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tv   BOCC Budget Finance Committee  SFGTV  November 4, 2021 1:30pm-3:01pm PDT

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encompass new the contractor's technique and installing the 36" casings and the 24" casings. inadvertently removes soil from beneath the structure. and just squeezing the pile and resulting in volume changes. and piles have been installed and resulted in volume change
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and settlement. a secondary cause into the sand and support the existing piles that have dense fied them and we think that has some expense as well. >> supervisor peskin: and just relative to the behavior of the structure during the insulation of the casings and the piles, maybe we can just take it from the top. the design that you propose that the edrt reviewed and were otherwise peer reviewed as mr. lip said consisted of 52 casings, correct?
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and 52 piles that you would in essence tie back to i assume you started with the casings. when did you start and how -- when did you start detecting the accelerated differential settlement? >> it started in may of this year. we began to detect small amounts of increased settlement almost immediately. and as additional casings and piles were installed, the increase in settlement became more severe. by the end of july, the
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contractor had installed a total of 33 of the 52 casings consisting of call the casings along fremont street and about two thirds of the casings on mission street. they had also installed at that time, six of the 24 -- i'm sorry. three of the 24" piles. at that point in time, i became concerned and i asked the contractor some following 36" casings continuing with the 24s so they can understand which of those two operations and.
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>> supervisor peskin: as of right now, 6, 24" piles. >> those are located at the south end of fremont street. from the driveway north. >> supervisor peskin: and then you see 36" casings after the 33 up until you did the quote unquote test recently? >> is that correct. >> and they permit us to install some additional 36" cases. as of today, there are a total of 36 installed. >> supervisor peskin: and, are you still going for 52 or are you revising the plans to have less casings and piles? >> we did submit a proposal to
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the city. we have not yet seen impact. >> supervisor peskin: and the quote unquote successful installation of the test casing and subsequent casings, what did you -- what was done differently relative to method? >> on the 36" casing, we did much more careful control of where the ends of the casings would be stopped -- it's possible that we do 100' length. the contractor has to make splices in the casings and so we controlleded where those splices would be made so that the tip of the casing would not be that could be pushed up into
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the casing while -- we also acquired much more careful control on the depth of plug and the end of the casing and the amount of water fill in the casing while they're installing it to provide waste at the end of the casing to prevent material from piping up into the casing. >> supervisor peskin: so less ground. >> we also put measures to isolate the installation equipment -- to isolate the vibration from the installation equipment from the piles that had already been installed. when we installed the pilot casing a few weeks ago, we have extensive measurement of operations both at street level and the casings and at depth within the same layer and we have determined that we have successfully mitigated the vibration. and ground loss measures on the
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36s also appear to be successful. >> supervisor peskin: and, the techniques that are being utilized in this are techniques that have otherwise been utilized in other situations, is that correct? >> the installation techniques that are being used here have not been used in the san francisco bay area previously, but the contractor who is doing this work has used these techniques and other sites around the city. >> supervisor peskin: so is this good to new any explanation as to why these techniques that have been used in other places in the united states were not implemented earlier in this between may and when you ceased in late august
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and commence the test recently? >> i have no way looking at that. i can tell you the soil at every site even at different sites within the city vary quite a bit and the techniques that are used in one place technically may not be as effective in other locations. >> supervisor peskin: and just in the placement of the first 30+ casings, what kind of monitoring regimen was employed then versus what has been since implemented in the pilot? >> there are a series of 38 settlement markers that are surveyed upon. in the basement of the building that have been surveyed every week since the construction
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started. in addition, there are a series of prisms mounted on the side of the building and also at the top that give digital read-outs not only of settlements, but also horizontal movements of the buildings at different levels. those also were being monitored at a weekly basis. we are now monitoring a prism on the side of the building.
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>> supervisor peskin: so the difference is not that you installed more prisms or more monitors, but was that you monitored them more frequently, is that correct? >> that's correct. >> supervisor peskin: but it's not the monitoring that decreased the differential settlement during the test pilot, it is the change, means and methods? >> that is also correct. >> supervisor peskin: okay. thank you for all that. please proceed. >> okay: in late august, when
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i put the moratorium on the compilation. the tilt on the plot at the top is tilted to the north. the plot on the bottom is tilt of the building to the west towards fremont street. in 2009 with construction completed, the building was holding about 4" to the north.
