SPECIAL EDITION OF THE DUTCH INDEPENDENT JOURNAL GEOTECHNIEK SINCE 1997 t e c h n i e kSPE 919 OTEL GEAJOURN L DUSPECIA 97 CHNIEKTE CHT YEAR 26 - SPECIAL STRESS WAVE CONFERENCE - SEPTEMBER 2022
Prinsessegracht 23 Tel. +31 (0)70 391 99 00 2514 AP Den Haag www.kivi.nl
Allnamics Pile Testing & Geotechnical Experts Waterpas 98 2495 AT Den HaagTel. +31 (0)88 255 62 64 The Netherlands www.allnamics.com
Veurse Achterweg 10Tel. +31 (0)70 311 13 33 2264 SG Leidschendam www.fugro.com
P.O. Box 88Tel. +31 (0)299 31 30 20 1462 ZH Middenbeemster www.vanthek.nl
GEO2 Engineering B.V.Tel. +31 (0)346 769 046 Computerweg 11 www.geo2.nl 3542 DP Utrecht The Netherlands
Oudsas 11Tel. +31 (0)183 50 11 22 4251 AW Werkendam www.hakkers.com The www.nvaf.nl(NVAF)AannemersNederlandseNetherlandsVerenigingFunderingswerkenP.O.Box12183840BEHarderwijkTheNetherlandsTel.+31(0)341456191
This Stress Wave Conference Special is published by Uitgeverij Educom v.o.f. Geotechniek is the leading independent journal for geotechnical professionals in the Netherlands and Belgium since 1997.
P.O. Box 25296, 3001 HG Rotterdam, The Netherlands Tel. +31(0)10 425 6544 email@example.com Publisher: Mr. R.P.H. Diederiks
© Copyrights uitgeverij Educom, September 2022 © ISSN 1386-2758 www.vakbladgeotechniek.nl
THIS STRESS WAVE CONFERENCE SPECIAL IS POWERED BY NetherlandsThe DelftMH2600 177BoxOP es nldeltarerwww es nlininfo@deltarerfo 7382(0)88 335. +31TeTel
2 SEPTEMBER 2022GEOTECHNIEK - STRESS WAVE CONFERENCE SPECIAL
DEVELOPMENT OF ADVANCED PILE INTEGRITY TEST METHODS FOR CAST IN-SITU PILES
Paul Hölscher / Victor Hopman / Aukje Veltmeijer
VAN ’T HEK - OFFERING SPECIALIST SERVICES AROUND THE WORLD
RAPID LOAD TESTING OF FOUNDATION PILES IN B ARCELONA
Marcel Bielefeld / Rob van Dorp / Nicolas Moscoso
Carlos Fernandez Tadeo / Gerald Verbeek
BI-DIRECTIONAL O-CELL® FOUNDATION TESTING- TO OPTIMISE FOUNDATION DESIGN SAFELY AND SUSTAINABLY
Melvin England / Maarten Profittlich
14 CONTENT 3 SEPTEMBER 2022GEOTECHNIEK - STRESS WAVE CONFERENCE SPECIAL
Paul Hölscher Deltares
Victor Hopman Deltares
Aukje Veltmeijer University of Technology
DEVELOPMENT OF ADVANCED PILE INTEGRITY TEST METHODS FOR CAST IN-SITU PILES
Traditional sonic testing of cast-in situ foundation piles is cheap and reliable. However, for deeper or less pronounced defects the reliability is limited. Measurements often lead to discussion on the question whether the defect is acceptable or not. To solve this, additional more accurate independent methods to determine the real size of the defect is desired.
New methods are suggested (e.g. ) but the reliability of these methods is unknown. In this research we tried to get more insight, by comparing the results of all methods on 20 test piles with intentionally created defects. Two new methods are discussed in more detail.
A field test with 20 cast in-situ piles had been created. The site is located at the office of Deltares in Delft. The soil profile has about 8 m soft soil with
some peat and clay layers above a sand layer of about 4 m. The piles (10 m length) had their toes in this sand layer, but had been designed for testing only, not for bearing capacity.
Seventeen piles had one or two realistic defects such as bulges, necks and fractures. The bulges were created by injection of concrete through in advance installed pipes. The necks were prepared by tires filed with clay that were placed in the pile during installation. The fractures were created by a heavy lorry that hits the pile softly.
The piles were prepared for application of several advanced inspection methods (see Figure 1):
– Sixteen piles had a single tube in the centre of the pile. This facilitates Single Hole Sonic Logging (SHSL, see e.g. ) and Seismic Tube (ST). The seismic tube will be discussed in Section 4.
– Four piles had three equidistant holes facilitating
Cross-Hole Sonic Logging (CHSL).
– All piles had one or two deep accelerometers for Deep Acoustic Check (DAC). This method will be discussed in Section 3,
– Some piles had Discrete Temperature sensors (DT) and Fibre Optics (FO) to measure temperature.
