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Home My WebLink AboutSWP272253 TERRA ASSOCIATES Inc. +° `A"' Consultants in Geotechnical Engineering, GeolpgyW CioFR�,�rorr A ` and ii� E t V E Environmental Earth Sciences t� , D BUILDING pf."'SION January 20, 1996 Project No. T-2865 Mr. Thomas W. Ichelson Environmental Development Corporation P.O. Box 1574 Bellevue, Washington 98009 Subject: Supplemental Geotechnical Exploration Springbrook Apartments(Formally The Cottages) Talbot Road Renton, Washington Reference: Geotechnical Report, The Cottages, Project No. T-2865, by Terra Associates, Inc. dated May 5, 1995 Dear Mr. Ichelson: As requested, we have completed a supplemental geotechnical study for the subject project. We previously completed a geotechnical study for the southern half of the site and presented our results and design recommendations in the referenced report. The purpose of our additional work was to determine if the soil conditions under the added north property were consistent with those previously identified. We also evaluated if the geotechnical design recommendations provided would be valid for this area. SURFACE The location of the site is shown on the Vicinity Map, Figure 1. The added north property is approximately 170 feet wide and 670 feet long. The west and central areas of the site are vegetated with blackberries and small trees. To the east is a denser forest composed of deciduous trees. An old foundation and floor slab were also observed in the central portion of the site. We understand that a subsurface drain was installed along the east slope toe to a depth of approximately 15 feet. We also observed stockpiles of construction debris which were recently placed on the site. These stockpiles include a large asphalt pile in the east half of the site and several soil stockpiles in the central area. 12525 Willows Road, Suite 101, Kirkland, Washington 98034 0 Phone (206) 821-7777 . 73 � g Mr. Thomas W. Ichelson January 20, 1996 The topography of the added north property is consistent with the previously studied south property. In general, the site slopes gently down to the west at a grade of approximately seven percent with a total elevation change of about 86 feet. East of the development, the forested slope rises to the east over a gradient of about 17 percent. SOILS We excavated three additional test pits on the site. In general, the topsoil unit we observed was 8 to 18 inches thick. Directly below the topsoil, a one to two foot thick silty sand to sandy silt was encountered. Underneath the silty sands, the soil units varied. To the west, we found a sandy glacial till to depths of nine feet. To the east, a brown silty sand with gravel (out,,vash) was observed to depths of ten feet. In the central area of the new parcel, a mixture of silty sands to clayey silt was found to depths of 11 feet. A more detailed description of the subsurface conditions we encountered is presented on the Test Pit Logs, Figures 3 and 4. The test pit locations are shown on Figure 2. DISCUSSION AND RECOMMENDATIONS Based on our observations, in our opinion, the recommendations and conclusions in our referenced report will be valid for the added north property. However, the remnants of past and recent site activities on the parcel will need to be addressed to establish suitable subgrade conditions for supporting building foundations and pavements. When the east slope toe drain was installed, excavated soils were spread out over the organic