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HomeMy WebLinkAboutR-425402A PORTION OF THE NW 1/4 OF SECTION 19, TOWNSHIP 23 NORTH, RANGE 5 EAST, W.M., KING COUNTY, WASHINGTON Nt I O 0 w U) I— z Cw G w > O rr n G 0 z Q z O 0 Q 0 z_ 0 m a 0 Q U) ►i CJ z J GEOTECHNICAL ENGINEERING NOTES THE FOLLOWING IS EXCERPTED FROM SECTION 4.0 OF THE GEOTECHNICAL ENGINEERING REPORT PREPARED BY MIGIZI GROUP, INC., PROJECT Z0363, DATED 9/26/22. 4.0 CONCLUSIONS AND RECOMMENDATIONS IMPROVEMENT PLANS INVOLVE THE CONSTRUCTION OF A NEW 2—STORY ADDITION TO THE NORTHWEST CORNER OF THE EXISTING BUILDING. THE NEWLY ADDED SPACE WILL BE 695 SF FOR BOTH THE FIRST AND SECOND FLOORS WHICH TOTALS 1,390 SF. SPECIFICALLY, A NEW STAIRWELL, ELEVATOR SHAFT, AND STORAGE ROOMS WILL MAKE UP THE ADDITION. THE ADDITION IS TO BE BUILT WITH SLAB —ON —GRADE AT THE EXISTING GRADE OF THE SITE. WE OFFER THE FOLLOWING RECOMMENDATIONS: • FEASIBILITY: BASED ON OUR FIELD EXPLORATIONS, RESEARCH AND EVALUATIONS, THE PROPOSED IMPROVEMENTS AND PAVEMENTS APPEAR FEASIBLE FROM A GEOTECHNICAL STANDPOINT. • FOUNDATION OPTIONS: OVER —EXCAVATION OF SPREAD FOOTING SUBGRADES TO A DEPTH OF 3 TO 5 FEET AND CONSTRUCTION OF STRUCTURAL FILL BEARING PADS WILL BE NECESSARY FOR FOUNDATION SUPPORT OF THE PROPOSED ADDITION. IF FOUNDATION CONSTRUCTION OCCURS DURING WET CONDITIONS, IT IS LIKELY THAT A GEOTEXTILE FABRIC AND/OR A PACKED LAYER OF QUARRY SPALL ROCK, PLACED BETWEEN BEARING PADS AND NATIVE SOILS, WILL ALSO BE NECESSARY. RECOMMENDATIONS FOR SPREAD FOOTINGS ARE PROVIDED IN SECTION 4.2. • FLOOR OPTIONS: BASED ON EXPLORATIONS ACROSS THE SITE, WE RECOMMEND THAT FLOOR SECTIONS BE OVER —EXCAVATED TO A MINIMUM DEPTH OF 1 % FEET, THEN PLACEMENT OF SUITABLE AND PROPERLY COMPACTED STRUCTURAL FILL AS A FLOOR SUBBASE. RECOMMENDATIONS FOR SLAB —ON —GRADE FLOORS ARE INCLUDED IN SECTION 4.3. IF FLOOR CONSTRUCTION OCCURS DURING WET CONDITIONS, IT IS LIKELY THAT A GEOTEXTILE FABRIC AND/OR A PACKED LAYER OF QUARRY SPALL ROCK, PLACED BETWEEN BEARING PADS AND NATIVE SOILS, WILL ALSO BE NECESSARY. FILL UNDERLYING FLOOR SLABS SHOULD BE COMPACTED TO 95 PERCENT (ASTM: D-1 557). • PAVEMENT SECTIONS: AFTER REMOVAL OF ANY ORGANIC —RICH MATERIALS UNDERLYING PAVEMENT AREAS, WE RECOMMEND A CONVENTIONAL PAVEMENT SECTION COMPRISING AN ASPHALT CONCRETE PAVEMENT OVER A CRUSHED ROCK BASE COURSE OVER PROPERLY PREPARED (COMPACTED) SUBGRADE OR GRANULAR SUBBASE. GIVEN THE RELATIVE LOOSE/SOFT CONDITION OF NATIVE ONSITE SOILS, WE RECOMMEND AN OVER —EXCAVATION IN PROPOSED CONCRETE AND ASPHALT AREAS OF 2 FEET, WITH THE