– The distance between the piles was large enough to facilitate pushing a seismic cone along the pile to test Parallel Seismics .
– All piles were tested by traditional sonic testing by several experienced companies.
Based on the measurements all involved parties made a blind judgement of all piles, using their own methods. Based on the comparison of the predictions and the created defects, and experience of the field test the applicability of methods is discussed.
– The traditional PIT with one transducer and a hammer blow at the pile top turned out be the most reliable.
– The temperature measurements by the fibre optics and the acoustic SHSL give comparable results. The temperature method requires the installation of a fibre in the pile, the SHSL method requires a central hole. Both methods did not yet give additional information on the size of a defect. The temperature method is very fast, it measures during the curing. This gives the shortest response time after pooring the pile, since there is no need to wait for pouring of the concrete.
– The PS gave reasonable results, under the condition that the transducer is not coupled to the rod. This requires an uncoupling mechanism, that can coupled again in the soil, or the measurement should start at sufficient depth. The advantage of the method is that it doesn’t require preparation in the piles, but the site must be accessible for heavy equipment.
– ST, DAC and CHSL didn’t give results. ST measurements required additional interpretation. DAC was hindered by failure of the transducer that was used at the pile head. The number of piles with three tubes was too low to give a judgement over CHSL.
Figure 1– Overview of the methods that are tested.
4 SEPTEMBER 2022GEOTECHNIEK - STRESS WAVE CONFERENCE SPECIAL
Cast in-situ piles are sensitive for defects during installation. Therefore, integrity of the pile-shaft must be tested. Traditional sonic testing often leads to discussion on the acceptance of piles. More advanced methods that give reliable information on concrete quality and diameter of the pile at distrusted locations
Results of Deep pileCheckAcousticat6.
are required. This paper describes a field test in which several of these methods have been evaluated. Two methods (Seismic Tube and Deep Acoustic Check) are presented in more detail.
After the tests, seven piles have been removed. The selected piles had the largest difference between the intended defect and the defect detected by the measurements interpretation or had very different answers from the measurments. After removal, these piles were inspected visually and (later on) the circumference has been measured. It shows that the creation of a neck with a rubber tire worked well, although some tires were damaged and felt down to the toe of the pile. Injection by concrete to did create some bulges but was hampered by blockage of the pipes. It turns out to be important to regain the piles to check the defects precisely.
3. Deep Acoustic check
The basic idea of the Deep Acoustic Check is to add cheap (lost) transducers (Mems) deep in the pile.
The signals that are measured by these deeper transducers, can be interpreted by similar methods as the traditional transducers at the pile head. The method has been tested experimentally in the field-test after the initial work. The applied Mems accelerometers are sufficient sensitive to get (after integration) velocities in the pile that can be inter-
shows a summary of the defects in two piles that were excavated and inspected after testing. The piles had been selected on discussion about the real defects. This inspection showed that the intended defects were often not as expected.
Figure 4–Diameter of piles fromcircumferencemeasuredforpile6andpile8.
Figure 3 – Results of Deep Acoustic Check at pile 8.
Table 1 –Summary defects in piles
Length pile [m]8.94 9.15
Depth transducer 1 [m]4.4 5.7
Derived wave speed [m/s]4541 4341
Depth transducer 2 [m]6.4 6.7
Derived wave speed [m/s]4451 4376
Shallow defectnone none
Deep defectbulge bulge
Depth defect [m]7.5 8.0
Figure 2 shows an example of a measurement on Pile 6. The figure is presented as a seismogram, with on the horizontal axis the time, and on the vertical axis the position and amplitude. Pile 6 has one transducer at the pile head and two deep transducers at 4.4 m and 6.4 m under the pile head.
Figure 3 shows similar results for pile 8.The signal
of the transducer at the head suffers from the integration. This suggest that for this position the mems require a very high sampling rate to be able to integrate to velocity. A traditional transducer might be preferable. Deeper transducers have less influence of this aspect, presumably since the very high frequencies are damped during propagation.
Figure 2 shows that the actual wave speed can be determined accurately. The determined propagation of the waves is shown by dashed lines. For this short pile this is not very relevant, but for longer piles the uncertainty on wave speed hinders the accurate determination of pile length. The deep transducers solve this quandary.
Figure 4 shows the diameter on depth for both pile 6 and 8. The circumference had been measured,
5 SEPTEMBER 2022GEOTECHNIEK - STRESS WAVE CONFERENCE SPECIAL
and under the assumption of a circular cross-section, the diameter is derived. Pile 6 has a clear bulge close to the toe. The transducers are well above the defect, but this defect is close to the toe. The toe reflection hinders the interpretation. Pile 8 has two bulges. The two transducers are in the highest (closest to the pile head) bulge. This complicates the interpretation.
