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Home My WebLink AboutWWP270364 ai Converse Consultants Geotechnical Engineering and Applied Sciences August 7 , 1984 83-5213-01 City of Renton Municipal Building Renton, Washington 98055 Attention: Mr. Robert Bergstrom City Engineer Subject: Geotechnical Evaluation Maintenance Road Repair Rolling Hills Sewer Trunk Renton, Washington Gentlemen : This letter summarizes the results of our evaluation of the proposed maintenance road repair to be performed adjacent to the Rolling Hills Sewer Trunk in Renton , Washington . Our scope of services was presented in our proposal to you dated November 14, 1983, for which we received authorization on December 8, 1983. Project Description The proposed repair work is shown on the plans you provided to us, sheets 3 and 4 of 4, "Rolling Hills Sewer Trunk Road Repair," dated February 22, 1984. We understand the work will include regrading the existing dirt road from about Sta. 0+00 to 6+50 . Asphalt pavement will be placed from about Sta . 1+17 to 3+50. Approximately 65 feet of gabion retaining wall will be constructed from about Sta. 2+35 to 3+00. Our interest was in the area of the proposed 65 foot long yabion retaining wall as shown on Drawing 1 . As indicated on Drawing 2 , the gabion wall is planned to be four units high (12 feet) with a face sloped at 1H:8V (horizontal to vertical ) . The bottom two courses will be two units wide, and the top two courses will be one unit wide . The existing slope is planned to be cut back about five feet and dressed to about a 1H:2V slope. Backfill behind the Converse Consultants,Inc. 300 Elliott Avenue West Suite 350 Seattle,Washington 98119 WWV 2,77bb�q Telephone 206 285-5200 Mr. Robert Bergstrom City Engineer City of Renton August 7 , 1984 Page Two wall is to consist of crushed stone. The backfill will support a pave- ment section consisting of two inches of asphalt over six inches of crushed rock base. Field Exploration and Subsurface Conditions The initial field work was performed in May 1984, and consisted of two test pits, that ranged from four to seven feet deep (excavated with a City of Renton backhoe) and four hand excavated test pits with depths between 15 to 32 inches. We also checked for cracks in the apartment buildings and sidewalks adjacent to the slope in the gabion wall area. Additional hand explorations were performed in August 1984 . The explor- ations were located as shown on Drawing 1 . Descriptions of subsurface conditions at each exploration are presented on the test pit logs attached to this letter. In general , our explora- tions indicated a unit of topsoil and/or fill over sandstone . The sand- stone ranged from a weathered , weak rock to a residual soil consisting of fine to medium sand . On the slope that will be adjacent to the gabion wall there was 12-18 inches of weathered sandstone mixed with silty, fine to medium sand . On the existing maintenance road surface there was from approximately 10 inches to more than 32 inches of topsoil and fill . Subsurface conditions on the slope above the maintenance road consisted of up to about 12 inches of topsoil over weathered sandstone; however, the sandstone was often exposed on the slope surface. On the opposite (east) side of the creek , and in the bottom of the creek, weathered sandstone was also exposed . Based on our explorations and observations , we inferred that, in general , weathered sandstone was present below a relatively thin layer of topsoil and/or fill . The two backhoe test pits (located at about Sta. 0+75, 20 right and Sta . 1+25, 20 Right) encountered loose to medium dense silty sand fill to the termination depths of four and seven feet. At Sta . 