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HomeMy WebLinkAboutCT 14-10; POINSETTIA 61; RESPONSE TO GEOTECHNICAL REVIEW COMMENTS; 2018-01-24.. 4 A U<CUP DELTL\ January 24, 2018 Lennar Homes 25 Enterprise, Suite 300 Aliso Viejo, California 92656 Attention: Mr. Jamison Nakaya SUBJECT: Mr. Nakaya: RESPONSE TO GEOTECHNICAL REVIEW COMMENTS Poinsettia 61 Development Carlsbad, California We are proving herein our responses to the referenced third party geotechnical review comments regarding the Poinsettia 61 development in Carlsbad, California (Hetherington, 2018). Each comment is reiterated below (in italics}, followed by our response. Comment No. 1: The Consultant should review the project grading, MSE retaining wall, and foundation plans, provide any additional geotechnical recommendations considered necessary, and confirm that the plans have been prepared in accordance with the geotechnical recommendations. We have previously reviewed the project grading and MSE retaining wall plans as described in the referenced review letters (GDC, 2016, 2017b}. We provided additional geotechnical recommendations regarding conformance testing of the soils that are proposed for use in the retained zone of the MSE walls (GDC, 2017b}. We confirmed that the geotechnical aspects of the plans conformed to the intent of the referenced recommendations (GDC, 2014, 2017a}. Preliminary geotechnical parameters for use in post-tension slab foundation design for the planned residential structures were provided in Section 6.4 of the referenced geotechnical investigation (GDC, 2014}. We noted that our preliminary foundation recommendations should be considered subject to revision based on the conditions observed by Group Delta Consultants during mass grading of the site. In our opinion, the final foundation design parameters should be provided in the as-graded geotechnical report after the site is graded. It should be noted that the foundation plans for the residential structures have not yet been prepared. These foundation plans will be finalized and reviewed by Group Delta Consultants once the site is rough graded, and the as-graded conditions for each lot are known. • • Response to Geotechnical Review Comments Poinsettia 61 Development Lennar Homes GDC Project No. SD412B January 24, 2018 Page 2 Comment No. 2: The Consultant should provide a description of proposed development including grading, structures/improvements, drainage, use, foundation type, estimated structural loads, etc. We provided a description of the site conditions and proposed development in Sections 1.2 and 1.3 of our geotechnical investigation report (GDC, 2014). Additional information regarding the proposed structures and improvements, drainage, foundation type and estimated structural loads were provided in the referenced supplemental documents {GDC, 2016, 2017abcd). Additional foundation recommendations for the residential structures will be provided in the as-graded geotechnical report after the site is mass graded. Comment No. 3: The Consultant should provide a detailed description of the site geologic structure (bedding, fracturing, faulting, etc.) including reported regional trends of bedding and faulting. The Geology and Subsurface Conditions at the site were described in detail in Sections 3.0 through 3.4 of the referenced geotechnical report {GDC, 2014). A Regional Geologic Map was presented in Figure 3A of the report. No consistent trends in the bedding within the site vicinity were apparent on the regional geologic map. Based on our geologic observations of the cut slopes along Poinsettia Lane within the project site, the bedding within the Santiago Formation on site appears to be relatively flat-lying. No faulting was observed on site, as described in Section 4.1 of the referenced report (GDC, 2014). Detailed fault maps were provided in Figures 4A and 4B of the report. The faults maps show that the active dextral faults in San Diego county generally strike northwest-southeast. Comment No. 4: The Consultant should provide a geotechnical map/plot pion utilizing the latest grading plan for the project to clearly show (at o minimum) o) existing site topography, b} proposed structures/improvements, c) proposed finished grades d) locations of the subsurface exploration, and e) geologic structure. The Geotechnical Map (Plate 1) provided in the referenced geotechnical investigation showed all of the information requested by the reviewer, including (a) existing site topography, b) the proposed