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By Monica R. Garcia, Antonio Alberto S. Correia, Paulo J. Venda Oliveira

"The aim of this paper is to analyze the creep behavior of a Portuguese soft soil stabilized with binders in one-dimensional conditions, based on oedometer creep tests. The study focuses on the analysis of the effect of the binder content and binder type on the creep behavior of a stabilized soil. The results show that the best binder type for this soil, in terms of creep behavior, is composed of Portland cement and fly ash with a dry weight proportion of 75/25, as this promotes the development of secondary pozzolanic reactions. The results also show the decrease in the secondary compression index with the increment of the binder content, since it promotes an increase in the cementation bonds between soil particles. The general analysis of the results shows a clear dependence on C??and qu, until values of qu of 1500 kPa; after that this relationship is negligible.INTRODUCTIONThe geotechnical structures (such as embankments, dams and buildings) built on organic soils exhibit notable creep deformations, which increase the maintenance and exploitation costs and can even compromise their functioning. To attenuate the creep effects of the soft ground, some improvement techniques are frequently used, such as preloading or reinforcing the soil foundations with vertical rigid inclusions, like concrete piles, stone columns or deep mixing columns (DMCs). However, the installation of DMCs in the soft ground induces (via the arching effect) a transfer of stresses from the soft soil to the DMCs, which causes an increase in the creep settlement on the DMCs (Venda Oliveira et al. 2011).Notwithstanding the fact that the creep behavior of clays has been the object of several studies (Leroueil et al. 1985; Mesri and Castro 1987; among others), the study of the creep behavior of soil-binder admixtures has been practically ignored by the scientific community. The few studies on this theme have revealed that a stabilized soil’s creep behavior is dependent on: the type of binder (Venda Oliveira et al. 2013), the binder content (Correia 2011; Bobet et al. 2011; and Venda Oliveira et al. 2013), the stress level applied during the creep phase (Venda Oliveira et al. 2013), the organic matter content of the natural soil (Venda Oliveira et al. 2012; 2014), and the curing conditions (humidity, vertical stress applied during curing, and curing time) (Correia 2011; Venda Oliveira et al. 2012).The aim of this paper is to contribute to a better understanding of the creep behavior of a soil-binder admixture, by examining the results of oedometer creep tests. The study focuses on the analysis of the effect of the binder content and binder type on the creep behavior of a stabilized soil. Additionally, the creep behavior is correlated with the effective vertical yield stress and the unconfined compressive strength (UCS)."

Jan 1, 2015

By Racquel Nottingham, Marc Mastrantuono, Freddy Lopez

In the digital era that we live in, connectivity and mobility play a decisive role in our daily activities. In this context, insufficient telecommunication infrastructure gives origin to the so called “dead zones” (areas with poor or non-existing cell phone reception), which hinder economic development in small communities and in many rural areas, since they remain invisible to a larger marketplace due to the inadequate cellular coverage. Several countries are working to identify these dead zones and with this information, establish strategies together with mobile providers in order to improve the existing mobile networks by expanding the coverage areas. As a result of the analysis, it is expected that thousands of telecommunication towers for 4G and 5G networks will be erected in the coming years. Telecommunication towers are slender elements that require large shallow foundations to verify primarily the safety against overturning. However in remote areas, it can be advisable to consider alternatives to the conventional shallow foundations, in order to optimize the use of materials (concrete, reinforcement steel, etc.). The following article presents an overview of intervention projects, where telecommunication towers were founded on micropiles. The micropiled foundations allowed to reduce considerably the dimensions of the originally planned shallow foundations. Furthermore, the use of micropiles allows for additional optimization, in combination with pre-fabricated foundations (i.e., precast concrete elements, etc.). This paper will focus mainly on the design and the execution of the micropiled foundation.

