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Home My WebLink AboutGeoTech Investigation - BLD Engineering / Geo-tech Reports - 4/29/1999 DAMES & MOORE A DAMES&MOORE GROUP COMPANY 1 1 I i GEOTECHNICAL INVESTIGATION PROPOSED COMMUNICATION TOWER BELFAIR/SHEARER,SITE WA0167-1 BELFAIR,WASHINGTON j For NEXTEL COMMUNICATIONS D&M JOB#33415-068-163 April 29, 1999 MASTER FILE Site No.WA 2�62-1 Site Name 'LeScir(ckea0e,- Category 5 J DAMES & MOORE A DAMES&MOORE GROUP COMPANY 500 Market Place Tower April 29, 1999 2025 First Avenue Seattle,Washington 98121 206 728 0744 Tel Mr. Michael Branden 206 727 3350 Fax Nextel Communications 1750 112`h Avenue, Suite C-100 Bellevue,Washington, 98004 Report of Geotechnical Investigation Proposed Communication Tower Belfair/Shearer, Site WA0167-1 Belfair,Washington D&M Job#33415-068-163 Dear Mr. Branden: This report presents the results of a geotechnical investigation performed near the proposed communication tower site. The tower site is located in the center of the vacant lot on the Shearer property at N.E. 350 Mast Road in Belfair, Washington. Figure 1 is a vicinity map showing the location of the project site. Authorization for our services was provided by your Purchase Order No. 265466, dated April 8, 1999. We understand that the site will consist of a monopole communication tower, approximately 150 feet in j height. Specific foundation loads were not available at the time of this report. Overturning loads are anticipated to govern foundation design. We understand that typical loading conditions for this type of tower include vertical loads in the range of 20 to 30 kips, lateral loads of 20 to 35 kips and overturning movements of 1,600 to 2,400 kip-feet. We understand that a pre-fabricated I I' x 20' shelter will be installed to house the associated equipment. SCOPE The scope of this report is outlined in our standard proposal to Nextel, dated February 5, 1996. The services included; completion of one geotechnical boring, laboratory testing of soil samples to assess physical properties of site soils for correlation with established strength and compressibility relationships, the development of recommendations for foundation support of the tower, and preparation of this report summarizing the investigation and presenting our conclusions and recommendations. SITE CONDITIONS The proposed tower was to be located near the water tank on the Shearer property but was later relocated about 800 feet northwest of the tank. The soil boring for this project was drilled at the original proposed site location. Figure 2 is a site plan showing property line locations, location of the original and the new site, and the location of soil boring (B-1-99). The proposed tower location is in a vacant lot near the Shearer home at an elevation of approximately 345 feet above mean sea level. 2 G:\WPDATA\163\REP0RTS\Nexte1 Belfair.doc Offices Worldwide DAMES & MOO RE A DAMES&MOORE GROUP COMPANY Nextel Communications April 29, 1999 Page 2 Our knowledge of the subsurface conditions at this site is based on drilling one boring(13-1-99)to a depth of 29 feet beneath the existing grade at the original tower location and geologic information published by the U. S. Geologic Survey for the area. Boring B-1-99 was advanced using a drill rig equipped with a 4- inch-internal-diameter(ID) hollow-stem auger. A graphical representation of the boring log is presented on Figure 3. The subsurface materials were classified in accordance with the Unified Soil Classification System, Figure 4. Samples were obtained using a split barrel standard penetration test(spt)sampler. The samples were then transported to our Seattle laboratory for further testing. Tests for moisture content, density and fines content were performed. The results of the tests are shown on the boring log. According to published geologic information, the proposed site is underlain by a layer of sand and gravel overlying glacial till. Subsurface conditions at the boring consisted of about 2.5 feet of sand and gravel followed by very dense silty sand with gravel (glacial till) that extended to the final depth of the boring at 31.5 feet bgs. At the time of our exploration, groundwater was encountered at a depth of about 21 feet. 1 DISCUSSION AND RECOMMENDATIONS i GENERAL 1 Although the boring performed to determine the subsurface conditions at the proposed tower location was drilled at the original site location(about 800 feet away from the new site), based on information from the