1+25, 20 right, the fill contained a significant amount of logs, roots, and other organ- ic debris. Vertical and/or horizontal displacement along construction joints was noted in the sidewalk of the apartment buildings. We recommend that a detailed crack survey be performed immediately prior to construction . Crack locations , and magnitudes of horizontal and vertical displace- ments, should be carefully documented . Converse Consultants. Inc. Mr. Robert Bergstrom City Engineer City of Renton August 7 , 1984 Page Three Conclusions and Recommendations - Gabion Wall An analysis was performed to evaluate the stability of the proposed gabion wall . In accordance with our proposal , the stability of the existing slope was not analyzed . Instead , we recommend that the pro- posed construction disrupt the existing slope as little as possible to minimize potential cause for slope instability. In our analysis, we assumed the geometries indicated on sheet 4 of 4 of your plans . Gabion fill was assumed to have a density of at least 105 pcf (pounds per cubic foot) and crushed stone backfill was assumed to have an average density of 115 pcf and an effective friction angle of 40 degrees. Truck loading from City dump trucks was assumed not to exceed 30 kips gross vehicle weight per truck . Based on these assumptions and the soil conditions inferred from our explorations, Factors of Safety of 1 .4 for both overturning and sliding were calculated . In addition, we estimated that the allowable bearing capacity of foundation soils exceeds the anticipated loading . In order for our analysis to be valid , it is important that material specifications be consistent with our assumptions . Gabion baskets should be approximately 3 feet high by 3 feet wide, and should be fab- ricated in accordance with the 1984 Washington State Department of Transportation Standard Specifications for Road , Bridge, and Municipal Construction, (subsequently referred to as the "Specifications%) Section 6-09 .3(6) . Gabion fill should consist of sound rock ranging in size from 4 to 8 inches . The shape and gradation of rock should be such that a unit weight of at least 105 pcf is achieved , as measured in accordance with Section 6-09 .3(6)F of the Specifications . Backfill between the gabion wall and native soil should consist of 1-1/4-inch minus crushed stone conforming to Section 9-03 .9(3) of the Specifica- tions, or of free draining granular fill conforming to Section 9-03 .9(1) of the Specifications. It should be placed in loose lifts not more than 8 inches thick, and compacted with hand operated equipment to form a dense unyielding surface. The bottom course of gabions should bear on medium dense to dense native sand or weathered sandstone. The bearing surface should be smooth and free of loose soil . If the surface is uneven, it may be leveled with shot rock similar to that used to fill the yabions . The creek side toe of the gabion wall should be protected from scour by a layer of rip-rap. At this time, we do not have sufficient information Converse Consultants. Inc. Mr. Robert Bergstrom City Engineer City of Renton August 7 , 1984 Page Four (such as high water levels or flow velocities) to provide recommenda- tions as to rip-rap size. If this information is available at a later time, we would be pleased to provide rip-rap recommendations. In order to minimize potential disturbance to the existing slopes, we recommend that cuts be minimized. Cutting of the slope above the main- tenance road is strongly recommended against . Cutting of the slope below the road (behind the gabion wall ) should be limited as much as possible; it is preferrable to reroute the creek slightly east than to cut into the west bank a significant distance. Pavement The proposed pavement section should be suitable for occasional use by maintenance equipment, provided the subgrade is suitably prepared . Near the gabion wall , crushed stone backfill , if properly compacted as recommended above should provide a stable subgrade. Elsewhere, sod and highly organic soil should be stripped . The exposed surface should be proof rolled with heavy rubber tired equipment, and any soft areas should be excavated , backfilled, and compacted to provide a firm un- yielding subyrade. We understand up to about five feet of cut may be required in the region of Sta. 1+25. The fill soil encountered in our test pits in this area was wet , silty sand that contained a significant amount of roots, logs , and stumps. This soil is not suitable for reuse as fill unless organics are removed and the soil is dried to near the optimum moisture content . Once the cut is completed , the exposed subgrade should be proofrolled and improved as recommended above. We trust this letter satisfies your