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DIB�LE ENGINEERS, INC. <br />Professional Structurai Engineering Services <br />Ken 1-larer, Condaminium La�v Group, YLl_.0 <br />For: View Ridge Condominiums HnA <br />425 45`�' ST SW <br />Everett, WA 98203 <br />November 15, 2013 <br />DEI Projcct: 13-311 <br />�i ��2 -02 � <br />Structural <br />Review <br />Summ�xry <br />Re: View Ridgc Conclominiums-I3uilding 421 Retaining Wall Strengthening Review <br />�verett, WA <br />Dear Mr. Harer: <br />Dibble Lngineers Inc. (UL'1) revietiaed the helical pile demand loads at tf�e pr-aposed basement �vall lateral <br />sti•engthenin� in Building �25. DEI understands that the e���mers of Vie�v Ridge Condominiurns requested <br />veritication oftt�e recommended helical pile capacity stated in I�'elson Geotechnical Associates, Inc. (NGA) <br />evaluation letter dated August 10, 2012. The owners also rec7uested an e�planation of benefits, casts, and risks <br />associated if the �ti�alt strengthening is omitted from the repair scope and a mechanism to monitor for lateral <br />failure. <br />The lateral strengthening ��as initially recommended by I�'GA after their site investigation of apparent settlement <br />of thc sol�theastcrn end of Building 425. VVhile investigating the settlement, NGA noted that the concrete <br />basement �valls do not appear to be retaining �valls cc�nstructed to resist the lateral earth presstu•es associated ���ith <br />the a�prosimately 10' of soil these �valls are retaining. DF.,I visited the site on September 27, 2013 and also <br />observed that ttie conca-etc basement ��ralls do not appear to be retaining �valls. NGA in conjunction �vith <br />Structural Desi�n Associates rec�mmended stren�,nhening the basement ��-alls �vith diagonal steel braces in the <br />interior side ofthe basement walls that connect to a��ile cap that is supported witli helical anchors. <br />Diagonat Brace Helical Pile Demand <br />For this analysis, DF,I assumed there are (4) helical piles per pile car ���ith a 3" pitch batter (3"l�orizontal to 12" <br />vertical). Neither the number of he(ical piles in each pile cap nor the batter is called out in SDA's detail of the <br />pile cap. �Ve also ass�nned that the braces are spaced at 12' on center. SDA's August 29, 2012 letter indicates a <br />12' on center brac�e spacing, but SDA's March 1:>, 2013 plan indicates spacing less than 12' on eenter. DEl used <br />thc SO pouncls per cEibic foot lateral earth pressure fran NGA's August 10, 2012 evaluatia�i letter. <br />f3ased upon the ab�ve info�7nation, the tna�imum pile cornpt•cssivc demand is 15,140 Ibs and the maximum pile <br />tensile demand is 9,100 Ibs. <br />Ex�lanation of I2isk <br />NGA's evaluation letter noted evidencc of ���ater accu►riulatin� bchind the concrete �valls and provides several <br />methods to b�th reduce and evacuate the water accu��tulation in addition tc� the ti4alt brace strengthening. The <br />hydrastatic pressure behind the «�all iE�creases the lateral pressures to the basernent ���all. The lateral }�ressure used <br />in tlye abo��e analysis docs not include hydrostatic pressurc. Both NGA and DEI obsen�ed that the basement «�alls <br />do not appear to be retaining �valls designed to resist lateral pressures. I`GA's recommendations appear to <br />adequately mitigate the lateral pressures on the basement �valls. <br />1029 �1cu•ker SJree! Page 1 of 2 P. 925-82$-4200 <br />h'r,•k[rrncl, Yd'A 98033 I: �#2_i-,Y27-6131 <br />