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1

Estimation of Screw Displacement Pile-Bearing Capacity Based on Drilling Resistances

Krasiński Adam

Studia Geotechnica et Mechanica

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2023

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Vol. 45, nr s1

282--292

EN

This article presents an engineering, empirical method of estimating the bearing capacity and settlement characteristics Q-s of screw displacement piles and columns, based on soil resistance encountered during the drilling to form piles/columns in the ground. The method was developed on the basis of correlation analyses of the test results of 24 piles made during the "DPDT-Auger" research project (Krasiński et al., 2022a). In the proposed method, the load capacity of a screw displacement pile is estimated using two main parameters of auger screwing resistance: torque MT and the number of auger rotations per depth unit nR. The method applies to piles and columns made with a standard screw displacement pile (SDP) auger and with the proprietary, prototype DPDT (displacement pile drilling tool) aguer, patented in Poland (2020). Based on the estimated ultimate capacities of the pile shaft and base, an approximate method of predicting the pile settlement characteristics Q-s was also proposed, using the transfer function method. This article describes a correlation procedure of field test results together with their statistical analysis and presents a method of estimating the pile-bearing capacity based on correlation results. A calculation example is also provided. The conclusion looks at the useful practical applications that could be found for the proposed method.

2

FEM modelling of screw displacement pile interaction with subsoil

Więcławski Paweł, Krasiński Adam

Archives of Civil Engineering

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2023

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Vol. 69, nr 4

157--170

EN

Predicting the Q-s settlement characteristics of piles is an important element in the designing of pile foundations. The most reliable method in evaluating pile-soil interaction is the static load test, preferably performed with instrumentation for measuring shaft and pile base resistances. This, however, is a mostly post-implementation test. In the design phase, prediction methods are needed, in which numerical simulations play an increasingly popular role. This article proposes a procedure for numerically modeling the interaction of screw displacement piles with soil using the ZSoil 2D FEM program. The procedure takes into account technological characteristics of this type of pile, such as the process of soil expansion during the screwing-in of the auger and the pressure of concrete mix after pile concreting. They significantly affect the soil stress state, which is a key parameter for the pile load capacity. Geotechnical parameters of the subsoil were adopted from CPTU probing and laboratory tests. Due to the physical complexity, a constitutive soil model “Hardening Soil” (HS) was used in the analyses. The modeling procedure was calibrated on the basis of the static load test results of several instrumented piles, which were carried out as part of the “DPDT-Auger” research project. As a result of these calibrations, generalized recommendations were derived for an entire single pile modeling process with the axisymmetric system of ZSoil program. These can be useful in the reliable FEM prediction of the Q-s characteristics for screw displacement piles for practical engineering purposes.

PL

Prognoza osiadania pali fundamentowych pod wpływem obciążeń zewnętrznych jest kluczowym zagadnieniem w projektowaniu posadowień głębokich. Dysponując charakterystyką „Q-s” (obciążenie - osiadanie) można z dobrą dokładnością określić w jaki sposób będzie zachowywała się konstrukcja w trakcie budowy i użytkowania. Najlepszą metodą weryfikacji współpracy pali z podłożem jest próbne obciążenie statyczne, szczególnie cenne w przypadku pali oprzyrządowanych, gdy poza globalną charakterystyką dysponujemy dodatkowo pomiarami oporów gruntu pod podstawą i tarcia na pobocznicy. Ze względu na ograniczenia techniczne i ekonomiczne nie zawsze istnieje możliwość wykonania satysfakcjonującej liczby testów w terenie z zaawansowanym oprzyrządowaniem pomiarowym. Problem częściowo rozwiązuje możliwość symulacji numerycznej. W artykule przedstawiono propozycję procedury modelowania współpracy pali przemieszczeniowych, formowanych za pomocą świdrów rozpierających DPDT, z ośrodkiem gruntowym w programie ZSoil 2018. Rozpatrywany problem potraktowano jako zagadnienie początkowo-brzegowe, dotyczące pala pojedynczego, wymodelowane w układzie osiowo-symetrycznym. Pal wyrażono za pomocą elementów objętościowych. Przedstawiona procedura uwzględnia czynniki technologiczne charakterystyczne dla tego typu pali, takie jak proces rozpierania gruntu przez wkręcanie świdra czy ciśnienie mieszanki betonowej. Procesy te wymodelowano sposobami zastępczymi. Wpływają one istotnie na stan naprężenia w gruncie, czyli kluczowy parametr, od którego zależy nośność pala. Wzdłuż linii styku pala z gruntem (wzdłuż pobocznicy i pod podstawą) zastosowano elementy kontaktowe („interface”). Elementy te są opisywane typowymi parametrami gruntowymi, ale oprócz tego parametrami Kn_mult oraz Kt/Kn. Wartości tych oraz innych parametrów określano na podstawie prób kalibracyjnych. W modelu geometrycznym, uwarstwienie podłoża gruntowego dostosowywano do profilu geotechnicznego wyznaczonego z sondowania statycznego CPTU. Ze względu na znaczną złożoność zagadnienia (fazy z obciążeniami i odciążeniami), w analizach wykorzystano model konstytutywny gruntu „Hardening Soil”. Procedura modelowania została skalibrowana na podstawie wyników próbnych obciążeń statycznych kilku pali oprzyrządowanych pomiarowo, które wykonano w ramach projektu badawczego „DPDT-Auger” nr POIR.04.01.04-00-0124/18 dofinansowanego z NCBiR i środków UE. W wyniku kalibracji wyprowadzono uogólnione zalecenia dotyczące całego procesu modelowania pala pojedynczego w układzie osiowosymetrycznym programu ZSoil, jak również dotyczące wartości parametrów poszczególnych etapów tego modelowania. Pozwolą one na miarodajne i wiarygodne prognozowanie MES charakterystyk “Q-s” pali przemieszczeniowych wkręcanych, przydatnych w praktyce projektowej.