residential structures and road improvement, c) proposed finish grades, d) locations of the subsurface explorations (including the previous explorations completed by Geocon). and e) geologic structure {GDC, 2014). When the grading plans were modified in August of 2017 to include a variety of MSE walls around the site perimeter, we completed supplemental slope stability analyses evaluating the newly proposed structures and improvements, as well as the proposed finish grades for the perimeter slopes that were modified {GDC, 2017b). Note that the revised building pad grades do not vary substantially from the grades shown on the Geotechnical Map, outside of the MSE wall areas. In our opinion, revising the Geotechnical Map using the latest grading plan to show the revised grading throughout the site is unnecessary. ~:t GRCLP CEL TL\ ~~ C: \Files\Projects\SD412 B\16"0012. doc • • Response to Geotechnical Review Comments Poinsettia 61 Development Lennar Homes GDC Project No. 50412B January 24, 2018 Page 3 Comment No. 5: The Consultant should provide geologic cross-section(s) utilizing the latest grading plan showing (at a minimum) a) existing site topography, b} proposed structures/improvements, c) proposed finished grades, d) geologic structure, contacts, etc., e) slope setbacks for neor slope structures/improvements and f) locations of the subsurface exploration. Slope stability analyses output plots do not provide this data. It is our opinion that preparation of additional geologic cross sections as requested by the reviewer is not necessary. We included nine geologic cross sections in the slope stability section (Appendix C) of the initial geotechnical investigation report (GDC, 2014). We prepared another eight geologic cross sections at key locations in the referenced MSE wall plan review letter (GDC, 2017b). Additional cross sections were also provided at the abutment locations in the referenced foundation report for the bridges (GDC, 2017d). All of the slope stability cross sections that we have prepared for this project do show the existing site topography (a), proposed structures/improvements where applicable (b), the proposed finished grades (c), and the geologic structure (d). Therefore, we disagree with the reviewer's assertion that the slope stability figures do not provide the necessary data. Our recommended slope setbacks (e) were described in detail in Section 6.4.4 of the referenced geotechnical investigation report, and do not need to be shown on the geologic cross sections, in our opinion. The locations of our subsurface explorations with respect to the cross sections were shown on the Rough Grading Plan (Figure 2A) in the referenced investigation, and do not need to be projected onto the cross sections used for our slope stability analyses (GDC, 2014). Comment No. 6: The Consultant should provide a statement as to the impact of the proposed grading and construction on adjacent properties. It is our opinion that the proposed grading and construction will not have an adverse impact on the adjacent properties. Most of the remedial excavations required to construct the perimeter slopes and walls can be completed without off-site grading. One area along the northern property boundary may require some off-site grading to construct the planned MSE walls, if approved by the adjacent property owner. If permission to grade off-site in that area is not granted, Lennar has developed an alternative plan to use temporary solider pile shoring to complete the required excavations without off-site grading in that area. Comment No. 7: The Consultant discusses two sheared claystone beds identified by Geocon at the site, but does not provide the subsurface exploration logs by Geocon or include these beds in the slope stability analyses models. The Consultant should provide the logs of all subsurface exploration, include the sheared cloystone beds on the geologic cross-sections and slope stability analyses models, and address required mitigation. !i\ ~ GRCLF CELTA C:\Files\Pro jects \SD412 B\lB-0012. doc ' • ' Response to Geotechnical Review Comments Poinsettia 61 Development Lennar Homes GDC Project No. SD412B January 24, 2018 Page 4 The basal elevations of the two "sheared" claystone beds noted by Geocon, as well as two additional claystone beds encountered in our subsurface explorations, were described in Section 3.1 of the referenced report (GDC, 2014). These four claystone beds were encountered at basal elevations of approximately 226, 235, 245 and 