The behaviour has been examined of piles installed in clay subject to a rapid load testing method known as the Statnamic test. The Statnamic method is easier and quicker to mobilise than a static test and is less complex to analyse than dynamic pile load tests. This investigation consisted of a laboratory study of the effect of the rate of loading on pile behaviour in clay and a field test of a pile in glacial clay to calibrate the findings of the laboratory study. The effects of penetration rate and Statnamic loading on model pile behaviour have been studied using an instrumented clay calibration chamber. The effect of rate of loading on the pile's capacity was quantified using constant rate of penetration tests (CRP) at different pile penetration rates. This allowed viscous soil damping characteristics to be determined and a new Statnamic analysis method incorporating rate dependant soil behaviour to be developed. This rate dependant behaviour can be represented by modification of a non-linear rate law proposed by Randolph & Deeks (1992). A field pile testing facility was developed in glacial till. To test the success of the new Statnamic analysis, a class A prediction of static pile behaviour from prototype pile load testing was undertaken. Encouraging results were obtained for the prediction of ultimate static pile behaviour, but the analysis method under predicted soil-pile stiffness. A soil inertial component was added to the analysis, based upon instrumentation readings, which improved the predicted static soil-pile stiffness. Results from prototype pile testing show that the stiffness during Statnamic and static load tests was very similar up to 50% of the ultimate static pile capacity. Thus, rapid load testing may be used for verification of pile settlements at working loads in clays. At the present level of understanding of testing in clays, rapid load pile tests should not be carried out in isolation. Ideally, tests should be used in conjunction with a static test that will allow back figured parameters to be derived for analysis.

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No description available.

No description available.

No description available.

Soil-pile-structure interaction analysis is the simultaneous consideration of the structural frame, pile foundations, and the soil forming the founding material. Failure to consider soil-pile-structure interaction in design will lead to a poor prediction of load distribution within the structure. A poor prediction of load distribution will cause the structure to deform under loads that have not been calculated for. This may result in the structure cracking or the overstressing of columns. If the actual load distribution significantly differs from that designed for, the factor of safety on structural elements may be substantially decreased. Despite the importance, there are currently no studies quantifying the effect of soil-pile-structure interaction for simple office structures. As a result the effects of soil-pile-structure interaction are often deemed unimportant, and ignored in the design of simple structures. Numerical methods are often relied upon to consider soil-pile-structure interaction for complex structures, such as tall towers. However in their current form they are limited because the meshes required for analysis, especially when in three dimensions, are difficult to verify, and take a long time to set up and run. Therefore this thesis proposes a meshing method within the framework of the finite element method that allows large, complex, and non-symmetrical pile foundation layouts to be meshed in a manner that is quick, can be easily checked, and significantly reduces the analysis run time. Application of the meshing method to an office structure (recently designed for the 2012 Olympic Games) has allowed the effects of soil-pile-structure interaction to be quantified. The subsequent normalisation of the results provides a method for assessing when it is necessary to consider soil- pile-structure interaction in future design. Comparison between the monitored performance of 'The Landmark' (a 330m tower founded on a piled raft) and numerical predictions have demonstrated the importance of correct ground stiffness selection for achieving accurate predictions of piled raft settlement, and load distribution. The role of single pile load tests and in situ testing for ground stiffness selection for piled raft design has also been assessed

Reviewing the development of offshore wind farms, large-diameter monopiles have been widely used as foundations for offshore wind structures. Unlike onshore foundations which are mainly used to transmit vertical load into the ground, offshore foundations are usually subjected to large environmental loads from wind, wave and current which could exceed 30% of their gravity load. In order to improve the lateral resistance of monopiles, a finned pile has been proposed. Empirical and Numerical methods were used to simulate pile head lateral load and displacement (P-Y) curves, and the efficiency of fins under static loading has been estimated. Pile soil response along the pile was predicted based on the distribution of deflection, bending moment, shear force and soil resistance. Three-dimensional charts from FEM analysis represent pile and soil responses especially the soil reaction around the fins. To compare the lateral resistances of a monopile and of finned piles with various fin dimensions, 1 G model tests were carried out. Tests were conducted in a 1 cubic metre steel tank filled with dry dense sand. Based on the results of ultimate lateral loads, fin efficiency under static and repeated loadings was determined. A modified relationship of load deflection behaviour has been suggested. Small-scale lateral cyclic load tests were performed in order to determine the effect of fin length on the lateral displacement of laterally loaded piles. Ten thousand cycles were used in each test to represent twenty years of environmental loading on offshore structures. Variables included the magnitude, frequency and direction ofthe load, the pile tip condition and the fin length. The efficiency of fins was evaluated by measuring the reduction of displacement of the pile head. The relationship between maximum load and displacement established from lateral load-displacement curves demonstrates that fins have significant impact on vertical and horizontal displacements. Piles subjected to combined loads were tested, and the failure envelopes of normalised combined loads represent the lateral resistance increase resulted from the use of finned piles. Under combined cyclic loading with various load features, a finned pile showed better performance in lateral resistance than a monopile. In order to achieve the optimum fin efficiency, the ideal fin width should be equal to half of the pile diameter and the fin length should be equal to half of the pile length. Outcomes from this research provide concepts for laterally loaded piles and useful parameters for the design of finned piles. The device of cyclic loading system and the use of 3D finite element method (FEM) can be applied in the future study of finned piles.

