Search Documents

By Chetan D. Savani, Mike K. Muchard

The necessity to evaluate undocumented foundation lengths is essential in assessing the useable life, need for scour protection, retrofitting, or full reuse of existing bridge foundations. For this purpose, Parallel Seismic Testing (PST) has the best accuracy and is applicable to the widest range of foundation configurations used in bridge construction of any test method. Although not limited to bridges, PST case studies are presented involving two bridges. To preface the case study discussions, an overview of the PST method is given along with its results and analysis thereof. In one of the cases, we were afforded the rare opportunity to see the existing piles being extracted long after the PST testing program was completed. The resulting Class A prediction reaffirms the accuracy of the method. Versatility of the PST method is also exemplified in the two cases presented, where unique situations from complex foundation systems were overcome by analysis to provide successful results.

By Leena Korkiala-Tanttu, Noora Lindroos, Juha Forsman

"Construction works at the Helsinki city sea shoreline requires dredging and handling of contaminated sediments. Most of these soft dredged sediments are regarded as too poor quality material for earth construction purposes. Mass stabilization technology has been applied to improve the technical and environmental properties of the dredged sediment in order to utilize the material in construction. The treatment site presented in this article is placed in the West Harbor where the dredged sediments are disposed in basins, mixed with binders by mass stabilization and transported to utilization sites. The volume of these basins is about 90 000 m3. So far these basins have been used three times during the years 2011-2014. The most applied binder has been cement. Its high price and carbon footprint have encouraged use alternative binders. Other used binder materials include fly ash and end product of desulphurization from coal combustion, and fly ash from combustion of Estonian oil shale. The technical and environmental properties of stabilized sediments have been studies in the laboratory and in situ thoroughly. Some properties of the stabilized sediments which have been studied are: compression strength, modulus, hydraulic conductivity, leaching of contaminants, etc. The leaching test results show that heavy metal leaching is very low with all binder materials tested.1. INTRODUCTIONContaminated marine sedimentsMarine sediments in the coastal areas are often contaminated as a consequence of industrial and port activities, as well as the influence of cities located there. Construction activities and reclamation of shore line require dredging and handling of contaminated sediments since the level of contamination inhibit dumping of dredged sediments into the sea. Based on their technical properties, most of these dredged soft and watery sediments (clay, gyttja, etc.) are regarded as too poor quality material for earth construction purposes. Economic, sustainable and environmentally safe management of contaminated, dredged sediments is a key issue in many construction sites.In the City of Helsinki, mass stabilization technology has been applied to improve the technical properties of the dredged sediments in order to utilize the material in construction. Owing to stabilization / deep mixing / solidification, also the contamination is encapsulated in a monolithic solid of a high structural integrity. Thus, contaminants migration is restricted by the decreased surface area exposed to leaching.The treatment site presented in this article is placed in the West Harbor (a place of Helsinki called Jätkäsaari) where dredged sediments are disposed into stabilization basins, mixed with binders by mass stabilization and then transported to final utilization sites. The location and principle of these basins is presented in Figures 1-4. The overall volume of these four stabilization basins is about 90 000 m3."

Jan 1, 2015

By Dipl. -Ing. (FH) Thomas Schmitt, Dr. Melvin England

Foundations in Geneva are difficult and expensive due a large overlayer of clay and silt above competent bearing material in the moraine. Common foundation schemes use deep barrettes or bored piles, first passing large, weak layers of soil before finally reaching acceptable, solid moraine with reasonable values of skin friction and end bearing resistance, thus requiring further deep penetration for the necessary length for load transfer in the moraine. Depths of more than 60 m (200 ft) in Geneva are common in this region. At the Onyx-Project Geneva Implenia Foundation Company also encountered these circumstances. Despite usual solutions Implenia referred to an old and well known, but still intelligent and in today’s words smart, efficient and economical solution. Using small shafts, passing the large layers of clay and silt, ending with the pile toe in the underlaying moraine with a belled or underreamed base was the technic adopted to save drilling time, reduce spoil and concrete, so finally reducing the CO2 footprint. Piles with enlarged base (“belled” or “underreamed”) are reported at the beginning of the 20th century, for example at Chicago, which has a quite similar geotechnical structure as Geneva with the need of deep foundations. The first pile base enlargements were built in hand-dug caissons with wood lagging and steel ring bracing. In the 50s and 60s piling works were more and more mechanized, driven by the development of more powerful cranes and specialized drill rigs. Additionally the first tools for mechanized base enlargement were invented around that period. This report describes the project situation at Geneva, the drilling and enlargement technique of the pile base, the verification of the design values with an in-situ bi-directional load test and the smart execution by reduction of CO2 and costs.

