The URL can be used to link to this page

Home My WebLink AboutBLD2015-00195 - GEOTECH • er.„-t> _'� NORTHWESTERN TERRITORIES, INC. 717 SOUTH PEABODY STREET,PORT ANGELES,WA 98362 ■ ; Engineers_ Land Surveyors-Geologists I Construction Inspection-Materials Testing Port Angeles(360)452-8491 E-Mail:inro'ntilu.com NT/ July 2,2015 Mr. Michael Bair 5411 Highway 20 Port Townsend,WA 98368 Subject: Geotechnical Review of Plunge Pool At The Bair Residence Jefferson County Parcel ff 901051001 5411 Highway 20, Port Townsend, Washington Dear Mr. Bair Others Concerned, In June of 2015, Northwestern Territories, Inc. (NTI)reviewed the geotechnical and geologic hazard aspects of the proposed spa pool to be constructed at the subject parcel. Trent Adams,Geotechnical Engineer in Training and Steve Luxton,Senior Geotechnical Engineer,completed a site inspection on June 22,2015. An extensive geotechnical study of the site was completed in 2011 by the undersigned Engineer. 1.0 The Proposed Action—Modest in Scale and Impact During the June site visit, Mr. Bair pointed out the site of an 8-foot by 8-foot spa pool that is to be constructed at the western edge of the existing patio. That patio is situated on the west side of the house and the pool's western edge was found to be approximately 88 feet from the rim of the marine bluff on the west and approximately 175 feet east of the shoreline's ordinary high-water line. A scaled site plan showing the position of the pool with respect to the house and bluff is attached as Attachment 1. A field review of the site showed that conditions were unchanged from the site investigation completed in March of 2011. We reviewed a drawing of the proposed pool provided by Mr.Bair entitled Partially In-Ground Modular Therapy Spa dated May 19,2015. The plans call for 75 pounds per square foot of foundation bearing strength for every foot of pool depth. For the selected pool,this results in a bearing load of 319 pounds per square foot for the water and approximately 150 pounds per square foot for the concrete footings supporting the pool. In total then,a bearing capacity of less than 500 pounds per square foot is required. The referenced spa drawing is included herewith as Attachment 2. r r Il JUL - 2 2015 !� LJ , JEF ERSCNi COUNTY DEPT OF COMMUNITY DEVELOPMENT • • Geotechnical Review of Plunge Pool 12015 , ), {ate. -4 $ '`ym,".Y`" ti. 1 '�� µ r ..jf 2.0 Setback and Foundation Recommendations The March 4,2011,Geotechnical Report by NTI included a recommendation for structural setback. The suggested minimum setback recommended in the report was 60 feet with a minimum vegetated buffer of 35 feet. Observations down-slope of the spa confirmed the presence of a thick glacial till formation with considerable strength that was found earlier to underlie the site. As noted above,the spa pool is to be located at a setback of 88 feet from the rim of the bluff,well within the recommended zone of safety. In Photograph 1 shown above,the plunge pool is to be located at the edge of the concrete patio wall shown on the right. The 2011 report made recommendations for soil bearing strength backed on test pit observations. For shallow footings,the earlier study recommended a bearing capacity of 2,000 pounds per square foot. Thus,the allowable bearing capacity is well in excess of the required bearing strength designated by the manufacturer of the spa. In summar Y.in our opinion,the spa pool as planned is entirely appropriate and safe from the geotechnical and geologic hazard point of view. Please refer to the cited Attachments for more specific information. 3.0 Drainage Recommendations The pool"box"will be set inside the concrete"vault"with spacing provided between the box and the vault. Within that open space,a floor drain will be provided to prevent the outer section from filling with water from the pool and from rainfall. The total new impervious surface a 2 iJ I��S i I; ,? JUL - 2 2015 DEPT.OF COMMUNITY DEVELOPMrNT 0 • Geotechnical Review of Plunge Pool 1 2015 about 88 square feet. There will be a small,—2"—4"diameter outlet drain pipe outside the vault that would disperse runoff through roughly 85 feet of vegetation before it gets to the bluff's rim. In our opinion,the proposed method for drainage control is appropriate since the total catchment area of surface runoff is quite small and because runoff will be dispersed through a lengthy span of native vegetation. 4.0 The Limitations of Our Investigation, Findings,and Conclusions This reconnaissance study was completed without the use of deep subsurface borings and without observations and measurements over long periods of time. The observations and conclusions were derived principally from surface observations and inferences from surface observations. Undiscovered and unseen conditions in the subsurface could exist that would affect the observations and conclusions of this report. Users who require a higher degree of reliance on this assessment may wish to obtain more detailed studies. The observations and conclusions of this report apply only to the subject property and they are not transferable to nearby or adjoining property. This report is the sole property of Mr. Micheal Bair, applies only to the described site,and may be used by others only with his permission. NTI Engineering and Land Surveying warrants that this report and the related study were conscientiously prepared in accordance with the practice of professional engineering and according to the principals of geologic science. No other warranty,neither expressed nor implied, is provided herewith. Thank you for asking us to complete this geotechnical review. NTI Engineering and Land Surveying Sincerely yours, �t� of wAS�M �'O 1 4Z156), qNsiONAL / r Steve S. Luxton MSc,PE Trent T.Adams BSCE, EIT Senior Geotechnical Engineer Geotechnical Project Manager r. I C 1H0VI r i 3 ! - JUL - 2 205 1 