265 feet MSL. The geologic cross sections used for our slope stability analyses did model these claystone beds, which are shown in green on Cross Sections A, B, E, G, H and I from our initial investigation (GDC, 2014). as well as Cross Sections A, B, C and G from our MSE supplemental report (GDC, 2017b). Our geotechnical investigation included continuous sampling in Borings B-2 and B-3 at the elevation of the claystone beds. These borings were located near the top of the highest cut slopes proposed along the northern edge of the property. We did encounter a fissured sandy fat claystone (CH) bed located at an elevation of 265 feet in those borings, but the claystone did not appear to have been previously sheared. A sample of the claystone was tested for shear strength indicating a peak strength of 24°, and an ultimate strength of 19°, as shown in Figure B-5.14 of the investigation (GDC, 2014). We used the shear strength from that test to model the fissured claystone beds in our slope stability analyses. Additional geologic observation and testing will be conducted during grading to confirm the anticipated geologic conditions that were incorporated into our stability analyses. It should be noted that 2:1 cut slopes up to 45-feet high were excavated along Poinsettia Lane in 2010, immediately adjacent to Geocon's 2006 borings 06GB-1 and 06GB-3, as shown on the Geotechnical Map in our investigation (GDC, 2014). These cut slopes extend down to an elevation of 247 feet along Poinsettia Lane, and expose the Santaigo Formiaton bedding that will be encountered in the highest cut slopes along the northern edge of the property. The cut slopes along Poinsettia Lane do not show indications of adverse bedding or slope instability that would occur if the claystone beds encountered by Geocon were in fact previously "sheared". Geocon's borings logs have previously been submitted to the City of Carlsbad, and should be available for review from the City (or they may be obtained directly from Geocon). We have provided an updated interpretation of the geologic conditions at the site based on our borings, laboratory testing, and geotechnical analyses (GDC, 2014). We do not feel that it is appropriate to reproduce Geocon's borings logs in our geotechnical report, as requested by the reviewer. Comment No. 8: The Consultant has recommended additional field exploration in order to provide bridge foundation recommendations. This work should be performed and reported, and should provide bridge foundation recommendations. The additional subsurface explorations and analyses have recently been completed for the proposed bridges on Poinsettia Lane. The investigation included four borings at the three-span bridge support locations to depths of up to 100-feet below existing grades. Bridge foundation recommendations were provided in the referenced Foundation Report (GDC, 2017d). d~ GRCLF OEL T.l\ C:\Files\Projects\SD412B\18-0012. doc • • • • ' Response to Geotechnical Review Comments Poinsettia 61 Development Lennar Homes GDC Project No. SD412B January 24, 2018 Page 5 Comment No. 9: The Consultant should update/modify recommendations to reflect the 2016 California Building Code. In general, the geotechnical recommendations provided in our 2014 geotechnical investigation remain applicable to the 2016 California Building Code (CBC). Geotechnical parameters for use in post-tension slab designs that area consistent with the 2016 CBC will be provided in the as- graded report. The updated 2016 CBC seismic design parameters are shown in the attached Tables 1 and 2. Note that the seismic design parameters have not changed from the 2013 CBC. Comment Na. 10: The Consultant should provide an opinion with respect to the stability of slopes including temporary, gross (static and seismic}, and surficial stability . We addressed gross static, seismic and surficial slope stability in Section 6.3.9 and Appendix D of the referenced geotechnical investigation (GDC, 2014). We addressed temporary slope stability in Section 6.3.10 of the 2014 report. Provided that the site is graded in accordance with our recommendations, we concluded that the static, seismic and temporary slope stability would be adequate. Our analyses indicated that the static safety factor of the proposed slopes will exceed 1.5, and that the safety factor of the proposed temporary 1:1 cut slopes will exceed 1.2. Our analyses also indicated that the proposed slopes will experience less than 1 inch of total deformation due to the anticipated