May 1, 2022

By Abhijit Saha

"The stone columns improve the performance of foundations on soft and loose soil due to the ability of composite ground to sustain increased structural loads under reduced settlements. The interaction between the two basic elements: the ambient subsoil and installed column, present a complexity of behaviour, both in terms of applied stresses and resulting strains. Moreover, as the same is provided in-group in a regular array beneath foundations, the performance of an individual column is likely to be influenced by the presence of neighbouring columns. The present paper addresses this very issue. Analysis of reported field hydro-test data of large diameter oil storage tanks in soft ground in reference to some existing theories led to the development of the stone-column ‘group efficiency factor’. In order that such factor is of general use, it was felt necessary to examine the applicability of the factor to different sizes of groups under varied subsoil conditions. With this in view, some model test results reported in literature of single and group of columns have been analysed and in the process an explicit relationship regarding the stone-column ‘groupeffect’ could be established.INTRODUCTIONThe field application of the stone column technology has gained momentum than the intricate design methodology due to its simplicity in installation and intuitive performance. The ground improvement is due to the complex interaction within the ‘unit-cell’ comprised of the installed column in ambient ground under sustained vertical stress; in association with the interdependence of problem geometry and material properties of the two different soils-one 'native' and the other 'back-filled'. The beneficial effects are increased load capacity, reduction in total and differential settlements, minimization of post construction settlements effected by accelerating consolidation, reduced risk of soil liquefaction, aiding in improvement of slope stability of embankments and natural slopes and effecting changes in the dynamic response. The ‘unit-cell’ concept of a tributary soil cylinder encapsulating an installed column with some reasonable assumptions and boundary conditions (Aboshi et al, 1979; Balaam & Booker, 1981; Van Impe & De Beer, 1983; Priebe, 1976; Saha & De, 1994; Saha; 2005, 2006, 2007, 2011, Saha & Das; 2007) deals with the load-settlement behaviour of the composite system. The present investigation is based on published field data from literature & validated with experimental study reported in literature. The study addresses the effect of group interaction of stone columns beneath a large area loading on ground settlement. The hydrotest load-settlement data of 12 large diameter oil storage tanks founded on stone column reinforced soil at Haldia1 and Kandla2 refinery sites in India; reported by Som (1997), has been analysed to quantify the group efficiency. The results as obtained are compared with experimental study on 2, 3 and 4 stone column groups at different spacing-diameter ratios in soft clay3 reported by Rao et al (1997) to validate the above analysis. A unique relationship between the column spacing and group efficiency has been obtained."