PLACEMENT AND COMPACTION OF A SUITABLE STRUCTURAL FILL SUBBASE. ALL SOIL SUBGRADES BELOW 2 FEET 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 12 INCHES AND REPLACED WITH A SUITABLE STRUCTURAL FILL MATERIAL. • GEOLOGIC HAZARDS: DURING OUR SITE RECONNAISSANCE, ADVANCEMENT OF SUBSURFACE EXPLORATIONS, AND GENERAL EVALUATION OF THE PROPOSED DEVELOPMENT, WE DID NOT OBSERVE ANY EROSIONAL, LANDSLIDE, SEISMIC, SETTLEMENT, OR OTHER FORMS OF GEOLOGIC HAZARDS WITHIN THE SUBJECT PROPERTY. GIVEN THIS FACT, WE RECOMMEND THAT NO BUFFERS, SETBACKS, OR OTHER FORMS OF SITE RESTRAINTS BE IMPLEMENTED TO ADDRESS THESE POTENTIAL HAZARDS. THE FOLLOWING SECTIONS PRESENT OUR SPECIFIC GEOTECHNICAL CONCLUSIONS AND RECOMMENDATIONS CONCERNING SITE PREPARATION, SPREAD FOOTINGS, SLAB —ON —GRADE FLOORS, DRAINAGE SYSTEMS, 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. THE MAJORITY OF THE SITE IS PAVED, AND MINIMAL TO NO STRIPPING IS ANTICIPATED FOR THIS PROJECT. SITE EXCAVATIONS: BASED ON OUR FIELD EXPLORATIONS, WE ANTICIPATE THAT EXCAVATIONS WILL ENCOUNTER DENSE FILL SOILS IN CLOSE PROXIMITY TO EXISTING GRADE, AND LOOSE/SOFT FINE—GRAINED ALLUVIAL SOILS WITH DEPTH. THIS MATERIAL CAN BE EASILY EXCAVATED UTILIZING STANDARD EXCAVATION EQUIPMENT. DEWATERING: WE ANTICIPATE THAT SITE EXCAVATIONS WILL ENCOUNTER GROUNDWATER AT SHALLOW DEPTHS DURING PERIODS OF EXTENDED PRECIPITATION. IN ADDITION, IF EXCAVATIONS OF TRENCH LINES ARE LEFT OPEN FOR AN EXTENDED PERIOD, SLOW SEEPAGE OF GROUNDWATER MAY BE OBSERVED. IF GROUNDWATER IS ENCOUNTERED DURING REGULAR EARTHWORK ACTIVITIES, WE ANTICIPATE THAT AN INTERNAL SYSTEM OF DITCHES, SUMPHOLES, AND PUMPS WILL BE ADEQUATE TO TEMPORARILY DEWATER SHALLOW EXCAVATIONS. 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 AND COVERED IN PLASTIC SHEETING TO PREVENT SLOUGHING AND COLLAPSE, • TEMPORARY CUT SLOPES IN SITE SOILS SHOULD BE NO STEEPER THAN 11hH: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 ADDITION 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 OVER —EXCAVATED 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: • SURFICIAL ORGANIC SOIL AND ORGANIC —RICH TOPSOIL: WHERE ENCOUNTERED, SURFICIAL ORGANIC SOILS, LIKE DUFF, TOPSOIL, ROOT —RICH SOIL, AND ORGANIC —RICH FILL SOILS, ARE NOT SUITABLE FOR USE AS STRUCTURAL FILL UNDER ANY CIRCUMSTANCES, DUE TO HIGH ORGANIC CONTENT. CONSEQUENTLY, THIS MATERIAL CAN BE USED ONLY FOR NON—STRUCTURAL PURPOSES, SUCH AS IN LANDSCAPING AREAS. • ALLUVIAL SILT AND SILTY SAND: THE ALLUVIAL SILTY SAND THAT UNDERLIES THE SITE IS VERY MOISTURE SENSITIVE AND WILL BE DIFFICULT TO IMPOSSIBLE TO REUSE DURING MOST WEATHER CONDITIONS. THE MAJORITY OF THIS SOIL TYPE IS CURRENTLY ABOVE THE OPTIMUM MOISTURE CONTENT AND WILL NOT COMPACT ADEQUATELY UNLESS EXTENSIVELY AERATED OR TREATED WITH CEMENT. 