEOTEXTILE FABRIC, PLACED BETWEEN THE STRUCTURAL FILL FLOOR SUBBASE AND NATIVE SOILS, WILL BE NECESSARY. RECOMMENDATION FOR SLAB -ON -GRADE FLOORS ARE INCLUDED IN SECTION 4.3 FILL UNDERLYING FLOOR SLABS SHOULD BE COMPACTED TO 95 PERCENT (ASTM:D-1557) • PAVEMENT SECTIONS: WE RECOMMEND OVER -EXCAVATION OF PAVEMENT SUBRADES TO A MINIMUM DEPTH OF 12 INCHES, THEN PLACEMENT OF PROPERLY COMPACTED STRUCTURAL FILL AS PAVEMENT SUBBASE. WE RECOMMEND A CONVENTIONAL PAVEMENT SECTION COMPRISED OF AN ASPHALT CONCRETE PAVEMENT OVER A CRUSHED ROCK BASE COURSE OVER A PROPERLY PREPARED (COMPACTED) SUBGRADE OR A GRANULAR SUBBASE. ALL SOIL SUBGRADES SHOULD BE THOROUGHLY COMPACTED, THEN PROOF -ROLLED WITH A LOADED DUMP TRUCK OR HEAVY COMPACTOR. ANY LOCALIZED ZONES OF YIELDING SUBGRADE DISCLOSED DURING THIS PROOF -ROLLING OPERATION SHOULD BE OVER EXCAVATED TO A DEPTH OF 2 FEET AND REPLACED WITH A SUITABLE STRUCTURAL FILL MATERIAL. • INFILTRATION CONDITIONS: AS INDICATES IN THE SOIL CONDITIONS SECTION OF THE REPORT, THE SITE IS UNDERLAIN BY ALLUVIAL SOILS, WHICH CAN BE READILY SUBDIVIDED INTO FOUR SOIL HORIZONS: UPPER FINE-GRAINED, INTERMEDIATE GRAVEL, INTERMEDIATE FINE-GRAINED, AND DEEP GRAVELS. GIVEN THE FACT THAT GROUNDWATER LEVELS RISE HIGHER THAN 8Y2 FEET BELOW EXISTING GRADE, THE UPPER FINE-GRAINED SOIL HORIZON IS THE ONLY HORIZON WHICH COULD POTENTIALLY SUPPORT INFILTRATION. THIS MATERIAL RANGES IN COMPOSITIONS FROM SILTY SAND TO SILT, THE LATTER OF WHICH SHOULD BE CONSIDERED RELATIVELY IMPERMEABLE. GIVEN THE HYDROGEOLOGIC SETTING OF THE PROJECT AREA, WE DO NOT INTERPRET INFILTRATION AS BEING FEASIBLE FOR THIS PROJECT, AND SITE PRODUCED STORMWATER SHOULD BE MANAGED THROUGH DETENTION, OR DIVERTED TO AN EXISTING [STRUCTURE] ALONG SW 12TH ST. THE FOLLOWING SECTIONS OF THIS REPORT PRESENT OUR SPECIFIC GEOTECHNICAL CONCLUSIONS AND RECOMMENDATIONS CONCERNING SITE PREPARATION, SPREAD FOOTINGS, SLAB -ON -GRADE FLOORS, SUBGRADE AND RETAINING WALLS, ASPHALT PAVEMENT, AND STRUCTURAL FILL. THE WASHINGTON STATE DEPARTMENT OF TRANSPORTATION (WSDOT) STANDARD SPECIFICATIONS AND STANDARD PLANS CITED HEREIN REFER TO WSDOT PUBLICATIONS M41-10, STANDARD SPECIFICATIONS FOR ROAD, BRIDGE, AND MUNICIPAL CONSTRUCTION, AND M21-01, STANDARD PLANS FOR ROAD, BRIDGE, AND MUNICIPAL CONSTRUCTION, RESPECTIVELY. 4.1 SITE PREPARATION PREPARATION OF THE PROJECT SITE SHOULD INVOLVE EROSION CONTROL, TEMPORARY DRAINAGE, CLEARING, STRIPPING, EXCAVATIONS, CUTTING, SUBGRADE COMPACTION, AND FILLING. EROSION CONTROL: BEFORE NEW CONSTRUCTION BEGINS, AN APPROPRIATE EROSION CONTROL SYSTEM SHOULD BE INSTALLED. THIS SYSTEM SHOULD COLLECT AND FILTER ALL SURFACE WATER RUNOFF THROUGH SILT FENCING. WE ANTICIPATE A SYSTEM OF BERMS AND DRAINAGE DITCHES AROUND CONSTRUCTION AREAS WILL PROVIDE AN ADEQUATE COLLECTION SYSTEM. SILT FENCING FABRIC SHOULD MEET THE REQUIREMENTS OF WSDOT STANDARD SPECIFICATION 9-33.2 TABLE 6. IN ADDITION, SILT FENCING SHOULD EMBED A MINIMUM OF 6 INCHES BELOW EXISTING GRADE. AN EROSION CONTROL SYSTEM REQUIRES OCCASIONAL OBSERVATION AND MAINTENANCE. SPECIFICALLY, HOLES