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Home My WebLink AboutAMEND 2017-0012; LA COSTA TOWN SQUARE PARCEL 3 RESIDENTIAL; STANDARD WAVIER REQUEST; 2019-04-16CITY OF CARLSBAD Standard Waiver Request Project Number: Amend 2017-0012/CT 2017-0003/PUD 2017-0004/SDP 2018-0018 (OEV2017-0178- LA COSTA TOWN SQUARE PARCEL 3 RESIDENTIAL Date of Request April 16, 2019 Project Location: Intersection of La Costa Avenue & cane Tjmiteo APN: 223-050-73 Requestor Name:. __ _,T"""R..,.C._R...,..ET.._.A~l=L ____ Telephone (949) 662-2144 Address: 4695 Macarthur Court, Suite 700 Newport Beach. CA. 92660 Waiver Request: The project requests a reduction from the required minimum 15-foot building setback as required per the CBC 1808.7.1 (Building Clearance from Ascending Slopes} and Engineering Standard GS- 15. Justification for Request: The project requests a reduction in the 15-foot building setback for Buildings 5 thru 16 down to a minimum of 4-feet. The request for reduced building setbacks is made in order to maintain the minimum density for the site, maintain adequate setbacks for landscaping along Private Drive Aisle 'B' and maintain the required minimum slope edge setback from La Costa Avenue. Supportive Material / Mitigation: Material has been submitted as part of this request to support the requested reduction in setbacks and provide for mitigation. Please refer to the attached SCST Slope Assessment dated October 23, 2018, the SCST Mudslide Analysis dated February 21, 2019, the SCST Slope Fence Retrofit dated March 7, 2019 and the Red One MSE Retaining Wall Visual Inspection dated March 7, 2019. . . 1'ed one engineering Inc March 7, 2019 TRC Retail 4695 MacArthur Court, Suite 700 Newport Beach, CA 92660 Attention: Mr. Brian Carey Subject: MSE Retaining Wall Visual Inspection La Costa Town Center City of Carlsbad, California Per your request, this letter presents the results of our visual inspection of the existing MSE wall. Background Red One Engineering designed a number of segmental retaining walls for the development of La Costa Town Square (Center). One large plantable segmental retaining wall is located below the commercial site and adjacent to an undeveloped parcel. The undeveloped parcel was originally referred to as the "Office" site. The wall was permitted with the City of Carlsbad as project no. C.T. 08-07 and drawing no. 474-7A. Site Visual Inspection I first visited the site on December 13, 2018 to perform a visual inspection of the wall. I walked the bottom and top of wall to look for irregularities and observe the general surrounding conditions. I also attempted to locate the wall subdrain outlets. Results of Site Visual Inspection After my site visual inspection, I made the following observations and comments via e-mail to TRC Retail: 1. I was unable to locate the subdrain outlets in the basins and on the slope due to vegetation growth. I would like to have these outlets located and demonstrate they are free, clear and operable. 2. The drainage ditch above the wall contains slough from the slope and is blocked in at least 3 locations by vegetation. The vegetation is primarily located at the 3 bougainvillea locations. The brow ditch should be cleared of soil, rock and trash and all vegetation should be cut back so the brow ditch flows freely. 1295 distribution way, vista, califomia 92081 phone 760.410.1665 facsimile 760.509.0078 matt@red1engineering.com 3. There is a catch basin inlet at the west end of the wall that is covered with a piece of plywood. The catch basin inlet should clear of all obstructions. 4. The plantable walls are typically planted with vines. There are locations where small trees appear to be growing from the face of wall. These should be removed as continued growth will cause damage to the block facing. Return Site Visit TRC Retail and their property manager addressed the issues raised and I returned to the site on February 8th, 2019 for a follow up visual inspection. I observed the following: 1. I was still unable to locate the subdrain outlets in the basins. 2. The drainage ditch above the wall was free and clear. The vegetation had been cut back significantly and the soil, rock and trash were removed from the bottom of the ditch. 3. The piece of plywood obstructing the drainage inlet had been removed. 