U.S.G.S. (Department of Interior, U.S.G.S. Map 1-853-D), we anticipate the conditions at the new site location to vary only slightly. The following table (Table 1) lists the estimated pertinent engineering characteristics of the soils encountered during our geotechnical investigation. The soil properties presented in Table 1 are based on published correlations between N-values and soil shear strength. Good engineering judgment and appropriate safety factors should be used in the design of the tower foundation. TABLE 1 CHARACTERISTICS OF SOILS ENCOUNTERED Depth Description Total Unit Friction Cohesion Skin Friction (feet) Weight Angle Intercept (psf) (pcf) (degrees) (psf) 0-2 Sandy Gravel 135 35 0 0 2-31 Very Dense Sand 125 41 0 900 w/silt K:\Wp\WPDA"rA\163\REPORTS\Nextel Belfair.doc Offices Worldwide i DAMES & MOORE A DAMES B MOORE GROUP COMPANY Nextel Communications April 29, 1999 Page 3 Drilled Pier Foundation We recommend that the proposed monopole communication tower be supported on a drilled pier founded in the underlying gravel. For loads in the range given below, we estimate that a drilled pier with a minimum diameter of 48 inches and a minimum embedment of 30 feet will be required. Such a pier is expected to resist a combination of lateral load of 35 kips and an applied overturning moment of 2,400 foot-kips with an accompanying lateral deflection of less than approximately '/2-inch at the top of the pier. This estimate is based only on geotechnical considerations, and the ability of the pier to structurally withstand these loads must be separately evaluated. The lateral load and overturning moments will likely govern foundation design for the tower. However, allowable end bearing pressures of 20 ksf may be used for design with embedment depths of 30 feet or greater. This value may be increased by one-third for transient loads from wind or seismic forces. Allowable skin friction values are given above, in the table of soil properties. Hard drilling conditions should be anticipated below 2.5 feet at this site. Ground water is not anticipated above 20 feet. However, if groundwater is encountered, some caving of the hole may occur during drilling. Site Preparation 4 We anticipate that grading required for site development should be minimal. If site grades are to be raised, we recommend that imported fill materials should consist of non-organic, granular material with no particles larger than 3 inches nominal diameter. Imported fills placed during wet weather conditions should consist of well-graded sand and gravel, or crushed rock materials containing less than 5 percent fines (silt-and clay-sized material passing the No. 200 sieve). The crushed rock should be a clean, well-graded, free draining material having no more than 5 percent passing the No. 200 sieve and a maximum particle size of 1'/2-inches. The rock should be compacted to 95 percent of the maximum density established in accordance with ASTM Test Method D 1557. All fill should be placed in uniform, relatively horizontal lifts and compacted to at least 95 percent 1 relative compaction as evaluated by ASTM Test Method D 1557. The optimum lift thickness will depend on the type of compaction equipment used, but should generally be less than about 12 inches in loose thickness. Fill should be placed on a firm, unyielding subgrade. Care should be taken to avoid disturbance of loose and/or soft subgrade soils. 1 G:VPDATA\163\REP0RTS\Neate1 Belfair.doc Offices Worldwide DAMES & MOORE A DAMES&MOORE GROUP COMPANY Nextel Communications April 29, 1999 Page 4 Construction Monitoring and Testing We recommend that Dames & Moore be retained to provide construction monitoring and testing services during foundation preparation. The purpose of our field monitoring services is to confirm that site conditions are as anticipated, to provide field recommendations as required based on conditions encountered, and to document the activities of the contractor to assess compliance with the project recommendations provided by Dames &Moore. CLOSURE The analyses, conclusions, and recommendations presented in this report are based on site conditions as they existed at the time of our field exploration, and further assume that the conditions encountered in our exploratory boring are representative of subsurface conditions within the project area. If conditions different from those described in this report are encountered during construction, Dames & Moore should be advised at once so that additional or