IN THE FILTER AND AREAS WHERE THE FILTER HAS SHIFTED ABOVE GROUND SURFACE SHOULD BE REPLACED OR REPAIRED AS SOON AS THEY ARE IDENTIFIED. TEMPORARY DRAINAGE: WE RECOMMEND INTERCEPTING AND DIVERTING ANY POTENTIAL SOURCES OF SURFACE OR NEAR -SURFACE WATER WITHIN THE CONSTRUCTION ZONES BEFORE STRIPPING BEGINS. BECAUSE THE SELECTION OF AN APPROPRIATE DRAINAGE SYSTEM WILL DEPEND ON THE WATER QUANTITY, SEASON, WEATHER CONDITIONS, CONSTRUCTION SEQUENCE, AND CONTRACTOR'S METHODS, FINAL DECISIONS REGARDING DRAINAGE SYSTEMS ARE BEST MADE IN THE FIELD AT THE TIME OF CONSTRUCTION. BASED ON OUR CURRENT UNDERSTANDING OF THE CONSTRUCTION PLANS, SURFACE AND SUBSURFACE CONDITIONS, WE ANTICIPATE THAT CURBS, BERMS, OR DITCHES PLACED AROUND THE WORK AREAS WILL ADEQUATELY INTERCEPT SURFACE WATER RUNOFF. CLEARING AND STRIPPING: AFTER SURFACE AND NEAR -SURFACE WATER SOURCES HAVE BEEN CONTROLLED, SOD, TOPSOIL, AND ROOT -RICH SOIL SHOULD BE STRIPPED FROM THE SITE. OUR SUBSURFACE EXPLORATIONS INDICATE THAT THERE ARE MINIMAL ORGANIC SOILS ONSITE BELOW THE ASPHALT PAVEMENT IN THE VICINITY OF THE PROPOSED SERVICE BAY ADDITION BUT REACHES THICKNESS OF UPWARDS OF 12 INCHES IN THE VICINITY OF THE NEW BROTHERTON CADILLAC COMPOUND. STRIPPING IS BEST PERFORMED DURING A PERIOD OF DRY WEATHER. SITE EXCAVATIONS: BASED ON OUR EXPLORATIONS, WE EXPECT THAT THE VAST MAJORITY OF PROJECT EXCAVATIONS WILL ENCOUNTER POORLY CONSOLIDATED FINE-GRAINED ALLUVIAL SOILS, WHICH CAN BE READILY EXCAVATED USING STANDARD EXCAVATION EQUIPMENT. DEWATERING: OUR EXPLORATIONS ENCOUNTERED GROUNDWATER IN EVERY SUBSURFACE BORING AT A DEPTH OF APPROXIMATELY 8Y2 FEET BELOW THE SURFACE. WE ANTICIPATE THAT AN INTERNAL SYSTEM OF DITCHES, SUMP HOLES, AND PUMPS WILL BE ADEQUATE TO TEMPORARILY DEWATER SHALLOW EXCAVATIONS. IN ORDER TO DEWATER DEEPER EXPLORATIONS BELOW THE REGIONAL WATER TABLE, EXPENSIVE DEWATERING EQUIPMENT, SUCH AS WELL POINTS WILL NEED TO BE UTILIZED.. TEMPORARY CUT SLOPES: AT THIS TIME, FINAL DESIGNS AND CONSTRUCTION SEQUENCING HAVE NOT BEEN COMPLETED TO FACILITATE PROJECT PLANNING WE PROVIDE THE FOLLOWING GENERAL COMMENTS REGARDING TEMPORARY SLOPES: • ALL TEMPORARY SOIL SLOPES ASSOCIATED WITH SITE CUTTING OR EXCAVATIONS SHOULD BE ADEQUATELY INCLINED TO PREVENT SLOUGHING AND COLLAPSE, • TEMPORARY CUT SLOPES IN SITE SOILS SHOULD BE NO STEEPER THAN 1Y2H:1V, AND • TEMPORARY SLOPES SHOULD CONFORM TO WASHINGTON INDUSTRIAL SAFETY AND HEALTH ACT (WISHA) REGULATIONS THESE GENERAL GUIDELINES ARE NECESSARILY SOMEWHAT CONSERVATIVE (STEEPER TEMPORARY SLOPES MAY BE POSSIBLE). AS THE PROJECT PROGRESSES, TEMPORARY GRADING PLANS ARE DEVELOPED, FINAL SITE FEATURES ARE BETTER DEFINED, AND A CONTRACTOR IS ENGAGED, MGI MAY MODIFY THESE GENERAL GUIDELINES TO ALLOW STEEPER SLOPES. SUBGRADE COMPACTION: EXPOSED SUBGRADES FOR THE FOUNDATIONS OF THE PLANNED ADDITIONS SHOULD BE COMPACTED TO A FIRM, UNYIELDING STATE BEFORE NEW CONCRETE OR FILL SOILS ARE PLACED. ANY LOCALIZED ZONES OF LOOSER GRANULAR SOILS OBSERVED WITHIN A SUBGRADE SHOULD BE COMPACTED TO A DENSITY COMMENSURATE