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 2%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 FOOTINGS IN OUR OPINION, CONVENTIONAL SPREAD FOOTINGS WILL PROVIDE ADEQUATE SUPPORT FOR THE PROPOSED ADDITION, IF THE SUBGRADES ARE PROPERLY PREPARED. DUE TO THE SOFT SOILS THAT UNDERLIE THE SITE, OVER— EXCAVATION OF SPREAD FOOTING SUBGRADES, TO A DEPTH OF 3 TO 5 FEET, AND THE CONSTRUCTION OF STRUCTURAL FILL BEARING PADS, WILL BE NECESSARY FOR FOUNDATIONAL SUPPORT OF THE NEW ADDITION. 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 POST— CONSTRUCTION SETTLEMENTS, CONTINUOUS (WALL) AND ISOLATED (COLUMN) FOOTINGS SHOULD BE AT LEAST 18 AND 24 INCHES WIDE, RESPECTIVELY. BEARING SUBGRADES: FOOTINGS SHOULD BEAR ON MEDIUM DENSE OR DENSER, UNDISTURBED NATIVE SOILS OR PROPERLY COMPACTED STRUCTURAL FILL WHICH BEARS ON UNDISTURBED MEDIUM DENSE TO VERY DENSE NATIVE SOILS. STRUCTURAL FILL BEARING PADS, 3 TO 5 FEET THICK AND COMPACTED TO A DENSITY OF AT LEAST 95 PERCENT (BASED ON ASTM: D-1557), SHOULD UNDERLIE SPREAD FOOTINGS FOR THE PROPOSED CONSTRUCTION. IF FOUNDATION WORK OCCURS DURING WET CONDITIONS, IT IS POSSIBLE THAT A GEOTEXTILE FABRIC, PLACED BETWEEN THE BEARING PAD AND NATIVE SOIL, WILL BE NECESSARY. REFER TO THE STRUCTURAL FILL SECTION OF THIS REPORT. IN GENERAL, BEFORE FOOTING CONCRETE IS PLACED, ANY LOCALIZED ZONES OF LOOSE SOILS EXPOSED ACROSS THE 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. STRUCTURAL FILL BEARING PADS SHOULD BE COMPACTED TO A DENSITY OF AT LEAST 95 PERCENT (BASED ON ASTM: D-1557). LATERAL OVER —EXCAVATIONS: 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. THEREFORE, 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 DENSE, PROPERLY PREPARED BEARING PADS CAN BE DESIGNED FOR MAXIMUM ALLOWABLE SOIL BEARING PRESSURES LISTED IN THE FOLLOWING TABLE: BEARING PAD THICKNESS (FEET) ALLOWABLE BEARING PRESSURE (PSF) 3 1,500 4 2,000 5 2,500 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 DENSE OR DENSER STATE, WE ESTIMATE THAT TOTAL POST —CONSTRUCTION SETTLEMENTS OF PROPERLY DESIGNED FOOTINGS BEARING ON PROPERLY PREPARED SUBGRADES WILL NOT EXCEED 1 INCH, UNDER STATIC CONDITIONS. DIFFERENTIAL SETTLEMENTS FOR COMPARABLY LOADED ELEMENTS MAY APPROACH ONE—HALF OF THE ACTUAL TOTAL SETTLEMENT OVER HORIZONTAL DISTANCES OF APPROXIMATELY 50 FEET. FOOTING