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>> in november of 2020, when construction started, the building was helping about 7" to the north and 17" to the west. in august of this year, when i instituted the moratorium and 23" to the west and as of today, it's about can. >> supervisor peskin: mr. hamburger, i've heard in the past where we have a duty as the department of building inspection and the board of supervisors to inquire. at what point, should we particularly in a seismically
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proned region. at what point do we worry about structural failure. ? >> it's an excellent question. i've been asked this a number of times. i started back in 2018 and what we've done -- what we've done is we created an analytical model of the building. this is the same type of model used the design what the building code called the maximum considered. 1500 years or so. it has the magnitude of the 1906 san francisco earthquake,
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but has an indentation of a location that reduces more severe compared to as i said, the building is holding 12" to the north and 28" to the west. we had evaluated it previously and the ezrt reviewed and concurred that the building was safe at that level of deflection we lacked at the building as much as almost 3' to the north and almost 80" to the west. and we've concluded that the building is still able to safely resist its maximum considered earthquake shaking not that we expect the building will ever be permitted to go that far. i will mention that the edrt
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has seen those results but has not had the opportunity to review that. [please stand by]
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>> we have successfully tested the 36-inch casing. our next step is testing 24-inch casing in two weeks. based on the results of the testing of the 36 and 24, we will be able to project how much settlement will occur to the building and how much sloping. we will have a conversation with the homeowners and with the
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building department as to how much additional sloping they will accept. we will trim the project to allow the piles not acceding that limit. i will note the upgrade is voluntary. the piles that we install and attach to the building will improve performance and will reduce amount of settlement that occurs over the years. at this point we are looking to see how many piles we, the city, homeowners can afford without causing excessive tilt in the building so the behavior in the future will be improved. >> mr. hamburger, i thought there was a chance to find out if it was on a specific slide or wait until the presentation is done before asking your
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question? >> i think it is just a quick question between this slide and the last slide. maybe i missed the point here that was already made. you mentioned from a technical perspective you consider a tilt up to 40 inches is acceptable limit. knowing that right now from what you indicated the tilt is 9.5 inches north and 23.5 inches west. in the event from your estimate or i don't know if this is the right question to ask you. in the event that -- because the work has begun and it tilts more and settles more unexpectedly. in the event what you are about to do now with the new solution
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that you are moving forward in the event it doesn't work again, how fast do you think -- how much time do we have until it is no longer acceptable? >> before the initiative the building was settling about one eight inch per year and tilting at one-half inch per year. when we stopped construction of the piles in august the building returned to those rates of settlement. we are currently at almost 30 inches of tilt. we have another 10 inches of tilt which could occur at the rate of a half inch per year. that could be 20 years if we did nothing. >> thank you. >> thank you, supervisor chan. i apologize for cutting you off,
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supervisor peskin. >> none of us are geotechnical or structural experts so this may sound like a simplistic question. mr. hamburger, do you think this building would have been better off without the fix or is it too early to tell? what is your take on that? >> if we had not done the fix, the building would have settled and tilted as it currently has today in about four years. the building would have been better off today but not better off four years from now. >> four or 40? >> four. >> even with the limited number of piles that we have installed at the moment, if we put these piles into the building and off the building to the piles that will improve the building's
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future performance beyond what it would otherwise have been to the extent we can successfully install additional piles that will improve the building future performance. i would not say the building would have been better off if we had not done what we have done. >> all things being equal, the fix was not necessary? >> in our opinion the fix has never been necessary from a structural perspective, from a safety perspective. >> got it. you are saying if this thing does not reach equalibrium and sees tilting eventually it is going to get to 40 inches or 28 inches? is that fair to say? did you say that? >> 28 inches now.
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>> i thought you said 23.5. then you said 28 inches. i am confused. >> you are correct. the reason is summing the tilt to get the tilt quantity in the north west direction which is more of the tilt to the north arwest. >> got it. consolidation causing the tilt we are not installing piles is self-limiting behavior. if you think about the sponge someone squeezing water. if you grab a wet sponge and apply pressure with your hand and you squeeze water out, water will come out for a while then stop. consolidation is a self-limiting behavior. we expect to happen over time as
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the consolidation continues and more and more water is squeeze the out of the soil, it will self-limit and stop. i think it will self-limit in about 40 inches. >> 40 inches. you are saying you think it will get to 40 earlier that 40 is the acceptable limit? >> yes. >> then if it goes to 41 or 48, which the edrt and other peer reviewers haven't looked at that is the point of no return, in your estimation? >> i wouldn't call it point of no return. i would call it a point at which the building's ability to resist maximum earthquake.