WITH THE SURROUNDING SOILS. IN CONTRAST, ANY ORGANIC, SOFT, OR PUMPING SOILS OBSERVED WITHIN A SUBGRADE SHOULD BE OVEREXCAVATED AND REPLACED WITH A SUITABLE STRUCTURAL FILL MATERIAL. SITE FILLING: OUR CONCLUSIONS REGARDING THE REUSE OF ONSITE SOILS AND OUR COMMENTS REGARDING WET -WEATHER FILLING ARE PRESENTED SUBSEQUENTLY. REGARDLESS OF SOIL TYPE, ALL FILL SHOULD BE PLACED AND COMPACTED ACCORDING TO OUR RECOMMENDATIONS PRESENTED IN THE STRUCTURAL FILL SECTION OF THIS REPORT. SPECIFICALLY, BUILDING PAD FILL SOIL SHOULD BE COMPACTED TO A UNIFORM DENSITY OF AT LEAST 95 PERCENT (BASED ON ASTM: D-1557). ONSITE SOILS: WE OFFER THE FOLLOWING EVALUATION OF THESE ONSITE SOILS IN RELATION TO POTENTIAL USE AS STRUCTURAL FILL: • ALLUVIAL SILT AND SILTY SAND: THE ALLUVIAL SILTY SAND THAT UNDERLIES THE SITE IS VERY MOISTURE SENSITIVE AND WILL BE DIFFICULT OR IMPOSSIBLE TO REUSE DURING MOST WEATHER CONDITIONS. IT IS CURRENTLY ABOVE THE OPTIMUM MOISTURE CONTENT AND WILL NOT COMPACT ADEQUATELY UNLESS AERATED. REUSE IS NOT RECOMMENDED, AND THIS MATERIAL SHOULD ONLY BE USED FOR NON-STRUCTURAL PURPOSES, SUCH AS IN LANDSCAPING AREAS. • ALLUVIAL GRAVEL: ENCOUNTERED AT INTERMEDIATE AND SIGNIFICANT DEPTHS BELOW GROUND SURFACE, THIS MATERIAL IS INTERBEDDED WITH ITS MORE FINE-GRAINED COUNTERPART. GRAVELLY SOILS WHICH UNDERLIE THE SITE ARE RELATIVELY IMPERVIOUS TO MOISTURE CONTENT VARIATIONS AND CAN BE REUSED AS STRUCTURAL FILL UNDER MOST WEATHER CONDITIONS. PERMANENT SLOPES: ALL PERMANENT CUT SLOPES AND FILL SLOPES SHOULD BE ADEQUATELY INCLINED TO REDUCE LONG-TERM RAVELING, SLOUGHING, AND EROSION. WE GENERALLY RECOMMEND THAT NO PERMANENT SLOPES BE STEEPER THAN 2H:1V. FOR ALL SOIL TYPES, THE USE OF FLATTER SLOPES (SUCH AS 21/H:1V) WOULD FURTHER REDUCE LONG-TERM EROSION AND FACILITATE REVEGETATION. SLOPE PROTECTION: WE RECOMMEND THAT A PERMANENT BERM, SWALE, OR CURB BE CONSTRUCTED ALONG THE TOP EDGE OF ALL PERMANENT SLOPES TO INTERCEPT SURFACE FLOW. ALSO, A HARDY VEGETATIVE GROUNDCOVER SHOULD BE ESTABLISHED AS SOON AS FEASIBLE, TO FURTHER PROTECT THE SLOPES FROM RUNOFF WATER EROSION. ALTERNATIVELY, PERMANENT SLOPES COULD BE ARMORED WITH QUARRY SPALLS OR A GEOSYNTHETIC EROSION MAT. 4.2 SPREAD FOOTING IN OUR OPINION, CONVENTIONAL SPREAD FOOTINGS WILL PROVIDE ADEQUATE SUPPORT FOR THE PROPOSED STRUCTURES IF THE SUBGRADE IS PROPERLY PREPARED. WE OFFER THE FOLLOWING COMMENTS AND RECOMMENDATIONS FOR SPREAD FOOTING DESIGN. FOOTING DEPTHS AND WIDTHS: FOR FROST AND EROSION PROTECTION, THE BASES OF ALL EXTERIOR FOOTINGS SHOULD BEAR AT LEAST 18 INCHES BELOW ADJACENT OUTSIDE GRADES, WHEREAS THE BASES OF INTERIOR FOOTINGS NEED BEAR ONLY 12 INCHES BELOW THE SURROUNDING SLAB SURFACE LEVEL. TO REDUCE COST -CONSTRUCTION SETTLEMENTS, CONTINUOUS (WALL) AND ISOLATED (COLUMN- FOOTINGS SHOULD BE AT LEAST 16 TO 24 INCHES. BEARINGS AND SUBGRADES: GIVEN THE POOR CONSOLIDATION OF NEAR SURFACE SOIL DEPOSITS IN THE VICINITY OF THE PROJECT AREA, STRUCTURAL FILL BEARING PADS, 3 TO 4 FEET THICK AND COMPACTED TO A DENSITY OF AT LEAST 95 PERCENT (BASED ON