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By Renato P. Cunha

The paper explores a parametric analysis of a four-pile group in contact (hence piled raft) and without contact (hence standard pile group) with the superficial soil layer, under a combined set of loadings (moment M, vertical V and horizontal H forces). The major design parameters of interest, as total and differential settlements, and raft bending moments and shear stresses are assessed under aforementioned distinct conditions. The slenderness ratio of the piles is also varied along the analyses, allowing the establishment of its influence on the derived parameters.

Jan 1, 2006

By Rajesh A. Vaidya

A large scale piling work is undertaken in India for an important fast track industrial project. Thousands of solid square precast concrete piles are driven to depths of around 50m. Soils encountered are of alluvial origin with very soft clays varying in thickness from 10 to 18m at the top followed by medium dense to dense and occasionally very dense sand, stiff clay and finally dense to very dense sand layer as the founding layer. Recent site grading with around 4 metres thick hydraulically filled river sand necessitated driving the piles to the bottom sand layer to avoid problems on account of negative skin friction and to achieve optimum pile capacity. A process approach suggested by Bell et al (2002) to promote better understanding of the pile behaviour, pile capacity, and parameters assumed at design stage for static capacity and for wave equation analysis is followed with an aim to bring in effective economy in terms of pile length and pile installation speed. Soil investigation work is also undertaken in stages to cut down pile wastage. A judicious combination of PDA and static pile load tests is followed. Pile Driving Analyser (PDA) tests at end of driving and also at various stages of recovery of pile capacity are carried out to understand the pore pressure dissipation phenomenon. The paper attempts to present some of the valuable experiences that would go to establish precast pile as a very effective alternative to driven cast-in-situ piles and bored piles which are very common in this part of the world despite their limitations in terms of economy, speed and certain geotechnical aspects.

Jan 1, 2007

By Matthias Pulsfort, Jiarui Du, Torsten Wichtmann, Achim v. Blumenthal, Diethard König, Rowena Verst

The influence of the interaction between support fluid and soil, e.g., filter cake formation, on the shear stress transfer in the soil-concrete interface of diaphragm walls and bored piles is still controversially discussed. Actual research on the soil-concrete interface using bentonite suspensions indicates that shear stress transfer is underestimated by existing standards. Investigations on the soil-concrete interface using polymer solutions are rare. Therefore, complementary field investigations and systematic laboratory studies were conducted to analyse the soil-concrete interface using both bentonite suspensions and polymer solutions. Thickness and composition of real-scale filter cakes were investigated on several slurry wall construction sites, where bentonite suspensions were used. Direct shear tests (60 mm x 60 mm) were executed for soilbentonite mixtures with varying amounts of bentonite and different granular fines representing a realistic bandwidth of in-situ filter cake compositions. Larger direct shear tests (300 mm x 300 mm) with preceding horizontal penetration, subsequent vertical tremie concrete placement, and filter cake consolidation were performed using both bentonite suspensions and polymer solutions. The results support the view that shear stress transfer in the soil-concrete interface can be described by a wall friction angle in a range of 25° to 30° for bentonite suspensions and between 35° and 40° for polymer solutions in non-cohesive soils.

