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By Nagarajan. D, Raja Rajan. K, Vijayakumar. T

Major bridges crossing mighty rivers must be constructed in flowing water. Constructing the sub-structure in water has been a challenging job for contractor. Special construction techniques with marine fleets to be adopted for waterfront construction. Enabling works like temporary piling platform and cofferdam used for pile and pile cap construction. Apart from this, enabling works like load out jetty to transport the materials from land to water; temporary walkway for access of workman to work location; temporary access bridge for construction vehicles movement; temporary liners for tower crane foundation; Concrete block to act as dead man anchor for barge movements were all required by the contractor for smooth functioning of site as per construction schedule. Investment in enabling works by contractor plays a significant role on profit margin of the project and of course with utmost safety. Design of enabling works for waterfront structures involves hydrological data like afflux, bathymetry survey, current force, scour depth and wave force to be taken cautiously for safe and economic design. Type of foundation and pile/well cap top level corresponding to water levels shall influence the construction scheme. Usage of geotechnical software like Wallap and Plaxis required for enabling work design to enhance the safety of the structure. Bathymetry and soil condition play a critical role in design and construction of enabling works. Water Discharge quantity in river along with water levels like low water level, high flood level, seasonal fluctuation of water levels has a great impact on design of enabling works. Establishing enabling works for waterfront construction near to an existing bridge is an additional challenge for the contractor. Along with design, constructing the enabling works in water requires special construction methodology and sequence of work. This paper shall provide insights on overview of design and construction of enabling works for waterfront construction.

Nov 1, 2022

By Kevin Green, Iván Contreras, Aaron Grosser, Jon Ausdemore, Rachel Leier, Amr Ragy

"Construction of a new tailings dam was required to increase tailings storage capacity at a trona mine near Green River, Wyoming. The new dam was founded on overburden soils underlain by both fractured and competent bedrock. The stored tailings and water had high salt content, resulting in salty seepage water. To reduce the impact of the salty water on groundwater and the Green River, the design of the new tailings dam included a 257,260 SF (23,900 m2) seepage cutoff extending into competent rock.An extensive subsurface characterization was performed prior to completing the design and suitable seepage cutoff methods were evaluated. The approach selected was a full replacement panel using hydromill and clamshell for construction and self-hardening slurry (SHS) for the wall material. Laboratory testing was performed and ongoing monitoring has continued to evaluate the hydraulic conductivity and seepage cutoff performance in the briny environment.The paper includes project background, the collaborative approach and outcomes of the QA/QC program, and the monitoring results for the seepage cutoff wall.PROJECT BACKGROUNDCiner Wyoming, LLC (formerly OCI Wyoming, LLC) owns and operates the Big Island Mine facility near Green River, Wyoming. This underground trona mine has produced soda ash since 1962. The Greater Green River Basin covers much of southwestern Wyoming and extends into northeastern Utah and northwestern Colorado. The Ciner facility is located in the Green River Basin, which is part of the Wyoming Basin physiographic province. The Green River runs to the west and the south of the Ciner facility.Beginning in the early 1990s, Ciner primarily disposed tailings underground in mined-out panels. However, in recent years, underground storage has become limited and some disposal has transitioned to the ground surface. Long-term planning revealed a need to expand Ciner’s surface tailings disposal capabilities. Pond 2, a previously permitted disposal area, was identified as the most viable location for a storage facility. The Pond 2 site is directly north of the Ciner plant facilities, northwest of the active Upper Delta tailings storage facility, and northeast of the Green River (Fig 1)."

Jan 1, 2016

By Sailesh S. Author

The current design method for soil-cement (SC) columns improved soft clayey ground under the highway embankments assumes a slip circle failure surface shearing through the columns and the soils using a weighted average shear strength. However, the results from the laboratory centrifuge model test and numerical analysis indicate that in many cases, the SC columns fail by bending. Some researchers have proposed methods for estimating the maximum embankment loading for bending failure of SC columns, but those methods have limitations in correctly considering the internal shear stresses or not applicable for the group SC column improvement. Numerous model embankments on SC columns have been simulated by three-dimensional (3D) finite element analysis (FEA) and the mechanism of bending failure and the magnitude of the bending moment in the SC columns under embankment load has been investigated. Based on the simulated results, the design method for the estimation of the bending failure of floating SC columns has been proposed. The predicted results from the proposed method agreed with the existing field condition of one embankment in Saga, Japan reported in the literature in terms of the stability of columns. Hence the proposed method can be used for the design of floating SC columns in the soft ground.