Sep 8, 2021

By P. Seethalakshmi, Yatakuri Yaswanth Naidu

The use of a single pile, group of piles with pile cap, piled raft foundation system, etc., are prevalent in transferring the superstructure load from the soft soil layers to the firm underground layers to reduce the settlement and improve the bearing capacity. The recent development of disconnected piled raft foundation has gained greater importance in improving the load transfer mechanism among the pile, raft, and subsoil by reducing the vulnerability of the greatest axial force on the pile head which leads to pile failure. The present study aims at analyzing the performance of unreinforced and Geogrid reinforced disconnected piled raft foundations under vertical loading using the commercially available finite element software PLAXIS-3D. A parametric study was conducted on unreinforced and reinforced disconnected piled raft foundations to explore the effect of varying pile stiffness as well as the inclusion of Geogrid layer on the load vs settlement, the load sharing ratio of piles and raft, and the distribution of axial load and bending moment along the length of the pile. The Mohr-Coulomb model was used for the granular cushion layer while the Modified Cam Clay model was used for soft clay underlain the sand layer. Raft and piles were assumed to be rigid and linear elastic. The results showed that axial force taken by piles with higher stiffness was maximum while settlement at the bottom tip of the pile with higher stiffness was maximum in both reinforced as well as unreinforced disconnected piled raft systems.

Sep 1, 2022

By Rangaswamy. K, Naga Sivaji

A stone column is one of the most commonly employed methods of ground improvement techniques. This method used to increase the strength, decrease the compressibility of loose granular and finegrained soils. Also, it accelerates the consolidation in clays and reduces the liquefaction potential of sands and silt soils. In general, the stone column contains 15 to 75mm stone aggregates. In reality, it is not easy to avail the natural stone aggregates due to unavailability in locally nearby places. Present work aims to replace the stones partially or entirely by scrap tyre chips as an alternative material. The utilisation of recycled tyre chips in ground improvement is an environmentally friendly solution and avoid the disposal of tyre chip waste in large pits. Model tests conducted on marine clay with encased end bearing stone columns (ESC) constructed with a mixture of stone aggregate and tyre chips with sizes 4.75 to 10mm. The column diameter is 75 mm, L/d ratio maintained to 5.3. Non-woven geotextile wrapped encased stone column has introduced in the soft marine clay model. Encasement prevents the lateral squeezing of aggregates into the surrounding clay and protects the drainage function of the stone column. A set of load-settlement tests were conducted on both the clay model and clay model treated with the stones-tyre chips column. The model was loaded by the tri-axial loading frame. Shear strength parameters of stones and tyre chips were determined by large size direct shear tests. Model test results are concluding that the load-carrying capacity of the clay is improved significantly after installing the stone column in it. The encasement increases the load-carrying capacity and stiffness of the ordinary stone column. It is also proved that the stone aggregate could be replaced partially by tyre chips up to 60% without a significant reduction in its performance.

Nov 1, 2022

By Brain E. Ladd

A load test program was performed on two auger cast piles constructed in the Inner Coastal Plain geology of North Carolina. Both test piles were installed through Coastal Plain deposits and into underlying Piedmont residual soils; one test pile was embedded into partially weathered rock (PWR). The recommended 100-ton design load was confirmed by a test program that included instrumenting the piles with strain gages. The two piles performed differently during the load tests due to the effect of embedment into PWR. Loading Test Pile No. 1, which was not embedded into PWR, to failure at about 230% of the design compressive load allowed for evaluation of the mobilization of the ultimate shaft and end bearing resistances. Mobilization pile resistance was evaluated by comparing shaft and end bearing resistances to top of pile deflection (?) normalized by the pile diameter (D). For Test Pile No. 1, the ultimate average shaft resistance was achieved at ?/D of about 7.5% and ultimate end bearing resistance at ?/D of about 9.5%. Test Pile No. 2, embedded into PWR, achieved a ?/D of only about 4% at 200% of the design load and was not loaded to failure. Shaft resistance was mobilized at a different rate within each individual geologic layer, i.e. ultimate shaft resistance did not occur simultaneously for all geologic layers. As the available total shaft resistance was exceeded and end bearing mobilized, the unit shaft resistances reduced from the peak values. A modified Davisson offset using ?/D of about 6.5% appears applicable for evaluating the ultimate capacity of auger cast piles in the Inner Coastal Plain.