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[indiscernable] >> maybe this is not a question for you but mr. eaga in who joined the call. with all of this and sorry for the technical termmucking around in the dirt and the existing load measured in kips, do you or does the goio tech think there is any defamation of the substrate? are different layers sheering within the subsurface? >> no, i don't think there is sheering. i think that what the
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installation of piles has done has -- obviously if you get settlement, you are causing additional consolidation settlement or second dairy compression settlement during this process. i don't think it has caused sheering of concern within the sub soil strata. >> relative to the condition of the matt, the 10-foot slab matt. i will ask this question. i never did get answers or good enough answers to this question a half step years ago when we were holding the hearings. was that done in one pour or multiple pours? do you know? >> i do know that was done in one continuous pour that lasted
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more than a day. hundreds of trucks would come and depossit is the concrete. >> it gets hot. did you cool it. >> i was not the structural engineer. it is typical in large foundation pours of big buildings like this to ice the concrete. i assume that was done here. >> this is a separate question. i will start trying to turn it over to the next speakers, but i mean again, none of us here are remotely experts in this field. i did start out as an earth sign measure in the math kicked my
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behind. i have not spoken to most of these folks, but i have the same access to the internet and the television that everybody else does. i see this parade of credentialed experts and i can look them up on the internet. they are structural or geotechnical engineers in good standing, licensed in the state of california. we all know their names. some of them have taken upon themselves to e-mail me and robert pike is in the record and date williams we saw on tv and somebody from uc berkeley and larry carp and the list goes on. one was concerned about dishing of the matt. any thoughts for mr. eagan or
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mr. hamburger if there is defamation of the mat. >> it has dished. when detailed measurements of the elevation started to be taken in 2009 with the survey markers, it cuts off the addition of the matt. we are continuing to monitor those with the survey. the mat has not improved at all since 2009. the building has been settling and tilting at the rigid bottom as you see on the slide here with no additional dishing of the mat. i would like to note my analysis of the building included a detailed model of the building map. before we apply an earthquake load to the structure we apply that dishing to the model to
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stimulate the effect of what has occurred. the analysis indicate we have reviewed it and that dishing has not compromised the mat. >> i have been in the basement of the building and seen the cracks. there is obviously water in intrusion.does the modeling tako account any of the corrosive activities occurring in the basement? >> the water leakage that you are referring to as well as the cracking of the basement walls which are not in this building. it was constructed together with adjacent mid-rise building. the garage for both buildings is in the five level of basement of
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the mid-rise knowledge. all -- mid-rise building. all of that damage is in the mid-rise building. i have not evaluated the safety of the mid-rise. it has not compromised the tower ability. >> okay. mr. eagan, do you agree with that? >> yes. >> thank you. i i assume all of you in this relatively small tight admitted expert community know one another. do you talk to each other? are these people looking to be on tv or what is your take about the skepticism we are seeing from other industry experts on television set? >> i don't really care to speculate as to the motive of these individuals. i will say in the san francisco
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bay area there are at least 2000 structural engineers. i assume several hundred geotechnical engineers all members of the structural engineers association of northern california. i was once part of that. the fact that a half dozen engineers think there is a big problem. i wouldn't suggest that is representative of the engineering communititive in the bay area. i will also say the engineers who have been vocal and in the press could not possibly have done the level of analysis i have done over the seven years i have been involved with this building. >> thank you, mr. hamburger. you are not speculating that is a good thing. i have not spoken to most of them. i do always read their
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submissions with interest. would you like to wrap up? we can go to briefly in charge of overseeing construction for the homeowner's association. any last slides, mr. hamburger. >> one last slide on the project schedule. there is a detailed schedule developed by the contractor 22 month construction period. at the time construction halted in august at my direction about 10 of those 22 months had elapsed. the project was on schedule at that time. assuming we get permission to restart construction, i am saying in december of this year, it will take about another year to complete the project. that would be december of next
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year. steps will be permitted and will have arrested and stopped further settlement of the building upon submission and allow gradual settling on the south and east side with the effect of recovering the tilt that has occurred over time. thank you for your attention. >> thank you very much, mr. hamburger. congratulations on the new means and methods that have proved at least initially successful. i wish they had been implemented earlier in this fix. we are where we are. mr. dutro, good afternoon. >> good afternoon, supervisor peskin. thank you for giving us time for discuss this project. i will be very brief. my role is to oversee the
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project for the homeowners, taking into account the budget and the schedule. we have at the same time engaged a mechanical engineer to review the interior of the building to ensure that the interior of the building remains functional for the homeowners. then in regard to the intrusion that you mentioned, supervisor peskin as mr. hamburger indicated in the parking garage underneath the mid-rise building. we have a design team designing a fix to water proof that section of the building to keep the residents safe. there is no currently no life safety issues associated with
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the interior functions. we will continue to monitor those for the homeowners. >> thank you. one quick question. relative to the integrity of the mat slab. do you know whether or not that thing was iced when they did it in one pour? >> no, i was notes involved in the original construction. >> have you undertaken any ground penetrating radar investigation of the mat? >> no, we haven't done anything to that extent. we relied on professional engineers, hamburger, eagan to guide us to the activities and further investigation would be needed to ensure the safety of the building. >> they have not recommendedded
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using ground penetrating radar technology? >> no. >> if i may. as part of the original investigation performed back in 2014-2015-2016. gpr would not be use full because of the depth of the matter it could not penetrate. [indiscernable] through the depth of the mat and removed from the mat and examined. there was no significant be cracking in the cores. we are confident that concrete is in good shape. >> thank you, mr. hamburger. if there are no questions, mr. chairman, i want to thank the hoa and their three representatives, four representatives for their presentation and answering of