May 1, 2022

By P. K. Ray, Sudip Kumar Koley, Sainath M. Reddy, Devulapalli L. S Rasagna

Bangalore Metro Rail Project- phase II is one of the technological challenging project, particularly construction of underground metro rail system. The Bengaluru city is very congested area and connecting metro rail system with existing transportation networks is equally challenging. In this phase-II, the Underground metro is being constructed by blasting hard rock formation and supporting the shear zone. Most of the subsurface rock formations comprise of granitic Gneissic formations are of Precambrian age and shear zones that includes friable a thin weathered rock formation. With such subsurface geological conditions, , the anticipated construction challenges include : A) deep excavation of hard rock mass under old and sensitive structures and buildings, by controlled blasting; B) variation in the rock grade from grade I to grade V; C) weak rock mass at shear zone resulted in planar failure beneath the retaining wall; D) water seepage along shear planes; E) selection of a suitable method to conducted blasting near high voltage electrical machinery or power cables. This paper describes the methods adopted to mitigate these technological challenges and to meet stringent environmental compliances. These includes study and application of various geological, geotechnical parameters to develop a proper line drilling and controlled blasting techniques to minimize the ground vibrations and controlling the rock fragmentation and to optimize the equipment performance in terms of productivity and time schedules. The “Phase 2” software of “Rocscience” has been used and Regression analysis has been carried out by using MCD (Maximum Charge per Delay) and PPV (Peak Particle Velocity) to estimate with FOS (Factor of safety) for sensitive places such as nearby high rise buildings and electrical transformers.re.

Sep 1, 2022

By Alice Y. Tseng, Dan MacLean

"Corrosion protection of all deep foundation systems made of steel is THE issue when considering durability of the element in the long term. Protecting steel from corrosion and maintaining the steel tendon cross sectional area ensures a competent and durable system. The foundation of a building is usually difficult to repair and therefore high risk is taken when unknowingly choosing a non-adequate solution.Requirements according to EN 1990 (Eurocode 0 or EC 0) on construction durability requires a service life over 100 years. How can a service life over 100 years be achieved? How shall bare steel be protected in soil, which sometimes could be an aggressive environment to the steel? Which corrosion protection methods are commonly used in Europe and in North America?This paper will focus on hollow bars used as Micropiles, Anchor piles and Soil Nails. It gives an overview about the state of the practice in regards to corrosion protection (including head construction) and evaluates different options following the European Standards focusing on type of material and method of installation. Further the different corrosion protective methods such as thickness of grout body, coating types and sacrificial loss are listed with the pros and cons evaluated.Based not only on North American standards like FHWA “Micropile Design and Construction Guidelines”, FHWA Geotechnical Engineering Circular No. 7 for “Soil Nail Walls“ and Post-Tensioning Institute “Recommendations for Prestressed Rock and Soil Anchors”, but also European standards like EN 14199 “Execution of special geotechnical works – Micropiles”, EN 14490 “Execution of special geotechnical works - Soil nailing”, EN 1537 “Execution of special geotechnical work – Ground anchors“, and other relevant standards, all possibilities of protecting the hollow bars and the steel quality will be introduced, discussed and compared ."

Jan 1, 2017

By Takefumi Takuma, Hiroyuki Nishimura, Shigeru Kambe

"In order to achieve tubular pile driving with low noise and low vibration, the Press-in Piling Method has been adopted on many projects. The method utilizes reaction force derived primarily from previously driven piles to push in the next pile into ground. With attachments, the Press-in piling equipment can deal with hard soil as well as difficult site conditions. At West Toronto Diamond Rail Grade Separation Project in Toronto, Canada, the Press-in piling equipment drove more than 500 of 914 mm (36 inches) diameter tube piles in length of 12 to 25 meters (39 to 82 feet) to construct earth-retaining walls for railway grade separation. Myoshoji River Restoration Project in Tokyo, Japan drove some 600 of 1,000mm (39.4 inches) diameter tube pipe sections in length of 11 to 22 meters (36 to 72 feet) by the rotary Press-in piling equipment to increase the flood drainage capacity of an existing river in highly populated area of the city. Both projects exemplify the advantages of the method in urban settings.1. BACKGROUNDThe Press-in Piling Method was invented some forty years ago in Japan, where a very large number of construction projects were causing widespread construction pollution, especially by pile driving work in densely populated areas. The method has been providing solutions for piling projects which could not have been built otherwise due to the noise and vibration impact to the surrounding communities. The method can be used with various types of piles including sheet piles, tubular piles, concrete sheet piles and so on. With high pressure water jet and continuous flight auger attachments, the Press-in piling equipment can deal with dense sand, stiff clay, gravels, boulders and even soft rock without employing a different set of equipment."