Jan 1, 2015

By Chandramohan P. V., Ravi Kishore

"An underground reservoir was to be constructed at Doha in Qatar. Simsima lime stone is present at the bottom. When the reservoir is empty, there will be uplift at the bottom but this will change to downward load when it is full. The rock at the bottom had high bearing capacity to resist downward load. But uplift had to be resisted by piles or anchors. The reservoir has a size of 120mx80m. Shrinkage and creep of concrete coupled with thermal contraction imposed a horizontal movement of 26mm on the extreme piles. So, piles have to accommodate this as well. This unique situation needed a unique solution. The solution was to provide piles with flexible high tensile strands to take tension. An annular space near the head of the pile would facilitate horizontal movement as well. Compression load was directly passed on to the raft bearing on rock.INTRODUCTIONAn underground reservoir for storage of drinking water was to be constructed at Doha, Qatar. The reservoir was proposed to have a plan size of 120m x 80m. Clear height inside the reservoir was proposed as 17.2m, from the bottom of roof to the top of bottom raft. Overall height of the reservoir at the outlet from the top of the roof to the bottom of raft was to be 21.2m. For the sake of inspection and in order to prevent pollution from the surroundings a gallery was planned around the reservoir. This could accommodate pipelines as well. This gallery was 3.0m wide on three sides and 8.4m wide on the outlet side.The gallery had removable gratings as cover in order to facilitate maintenance. Capacity of the reservoirwas proposed to be 40million gallons. The reservoir is divided into four compartments with baffle walls in each one for water circulation. Roof of the reservoir is kept at 300mm above ground level. There are two levels of car park on top of the reservoir. Top of the reservoir roof is at +14.35. Bottom varies from - 6.68 to -7.08. Lowest water table is at +6.00. Concrete structure of the reservoir was designed by a local consultant. The Navayuga Engineering Company was entrusted with the construction. Please see Figs 1 and 2."

Jan 1, 2017

By Aditya Ayithi, William G. Ryan, Dean Herbst

"For rock socketed drilled shafts, it is a common practice not to include the frictional resistance of overburden soils into the nominal capacity estimation. The primary reason often being cited is “overburden soils resistance is negligible compared to that of rock socket resistance.” However, in certain geological conditions, where the rock layer is located at greater depths, friction resistance from overburden layers can be significant. In addition, at such great depths, shaft drilling becomes very complicated and expensive. In these situations, considering the resistance of the overburden layers can be an economic alternative.This paper presents a case study of an Osterberg cell (O-cell) load test conducted on a 161.8 feet long and 78-inch diameter instrumented test shaft. Based on initial designs, a 72-inch diameter rock socket of lengths 23 and 26 feet was required to provide a LRFD factored friction resistance of 3,200 kips. The load test results revealed that the material in the 72-inch diameter socket does not represent a true rock. However, the test results also proved that the factored friction resistance of overburden layers is greater than the required design resistance. Based on the load test results, it was decided to allow the overburden soils frictional resistance to be considered in the shaft design, resulting in significant economic savings.INTRODUCTIONRock socketed drill shaft design guidelines of various State Department of Transportation (DOTs) agencies allow friction and/or end bearing resistance of only the rock socket portion into the design capacity estimation. It is typical to neglect the frictional resistance of overburden soils. However, in certain geological conditions where the rock layer is at greater depths, friction resistance of the overburden soils can be significant. In this case the friction resistance of overburden soils was verified via the specified instrumented O-cell test program and then used as part of the design capacity.PROJECT DESCRIPTIONAs part of I-29 improvement project, Iowa Department of Transportation (Iowa DOT) planned to replace the dual four lane bridges that cross the Floyd River in Sioux City, Iowa with dual six lane bridges (Fig. 1). Expected benefits from this improvement include improved safety, traffic operations and roadway infrastructure conditions.BRIDGE SUBSTRUCTUREThe project consists of two individual bridges; a new south bound bridge and a new north bound bridge. The south bound bridge is 646-ft long and the north bound bridge is 644-ft long. Both are six-span, pretensioned and pre-stressed concrete beam bridges of varying width. Bridge foundations were designed such that the abutments of both bridges will be supported on driven steel piles and the bridge piers will be on drilled shaft foundations."