surface layer. To prepare this area for construction, these soils should be removed and the underlying organic surface layer should be stripped to expose competent native soils. The soils can then be replaced and compacted as structural fill as described in the referenced report. Similar considerations will need to be given to areas of the site containing soil and debris stockpiles. The new site plan shows that four buildings will be cut into the toe of the east slope. In our opinion, this planned construction will not impact the current stability of the slope, provided the excavation and subsequent building foundation are completed and designed in accordance with the recommendations outlined in the referenced report. The new site plan also shows a detention vault in the west central area. A detention pond was previously planned for the southwest corner. Due to an occupied residence at the vault location, no test pit exploration was conducted. However, design of the vault foundation and walls can be completed using the previously provided design parameters. Project No. T-2865 Page No. 2 Mr. Thomas W. Ichelson January 20, 1996 LIMITATIONS This report is the property of Terra Associates, Inc. and was prepared in accordance with generally accepted geotechnical engineering practices. This report is intended to supplement the referenced geotechnical report and is for specific application to the Springbrook Apartments. This report is for the exclusive use of Environmental Development Corporation and their authorized representatives. No other warranty, expressed or implied, is made. The analyses and recommendations presented in this report are based upon data obtained from the test pits advanced on-site. Variations in soil conditions can occur, the nature and extent of which may not become evident until construction. If variations appear evident, Terra Associates, Inc. should be requested to reevaluate the recommendations in this report prior to proceeding with construction. We appreciate the opportunity to be of continued service to Environmental Development Corporation during the preliminary design phase of this project and look forward to being of continued service during the final design and construction phases. If you have any questions or need additional information, please call. Sincerely yours, TERRA AS MINC. J. 4. 'mil � � •� � .,•.' Davidush 1 c_ Engine r►n Ge y. 6742 . 0 1.EN T eodore J. Princi al Engineer - EXPIRES DPL :e Encl: Figure 1 - Vicinity Map Figure 2 - Exploration Location Plan Figures 3 and 4 - Test Pit Logs Project No. T-2865 Page No. 3 � � - w d '�, , . �xro s �, I tt J h E •If�i•r,•:. `y�, � I w �,.� � �.•rc;,;, '�� ^5 -.---- ' 1E2NO: <'� ST i`� ttl tt.iissT r>< �. J p c hr rTH PAW NE70900 ;bErH STSE I647H1 -ST a< :17700 E' i. S,g,,,_.!V ~� St IEE7. ) 3 IE57x S, .y7rl4� ' <JSCF jf. 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VICINITY MAP TERRA SPRINGBROOK ASSOCIATES RENTON, WASHINGTON •• Geotechnical Consultants Proj. No.2865 Date 1/96 Figure 1 • 11 I I A ( � �' � ry = n k I I I / - / � ( / �� 1 I f , 1• 1 1 ! f ; 1 1 I 1 + 1 1 1 1 1 ! / l ! 1 I I III ,�a I I / , I f �� ' '�� { '• 1 I I I 1 { J l / 1 1 ! ! 1 1 , I I TP-9 I I , i J 1 1 11 , I I I 1 11 I I 3 4 !' + t ( ' ' !+ I • I ® I I I I 1 1 1 I I 2 // 0 ' f/ / / - I l / 1 £ /•i r 1 11 1 1 1 1 1 1 1111 11 41 i ® A l7 /A !! TP-10 TP-8 I I I ! I 1�'1 _ r !. 111Cj ! / — � 1 1 I It l a, B // 1 \ - T---- -}rT '- �'= - __• /l`. J J r Il I ; 1 ! I I /I ! ___ � ' J ! T•r\1 � I 1 1 I ! �/ I I { I I r �I� ��, 1 - —�'_�'��1!