Jan 1, 2015

By Nicolas Denies, Jeroen de Leeuw, Bart Lameire, Jan Maertens, André Vervoort, Flip Hoefsloot, Noël Huybrechts, Flor De Cock

"In recent years, the Deep Mixing Method has increasingly been applied for the construction of earth and water retaining structures. From practice, it has been experienced that there is a real need to develop execution and design rules adapted to the function of the soil mix wall (retaining wall, water barrier, foundation solution or a combination) including the temporary or permanent character of the application. Based on the results of the BBRI Soil Mix project (2009-2013), a design approach has been developed in collaboration with the SBRCURnet. The present paper briefly discusses the principles of this design approach which takes into account the function of the soil mix wall and the characteristics of the soil mix material. The interaction between the soil mix material and the steel reinforcement can be considered in the calculations depending on the function of the soil mix wall. Design and quality control requirements are given in function of the application and take the lifetime of the structure into account. Durability aspects of the soil mix material are therefore considered in the present design approach.INTRODUCTIONSince several decades, the deep mixing method is used for ground improvement works. A more recent application is the use of soil mix as structural elements such as in the case of the earth-water retaining soil mix walls. Since 2000, due to the economic and environmental advantages of the method, this particular application has shown an amazing growth in Belgium and in the Netherlands. A typical excavation (16 m depth), realized with CSM (Cutter Soil Mix) panels, is shown in Fig. 1. For temporary applications, the questions related to the mechanical characteristics of the material, its permeability and its adherence with steel have been investigated with success within the framework of the BBRI Soil Mix project (2009- 2013) (see Denies et al. 2012 for more details). The durability of the soil mix material remains a complex topic while permanent applications are more and more observed in practice. In order to define an obvious design approach, it was necessary to clarify the potential functions of soil mix walls and to establish the requirements related to their design and construction. The BBRI (in Belgium) and SBRCURnet (in the Netherlands) have therefore worked together to publish guidelines in the form of a handbook titled ‘Soil Mix Walls’ (publication foreseen in 2015). In this handbook, a methodology is proposed for the design of the soil mix walls for which the interaction between steel and soil mix can possibly be taken into account dependent upon the application. Each potential function of the soil mix wall is described (e.g. earth retaining wall, cut-off wall, etc.) and the temporary or permanent character of the application is always considered."

Jan 1, 2015

By Viswanadham B. V. S., Babu K. V

Many refineries are in the process of revamping and expanding their existing facilities. Most of the refineries are located in coastal areas due to ease of transportation and storage of crude oil. Considering the criticality of structures as well as prevailing soil conditions, most of the structures are supported on pile foundations. In depth review of sub-surface investigations data followed by liquefaction assessment of the site, it is noticed that site is prone to liquefaction during the seismic event. Among various techniques, driven cast-in-situ piles were selected to mitigate liquefaction. Static cone penetration tests were conducted during the pre and post installation of driven cast-in-situ piles at identified locations. Analysis of cone penetration test data shows that considerable ground improvement has been achieved post-installation of driven cast-in-situ piles.

Sep 1, 2022

By Paul R. Lear

Sustainability continues to be an important aspect of remediation and infrastructure projects. Deep soil mixing (DSM), a common construction and remedial technology, can easily incorporate the following sustainability best management practices (BMPs), including Minimizing Total Energy Use and Maximizing Use of Renewable Energy; Minimizing Air Pollutants and Greenhouse Gas (GHG) Emissions and Maximizing Use of Machinery Equipped with Advanced Emission; Minimizing Water Use and Impacts to Water Resources; Beneficial Reuse of Materials/Reduction of Materials and Waste Reduction; Use of Local Labor and Supplies. This paper focuses on the sustainability of DSM treatment and provide carbon footprint calculations at least one completed DSM project which used these sustainability BMPs to demonstrate the environmental impact of the sustainability.