The interpretation shows that the transducer should be located a sufficient distance above the defects. This distance should be at least the length of the impact wave in the pile. In this case, the wave speed is 4500 m/s and duration of the blow
is 0.7 ms. The length of the wave is thus 3.1 m. The transducer is 1.6 m above the neck, so the incoming wave and reflected wave are interfering. However, the different shape of the measured signal at top and at depth shows that there is a neck below.
Since the bulges in these piles are close to the pile toe, the interpretation is challenging. This shows that tests on short piles have limited value for research, since the signals are interfering too much.
4. Seismic tube
The Seismic Tube has been specially designed to gain detailed information of defects, by the application of high-frequency (about 50 kHz) acoustic waves. The seismic tube has two acoustic sources and 8 equidistant acoustic receivers in between. The idea is based on the methods used for seismic surveys. The presence of two sources makes it possible to use two acoustic signals at one position. The present of 8 receivers makes it possible to create a seismic profile.
The instrument is lowered into a tubular hole in the pile, see Figure 5. By performing the measurement with the Seismic Tube at different heights, a measurement is obtained that is comparable to the Single Hole Sonic Logger. However, the presence of eight transducers (instead of one, as with the SHSL) makes it possible to apply seismic interpretation techniques.
Figure 6 shows a measurement as seismogram, i.e. the time signals are presented at the position where it is measured. The signals are multiplied with a factor that is proportional with the distance between the transducer and the source. This
avoids that the decay of the signals makes the signals further away almost invisible. This figure suggests that the decay is quadratic with distance. However, the cumulative energy in the signals shows that the energy decay is less, about amplitude multiplied with square toot of
that had been measured in the test field have been analyzed more in detail by Veltmeijer . One of the methods tested is the wellknown surface wave inversion (e.g. MASW), but this did not lead to a useful result. This analysis lead to the conclusion that several wave types are propagating in the pile. They can be picked by the arrival times:
– a direct wave propagating parallel with the pile axis (straight characteristic)
– a “surface” wave (Stoneley wave) propagating parallel with the pile axis (straight characteristic)
– a refraction wave (curved characteristic)
– a reflected wave (curved characteristic)
– a reflected refraction wave (curved characteristic)
Veltmeijer also created an interpretation tool that can be used for picking the waves from the measured signals Figure 7 shows an example.
The tool shows that the complex structure of the waves propagating in the pile can be understood. The first arrivals give information on the wave speed in the concrete and thus the quality of the concrete in the core. To determine the diameter of the piles locally the reflected waves must be determined, while these waves interfere with the direct waves that arrive in positions further away only slightly earlier.
Figure 6– Measurement in Pile 13 at 5.67 m depth presented as seismogram. The legend presents the multiplication factors for the signals.
Figure 3 – Example of wave picking tool, showing the complex wave system .
Figure 5– The seismic tube is placed in the hole in a pile.
6 SEPTEMBER 2022GEOTECHNIEK - STRESS WAVE CONFERENCE SPECIAL
This research also shows that the frequency about 50 kHz of applied source of the seismic tube seems
Thesufficient.toolwas tested for practical engineering but turned out to be too sensitive for user choices. This means that the method has been proven to be possible, but improvement is still required. This can be carried out by improvements of the instrument or automation of the interpretation procedure. Especially an approach which is based on source characteristics. If the direct wave and surface waves are distinguished from the other waves, the seismic tube offers the possibility to get insight in the thickness of the piles.
The results of this analysis also have consequences for the interpretation of Single Hole Sonic Logging, where only one transducer is used. The waves that carries information on the diameter of the pile are the reflected and refracted waves. These waves are not very strong and always in the shadow of the direct waves. This suggests that SHSL is a useful tool for checking the concrete quality, but not for evaluation of the pile diameter. This agrees with the findings by Palm . Application of a seismic tube is expected to give more precise information on quality of concrete.
The experience during the installation of the test piles shows that the creation of artificial defects is complicated. Removal of the piles after testing and proper inspection is essential to evaluate the real
advanced technologies described in this paper have potence to give more insight than experienced engineers get by traditional PIT. However further development and more experience are needed. The DAC method seems useful for longer piles. The position of the transducers must be optimised for the pile length and the expected positions of the defects. The Seismic Tube gives good information on the concrete quality (from the wave speed). To derive the diameter, the interpretation needs the discrimination of direct waves and waves that are reflected form the edge. This research will start with experimental work at the demonstration day at the Stress Wave Conference in September 2022.