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questions. i will move to our department of building inspection. i don't know if all of you are familiar before patrick is with us to ask questions. mr. ferrara has a powerpoint and is an engineer so with that. if you can walk us through the role of d.b.i. in the permitting process that would be greatly appreciated. >> good afternoon, supervisor peskin and the rest of the committee. as mr. peskin has said i am new to the department. i am the deputy director for permit services. i have studied in late september working for 40 years in the industry in design construction
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and previously served in building departments throughout the state and in private sector. in the past few weeks i acquainted with the project and the department has control oversight and is actively participating for the review of the proceedings during construction. you have heard quite a bit of technical information about the project from mr. hamburger. my focus here is to underscore the d.b.i. role regarding this project. current and future oversight as you said at the beginning of the presentation and the current status of the project. i will then hand be it over to professor dear line of the
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engineering design review team and dr. ben turner who we have since retained from dan brown and associates a national drilling expert in the field. >> the role of d.b.i. as most building as any building department is that to ensure that the building code is being enforced to the maximum extent possible. the building codes offer clear and state guidelines. they are acceptable and what we are here to ensure that construction appears to those boundaries. i think, john, you need to mute
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your microphone. essentially we are driven by design proposals and constraints. we don't tell the design professional, project sponsors what to do. we ensure the proposal is code compliant. that gives us a stronger position to guide and enforce the code without directing the design or construction. this is how all building departments work up and down the state and across the nation as well. if the project varies from code compliant we ask them to correct it. if necessary to shut down operations. public safety is always our first intent. department uses construction proposals, complaints and observations as a prime resource of input to ensure the building codes is commyatt.
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we -- compliant. this allows us to review the scope of work. we have a highly educated team in my career. san francisco plan check engineers are probably the most qualified that i have seen in the building departments that i have administered. we have several advance dee dee's and structural technical engineering here. they are involved in the retrofit. we once the building permit is issued. it will be to inspect the project to make sure it com ports to the plan we were approved. we oversee special inspections and materials, tickets delivered to the site.
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last we respond to complaints of unsafe conditions. that is what we are doing at the millennium tower. in this case we have gone beyond our original scope in several areas. one of which is that we have scheduled biannual inspections to go through and ensure safety of the structure. any minor code violations that come along with those inspections are rectified along the way. the homeowners association have contracted with several other inspectors or teams to go through and do an analysis of the building. we review those and comment on those as necessary. of course, we have been instrumental in
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compiling the engineering design review team and this additional layer of expert oversight helps supplement the internal expertise we have. this continuous monitoring off the project and the construction that actually led to the discovery of the accelerated tilt that we experienced this last summer. >> mr. hamburger made a point saying that he on behalf of the project sponsor of the homeowners association halted the work in late august. what role did d.b.i. play? can you give us background on that. clearly d.b.i. even though you knew there was accelerated
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settlement did not invoke powers to halt installation of the 36-inch much casings and 26-inch piles. tell us behind-the-scenes considerations? >> from what i understand the monitoring of the settlement was essentially started around the same time as the 36-inch casings were beginning. it wasn't until june 23rd that we receive the data from the design team and the field. at the same time we were involved in the changing of the scope from the 52 piles to 42 piles mr. hamburger talked about. essentially we began reviewing settlement data as soon as we got it, and you heard
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mr. hamburger talk about halting the 36-inch casings and continuing on the 24. this was kind of methodology to make sure that it was, you know, what was responsible for the settlement. the 36 or 24. halt one to continue on the other one. this process of deduction and communication back and forth between the engineering design review team and the design engineer took some time. eventually we requested that they halt the continuation. mr. hamburger was the ultimate decision-maker to do that. >> aren't you guys the ultimate decision-maker? you can issue stop work on construction of any kind anywhere in the square files of
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the town, can't you? >> we can do that. this is a consensus of review. the conversation that happens between the design engineer, edrt and d.b.i. is one of general agreement. it takes all three of us to make that decision. yes, you are right. we do have that ability to do that. in this case it was just suggested that they stop. >> so they stopped at your suggestion. please proceed. i know that my three colleagues are about to mute me. let's go on. >> i can go through this slide quickly. i did say earlier we oversee and
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don't determine the means and methods for the contract. that is up to design professional and contractor to come up with that. we will talk about the timeline quickly. i touched on this a moment ago. this is just a rough visual for the ongoing proceedings starting in may when the 36-inch much casings began. then we went into the 24-inch casings. it was discovered the accelerated settlement was going on. there was a period of discussion before the proceedings were actually halted. then a discussion again to restart with the pilot you
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talked about in early october. during that process also it was decided to get in additional oversight. because it is means and methods we found dan brown and associates a nationally recognized drilling expert to join the team to evaluate the means and methods for the installlation. i wanted to start this by saying that conditions at 301 mission are stable. the building is structurally sound by all of the information that i have reviewed and the eert has had. we know the building is habitable and serviceable through various inspections and we monitor with the help of the
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homeowners association and their team of experts that come in and address matters as are needed. the current tilt is at 22.5 northwest of the building. that is holding steady. we had successful installations of the pilot piles. we proved it's on pile number 34 as well. the elevator. >> 34 of 42? >> that the 34 of 42, that's correct. >> the 42 as opposed to 52 permanent casings and piles? d.b.i. signed off on the revised lester number of casings and piles? >> i have to defer to my team on that. i believe that. patrick. >> thank you, supervisor peskin and chair preston for holding
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this hearing. we have not signed off on the reduction from 52 to 42. it is currently being reviewed. >> mr. reardon, while i you on here. it is not fair to ask mr. ferrara. can you tell us how the members of the engineering design review team were selected? and who they work for? >> yes, supervisor. i wasn't in that department at the time either. i believe it included the city administrator at the time and decision was made in consensus with d.b.i. along with the city administrator to select this team of professionals.