Sep 8, 2021

By Spencer Ness, Yazen Khasawneh, William Tjaden, Mohammad Nassim

The evaluation of long-term performance of the wind turbine structures is essential in lowering the Levelized Cost of Electricity (LCOE) from wind sources. The required maintenance of the wind turbine foundation during the design-life time of the wind turbine may result in escalated cost, if not properly evaluated during the planning and designing phases. The degradation of the foundation soils’ stiffness due to the accumulation small plastic strains resulting from normal and/or extreme operating cyclic loading may result in escalating the O&M cost. The foundation’s stiffness degradation will result in a shift of the wind turbine system natural frequency, which may result in amplifying the vibrations generated at the hub. The anticipated shift of the wind turbine system natural frequency during the design-life time should be investigated through numerical simulations of the anticipated dynamic loading utilizing soil constitutive models that are capable of capturing the foundation stiffness degradation due to the accumulation of such small plastic strains. This study presents the validation of an element model that will be used to evaluate the performance of existing and/or proposed constitutive model.

Oct 1, 2022

By N. Schmitz

This paper explains how new digital solutions improve reverse circulation drilling operations. Upgrading field-proven reverse circulation drilling (RCD) rigs with new digital technologies enables semiautomated drilling, with upgrade options for fully automated & remote drilling. Key elements of the improvements are electrically controlled valve systems, process instrumentations, a state of the art machine controller and drilling operation via a touch control panel. Automation of core processes, such as adding drill pipes, reduces set-up times, increases machine uptime for drilling and as a result efficiency. While drilling, sensors provide continuous feedback, which is used to automatically adjust e.g. the weight on bit to the optimum; resulting in an increased rate of penetration and less wear and tear. While in the past hydraulic power packs (HPU) have typically been operated at a constant high-performance level with related high fuel consumption, a new interface between the machine controller and the power unit regulates the HPU performance exactly according to the actual drilling operation needs. This leads to significant fuel consumption reduction. The safety benefits of the digital improvements are the ability to remotely operate the rig in challenging site conditions via a mobile operator panel.

Sep 8, 2021

By Mitsuhiro Shibazaki

Generally, water-soluble polymers are effective in convergence of water jet ejected from a nozzle as they add viscosity to water. However, excessive additional polymers (added to keep water viscous) could increase friction on the contrary. Therefore, we have totally modified the jetting system from every possible aspect, such as the shape and upstream conditions of a nozzle in order to keep the flow spread to the minimum as stated in my presentation.

Feb 10, 2003

By Christopher J. Ramsey, Don W. Dotson

"An existing four lane section of US 27 was widened to eight lanes. The project lies in the rugged Valley and Ridge Province of the Appalachian mountains starting at the Tennessee River in Chattanooga, Tennessee and extending 2.6 km north to Signal Mountain Boulevard. This terrain presented many challenges to accommodate the road widening in the narrow, rugged topography. Multiple tiered wall systems consisting of large tieback walls, post-tensioned reaction blocks, and gravity MSE walls for a total of approximately 30 retaining walls were required. The retaining walls served to stabilize the thrust faulted geology while also minimizing right-of-way acquisitions. The cut walls consist mainly of a tiered system of tied-back soldier piles walls with cast-in-place concrete facing. Cast-in-place pile shear walls were required along the toe of existing MSE walls to maintain stability during construction. This paper discusses the design methodology, which includes a hybrid (rather than traditional) earth pressure diagram intended to reduce life-cycle maintenance and long-term performance. Further this paper addresses wall construction, slope stability analysis, landslide mitigation alternatives, soldier pile wall design features, site challenges, monitoring and performance (to date) of the wall systems.INTRODUCTIONThis project involves the proposed widening of US Highway 27 (State Route 29) from the north end of the Tennessee River Bridge at Manufacturer’s Road to State Route 8 (Signal Mountain Road), approximately 2.64 km of roadway (Fig. 1). The project site is located adjacent to the Tennessee River on the north side of downtown Chattanooga, Tennessee in Hamilton County. The existing, limited access highway is to be widened from four lanes (two northbound and two southbound) to a minimum of eight lanes. Some portions of the alignment will expand to as much as ten lanes where northbound and southbound ramp acceleration/deceleration lanes coincide.In addition to the number and heights of cuts and fills involved, a major factor in determining an economical design for the alignment is the complicated geologic conditions along the roadway alignment. The existing roadway is situated between several steep cut slopes, some of which are only marginally stable or currently exhibit signs of instability. Due to the proximity of the project to the downtown area, the steep slopes along the alignment, and the relatively dense population near the alignment, widening the pavement and constructing cut and fill slopes to a stable configuration would result in major land acquisition for slope right-of-way."