revised recommendations may be provided where necessary. This report was prepared for the exclusive use of the Nextel Communications. It should be made available to prospective contractors for information on factual data only and not as a warranty of subsurface conditions. We appreciate the opportunity of providing these services. If you have any questions or require further information, please call. , Very truly yours, x DAMES &MooRE .e 35022 Timothy l�e G. ckerle P.E. 4 �` Project Engineer s�IONAt, W. Martin McCabe, P.E. EXPIRES: 11/10:oo Senior Geotechnical Engineer Attachments: Figure 1 - Vicinity Map Figure 2 - Site Plan Figure 3 - Log of Boring Figure 4 - Unified Soil Classification System G:\WPDATA\163\REP0RTSWex1e1 Belfair.doc Offices Worldwide - jv Project 9 Location ? �: Washington ---��---f — �-- - �� •..cam_ .. . J a Subject Property t• i �i yr vy f;� 1f JJ � -, � , � 'j � � ,. � lfair• � � fo / �o cnvr xa o '(P J j 01 � i� �j ,,-.;3r-'�•.: Mobi�eNo4fie rk nk yrJ� ✓� i S ' s' 2 li :r. / O •�.-/q Per ,.� 3. •,.- ay ``ti'�< ..�+"�'' > , If ,. :� �vr v�. A • x�:43':trJ,E•.._ J'�yC1l« - -. �ozfs; .w.'..`• � / � rM Map created with TOPO! 01997 Wildflower Productions,www topo.com, based on USGS topographic map 0 0.5 1.0 wimmumi Scale in Miles Figure 1 DAMES & MOORE VICINITY MAP A DAMES&MOORE GROUP COMPANY Nextel Communications Job No.33415-068-163 Communications Tower/Belfair,Washington, #WA0167-1 O 3 o N I I i I I I I I 1 I 1 I I I I , r I I 1 cc I I Proposed Lease Area Existing Buffer I I , I I I I I 1 _.J 14o- Property Boundary Former Proposed �/ ,� �� LEGEND Lease Area / j Boring location Existing Water Tank and Lease Area 0 100 200 MEMEL— F,pproximate Scale in Feet Figure 2 DAMES & MOORE SITE PLAN A DAMES 3 MOORE GROUP COMPANY - Nextel Communications Job No.33415-068-163 Communications Tower/Belfair,Washington, #WA0167-1 0 U ' s . m \� 05� Surface Conditions 0\0 GW SAND and GRAVEL SM Brown,silty SAND with some gravel(very dense)(dry) 5 s 1 Ss ' l 10 7 2 50/ Brown,silty SAND with some gravel(very dense)(dry to damp) 5" SPT refusal at 10'5" VL c_ L 15 7 3 58 ' Brown,gravelly SAND and SILT(very dense)(damp) CL a� 0 20 8 4 68 ' j. Brown,gravelly SAND and SILT(very dense)(mast) Groundwater level at 21' >J 25 10 5 50/ Brown,silty,gravelly SAND(very dense)(moist) 5" 30 7 s 5/ ■ 1" I7< j SPT refusal at 30'7" Total depth—31.5' Drilling method: HSA Drill date: 4/23/99 Sampling method: SPT, 140# Approximate Ground Surface Elevation: 345' Figure 3 DAMES & MOORE Log of Boring B-1-99 A DAMES 6 MOORE GROUP COMPANY Nextel Communications Job No.33415-068-163 Communications Tower/Belfair,Washington, #WA0167-1 e Major Divisions Graphic Letter Symbol Symbol Typical Descriptions Well-Graded Gravels, ... . Little or no Fines GW Gravel-Sand Mixtures, Gravel and Clean Gravels I Gravelly Soils (little or no fines) o C)0 Poorly-Graded Gravels, 0 oo GP Gravel-Sand Mixtures, Coarse Grained p o Little or no Fines Soils Silty Gravels, GM Gravel-Sand-Silt Mixtures More than 50%of Gravels with Fines 21 Coarse Fraction (appreciable amount Retained on of fines) Clayey Gravels, No.4 Sieve GC Gravel-Sand-Clay Mixtures 1 1 Well-Graded Sands, 7 4 7 4 SW Gravelly Sands, Sand Clean Sand Little or no Fines and (little or no fines) .......... Sandy Soils .......... Poorly-Graded Sands, More than 50% SP Gravelly Sands, .......... .................... .......... of Material is Little or no Fines .......... Largerthan No.200 Sieve Size a a Silty Sands, More than 50%of Sands with Fines 4 SM Sand-Silt Mixtures Coarse Fraction Passing through (appreciable amount No.4 Sieve of fines) Clayey Sands, SC Sand-Clay Mixtures Inorganic Silts and Very Fine Sands, ML Rock Flour,Silty or Clayey Fine Sands or Clayey Silts with Slight Plasticity Fine Grained Silts Liquid Limit Inorganic Gays of Low to Medium Soils and Less than 50 CL Plasticity,Gravelly Clays,Sandy Clays, Clays Silty Clays,Lean Clays Organic Sifts and Organic OL Silty Clays of Low Plasticity Inorganic Silts,Micaceous or MH Diatomaceous Fine Sand or Silty Soils More than 50% of Material is Silts Liquid Limit Inorganic Clays of High Smaller than and Greater than 50 CH Plasticity,Fat Clays No.200 Sieve Size Clays I Organic Clays of Medium to OH High Plasticity,Organic Silts Peat,Humus,Swamp Soils Highly Organic Soil PT with High Organic Contents Figure 4 DAMES & MOORE UNIFIED SOIL CLASSIFICATION SYSTEM A DAMES&MOORE GROUP COMPANY Nextel Communications Job No.33415-068-163 Communications Tower/Belfair,Washington, #WA01 67-1