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>> do you know how it worked? >> i am not aware exactly how that happened at the time, supervisor. i can get back to you with that information. >> so they were originally hired and paid for and worked under then city administrator naomi kelly and that function was transferred to d.b.i. they are now consultants to the department of building inspection, is that correct? >> that is my understanding, yes. >> supervisor peskin, i want to go to supervisor chan with a comment. >> thank you. my question is earlier mr. hamburger said the limit for this tilt is about 40 inches from acceptable design
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standpoint. do you agree to that? >> supervisor chan, we actually just started those discussions this morning in a meeting. the information is relatively young. in front of the edrt. there was about two hours of very technical discussion this morning. we are in the process of reviewing that. >> what will happen? i am curious in the case that you have a difference of opinion about what is an acceptable limit? what is the process to resolve that difference of opinion? meaning, you know, whether you find it too much or how would you do that? how would you resolve that if you don't agree that 40 inches is acceptable limit? >> that is a great discussion.
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it is very -- it is a series of. it is a discussion among all design professionals. as well as the members of the edrt. we go back and forth. i have seen greg dear line and marco on the team request additional information from the design professional and they are to prove that theory for the engineering design review team and come back and prove it or refute it. it is that process of back and forth. eventual consensus of everyone that we can move forward that results in the decision or the way to go. >> in my line of questioning was to mr. hamburger.
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the attitude of supervisor peskin asked. without the face, you know, we are seeing, you know, the challenges of that the tower would face in terms of tilting would have significantly impacted without the fix within four years. with the fix maybe we have like 20 years. would you agree to that or do you agree with his assessment? >> my experience with this type of building and -- i'm sorry. my experience in fact i was asked by internal executive team about that same thing.
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>> their visual cues to what is going on at the building. if we come out of an earthquake and the building has suffered trauma of some sort. it is not necessarily catastrophic effect. it is not brittle. you will see beams and that sort of thing. these official cues are fuses that are designed to alert us ahead of time as to remediate building or evacuate the building and demollish it if needed. >> okay. thank you for that. i personally have not been into
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the building. sounds to me there seems to be some visual cues from what supervisor peskin had talked about earlier in terms of the cracks that he was seeing. thank you so much. i am done with my questions for now. i may have more later. thank you. >> thank you. supervisor peskin. >> let's keep going. >> next slide please. what d.b.i. is doing. during actual installation is that we have set a threshold. design team and engineering design review team has agreed a quarter inch maximum settlement is what is acceptable. if it were to pass this we would
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pause construction evaluate and react accordingly. during the installation, dan brown and associates monitored the last two casings to make sure that the program for installation is being followed and that it is proving out and the results have proved that minimal settlement occurred using these procedures. the department sends out a senior building inspector every single day to make sure that the monitoring is going on and that we are recording thepertty net data to submit to the edrt for review after reinstallation. the daily measurements are taken. mr. hamburger told you during installation these are hourly measurements and the measurements continue to happen
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daily basis. >> two quick questions. i assume that the stepped up monitoring would be applied to all future installations not just the test casing and the test pilot? >> that's correct, yes. we have seen that we get better or more telling results from the exterior prisms the reflectors on the surface of the building as it reacts to the work going on. the higher the prism the more movement to be reflected on what is going on at the foundation. >> it is not a show stopper. is the project sponsor paying
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for d.b.i. staff time on all of this? >> mr. reardon, i will ask you. >> not as of right now, supervisor peskin. we are looking at the resources we are pouring into this project and continue to and we are evaluating that right now. >> you do have the legal ability to charge for your time, i assume? >> i will have to check with our city attorney on that in relation to what we can and cannot charge for. we have charged a fairly sizable amount of money at the issuance of the permit. i can check on that to see what it is we can do. >> mr. ferrara or other reardon, it sounds like the hourly prism measurements and ground vibration monitoring for the test casings and new means and
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methods are being provided to d.b.i. in realtime or close to realtime, but it sounds like that did not happen between may when this project started and june the 23rd. why not? >> so the plans issued required monitoring. it stated that if the monitoring exceeded specific numbers that the design professional responsible for the project was to stop the work. that is what is drawings indicated. prior to june 23rd we requested those numbers to review.
