In this paper, the whole process of pile construction and performance during loading is modelled via large deformation finite element methods such as Coupled Eulerian Lagrangian (CEL) and Updated Lagrangian (UL) Numerical study consists of installation process, consolidation phase and following pile static load test (SLT) The Poznan site is chosen as the reference location for the numerical analysis, where series of pile SLTs have been performed in highly overconsolidated clay (OCR ≈ 12) The results of numerical analysis are compared with corresponding field tests and with so-called “wish-in-place” numerical model of pile, where no installation effects are taken into account The advantages of using large deformation numerical analysis are presented and its application to the pile designing is shown

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Influence of Installation Effects on Pile Bearing Capacity in Cohesive Soils – Large Deformation Analysis Via Finite Element Method

Excess pore water pressure (EPWP) development and decay due to the installation and static loading tests of controlled modulus columns (CMC) in soft soil was measured with piezometers equip...

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Pore Water Pressure Development in Soft Soil due to Installation and Loading of Controlled Modulus Columns

Abstract—Sydney’s booming real estate market has pushed property developers to invest in historically “no-go” areas, which were previously too expensive to develop. These areas are usually near rivers where the sites are underlain by deep alluvial and estuarine sediments. In these ground conditions, conventional bored pile techniques are often not competitive. Contiguous Flight Auger (CFA) and Drilled Displacement (DD) Piles techniques are on the other hand suitable for these ground conditions. This paper deals with the design and construction challenges encountered with these piling techniques for a series of high-rise towers in Sydney’s West. The advantages of DD over CFA piles such as reduced overall spoil with substantial cost savings and achievable rock sockets in medium strength bedrock are discussed. Design performances were assessed with PIGLET. Pile performances are validated in two stages, during constructions with the interpretation of real-time data from the piling rigs’ on-board computer data, and after construction with analyses of results from high strain pile dynamic testing (PDA). Results are then presented and discussed. High Strain testing data are presented as Case Pile Wave Analysis Program (CAPWAP) analyses.

Design and Construction Validation of Pile Performance through High Strain Pile Dynamic Tests for both Contiguous Flight Auger and Drilled Displacement Piles

The installation of driven displacement piles in clays creates vertical soil movement that is commonly known as heave. Numerous researchers have developed theoretical models to calculate the expected volume of soil heave due to pile driving.Screw auger displacement piles are a relatively new and, due to their cost-effectiveness, increasingly popular piling technique that has been used successfully in Australia and New Zealand over the past two decades. Soil heave in clays during the installation of screw auger displacement piles has not been investigated in detail, even though the effects are commonly known throughout the industry. The authors introduce some of the most popular general soil heave theories and compare their validity to screw auger displacement pile applications. The paper presents the measured ground heave results of three screw auger displacement piles during a field test in hard clay and correlates the results with the well-established SSPM heave theory.The installation process of driven and screw auger displacement piles is fundamentally different and the paper investigates and discusses whether or not common heave models for driven piles can be applied to screw auger displacement piles where the soil at the auger tip is physically cut, sheared and disturbed by the action of the auger.

Influence of pile installation techniques on ground heave in clays

Piles or deep foundations are elements for transferring the load of structures to the substructure and soil layers with more suitable conditions to guarantee the stability of the structure and provide proper service by them. In this regard, the driven and bored piles are commonly used, but high noise and vibration of the driven piles, as well as difficulties and limitations in implementation of the bored piles, have led to the use of a new alternative type of piles installed in the soil using torque and a small amount of compressive axial force. Helical and drilled displacement piles can be mentioned as new types of these piles. Considering the increasing use of these piles, still a few studies have been conducted on them and there is a need for further research on their behavior in different soils and conditions. Therefore, in the present study, in two field and experimental sections, behavior of these piles was evaluated by performing tensile and compressive loading tests. Three models of helical, Tsubasa, and drilled displacement pile were implemented and loaded in experimental section in the frustum-confining vessel of the Amirkabir University of Technology (FCV-AUT) and were compared with the previous works in field section. Our results revealed that drilled displacement pile had better performance than other piles under tension and compression, and it had harder behavior and better capacity than the other two piles in both experimental and field conditions. Also, the required torque of this pile had higher values ​​compared to other piles.