By Achyut Kumar Allady, Praveen Arumughan

NCHRP Synthesis 418 (2011) entitled, “Developing Production Pile Driving Criteria from Test Pile Data” details the occurrence of dichotomy between pile Skin resistance and pile Tip resistance mobilizations at different times for different hammer blows during pile driving operations. With increasing usage of High Strain Dynamic Testing (HSDT) the engineering community started paying more attention to this occurrence of dichotomy resulting in overdriving, pile damage, increased claims, and loss of time. To overcome the dichotomy limitations of HSDT, NCHRP recommends, “the use of superposition to combine the back-calculated tip resistance from a blow on initial drive or from redrive with the back-calculated skin resistance from the early blows at the beginning of restrike”. However, the current practice of external mounted gauges and signal matching for a single blow are unable to evaluate independently the Skin resistance and Tip resistance to achieve the goal of determining the optimum Total Pile Capacity using the superposition. This paper discusses advancements of science and technology with sensors embedded at the pile top and pile tip, the data collected is analyzed by the state-of-the-art FDOT Method to determine Skin and Tip resistances independently for every blow. Independent Tip and Skin resistances each with a Resistance Factor can be summed up to obtain optimum Total Pile Capacity. Additional benefits of determining independent Skin and Tip resistances include obtaining lost skin capacity due to scour, due to pre-drilling/preforming and uplift tension capacity. Furthermore, the benefits of embedded sensors include increased quality control/quality assurance through 100% testing, accelerated construction, life cycle monitoring and asset management.

May 1, 2022

By Brian E. Ladd

"A load test program was performed on two auger cast piles constructed in the Inner Coastal Plain geology of North Carolina. Both test piles were installed through Coastal Plain deposits and into underlying Piedmont residual soils; one test pile was embedded into partially weathered rock (PWR). The recommended 100-ton design load was confirmed by a test program that included instrumenting the piles with strain gages. The two piles performed differently during the load tests due to the effect of embedment into PWR. Loading Test Pile No. 1, which was not embedded into PWR, to failure at about 230% of the design compressive load allowed for evaluation of the mobilization of the ultimate shaft and end bearing resistances. Mobilization pile resistance was evaluated by comparing shaft and end bearing resistances to top of pile deflection (d) normalized by the pile diameter (D). For Test Pile No. 1, the ultimate average shaft resistance was achieved at d /D of about 7.5% and ultimate end bearing resistance at d /D of about 9.5%. Test Pile No. 2, embedded into PWR, achieved a d /D of only about 4% at 200% of the design load and was not loaded to failure. Shaft resistance was mobilized at a different rate within each individual geologic layer, i.e. ultimate shaft resistance did not occur simultaneously for all geologic layers. As the available total shaft resistance was exceeded and end bearing mobilized, the unit shaft resistances reduced from the peak values. A modified Davisson offset using d /D of about 6.5% appears applicable for evaluating the ultimate capacity of auger cast piles in the Inner Coastal Plain.INTRODUCTIONAuger-cast-in-place (ACIP) piling was developed in the 1940’s and patented in 1956 (Neely, 1991). Since patent expiration in 1973, ACIP piles are abundantly used in the United States, particularly in the southeast. However, most literature addresses driven piles constructed in sand and clay with lesser discussion of drilled piles. Conventional design methodologies (a- method, ß-method, SPT or CPT correlations, etc.) are based on data derived from numerous projects in a great variety of geologies. O’Neil (2001) notes that there are significant levels of uncertainty in the “universal” databases as evidenced by coefficients of variation of 0.35 to 0.40 for geotechnical parameters (su, SPT-Nvalue, etc.) used to estimate pile capacities.There is a need to develop local databases developed from data obtained from load tests that measure shaft resistance and end bearing. This paper presents the results of load tests conducted on axially loaded auger-cast-in-place piles constructed in the Inner Coastal Plain geology of North Carolina. Shaft resistance, end bearing, and movements that initiated mobilization of these resistances are described. The information presented herein can be used to refine geotechnical correlations and parameters applied in auger cast pile design methodologies."