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[please stand by]
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and then we review it and once a week we get together as a team. the design professional and d.b.i. and d.r.t. members and we review that and discuss it and see what we learned, if anything. decide to act on it, slow things down or analyze it a little bit more or move forward. next slide, please. i've covered this already, daily inspections by the building inspector to go out there, weekly coordination occurs. as well as we've asked mr. hamburger to come up with that
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threshold, right? what we consider a structural safety issue with the building and that's currently being reviewed. every complaint that is -- that arises out of the building we actively engage in to review it and to get compliance. and ultimately, we're making sure that the building continues to be habitable for the occupants and serviceable for the building maintenance. you know, make sure the sewage is running the right direction and the elevators and so on and so forth are working correctly. if the soil settlement reaches more than a quarter inch, we ask that the retrofit stop and we caucus how to move forward. >> when you say for casing, installation, does that mean
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casings and piles? >> correct. so there is a casing that is run down for the 24 as well, but, yeah, people tend to use piles for the 24-inch as well, but there is casing that is run down for the 24 inches as well. >> i'm saying is the tolerance for shutdown a quarter inch per casing and per pile? >> no, it's per installation, so it's -- well, actually, i'd have to ask mr. hamburger about that. >> supervisor peskin: okay. remember that through the process of elimination, what we realized was that the casings are causing differential settlement and the piles are causing differential settlement. that is what the sinking of the six piles showed us, it wasn't just a casing problem, it was a casing and pile problem. my problem is, if it's 42 or 52 and you've done six of them, and
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you're doing a little less than a quarter inch of settlement per and that does not lead to a shutdown, the cumulative is many inches. and i think that you guys started with soil sediment in excess of an 8 inch per casing and per pile. i just want to get some clarity on that. >> these limits were per casing, so if a 36 inch casing installation was to exceed a quarter inch, we can stop it. if a 24 inch were to exceed a quarter inch, we would stop it. i will point out that the settlement that has occurred throughout construction, i said it before, is only an inch and a quarter. the maximum amount of settlement that any one has caused is a
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little bit more than an eighth of an inch. so we're not looking at many inches and we will not allow many inches of sediment to occur. >> supervisor peskin: but even if you did the math -- if you did 52 -- i mean i appreciate there is a little more than an eighth of an inch, but every remaining pile, assuming you have 46 to go, 36 to go -- but if you've got 46 to go even at an eighth of a inch, that's another half a foot of settlement, right? >> i haven't done that math. we would not install that many piles. in fact, once we install a 24-inch test pile we are required to come back to dbi and project how many settlement will occur if we complete based on the results of that test, then
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we -- [indiscernible] if it's not, work in such a way to prevent that from happening. >> supervisor peskin: thank you. >> okay. next slide. i think i'm done. so with that, i'd like to introduce the engineering and design team, which is chaired by professor greg deerline. marco shah, who another structural engineer on the team. greg shields who is geotechnical engineer and dr. donnie who is also of a geotechnical specialty as well. so i'll hand it over to greg. >> just to jump in. in terms of just a little time check. i see a long list of folks and i
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want to -- >> yeah, we can continue this to another hearing because there is obviously we have to wait for the 24-inch test, but the thing that you said earlier and maybe i fell asleep for a minute, had a slide, t technical aspects. did you just show us that slide? >> that was one of the slides i prepared on the edrt. >> perfect. i want to talk about that slide. mr. chairman, what is your will? >> it's fine to proceed. i just wanted to make sure and maybe get an estimate of how much time if we're moving into a new presentation. -- by the design review team, what the time estimate and we also, of course, need to allow time for public comment as well. >> i think in terms of the slides i have prepared, there are just four or five of them.
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definitely less than 10 minutes. >> okay. three of the four edrt members have been enlisted by the city managers office to perform all of the retrofit as proposed to review studies of the safety of the building and supervisor peskin, if you remember, the hearing in august 2017, we reported on that on behalf of our committee. since we've been looking at the foundation retrofit, working with the department of building inspection, that's when va danny
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was added to this. we meet with the dbi and the design team, the proposals for the design team, the drawings, the calculations, the analysises and the assumptions behind those things. then we put them with additional questions and then when it's resolved, it's the consensus of the group. not one of us has more clout than the other. we discuss all these things together. just wanted to point out that our review team works under the san francisco administrative bulletin 82. and that's to provide the independent objectives we have technical review of aspects of the design and reporting that back to the building inspection. and also what we do and what dbi
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doesn't replace the quality assurance measures that are ordinarily expected of the structural engineer of record for the design. the two things ways we've been enlisted back from 2018 to august 2019, that was the time in which we reviewed the permit request for the foundation upgrades. these were drawings and calculations to substantiate issuance of a permit. and then more recently in december 2020, we were enlisted to continue in our review capacity during construction. i want to emphasize that our role during construction is really still focused on design issues. that is some pile tests that are done in the course of construction that provides geotechnical parameters to finalize some of the design values. there is changes in the design, so we're there to review those. and in the case of the monetary
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and the excessive settlement, we look at implications of those and we're here to review those. you've heard previously about as ron hamburger described the objectives of the retrofit. the key part of our role is to ensure that the requirements that the san francisco existing building code for voluntary seismic improvements, which is dealing with the structural safety of the building under the gravity load and earthquake loading. the key focus is paying attention to that in addition to the other objectives. and that the design team is following the perform-based guidelines that are permitted under the san francisco administrative bulletin 83 and further that referenced guidelines for performance-based design of new tall buildings. ron hamburger mentioned that previously.