Jan 1, 2015

By Joseph A. Sopko

The first documented procedures for designing frozen earth structures are over 50 years old, implemented long before the introduction of the Finite Element Method (FEM). Since that time, the development of three-dimensional models has made the traditional and often over-conservative methods relatively obsolete. This paper discusses a new approach that is largely dependent on the analysis of internal stresses with the frozen structure and comparison to frozen soil laboratory tests. A specific design process is discussed related to initial field investigation, laboratory testing, structural and thermal analysis, and performance monitoring. The design results are compared to case histories in the field that verify the procedure. BACKGROUND One of the first documented methods to designing frozen earth retaining structures was by Sangar (1968). Methodical refinements were published by (Harris 1995) and published by the International Symposium on Ground Freezing in 2002 (Andersland et al. 1991). The structural design or thickness of the frozen mass was based on the unconfined compressive strength of the frozen soils. Two simple equations for determining the thickness of a frozen shaft are shown in Fig. 1 and the first two equations below.

Jan 1, 2019

By D. S. Yang, Y. D. Wang, G. Watanabe, A. P. Notaro

"Deep soil mixing (DSM) walls reinforced with steel soldier piles were installed for excavation support and groundwater control for the construction of a grade separation structure at the intersection of Warren Avenue and the Union Pacific Railroad in Fremont, California to mitigate traffic conditions during the busy commute hours and for the extension of San Francisco Bay Area Rapid Transit (BART) system. Instead of treating the DSM wall as a temporary structure, the reinforced DSM walls were integrated in the design of the permanent structures including retaining walls, and the abutments and pier of the railroad and BART bridges. The integration of steel members inside the DSM wall as part of the permanent structures is an innovation which facilitates the use of top down construction techniques to speed construction and utilizes the steel soldier piles that would have been disregarded after the use as a temporary shoring wall. This paper will review the background of the project and DSM method and present the design and construction of the DSM wall composite structure for this grade separation project.INTRODUCTIONUsing the concept of mixed-in-place piles initiated in the 1950’s in the United States, Japanese contractors in the late 1960’s and early 1970’s installed single mixed-in-place soil-cement piles along a row to create a wall for excavation support and groundwater control. Due to the high groundwater conditions in most of the coastal cities in Japan, wall continuity and uniformity became the requirements of soil-cement walls for reliable groundwater control to minimize ground movement and impacts to adjacent buildings and facilities. In late 1970s, Seiko Kogyo, Co. Ltd. developed the Soil Mix Wall (SMW) method, which uses a triple auger mixing tool to improve the uniformity and continuity of soilcement wall. The SMW method is considered a wall installation method in contrast to the Cement Deep Mixing (CDM) method, also developed in Japan, for ground stabilization in soft soils, especially in the marine environment. In the U.S., generic terms like DMM (Deep Mixing Method), DSM (Deep Soil Mixing) or CDSM (Cement Deep Soil Mixing) are used by various government agencies and private organizations to describe the soil mixing technologies without differentiating the origin, procedure and application. The method used in this project is called DSM method by the project owner, Santa Clara Valley Transportation Authority (VTA), to produce a single continuous soil-cement wall for use as shoring wall and composite structure. The mixing tool for DSM wall installation can vary from 3 to 6 mixing augers. Due to the need to install steel soldier piles into the DSM wall for resisting lateral forces, high water cement ratio slurry with bentonite is used to produce low strength soil-cement, generally in the range of 70 to 100 psi (500 to 690 kPa), with high fluidity to facilitate the installation of steel soldier piles. To maintain the wall continuity for groundwater control, overlapping of one full DSM column is made between neighboring elements using two types of installation procedures as illustrated in Figures 1a and 1b. Steel soldier piles, as shown in Figure 2, are used to reinforce the soil-cement wall to resist the lateral shear force and bending moment induced during the excavation."