Jan 1, 2017

By Ross Cutts

As a public servant geotechnical engineer, I observed how costly and valuable geotechnical field explorations are to the success of every project. Often however, the field exploration is a long and complex process that is made less efficient by the difficulty of retrieving and utilizing nearby internal or external historic geotechnical datasets. As an employee of a public agency, we would often start our investigations for every project from scratch, given the difficulty of locating and utilizing historic geotechnical data. This is an ethical and technical failing of our profession. When we start subsurface explorations from scratch, not only do we often duplicate investigations, we are also likely defaulting to reapplying tradi- tional test methods that yield con- servative geotechnical parameters, resulting in overly conservative and potentially costly construction. To address this issue while working as a public servant, I started a research program with Yunfeng Zhang, Ph.D., of the University of Maryland, to build a tool that could compile internal historic geotechnical data and extract additional value from it, using machine learning. This tool was able to provide, upon request, nearby historic geotechnical data, estimated soil parameters and recommendations for geotechnical test methods best suited for a given project site. This prevented common field ex- ploration problems such as, requesting duplicate data, requesting test methods that were not applicable for the project geology, not realizing presence of karsts, missing permits for wetlands, private property and others. This tool allowed for more efficient field investigations with regards to time and money saved. There was one problem with this tool: it could only be used by internal employees of a single state's depart- ment of transportation (DOT) for which this data was compiled. I realized at that point that it would be of tremendous value to make this concept universally accessible to the geotechnical engi- neering profession. I left public service to devote time to building a platform that would host historic geotechnical data from publicly funded sources throughout the country. The tool I helped build as a public servant was the foundation of Geosetta, a nonprofit company dedicated to serving the geotechnical profession. The nonprofit structure was adopted to prevent acquisition by a for-profit company and to ensure that Geosetta remains an independent steward of our profession's valuable data. Geosetta provides a GIS (geographic information system) platform that enables users to view historic geo- technical data and extract value from it with machine learning-based predictions and visualization tools. This data is provided in an open and interchangeable format called DIGGS, which stands for Data Interchange for Geotechnical and Geoenvironmental Specialists, making it easy for users to integrate it into their workflows. Geosetta is collaborating with the American Society of Civil Engineers' Geo-Institute and other sponsors to extract public data at no cost to the agency and provide the profession with free access to the existing data and access to advanced tools through a subscription to support the nonprofit mission.

Nov 1, 2023

By Dinesh R. Katti

Caissons which are locally known as well foundations, which may very in diameter from 30 m to more than 30 m and in majority of the cases having depth to diameter ratio between 1 to 1.5, are normally used to support piers of long span bridges or tall structures, which transmit high magnitude of axial load, horizontal thrust and moment. On the basis of depth to diameter ratio the foundation system appears to fall in the category of shallow foundations but due to deep excavation, it is observed that part of the moment acting on the caisson is shared by due the sides due to development of passive resistance. The problem is statically indeterminate and three dimensional in nature. To ascertain the various parameters needed for design, such as moment shared by base and sides, horizontal and vertical displacement and tilt, and base and side contact pressure diagrams need to be obtained from nondimensional relations of parameters with respect to D/B ratio derived from large scale model studies conducted by Katti etal at IIT, Bombay under MOT Project between 1976 and 1988 and later on at UNEECS. On the basis of above data on attempt is made to put forward guide lines for selection of parameters for design of caisson foundations / well for following cases for opening us some discussion. The cases are cohesive soil at the side and cohesive soil, or sand or soft rock or hard rock at the base.

Jan 1, 1996

By Mohamed Hassan, Matthias Seip, Steffen Leppla

In the east of Frankfurt am Main, Germany, a new high-rise building is planned directly next to the river Main. The high-rise building will have a height of about 75 m and will be founded on a Combined Pile-Raft Foundation (CPRF) in the tertiary marl. The new structure will be constructed next to important, sensitive traffic infrastructure. The foundation of the new high-rise building adjoins directly existing historic quay structures, which are more than 100 years old. For analysis of the stability and the serviceability of the heavily eccentric loaded foundation of the new high-rise building and the existing structures and for the investigation of the soil-structure interaction complex three dimensional, non-linear numerical simulations have been carried out. These numerical simulations take into account all geometric and material specific boundary conditions, including the history of the construction of the whole area. The paper introduces into a very complex construction project in which the investigation of the soil-structure interaction has an important role. The three-dimensional numerical simulations are explained and the results are shown.