This work has been founded by the companies that were participating in the project: van ‘t Hek, Brem, Hektec,Volker Staal en Funderingen, Fugro,
Profound, Leiderdorp Instruments and Directorate-General for Public Works and Water Management and the research program Geo-impuls 
Deltares is an independent institute for applied research in the ﬁeld of water and subsurface. Worldwide, we work on smart technological innovations and sustainable solutions for societal challenges
hclaietcsoforstionluso ovationinnalologichntec , widewdorl. Weacfursubs e ﬁhn th ircaseed rlieppa denepdeinnaissrealteD sgenllea leabaintssudansn tramn sk oore w dnr aatef wd ole fortetitusinnt sstructure dationsFoun• nl aai, rRoad• lofandDikes• ork on geote wW ddergrounundan rastructurenfe ielinipd p defefencesdoo echnics inwwwgeotprooClimate• deltares.nlwww worksnetf
 Hopman, V., Hölscher, P., report Opzet testlocatie voor in de grond gevormde palen - COB, de2016. Groot, P.H., report The parallel Seismic detection of defects in pile foundations, MSc report TU-Delft, the Netherlands, 2014 https:// FULLTEXT01.pdf.www.diva-portal.org/smash/get/diva2:542054/Engineering,(KTH),inofAugustleagueMSc-thesiscreatedtionrepository.tudelft.nl/.Geoimpuls,seehttp://www.geoimpuls.orgVeltmeijer,A.,SeismicPropertiesofFounda-Piles,Diameterdeterminationofin-situfoundationpilesusingtheSeismicTube,AppliedGeophysicsResearch,IDEADelftUniversityofTechnology/Deltares,2019Palm,M.,Single-holesoniclogging,Astudypossibilitiesandlimitationsofdetectingflawspiles,MScreport,RoyalInstituteofTechnologyDepartmentofCivilandArchitecturalStockholm,Sweden,2012, www.deltares.nl
We work on geotechnics in
Adv-Geotechniek-From experimental research to practical application-Geotechniek-2022-208x134mm.indd 1 15-03-2022 08:29
7 SEPTEMBER 2022GEOTECHNIEK - STRESS WAVE CONFERENCE SPECIAL
The experience we can offer in the field of foundation works is unique. Fundex can be engaged in any role: • for advisory and study for existing and new customers, • as main- and subcontractor in Benelux projects, • as a partner in international projects or in temporary associations.
Fundex has built up world fame over the years. With more than 60 years of experience and a range of multifunctional foundation techniques, we are your flexible partner in every project.
Funderingstechnieken Verstraeten BV Brugsevaart 6 4501 NE Oostburg Tel. +31 (0)117 45 75 75 www.fundex.nl
PARTNER IN PILING AND DRILLING PARTNER IN PILING AND DRILLING Marine dolphins PARTNER IN PILING AND DRILLING
8 SEPTEMBER 2022GEOTECHNIEK - STRESS WAVE CONFERENCE SPECIAL
VAN ’T HEK: OFFERING SPECIALIST SERVICES AROUND THE WORLD
The family owned company Van ‘t Hek was founded in 1945 in the Netherlands as a General civil contractor. In the 1970’s the company put focus on the execution of Deep Foundations by Piling and sheet pile retaining structures as a sub-contractor. Back in the day it were mainly timber - and precast concrete piles for civil works, housing and commercial building projects that Van ’t Hek drove with self build dragline based piling rigs.
Today Van ’t Hek is market leader in the Netherlands and holds this position for already a decade. It is part of the Van ’t Hek Group, together with other subsidiary that focus on Piling or related services, each with it’s own specialization. Van ’t Hek Group is still family owned and the third generation is in charge.
Van ’t Hek is seen around the world offering it’s specialist service that, dependent on the client’s wishes can extend from pile design, through execution to pile testing and environmental monitoring and the design and construction of Special Purpose
ThisEquipment.selection of “groundbreaking” projects reflects Van ’t Hek’s current capabilities, however not exhaustive as it is usually the client’s dreams that make us push the boundaries even further.
Port of Poti, Georgia
For a Quay wall reconstruction in the Port of Poti in Georgia, Van ’t Hek installed not only Zshaped sheet piles but also some cellular cofferdams as part of a pier extension. The modular guiding frame based on separate adjustable piling platforms were designed by our in-house mechanical engineers (Hektec) and built in our own steel workshop.
Ing. Patrick IJnsen Executive Board Member Van ’t Hek Groep
Kobelco CKE 2500 Piling Rig
Some clients ask us to do the works, other ask us if they can rent our rig, this client ask us to build one… So we did! On the base of a 250 tons dragline crawler crane, we build a piling rig with a maximum capacity of 72 ton for the Pile + hammer weight, able to install piles in a rake position up to 3:1 and even 1:1 with the optional “Flying Leader” configuration.
Amsterdam “Sluishuis” Project
To enable the construction of this Iconic building in a lake, Van ‘t Hek placed a temporary sheet piled double cofferdam to create the construction pit in which steel screw injection piles with a tip diameter of 1000 mm and a length of 65,0 m were installed in order to support the cantilever structure of the building.