Jan 1, 2015

By Venkatesh S. V J, Shubha M, Srilakshmi G

Choosing for the best option of pile foundations to overcome large lateral and uplift loads for the foundations in transmission line towers/offshore environment is still being a concern to achieve the required capacities but also by considering the suitability aspect in the environment. The objective of this paper is to review the methods that have been done for knowing the uplift resistance and lateral resistance of pedestal piles. Investigations by different methods such as experimental studies, numerical and analytical studies have been done by various researchers in order to evaluate the response of a belled pile. These methods are discussed in this paper and the comparison with straight shaft pile based upon the test and analysis. The results indicated that the uplift resistance and lateral resistance were significantly increased with the adoption of belled piles than straight shaft piles.

Sep 1, 2022

By Michael Hughes, Selva Selvamohan, Ray Costa

"Cutoff walls are commonly used to mitigate underseepage problems for levee remediation projects. At abrupt changes in seepage cutoff wall depths there is a potential for water to flow around the back of the deeper cutoff wall leading to elevated seepage pressures on the landside that could result in exit gradients exceeding design criteria. This condition is referred to as end-around-effects and is a complex problem that requires detailed and time consuming 3-D numerical modeling to represent accurately. This paper presents a simple approach for assessing end-around-effects using the results of 2- D seepage analysis to determine if lateral extension of the deeper portion of the cutoff wall is required. This simplified approach provides a pragmatic solution to a complex 3-D problem. The presented procedure was used as part of the Feather River West Levee Project in Yuba City, California, to assess end-around-effects at 26 locations. The results showed that wall extensions of up to 100 feet were needed at only 2 locations.INTRODUCTIONAs the lead geotechnical consultant for the Feather River West Levee Project, AECOM were responsible for designing levee remediation works for approximately 35 miles of levee protecting the area around Yuba City, California, and communities to the north and south. Due to land use constraints, seepage cutoff walls were the main remediation alternative selected to address underseepage issues for the project.As part of the design review process, the California Department of Water Resources (DWR) requested AECOM to look at 26 locations along the levee alignment where the depth of cutoff wall changed abruptly from shallow to deep, or vice versa. At these locations there was the potential for seepage pressures to pass behind the deeper section of cutoff wall and stress the blanket layer landward of the cutoff wall. A condition referred to as end-around-effects.End-around-effects involve complex 3-D ground conditions that have traditionally been addressed by laterally extending the deeper section of cutoff wall an arbitrary distance based solely on engineering judgment. In discussions with DWR, AECOM developed a simple procedure to provide a more objective assessment of end-around-effects without the need for detailed and time consuming analysis. This procedure allows the engineer to make an informed decision of whether end-around-effects are a problem at the location of a cutoff wall transition rather than laterally extending the deeper section of cutoff wall an arbitrary distance based on engineering judgment alone."