Jan 1, 2016

By Alessandro Bertero, Stefano Valagussa, Filippo Maria, Wesley Schmutzler, Leoni

"Abstract The Deep Mixing Method (DMM) represents a viable solution to improve the adverse geotechnical properties of foundation soils. Differences and the importance of performing pre-construction laboratory and field tests will be highlighted. Comparative analyses and interpretations between the various lab and field stages, along with accumulated information about soil properties and QC results, allowed fine-tuning of the production parameters throughout almost the entire project.Two projects where the US Army Corps of Engineers selected the Deep Mixing Method (DMM) for the required stabilizations, and a third project completed in Italy, will be illustrated:•,?the LPV 111 Project (New Orleans - LA – USA); DMM was used for groundimprovement/foundation strengthening and consequently stabilize and support the burden of the new levee.•,the Rio Puerto Nuevo Project (San Juan - PR - USA); DMM was applied to improve the soils adjacent to a 90” forced sewer main relocation and to improve the soils for the base of a new drainage channel•,the new Italian high speed railway project (Florence Italy); DMM technology was applied to realize a a TBM break in/break out, foreseen originally by jet-grouting.IntroductionThe Deep Mixing Method (DMM) represents a viable solution to improve the adverse geotechnical properties of foundation soils. The effectiveness of working parameters depends largely on the physical and mechanical properties of the soil to be treated. Therefore, well designed laboratory and field test programs, aimed to disclose the interaction between the site-specific soils and the mixing parameters, are essential to achieve the desired end product."

Jan 1, 2014

By Greg Plutko

Laboratory testing has shown that the Marsh Funnel test can be significantly impacted by long-chain polymer entanglement. In general, shorter hydration time leads to more chain entanglement which in-turn, leads to higher marsh funnel values that values seen for longer mixing. This trend makes it very difficult to predict funnel-viscosity on successive days. Data is presented which helps to explain this chain interaction effect on Marsh Funnel data and how it differs from traditional Fann viscosity. The data suggest that this long-chain polymer entanglement occurs more in samples with less hydration time and decreases as hydration time increases. There is also suggestion that higher polymer concentrations have a greater drop-off in marsh funnel viscosity for a given aging length than do lower solids slurries. Fann rheology was shown to be much less impacted by the hydration time of the PHPA polymers than was Marsh Funnel viscosity. This suggests that the Marsh Funnel viscosity is impacted by some aspect of the slurry that does not affect Fann rheology as strongly. It is known from literature that longer-chained polymers have more potential to entangle and our data support the theory that the Marsh funnel viscosity is greatly impacted by this polymer-chain ‘roping’ entanglement.

By Adam Gerondale, David Hemstreet, Lisheng Shao, Kenji Yamasaki

"Foundation soils of a proposed single-span bridge over a busy railroad in Anchorage, Alaska included a layer of sensitive, non-plastic to low-plasticity silt. Slope stability analyses showed that, without ground improvement, the proposed abutments would not be stable immediately following the design earthquake due to the liquefaction of the sensitive silt. Wet soil mixing was selected to mitigate the liquefiable soils and assure abutment stability because: (i) it is a non-vibratory method and can be used for areas adjacent to the railroad tracks and underground utilities, as well as in areas not sensitive to vibration; and (ii) preand post-ground improvement testing, such as SPT or CPT, is not required. Eliminating the liquefaction hazard at the site also allowed for the abutments to be economically supported on shallow spread footings. A total of 511 soil-cement columns were constructed at the two abutments, each with a diameter of 8 feet (2.4 m) and an average length of 20 feet (6.1 m), extending from about 30 to 10 feet (9.1 to 3.0 m) below finished ground elevation. The columns were laid out in a shear wall pattern (in the longitudinal direction of the bridge) to increase stability under the loading by approach embankments.INTRODUCTIONAlaska Department of Transportation and Public Facilities (Alaska DOT&PF) is currently constructing West Dowling Road Overcrossing in Anchorage Alaska. It will be a single-span, steel box girder bridge approximately 200 feet (61 m) long and 100 feet (30 m) wide. It will have approach embankments, about 40 feet (12 m) high, on both sides. It will carry the new extension of West Dowling Road over double tracks of Alaska Railroad and Arctic Blvd. Foundation soils of the abutments consist of surficial fill and peat layer underlain by soft silt which is likely to liquefy and lose strength under shaking by a design earthquake. Both deep and shallow foundations were considered to support the bridge abutments. The design team pursued the option of improving the foundation soils and using shallow footings. Several ground improvement methods were evaluated, out of which wet soil mixing was selected as the best option.In situ wet soil mixing (hereinafter simply soil mixing) is mechanical mixing of soil in its location with cement slurry and produces soil-cement (soilcrete) columns that are stronger, less permeable, and less compressible than the original soil. Soil mixing is used for various applications including reinforcement of soft soils, excavation support, liquefaction mitigation, cutoff walls, etc. This paper presents a case history of soil mixing successfully used to improve foundation soils of bridge abutments to allow the use of spread footings."