seismic loading. Comment No. 11: The Consultant should provide and address global stability of the proposed MSE retaining walls. We provided supplemental slope stability analyses for the MSE walls in the referenced letter (GDC, 2017b). We came to the same conclusions described in Comment No. 10 above regarding the static, seismic and temporary stability of the proposed MSE walls. Our analyses indicated that the static safety factor of the proposed MSE walls and slopes will exceed 1.5, and that the safety factor of the proposed temporary 1:1 cut slopes will exceed 1.2. Our analyses also indicated that the proposed MSE walls and slopes will experience less than 1 inch of total deformation due to the anticipated seismic loading. It should be noted that an earthen buttress was initially recommended for the large cut slope along the northern edge of the property due to the presence of fissured claystone {GDC, 2014). Our supplemental analyses for the MSE walls indicate that proposed geogrid lengths will provide an equivalent buttressing effect and width as the unreinforced earthen buttress initially proposed in that area. A subsurface drainage system will also be provided for the MSE walls as shown on the wall plans. Comment No. 12: The Consultant should provide a statement as to whether the foundation and slab recommendations ore consistent with the requirements of Section 1808.6 (expansive soils) of the 2016 California Building Code. )~ #c' ~ GROUP CEL TL\ ·~ C:\Files\Projects\S0412 B\18-0012. doc • • • Response to Geotechnical Review Comments Poinsettia 61 Development Lennar Homes GDC Project No. SD412B January 24, 2018 Page 6 In general, most of the site soils are granular in nature, and have a very low to low expansion potential based on common criteria. The expansion index test results were provided in Figure B-2 of the referenced investigation (GDC, 2014). All of the samples we tested had an Expansion Index below 50 (most were below 20). with the exception of the claystone of the Santiago Formation, which was very highly expansive (El-154). In Section 6.3.3 of the referenced geotechnical investigation, we provided recommendations for the mitigation of expansive soils at the site (GDC, 2014). In areas where the claystone beds will remain at or near finish grades for the building pads, we recommended over-excavating the pads to 4-feet below finish grade, and replacing with a low expansion soil (El<50). The post- tension slab foundation recommendations that will be provided in the as-graded report will be consistent with the requirements of the 2016 CBC. Comment No. 13: The Consultant should provide a description of recommended foundation embedment material(s), minimum embedment, minimum width and minimum reinforcement. We have recommended that post-tensioned slabs bearing on low expansion materials (El<50) be used to support the proposed residential structures. In our experience, the minimum embedment, width and reinforcement for post-tension slabs should be determined by the structural designer based on the geotechnical design parameters that we will provide in the as- grade report. For any conventional shallow foundations that may be associated with the structures, a minimum width of 12-inches and depth of 18-inches is recommended. Continuous foundations should be reinforced with at least two No. 5 bars at both top and bottom. Again, these parameters should be provided in the as-graded report, in our opinion. Comment No. 14: The Consultant should provide recommendations for cement type in accordance with AC/318. Corrosivity was discussed in Section 6.5.4, and the corrosivity test results were provided in Figure B-3 of the referenced investigation (GDC, 2014). Most of the samples we tested had a negligible sulfate content based on common criteria. However, one sample of the existing fill we tested did have a severe soluble sulfate content (likely due to the previous agricultural use). For concrete that will be in contact with severely corrosive soils, a Type V cement should be used, along with a maximum water to cement ratio of 0.45, and a minimum 28-day strength of 4,000 psi. The sulfate content of the finish grade soils within the building pads will be tested during grading (along with the expansion index). Recommendations for the mitigation of soil corrosivity will be provided in the as-grade report based on the test results. Comment No. 15: The Consultant should provide o list of recommended geotechnicol observations and testing during