May 1, 2022

By Matthew C. Janes, Mark C. Spence

"A former coal gasification site next to Rock Bay in Victoria, BC, Canada required a barrier to permit dewatering and excavation of the bay and surrounding property. The adjacent property owners had stringent requirements at the boundaries of their properties. Isherwood Geostructural Engineers designed a temporary steel sheet pile (SSP) water retention structure and excavation shoring system along the perimeter of the site. The project involved challenging geotechnical conditions in soft clay soils and a multi-faceted construction staging plan involving the diversion of two large storm water outfalls that drained into the bay. Despite a well-conceived design and construction plan, unexpected site conditions and delays led to significant changes in design and construction approach. Employment of the Observational Method and on-the-fly geotechnical investigation were instrumental in maintaining project momentum and schedule. The paper presents the geotechnical and geostructural design details and construction events as they transpired, highlighting the key issues, discussions and lessons learned.INTRODUCTIONFor over 100 years, the Rock Bay Site, in Victoria, British Columbia, Canada, had a legacy of contamination left behind from previous industrial activities. The site was the former location of a coal gasification plant that was in operation from 1862 to 1952. The site was also an infilling location for a nearby tannery and sawmill. The remediation of the Rock Bay Site involved the excavation and replacement of approximately 300,000 tonnes of contaminated soils on Transport Canada’s property. The project commenced in 2004 and has occurred over several phases on multiple properties. In the third and final phase of the project, a temporary steel sheet pile (SSP) excavation shoring system and ocean barrier wall – required to seal off the bay – was employed to enable disposal and replacement of approximately 90,000 tonnes of contaminated soils from the shoreline and base of the bay."

Jan 1, 2016

By Stefan Dahlin

The laboratory tests indicated low permeability but as I said, as a rule, the permeability in the field has been found to be higher. A high permeability has also been found when doing back calculations of rates of settlements in different cases. But as I also said, there's a need for further studies in this area.

Feb 10, 2003

By Peter Cali

There is one organization in Sweden, The Swedish Deep Stabilization Research Centre, which has been working with these questions and there is also a project, Eurosoilstab, within European Union to take a manual for deep stabilization.

Feb 10, 2003

By Michael Cianchetti, Nadir Ansari, Matthew Janes

"PROJECT DESCRIPTIONThe R C Harris Filtration Plant underwent an expansion to install an underground sludge treatment capability consisting of a series of underground tanks within stepped excavations 12m (39 ft) and 10m (33 ft) deep into compact, wet sands over stiff clays and clayey silts.Concerns regarding the original structure influenced designers to set the lateral deflection limit for the proximal front footing at 4mm (1/6 in), (0.03% excavation depth). The design-build team indicated at the time of tender that the movement criteria was unattainable using the tender design. Through extensive Fast Lagrangian Analysis on Continua (FLAC) and a novel construction geometry the design-build team crafted an alternative that produced significant savings over the original concept and met deflection concerns.GEOTECHNIQUEThe hillside site drops 14.5m (47.6 ft) over a distance of 53m (174 ft) between the existing Filter Building on the north and the Services Building on the south. The soils adjacent to the Filter Building consist of 6m (20 ft) of sandy fills, to the footing elevation, over compact sands and layered dense sands and silts to a depth of 10m (33 ft) below existing footing. Beneath the silts lies a 10m (33 ft) thick stiff clayey silt, 2m (6.6 ft) of sandy silt till (containing cobbles and boulders) and an artesian gravelly sand at a total depth of 30m (98.5 ft).The tender information was deemed inadequate to accurately determine soil parameters for a finite element analysis. As a result, the design-build team performed pre-tender Cone Penetrometer Testing (CPT), including dynamic analysis. The CPT data indicated stratigraphy consistent with the conventional bore hole exploration (SPT results) however, the CPT data provided consistently superior soil strengths. The CPT data indicated the sands and silts were dense to very dense throughout their full thickness. The clayey silts below the sands were found to have shear strengths in the 100 to 200 kPa (14.5 to 29 psi) range with an Over-Consolidation Ratio (OCR) ratio of 1.5 to 2. The dynamic analysis, while low strain, indicated very competent behavior with Young’s Modulus values in the 200 to 350 MPa (29,000 psi to 51,000 psi) range. The CPT derived shear moduli and OCR values were vital in determining the soil engineering parameters used for the FLAC analyses."