Experimental and field studies on the behavior of drilled displacement piles

Screw auger displacement piling tools have been successfully used throughout the global piling and ground engineering industry for decades. The technique can be used to install circular concrete elements referred to either as piles, to transfer structural loads into stiffer layers; or as rigid inclusions (known as drilled displacement columns, CSC, CMC, etc.), to reinforce and strengthen unsuitable ground as a soil improvement technique. The effect of installation parameters on screw auger displacement pile performance and load capacity in hard clay formations has not been investigated in detail and is the main scope of this research work. For both applications, it is desirable that the pile or column toes are embedded into a displaceable dense, stiff or hard bearing layer. Loads from the structure are then transferred directly (via piles) or indirectly (by settlement of the soft layer and the resulting negative skin friction along the column shaft) into this bearing layer. As the design methodologies for these applications are different, this research work introduces the latest applications and design philosophies for both screw auger displacement piles and rigid inclusions. As the typical diameters for screw auger displacement piling tools range from 270 mm to 610 mm, the working loads to be transferred are typically limited to 500 kN to 2,500 kN, depending on tool diameter and ground conditions. Both displacement piles and rigid inclusions are economical for use in projects with low to medium structural load-transfer requirements, like warehouses, embankment approaches or tanks. For soil improvement projects, rigid inclusions are usually designed by calculating the settlements of the entire soil block (as reinforced with rigid inclusions), typically using finite element methods. Analytical design methods cannot practically reflect the complex interaction between the stiff concrete columns and the softer surrounding soil; therefore, this interaction needs to be modelled by numerical means. For screw auger displacement piles, the additional load capacity caused by the soil displacement effect around the shaft and the base can be taken into account for the design work if there is sufficient evidence about the degree of the potential improvement. By considering increased skin friction because of soil displacement created during the pile installation process, piles could be designed to be shorter and more economical than would be possible using the traditional approaches used for conventional bored piers without any known improvement effects. The traditional ‘α-cu’ method and the approach for screw auger displacement piles developed by Bustamante and Gianeselli (1998) are introduced and used in this work. To compare the results of the design calculations with real load-settlement data, two different screw auger full-displacement piles (progressive displacement versus rapid displacement tools) and one small diameter Continuous Flight Auger (CFA) pile were installed with 4.0 m penetration into hard clay at a fully monitored field test site at Lawnton, QLD (Australia). The three piles were installed with different tool penetration rates and the pile load capacities (using axial static pile load tests) were compared in relation to installation parameters in similar ground conditions. CPTs were carried out before, during and after the installation process of the three piles to measure and analyse in-situ stresses in the ground. The measurements show that the declining penetration rates of the drill tool (which was the result of the underpowered piling rig installing the three initial test piles) reduces the cone pressure qc around the pile after installation, particularly below pile toe. To verify the finding that tool penetration rates are critical for stress development in the soil formation and to pile load capacity, an additional screw auger full-displacement pile was installed with a more powerful piling rig (140% additional rotational torque and 100% more vertical thrust). This setup was able to maintain a constant penetration rate during the entire installation process. It could be observed that the in-situ stresses after the installation process for this pile were considerably higher (more than 60% on average) compared to for the test piles installed with insufficient installation energy. Moreover, the measured soil-heave volume was reduced by about 50% when penetration rates were held constant during the penetration of the hard clay. Back calculations from the static load tests using Fleming’s method (1992) incorporating the in-situ stress measurements before and after tool installation indicated an up to 25% higher load capacity for the pile installed under the constant penetration rate compared to under declining penetration, using similar auger shapes and diameters in the same soil formation. This research work highlights the importance of utilising sufficiently equipped piling rigs with suggested minimum torque capacities of 250 kNm and vertical pull-down forces of 250 kN for the most effective installation of screw auger full-displacement tools into stiff/ hard clay bearing layers. Additionally, site trials should be carried out prior to the installation of the working piles/columns to proof that penetration rates can be kept constant with smaller piling equipment to achieve the proposed embedment lengths into the base stratum. Screw auger displacement piles installed with minimum constant penetration rates will easily meet and could potentially exceed the design requirements of the α-cu and Bustamante and Gianeselli methods (1998) in stiff/hard clay formations. As insufficiently powerful piling equipment caused load reductions for screw auger displacement piles and columns, the author recommends the introduction of installation factors to reflect the influence of installation parameters on pile/column load capacities.

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Martin Larisch

Papers

Behaviour of stiff, fine-grained soil during the installation of screw auger displacement piles