ASTM:D-1557), SHOULD UNDERLIE SPREAD FOOTINGS ON THIS SITE. IF FOUNDATION CONSTRUCTION OCCURS DURING WET CONDITIONS, IT IS POSSIBLE THAT A GEOTEXTILE FABRIC, PLACED BETWEEN THE BEARING PAD NATIVE SOILS, WILL BE NECESSARY. WE SHOULD BE CONSULTED IF ANY NEW FOUNDATIONS ARE TO BE PLACED ADJACENT TO EXISTING FOUNDATIONS. IN GENERAL, BEFORE FOOTING CONCRETE IS PLACED, ANY LOCALIZED ZONES OF LOOSE SOILS EXPOSED ACROSS FOOTING SUBGRADES SHOULD BE COMPACTED TO A FIRM, UNYIELDING CONDITION, AND ANY LOCALIZED ZONES OF SOFT, ORGANIC, OR DEBRIS -LADEN SOILS SHOULD BE OVER -EXCAVATED AND REPLACED WITH SUITABLE STRUCTURAL FILL. LATERAL OVEREXCAVATIONS: BECAUSE FOUNDATION STRESSES ARE TRANSFERRED OUTWARD AS WELL AS DOWNWARD INTO THE BEARING SOILS, ALL STRUCTURAL FILL PLACED UNDER FOOTINGS, SHOULD EXTEND HORIZONTALLY OUTWARD FROM THE EDGE OF EACH FOOTING. THIS HORIZONTAL DISTANCE SHOULD BE EQUAL TO THE DEPTH OF PLACED FILL. THEREFOR, PLACED FILL THAT EXTENDS 3 FEET BELOW THE FOOTING BASE SHOULD ALSO EXTEND 3 FEET OUTWARD FROM THE FOOTING EDGES. SUBGRADE OBSERVATION: ALL FOOTING SUBGRADES SHOULD CONSIST OF FIRM, UNYIELDING, NATIVE SOILS, OR STRUCTURAL FILL MATERIALS THAT HAVE BEEN COMPACTED TO A DENSITY OF AT LEAST 95 PERCENT (BASED ON ASTM:D-1557). FOOTINGS SHOULD NEVER BE CAST ATOP LOOSE, SOFT, OR FROZEN SOIL, SLOUGH, DEBRIS, EXISTING UNCONTROLLED FILL, OR SURFACES COVERED BY STANDING WATER. BEARING PRESSURES: IN OUR OPINION, FOR STATIC LOADING, FOOTINGS THAT BEAR ON PROPERLY PREPARED, STRUCTURAL FILL BEARING PADS 3 FEET THICK CAN BE DESIGNED FOR AN ALLOWABLE SOIL BEARING PRESSURE OF 1,500 PSF, AND FOOTINGS THAT BEAR ON PROPERLY PREPARED, STRUCTURAL FILL BEARING PADS 4 FEET THICK CAN BE DESIGNED FOR AN ALLOWABLE SOIL BEARING PRESSURE OF 2,000 PSF. A ONE-THIRD INCREASE IN ALLOWABLE SOIL BEARING CAPACITY MAY BE USED FOR SHORT-TERM LOADS CREATED BY SEISMIC OR WIND RELATED ACTIVITIES. FOOTING SETTLEMENTS: ASSUMING THAT STRUCTURAL FILL SOILS ARE COMPACTED TO A MEDIUM DENSE OR DENSER STATE, WE ESTIMATE THAT TOTAL POST -CONSTRUCTION SETTLEMENTS OF PROPERLY DESIGNED FOOTING BEARING ON PROPERLY PREPARED SUBGRADES WILL NOT EXCEED 1 INCH. DIFFERENTIAL SETTLEMENTS FOR COMPARABLY LOADED ELEMENTS MAY APPROACH ONE-HALF OF THE ACTUAL TOTAL SETTLEMENT OVER HORIZONTAL DISTANCES OF APPROXIMATELY 50 FEET. LATERAL RESISTANCE: FOOTING THAT HAVE BEEN PROPERLY BACKFILLED AS RECOMMENDED ABOVE WILL RESIST LATERAL MOVEMENTS BY MEANS OF PASSIVE EARTH PRESSURE AND BASE FRICTION. WE RECOMMEND USING AN ALLOWABLE PASSIVE EARTH PRESSURE OF 225PSF AND AN ALLOWABLE BASE FRICTION COEFFICIENT OF 0.35 FOR SITE SOILS. 