Jan 1, 2007

By Juhyung Lee

Numerical analyses were performed to analyze the behavior of two different type of suction piles (mono type and group type) under various soil layer conditions (uniform silty clay layer, uniform silty sand layer, and two-layer deposit consisting of clay and sand layers) and lateral loading locations (top, middle, and bottom of the suction pile). According to the results, mono suction pile shows maximum resistance when load is applied on its middle, regardless of the soil layer conditions, while group suction piles varies significantly according to the allowance on head rotation. When head rotation is allowed, the behavior of group type piles become similar to the behavior of mono suction pile. Whereas, when rotation is prevented, resistance is maximized when load is applied on the top head. Moreover, group suction piles show higher efficiency regardless of the ground condition and geological stratum. For further advances, concrete block on the top of group suction piles are suggested as an effective alternative method to prevent partial rotation and maximize ground resistance for group suction piles.

By Ilhan Chang, Ernest Nsabimana, Kiseok Kwak, Juhyung Lee, Young-Hoon Jung

"Numerical analyses were performed to analyze the behavior of two different type of suction piles (mono type and group type) under various soil layer conditions (uniform silty clay layer, uniform silty sand layer, and two-layer deposit consisting of clay and sand layers) and lateral loading locations (top, middle, and bottom of the suction pile). According to the results, mono suction pile shows maximum resistance when load is applied on its middle, regardless of the soil layer conditions, while group suction piles varies significantly according to the allowance on head rotation. When head rotation is allowed, the behavior of group type piles become similar to the behavior of mono suction pile. Whereas, when rotation is prevented, resistance is maximized when load is applied on the top head. Moreover, group suction piles show higher efficiency regardless of the ground condition and geological stratum. For further advances, concrete block on the top of group suction piles are suggested as an effective alternative method to prevent partial rotation and maximize ground resistance for group suction piles.IntroductionWith the development of offshore technology, applications and real site installations of suction piles are increasing significantly nowadays. They are generally used as mooring anchors in various floating structures, marine platforms, and offshore wind turbines. According to its convenience in installation and removal, suction type foundations are becoming good alternatives for deep ocean support systems. The bearing capacity is similar to the bearing behavior of ordinary offshore structures (piles or drilled shafts). The most common use of suction caissons is anchors for catenary mooring lines, where the chain angle at the mudline is close to zero (Randolph, 2002; Sharma, 2004).Recently, it is reported that a huge isolated single suction pile can be replaced by a group of moderatesized suction piles (Randolph et al. 2004). A single monopile is easy to be produced and installed in site. It is expected that monopile foundation is not applicable for deep depths because it has a limitation on penetration according to its huge side skin area (i.e. friction). Moreover, stiffness requirements sometimes render thicker pile wall conditions which are impractical to be produced."

Jan 1, 2017

By Goudschaal Mark R.

"The Museum of Science and Industry U-505 Submarine Relocation project in Chicago, IL consisted of building an underground reinforced concrete vault (37' deep) for the Museum's new U-505 exhibit. This WWII submarine was captured in 1944, had been located outdoors at the Museum since 1954 and was lowered into its new exhibit area in 2004. A unique combination of earth retention, water cut-off and underpinning systems allowed a forty-two foot (42') deep excavation underneath th is historic museum. The museum - originally built in 1893 for the Chicago World's Fair - was closely monitored for building movements throughout construction. The underpinning systems, construction activities and monitoring results are presented herein. IntroductionThe historic U-505 German submarine at the Museum of Science & Industry was restored, moved approximately 1,000' and then lowered into its new indoor home (Figures 1, 2 and 3). The new underground exhibit opened this year celebrating the 61st anniversary of the German submarine's capture on June 4, 1944. On this historic day, Captain Daniel V. Gallery, a Chicago native, led the Navy in the siege of this submarine near the coast of Africa. This U-boat was the only German sub captured by the United States Navy in WWII and the Enigma machines, codebooks and publications recovered from the sub helped the war effort."

