The Effect of Mechanical Remoulding on the compression and strength characteristics of a Mercia Mudstone

A series of laboratory tests have been undertaken as part of a larger study into the effect of continuous flight auger pile installation on the soil-pile interface in the Mercia Mudstone Group [1]. This paper reports the results of stress path triaxial tests on bulk samples of the mudstone which have been subjected to varying amounts of mechanical remoulding representing the remoulding that occurs due to the action of the auger. In addition, the water content at which remoulding takes place has been varied. The tests were undertaken to investigate whether the silt sized aggregates of clay particles that exist [2] within this soil could be broken up by the mechanical remoulding and whether this would affect the compression and strength properties of the mudstone. It was found that both mechanical remoulding and the water content at which this is carried out affect the subsequent response of the soil

Estudo de caso: edificação com fundações em estacas hélice contínua monitorada

It was analyzed a geotechnical design with continuous flight auger pile foundations in a venture with four buildings, located in Manaus (Amazonas State). The used criteria for the location of the boreholes, the grain size, and the structure (consistence and compactness) of the subsoil layers were studied. It was also verified the amount and the length of the piles, as well as the results of pile load tests.Keywords: foundations, flight auger pile, pile load tests.Analisou-se um projeto geotécnico de fundações, em estaca hélice contínua monitorada, de um empreendimento com quatro edificações, situado em Manaus (AM). Examinaram-se os critérios utilizados na locação dos furos de sondagem, realizou-se a análise granulométrica e se verificou a estrutura (consistência ou compacidade) das camadas formadoras do subsolo. Aferiu-se, ainda, a quantidade e o comprimento das estacas, bem como os resultados das provas de carga.Palavras-chave: fundações, estaca hélice, provas de carga

The Effect of Continuous Flight Auger Pile Installation on the Soil-Pile Interface in the Mercia Mudstone Group

The research reported in this dissertation examines the physical and chemical changes that occur to in situ soil at the soil-pile interface for continuous flight auger piles installed in the Mercia Mudstone Group. Four Continuous Flight Auger (CFA) piles were installed in the Gunthorpe Member of the Mercia Mudstone Group, central England. The effect on the soil-pile interface of overrotation of the auger during installation, and the addition of water during installation were investigated. Once the piles had been left to cure, they were excavated and returned to City University, London, with the surrounding soil. The excavated piles and soil were examined using a variety of microscopic and macroscopic techniques including inductively coupled plasma spectroscopy (ICP) and X-ray diffraction (XRD); with water contents, chemical content (ICP) and mineralogical content (XRD) tested. Plastic index and particle size distribution tests were used to show the physical effects of piling on the host soil and preliminary strength testing was carried out to provide insight into the strength characteristics of the soil surrounding the pile. In all four piles a distinct zone of remoulding was observed around the pile shaft. In each case the remoulded zone was a brown to red, clay rich layer varying between 0mm and 55mm in thickness. In almost all cases this remoulded zone had a structure and fabric which was not related to the in situ soil. Around all piles it was further noted that vertical fissures were present, and fanned out from the pile shaft in a clockwise direction. Two of the piles were installed with the addition of water. Around these piles it was noted that the remoulded layer often split into two or three distinct layers, with one of these layers often containing millimetre scale aggregations of green silt. Tests showed a higher percentage of clays present within this remoulded zone, and indicated that SiO2 (a major rock forming element and considered by some authors to be an aggregating agent within the Mercia Mudstone Group) was more abundant within remoulded than undisturbed soil. The clay fraction showed a low abundance of high swelling clays in all cases. It was concluded that installing piles within the Mercia Mudstone Group causes remoulding of the soil directly adjacent to the pile shaft. The least remoulding occurred when the pile was augered normally with no added water. All four remoulded zones contained fissures, fanning clockwise from the pile, however, these were more pronounced in the dry piles, while the wet piles had a more massive, granular texture to the remoulded zone. For all piles, except the pile which was over-rotated and installed with no added water, the percentage of clays within the remoulded zone was greater than outside the remoulded zone. This indicates that the aggregates of clays found naturally within the Mercia Mudstone Group may be split into their constituent clays during the piling process

Remoulding of the Mercia Mudstone Group around CFA pile shafts

A field test has been undertaken to investigate changes to in situ Mercia Mudstone at the pile soil interface after installation of four 5.5 m long 350 mm diameter CFA piles. The test investigated whether a remoulded zone exists, the extent of the zone, changes caused by remoulding and the effect of the installation method. The piles and surrounding soil were excavated after installation to a depth of just under 2 m. The sections of pile and surrounding soil were returned to the laboratory where a variety of detailed observations at both micro and macroscopic scales were undertaken, together with chemical and mineralogical analysis. It was found that a remoulded zone existed in all piles but that this varied in thickness both laterally and vertically around a pile. Across all piles the maximum thickness observed was 55 mm. The average thickness, fabric and texture were all affected by installation method. A distinctive vertically orientated fabric was observed in which up to four vertically orientated layers could be distinguished. There was evidence of changes in texture/fabric, structure, colour, mineralogy and chemistry

Test development for the investigation of soil disaggregation during slurry tunnelling

Slurry tunnelling uses a water based slurry to aid in tunnel face support and transportation of the excavated material. Unlike other tunnelling methods this requires expensive surface separation plant to remove the excavated ground from the slurry. Incorrect specification of this plant can lead to significant delays and added cost to a tunnel drive. Due to the tight budgets and space constraints this can cause contracts to become unprofitable, in particular where small diameter slurry tunnels are excavated by pipe jacking. For this reason accurate prediction of the size distribution of the soil particles and lumps in the disaggregating slurry is required. This research concerns the development of test procedures and methods of soil classification that will enable improved predictions of the degree to which soils/weak rocks will disaggregate during the slurry tunnelling process