present needs. If you have any further questions, please call . Sincerely, CONVERSE CONSULTANTS, INC. �A wA,^,y��(�_ Cc yin z � William M. Kuck Project Engineer �l�rRrs.iat WMK3:rky Converse Consultants,Inc. 1 / �1 zz X0 i / 4 p,7r fn ent eJ guild)Iding �LP,11E LEVEL San.saw.NH rim z144.Z Sly inv. X 135.6 0 top __-- __ _ 135 — 140 P—2 41.81 1t,74 V25�7 ,VC,55,5 AZ9,467 57-4. A/17 7&-") _�_-V 7 - Very stee ......... It 11W 124-29 iff, 6 106 100 '51 031 N 31 7&2 - + P 00 P- 1 - 3 9 0 417 52 M51-V 411-11<!!iZ1 C4,141A'1 ZIA�< /:1z5VC,5— 145 Z,,i= OUIAC 300�� 2 Oaffall /i! P&MO// 11.3.4 L I E z 94.6 0affall 114.5 -7 0, SST o - iNG 11V To e stream CJ4 /o/A/ A4Z ibo S/0,0,9 t /��' TE EX1257 z2lTCr l LEGEND: EXPLORATION PLAN Approx. test pit location ROLLING HILLS SEWER TRUNK MAINTENANCE ROAD Scale 1 11=20' Project No Renton, Washington Date Aug. 1984 83-5213 REFERENCE: Sheet 3 of 4, "Rolling Hills Sewer Trunk Road for The City of Renton Prepared by Drawing No Repair", dated 22 Feb 1984. im tS Geolechnical Engineering Checked by WMK Converse Consultan and Applied Sciences Approved By WMK 701' 01' ,84 K 1 1 � 1 � 1 \ yZ7 �cEss i CLASS "e" l- /`7/N. C�U9/1EFZ7 /ZO I NEW .¢' A!/G,Ll //D ------ - ---- - - -------- -- ___ - -- _ _ FED NEGV S7o/NE ,4G<�51Z.L it/E C�,B/On/ .4ZE,7,4//1//iU ALL . M/N 8'/,54 7T EX/ST C/4Z5EK 1 w5sT SST � T) S74. 2-1 zlI IVE� T SECTION A-A - GABION RETAINING WALL Scale Protect No ROLLING HILLS SEWER TRUNK MAINTENANCE ROAD NOTED Renton, Washington Date Aug. 1984 83-5213 REFERENCE: Sheet 4 of 4, "Rolling Hills Sewer Trunk Road Repair" , for The City of Renton Prepared oy' OM Drawing No dated 22 Feb. 1984. Checked by WMK 2 Converse Consultants a d Applied Sciences Engineering Approved By WMK TEST PIT TP-1 Depth ( feet) Description 0 .0 - 7 .0 SILTY SAND ( Fill ) gray-brown , fine to medium , trace gravel , some logs, roots and stumps; loose to medium dense, very moist to wet increasing organics at depth 5 .0 ' 8" diameter loy at depth 6.0' Bottom of exploration at 7 .0' No seepage encountered Completed 5/17/84 TEST PIT TP-2 Depth ( feet) Description 0.0 - 4.0 SILTY SAND (Fill ) , brown , fine to medium, some gravel and cobbles, trace organics; medium dense to dense, moist . Occasional quarry spalls in top 1 ' Bottom of exploration at depth 4.0' Refusal on boulder No seepage encountered Completed 5/17/84 U_ N O LOG OF TEST PITS ROLLING HILLS SEWER TRUNK MAINTENANCE ROAD Project No Renton, Washington 83-5213 for The City of Renton Drawing No Converse Consultants and Applied Sciences Engineering 3 TEST PIT TP-3 Depth ( feet) Description 0.0 - 0.8 SANDY SILT (Topsoil ) , brown; medium stiff, moist 0.8 - 1 .4 SAND (Weathered Sandstone) ; mottled tan and orange, fine to medium, trace silt; medium dense, moist. Bottom of exploration at 1 .4' (refusal ) No seepage encountered Completed 5/17/84 TEST PIT TP-4 Depth (feet) Description 0.0 - 1 .0 SANDY SILT (Topsoil ) ; brown; medium stiff to stiff, moist to very moist . Occasional quarry spalls 1 .0 - 2.3 SANDY SILT (Till Fill?) ; blue-gray, fine; stiff, moist . Occasional roots. 2 .3 - 2 .5 ORGANIC SANDY SILT (Topsoil ) ; dark brown; medium stiff, moist . Bottom of exploration at 2 .5' (refusal ) No seepage encountered Completed 5/17/84 s U_ 7 J O N O CL LOG OF TEST PITS ROLLING HILLS SEWER TRUNK MAINTENANCE ROAD Project No Renton, Washington 83-5213 for The City of Renton Dr awing No Converse Consultants and Applied Sciences Engineering nj A TEST PIT TP-5 Depth (feet) Description 0.0 - 2.0 SANDY SILT (Topsoil ) ; brown, mixed with SAND (Weathered Sandstone) , fine to medium; stiff/medium dense, moist . 