4.3 SLAB -ON -GRADE FLOORS IN OUR OPINION, A SOIL -SUPPORTED SLAB -ON -GRADE FLOORS CAN BE USED FOR THE PLANNED STRUCTURES IF THE SUBGRADES ARE PROPERLY PREPARED. WE OFF THE FOLLOWING COMMENTS AND RECOMMENDATIONS CONCERNING SLAB -ON -GRADE FLOORS. FLOOR SUBBASE: GIVEN THE POOR CONSOLIDATION OF NEAR SURFACE SOIL DEPOSITS IN THE VICINITY OF THE PROJECT AREA, WE RECOMMEND OVER -EXCAVATION OF SLAB -ON -GRADE FLOOR • Call 811 • ® two business days before you dig NO. REVISION SUBGRADES TO A MINIMUM DEPTH OF 1Y2 FEET, THEN PLACEMENT OF PROPERLY COMPACTED STRUCTURAL FILL AS A FLOOR SUBBASE. IF FLOOR CONSTRUCTION OCCURS DURING WET CONDITIONS, IT IS LIKELY THAT A GEOTEXTILE FABRIC, PLACED BETWEEN THE STRUCTURAL FILL FLOOR SUBBASE AND NATIVE SOILS, WILL BE NECESSARY. AL SUBBASE FILL SHOULD BE COMPACTED TO A DENSITY OF AT LEAST 95 PERCENT (BASED ON ASTM:D-1557). CAPILLARY BREAK AND VAPOR BARRIER: TO RETARD THE UPWARD WICKING OF MOISTURE BENEATH THE FLOOR SLAB, WE RECOMMEND THAT A CAPILLARY BREAK BE PLACED OVER THE SUBGRADE. IDEALLY, THIS CAPILLARY BREAK WOULD CONSIST OF A 4-INCH-THICK LATER OF PEA GRAVEL OR OTHER CLEAN, UNIFORM, WELL-ROUNDED GRAVEL, SUCH AS "GRAVEL BACKFILL FOR DRAINS" PER WSDOT STANDARD SPECIFICATION 9-03.12(4), BUT CLEAN ANGULAR GRAVEL CAN BE USED IF IT ADEQUATELY PREVENTS CAPILLARY WICKING. IN ADDITION, A LAYER OF PLASTIC SHEETING (SUCH AS CROSSTUFF, VISQUEEN, OR MOISTOP) SHOULD BE PLACED OVER THE CAPILLARY BREAK TO SERVE AS A VAPOR BARRIER. DURING SUBSEQUENT CASTING OF THE CONCRETE SLAB, THE CONTRACTOR SHOULD EXERCISE CARE TO AVOID PUNCTURING THE VAPOR BARRIER. 4.4 SUBGRADE AND RETAINING WALLS THE FOLLOWING GENERAL RECOMMENDATIONS SHOULD BE APPLIED TO THE DESIGN OF SUBGRADE AND RETAINING WALLS. WALL FOUNDATIONS: SUBGRADE AND RETAINING WALL FOUNDATIONS SHOULD BE DESIGNED ACCORDING TO THE RECOMMENDATIONS PRESENTED FOR SPREAD FOOTINGS IN SECTION 4.2. WALL DRAINAGE: DRAINAGE SHOULD BE PROVIDED BEHIND SUBGRADE AND RETAINING WALLS BY PLACING A ZONE OF DRAIN ROCK CONTAINING LESS THAN 3 PERCENT FINES (MATERIAL PASSING THE NO. 200 SIEVE) AGAINST THE WALL. THIS DRAINAGE ZONE SHOULD BE AT LEAST 24 INCHES WIDE (MEASURED HORIZONTALLY) AND EXTEND FROM THE BASE OF THE WALL TO WITHIN 1 FOOT OF THE FINISHED GRADE BEHIND THE WALL. SMOOTH -WALLED PERFORATED PVC DRAINPIPE HAVING A MINIMUM DIAMETER OF 4 INCHES SHOULD BE EMBEDDED WITHIN THE SAND AND GRAVEL AT THE BASE OF THE WALL ALONG ITS ENTIRE LENGTH. THIS DRAINPIPE SHOULD DISCHARGE INTO A TIGHT LINE LEADING TO AN APPROPRIATE COLLECTION AND DISPOSAL SYSTEM. BACKFILL SOIL: IDEALLY, ALL SUBGRADE WALL BACKFILL WOULD CONSIST OF CLEAN, FREE -DRAINING, GRANULAR MATERIAL, SUCH AS "GRAVEL BACKFILL FOR WALLS" PER WSDOT STANDARD SPECIFICATION 9-03.12(2). A GEOTEXTILE SHOULD BE PLACED BETWEEN THE DRAINAGE ZONE AND THE BACKFILL SOIL TO PREVENT DRAIN CLOGGING. BACKFILL COMPACTION: BECAUSE SOIL COMPACTORS PLACE SIGNIFICANT LATERAL PRESSURES ON SUBGRADE WALLS, WE RECOMMEND THAT ONLY SMALL, HAND -OPERATED COMPACTION EQUIPMENT BE USED WITHIN 2 FEET OF A BACKFILLED WALL. ALSO, ALL BACKFILL SHOULD BE COMPACTED TO A DENSITY AS CLOSE AS POSSIBLE TO 90 PERCENT OF THE MAXIMUM DRY DENSITY (BASED ON ASTM:D-1557); A GREATER DEGREE OF COMPACTION CLOSELY BEHIND THE WALL WOULD INCREASE THE LATERAL EARTH PRESSURE, WHEREAS A LESSER DEGREE OF COMPACTION MIGHT LEAD TO EXCESSIVE POST -CONSTRUCTION SETTLEMENTS. GRADING AND CAPPING: TO RETARD THE INFILTRATION OF SURFACE WATER INTO THE BACKFILL SOILS, WE RECOMMEND THAT THE BACKFILL SURFACE OF