Ll U JEFEERSOrl COUNTY C PT OF COf;i:MuN TY DE`1 OPMENT •�'r NORTHWESTERN TERRITORIES, INC. 717 SOUTH PEABODY STREET,PORT ANGELES,WA 98362 tEngineers: Land Surveyors-- Geologists Construction Inspection[- Materials Testing `• ' Port Angeles(360)452-8491 E-Mail:infot6?n64u.com NT/ July 2,2015 Mr. Michael Bair 5411 Highway 20 Port Townsend,WA 98368 Subject: Geotechnical Review of Plunge Pool At The Bair Residence Jefferson County Parcel#901051001 5411 Highway 20, Port Townsend,Washington Dear Mr. Bair Others Concerned, In June of 2015, Northwestern Territories, Inc. (NTI) reviewed the geotechnical and geologic hazard aspects of the proposed spa pool to be constructed at the subject parcel. Trent Adams, Geotechnical Engineer in Training and Steve Luxton,Senior Geotechnical Engineer,completed a site inspection on June 22,2015. An extensive geotechnical study of the site was completed in 2011 by the undersigned Engineer. 1.0 The Proposed Action—Modest in Scale and Impact During the June site visit, Mr. Bair pointed out the site of an 8-foot by 8-foot spa pool that is to be constructed at the western edge of the existing patio. That patio is situated on the west side of the house and the pool's western edge was found to be approximately 88 feet from the rim of the marine bluff on the west and approximately 175 feet east of the shoreline's ordinary high-water line. A scaled site plan showing the position of the pool with respect to the house and bluff is attached as Attachment 1. A field review of the site showed that conditions were unchanged from the site investigation completed in March of 2011. We reviewed a drawing of the proposed pool provided by Mr. Bair entitled Partially In-Ground Modular Therapy Spa dated May 19,2015. The plans call for 75 pounds per square foot of foundation bearing strength for every foot of pool depth. For the selected pool,this results in a bearing load of 319 pounds per square foot for the water and approximately 150 pounds per square foot for the concrete footings supporting the pool. In total then,a bearing capacity of less than 500 pounds per square foot is required. The referenced spa drawing is included herewith as Attachment 2. IUI - 2 2015 j 0 L. ,e, COUNTY DEPT OF COMMON!TY DEVELOPMENT W . Geotechnical Review of Plunge Pool 12015 got lam_,.Y. :- ,•. . .I. * r may.., f �/ 1•' � t 'c is 2.0 Setback and Foundation Recommendations The March 4, 2011,Geotechnical Report by NTI included a recommendation for structural setback. The suggested minimum setback recommended in the report was 60 feet with a minimum vegetated buffer of 35 feet. Observations down-slope of the spa confirmed the presence of a thick glacial till formation with considerable strength that was found earlier to underlie the site. As noted above,the spa pool is to be located at a setback of 88 feet from the rim of the bluff,well within the recommended zone of safety. In Photograph 1 shown above,the plunge pool is to be located at the edge of the concrete patio wall shown on the right. The 2011 report made recommendations for soil bearing strength backed on test pit observations. For shallow footings,the earlier study recommended a bearing capacity of 2,000 pounds per square foot. Thus,the allowable bearing capacity is well in excess of the required bearing strength designated by the manufacturer of the spa. In summary,in our opinion,the spa pool as planned is entirely appropriate and safe from the geotechnical and geologic hazard point of view. Please refer to the cited Attachments for more specific information. 3.0 Drainage Recommendations The pool"box"will be set inside the concrete"vault"with spacing provided between the box and the vault. Within that open space,a floor drain will be provided to prevent the outer section from filling with water from the pool and from rainfall. The total new impervious surface a -. -- -" •-• • H �� cV 2 lL I 1I JUL - 2 2015 DEPT.OF COMMUNITY DEVELOP...- Geotechnical Review of Plunge Pool 1 2015 about 88 square feet. There will be a small, -2"—4" diameter outlet drain pipe outside the vault that would disperse runoff through roughly 85 feet of vegetation before it gets to the bluff's rim. In our opinion,the proposed method for drainage control is appropriate since the total catchment area of surface runoff is quite small and because runoff will be dispersed through a lengthy span of native vegetation. 4.0 The Limitations of Our Investigation, Findings,and Conclusions This reconnaissance study was completed without the use of deep subsurface borings and without observations and measurements over long periods of time. The observations and conclusions were derived principally from surface observations and inferences from surface observations. Undiscovered and unseen conditions in the subsurface could exist that would affect the observations and conclusions of this report. Users who require a higher degree of reliance on this assessment may wish to obtain more detailed studies. The observations and conclusions of this report apply only to the subject property and they are not transferable to nearby or adjoining property. This report is the sole property of Mr. Micheal Bair, applies only to the described site,and may be used by others only with his permission. NTI Engineering and Land Surveying warrants that this report and the related study were conscientiously prepared in accordance with the practice of professional engineering and according to the principals of geologic science. No other warranty, neither expressed nor implied,is provided herewith. Thank you for asking us to complete this geotechnical review. NTI Engineering and Land Surveying Sincerely yours, $5. 0 ��y .of WAS/�r�-0 z, „ „NA, Steve S. Luxton MSc,PE Trent T.Adams BSCE, EIT Senior Geotechnical Engineer Geotechnical Project Manager C I 1-7 3 .r I J L. JEFFEgsN,'j)uNrr r I crr,Ffn '°, IAITYDRr")PPuI''Y