4. The small trees had been removed from the plantable cells on the face of the wall. Clearing of the Subdrain Outlets TRC and their property manager then worked with their landscape contractor to locate and clear the subdrain outlets in the basins. I was provided visual evidence of obstruction being removed from the subdrain and water flowing free and clear from the subdrain outlet. This worked was completed on February 12th , 2019. Recommendations It is our understanding the undeveloped parcel will be developed into multi-family housing. During that process and after development it is recommended the following items be continually addressed: 1. The subdrains should be maintained free and clear through a regular maintenance schedule until the development is complete. The site development designers should be made aware of the current subdrain outlet locations and provide permanent connections to the storm drain as a part of their final design. 2. The drainage ditch above the wall should be maintained free and clear through a regular ongoing maintenance program. 1295 distribution way, vista, california 92081 phone 760.410.1665 facsimile 760.509.0078 matt@red1engineering.com I • 3. The face of wall planting should be maintained to eliminate the growth of larger species that may take root in the planting cells. Conclusions The existing large plantable retaining wall located below the commercial site and adjacent to an undeveloped parcel appears to be structurally sound and performing as designed. The wall should continue to perform as designed provided the recommendations provided herein are observed. Please contact the undersigned with any questions. Sincerely, Red One Engineering, Inc. f/;Jtf{/l!J- Matthew M. Merritt RCE #68429 1295 distribution way, vista, california 92081 phone 760.410.1665 facsimile 760.509.0078 matt@red 1 engineering.com SLOPE FENCE RETROFIT -AN A.TL.t.S COMPANY- March 7, 2019 Mr. Brian Carey TRC Retail 4695 MacArthur Court, Suite 700 Newport Beach, California 92660 SCST No. 160518N Report No. 3 Subject: EXISTING SLOPE ABOVE PARCEL 3 -FENCE RETROFIT DESIGN LA COSTA TOWN SQUARE CARLSBAD, CALIFORNIA Dear Mr. Carey: In accordance with your request, SCST, LLC (SCST} has evaluated a retrofit for the existing slope fence north of Parcel 3 at La Costa Town Square in Carlsbad, California. We understand that there is a concern for impact loads resulting from a potential mudslide from the slope to the proposed residential buildings below. BACKGROUND SCST has previously evaluated and compared the impact loads that may result from a potential mudslide event to the load rating of the existing cable railing fence. The results from our previous mudslide analysis indicated that the existing fence configuration cannot resist the impact loads that would result from a 2-foot-deep mudslide event (referenced). Therefore, we concluded that a retrofit design is necessary to resist these loads. RECOMMENDATIONS Based on our analysis, the existing fence can be retrofitted with anchors and lagging. Details of our fence retrofit design are provided in Figure 1. As shown, the retrofit consists of anchoring each of the existing fence posts to the slope using ¼-inch diameter steel wire rope and "deadman" anchor blocks. The existing fence cables are not adequate to contain debris flow; therefore, we recommend installing 4-inch-thick timber lagging between the fence posts to contain the flow during a potential mudslide event. Configuration details including size, spacing, and embedment are illustrated on the attached figure. However, structural details including, but not limited to, member connections and concrete reinforcement have not been provided. The aforementioned structural details shall be provided by others. SCST. LLC Corporate ~ead9uarlers 6280 Riverdale Street San D,ec;o CA 92120 877 215 4321 619 280 4321 619 280 4717 www scst com + '1 Ii TRC Retail SCST No. 160518N-03 _L_a_t_o_s_ta_T_o_w_n_S_qu_a_re __ M_u_lt_i-F_a_m_i_ly_H_o_u_s_in_g_. P_a_r_ce_l_3 _______________ + Carlsbad, CA March 7, 2019 LIMITATIONS Changes in the condition of the site can occur with time, and changes in the standards of practice and government regulations can occur. Thus, the findings in this report may be invalidated wholly or in part by changes beyond our control. This report should not be relied upon after a period of two years without a review by us verifying the suitability of the conclusions and recommendations to site conditions at that time. In the performance of our professional services, we comply with that level of care and skill ordinarily exercised by members of our profession currently practicing under similar conditions and in the same locality. Subsurface conditions can vary from those encountered at the boring locations, and our data, interpretations, and recommendations are based solely on the information obtained by us. We will be responsible for those data, interpretations, and recommendations, but will not be responsible for interpretations by others of the