Author: Victoria Stephens (Page 4 of 4)

Sand compaction and accelerometer placement almost complete

February 3, 2016 / Victoria Stephens / 0 Comments

My second day onsite is going great. The sand contractor, Cromwell Contracting, has done a great job prepping the sand bed in the box for helical pile installation next Monday. The UCSD techs and I have been deciphering instrumentation plans from the previous project and placing accelerometers in each lift. Now we are working on the tedious task of hooking the accelerometer wires to the data acquisition system- made more difficult because this is a piggy back project with existing connections. But we’ll get it! After that, we will work on spooling and labeling the 152 strain gage cables to run next week after the piles are installed. More pictures to come!

A Cat Flew into the sand box….

February 2, 2016 / Victoria Stephens / 4 Comments

The weather doesn’t feel much different than Norman, Oklahoma. It is cold and sunny and windy, all with bright blue skies. But apparently cats fly in San Diego because one flew into the sand box this morning to start excavating the sand and tunnel. That means that we’ve officially started getting ready for helical pile installation which is slated for Monday, February 8th at 6:30 PST.

Leaving on a flat-bed…..

January 29, 2016 / Victoria Stephens / 1 Comment

The instrumented piles and caps were safely palleted and left OU on a TorcSill Foundations LLC flatbed this afternoon (Friday, January 29th, 2016). The piles are headed to Weatherford, OK to share the flat bed with some more equipment and then on to San Diego.

I fly to San Diego on Sunday the 31st! We are getting closer to a start-date for sure!

The instrumentation protection (two coats of epoxy and two coats of resin and fiberglass) looks strong! Let’s hope it holds.

We have a new tentative start date!

January 29, 2016 / Victoria Stephens / 0 Comments

The featured picture is one of our seismic skids donated by Magnum piering! Thanks so much! They are enroute to UCSD as I write.

We are slightly delayed, but I do have a signed and executed contract with the sand compactor, and he has agreed to be on the site on Tuesday, February 2nd to start removing the current tunnel test and recompacting the sand bed for the helical pile test. So here is an updated tentative schedule as far as I know it.

February 2nd – Meet Cromwell Contracting onsite to start removal of tunnel and sand back to original 8′ level

3rd – Wednesday – Cromwell Contracting continues to remove sand and start to compact in instrumented lifts

4th – Thursday – Sand Compaction continues

5th – Friday – Sand Compaction continues and should finish by early afternoon.

8^th – Monday – Do an initial shake on the sand bed in the morning and then start Installing piles

9^th – Tuesday – finish installing piles

10^th – Wednesday – hook up instrumentation

11^th – Thursday – hook up instrumentation

12^th – Friday – hook up instrumentation

15^th – Monday – UCSD CLOSED for President’s DAY

16^th – Tuesday – hook up instrumentation and check everything

17^th – Wednesday – possible first shake on just the piles (no weights)

18^th – Thursday – start putting the top caps and all-threads on and add concrete donut weights

19^th – Friday – add accelerometers to top of masses, check all instrumentation and possibly start the shaking sequences

22^nd – Monday – start shaking or finish shaking the inertial masses

23^rd – Tuesday – remove inertial masses and cut piles and place skids

24^th – Wednesday – load skids with sand

25^th – Thursday – finish loading skids with sand, place and hook up accelerometers and check instrumentation

26^th – Friday – start shaking sequence on skids

29^th – Monday – finish shaking sequence on skids and start removing instrumentation and piles

March 1^st – Tuesday – finish removing piles and get Cromwell Contracting on the schedule for removing all sand from test box.

What would a large-scale test be without DELAYS?

January 27, 2016 / Victoria Stephens / 0 Comments

The latest word I have is that the test is delayed. The start date is possibly the 3rd (Wednesday) or most likely the 8th (Monday). The inertial weights arrived in San Diego Monday and the skids are enroute to the site. Our piles and caps and other supplies are palleted and ready to be picked up on Friday the 29th by Torcsill. We are all ready to go – yet in a holding pattern. I’ll let you know when I know!