2 .0 - 2.7 SILTY SAND (Till Fill?) ; gray, medium dense, very moist to wet . Occasional roots Bottom of exploration at 2 .7' (refusal ) No seepage encountered Completed 5/17/84 TEST PIT TP-6 Depth ( feet) Description 0 .0 - 1 .0 SANDY SILT (Topsoil ) ; brown; loose, moist I 1 .0 - 1 .3 SAND (Weathered Sandstone) ; tan, fine to medium; medium dense, moist to very moist . T Bottom of exploration at 1 .3' ( refusal ) No seepage encountered Completed 5/17/84 i U_ N O LOG OF TEST PITS ROLLING HILLS SEWER TRUNK MAINTENANCE ROAD Proj,ctNo Renton, Washington 83-5213 for The City of Renton -- Drawing No 95RA Converse Consultants and Applied Sciences nng 5 W TEST PIT TP-7 Depth ( feet) Description 0.0 - 1 .5 SILTY SAND (Topsoil ) ; brown , fine to medium mixed with SAND (Weathered Sandstone) tan , fine to medium; loose to medium dense, moist. Bottom of exploration at 1 .5' No seepage encountered Completed 8/1/84 TEST PIT TP-8 Depth (feet) Description 0 .0 - 1 .3 SILTY SAND (Topsoil ) ; brown , fine to medium mixed with SAND (Weathered Sandstone) , tan , fine to medium; loose to medium dense, moist . Bottom of exploration at 1 .3' No seepage encountered Completed 8/1/84 TEST PIT TP-9 Depth (feet) Description 0 .0 - 1 .0 SILTY SAND (Topsoil ) ; brown, fine to medium, mixed with SAND (Weathered Sandstone) , tan, fine to medium; loose to medium dense, moist . I Bottom of exploration at 1 .0 ' No seepage encountered Completed 8/1/84 U L d O LOG OF TEST PITS ROLLING HILLS SEWER TRUNK MAINTENANCE ROAD Project No Renton, Washington 83-5213 for The City of Renton Drawing No Converse Consultants and Applied Engineering and Applied Sciences 6 KEY TO SOIL SYMBOLS AND TERMS TERMS USED IN THIS REPORT FOR DESCRIBING SOILS ACCORDING TO THEIR TEXTURE OR GRAIN SIZE DISTRIBUTIONS ARE GENERALLY IN ACCORDANCE WITH THE UNIFIED SOIL CLASSIFICATION SYSTEM. MAJOR DIVISIONS SYMBOLS TYPICAL NAMES TERMS DESCRIBING CONDITION, CONSISTENCY AND HARDNESS e GW Well-graded gravels, gravel- COARSE GRAINED SOILS (major portion retained on No. 200 sieve): sand mixtures, little or no Includes (1) clean gravels, (2) silty or clayey gravels, and (3) n . fines silty, clayey or gravelly sands. Consistency is rated according r r o to relative density, as determined by laboratory tests. o ' Descriptive Term Relative Density GP Poorly-graded gravels, Very loose 0 to 15% gravel-sand mixtures, little or no fines Loose 15 to /Ot zo 0 0 ^ u Medium dense 40 to 70% ♦o x m GM Silty gravels, gravel-sand- Dense 70 to 85% silt mixtures m R+ Very dense 85 to 100E FINE GRAINED SOILS (major portion passing No. 200 sieve): Includes (1) Inorganic and organic silts and clays, (2) gravelly, sandy or GC Clayey gravels, gravel-sand- silty clays, and (3) clayey silts. Consistency is rated according clay mixtures to shearing strength, as indicated by penetrometer readings or by m' direct shear tests. Descriptive Term Shear Strength (ksf) i n a s a o SW Well-graded sands, gravelly Very soft less than 0.25 ' o u" w sands, little or no fines Soft 0.25 to 0.50 ' ' o Firm 0.50 to 1.00 SP Poorly-graded sands, gravelly sands, little Stiff 1.00 to 2.00 ti or no fines Very stiff 2.00 to 4.00 o � o + a In Hard 4.00 and higher • ar a r n SM Silty sands, sand-silt ROCK: Includes gravels, cobbles, rock, caliche and bedrork mixtures materials. Hardness it related to field identification procedures s ! described below. " Descriptive Term Field Identification Test r SC Clayey sands, sand-clay Soft Can be dug by hand and crushed c v. mixtures by fingers w � Moderately Friable, can be gouged deeply Inorganic silts and very hard with knife and will crumble ML fine sands, rock flour, readily under light hammer silt or clayey fine sands, blows c y o a v+ or clayey tilts with slight Hard Knif plasticitye Scratch leaves dust trace, w911 withstand a few hammer blows before breaking ■ Inorganic clays of low to .. CL medium plasticity, gravelly Very hard Scratched with knife with a clays, sandy clays, silty difficulty, difficult to Mclays, lean clays break with hammer blows L � � OL Organic silts and organic �+ silty clays of low o plasticity " SOIL MOISTURE Inorganic silts, micaceous From low to high the soil moisture is indicated by: a MH or diatomaceous fine sandy n or silty soils, elastic Dry silts Slightly moist o Moist Very moist s ^ Wet " CH Inorganic clays of high u plasticity, fat clays ' SIZE PROPORTIONS z o '^ Designation. Percent by Weight OH Organic clays of medium to o high plasticity, organic Trace 0 to 10 o > silts o Little 10 to 20 o Some 20 to 35 Pt Peat and other highly v, organic soils And 35 to 50 GRAIN SIZE DISTRIBUTION CLAY SILT SILT--—— --SAND GRAVEL — IINI— +I. WDlur---r{ auxst�—flit •I" 1� SIEVE sill NUMBER 220 200 140 100 60 10 20 10 a 16' S{" 1' 1%-r I I 01 05 10 s0 1 0 C PARTICLE DIAMETER IN MILLIMETERS -� -�� i I � � � '�� -� , i -� `-J , I __i -4 '} � �,�� -� � � -_l �` i