information developed. Our services consist of professional consultation and observation only, and no warranty of any kind whatsoever, expressed or implied, is made or intended in connection with the work performed or to be performed by us, or by our proposal for consulting or other services, or by our furnishing of oral or written reports or findings. This opportunity to be of rofessional service is sincerely appreciated. Respectfully Sub SCST, LLC ~ Gillian Carzzarella, PE Project Engineer GC:ER:af:hu Attachments: References Figure 1 -Fence Retrofit Detail (1) Addressee via email: bcarey@trcretail.com Emil Rud Principal Geotechnical Engineer (1) Mr. Carlos Palafox, TRC Retail via email: cpalafox@trcretail.com 2 TRC Retail SCST No. 160518N-03 M ii La Costa Town Square Multi-Family Housing, Parcel 3 + ---------- Carlsbad, CA March 7, 2019 REFERENCES California Department of Transportation (2011 ), Trenching and Shoring Manual, dated August. Lindeburg (2015), Civil Engineering Reference Manual, Fifteenth Edition, page 45-21 , published November. NAVFAC (1986), Foundations & Earth Structures, Design Manual 7.02, dated September. Red One Engineering Inc (2012), "As-Built" Plans, La Costa Town Square Office, La Costa Avenue, Carlsbad, California, dated October 3. SCS&T (2015) "Final As-Graded Geotechnical Report, La Costa Town Square, Office Development, La Costa Avenue, Carlsbad, California", Project No. C.T. 01-09, dated November 13. SCST, Inc. (2017), Limited Geotechnical Investigation, La Costa Town Square Multi-Family Housing, La Costa Boulevard, Carlsbad, California, SCST Report No. 160518N-1, dated February 28. SCST, Inc. (2018), Slope Assessment, La Costa Town Square Multi-Family Housing, Parcel 3, La Costa Boulevard, Carlsbad, California, SCST Report No. 160518N-2, dated October 23. SCST, LLC (2019), Mudslide Analysis, Existing Slope Above Parcel 3, La Costa Town Square, Carlsbad, California, SCST Report No. 190049N-1 , dated February 21. SCST, LLC (2019), Proposal for Engineering Services, Existing Slope Above Parcel 3 -Fence Retrofit Design, La Costa Town Square, Carlsbad, California, SCST Proposal No. 19-0108, dated February 22. 3 4' 3' SCST, LLC 4"THICK LAGGING iMIN. EXISTING CABLE RAILING FENCE ~ ¼" DIAMETER 6 x 19 \-_ [\\~ I l¥'-'l+:-:-,..l.:C.::..:...::..:::: . .::.:... .,..---,~;;,....,.....:.._;.:i.;.,,.l!J ~II ,..,:,:;{I\}{:ti\d' -~ ~, . :'.·; --~-.-.... :.:'. ,:__,:._ ·>·:·-... ~m;:;:;il_\l~ :-.·<::::>·':;(Reinforced So1Dc'.:.' ·'' --~@11,\ 1:~11 ~~]r · .. •·· · _._.., .-. · · · · ·. . ... • ... ,. ,. ,, :···.· I -:1.ll-'\\\-111::=::\\1~ · · · · . "'· ......... --.. , .. -... · -l.llfii1rr ··:-.· ... · ..... ·< .. <·.<··':'->":i <:_':< l,E~m-1-·:,··· ... '.:::, .. · .... •--:..--·: ,:i .-:::-rg::W;:;=;1~111-l.l~ · •·.· ,· · ·. • :. , .... · -11 ~n-rro-1 :·~<:i:;;:_:-:: ·:'.:i'.::.'>:>>· 1r~~1W '.".· ·: ,. '•.: : . '• .......... ~ ,, '·:· \ ~~~mh .. ·· .. ·-.. -.. ~a, ~~~TI}= . .-.-. m :=\\ -. ~ ~~ln=r.-''' COMPACTED FILL COMPACTION) EADMAN BLOCK FENCE RETROFIT DETAIL La Costa Town Square Multi-Family Housing Date: March, 2019 Figure: Parcel 3 Slope Fence Retrofit ' Carlsbad, California By: OTC Job No.: 160518N-03 1 , SLOPE ASSESSMENT ---------+ -AN ATLAS COMPANY- February 21, 2019 Mr. Brian Carey TRC Retail 4695 MacArthur Court, Suite 700 Newport Beach, California 92660 Subject: MUDSLIDE ANALYSIS EXISTING SLOPE ABOVE PARCEL 3 LA COSTA TOWN SQUARE CARLSBAD, CALIFORNIA Dear Mr. Carey: SCST No. 190049N Report No.1 In accordance with your request, SCST, LLC (SCST) analyzed the impact of a potential mudslide on the slope north of Parcel 3 at La Costa Town Square in Carlsbad, California. This site consists of a proposed multi-family residential building pad bounded on the north by a segmental retaining wall up to approximately 22 feet high with an ascending slope up to approximately 20 feet high (Red One Engineering, Inc., 2012). An existing pedestrian cable railing fence is located at the top of the retaining wall. We understand there is a concern for the safety of residents resulting from a potential mudslide from the slope to the proposed residential buildings below. The purpose of our analysis was to evaluate the impact loads on the fence resulting from a potential mudslide event. To complete this assessment, we reviewed previous background data including a geological reconnaissance performed on the slope (SCST, 2018). Additionally, we reviewed available published research materials discussing impact loads resulting from debris flows. Based on our analysis, the estimated peak impact force on a rigid obstruction from a debris flow is equal to the summation of the static, dynamic, and