Seismic Research Project Update – January 24th

January 24, 2016 / Victoria Stephens / 1 Comment

Ten piles were selected to be arranged in the box, including 3.5” and 5.5” round piles and one 3” square pile (same cross sectional area as the round) with a single 10” helix, one double 8-10” helix and one push pile, to have one non-helical pile in the mix.

In order to collect quality information about the behavior of helical piles under seismic loading, these piles will be fully instrumented with strain gauges and accelerometers at key locations along the pile shaft.

The following are some photos of our preparation work thus far.

I will keep you posted on schedule. See you in San Diego!

Figure 6: Twenty-two concrete weights were fabricated weighing between 749 lbs and 955 lbs to act as the pile inertial masses. RamJack (9) and AMSquared Construction (13) constructed these weights. These weights will be stacked on top of each single pile in either triplicate, duplicate or single configuration. All 19,038 lbs were picked up from OU’s site Friday January 22nd and shipped via Patriot Express to UCSD.

Tentative Shake Table Schedule (subject to change)

January 24, 2016 / Victoria Stephens / 0 Comments

This testing plan is tentative and will most likely change throughout the duration of the test due to inevitable delays. I will keep you posted on our daily activity and schedule as we move through the test.

Day 1 – Thursday, February 4th: Low-amplitude shake on the sand bed to determine base properties.

Day 2 – Monday, February 8th: Torcsill to install Piles. (4)

Day 3 -Tuesday, February 9th: Torcsill to install remainder of piles. (6)

Day 4 – Wednesday, February 10th: Connect the strain gages from the piles to cables that will run to the data acquisition – each pile will have 10-18 strain gages. Update: We lost 27 gauges, so we have 125 remaining. Five of us spliced all 125 cables and ran them down to the data acquisition. Connect instrumentation to data acquisition – 26 connections made.

Day 5 – Thursday, February 11th: Place accelerometers at pile head (10) and run cables to data acquisition.Continue to connect instrumentation – 16 connections made. Make adjustments to skids and shake out concrete donut weights.

Day 6 – Friday, February 12th: Continue to connect instrumentation

Day 7 – Tuesday, February 16th: Continue to connect instrumentation and check all instrumentation connections.

Day 8 – Wednesday, February 17th: To study the kinematic behavior of the helical piles, a series of shakes will be conducted. It is important to not create a gap between the pile and the soil at this point. Once the shaking is complete, the accelerometers will be removed from the piles heads, the caps will be placed and then the concrete donut weights will be stacked. The accelerometers will be reattached to the top of the masses.

Day 9 – Thursday, February 18th: Donut weights will continue to be stacked if necessary. Instrumentation will be checked and the next shaking sequence (to study the inertial behavior of the helical piles) will be started. Once the shaking is completed, the accelerometers from the pile masses will be removed, the concrete weights will be removed and the piles will be prepared for the skid.

Day 10 – Friday, February 19th: Continue to prepare 8 piles for skids and attach skid. Start to load skid with sand. Each skid can hold 30 kips of sand. Continue to load skid with sand.

Day 11 – Saturday, February 20th: Continue to load skid with sand if necessary. Re-attach accelerometers that were on the concrete weights to the skid.

Day 12 – Monday, February 22nd: Check instrumentation from pile skids and Commence the “pinned” condition shake table testing phase (UCSD). The same series of shakes will be conducted. After the shaking is complete, convert the skids to a “fixed condition” by the addition of 2-bolts per leg (16 bolts).

Day 13 – Tuesday, February 23rd: Commence the “fixed” condition shake table testing. The same series of shakes will be conducted. Decide if any further shaking needs to be done. Once shaking is complete, start deconstruction – removal of sand from the skids, removal of accelerometers from skids, removal of skids, unhook the strain gages, uninstall the piles.

Day 14 – Wednesday, February 24th: Continue to deconstruct the helical pile test with Torcsill’s help.

How well do Helical Piles shake? Let’s find out!

January 24, 2016 / Victoria Stephens / 5 Comments

We are gearing up for the large-scale shake test at the University of California San-Diego Shake Table site with a tentative start date of February 1st, 2016. Please check back here often to find updates on schedule and a daily log of activities. You can also watch the live video feed at http://nees.ucsd.edu/video/. If you’d like to visit the test, please contact me and let me know when you will be arriving.