By Ali Ebrahimi, Jeremy M. Gasser, Cuneyt Gokmen, Paul J. Sabatini, Roneet Das, William Tanner, Amir Ahmadipur

There are safety concerns related to operation of heavy equipment over coal combustion residual (CCR) impoundments during construction of the impoundment closure programs. As part of a pilot study prior to a full-scale closure construction, an access pathway and working platform were designed and constructed to facilitate equipment access for construction of deep soil mixing (DSM) zones on the ash delta of a CCR impoundment. The access pathway and working platform was constructed using shallow mass mixing with cement at the CCR surface to address safety concerns related to the geotechnical behavior of CCR. This paper describes the data from the instrumentation system which was implemented to monitor the geotechnical performance of the CCR during the pilot study. The instrumentation system included monitoring of the ground movement, vibration, and porewater pressure within the ash delta of the CCR impoundment during a pre-construction load testing, equipment mobilization over the access pathway, and DSM column installation over the working platform. INTRODUCTION A deep soil mixing (DSM) pilot study was conducted at a coal combustion residual (CCR) surface impoundment to evaluate mix designs and construction techniques for the regulatory closure. The DSM columns will create a wall which will separate and retain the CCR in a consolidated footprint separate from the closure by removal portion of the footprint and provide a barrier between the two areas of the surface impoundment. Historically, the surface impoundment received CCRs including fly ash, bottom ash, boiler slag, and gypsum, along with other byproducts produced from flue gas desulfurization (FGD). The predominant CCR in this impoundment were fly ash and bottom ash. The primary goals of the DSM pilot study were to assess the mix design strengths and to evaluate DSM construction techniques that could reach the design mixing depths of up to 90 ft. The DSM test columns were installed on the CCR delta approximately 500 ft from the nearest impoundment dikes. Another objective of the pilot study was to develop, construct, and monitor an access pathway for safe passage and movement of construction equipment on the CCR delta.

Jan 1, 2019

By Arash Khosravifar, Ali N. Ibrahim

"Large areas of Iraq are covered with collapsible soils namely gypsiferous soil which is often used as the foundation soil for structures. In particular, the Mosul Dam foundation is comprised of high contents of gypsiferous soils. Intrusion of water through the foundation soil dissolves gypsum which acts as the binding material between soil particles. This phenomenon results in the formation of collapsible soils which can cause serious damages to the dam structure. The failure of Mosul Dam, with a reservoir as large as 11 billion cubic meter of water, can be catastrophic. In the past, Mosul Dam Authorities have been remediating the soil foundation by injecting cement mortar. This method has been proved not economic; therefore, new, more efficient, methods are desperately needed.This research study focuses on finding practical methods to remediate collapsibility of gypsiferous soils by improving their geotechnical properties. This study presents remediation of collapsible gypsum-rich soil by grouting. Three types of stabilizer materials were used to make the grout; (1) sodium silicate (Na2 O3 Si) which is a well-known chemical soil stabilizer, (2) bentonite slurry, and (3) silicone oil. The purpose for using these stabilizer materials is to provide an impermeable layer (waterproofing coat) around the gypsiferous soil particles and to fill the voids that may occur in the soil as a result of gypsum dissolution when subjected to water.A series of double oedometer (collapse) tests and direct shear tests were carried out on gypsiferous soils before and after remediation by grouting. The results show that the soil compressibility decreases in the grout-treated gypsiferous soil by reducing volumetric strain. Consequently, the potential for collapsibility decreases too. It was also shown that grouting, increases the shear strength of the soil at confining stresses smaller than 250 kPa by increasing the cohesion combined with a slight reduction in the internal friction angle.INTRODUCTIONGrouting is one of the ground improvement techniques which is often used to improve the loose foundation soils. Bruce (2003) provides step-by-step procedures on using grouting techniques for sealing dams and other water reservoirs. Grouting can be classified as permeation grouting, compaction grouting or hydraulic fracturing. Permeation grouting is an effective way to send the grout into the ground without disturbing the soil structure, i.e. free flow of grout into the soil voids where grouting is accomplished by injection of a fluid-like material that is capable of forming a gel and binding the soil particles together. Grout materials may be solution grouts or suspension grouts. The permeation grouting technique is generally used to minimize ground permeability and to control ground water flow, but it can also be used to strengthen and harden the ground (Raman et al., 2012)."