Principles of Foundation Engineering

A must-have resource for all foundation engineering courses, Principles of Foundation Engineering, 9th Edition provides a careful balance between current research and practical field applications as it introduces civil engineering students to the core concepts and applications of foundation analysis design. Throughout this best-selling book, Dr. Das and Dr. Sivakugan emphasize how to develop the critical judgment civil engineers need to properly apply theories and analysis to the evaluation of soils and foundation design. This new edition includes three new chapters that highlight developing topics. This edition also provides a wealth of worked-out examples and multiple new figures that emphasize the skills most critical for students to master as successful civil engineers

Distributed fiber optic monitoring of a CFA pile with a central reinforcement bar bundle

Abstract: In this paper, we present an application of distributed fiber optic sensor (DFOS) technology to measure the strain of a continuous flight auger (CFA) test pile with a central reinforcement bar bundle, during a static load test carried out in London. Being distributed in nature, DFOS gives much more information about the pile performance as compared to traditional point sensors, such as identifying cross-sectional irregularities or other anomalies. The strain profiles recorded along the depth of the piles from the DFOS were used to calculate pile deformation (contraction), shaft friction, and tip resistance under various loads. Based on this pile load test, a finite element (FE) analysis was performed using a one-dimensional nonlinear load-transfer model. Calibrated by the shaft friction and tip resistance derived from the monitored data, the FE model was able to simulate the pile and soil performance during the load testing with good accuracy. The effect of the reinforcement cage and central reinforcement bar bundle were investigated, and it was found that the addition of a reinforcement cage would reduce the pile settlement by up to 20%

Estudo de caso comparativo de projeto de fundação por estaca pré-moldada e hélice contínua

TCC (graduação) - Universidade Federal de Santa Catarina. Centro Tecnológico. Engenharia Civil.A busca por construções mais arrojadas, assim como a maior concentração de edificações devido ao crescimento urbano, exigiu inovações nos métodos construtivos de fundações. Uma das principais fundações que surgiu nesse período foi a estaca hélice contínua monitorada (EHC), por ser de rápida execução e causar poucos danos às edificações vizinhas. O presente trabalho tem como foco realizar a comparação dessa fundação mais moderna com a estaca pré-moldada de concreto, considerada mais antiga e clássica, para entender as diferenças em todas as etapas de estudo. A comparação foi feita por meio do dimensionamento de um estudo de caso. O estudo comparativo teve início nos processos executivos e suas limitações, partindo para o dimensionamento da capacidade de carga, carga admissível, carga de catálogo e, finalmente, o recalque. Para alcançar esses resultados, foi utilizado dados obtidos das investigações geotécnicas, da superestrutura da edificação e demais informações relevantes. Utilizou-se diversos métodos renomados e bibliografias de diferentes autores para atingir respostas com grau de confiabilidade adequado e de acordo com o que realmente é visto e empregado na prática.The search for bolder constructions, as well as the more concentration of buildings because of the urban growing, demanded innovations on the constructive methods of foundations. One of the main foundations that emerged in this period was the Continuous Flight Auger Pile (CFA), because of its fast execution and for causing minor damage to the buildings around. This thesis focuses on comparing this more modern foundation with the precast pile, considered more antique and classic, to understand the differences between them in all of the stages of study. The comparison was made through the design of a case study. The comparative study began with the executive processes and its limitations, and then continued with obtaining the load capacity, the yield stress, catalog stress and finally, the settlement. Data from geotechnical research, from the building’s superstructure and more relevant information were used to reach these results. Plenty of renowned methods and bibliography from many authors were very important to achieve the answers with adequate degree of reliability and according to what really is seen and put into practice

Comparative Investigation of Bored and Continuous Flight Auger Piles with Consideration of Green Concrete

Bored and continuous flight auger (CFA) piles are two widely used cast in place reinforced concrete pile types that are constructed employing different techniques, which affect their performance and capacity. However, both are classified as non-displacement piles and are designed accordingly using the same method. Therefore, the objective of this work is to comparatively investigate the axial and lateral performance of bored and CFA piles installed in sand. In addition, the potential of constructing sustainable piles utilizing green concrete mixture that incorporates treated oil sand waste (TOSW) was investigated. Fresh and hardened properties along with durability performance of CFA concrete mixtures incorporating 10%, 20%, 30% and 40% TOSW as partial replacement of sand were investigated. Six piles with the same nominal geometry were constructed using conventional and green concrete mixtures. The piles were subjected to axial monotonic compressive and uplift loading as well as monotonic and cyclic lateral loading. The test piles were exhumed after testing to investigate their dimensions and profile, surface roughness, and interface friction between soil and pile. The soil-pile interface conditions of bored and CFA piles were quantitatively characterized using fractal dimension to measure surface roughness. Finally, three-dimensional non-linear finite element models were developed utilizing Plaxis 3D software to simulate the behaviour of the bored and CFA piles under monotonic compression, uplift, and lateral loading. A parametric study was carried out to investigate the effect of the angle of internal friction and the pile diameter on its behaviour and capacity under different loading cases. The results showed that the addition of TOSW, up to 30% replacement of sand, did not adversely affect the performance of CFA concrete mixtures. CFA piles had higher compressive, pullout, and lateral ii capacity compared to bored piles. This was attributed to the increase in diameter of the CFA piles compared to the bored piles owing to the high pressure used for placing the concrete in CFA construction, which led to higher lateral soil confinement. It was also found that piles constructed employing concrete mixture incorporating TOSW had the same geotechnical performance as those constructed utilizing conventional concrete mixture. Finally, the numerical analysis demonstrated that the effects of construction technique should be accounted for in order to properly simulate the CFA pile behaviour