An investigation into the behaviour of pressed-in piles has been conducted. The press-in method of pile installation allows large pre-formed foundation piles to be constructed without the noise and vibration associated with conventional dynamic techniques, and with minimal requirement for temporary works. This investigation is divided into two parts; a fundamental study of the mechanics of press-in pile installation in sand and a sequence of field tests to examine the behaviour of pressed-in piles at full scale. The mechanics of pile installation have been studied using a plane strain calibration chamber. A new system for deformation measurement in plane strain modelling and other forms of geotechnical testing has been developed. This system combines techniques of digital photography, Particle Image Velocimetry (PIV) and close range photogrammetry. A series of validation experiments demonstrated that the system offers greater accuracy and precision than existing measurement techniques. This improved performance is achieved concurrent with an order-of-magnitude increase in the number of measurement points that can be established within the observed soil. A series of 8 calibration chamber tests is reported. The pattern of soil displacement during pile installation was measured. These measurements were of sufficient quality to allow soil strain paths during installation to be calculated. The influence of soil type and initial density was examined, and the post-installation strain distribution was found. The concentration of shear and volumetric strain close to the pile tip was quantified, and a reversal of strain direction as the soil passes around the pile shoulder was observed. A zone of highly compacted soil was observed immediately below the pile tip and along the pile shaft. Contraction of this sleeve of broken soil grains was observed with continued penetration of the pile. A mechanism is proposed to link this kinematic observation to the distribution of shaft friction close to the tip of displacement piles. A further mechanism is proposed to predict the distribution of external shaft friction along the upper part of a pile shaft. This mechanism is based on vertical arching theory, and is an extension of a previous approach for the prediction of internal shaft friction. Four series of field tests using pressed-in piles were conducted. The first series demonstrated that internal shaft friction is well predicted by vertical arching theory. Since vertical arching evolves according to an exponential function, pile performance can be dramatically influenced by only small changes to the governing parameters. The improvement of driveability using an internal driving shoe was investigated. The final series of load tests demonstrated a novel foundation solution in which the high shaft friction created by vertical arching can be ‘switched on’ after installation. This is achieved using a construction sequence involving H-section piles. During press-in installation of each pile, the geometry does not create vertical arching. During loading of the entire structure, arching occurs. This leads to a high positive group effect, and an efficient foundation structure.

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Groups of piles are commonly used as high capacity foundations. It is recognised that the load distribution among piles in a group will vary and it is thought that the inner piles are likely to make a relatively small contribution to the total load carried. The essence of the research undertaken is to establish the relative effectiveness of pile groups with either no inner piles (perimeter group) or a single central pile (target group) when compared to the more commonly used grid group arrangement. Pile groups in which the central piles were omitted were used for the Cannon Place redevelopment in london and provided the impetus for the research project. The main research technique used is geotechnical centrifuge modelling. Samples of overconsolidated kaolin clay were prepared and tested on the centrifuge at City University london. This provided a firm clay into which pile groups could be installed in a wide variety of arrangements. Three or four different pile groups were located in each centrifuge model and loaded to failure using a strain-rate controlled load actuator. The individual model piles were made of 5 mm diameter aluminium rod placed in holes pre-drilled in the consolidated kaolin prior to the centrifuge test. All piles extended to a depth 250 mm in the clay giving an lId ratio of 50. The ranges of pile groups tested are linear, circular and square perimeter, circular and square target and square grid. Single pile tests provided the reference pile capacities used to normalise the data from the 23 centrifuge models tested. The experimental work was complemented by a parametric numerical modelling study using the finite element programme Abaqus. This gave insight into the pile-soil interaction and permitted a more meticulous analysis of the soil stresses and displacements. In addition, the numerical modelling enabled extension to the original variables tested as part of the centrifuge experiments and the soil shear strength and lId ratio were varied. The pile groups failed in one of two ways: either as individual piles with the piles settling into the ground with no noticeable settlement of the soil surrounding a pile, or as a block with the soil contained within the outer ring of piles settling by the same or xxiv similar amount as the piles. The change from block failure to individual pile failure often occurred at a pile centre-to-centre spacing of about two pile diameters though variables such as number of piles, the presence of a target pile and the strength of the soil all had an effect. The efficiency of a pile group is defined as the load capacity of a pile group expressed as a ratio of the number of the piles in the group multiplied by the load capacity of a single isolated pile. It was demonstrated that a grid group arrangement was the least efficient of the groups tested, whereas a perimeter group arrangement could achieve higher efficiencies of greater than unity and the inclusion of a target pile could further enhance the group efficiency. It has been shown that a target group comprised of 17 piles (16 piles plus one central pile) has a significantly higher efficiency than a 5x5 grid group comprised of 25 piles, such that the capacity at lower settlements is the same for both groups.