A large number of precast concrete piles were driven into the construction prior to dredging and draining the building pit as foundation for the parking basement, before the construction pit bracing was applied. Piles with a temporary function were placed between the sheet piles of the building pit to hold up the formwork and scaffolding for the overhanging part of the building.
WWW.VANTHEK.COM 9 SEPTEMBER 2022GEOTECHNIEK - STRESS WAVE CONFERENCE SPECIAL
For a project in the old port of Barcelona large diameter (1.5 m) cast in-situ piles with design service loads 6 - 8 MN were constructed. The piles installed 28-35 m in a soil profile that mostly consisted of (silty) sand. On 2 of the first constructed piles full-scale bi-directional load tests were planned to check pile capacity. With this type of
RAPID LOAD TESTING OF FOUNDATION PILES IN BARCELONAFigure1–
load test, an embedded jack assembly is embedded in the pile shaft, pushing the upper part (shaft) up and the lower part (toe) down, with parts using each other for reaction. An essential limitation of the method is that the maximum test load is limited to the ultimate capacity of either shaft or toe, so ultimate capacity of the other will remain unknown. Unfortunately, this is what happened
with the bi-directional tests performed on the project: the pile toe failed before required capacity was reached, while the behavior of the shaft suggested that only a portion of its capacity was mobilized when the test had to be terminated. However, this could not be concluded from the available test results, so additional load tests were needed to be able to accept the pile design. These tests had to be performed on already constructed piles (50 pcs), which ruled out bi-directional testing. A different test method was needed, with the understanding that execution of the tests should take as little time as possible, in order to minimize the delay of the – already suspended –project.
Possible Pile Load Test Methods
Traditional static load tests (SLT) are considered the most reliable. However, performing takes a lot of transport and time, both for the construction of the reaction system and for the test itself. This results in high costs and a long execution time, especially in case of high test loads and multiple test piles, like in this case. This made SLT not
Figure2 –Specifics of dynamic and rapid testing.load
method is a dynamic load test (DLT), which offers high test productivity and eliminates the need for a reaction system. To perform a DLT, a single blow is applied to the pile head with an impact ram with a mass of 1%-2% of the required mobilized static capacity. The impact (5-15 msec) generates stress waves that are monitored by accelerometers and strain gauges mounted near the top of the pile. To estimate the mobilized static resistance, the recorded data is analyzed using signal matching techniques based on simulation of the stress wave propagation through the pile. However, the advantages of cost savings and short test duration are offset by a reduction in the accuracy of the test results as well as the relatively wide spread in results related to the user dependency of signal matching, especially for concrete piles. In addition, DLT involves peak loads on the pile that are much higher than the mobilized static capacity. So much higher, that DLT can damage a concrete pile. Simulations made for this project revealed that the required DLT was likely to damage the piles.
Carlos Fernandez Tadeo EspanaAllnamics
Bielefeld ExpertsPileAllnamicsTestingBV, NL Rob van Dorp ExpertsPileAllnamicsTestingBV, NL Nicolas Moscoso ExpertsPileAllnamicsTestingBV, NL Gerald Verbeek USAAllnamics
10 SEPTEMBER 2022GEOTECHNIEK - STRESS WAVE CONFERENCE SPECIAL
After the planned bi-directional load tests for a construction project in the port of Barcelona showed inconclusive results, execution of a large number of additional pile load tests was required, at short notice and with heavy test loads.
To avoid these drawbacks of DLT, it was decided to use another alternative method: Rapid Load Testing (RLT) using a StatRapid device. The devices generates a load with increased duration (100-200 msec) by free fall of a drop mass of 5% to 10% of the required test load on a specially developed spring cushioning placed on the pile head. To prevent any rebound, a catching mechanism is activated after the drop mass impacts the pile head. For each load cycle, the applied force, displacement and acceleration at pile head level are directly measured. By varying the drop mass and drop height multiple, increasing load cycles can be applied. Apart from extending the load duration, the spring system also greatly reduces the stresses in the pile head. Therefore, it is a particularly convenient test method for concrete piles.
Unloading Point Method (UPM)
Due to the increased load duration during RLT the pile can be assumed to behave as a rigid body, where velocity and acceleration are the same along the entire length of the pile. To ensure this is the case, international standards specify a minimum load duration Tload > 10 L/c where L is the pile length and c is the stress wave velocity through the pile.
On that basis Middendorp developed the Unloading Point Method (UPM), which is the commonly used method to analyze data obtained from a Rapid Load Test. The UPM is straightforward and, more importantly, is independent of the person performing the analysis. Rapid Load Testing and UPM are implemented in various international standards, among which ASTM D7383 in USA and Eurocode EN-ISO-22470-10:2016, which was applicable to the project in Barcelona.
The UPM centers around the point where the velocity of the pile equals zero (vupm = 0). At this point (tupm), that can be easily identified in the monitoring results (see picture), the displacement of the pile is maximal and the pile can be assumed to behave quasi-statically.