Jan 1, 2015

By Jason Herron, Joseph Brown

The common couplings for joining sections of helical piles with an outside diameter of 6.625 inches and 8.625 inches are square on square, flange to flange, external pipe sleeve, internal pipe sleeve, and welded joint. Each coupling type has advantages and disadvantages in efficiency, capacity, installation, and economics of the installed pile. All these coupling types have been used in the helical pile market in North America for various applications and designs. Many of these applications require on-site testing, but test records are not typically shared with the helical pile industry. Due to the lack of information available for square on square and flange to flange couplings, testing was done to compare the efficiency of installation, load to deflection response, and torque to capacity ratios of external pipe sleeve, square on square, and flange to flange couplings. Field installations and tension tests were performed in non-cohesive (sand type) soil near Caseyville, IL and in cohesive (clay type) soil in Centralia, MO. The data collected during these tests included rotations per foot during installation, installation torque, applied pressure, and deflection. The results of this testing are analyzed and discussed within this paper. The results indicate that the square to square coupling is the most efficient of the designs tested, but this conclusion cannot be fully justified without further testing due to the variability in the data gathered and the small number of piles tested. INTRODUCTION A helical pile is typically assumed to be a medium-displacement pile when its outside diameter is between 4.5 inches and 8 inches and a high-displacement pile when its outside diameter is greater than 8 inches. A helical pile designer has multiple options when selecting a coupling type for medium- to high-displacement helical piles. Each type of coupling has advantages and disadvantages and must be analyzed on the bases of efficiency, capacity, installation, and economics of a project. Typical couplings that are chosen by designers include square on square, flange to flange, external pipe sleeve, internal pipe sleeve, and welded joint. A helical pile must transfer axial, lateral, bending moment, and torsional loads, and the coupling must be designed to effectively and efficiently transfer each type of load. During the installation of a helical pile, the rate of penetration and the disturbance of soil layers play a critical role in the efficiency and torque to capacity ratio (Kt) of the pile. It is common for a coupling to protrude beyond the outside diameter of the pipe section being used. This is necessary for the function of certain coupling types and can facilitate the connection of couplings. However, it causes increased soil disturbance and reduce the rate of penetration due to soil bearing against the protruding portion of the coupling. A helical pile designer typically will work to minimize the coupling protrusion and create a pile with optimal installation efficiency but may choose a design with lower installation efficiency if it offers sufficient economic advantage.

Jan 1, 2019

By Kyle Kershaw

Micropiles are routinely used in the United States for foundation support and stabilization of slopes. In recent years, several retaining walls have been constructed using micropiles in an A-frame type configuration to support temporary and permanent excavations at sites with limited access and limited right-of-way. Typical A-frame micropile walls consist of a row of vertical micropiles at the face of the wall and a row of battered micropiles extending into the soil or rock to be retained. The two rows are then tied together with a pile cap such that the front pile acts primarily in bending and the back pile acts primarily in tension. Because of tight right-of-way constraints at a residential site in Aspen, Colorado, it was not possible to construct the wall using conventional shoring systems or micropiles in the typical A-frame configuration. Rather, the wall was designed such that the row of battered piles was installed at the wall face and the row of vertical piles was installed adjacent to the property line behind the wall. As a result of the reverse configuration of the A-frame wall, FLAC, a two-dimensional, finite difference software program, was used to model the soil-structure interaction. The final wall design consisted of both temporary and permanent retaining wall sections with maximum heights of 26 feet. Inclinometers were installed in several piles to monitor the behavior of the retaining walls during and after excavation. This paper presents an overview of the design method, a discussion of construction techniques, and a comparison between the FLAC model and the measured behavior of the wall in the field.

Jan 1, 2007

By Jonathan J. Dewsbury

It is argued that approximate computer based methods are only suited to modelling conventional piled rafts, for pile enhanced rafts where the interactions will be non linear three dimensional finite element analysis is required. However current 3D finite element analysis often relies on symmetry to reduce computational cost and there are concerns over the dependency of the results on the user. Therefore a new strategy within the finite element framework has been proposed. The main advantage of this strategy is that each stage of the model can be checked for consistency. There is also the added benefit that non symmetrical models can easily be constructed by tying the validated components together without dramatic increases in computational time. The proposed strategy compared well to the published results of a hypothetical example of a piled raft previously analysed with numerous methods by Poulos et al. (1997).

Jan 1, 2010