Title of Project: Large-Scale Shake Table Test to Quantify Seismic Response of Helical Piles in Dry Sands

Abstract of Project: Helical piles are deep foundation elements that look like, and are installed like, a large steel soil screw – they have a slender steel shaft with any number of round plates at the tip to provide support to the structure they hold. Helical piles are spun into the ground with a large torque motor and provide support through soil bearing on the plates and along the shaft. They come in many lengths and are often the foundation of choice for retrofitting existing buildings or new, urban construction, due to their small footprint and ability to create minimal disturbance to surrounding structures. Although helical piles are installed as foundation elements in seismically active areas such as New Zealand and Japan, they have not been used widely in seismically active areas of the United States. This lack of use is, admittedly, due to having no quantifiable data to illustrate the seismic behavior of helical piles. In addition, there are no side-by-side seismic comparisons to other deep foundation systems available, other than qualitative “survival” stories like those from the 2011 Christchurch earthquake.

After the series of earthquakes in 2011, the city of Christchurch was surveyed and it was found that all buildings/infrastructure constructed on helical piles sustained minimal structural damage, however, a large majority of the condemned buildings were constructed on other foundation types. The international community has qualitative proof that helical piles perform well in earthquake prone areas, but engineers have not quantified “why” those piles are superior foundation elements, and unfortunately, helical pile use in seismically active areas within the United States remains minimal. Therefore, this project seeks to find out “why” helical piles seem to behave so well in seismic regions by subjecting them to earthquake loads in the University of California – San Diego’s Large Shake Table.

These data are especially important and timely to generate because certain areas of the United States are now requiring seismic retrofits of existing buildings, yet engineers have a dearth of data regarding foundation systems to help make these structures safer. For example, in October 2015, the City of Los Angeles voted on a seismic ordinance that will require more than 13,000 structures, both pre-stressed concrete and soft-story wood structures, to be seismically retrofitted. Even though it is known from qualitative studies (e.g., New Zealand and Japan) that piles with comparatively small cross-section and high anchoring capacity, such as helical piles, are beneficial for seismic resistance seemingly due to their slenderness, higher damping ratios, ductility, and resistance to tip uplift, building codes and current state of practice have not been adequately developed for this pile type because no quantitative data exist. Research of seismic behavior of helical pile supported structures is therefore imperative to generate necessary data that will help ensure that helical piles are being correctly applied in seismic areas and establish quantifiable benefits and/or limitations of helical pile use in seismic areas. This project will benefit people living in seismic zones by educating engineers with full-scale helical pile experimental data so that they better understand how to design a building system that is safer, more resilient and sustainable for individuals and the community.

This critical, and first of its kind, study will provide data on the kinematic and inertial behavior of full-scale single helical piles and evaluate the contribution of the helix to overall capacity. Same size slender shafts will be tested with varying helix geometry (e.g., double versus single), as well as installation method (spun versus driven). The piles will be heavily instrumented to measure bending moments, shear and load; all of which will be used to quantify helical pile behavior, validate future numerical modeling endeavors, as well as focus additional future full-scale experimental testing efforts. This study will also quantify behavior of helical piles in a group in both a pinned and fixed condition. The rocking behavior of these group piles will be analyzed to determine how much load is transferred down to the helix level and how it differs between piles in the same group, which affects stability. The study will also compare and contrast the behavior of a driven pile to a helical pile. The results of this study will provide data on the effectiveness of steel shaft slenderness on pile dynamics, the contribution of the helix to overall capacity and rocking behavior, as well as pile group fixity. These results will be of interest to the deep foundation industry, design engineers, government and private entities that utilize deep foundations for infrastructure projects in seismically active areas.

The University of Oklahoma, School of Civil Engineering and Environmental Science202 W. Boyd St., Room 334Norman, OK 73019-0631Phone : (405) 325-5625Email : acerato@ou.edu

The University of Oklahoma, School of Civil Engineering and Environmental Science
202 W. Boyd St., Room 334
Norman, OK 73019-0631
Phone : (405) 325-5625
Email : acerato@ou.edu