EXTERIOR WALLS BE ADEQUATELY SLOPES TO DRAIN AWAY FROM THE WALL. IDEALLY, THE BACKFILL SURFACE DIRECTLY BEHIND THE WALL WOULD BE CAPPED WITH ASPHALT, CONCRETE, OR 12 INCHES OF LOW -PERMEABILITY (SILTY) SOILS TO MINIMIZE OR PRECLUDE SURFACE WATER INFILTRATION. APPLIED SOIL PRESSURE: WALLS THAT ARE DESIGNED TO MOVE 0.1 PERCENT OF THE WALL HEIGHT DURING AND AFTER CONSTRUCTION ARE USUALLY REFERRED TO AS UNRESTRAINED WALLS. WE RECOMMEND THAT UNRESTRAINED CANTILEVER WALLS SUPPORT SLOPES INCLINED AT 2H:1V OR FLATTER BE DESIGNED TO RESIST AN ACTIVE PRESSURE (TRIANGULAR DISTRIBUTION) OF 55 POUNDS PER CUBIC FOOT (PCF) FOR DRAINED CONDITIONS. THE RECOMMENDED PRESSURE DOES NOT INCLUDE THE EFFECTS OF SURCHARGES FROM SURFACE LOADS, HYDROSTATIC PRESSURES, OR STRUCTURAL LOADS. IF SUCH SURCHARGES ARE TO APPLY, THEY SHOULD BE ADDED TO THE ABOVE DESIGN LATERAL PRESSURES. TRAFFIC AND VEHICLE LOADS MAT BE MODELED AS AN ADDITIONAL 2 FEET OF WALL HEIGHT WALL SETTLEMENTS: WE ESTIMATE THAT THE SETTLEMENT OF THE WALL FOOTINGS CONSTRUCTED AS RECOMMENDED WILL BE ON THE ORDER OF 1 INCH OR LESS. MOST OF THIS SETTLEMENT IS EXPECTED TO OCCUR AS SOON AS THE LOADS ARE APPLIED. DIFFERENTIAL SETTLEMENT ALONG THE WALLS IS EXPECTED TO BE 1 INCH OR LESS OVER A 50-FOOT SPAN. 4.5 ASPHALT PAVEMENT SINCE ASPHALT PAVEMENTS WILL BE USED FOR THE NEW PARKING FACILITIES AND ROADWAYS, WE OFFER THE FOLLOWING COMMENTS AND RECOMMENDATIONS FOR PAVEMENT DESIGN AND CONSTRUCTION. SUBGRADE PREPARATION: WE RECOMMEND OVER -EXCAVATION OF PAVEMENT SUBGRADES TO DEPTHS OF 12 OR 24 INCHES, THEN PLACEMENT OF PROPERLY COMPACTED STRUCTURAL FILL AS PAVEMENT SUBBASE. IF CONSTRUCTION OCCURS DURING WET CONDITIONS, IT IS LIKELY THAT A GEOTEXTILE FABRIC, PLACED BETWEEN THE STRUCTURAL FILL PAVEMENT SUBBASE AND NATIVE SOILS, WILL BE NECESSARY. WE RECOMMEND A CONVENTIONAL PAVEMENT SECTION COMPRISED OF AN ASPHALT CONCRETE PAVEMENT OVER A CRUSHED ROCK BASE COURSE OVER A PROPERLY PREPARED (COMPACTED) SUBGRADE OR A GRANULAR SUBBASE, DEPENDING ON SUBGRADE CONDITIONS DURING PAVEMENT SUBGRADE PREPARATION. ALL SOIL SUBGRADES SHOULD BE THOROUGHLY COMPACTED, THEN PROOF -ROLLED WITH A LOADED DUMP TRUCK OR HEAVY COMPACTOR. ANY LOCALIZED ZONES OF YIELDING SUBGRADE DISCLOSED DURING THIS PROOF -ROLLING OPERATION SHOULD BE OVER EXCAVATED TO A DEPTH OF 2 FEET AND REPLACED WITH A SUITABLE STRUCTURAL FILL MATERIAL. ALL STRUCTURAL FILL SHOULD BE COMPACTED ACCORDING TO OUR RECOMMENDATIONS GIVEN IN THE STRUCTURAL FILL SECTION. SPECIFICALLY, THE UPPER 2 FEET OF SOILS UNDERLYING PAVEMENT SECTION SHOULD BE COMPACTED TO AT LEAST 95 PERCENT (BASED ON ASTM D-1557), AND ALL SOILS BELOW 2 FEET SHOULD BE COMPACTED TO AT LEAST 90 PERCENT. PAVEMENT MATERIALS: FOR THE BASE COURSE, WE RECOMMEND USING IMPORTED WASHED CRUSHED ROCK, SUCH AS "CRUSHED SURFACING BASE COURSE" PER WSDOT STANDARD SPECIFICATION 9-03.9(3) BUT WITH A FINES CONTENT OF LESS THAN 5 PERCENT PASSING THE NO. 200 SIEVE. ALTHOUGH OUR EXPLORATIONS DO NOT INDICATE A NEED FOR A PAVEMENT SUBBASE, IF A SUBBASE COURSE IS NEEDED, WE RECOMMEND USING