Jan 1, 2017

By Amr M. Sallam

A case history of utilizing a mat foundation enhanced with ?settlement-control? piles to support a high-rise building in Downtown Orlando is presented. Original geotechnical engineering studies, performed by others, recommended pile foundations due to difficult soil conditions and highly variable loads. The value engineering study performed by the authors provided alternative foundation system of the mat foundation enhanced by ?settlement-control? piles. The alternative foundation system required few iterations of structural and geotechnical analysis. A target stiffness for the settlement-control piles was selected by the structural engineer. Pile load tests were performed to verify the recommended pile geometry. A total of 81 auger-cast-in-place settlement-control piles 45-foot long 16-inch diameter were installed. A total of 24 columns were monitored for settlement, which showed substantially less settlement than predicted. It is the authors? opinion that the ?settlement-control? piles increased the mat stiffness, relieved the concentration of contact pressures around heavily loaded columns, and reduced potential differential settlement. Mat foundation with settlement-control piles provided border-line foundation solution between shallow and deep foundations and has the potential to be widely used in Central Florida for similar subsoil and loading conditions; however a thorough analysis using three dimensional Finite Element Modeling may be needed to refine the geotechnical evaluations.

Jan 1, 2009

By Silas C. Nichols, Jennifer E. Nicks

"Limit states design (LSD), or load and resistance factor design (LRFD), is a method to account for the uncertainty in loads and resistance through a reliability calibration that requires all applicable limit states (strength, service and extreme) to be checked during foundation design. LRFD has been in use internationally for several decades; however it wasn’t until recently that engineers working on highway projects were required to use the method for the design of highway bridges and other appurtenances. Although the bridge community has been using a form of limit states design for structural components since the early 1970s, the design of foundations for bridges, walls and other geotechnical features had long been performed using allowable stress design (ASD), whereby all uncertainty in loads and material resistance is combined in a single factor of safety. While the move to LRFD was viewed as a more rational approach for the design of bridges and structures, the transition to its use for geotechnical engineering has been met by many with confusion and difficulties in application. This article will revisit the history of transition from ASD to LRFD for geotechnical engineering, summarize the status of the transition and issues with its use, and briefly discuss some emerging research opportunities for improving and advancing the design platform.Background and HistoryUntil about a decade ago, foundations and substructures for bridges were traditionally designed using ASD, while the superstructure was designed using load factor design (LFD), a precursor to LRFD that incorporated factored design loads but no risk assessment. This combination led to uncertain and incompatible safety margins in design for the various bridge components. In 1986, the American Association of State Highway Transportation Officials (AASHTO) Subcommittee on Bridges and Structures (SCOBS) concluded that the standard bridge specifications in use at the time for U.S. transportation projects had significant inconsistencies and gaps, wasn’t up to date with emerging technology and that the development of new specifications was warranted. The proposed solution by the subcommittee was to transition to a more coherent method of design where applicable failure and serviceability conditions could be evaluated considering the uncertainties associated with loads and resistance."

