Monotonic and Cyclic Performance of Spun-Cast Ductile Iron Helical Tapered Piles

The performance of a novel piling system is investigated, which involves a spun-cast ductile iron (SCDI) tapered shaft fitted with a lower helical plate. It combines the efficiency of the tapered section, the competitive cost, effectiveness and durability of spun cast ductile iron with a rough surface and the construction advantages of helical piles. The system is installed using a fast, low vibration and reduced noise process. Seven instrumented piles including five SCDI tapered and two steel straight pipes were installed in sand using mechanical torque. The piles were subjected to cyclic and monotonic compression, uplift and lateral load tests. Different loading sequences were adopted to assess the effect of prior cyclic/monotonic loading on the piles’ performance. The installation torque was monitored and the resulting capacity-to-torque ratio was compared to the literature reported values. The compaction of the previously disturbed sand from the helix penetration due to the pile taper resulted in superior compressive behavior of the proposed system compared to the straight shaft piles. The tapered piles exhibited higher stiffness at lower displacements compared to the straight shafted piles and the helix increased their uplift resistance. In addition, tapered shafts enhanced the lateral stiffness and the helix provided fixation due to the passive bearing pressures on the helix surfaces, which further improved the lateral performance of the short helical piles. A three dimensional finite element model was established and calibrated using the experimental data. The model was then used to simulate the response of SCDI piles with different configurations when subjected to different loading conditions including axial and lateral as well as combined moment-horizontal loads. Under cyclic loading, the tapered helical piles exhibited better compressive performance while the straight shaft helical piles performed better in uplift loading. The proposed system stiffness remained practically unchanged through the cyclic lateral loading applied in the current study. The monotonic performance of the tapered helical piles in clay was numerically simulated. The results showed an increase in axial and lateral capacity and stiffness of the tapered piles over the straight shaft ones, with greater uplift-to-compressive capacity ratio than in sand

Performance of shallow anchor in ice-rich silt

Thesis (M.S.) University of Alaska Fairbanks, 2014Shallow anchor systems have been widely used for decades due to their time and cost efficiency. Yet when it comes to cold regions like Alaska, new challenges caused by the harsh environment need to be resolved before they are used extensively in cold regions. One challenge associated with anchor installation could be the potential thawing of warm permafrost due to the grout mortar hydration, which might undermine the capacity of the anchor. Another challenge is that due to low temperature the grout may cure slower or not cure at all, which will also result in a significant decrease in the ultimate strength of the anchor. Field tests were conducted to evaluate the performance of shallow anchors including duckbill anchors and grouted anchors with three types of different grouting materials, including Microsil Anchor Grout, Bentonite Clay and a newly-developed Antifreeze Grout Mortar. Constant-load creep test and pullout test were conducted to evaluate the performance of the anchors. Test results indicated that the anchors grouted with Antifreeze Grout Mortar caused the least permafrost disturbance and degradation, gained the largest tensile strength, exhibited the least creep displacement, and showed relatively large pullout capacity, and thus achieved the best performance among all types of shallow anchors

Underpinning strategies for buildings with deep foundations

Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2004.Includes bibliographical references (leaf 54).Nowadays, numerous underpinning methods are available to provide safe, fast and practical solutions to nearly any geotechnical problem related to the foundations of a structure. This paper discusses these techniques with an emphasis on grouting and micropiling underpinning systems. Furthermore, some practical case studies such as the current Boston Central Artery Project (Big Dig), where these techniques were adopted, are presented showing the main stages of their construction execution and their main advantages and disadvantages.by Ray Z. Kordahi.M.Eng

Performance of Helical Piles Retrofitted with a Novel Collar Vane Under Lateral and Torsional Loads

Helical piles are lightweight deep foundations designed to support both compressive and uplift loads by mobilizing the shear strength of soil adjacent to helical plates that are welded to an extendable shaft. Helical piles are relatively inexpensive, can be installed quickly utilizing non-specialized equipment, and they are suitable for a wide range of soil conditions. However, helical piles are precluded from many applications due to their inability to support substantial lateral and torsional loads. To overcome this limitation, a novel easy-to-install Collar Vane is implemented to augment the lateral and torsional capacity of helical piles. The Collar Vane consists of four steel fins welded to a hollow steel collar that wraps around the helical pile shaft. The Collar Vane (CV) is structurally coupled to the helical pile via flanges near the helical pile head to transfer lateral and torsional loads through the CV flanges to the soil. Two different Collar Vanes prototypes were manufactured, a `two-piece\u27 Collar Vane (CV2), tested in 2021, and based on the results of this prototype, a `one-piece\u27 Collar Vane (CV1) was manufactured and tested in 2022. Both prototypes were installed and tested in two different well-characterized soil conditions: homogeneous medium-stiff clay soil, and homogeneous dense sand soil. This thesis presents the field results of an instrumented full-scale helical pile with the Collar Vane subjected to monotonic, lateral and torsional loads; and cyclic, lateral and torsional loads. Displacements and loads were monitored using string potentiometers and load cells, respectively. Strain gauges installed to measure deformations facilitated the computation of the bending moment. The cyclic loading procedure consisted of approximately 1000 cycles at 0.125 Hz to evaluate the effect of cyclic loads on the helical pile which is envisioned to be implemented to support lightweight transportation structures. The study revealed that the Collar Vane significantly increases the lateral and torsional geotechnical resistance of helical piles. The increase in capacity is associated with the increment in the effective diameter attributed to the mobilization of geotechnical resistance in the upper soil profile. Moreover, strain gauge data suggest that Collar Vane reduces the amount of bending moment on the helical pile shaft by limiting the lateral displacement, reducing the need for a larger diameter pile shaft and hence, making possible a more efficient pile design. In addition, the measured torsional capacity was compared with predicted values using different well-known methodologies. Additionally, the Collar Vane was subjected to different cyclic loading ratios and it was found that the Collar Vane head stiffness degraded as the number of load cycles increased, the accumulated displacement was significant in the first 100 cycles, and a simple approach was proposed to determine the accumulated displacement in function of the number of cycles. Finally, a numerical analysis is performed using FEM software, to validate field torsional results, and a finite difference program, to compare an standard drilled shaft foundation element to the Collar Vane lateral response. Moreover, an example design of a roadside sign structure is shown to demonstrate the applicability of the Collar Vane