IMPORTED, CLEAN, WELL -GRADED SAND AND GRAVEL SUCH AS "BALLAST" OR "GRAVEL BORROW" PER WSDOT STANDARD SPECIFICATIONS 9-03.9(1) AND 9-03.14, RESPECTIVELY. CONVENTIONAL ASPHALT SECTIONS: A CONVENTIONAL PAVEMENT SECTION TYPICALLY COMPRISES AN ASPHALT CONCRETE PAVEMENT OVER A CRUSHED ROCK BASE COURSE. WE RECOMMEND USING THE FOLLOWING CONVENTIONAL PAVEMENT SECTIONS: MINIMUM THICKNESS DRIVEWAYS AND AREAS PAVEMENT COURSE AUTOMOBILE PARKING AREAS SUBJECT TO TRUCK TRAFFIC ASPHALT CONCRETE PAVEMENT 2 INCHES 4 INCHES CRUSHED ROCK BASE 4 INCHES 8 INCHES GRANULAR FILL SUBBASE (IF NEEDED) SURVEYED: WITIIF.1 DESIGNED: DKM/RJJ DRAWN: KLK/DKM CHECKED: DCD APPROVED: DCD 12 INCHES 24 INCHES CONCRETE PAVEMENT: WE UNDERSTAND THAT CONCRETE PAVEMENT WILL BE PLACED AT THE SITE DRIVEWAY, ALONG THE ACCESS WAY, AND AS A PAD FOR THE BACKUP GENERATOR. WE RECOMMEND THAT CONCRETE PAVEMENT HAVE A MAXIMUM THICKNESS OF 8 INCHES AND BE SUPPORTED ON PREPARED SOIL SUBGRADES AND AT LEAST 4 INCHES OF CRUSHED ROCK BASE AS RECOMMENDED ABOVE. COMPACTION AND OBSERVATION: ALL SUBBASE AND BASE COURSE MATERIAL SHOULD BE COMPACTED TO AT LEAST 95 PERCENT OF THE MODIFIED PROCTOR MAXIMUM DRY DENSITY (ASTM D-1557), AND ALL ASPHALT CONCRETE SHOULD BE COMPACTED TO AT LEAST 92 PERCENT OF THE RICE VALUE (ASTM D-2041). WE RECOMMEND THAT AN MGI REPRESENTATIVE BE RETAINED TO OBSERVE THE COMPACTION OF EACH COURSE BEFORE ANY OVERLYING LAYER IS PLACED. FOR THE SUBBASE AND PAVEMENT COURSE, COMPACTION IS BEST OBSERVED BY MEANS OF FREQUENT DENSITY TESTING. FOR THE BASE COURSE, METHODOLOGY OBSERVATIONS AND HAND -PROBING ARE MORE APPROPRIATE THAN DENSITY TESTING. PAVEMENT LIFE AND MAINTENANCE: NO ASPHALT PAVEMENT IS MAINTENANCE -FREE. THE ABOVE DESCRIBED PAVEMENT SECTIONS PRESENT OUR MINIMUM RECOMMENDATIONS FOR AN AVERAGE LEVEL OF PERFORMANCE DURING A 20-YEAR DESIGN LIFE, THEREFORE, AN AVERAGE LEVEL OF MAINTENANCE WILL LIKELY BE REQUIRED. FURTHERMORE, A 20-YEAR PAVEMENT LIFE TYPICALLY ASSUMES THAT AN OVERLAY WILL BE PLACED AFTER ABOUT 10 YEARS. THICKER ASPHALT AND/OR THICKER BASE AND SUBBASE COURSES WOULD OFFER BETTER LONG-TERM PERFORMANCE BUT WOULD COST MORE INITIALLY; THINNER COURSES WOULD BE MORE SUSCEPTIBLE TO "ALLIGATOR" CRACKING AND OTHER FAILURE MODES. AS SUCH, PAVEMENT DESIGN CAN BE CONSIDERED A COMPROMISE BETWEEN A HIGH INITIAL COST AND LOW MAINTENANCE COSTS VERSUS A LOW INITIAL COST AND HIGHER MAINTENANCE COSTS. 4.6 STRUCTURAL FILL THE TERM "STRUCTURAL FILL" REFERS TO ANY MATERIAL PLACED UNDER FOUNDATIONS, RETAINING WALLS, SLAB -ON -GRADE FLOORS, SIDEWALKS, PAVEMENTS, AND OTHER STRUCTURES. OUR COMMENTS, CONCLUSIONS, AND RECOMMENDATIONS CONCERNING STRUCTURAL FILL ARE PRESENTED IN THE FOLLOWING PARAGRAPHS. MATERIALS: TYPICAL STRUCTURAL FILL MATERIALS INCLUDE CLEAN SAND, GRAVEL, PEA GRAVEL, WASHED ROCK, CRUSHED ROCK, WELL -GRADED MIXTURES OF SAND AND GRAVEL (COMMONLY CALLED "GRAVEL BORROW" OR "PIT -RUN"), AND MISCELLANEOUS MIXTURES OF SILT, SAND, AND GRAVEL. IMPORT MATERIALS MEETING WSDOT STANDARD SPECIFICATION 9-03.14(1) GRAVEL BORROW WILL BE SATISFACTORY FOR USE AS