drag forces created by the mud flow (Vagnon & Segalini, 2016). We computed the static force by assuming a 2-foot-deep mudslide event acting on a maximum surface area of 4 feet per linear foot (i.e., the height of the fence). The dynamic force is a function of the velocity of the debris flow and the slope inclination (i.e., 2H :1V). We assumed the maximum velocity of the debris flow to be 1 foot per second. For this assessment, we neglected the drag force of the soil mass to yield slightly conservative results. The results of our mudslide analysis indicate an estimated peak force on the order of 450 pounds per linear foot of wall. Based on our review of the technical notes for the Sleeve-It 1224R System (Strata, 2011 ), the fence system has can handle a load of 50 pounds per linear foot applied at the top of the fence. This load is dependent on the maximum moment capacity of the pre-engineered foundation system. Consequently, it is our professional opinion that the existing fence configuration SCST, LLC Corporate Headquarlers 6280 Ri.e,dalc Street San D,ego CA 92120 577 215 4321 619 280 4321 619 250 4717 www scst com e.o TRC Retail SCST No. 190049N-01 '1 ii La Costa Town Square Multi-Family Housing, Parcel 3 + ----------- Carlsbad, CA February 21, 2019 cannot handle the impact loads that would result from a 2-foot-deep mudslide event. Therefore, a retrofit design is necessary to resist these loads. Specific recommendations for retrofit can be provided in a separate letter by SCST, if warranted. Changes in the condition of the site can occur with time, and changes in the standards of practice and government regulations can occur. Thus, the findings in this report may be invalidated wholly or in part by changes beyond our control. This report should not be relied upon after a period of two years without a review by us verifying the suitability of the conclusions and recommendations to site conditions at that time. In the performance of our professional services, we comply with that level of care and skill ordinarily exercised by members of our profession currently practicing under similar conditions and in the same locality. Subsurface conditions can vary from those encountered at the boring locations, and our data, interpretations, and recommendations are based solely on the information obtained by us. We will be responsible for those data, interpretations, and recommendations, but will not be responsible for interpretations by others of the information developed. Our services consist of professional consultation and observation only, and no warranty of any kind whatsoever, expressed or implied, is made or intended in connection with the work performed or to be performed by us, or by our proposal for consulting or other services, or by our furnishing of oral or written reports or findings. This opportunity to be of professional service is sincerely appreciated. Respectfully Submitted, SCST, LLC Gillian Carzzarella, PE Project Engineer GC:ER:af Attachment: References (1) Addressee via email: bcarey@trcretail.com Emil Rudo p , Principal Geotechnical Engineer (1) Mr. Carlos Palafox, TRC Retail via email: cpalafox@trcretail.com 2 TRC Retail SCST No. 190049Na01 m ii _L_a_c_o_s_ta_T_o_w_n_S_q_u_ar_e_M_u_lt_i-_Fa_m_i_ly_H_o_u_si_n_g,_P_a_rc_e_l _3 ______________ + Carlsbad, CA February 21, 2019 REFERENCES Ahmadipur & Qiu (2017), "Effect of a Soil Relative Density and the Inclination Angle of the Impact Force from A Granular Sliding Mass on a Rigid Obstruction", published June 6. Ahmadipur & Qiu (2018), "Impact Force to a Rigid Obstruction from a Granular Mass Sliding Down a Smooth Incline", Research Paper, published October 17. Hunsaker & Associates, (2018), "Vesting Tentative Map & Planned Development Permit, La Costa Town Square Parcel 3, Carlsbad, California", dated September 11. Red One Engineering Inc, (2012), "As-Built" Plans, La Costa Town Square Office, La Costa Avenue, Carlsbad, California, dated October 3. SCS&T, (2015) "Final As-Graded Geotechnical Report, La Costa Town Square, Office Development, La Costa Avenue, Carlsbad, California", Project No. C.T. 01-09, dated November 13. SCST, Inc. (2017), Limited Geotechnical Investigation, La Costa Town Square Multi-Family Housing, La Costa Boulevard, Carlsbad, California, SCST Report No. 160518N-1, dated February 28. SCST, Inc. (2018), Slope Assessment, La Costa Town Square Multi-Family Housing, Parcel 3, La Costa Boulevard, Carlsbad, California, SCST Report No. 160518N-2, dated October 23. SCST, LLC (2019), Proposal for Engineering Services, Existing Slope Above Parcel 3-Mudslide Analysis, La Costa Town Square, Carlsbad, California, SCST Proposal No. 19-0085, dated February 12. Strata (2011 ), Sleeve-It 1224R System -Fence and Pedestrian Rail Foundation for Segmental Retaining Walls, Version 11_F. Vagnon & Segalini (2016), "Debris Flow Impact Estimation on a Rigid Barrier", published July 22. 