BACKFILL: TO PROVIDE EROSION PROTECTION AND LATERAL LOAD RESISTANCE, WE RECOMMEND THAT ALL FOOTING EXCAVATIONS BE BACKFILLED ON BOTH SIDES OF THE FOOTINGS AND STEM WALLS AFTER THE CONCRETE HAS CURED. EITHER IMPORTED STRUCTURAL FILL OR NON —ORGANIC ONSITE SOILS CAN BE USED FOR THIS PURPOSE, CONTINGENT ON SUITABLE MOISTURE CONTENT AT THE TIME OF PLACEMENT. REGARDLESS OF SOIL TYPE, ALL FOOTING BACKFILL SOIL SHOULD BE COMPACTED TO A DENSITY OF AT LEAST 90 PERCENT (BASED ON ASTM: D— 1557). LATERAL RESISTANCE: FOOTINGS 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 250 PSF AND AN ALLOWABLE BASE FRICTION COEFFICIENT OF 0.35 FOR BOTH SOIL TYPES. 4 • Call 811 • ® two business days before you dig NO. 4.3 SLAB —ON —GRADE FLOORS IN OUR OPINION, SOIL —SUPPORTED SLAB —ON —GRADE FLOORS CAN BE USED IN THE PROPOSED ADDITION IF THE SUBGRADES ARE PROPERLY PREPARED. WE OFFER THE FOLLOWING COMMENTS AND RECOMMENDATIONS CONCERNING SLAB —ON —GRADE FLOORS. FLOOR SUBBASE: FOR THE PROPOSED ADDITION, WE RECOMMEND OVER —EXCAVATION OF SLAB —ON —GRADE FLOOR SUBGRADES TO A MINIMUM DEPTH OF 11,E FEET, THEN PLACEMENT OF PROPERLY COMPACTED STRUCTURAL FILL AS A FLOOR SUBBASE. IF FLOOR CONSTRUCTION IS TO OCCUR DURING WET CONDITIONS, IT IS LIKELY THAT A GEOTEXTILE FABRIC AND/OR COMPACTED LAYER OF QUARRY SPALL ROCK, PLACED BETWEEN THE STRUCTURAL FILL FLOOR SUBBASE AND NATIVE SOILS, WILL BE NECESSARY. ALL SUBBASE 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 LAYER OF PEA GRAVEL OR OTHER CLEAN, UNIFORM, WELL—ROUNDED GRAVEL, SUCH AS "GRAVEL BACKFILL FOR DRAINS" PER WSDOT STANDARD SPECIFICATION 9-03.12(4). ALTERNATIVELY, ANGULAR GRAVEL OR CRUSHED ROCK CAN BE USED IF IT IS SUFFICIENTLY CLEAN AND UNIFORM TO PREVENT CAPILLARY WICKING. IN ADDITION, A LAYER OF PLASTIC SHEETING (SUCH AS CROSSTUFF, MOISTOP, OR VISQUEEN) BE PLACED DIRECTLY BETWEEN THE CAPILLARY BREAK AND THE FLOOR SLAB TO PREVENT GROUND MOISTURE VAPORS FROM MIGRATING UPWARD THROUGH THE SLAB. DURING SUBSEQUENT CASTING OF THE CONCRETE SLAB, THE CONTRACTOR SHOULD EXERCISE CARE TO AVOID PUNCTURING THE VAPOR BARRIER 4.4 DRAINAGE SYSTEMS WE OFFER THE FOLLOWING RECOMMENDATIONS AND COMMENTS FOR DRAINAGE DESIGN FOR CONSTRUCTION PURPOSES. PERIMETER DRAINS: WE RECOMMEND THAT THE PROPOSED ADDITION, WHERE APPLICABLE, BE ENCIRCLED WITH A PERIMETER DRAIN SYSTEM TO COLLECT SEEPAGE WATER. THIS DRAIN SHOULD CONSIST OF A 4—INCH— DIAMETER PERFORATED PIPE WITHIN AN ENVELOPE OF PEA GRAVEL OR WASHED ROCK, EXTENDING AT LEAST 6 INCHES ON ALL SIDES OF THE PIPE, AND THE GRAVEL ENVELOPE SHOULD BE WRAPPED WITH FILTER