Mechanical Engineering: Prospectus of Courses Session 1937-38

Courses and timetables for the College of Technology, Bolton Street, Dublin 1

Development of icejet-based surface processing technology

The objective of the proposed work is to acquire knowledge needed for the development and deployment of manufacturing processes utilizing the enormous technological potential of water ice. Material removal by blasting with ice media such as particles, pellets and slugs was investigated. The ice media was accelerated by entrainment in a fluid stream (air, steam, liquid water, supercritical C02), impact of rotating blades, fluid expansion, etc. The ice-airjet has to replace sand blasting and the ice-waterjet has to replace the abrasive waterjet. Based on these results, technical approaches for surface processing and machining will be improved. A primary advantage of the ice media is movement toward more complete pollution prevention. With this technique, it is possible to eliminate both contamination of the substrate and generation of contaminated waste streams. In addition to the obvious environmental benefits, use of ice media has improved a number of key operational techniques, such as cleaning, decoating, polishing, deburring, drilling, cutting, etc. Production of ice media just-in-time at minimal environmental cost constitutes another advantage of ice-based technologies. A key objective of this research is to improve ice blasting so that it is not just feasible, but also technologically and economically efficient. An understanding of process physics and its application to the manufacturing operations are necessary in order to attain this objective. The feasibility and effectiveness of other than blasting ice-based technologies, such as precision temperature control, mixing, forming, etc. was also investigated. The principal issue in the use of the ice abrasives is formation of the ice particles. Two technologies of the particles formation were investigated. One of these technologies involves crushing and subsequent grinding of ice blocks. It is applicable at conditions when ice is readily available, for example at Arctic. Another process involved integration of water freezing and decomposition of the generated ice. It was shown that the size distribution of the particles is determined by the rate of the water supply and cooling conditions. The results of the experiments were used to suggest a technology for surface processing using ice powder. A process for formation of the powder of brittle materials was also discussed

NASA Tech Briefs Index, 1976

Abstracts of new technology derived from the research and development activities of the National Aeronautics and Space Administration are presented. Emphasis is placed on information considered likely to be transferrable across industrial, regional, or disciplinary lines. Subject matter covered includes: electronic components and circuits; electronic systems; physical sciences; materials; life sciences; mechanics; machinery; fabrication technology; and mathematics and information sciences

Mechanical Engineering: Prospectus of Courses Session 1934-35

Courses and timetables for the College of Technology, Bolton Street, Dublin 1

Micropitting and related phenomena in case carburised gears

Micropitting is a form of surface contact fatigue encounteredin bearingsa nd gears, under lubricating conditions, which lead to their premature failure. All gears are susceptible to micropitting, including spur, helical and bevel. Micropitting can occur with all heatt reatmentsa ppliedt o gearsa nd with both, synthetica nd mineral lubricants. It can occur after a relatively short period of operation and, after a certain number of cycles,g earsn eedt o be replacedd ue to the increasedn oisea nd vibrations causedb y the deviations of the tooth profile. Continuing operation of affected gears can lead to a catastrophic type of failure (i. e., tooth breakage). These considerations explain the increasing current interest in micropitting. It has been reported that micropitting in bearings is associated with a specific microstructural transformation in steel, i. e. martensite decay. However, to the authoes knowledge, this transformation has not been reported in gears. In the present work, extensive metallurgical investigations have been carried out and they revealed that the same transformation occurs in gears. The aim of this project was to describe the mechanism of micropitting by taking into account the influence of several controlling factors such as, material, surface finish, lubricant, load, temperature,s peeda nd, slide-to-roll ratio. Their influence is assessed with a fractional factorial experimentadl esign.S everaln on-destructivete chniquesh ave been used in order to monitor the specimen condition during and after running, such as X-ray diffraction, optical profilometry, light microscopy. The mechanical properties of the products of martensite decay, known as dark etching regions, white etching bands and butterflies are highly relevant to the fatigue behaviour of the steel. Nanoindentation and AFM techniquesh aveb eenu sedt o determinet hesep roperties. A micropitting mechanism correlated with the mechanism of martensite decay in gears is suggestedb asedo n thesea nalyses.EThOS - Electronic Theses Online ServiceNewcastle University Research Committee : Caterpillar Inc. : Design Unit - Gear Technology CentreGBUnited Kingdo