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HomeMy WebLinkAboutGeoTech Report Review for BLD2001-00764 - BLD Engineering / Geo-tech Reports - 10/5/2001 MASON COUNTY PUBLIC WORKS DIRECTOR/COUNTY ROAD ENGINEER Shelton,Washington 98584 DATE: October 5 h, 2001 INTER-DEPARTMENTAL COMMUNICATIONS TO: Rick Mraz, DCD - Planner FROM: Alan A. Tahja, P/W - Co. Hydr. Engr. DCD/Planniniz WO# 01-0174 SUBJ: Geo-Tech Report Review NAME: Bailor SFR at Lake Limerick BLD2001-00764 Rick, A geotechnical report prepared for the proposed Karen Bailor residence located on lot# 37, Sleaford Road in the plat of Lake Limerick, has been received and reviewed by Public Works. The report conforms to standards of engineering principles and practices for this time and place, and appears to conform to the minimum requirements of DCD for geotechnical reporting. Recommendations contained in the report should be made conditions for approval of proposed construction. Please feel free to contact me at County extension 461 if you have any questions regarding these comments, or if you feel any features need further discussion or attention. incerely, 4L l ' Akan A. Tahj File: H:\WP\GEO\REVIEWS\Bailor.doc 0. 4/ r P�2M �Z D a c, -rk� � tE7 VYot k Onts� RMiW by- 1 Numbed Authorized by; Type of Work Date; ° � 1 CHARGE TO: NAME AGENCY/COMPANY ' BiWNG ADDRESS i PHONE ' Pub.Works Person in Charge: 1-,� k M�A (0) Protect Time Llne: (from -to dates) "`"• • Pc*d Scut daze: —�•� �1� TO "-Lo —O/ Estimated Finish Dow: APPrm�h=%: ESTIMATED TOTAL is: �) �4 �o COST ESTIMATE TOTAL$ EQUIPMENT USED: vm Em 70TAL f'3 MATERIAL USED: (F) Act"Cost t3ARS: PROJ#: GATE ,� . U&TA LEA4 Hours TOTAL$ EQUIPMENT USED: Date � R pateOT MATE UAL USED: (G) BILLED DATE INV 9 TOTAL ALL PAID OATE REC1 CKN LD Z'00 I w. (XyGq GEOLOGICAL ASSESSMENT FOR HOME CONSTRUCTION ON LOT 37,SLEAFORD RD. MASON COUNTY, WASHINGTON Prepared For: PLANNING KAREN BAILOR SHELTON, WA Prepared By: Geotechnical Testing Laboratory Olympia, WA With Henry N. Alai, P.E. September 26,2001 I. Objectives The objectives of the Geotechnical Report are to: A. Access the surface and subsurface conditions prevalent on the subject site, which may have a bearing on its ultimate use as a site for residential development. B. Recommend measures that may serve to mitigate any conditions of concern. II. Site Conditions Assessment A. General The subject site, Lot 37, is located at Sleaford Road on Lake Limerick in Mason County, Washington. The Parcel Number is 321275400037. The lot is bounded by a moderate slope off Sleaford Road,by a steep wooded ravine on the south and by a gentle slope toward the north and west. The lot is the highest point in the surrounding area and runoff percolates into the ground and/or flows in a southerly direction toward the natural drainage areas that were established when the subdivision was approved. In the general vicinity of the site is a well developed residential neighborhood. B. Surface Conditions The lot itself had been previously graded for a home. When the area was leveled, some fill had been deposited and graded on the southern downhill side of the parcel to form a building site that is almost level. This part of the fill shows very little settlement and would have very little impact on the projected building. We assumed that no compaction of the fill had been done and that differential settlement had already occurred. The building area of the lot is completely clear of vegetation except for grasses. The wooded part of the lot consists mostly of trees and shrubs. Natural slopes surrounding the home site are less than 30%. A topographic map of the parcel is found on Exhibit A. A typical slope profile is also found in the Appendix. The slopes in the vicinity are identified as stable with no evidence of deep seated instability. Some evidence (i.e.,tree growth modification) of mass soil-creep movement are found on the south slope below the leveled building area. However,the slopes show no evidence of landslide activity. C. Subsurface Conditions The subsurface geotechnical investigation performed in September of 2001, consisted of an examination of the cut slope on the east side of the proposed home site and the road cuts entering the property. The resultant soil log produced from the site visit is included in the Appendix. As shown in the boring log, about 32"of sandy gravel overlay the semi-cemented gravely sandy soils at the site. The entire profile is well-consolidated. The stiffness of the underlying soils indicates a low potential for liquefaction during seismic activity. The native soils encountered in our investigation were found to be of a quaternary Vashon till. D. Hydrologic Conditions D.1 Surface Water Lake Limerick is located on the western side of the East Mason Lake Road and north of the subject property. Runoff from the general vicinity of the lot travels to the north and to a low marshy area. No surface water was found on the site. Runoff from the roof will become, in effect, surface water,and must be collected and conveyed down slope in such a way as to protect