_ 1__�I_ 1, I '8' L• -- - - / — 1i' — , / ,~ -r' cF—v11 '1. + 1V'l .+F7 17-1.1 1 ' l TP-6 I I it r 1 1 , 1 � I I' 7 I �! ,' ! 'i H f'�, .j ` i�� tJ 1 i1 � IC I ! 1 1 I J 1 1 f 1 I 1 ! I I r � I �+ I r r l III I l t +! 1 1 APPROXIMATE SCALE / c 1 F 1 I I 1 I ' 60 0 60 120 ft. � 1 �; I I ,, $ ' (,, �, TP-7 1 I IIt1111 ', ! � 1 + ! 1 I H 'i ' ( " � j l l i l ' i + ' ■ r i ' ' + ' 1 11 I � ! l l l l l , I { I I I I I II I I I C 15 I I 11 I I J A LEGEND: 14 c 17 1 ' 1 + 1 1 1 1 '! 111�IIIIIiI A ! 1 I ! A / T 1 1 I lI I I I I I I r I I i l l , APPROXIMATE TEST PIT LOCATION , �` , I i I E: r• ' , I ' i 1_ 1./ c / ! I 11 1 1 + I l l l t l l I I 17 'I -I — — ■ a + 11S t ,, it- 1 1 I i ! ! { I 1 I I 1 1 I !i I.! CURRENT GEOTECHNICAL STUDY TP-5• j11 , I I ,. , ,I _ • —�, 1 I�� I B � � APPROXIMATE TEST PIT LOCATION � ; 1 J ,: � i ! r I I I1 + I11 r1 ! � ' i �n �, i t / i i i i iji i i i i + PREVIOUS GEOTECHNICAL STUDY TITLED ' "THE COTTAGES" BY TERRA ASSOCIATES, TP-$ 1 f 1 I I I , I 1 I — r �, �' DATED MAY 5, 1995. 1_ —_ !J_ —' — , ! 1 -t__ — I I'1' � �'j + I I r' I II , ', ' I I I• I I I h ' ' •. 1 1 i( / tt / , I ! r I 1 I ! ! I I I ' I I I• ,' r 17 , /I l F 1 I ll ' ( I `� ( ' � ' r ' 1 1 1 1 11 1 ! I I I I I 1 1 + TP-4 I I �•Sr ,I 1 1 I + 1 II i; ' / j O, (� 12 / i 11 i i� 9 , r� I I r + I I I I TP-1 13 / ; i , I ' o F;J I �� H ,' II , r' i i i r i i I\'- REFERENCE: ' El i� E r 1 F ' 1 /I I ( + I I I I TP-2— I ' t SITE PLAN PROVIDED BY TRIAD ASSOCIATES i i i i i PROJECT No. UNKNOWN, UNTITLED, PRINTED i ! / / �;•'�i'�. � r �_ _- __ - __ __ _ -� ` �.--- --��.�___.' , - I l —,_ _ .T —/—!-I Ir. IJ 1 I I I 1 1 2 96. ' EXPLORATION LOCATION PLAN 9#Geotechnical TERRA SPRINGBROOK ASSOCIATES RENTON, WASHINGTON Consultants Proj. No.2865 Date 1/96 Figure 2 Test Pit No. TP-8 Logged by: DPL Approximate Elev. 167 Date: 1/8/96 Depth USCS/ W (ft.) Graph Soil Description W 0— 12 to 18 inches Topsoil. :MflL I I Dark brown sandy SILT,wet, soft, roots. 18.6 S M Grey-brown silty SAND with gravel,wet, mottled, loose. 13.1 Brown silty SAND with gravel, moist, dense, cemented. 5 Some cobbles. (Glacial Till) 13.1 SM 1 13.61 A. 10— Test pit terminated at 9.5 feet. Minor groundwater seepage I to 3.5 feet. No caving observed. 15— Test Pit No. TP-9 Logged by: DPL Approximate Elev. 208 Date: 1/8/96 Depth USCS/ Soil Description W Graph (%) 0 8 to 12 inches Topsoil. s M Reddish-brown silty SAND with gravel, moist, loose, roots. Brown silty SAND with gravel, moist, medium dense, some 9.0 .. ........ ... cobbles, fine to medium grains. (Outwash) 5 M 7.8 10- - Test pit terminated at 10 feet. No groundwater seepage encountered. Some caving. 15— TEST PIT LOGS TERRA SPRINGBROOK APARTMENTS ASSOCIATES RENTON, WASHINGTON Geotechnical Cohsultants Proj. No. T-2865 I Date 1/96 Figure 3_j Test Pit No. TP-10 Logged by: DPL Approximate Elev. 196 Date: 1/8/96 Depth GraphW Soil Description 8 to 14 inches Topsoil. Grey-brown sandy SILT,wet, firm, mottled, fine grained. 20.0 Brown silty SAND with gravel interbedded with silt and clayey 14.5 SM/ silt lenses, moist, medium dense, some cobbles, slightly 5 /M L I cemented. Blue-grey sandy SILT to clayey SILT, wet, stiff, some gravel. 16.0 ML Boulder at 9 feet. 10— Tfl Test pit terminated at 11 feet. Minor groundwater seepage from I to 3 feet. Minor caving above 6 feet. 15 TEST PIT LOGS TERM SPRINGBROOK APARTMENTS ASSOCIATES RENTON, WASHINGTON • Geotechnical Consultants Proj. No. T-2865 I Date 1/96 Figure 4