grading and construction . I)\ t:-~ GR.CLP CEL TA C:\Files\Projects\SD412B\18-0012.doc • • Response to Geotechnical Review Comments Poinsettia 61 Development Lennar Homes GDC Project No. SD412B January 24, 2018 Page 7 We described the required geotechnical tests and observations during grading and construction in detail in various sections of the referenced reports. In summary, the geotechnical consultant and geologist (or their designated field personnel) should test and observe all earthwork and fill placement for proper compaction and moisture. Geologic observations should be provided at the removal bottoms for the existing alluvium and fill, and at the required pad over-excavation bottoms for cut/fill transitions and expansive soils, prior to placing new fill. Geologic observation of the cut slopes and benching should also be provided. Continuous inspection and testing should be conducted for the geogrid walls, including grid type, location and length, and all subsurface drains, wall drains, and outlets should be observed prior to backfill. New pavements should be tested for compaction of subgrade, base and asphalt, and the materials used in the pavement sections should be sampled and tested for conformance to the specified gradation and quality parameters. Al foundation excavations should be observed prior to placing steel and concrete. We appreciate this opportunity to be of continued professional service. Please feel free to contact the office with any questions or comments, or if you need anything else. GROUP DELTA CONSULTANTS Matthew A. Fagan, G.E. 2569 Senior Geotechnical Engineer James C. Sanders, C.E.G. 2258 Associate Engineering Geologist Distribution: (1) Addressee, Mr. Jamison Nakaya (Jamison.Nakaya@Lennar.com) (1) Hetherington, Mr. Mark Hetherington (mdh@hetheringtonengineering.com) (1) O'Day Consultants, Mr. George O'Day (Georgeo@odayconsultants.com) (1) City of Carlsbad, Ms. Tecla Levy (Tecla.Levy@carlsbadca.gov) f ) ~ GRCUP DELTA C:\Files\Projects\SD412 B\18-0012. doc • • • Response to Geotechnical Review Comments Poinsettia 61 Development Lennar Homes REFERENCES GDC Project No. SD412B January 24, 2018 Page 8 Group Delta Consultants (2014). Report of Geotechnicol Investigation, Poinsettia 61 Development, Carlsbad, California, Document No. 14-0188, November 20 . Group Delta Consultants (2015). Slope Stability Considerations, Poinsettia 61 Development, Carlsbad, California, Document No. 15-0029, March 6. Group Delta Consultants (2016). Remedial Grading Summary and Plan Review, Poinsettia Development (EIR 15-03}, Carlsbad, California, Document No. 15-0102, September 21. Group Delta Consultants (2017a). Supplemental MSE Retaining Wall Recommendations, Poinsettia 61 Development, Carlsbad, California, Document No. 17-0081, July 12. Group Delta Consultants (2017b). Geotechnical Review of MSE Wall Plans, Poinsettia 61 Development, Carlsbad, California, Document No. 17-0100, August 28. Group Delta Consultants (2017c). Supplemental Infiltration Information, Poinsettia 61 Development, Carlsbad, California, Document No. 17-0145, December 8. Group Delta Consultants (2017d). Foundation Report, Poinsettia Lone Bridges, Carlsbad, California, Document No. 17-0065R, December 22. Hetherington Engineering (2018). Third-Porty Geotechnical Review {First Review), Poinsettia 61 Development, Carlsbad, California, GR2017-0052, 4 Pages, January 2. O'Day Consultants (2017). Rough Grading, Storm Drain and Retaining Wall Plans and Details for Poinsettia 61, Sheets 1 through 38, August 21. Moffatt and Nichol (2017). Poinsettia Bridge Foundation Plans, 2 Sheets, October 4. Soil Retention Designs Inc. (2017a). Verdura Retaining Wall Plans for Poinsettia 61, Sheets 21 through 38, August 18. Soil Retention Designs Inc. (2017b). Verdura Retaining Wall Design Summary and Calculations for Poinsettia 61, SRO Project No. 1704-003, August 21. r~ ~ GRCLP CELTL\. C:\Files\Projects\S0412. B\lB-0012.. doc • • • • • • • • TABLE 1 2016 CBC ACCELERATION RESPONSE SPECTRA (SITE CLASS C) GDC PROJECT NO. SD412, Poinsettia 61 Development Site Latitude: 33.1106 Site Longitude: -117.2767 Ss• 1 075 g = short period (0.2 sec) mapped spectral response acceleration MCE Site Class B (CBC 2010 Ag. 1613.6(3) or USGS Ground Motion CalcoJator) S1• 0415 g = 1 O sec penod mapped spectral response acceleralion MCE Site Class B (CBC 2010 Ag. 1613.6(4) or USGS Ground Motion CalcoJator) ,_ Site Class• C = Site Class definrtion based on CBC 2010 Table 1613.6.2 i F,• 1 000 = Site Coefficient applied to S, to account for soil type (CBC 2010 Table 1613.5.3(1)) ~ F,• 1386 = Srte CoefflCient applied to 51 to account for soil type (CBC 2010 Table 1613.5.3(21) TL• -800 sec= Long Penod Transrtion Period (ASCE 7-05 Agure 22-16) SMS• 1.075 = site class modified short period (0.2 sec) MCE spectral response acceleration= F, x S, (CBC 2010 Eqn. 16-36) 5 5111• 0.575 = site class modified 1.0 sec period MCE spectral response acceleration= F, x 51 (CBC 2010 Eqn. 16-37) 0.. S,,.