Jan 1, 2015

By Thomas Domanski

Any type of deep excavation whether for Bored Piling, Diaphragm Walls or Contiguous Bored Piling Walls depends on forming a stable borehole with a defined cross-section to receive safely the permanent materials. In modern construction the excavation depth can reach well the range of 100 m and above. The diameters of the Piles reach often sizes of 2.5 m and bigger. Top casings in Bored Piles (Diaphragm Wall none) are rather short and stability below the casing, need to be secured by stabilization slurry. The boreholes need to be formed through a variety of different materials and stand open for an extended period. Without a safe stable borehole, it is impossible to produce quality products and work cost-efficient. The understanding and proper usage of a suitable slurry is a key element essential for the delivery of Foundation Elements with high quality and within a reasonable budget. The setting of mechanical and rheological parameters in specifications is necessary and helpful, but probably insufficient to embrace and control such a key element in the practical implementation of foundation construction. The proper selection, design, implementation and supervision of slurries on site requires both from Contractors and Engineers to understand how different slurries do function. Only with this knowledge the right decisions in slurry operations can be made. This talk is directed to give some help to both, Contractor’s and Engineer’s, in understanding how different type of slurries do work. (Which ones should be preferred in what kind of soils.) The better knowledge will help the Contractor to control cost and enhance production. The Engineer will be able to assist in arriving at the appropriate technical choices and include in the specifications.

Sep 1, 2022

By WenJun Dong

This paper presents the stability assessment of the steel pipe piles that are used to support a deadman beam to anchor an adjacent bulkhead wall. Finite element analyses are performed to assess the stability of the bulkhead wall and determine the required tie-back force to the pile. The piles are relatively close to the bulkhead wall such that their soil resistance wedge zones are not fully developed but truncated by the bulkhead wall. The reduced lateral resistance capacity of the anchor piles is determined by applying the Coulomb wedge method on the truncated soil passive zones between the pile and wall. Both the conventional soldier pile stability (in terms of force and moment equilibrium) and Winkler soil spring (for soil-pile-interaction) analyses are used to assess the stability of the anchor piles.