STRUCTURAL FILL DURING DRY WEATHER. RECYCLED ASPHALT, CONCRETE, AND GLASS, WHICH ARE DERIVED FROM PULVERIZING THE PARENT MATERIALS, ARE ALSO POTENTIALLY USEFUL AS STRUCTURAL FILL IN CERTAIN APPLICATIONS. SOILS USED FOR STRUCTURAL FILL SHOULD NOT CONTAIN ANY ORGANIC MATTER OR DEBRIS, NOR ANY INDIVIDUAL PARTICLES GREATER THAN ABOUT 6 INCHES IN DIAMETER. FILL PLACEMENT: CLEAN SAND, GRAVEL, CRUSHED ROCK, SOIL MIXTURES, AND RECYCLED MATERIALS SHOULD BE PLACED IN HORIZONTAL LIFTS NOT EXCEEDING 8 INCHES IN LOOSE THICKNESS, AND EACH LIFT SHOULD BE THOROUGHLY COMPACTED WITH A MECHANICAL COMPACTOR. COMPACTION CRITERIA: USING THE MODIFIED PROCTOR TEST (ASTM: D-1557) AS A STANDARD, WE RECOMMEND THAT STRUCTURAL FILL USED FOR VARIOUS ONSITE APPLICATIONS BE COMPACTED TO THE FOLLOWING MINIMUM DENSITIES: FILL APPLICATION MINIMUM COMPACTION FOOTING SUBGRADE AND BEARING PAD 95 PERCENT FOUNDATION BACKFILL 90 PERCENT ASPHALT PAVEMENT BASE 95 PERCENT ASPHALT PAVEMENT SUBGRADE (UPPER 2 FEET) 95 PERCENT ASPHALT PAVEMENT SUBGRADE (BELOW 2 FEET) 90 PERCENT SUBGRADE OBSERVATION AND COMPACTION TESTING: REGARDLESS OF MATERIAL OR LOCATION, ALL STRUCTURAL FILL SHOULD BE PLACED OVER FIRM, UNYIELDING SUBGRADES PREPARED IN ACCORDANCE WITH THE SITE PREPARATION SECTION OF THIS REPORT. THE CONDITION OF ALL SUBGRADES SHOULD BE OBSERVED BY GEOTECHNICAL PERSONNEL BEFORE FILLING OR CONSTRUCTION BEGINS. ALSO, FILL SOIL COMPACTION SHOULD BE VERIFIED BY MEANS OF IN -PLACE DENSITY TESTS PERFORMED DURING FILL PLACEMENT SO THAT ADEQUACY OF SOIL COMPACTION EFFORTS MAY BE EVALUATED AS EARTHWORK PROGRESSES. SOIL MOISTURE CONSIDERATIONS: THE SUITABILITY OF SOILS USED FOR STRUCTURAL FILL DEPENDS PRIMARILY ON THEIR GRAIN -SIZE DISTRIBUTION AND MOISTURE CONTENT WHEN THEY ARE PLACED. AS THE "FINES" CONTENT (THAT SOIL FRACTION PASSING THE U.S. NO. 200 SIEVE) INCREASES, SOILS BECOME MORE SENSITIVE TO SMALL CHANGES IN MOISTURE CONTENT. SOILS CONTAINING MORE THAN ABOUT 5 PERCENT FINES (BY WEIGHT) CANNOT BE CONSISTENTLY COMPACTED TO A FIRM, UNYIELDING CONDITION WHEN THE MOISTURE CONTENT IS MORE THAN 2 PERCENTAGE POINTS ABOVE OR BELOW OPTIMUM. FOR FILL PLACEMENT DURING WET -WEATHER SITE WORK, WE RECOMMEND USING "CLEAN" FILL, WHICH REFERS TO SOILS THAT HAVE A FINES CONTENT OF 5 PERCENT OR LESS (BY WEIGHT) BASED ON THE SOIL FRACTION PASSING THE U.S. NO. 4 SIEVE. D C. O of 4� l v 46449 Isn OM sitts&hill I CIVIL I STRUCTURAL I SURVEY 4815 CENTER STREET I TACOMA, WA. 98409 PHONE: (253) 474-9449 I FAX: (253) 474-0153 http://www.sittshill.com/ Project No.: 19480 Project Mgr.: DCD Proj. Engineer: DKM/RJJ Proj. Drafter: KLK/DKM R-422904 IN COMPLIANCE WITH CITY OF RENTON STANDARDS ENJ LOPMENT ENGINEERING anders 05/08/2023 SCALE: DATE: VERTICAL AL;: NA 11988 983/1 • BROTHERTON BUICK-GMC - RENTON AS NOTED HORIZONTAL: NAD 1983/1991 CITY O F I;R FIELDBOOK: RENTON PAGE: ONE INCH DATUM • DRAWING NO: AT FULL SCALE Planning/Building/Public Works Dept. GENERAL GEOTECHNICAL NOTES CO.2 B IF NOT ONE INCH SCALE ACCORDINGLY SHEET: ^ OF: N T O O O I N N Ids Ln N T O O O N Q J LO O co O O N N WE