The total pile resistance during a load test can be split into three components: static, dynamic and inertial. See [Eq. 1]:
With k the static soil stiffness, C the soil damping, m the pile mass and with u, v and a respectively displacement velocity and acceleration of the pile.
This was possible by performing Rapid Load Tests (RLT), using a StatRapid device. In total 25 tests up to 12 MN were executed within 9 working days, putting the project back on track.
Figure3 – Measurements needed to determine static resistance using the Unloading Point Method (UPM).
The fact that v = 0 at tupm implies that Fdynamic = 0 at tupm in [Eq. 1]. Furthermore, given the equilibrium of forces, the measured force from the Rapid Load Test (FRLT) can be expressed as shown in [Eq. 2].
FRLT = Fsoil = Fstatic + 0 + Finertia =(k∙u)+0+(m∙a)
Rearranging [Eq. 2], the mobilized static resistance (Fstatic ) can be computed using [Eq. 3].
Fstatic = FRLT - Finertia = FRLT-(m∙a)
In this equation, the pile mass (m) is known and all other factors at tupm are measured directly; using load cells (FRLT), accelerometers (a) and optical sensor (displacement). With all factors at tUPM known, the mobilized static resistance Fstatic can be
behavior, RLT is still a quick test, that does not capture time-dependent phenomena like creep or pore pressure dissipation. Therefore, the value of Fstatic determined using [Eq. 3] needs some correction to take these so-called loading rate effects into account. See [Eq. 4], where η represents the loading rate effects factor on soil type. Typical values for η are 1.00 for rock,
Figure4 – Direct monitoring of force, displacement & acceleration.
0.94 for sand and 0.66 for clay. [Eq. 4]
Fstatic,corrected = η· Fstatic
Test strategy and safety philosophy
For load testing it is common to require a factor of safety (FoS) of 2.0 for the test piles. With design working loads 6-8MN that implied required test loads of 12-16 MN. The only StatRapid device that was available within the required time frame had a 40 ton drop weight with 10 MN nominal test capacity. Higher loads are also possible, but with shorter load duration, which can only be accepted as long as the criterion Tload > 10 L/c remains Computerfulfilled.
simulations performed in advance to establish the maximum possible test load that still fulfilled this criterion, revealed that loads up to 12-13MN could be achieved in this case. It should be noted that in foundation works, increasing safety is about reducing uncertainty. Uncertainty is better reduced by testing more piles with lower FoS than by testing less piles with a higher individual FoS. The client and local authorities acknowledged this and accepted the proposal to test 50% of the already installed piles (25 pcs)
11 SEPTEMBER 2022GEOTECHNIEK - STRESS WAVE CONFERENCE SPECIAL
Figure5 –Cyclic Loaddiagramload-displacementfromaRapidTest.
Figure6 –Corresponding diagramload-displacementstaticderivedfromtheRapidLoadTest.
Figure7 –Moving the fully assembled and loaded test device.
with test loads corresponding to a FoS of at least 1.20 – 1.30. Among the test piles were the piles that had also been subjected to the inconclusive bi-directional tests.
The 25 test piles were divided over 4 different load classes, with required minimum test loads varying between 8 and 11 MN. Rapid Load Tests were performed in accordance with a dedicated test protocol. The first test piles were tested in 5 load cycles with a gradually increasing test load, in order to establish a good understanding of the soil response. Given the small plot size and limited site variability, subsequent tests could then be optimized by applying only 2 load cycles: the first one to confirm the soil stiffness and the second to mobilize the required capacity. In cases where test results seemed different from average, additional load cycles were performed to obtain extra data for the load- displacement curve for that particular pile. Each load cycle took approximately 10 to 15 minutes to perform. For this project, a 400-ton crane was
chosen, which was able to move the fully assembled device (63 ton) from one pile location to the next. Using this procedure the 25 load tests were performed within 9 working days, with an average of 3 tested piles per day. The last test pile was used for a small experiment, applying the maximum drop height of the device (4,0 m) and monitor load duration and maximum test load.
An overview of the main results is shown in the table. On average, the mobilized static resistance corresponded to FoS = 1.19 – 1.34. It should be noted that mobilized capacity is a safe lower bound value of ultimate capacity, because none of the piles failed during the tests.
After an inconclusive bi-directional load test at the start of the project, Rapid Load Testing was successfully applied to confirm the axial resistance of 50% of the already installed piles. By testing 25 piles in 9 working days, with test loads 8-12 MN and positive test results, the confidence in the
pile design was restored and installation of the remaining 368 piles could be resumed. An open mind regarding safety philosophy on the side of client and authorities, as well as excellent coordination between general contractor and testing contractor were key to the successful completion of this testing work, without any further impact to the overall project schedule.