downslope soil from erosion. D.2 Groundwater Groundwater was not observed or encountered. No instances of seeps of groundwater were seen on the slopes on or adjacent to the parcel. Normal footing drains for the dwelling will not be required for construction. The groundwater conditions should be of little concern for the ultimate development of the site. III. Regulatory Requirements for Development Development of the parcel is subject to requirements of the Mason County Building and Planning Departments, which regulate slope stability. The Landslide Hazard Ordinance includes criteria for erosion, landslide, and seismic hazard areas. If the criteria defining these as hazard areas are not met by the characteristics of the site, then it can be argued that the parcel is not within a geologically hazardous area. Otherwise,a permit for development of the site can be issued by the County to mitigate the hazardous conditions encountered. The following narrative will address the relevant sections of the County's Ordinance: Erosion Hazard Areas The native soil found on the site, (Ac)Alderwood gravelly sandy loam415-30% slopes, is described in the USDA-SCS Soil Survey of Mason County, WA (1960) as having little erosion hazard. Very little construction activities are anticipated for the home so we do not believe that an erosion hazard exists. No construction is expected to take place on the slopes. The home will be placed on the level area of the lot. Otherwise, there is no 'evidence of soil erosion anywhere on the site to suggest that the site should be included in the Erosion Hazard Area designation. Landslide Hazard Areas There is no evidence of soil mass movement in the vicinity of this parcel, and the site generally does not match the criteria set forth in the Critical Areas Ordinance for designation as a Landslide Hazard Area. The US SCS maps the area of the home as having 15-30% slopes. The ordinance#88-00 Classification for landslide hazards regarding hillsides and springs(A. 1. e.)are not applicable. Seismic Hazard Areas The well-consolidated site soils exclude the site from inclusion in this category. This project is located within a"Zone 3 Area"as per the 1997 edition of the Uniform Building Code. IV. Slope Stability Analysis Based on the geotechnical investigation,a model of site slope stability was prepared to assess the instability of the slope under static and dynamic loading. Native soils were modeled based on a unit weight of 133.21bs/ft3 and an internal angle of friction(0)of 35.50. The resultant model, in spreadsheet form, is included in the Appendix. There is no evidence of deep seated instability in the site slope that would prevent development of the site for residential-construction. V. Cut& Fill slopes and Site Grading Requirements No cutting or filling is required or anticipated for the project. VI. Foundation Design Recommendations On the basis of the data obtained from the site and the test results from the various laboratory tests performed, GEOTECHNICAL TESTING LAB recommends that the III following guidelines be used for the net allowable soils bearing capacity. Net Allowable Footing ASTM D 1557 Soils Bearing Depth Sub grade Compaction Capacity surface 90% 2,000 lbs./ft2 Any excessively loose or soft spots or areas that do not meet the compaction requirements that are encountered in the footing sub-grade will require over-excavation and backfilling with at least 2 ft. of structural fill. In order to minimize the effects of any slight differential movement that may occur due to variations in the character of the supporting soils and any variations in seasonal moisture contents, it is recommended that all footings be suitably reinforced to make them as rigid as possible. VII. Soil Compaction All soil beneath the footings shall be placed in the firm native soil. VIU. Proposed surface drainage The only hard surface area that will collect water will be the roof of the proposed home. We recommend that all downspouts be tight lined to a discharge area such as a seepage pit. Subsurface drainage will not pose a problem to the home. IX. Lateral earth pressures The following data was determined for the on-site soils: Lateral Pressure Active coefficient 0.30 Passive (lbs/sq. ft.) 250 Friction (coefficient) 0.40 X. Erosion and Sedimentation Control Best management practices for construction site erosion control must be implemented during and after site development to insure that down slope soil and water resources are not impacted by construction activities. See Exhibit C for details for a silt fence that can be constructed should the site need earthwork. However, extensive earthwork is not anticipated. XI. Structural fill We do not anticipate that fill will be needed for the home but should it become necessary, the on-site soils may be used for structural fill. XL Laboratory Data Along with the field investigation, a supplemental laboratory testing program was conducted to determine additional pertinent engineering characteristics of the foundation materials necessary in analyzing the behavior of