Sep 8, 2021

By Harry Schnabel, Mitchell L. Fong, Douglas R. Jenevein, Thomas S. Lee

"The Warm Springs Extension (WSX) is one of a series of projects that will eventually extend the Bay Area Rapid Transit System (BART) from Fremont to San Jose, California. A cut and cover tunnel was used for a portion of the extension that runs through Fremont Central Park to minimize the impacts that an at-grade railway would have on the Park. A cement deep soil mix (CDSM) wall was selected by the engineer as the preferred method of providing structural support and groundwater cut-off for a portion of the tunnel where it passes through an important aquifer and near Lake Elizabeth. In addition to the CDSM wall, a jet grout plug was constructed at the base of the tunnel to provide a complete groundwater cut-off.This paper will discuss the unique quality assurance and quality control measures taken for the soil mix wall and jet grout plug as well as the methods used to repair leaks and mitigate water seepage through the exposed wall and grout plug.PROJECT DESCRIPTIONThe Bay Area Rapid Transit (BART) Warm Springs Extension (WSX) project is located south of the existing Fremont BART station extending 8.9-km (5.4 miles) to Warm Springs District in Fremont, California. The WSX project has been divided into two contracts with different delivery methods. In order to minimize impacts to Fremont Central Park, a subway was selected at this portion of the alignment under a conventional design/bid/build contract.The Fremont Central Park Subway (FCPS) which begins on the south side of Walnut Ave and ends just north of Paseo Padre Parkway and is about 2.3-km (1.4 miles) long. Fig. 1 shows the entire WSX and the FCPS project. The FCPS contract consists of a cut-and-cover subway box, subway transition structures, ventilation structures and a section of which transverses Lake Elizabeth (a man-made lake). The geologic conditions consist of fill (sand, silt, clay and construction debris), Young Alluvium (clay and silt), Basin Deposits (clay, silt, and sand), and Older Alluvium (sand and gravel) as shown in Fig. 2.HYDROGEOLOGY OF THE PROJECT SITEThe FCPS is dominated by two geologic features - the Hayward Fault and the Above Hayward Fault (AHF) aquifer. The AHF aquifer provides a significant source and storage of water for the local water district. The underground subway will penetrate this aquifer and is up to 11m (36 ft) below the groundwater table. No groundwater was allowed to be pumped during construction of the subway box by Alameda County Water District (ACWD). To facilitate excavation for the subway box, temporary cut-off walls and a grout plug were designed to retain and resist high differential hydraulic pressure. The following section describes the selection of a deep soil mixing method for water cutoff. Design of the grout plug has been described in Lee, et al., 2011 and Fong and Lee, 2009, and is not the focus of this paper."

Jan 1, 2015

By Jeffrey C. Evans, Daniel G. Ruffing, Hejintao Huang

Soil-bentonite slurry trench cutoff walls are the most common type of vertical cutoff wall used in the US for seepage control and for passive control of contaminant migration at environmental sites. Design considerations are often limited to constructability considerations and a target hydraulic conductivity. With design-build contracts common, the backfill design is often left to the contractor. As a barrier soil, the hydraulic conductivity of bentonite slurry wall backfill is typically required to be equal to or below 1x10-7cm/s. The importance of stress state upon the hydraulic conductivity as well as the expected stresses are both established in the literature. Grain size distribution of the base soil and bentonite content both affect compressibility and hydraulic conductivity. This paper describes the results of studies undertaken to evaluate the interrelationships between compressibility, hydraulic conductivity, grain size distribution, and bentonite content. Three base soils were used representing a range of soils found on typical construction projects. Using these base soils, mixtures containing a range of dry bentonite contents from 0% to 5% were prepared to a slump consistent with field practice. The compressibility and hydraulic conductivity were measured in consolidometers adapted for falling head permeability tests at the end of each load increment. These experiments yielded the relationship between effective stress and hydraulic conductivity as well as consolidation characteristics including time rate of consolidation and coefficients of compressibility. The experimental results are then used to indirectly evaluate stress development and to assess the time needed for consolidation. The findings show a substantial decrease in hydraulic conductivity as effective stress increases, regardless of base soil type and dry bentonite content, a relative insensitivity of stress development to backfill compressibility, and a wide range of values for coefficient of consolidation depending upon backfill mixture and stress level.

Jan 1, 2016

By Steve Davidow, Scott Tunison

As the demand for electric power grows and generation facilities are constructed in more remote areas, the industry faces an increasing number of foundation construction challenges. The importance of quality geotechnical information prior to construction is accentuated by the linear nature of the projects and the potential for drastic changes from one end to the other, but is often difficult or unfeasible to obtain. Alignments are crossing remote, rugged and/or environmentally protected terrain, and completing a comprehensive geotechnical program is made challenging from an access or economic standpoint, or both. In these situations, the industry needs a flexible foundation alternative. This paper will present micropiles as that alternative and demonstrate how the implementation of micropile foundations mitigated these challenges on the Koolau-Wailupe 46 kV Circuits in Oahu, Hawaii, which involved rugged, steep slopes and helicopter construction methods. It will detail the selection of micropiles over other foundation options, micropile and steel pile cap design methodologies, foundation construction, and quality control. Special attention will be given to the unique geology in the area, and why precise identification of saprolite and basalt layers was integral to the successful performance of the foundations. The intention is to communicate the benefits of a flexible solution based on continuous collaboration between design and construction.