• 0.717 = site class modified short penod (0.2 sec) Design spectral response acceleratoon = 213 x s ... (CBC 2007 Eqn. 16-38) ,_ So,• 0.383 = site class modified 1.0 sec period Design spectral response acceleration= 213 x SM, (CBC 2007 Eqn. 18-39) ::, 0 T,• 0.107 sec= 0 2 S01/S05 = Control Period (left end of peak) for ARS Curve (Section 11 4 5 ASCE 7-05) Ta• 0.535 sec= S01/Sos = Control Penod (rigtt end of peak) for ARS Curve (Section 11.4 5 ASCE 7-05) T Design MCE lsecondsl Sa (g) Sa (g) 0000 0.28( 0 43U 0107 0.717 1.075 0535 0.717 1.075 1.2 0600 0639 0.959 I 0.700 0.548 0.822 0 800 0.479 0 719 0900 0.426 0.639 ' -Design 1 000 0.383 0575 1.0 1 100 0.349 0.523 Cl 1 200 0.320 0.479 ~ \ 1300 0 295 0.442 C ' -MCE 0 1.400 0.274 0.411 ., 1500 0.256 0.383 ~ 0.8 ' Q) z 1.600 0.240 0.359 i 0 1.700 0.226 0.338 g 1.800 0.213 0.320 ~ ' ::, 1900 0202 0.303 ~ l " ~ 2 000 0 192 0.288 0 0.6 I ' I.J 2100 0.183 0.274 ~ ~ ~ .. :I 2200 0174 0.261 ::, Cl) a: 2300 0.167 0 250 , .... "' ,_ "' bl 2.400 0.160 0.240 0.4 0.. 2.500 0.153 0.230 "' .... ., 2600 0147 0.221 .......... ........ .... 2700 0142 0.213 I ......... l'°"o 2.800 0.137 0.205 ... ..... .... ......... -..... ........... 2900 0.132 0.198 0.2 3000 0128 0.192 3.100 0.124 0186 3.200 0.120 0 180 3.300 0.116 0 174 3.400 0113 0.169 0.0 3500 0.110 0.164 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4 .0 3600 0.107 0.160 3 700 0.104 0155 3.800 0 101 0.151 Period (seconds) 3900 0.098 0147 4.000 0 096 0144 4.000 0.096 0.144 • • • • • • TABLE 2 2016 CBC ACCELERATION RESPONSE SPECTRA (SITE CLASS D) GDC PROJECT NO. SD412, Poinsettia 61 Development Site Latitude: 33.1106 Site Longitude: -117.2767 S.• 1075 g = short period (0.2 sec) mapped spectral response acceleration MCE Site Class B (CBC 2010 Ag. 1613.5(31 or USGS Ground Motion CalcoJator) S,• 0415 g = 1.0 sec period mapped spectral response acceleration MCE Srte Class B (CBC 2010 Ag. 1613.5(41 or USGS Ground Motion Calculalorl ... Site Class= D = Site Class definition based on CBC 2010 Table 1613.5.2 :::, Q. F,• 1.070 = Site Coefficient applied to S, to account for soil type (CBC 2010 Table 1613.6.3(11) :!: F,• 1.585 = Site Coefficient applied to s, to account for soil type (CBC 2010 Table 1613.6.3(2)) TL• 800 sec= Long Period Transition Period (ASCE 7-06 Figure 22-16) -SMS• 1.150 = site class modified short period (0.2 sec) MCE spectral response acceleration= F, x s, (CBC 2010 Eqrc 16-36) ... SM1• 0.658 = site class mod~ied 1.0 sec period MCE spectral response acceleration= F, x S, (CBC 2010 Eqrc 16-37) :::, Sos=-0.767 = site class modified short period (0.2 sec) Design spectral response acceleration= 2/3 x SMS (CBC 2007 Eqrc 16-38) Q. ... So,• 0.439 : site class modified 1.0 sec period Design spectral response acceleration = 2/3 x SM, (CBC 2007 Eqrc 16-39) :::, 0 T,• 0.114 sec = 0.2 S01/S05: Control Period (len end of peak) for ARS Curve (Section 11.4.5 ASCE 7-05) Ts• 0.572 sec= S01/S05 : Control Period (right end of peak) for ARS Curve (Section 11.4.5 ASCE 7-05) T Deslan MCE tsecondsl Sa (g) Sa (g) 0.000 0.307 0.460 0.114 0.767 1.150 0.572 0.767 1.150 1.2 0.600 0.731 1.096 I 0.700 0.626 0.940 I 0.800 0.548 0.822 0.900 0.487 0.731 \ -Design 1.000 0.439 0.658 1.0 1.100 0.399 0.598 O> 1.200 0.365 0.548 ~ 1.300 0.337 0.506 C ' -MCE 0 1.400 0.313 0.470 ~ 1.500 0.292 0.439 cjj 0.8 1, z 1.600 0.274 0.411 ai 0 1.700 0.258 0.387 0 ... ;:: 0 :5 1.800 0.244 0.365 <( ' ', :::, 1.900 0.231 0.346 ~ ~ 2.000 0.219 0.329 u 0.6 ' I\ (.) 2.100 0.209 0.313 8. '" ~ :E 2.200 0.199 0.299 :::, (/) ~ I~ 0:: 2.300 0.191 0.286 ~ ... "' ~ &l 2.400 0.183 0.274 0.4 Q. 2.500 0.175 0.263 ~ to.... I'~ Ul 2.600 0.169 0.253 """ ~ """ 2.700 0.162 0.244 ro -2.800 0.157 0.235 ~ ,.... """' j,.., """' """' ,...._ ~ .... ~ 2.900 0.151 0.227 0.2 3.000 0.146 0.219 3.100 0.141 0.212 - 3.200 0.137 0.206 3.300 0.133 0.199 3.400 0.129 0.193 0.0 3.500 0.125 0.188 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 3.600 0.122 0.183 3.700 0.119 0.178 3.800 0.115 0.173 3.900 0.112 0.169 Period (seconds) 4.000 0.110 0.164 4.000 0.110 0.164