Jan 1, 2005

By Nabil F. Ismael, Mohamed El Deeb

"The behavior of laterally loaded step tapered bored piles in calcareous sand was examined by field tests. Lateral load tests were carried out on straight and step tapered bored piles 5.3 m long embedded 5 m below ground level. All piles were installed by augering. The straight piles were 0.2 m, and 0.3 m in diameter. The step tapered piles have a diameter of 0.3 m along the upper 10%, 20%, and 40% segment, respectively, changing to 0.2 m for the lower section. Two piles were instrumented with strain gages to measure the bending strains. All tests were carried out to failure. The purpose being to examine the ultimate lateral capacity and the deflection at working loads. Test results indicate non linear response and substantial increase in lateral capacity and decrease of deflection for the step tapered piles compared with the 0.2 m diameter straight shaft piles. However, beyond a depth of 40% of the pile length, the strengthening of the pile section by enlargement of its diameter had little effect on the lateral capacity and the deflection of step tapered bored piles.IntroductionFor many structures on pile foundations the ultimate capacity under lateral loads is important and may be the controlling factor in foundation design. Examples include transmission tower foundations and fender piles at sea port facilities. Increasing loads on these structures has resulted in piles of large diameter and depth at a significantly higher cost.In this work, the use of step tapered bored piles with a larger diameter along the upper segment of the piles is examined by field testing and analysis on single piles in calcareous desert sands. Lateral load tests were carried out on straight and step tapered piles 5.3 m long embedded 5 m below ground level. The straight piles were 0.2 m, and 0.3 m in diameter. The step tapered piles had a diameter of 0.3 m along the upper 10%, 20%, and 40% segment, respectively, changing to 0.2 m for the lower section. Two piles were instrumented with strain gages to measure the bending strains. All tests were carried out to failure. The purpose being to examine the ultimate lateral capacity and the deflection at working loads for step tapered bored piles."

Jan 1, 2005

By Tony Suckling

The commercially available finite element program Plaxis has a key benefit over other finite element analysis programs in that it has a relatively simple user interface to input and output data. This benefit though may also be it?s weakness in that anyone, regardless of their grounding in geotechnical engineering, may use the program and produce results for design. It is essential, as for all engineering design, that the models are checked by competent engineers. This paper describes the key recurring problems found by the authors when checking Plaxis models, such as the generation of the initial in-situ ground stresses and the modelling of groundwater. Interestingly, the authors have not encountered similar problems when checking finite element models produced using other programs and conclude that this may be due to the higher calibre of modeller needed to use these other programs. The geotechnical industry is in a situation at the moment where senior managers who may not have been trained in finite element modelling are relying on less experienced staff who have had some training in modelling, either at university or post graduation. The quality of this training is variable and all organisations running easy to use programs need to be aware of the potential risks and dangers. Management procedures and engineering checks that are essential to validate the results of these models are described, assuming that those in charge are not experienced modellers themselves. The model checking process by competent persons is absolutely essential and it is hoped that this paper will help those organisations that do not have such procedures as part of their own internal Quality Assurance or design validation system. The procedures described are valid for all finite element programs.

Jan 1, 2010

By William B. Conway

This paper will describe the large caisson pier foundations for four of the bridges crossing the Mississippi River in the New Orleans area; and will discuss some of the unusual problems encountered during their sinking. Certain settlement phenomena experienced during their service life will also be related: The four bridges in order of their construction: The Huey P. Long Bridge, River Mile 106.1, completed in 1935 The Greater New Orleans Bridge No. 1, River Mile 96.0, completed in 1958 The Hale Boggs Bridge, River Mile 121.6, completed in 1983 The Greater New Orleans Bridge No. 2, River Mile 96.1, completed in 1988 Each of these bridges employed large open-dredged concrete caissons as foundations for one or more of the river piers, with the smallest being the 65ft by 102ft caissons for Piers I and II of the Huey P. Long Bridge and the largest being the 99ft by 214ft caisson for Pier II of the Greater New Orleans Bridge No. 2. The Huey P. Long caissons are founded in a dense fine sand at -170 while all of the other bridge caissons are founded in hard preconsolidated clay at elevations varying from -150 to -185. The Huey P. Long Bridge is currently being widened without increasing the caisson foundations under any of the river piers; and the design reasoning that led to this decision is presented.

Jan 1, 2013