By Siavash Mahvelati, Alireza Kordjazi, Joseph Thomas Coe

Deep foundations are often constructed as end bearing members with a significant amount of their capacity derived from bedrock. Sites with highly variable bedrock conditions therefore present a unique challenge when attempting to estimate the design elevation of deep foundations. Typical subsurface characterization techniques such as drilling, standard penetration testing (SPT), and cone-penetration testing (CPT) may fail to adequately establish top-of-rock elevation in geologic settings prone to karst and/or significant amounts of residuum, saprolite, and deformed bedrock. Seismic surface wave geophysical methods have been increasingly used to map bedrock topography in such settings. However, the current standard of practice for these methods introduces resolution limitations in spatially variable subsurface conditions due to averaging effects from the analytical framework used to process the acquired data. This study explores the use of a tomographic approach with full waveform inversion (FWI) to map top-of-rock elevations at a numerically simulated site representative of highly variable bedrock topography. Comparisons are made with seismic refraction (SR) and a dispersion-based multichannel analysis of surface waves (MASW) approach as more commonly used in geophysical subsurface investigations. The results highlight that FWI provides a superior estimate of top-of-rock topography than SR and MASW at a cost of a significant increase in the required computational resources and time.

Sep 8, 2021

By Siavash Mahvelati, Alireza Kordjazi, Joseph Thomas Coe

Deep foundations are often constructed as end bearing members with a significant amount of their capacity derived from bedrock. Sites with highly variable bedrock conditions therefore present a unique challenge when attempting to estimate the design elevation of deep foundations. Typical subsurface characterization techniques such as drilling, standard penetration testing (SPT), and cone-penetration testing (CPT) may fail to adequately establish top-of-rock elevation in geologic settings prone to karst and/or significant amounts of residuum, saprolite, and deformed bedrock. Seismic surface wave geophysical methods have been increasingly used to map bedrock topography in such settings. However, the current standard of practice for these methods introduces resolution limitations in spatially variable subsurface conditions due to averaging effects from the analytical framework used to process the acquired data. This study explores the use of a tomographic approach with full waveform inversion (FWI) to map top-of-rock elevations at a numerically simulated site representative of highly variable bedrock topography. Comparisons are made with seismic refraction (SR) and a dispersion-based multichannel analysis of surface waves (MASW) approach as more commonly used in geophysical subsurface investigations. The results highlight that FWI provides a superior estimate of top-of-rock topography than SR and MASW at a cost of a significant increase in the required computational resources and time.

Oct 1, 2021

By Eric S. Lindquist

Two microtunnel access shafts were constructed using the Cutter Soil Mixing (CSM) method in the San Joaquin Delta region of California, east of San Francisco. Unlike conventional slurry walls and diaphragm walls that utilize concrete, soil mixing relies on blending the soils in situ with a cement slurry to create a soil-cement wall. Cutter Soil Mixing technology utilizes two sets of vertically mounted cutting wheels rotating about a horizontal axis to produce rectangular panels of treated soil. Overlapping of the soil mixed panels enabled the construction of two circular shafts. CSM panels were constructed to a depth of 29 m (95 ft) for the microtunnel jacking shaft and to a depth of 19 m (63 ft) for the microtunnel receiving shaft. The site presented several challenges, including the high depth of treatment, the variable nature of the alluvial soils, and the high water table. This paper describes the CSM technique and presents the design, construction, quality control measures and advantages of using this method for this project.