–Hölscher P.; Tol van F. (2009). Rapid Load Testing on Piles, Boek, ISBN 978-0-415-48297-4 ; e-book: 978-0-203-88289-4 , P.1-180 , CRC Press/Balkema.
–Jardin R.J., Chow.F.C., Overy.R.F. and Standing. J.R. (2005) ICP Design methods for driven piles in sand and clays. Thomas Telford London, 97. –Middendorp. P. (2000). Keynote lecture: Statnamic the engineering of art., International Conference on Application of Stress Wave Theory to Piles, Sao Paulo, Brazil, P.551-562 , A.A. Balkema.
–Hölscher, P., van Tol, A.F., Middendorp, P. (2008). European standard and guideline for Rapid Load Test, 8th Int. Conf. Application of stress-wave theory to piles, Lisbon, P.699.
Figure8 – Cyclic load-displacement diagram from a Rapid Load Test.
12 SEPTEMBER 2022GEOTECHNIEK - STRESS WAVE CONFERENCE SPECIAL
Whether as a supplier of hardware and software for foundation testing and pile driving simulation or as a reliable advisor in these areas, Allnamics’ activities are founded on 50 years of experience with foundation piles, impact driven as well as vibro driven, onshore as well as offshore.
During those years our staff was intimately involved in the development of multiple testing methods, such as low strain dynamic testing, high strain dynamic and Rapid Load Testing
With these capabilities, Allnamics is ready to support the installation of deep foundations around the world.
ALLNAMICS GEOTECHNICAL & PILE TESTING EXPERTS
• STATRAPID PILE LOAD TESTING • STATIC AND DYNAMIC LOAD TESTING (SLT/PDA) • SIMULATIONS OF PILE INSTALLATION FOR IMPACT AND VIBRATORY HAMMERS • QUALITY CONTROL OF NEW AND EXISTING FOUNDATIONS • MONITORING PILE INSTALLATION (PDA/VDA) • ALLWAVE DRIVEABILITY SOFTWARE • PDR PILE MONITORING EQUIPMENT ALLNAMICS.COMAMItestingandpiledrivingsimulation TIC AND DYNAMIC LOSTATATA• TED• T/PDA)OAD TESTING (SLLT Testingon VE SALLWAWALW• AMONITORING PILE INSTTA• TIONSFOUNDAAT • TORY HAMMEANDVIBRAATTIONS INSIMULAAT• ALLAEQUIPMENTARESOFTWWATION(PDA/VDA)AT ACTTION IMPSTALLAATTA • 13 SEPTEMBER 2022GEOTECHNIEK - STRESS WAVE CONFERENCE SPECIAL
Melvin England Fugro TestingFoundation(Loadtest)
BI -DIRECTIONAL O-CELL® FOUNDATION TESTING: TO OPTIMISE FOUNDATION DESIGN SAFELY AND SUSTAINABLY
Worldwide awareness of climate change continues to increase, as do calls for action. Reducing our carbon footprint is a priority if we hope to minimize the impact of global warming. Concrete production is responsible for 5% to 7% of total CO2 emissions worldwide. The construction industry, and in particular the foundation industry, can take steps to reduce their contribution.
Accurate foundation design is a critical area for efficient use of concrete and steel in the ground. Calibration of the design of foundations can unlock huge savings in terms of material usage and project
Photo1 – Construction work in Geneva; the carbon footprint on the project was reduced by one third (420 tonnes) using, among other things, electric concrete trucks.
timescales and these are best done by full-scale load testing to evaluate the pile or barrette behaviour.
Bi-directional pile load testing
Full-scale static load testing can be performed by either applying the full test load at the head of the foundation in the traditional manner, with kentledge or a reaction beam and anchor piles, or performed bi-directionally by casting the loading element within the foundation itself. O-cell® bi-directional load testing can be used to verify the pile performance and compare it against the design in the most efficient, safe and cost-
Tabel1 –Savings due to base Fugro).(Source:enlargementImplenia/
effective manner of all types of foundations –particularly for larger test loads. The following project examples illustrate some of the benefits of using bi-directional load tests and how effective they are at reducing carbon emissions.
Two construction projects in Switzerland Foundations for an extension to the Rolex factory are being constructed in Geneva. Ground conditions in the area are characterised by soft post glacial deposits with the moraine layer found at more than 50 m. With a traditional nominally cylindrical pile design the toe of the piles would be found in the moraine. Instead an alternative pile installation technique using a ream was considered and the behaviour of two test piles verified with O-cell®
design piles have a significantly smaller diameter considerably reducing the volume of the piles and therefore the material extracted, concrete used, transport requirements etc. Table 1 below shows the comparison between the initial
Photo2 – Photo 2: BAUER
Spezialtiefbau GmbH verified the foundation design for a more cost-efficient and less time-consuming solution. Profittlich TestingFoundation(Loadtest)
14 SEPTEMBER 2022GEOTECHNIEK - STRESS WAVE CONFERENCE SPECIAL
traditional pile foundation plan and the alternative Onsolution.another
project for the Swiss private bank, Pictet, three barrettes were load tested, at different depths, to optimise their design. In addition to the benefits of using bi-directional load testing the contractor used electric concrete trucks (see photo1).