3 l:> z a: w w iii SLOPE ASSESSMENT ---------+ October 23, 2018 Mr. Scott Grady TRC Retail 3 SCST No. 16051 SN Report No. 2 4695 MacArthur Court, Suite 700 Newport Beach, CA 92660 Subject: SLOPE ASSESSMENT LA COSTA TOWN SQUARE MULTI-FAMILY HOUSING, PARCEL 3 LA COSTA BOULEVARD CARLSBAD, CALIFORNIA References: 1.) Hunsaker & Associates, (2018), "Vesting Tentative Map & Planned Development Permit, La Costa Town Square Parcel 3, Carlsbad, California", dated September 11 . 2.) SGS& T, (2015) "Final As-Graded Geotechnical Report, La Costa Town Square, Office Development, La Costa Avenue, Carlsbad, California", Project No. C.T. 01-09, dated November 13. 3.) SCST, Inc. (2017), Limited Geotechnical Investigation, La Costa Town Square Multi-Family Housing, La Costa Boulevard, Carlsbad, California, SCST Report No. 160518N-1 , dated February 28. Dear Mr. Grady: In accordance with you r request, SCST, Inc. (SCST) performed a reconnaissance assessment of the geotechnical conditions of the slope above the subject site. This site consists of a proposed multi-family residential building pad bounded on the north by a segmental retaining wall up to approximately 22 feet high with a sloping backfill up to approximately 20 feet high (Reference 1 ). The purpose of the subject assessment is to provide an opinion of the slope condition for consideration of mitigations to protect the buildings from potential slope failures or impact from potential falling rocks and/or debris from the slope. To do this assessment, we reviewed previous background data and performed a geological reconnaissance of the slope. SCST observed construction of the retaining wall and the mass graded fill slope above the wall (Reference 2). SCST later prepared geotechnical recommendations (Reference 3) for the development of the subject parcel. From our review of the reports, the slope is comprised of compacted fill with rocks up to 6 to 8 inches in dimension. The slope is now covered with mature landscaping consisting of ground cover and occasional shrubs. The subject development will connect the retaining wall drainage to buried storm drain pipelines. Based on our background review and reconnaissance, the slope is not considered subject to slope fa ilures or falling debris. Due to the potential for rocks 6 to 8 inches in dimension to become loose SCST, Inc. Corporate Headquarlers: 6280 R,verdale St reel + San D,ego CA 92120 877.215 4321 619 280 4321 619 280 4717 www scsl corn TRC Retail SCST Job No. 160518N : _La_c_os_t_a_T_o_w_n_s_q_u_ar_e_M_u_lt_i-_F_am_ily_H_ou_s_in_g_,_P_a_rc_e_l3 _______________ •+ Carlsbad , CA October 23, 2018 from the fill slope, it is possible that such rocks could escape the brow ditch. Specific recommendations can be provided for barriers for such debris, if needed. Changes in the condition of the site can occur with time, and changes in the standards of practice and government regulations can occur. Thus, the findings in this report may be invalidated wholly or in part by changes beyond our control. This report should not be relied upon after a period of two years without a review by us verifying the suitability of the conclusions and recommendations to site conditions at that time. In the performance of our professional services, we comply with that level of care and skill ordinarily exercised by members of our profession currently practicing under similar conditions and in the same locality. Subsurface conditions can vary from those encountered at the boring locations, and our data, interpretations, and recommendations are based solely on the information obtained by us. We will be responsible for those data, interpretations, and recommendations, but will not be responsible for interpretations by others of the information developed. Our services consist of professional consultation and observation only, and no warranty of any kind whatsoever, expressed or implied, is made or intended in connection with the work performed orto be performed by us, or by our proposal for consulting or other services, or by our furnishing of oral or written reports or findings. This opportunity to be of professional service is sincerely appreciated. Respectfully Submitted, SCST, INC. Elizabeth White, GIT Staff Geologist EW:ER:hu Emil Rudolph, GE 2767 Principal Geotechnical Engineer (1) Addressee via e-mail: sgrady@trcretail.com (1) Mr. Brian Carey, TRC Retail via e-mail: bcarey@trcretail.com 2