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next slide. so i have two slides to talk about, supervisor peskin, the key technical aspects you were alluding to. the first is during a permit review, the initial stages we worked on over a year ago. what is identified here is a key technical aspects of that. i just wanted to touch briefly on. you heard details of this from ron hamburger earlier, i won't repeat that. but the perimeter piles, these are steel piles that go down to rock, through the clay layers and then settlement on the mission and fremont streets. it was an intentional part of the design in the geotechnical engineers would agree to minimize any disturbance to the soil, any of the so-called ground loss. obviously there are effects that were larger than expected, but
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the basic design principles, the solution or the proposal to minimize those effects. here is focusing on the earthquake safety, looking carefully at the detailed analysis of the structure and the foundation. but both the existing case, if we're thinking about that, and going through construction until the retrofit is completed. and then beyond that, the safety of the retrofitting structure, considering the pile configurations. during the course of the permit, the design team has looked at the safety of the existing building under the tilt. as ron hamburger mentioned previously, they also looked at tilt of twice that amount anticipating that there would be some settlement. some did occur just naturally between july and last january, up to 17 inches, but through
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crushings -- construction. so that is a key part of the retrofit. once these piles are in, they're connected back to the building through this 10-foot mat. so a key of the review is looking at the details of that. there is a ductal fuse that is the way the new piles are connected to the mat to ensure that this mat extension and the mat that it's attached to don't get overloaded. we also looked at estimates of long-term settlement. i think one point i would like to emphasize here that i don't think was conveyed earlier. once this retrofit is installed as it is designed along the mission and fremont street, that will rest the settlement of those spots. and the long-term settlement that will continue to occur on the other sides of the building will, in fact, recover tilt. so once this is tilting to the northwest now, once this retrofit is in place, the
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original design anticipates that there will be continued settlement of the building but, in fact, that's going to recover some of the tilt over the life of the building. >> can you hang on a second? i appreciate this. but just going back to the first thing, perimeter piles. i mean in this process did the edrt predict or model or analyze hamburger/eagan's predictions as to what increased amount of settlement and differential settlement this fix would bring about? >> well, we reviewed all of their reports in detail. and as part of their study, they did not look at what would be to try to estimate the settlement that occurred during construction due to the pile installation method, but they did look carefully at once the
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piles -- new piles were in place, what would be the continued settlement of the building and looking at the properties and the soil and n. their study included a sensitivity study to look at how the estimates of future settlement would vary based on the range of the parameters. >> commissioner peskin: that seems a little weird that you wouldn't analyze -- far be it for me, again, maybe i'm not an expert, but you would think that you would try to analyze what the fix was going to be with increased settlement. but separate and apart from that, is it your belief that it wasn't the design, but the means and method, ie, the excess ground loss that led to the accelerated tilt? >> well, yeah, because the
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design itself is not causing the excess tilt. it's the installation of these piles. now the question of whether the installation of the piles is a design feature or part of the means and methods. the point i'm trying to make here is that the design shows chose the type of piles that was to minimize disturbance to the ground. sometimes piles are put in with drilled shafts that don't have the steel lining. but those ones will tend to cause more ground loss. so that type of solution was dismissed on this project in favor of the steel piles. but the settlement estimates that were made during the developing the design and part of the permit review, again, we're looking at the settlements kind of post construction. >> commissioner peskin: so relative to future tilt, professor deerline, if we can do apples to apples, which is
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hamburger is using a northwest tilt combined number of currently 28 inches and apparently historically said that the red alert number was 29, but now is saying it's 40 to 47? how does this westward tilt number of 29, which is twice the 14.3 that was july of '19, which is now well north of 14.3, how does this number relate to that number? and what do you think is where this city should get nervous? i mean, i did hear mr. pereira say eventually demolish if needed. >> okay. well, the tilt numbers that we're talking about are roughly proportional. so the ones that are quoted on this slide, which is where -- there is more tilt to the west
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than there is to the north. and as the piles and casings have been put up fremont street, they caused more tilt to the west. if i could just focus on these numbers, with again are proportional if you look at the ratios to the ones to ron hamburger was talking about. in 2019, it was tilting to the west 14 inches. we did analyses to see if the building were safe if it were to tilt to the west 29 inches. the current is 22.35, or 23 inches we'll see. what ron reported, which the first we saw of that was in a conference call this morning. so we've not reviewed it. is the westward tilt could increase to 79 inches and it would still be safe. now we've not reviewed that yet, so we're not going to make a