3

Results of the “DPDT-Auger” research project on screw displacement piles

Krasiński Adam, Słabek Andrzej, Więcławski Paweł, Wiszniewski Mateusz, Kusio Tomasz, Tisler Witold

Architecture Civil Engineering Environment

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2023

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Vol. 16, no. 3

89--99

EN

The main objective of the “DPDT-Auger” research project was to test the prototype DPDT auger for forming screw displacement piles in the ground (patented in Poland in 2020). An additional aim was to develop design methods and rules for the making of such piles. The augers and piles were first tested on a model scale, and then more extensively in the real scale on experimental field plots. The results found the overall functionality of the DPDT auger to be good, and in several aspects better than that of the SDP auger. The load-bearing capacities and Q-s characteristics of piles made with both augers were considered comparable. All the conducted tests and their derived dependencies together with the results of in situ subsoil tests allowed for the development of empirical calculation methods and prognostic procedures, useful for designing and producing piles with DPDT and SDP augers. FEM numerical simulation rules for the considered piles were also developed, verified and calibrated by the results of real pile tests. This article describes only the most important final results of the research project but not the detailed results of the numerous tests and analyses that were carried out. Also omitted are the results of model tests and numerical simulations, as well as the implementation and acceptance recommendations, as they have already been or will be the subject of separate publications.

4

Pile model tests using strain gauge technology

Krasiński A., Kusio T.

Studia Geotechnica et Mechanica

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2015

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Vol. 37, nr 3

49--52

EN

Ordinary pile bearing capacity tests are usually carried out to determine the relationship between load and displacement of pile head. The measurement system required in such tests consists of force transducer and three or four displacement gauges. The whole system is installed at the pile head above the ground level. This approach, however, does not give us complete information about the pile–soil interaction. We can only determine the total bearing capacity of the pile, without the knowledge of its distribution into the shaft and base resistances. Much more information can be obtained by carrying out a test of instrumented pile equipped with a system for measuring the distribution of axial force along its core. In the case of pile model tests the use of such measurement is difficult due to small scale of the model. To find a suitable solution for axial force measurement, which could be applied to small scale model piles, we had to take into account the following requirements: – a linear and stable relationship between measured and physical values, – the force measurement accuracy of about 0.1 kN, – the range of measured forces up to 30 kN, – resistance of measuring gauges against aggressive counteraction of concrete mortar and against moisture, – insensitivity to pile bending, – economical factor. These requirements can be fulfilled by strain gauge sensors if an appropriate methodology is used for test preparation (Hoffmann [1]). In this paper, we focus on some aspects of the application of strain gauge sensors for model pile tests. The efficiency of the method is proved on the examples of static load tests carried out on SDP model piles acting as single piles and in a group.

5

The analysis of soil resistance during screw displacement pile installation

Krasiński A.

Studia Geotechnica et Mechanica

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2014

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Vol. 36, nr 3

49--56

EN

The application of screw displacement piles (SDP) is still increasing due to their high efficiency and many advantages. However, one technological problem is a serious disadvantage of those piles. It relates to the generation of very high soil resistance during screw auger penetration, especially when piles are installed in non-cohesive soils. In many situations this problem causes difficulties in creating piles of designed length and diameter. It is necessary to find a proper method for prediction of soil resistance during screw pile installation. The analysis of screw resistances based on model and field tests is presented in the paper. The investigations were carried out as part of research project, financed by the Polish Ministry of Science and Higher Education. As a result of tests and analyses the empirical method for prediction of rotation resistance (torque) during screw auger penetration in non-cohesive subsoil based on CPT is proposed.

6

Comparative model tests of SDP and CFA pile groups in non-cohesive soil

Krasiński A., Kusio T.

Studia Geotechnica et Mechanica

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2014

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Vol. 36, nr 4

7--11

EN

The research topic relates to the subject of deep foundations supported on continuous flight auger (CFA) piles and screw displacement piles (SDP). The authors have decided to conduct model tests of foundations supported on the group of piles mentioned above and also the tests of the same piles working as a single. The tests are ongoing in Geotechnical Laboratory of Gdańsk University of Technology. The description of test procedure, interpretation and analysis of the preliminary testing series results are presented in the paper.

7

Numerical simulation of screw displacement pile interaction with non-cohesive soil

Krasiński A.

Archives of Civil and Mechanical Engineering

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2014

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Vol. 14, no. 1

122--133

EN

A trial numerical simulation of screw displacement pile interaction with non-cohesive subsoil during the transfer of compression load is described. The simulation was carried out in an axisymmetric system using the Plaxis 2D-FEM computer programme. The technological phases of pile installation in the ground were numerically modelled using equivalent processes which provided similar effects to real technical actions. The results of the numerical calculations were verified by comparing them with the load test results of a real pile in the field. The analysis shows that, apart from the technological elements, a proper numerical simulation of screw displacement pile interaction with non-cohesive soil also needs to take into account soil characteristics as defined in the critical state theory.