FABRIC TO REDUCE THE MIGRATION OF FINES FROM THE SURROUNDING SOILS. IDEALLY, THE DRAIN INVERT WOULD BE INSTALLED NO MORE THAN 8 INCHES ABOVE THE BASE OF THE PERIMETER OF THE FOUNDATION. DISCHARGE CONSIDERATIONS: IF POSSIBLE, ALL PERIMETER DRAINS SHOULD DISCHARGE TO A MUNICIPAL STORM DRAIN, OR OTHER SUITABLE LOCATION BY GRAVITY FLOW. CHECK VALVES SHOULD BE INSTALLED ALONG ANY DRAINPIPES THAT DISCHARGE TO A SEWER SYSTEM, TO PREVENT SEWAGE BACKFLOW INTO THE DRAIN SYSTEM. RUNOFF WATER: ROOF —RUNOFF AND SURFACE —RUNOFF WATER SHOULD NOT DISCHARGE INTO THE PERIMETER DRAIN SYSTEM. INSTEAD, THESE SOURCES SHOULD DISCHARGE INTO SEPARATE TIGHTLINE PIPES AND BE ROUTED AWAY FROM THE BUILDINGS TO A STORM DRAIN OR OTHER APPROPRIATE LOCATION. GRADING AND CAPPING: FINAL SITE GRADES SHOULD SLOPE DOWNWARD AWAY FROM THE BUILDING SO THAT RUNOFF WATER WILL FLOW BY GRAVITY TO SUITABLE COLLECTION POINTS, RATHER THAN PONDING NEAR THE BUILDING. IDEALLY, THE AREA SURROUNDING THE BUILDING WOULD BE CAPPED WITH CONCRETE, ASPHALT, OR LOW —PERMEABILITY (SILTY) SOILS TO MINIMIZE OR PRECLUDE SURFACE —WATER INFILTRATION. 4.5 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. RECYCLED ASPHALT, CONCRETE, AND GLASS, WHICH ARE DERIVED FROM PULVERIZING THE PARENT MATERIALS, ARE ALSO POTENTIALLY USEFUL AS STRUCTURAL FILL IN CERTAIN APPLICATIONS. IMPORT SOILS USED FOR STRUCTURAL FILL SHOULD NOT CONTAIN ANY ORGANIC MATTER OR DEBRIS, NOR ANY INDIVIDUAL PARTICLES GREATER THAN 4 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 SLAB —ON —GRADE FLOOR SUBGRADE AND SUBBASE 95 PERCENT ASPHALT PAVEMENT BASE AND SUBBASE 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 FILLS 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. SURVEYED: SCALE: A' DESIGNED: AS NOTED DKM DRAWN: KLK ONE INCH CHECKED: DCD AT FULL SCALE IF NOT ONE INCH REVISION BY DATE APPR APPROVED: SCALE ACCORDINGLY DCD VERTICAL: NAVD 1988 HORIZONTAL: NAD 1983/1991 DATU M C TY OF RENTON Plan ning/Building/Public Works Dept D �C. l,9 �r 46449�p O C/S-��" r'w c• NAL ENG` `a. sitts&hill 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/ REISSUED FOR PERMIT Project No.: Proj. Engineer: OCTOBER 30, 2023 19682 i Project Mgr.: DCD DCD i Proj. Drafter: KLK R-425402 IN COMPLIANCE WITH CITY OF RENTON STANDARDS DEVELOPMENT ENGINEERING SAMorman 12/05/2023 WASHINGTON STATE AUTO DEALERS ASSOCIATION (WSADA) 621 SOUTHWEST GRADY WAY, RENTON, WA 98057 WSADA BUILDING ADDITION AND IMPROVEMENTS GENERAL GEOTECHNICAL NOTES DATE: 022.11.30 FIELDBOOK: PAGE: DRAWING NO: CO.1 SHEET: 0R Cfl N T O O M N u H H N N Q J