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judgment on that. now the 40 inches is something much less than that, which is more of a practical or a serviceable limit on tilt. but the casing and another point that ron made is that -- ron hamburger made, is that once the next indicator pile of the 24-inch pile is put in and they can make a better estimate if they proceed with the original retrofit plan how much settlement do they expect to occur through construction? then the key thing is to be to look at that amount of settlement and make sure it's far less than any of these thresholds that would impact the structural safety of the building. okay. so the last bullet point here really that leads into the next
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slide is that one part of the permit review -- and this was mentioned before -- is that a requirement that monitoring occurred to the building weekly. there was also some holes put in with down hall monitoring for water tabling and so forth. if you go to the last slide. so then during construction, for the first few months of this year, january through march, we were busy reviewing information from additional soil testing and a couple of test piles that were put in to help finalize the geotechnical parameters to establish the capacity of these piles. the load they could take into the rock. we also then starting about april were reviewing modifications to design. and you heard mention already of major modification is a proposal to scale back from 52 to 42 piles. so we have been looking at those
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and, in fact, we did issue a letter back in july, the review team had gone through that 42 proposal and made comments on that fact which was basically to support that design decision back to dbi. then since that time, the casings have been installed, we are meeting frequently with the design team and the contractor to evaluate the causes of that settlement and how they might mitigate it through these modified installation procedures. again, you've heard that the modifications made to the 36-inch casing so far have been successful. pending though is what is going to happen with the 24-inch piles. and the last thing that we've been focusing on, ron hamburger mentioned, the design team is already looking at contingency
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plans in the event that continued piles with lead to an unacceptable amount of settlement under ways that they could scale back the retrofit and achieve the piles. we brought in dan brown and associates who are experts in deep foundation construction, to help us review and help advise what the design team and the contractor are proposing for the mitigation procedures. so i'd like to, if i could turn it over to dr. ben turner from dan brown and associates who has been, along with dan brown, part of these discussions looking at the causes and mitigation methods and also ben has been on
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site for these two 36-inch casings that were installed. he has a couple of slides and can be available to answer questions. >> commissioner peskin: before we do that, and thank you, colleagues for your indulgence. a couple quick things. professor, i neglected to do what we did half a decade ago was to give your findings -- >> most of my time in life is a professor at stanford university. i've been a structure engineer for 40 years, but academia for 35 or 10 of those years. doing research and teaching and structural and earthquake engineering. part of our faculty appointment allows us to spend a certain amount of time on doing outside activities that are related to our research and teaching.
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and it's through that, that i've been involved in kind of reviewing this project and also worked on other reviews for the department of building inspection. >> commissioner peskin: thank you for that and sorry for failing to ask that in the beginning. but relative to geotechnical expertise, that's not your specialty? >> no, that's not my specialty. >> commissioner peskin: and i do want to hear more and i would like to hear about a similarly situated project, foundation system, virtually identical, but we'll get to that on another occasion, because i think we should do this again in january. but do you, mr. deerline, want to speculate why we're people, experts in the profession, who i mentioned, are sending us letters with different analyses than that of the edrt and the engineer of record?
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>> well, a couple of things on that. as ron indicated, i don't want to speculate on people who are sending the comments forward. some comments came in during the review of the permit back in 2019 time frame. and at that time they were sent to d.b.i., d.b.i. forwarded them to us and we considered those in our review. we thought about those questions and if we i greed it should be -- agreed it should be answered, we reviewed it with the team. so now in terms of the -- well, those comments maybe what came up more recently, one comment would be many of those criticisms are based on incomplete information. because there is a lot of background information and some
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of that becomes available through sunshine laws, but there is an awful lot of understanding that comes about through the many meetings we have with both the design team and even amongst the edrt debating the issues, delving into these things. the analyses need to be integrated with a lot of judgment. we have two geotechnical engineers working with marcus and myself collectively looking at the issues. >> commissioner peskin: i appreciate that. and by the way -- and i'm in no way -- going to be very clear -- casting any professional doubt on those two gentlemen, but insofar as mr. hamburger indicated early on in today's hearing that part of the original problem was if i may,
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you know, be pointed, was the geotechnical analysis or problems in the geotechnical analysis done by treadwell and rolo now a decade and a half ago and the structural guy is only as good as the geo tech guy. and half the edrt comes from treadwell and rolo. i'm going to leave it there. [please stand by] [please stand by]
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