Fugro has completed a successful load-testing programme on Germany’s longest rotary bored piles as part of the foundation design verification for the planned Elbtower construction in Hamburg.
On completion, the 244 m high Elbtower will be the third tallest skyscraper in Germany and forms part of a 157 hectare megaproject to redevelop the former harbour and industrial areas of HafenCity.
Located on low load-bearing ground near the Elbe river, the Elbtower’s foundations will rest on long piles to transfer the load to a deep load-bearing soil layer and prevent long-term settlement. Deep foundation contractor BAUER Spezialtiefbau GmbH constructed several bored test piles up to 111.4 m long and 1850 mm in diameter, and Fugro provided unique load-testing and measurement technology for the pile-testing programme. The advantage of Fugro’s in situ load testing, especially on piles of this size and ultimate load-bearing capacity, is that clients can verify and potentially optimise their foundation design without the
need for costly and time-consuming installation of reaction piles used in traditional load testing.
High speed rail lines across Europe
Fugro is also involved at numerous sections of HS2, the UK’s new high speed rail network, including foundation testing programs. HS2 will integrate new railway lines and upgrades across Britain’s rail system to deliver faster travel to many towns and cities not directly on the HS2 route, including Liverpool, Sheffield, Leeds, Nottingham and
of new high-speed line is already under construction between Crewe and London, employing around 25,000 people. In total, the Government is planning over 260 miles of new high-speed line across the country. HS2 trains will be powered by zero carbon energy for a cleaner, greener future.
Some of the first contributions for the tests in the chalk of the Chilterns has provided a possible foundation size reduction of 70 % when compared with the original design. One of the most recent projects is the foundation test program at Birmingham Curzon Street Station (photo 3). This station will be at the heart of the high-speed rail network in the West Midlands. It will be one of the most environmentally friendly stations in the world. Two key benefits of our full-scale pile testing program are the saving on materials due to shorter
pile lengths and increased design confidence.
Summary and conclusions
Worldwide awareness of climate change continues to increase, as do calls for action. Reducing the carbon emissions for buildings and infrastructure can help to limit global temperature rise and achieve a net zero future. Concrete production is responsible for 5% to 7% of total CO2 emissions worldwide. The construction industry, and in particular the foundation industry, is able to take steps to reduce their contribution. One potential saving is through optimising the foundation of (high-rise) buildings, bridges and infrastructure
foundation design is a critical area for efficient use of concrete and steel in the ground. Calibration of the design of foundations can unlock huge savings in terms of material usage and project timescales and these are best done by full-scale load testing to evaluate the pile or barrette behaviour. O-cell® bi-directional load testing can be used to verify the pile performance and compare it against the design in the most efficient, safe and cost-effective manner of all types of foundations –particularly for larger test loads. The project examples described in this article show that using full-scale static load testing with O-cell® bi-directional testing can reduce carbon emissions and improve project efficiencies.
Photo 3– Artist impression of Birmingham Curzon Street Station where pile design is being verified with O-cell® bi-directional testing (source: hs2.org.uk).
15 SEPTEMBER 2022GEOTECHNIEK - STRESS WAVE CONFERENCE SPECIAL
To ﬁnd out more firstname.lastname@example.org Full scale static load test Safer and more cost eﬀective than traditional tests Magnitude of load only limited by the ground conditions More than 30 years of experience in over 60 countries O-CELL® BI-DIRECTIONAL TESTS TO OPTIMISE YOUR FOUNDATION DESIGN SAFELY & O-CSUSTAINABLY BI-DIRECT TIMIO OPT FOUNDATAT LCELE ALN R IO S OUE Y TIONGNISED oac ltatie scall sFul comore adloofMagnitude 0 eMore than 3 S ondtm t N esd t t testhantiveeﬀecost cgroundtheited 0 countries lid xperience in over 6 DESIG Y TIO T SUSTAAINABLYL s s ondition moutTo loadtest@fug m ore gro.co Research Design & Constructch ConsResear truct Interested?Takealookatwwwwerkenbijhakkerscomorvisitoursocials ‘Probability theory can be applied to driveability predictions to quantify refusal risk’ TaTakealookatwInterested? comorvisitoursocialskerswerkenbijhakwwtwInterested? Take a look at www.werkenbijhakkers.com or visit our socialst wTaTakealookaInterested? om or visit our socialskers.cw.werkenbijhakw 16 SEPTEMBER 2022GEOTECHNIEK - STRESS WAVE CONFERENCE SPECIAL