Jan 1, 2010

By Ronaldo Luna, Donald Deardorff

"The use of load and resistance factor design (LRFD) is well documented since the 1960s for structural applications when it was first adopted into the American Concrete Institute Building Code in 1963 and was established for geotechnical applications by the Danish Geotechnical Institute about the same time under the name of Limit State Design (LSD).The Federal Highway Administration required all federally funded projects to use the LRFD method by 2007. Due to this funding requirement, recent LRFD research for geotechnical applications has focused on common bridge foundations (i.e., driven or drilled shafts), resulting in good documentation for design using these methods. Unfortunately, the practicing geotechnical engineer does not intuitively know how to create resistance factors for deep foundations systems that have design methodologies and installation techniques significantly different from driven or drilled shaft foundation systems.Helical anchors typically use semiempirical methods for preliminary capacity design and a torque correlation methodology during installation to verify required capacity. Here we provide basic information on the LRFD methodology for helical anchor design. Additionally, the First- Order Second Moment (FOSM) method is applied to a previous helical anchor study (Hoyt and Clemence 1989) to determine resistance factors for an ultimate tension capacity strength limit state.MethodologyThe concept of the LRFD method is to establish factors for both the load and resistance that account for uncertainties using probability theory. The factors increase the nominal load and/or decrease the nominal resistance such that the probability of failure is an acceptable value. LRFD also accounts for the effects of load combinations (dead, live, seismic, wind, etc.) by determining the probability of the combined occurrence. The general form of the LRFD equation used by American Association of State Highway and Transportation Officials (AASHTO) is:"

Jan 1, 2009

By Thomas Billups, Brendan FitzPatrick, Doug LeDo, David Carchedi

"Working in urban environments presents unique logistical challenges beyond those typically associated with traditional geotechnical analysis and design. These challenges often include working on sites with limited access and laydown area, vibration concerns for adjacent structures and the need to work from variable elevations or within excavations. This paper describes the use of the modular Ductile Iron Pile system, a low-vibration driven micropile, on two urban projects on the Johnson & Wales University campus in Providence, Rhode Island. The paper describes the successful implementation of Ductile Iron Piles installed to develop capacity in end-bearing on one site and friction on the second site. Design, installation and quality control operations are all presented as well as the results of full-scale load testing performed on non-production test piles. This paper is of importance to the industry because it describes a versatile option for project teams as an alternative to traditional micropiles, helical piles or other deep foundation systems for urban sites.INTRODUCTIONWorking in urban environments presents unique logistical challenges beyond those typically associated with traditional geotechnical analysis and design. These challenges often include working on sites with limited access and laydown area, vibration concerns for adjacent structures and the need to work from variable elevations or within excavations. Two recent projects in downtown Providence, Rhode Island faced a combination of problematic soil conditions and urban construction challenges including vibration concerns. Both projects were a part of the Johnson and Wales University campus development. Figure 1 illustrates the urban locations of the sites."

Jan 1, 2016

By Martin D. Larisch

The construction of diaphragm walls and most large-diameter bored piles (piers) is often carried out under drilling support fluids to temporarily stabilise the excavation prior to concrete placement. In most cases such fluids are either mineral-based slurries (bentonite) or polymer support fluids. The working mechanisms of these two fluid types are fundamentally different. Designers need to consider possible fluid-related impacts on the permanent design performance of the project-specific deep foundations as well as for the temporary excavation stage during construction. Robust design methods for bentonite slurry-supported excavations have been developed in the last few decades and the working principles and associated risks of such mineral-based slurries are understood reasonably well. However, such meth-ods have not been developed in detail for polymer-based drilling fluids. This document provides a brief overview of the main characteristics of bentonite- and polymer-based drilling fluids as a guide for construction practitioners and design engineers alike. The paper also high-lights some common construction risks related to casing installation and the selection of suitable fluid systems for different ground conditions. Typical defects caused by the incorrect application of drilling support fluids, and their pro-active mitigation, are discussed, too. In addition, the basic concepts of sta-bility calculations for bentonite fluid-supported deep excavations are briefly introduced and their ap-plicability for other fluid types such as polymer-based support fluids or water are reviewed.

Nov 1, 2022