the proposed structure. Selected sar ples,were subjected to amain analysis and a shear test Nvas—Ufo:med on samples taken from the site for the purpose of determining the internal angle of friction to confirm the stability of the slope. The results are included in the appendix. XIII. Foundation Setback In compliance with 1997 UBC Section 1809, any building foundation must be placed in observance of an H/3 foot setback from the existing crest of the slope on the site. As shown on Exhibit a substantial building site remains for development if this setback � � r requirement and others imposed by Mason County are met. Compaction tests must be conducted on any fill soils under the proposed home to determine if these soils conform to 90% of the maximum dry density as per ASTM D-1557 as recommended above. Storm water Management Evidence of storm water runoff on this site has been minimal because of the vegetation on the sloping portions of the site. Except for the roof runoff, which will be collected as mentioned above,we do not anticipate a problem. XIV. Conclusion The subject parcel does not meet the defining criteria for inclusion in any of the Hazard Areas included in the Mason County Critical Areas Ordinance and may be safely developed with the recommended mitigation measures described above. XV. Limitations We have prepared this report for Karen Bailor for use on the above referenced site for the construction or placement of a home. The data used in preparing this report should be provided to prospective contractors for their bidding or estimating purposes only. Our report, conclusions and interpretations are based on data from others and limited site reconnaissance, and should not be construed as a warranty of the subsurface conditions. Variations in subsurface conditions are possible and may also occur with time. A contingency for unanticipated conditions should be included in the budget and schedule. Sufficient testing and consultation should be provided by our firm during construction to confirm that the conditions encountered are consistent with those indicated by the field review, to provide recommendations for changes should the conditions revealed during the work differ from those anticipated, and to evaluate whether earthwork and foundation installation activities comply with our recommendations. The scope of our services does not include services related to environmental remediation and construction safety precautions. Our recommendations are not intended to direct the contractor's methods, techniques, sequences or procedures, except as specifically described in our report for consideration in design. If there are any changes in the loads, grades, locations, configurations or type of facilities to be constructed,the conclusions and recommendations presented in this report may not be fully applicable. If such changes are made, we should be given the opportunity to review our recommendations and provide written modifications or verifications, as appropriate. Respectfully submitted, Harold Parks Engineering geologist �( N. •y • v ..•�wasy;•.<y� • %-t J*At- • :AT • ,p q 18020 • J •� •• mo -O.GISTEV.0- 1 ••s;o -•.....••' TS10 VAt E*6 s�a� GEOTECHNICAL TESTING LABORATORY VICINITY MAP �. - 00 I i� 2 0 0 2 w 1� 1� ��qFO i 46I -`s' 4 - 10011 Blomberg Street SW, Olympia,WA 98512 ��'� U�iE�%iV`- �r fir' ;�. _ � I Line Property� 1 Proposed Home i f ',shed 1 212 t r: SCALE: 1 " = 20 ' -' Contour Intervals : 2 ' Karen Bailor / �'' GEOTECHNICAL TESTING LAB Date: Sept. ,2001 File#: Boring Log#: I Client: Bailor Boring Type: road cut Depth Drilled: 8 feet Depth Field Change Percent Minus (in) Description in Soils %M I N I Qu I Qp V LL Pl, PI 3/411 #4 #200 Comments 6 duff -------------- 12 silty sandy gravel -- ------ ---------------- ---------- ------- - 18 --------------------------- ------ ----------- 24 ; 1 2500 non- ;plastic roots 30 .......... ............... ---------- ....:-------------------------- -------- -----------—1------ ------ 36 : ----------------- ........ ---- ------- ------------------ ------ -------- 42 : ................................. -------- ------- 48 ---------------------------- -------- ....... 54 : -:-------------------------- ---------I-------1� 60 : .....:-------------------------- 66 : ----------------------------- 72 : sandy gravel -------------------------- 78.. ------------ ------ 84 ---:--------------------------- 90 : --------------------------- 96 ..........--------- --------I-------r... 102 and boring --------------------------- -------- -- 108 --------------------------- -------- ------- 114 ----:-- -------- ------- -----I-------:-------------------------------------------- 120 126 132 ..................... ...... -------- ........ 138 -------- -------------------------------............ -------------------- ........ 142 ............................... ------------------------------- ------------- ------------------- 149 -----:�-------------------------- 154 - ....:--------------------------- 160 : ---------- ...... .... 166 ........... ------ -------- -------- 172 178