Jan 1, 2015

By Jeffrey C. Schuh, Logan Bloemer, Daniel P. Dietzler

Over the past 30 years, the authors have encountered numerous projects where recognizing the geology, soil properties and groundwater conditions, and considering alternative construction techniques have promoted efficient and cost-saving construction. The construction documents for these projects, produced by various engineering firms, provided basic information on geotechnical conditions. The authors became involved in each project either because there was a problem during design or construction or, as a contractor, won the project because they saw a value engineering opportunity to take advantage of the geologic setting of the project to design and build alternatives to what the designer depicted. Understanding the geologic setting is critical before planning and designing begins. Being able to work with the geology and the materials on site is preferred before specifying more costly and complex solutions, which often require the importing of materials and adherence to unnecessary and/or inappropriate specifications. Failing to understand the geology or not knowing all the techniques available for construction can lead designers to develop solutions that could be inappropriate. This paper presents several examples of value engineering and project performance enhancements developed through knowledge of basic soil mechanics and implementing innovative solutions. History and Background Most people attend DFI meetings, present their experiences, listen to others, and read articles and papers with the hope they can learn from others. Geotechnical engineers and contractors often interface with others in the execution of projects who have, at best, a rudimentary knowledge of geology and soil mechanics. Of course, there is a need for architects, bankers, and regulators, etc., but they typically do not have much interest in the nuances of geotechnical engineering, which relies on both art and science. Thus, significant time is spent educating counterparts in the need for comprehensive subsurface investigation programs and the intricacies of construction in the “dirt,” as they typically refer to soil and rock.

Jan 1, 2019

By Mohini Patel, Jahnavi Parmar, Pranav R. T Peddinti

Expansive clays pose a variety of geotechnical problems. Although the admixture stabilization is proven to address their problematic swelling and shrinkage characteristics, the influence of unsaturated condition on the engineering performance of these soils needs further research attention. In addition, highly saline soils with high organic content would further alter their performance. A similar soil stratum was encountered at the Gulf of Cambay, Bhavnagar district, India. High salinity in the in-situ expansive soil of basaltic origin and the prevailing unsaturated condition, enforces the engineers to look out for possible soil treatment methods. In this regard, the present work attempts to analyze the unsaturated behaviour of this soil when fly ash is used as an admixture. A comparative study for stabilized and unstabilized mixes is performed in terms of their unconfined compressive strength, electrical conductivity, swell characteristics and California Bearing Ratio.

May 1, 2022

By Richard Schmidt, Lijun Deng, Mohamed Abdelaziz, Weidong Li

Helical piles are widely used as a foundation supporting a variety of different structures. Understanding the axial behaviour of helical piles is required to confirm the engineering design. Helical pile research is often conducted in the field, but this method can be prohibitively expensive in some cases. Geotechnical centrifuge modeling offers an alternative method for the helical pile research and practice. A series of axial load tests of helical piles installed into cohesive soils were conducted on the geotechnical centrifuge at the University of Alberta. The objective was to investigate the effects of inter-helix spacing and soil strength on the axial behaviour of helical piles. Four types of aluminum model helical piles including one single-helix pile and three double-helix piles with various inter-helix spacing ratios were tested. Both compressive and tensile loading tests were conducted. All model piles were instrumented with multiple strain gauge stations. The clay had an undrained shear strength of approximately 50 kPa and 120 kPa. The test results indicate that there is a transitional failure mode between the two widely recognized failure modes, i.e., individual plate bearing and cylindrical shearing. The shaft adhesion was significantly reduced by the helix. Axial capacities were comparable to the field test results.

By Jianhua Wang, Jianming Yao, Zhen Meng, Jinjian Chen

"Drilled screw pile is a newly developed displacement pile foundation which has been applied in soft clay for many years. Compared with traditional circular displacement pile, It is characterized by high bearing capacity, small volume and small squeezing effects. For the purpose of investigating the squeezing effects of drilled screw pile, a full scale field monitoring test with two test piles was performed. Detailed soil horizontal displacement and pore pressure measurements were conducted in the vicinity of the two drilled screw piles during penetration and subsequent soil consolidation. It can be concluded that the horizontal displacement of the surrounding soil induced by the installation of a drilled screw pile is mainly in a circular region with a diameter of 3 m (r/D<6), and the compaction effect outside the area can be essentially negligible; The excess pore pressures measured at the same time increase with depth throughout the entire process of consolidation, and its dissipation shows an exponential decay as a function of time.INTRODUCTIONA knowledge of the displacement and stress changes induced in the soil surrounding a pile is very important for evaluating pile performance. Numerous field and laboratory research projects have examined loading conditions, total soil stresses, and excess pore pressures during and following pile installation (Pestana et al., 2002). A relatively comprehensive and detailed review of these experimental works from 1948 to 2002 was presented by Pestana et al. (2002). More recently, Xu et al. (2006) conducted a field experiment to study displacements and stresses in the vicinity of two pipe piles during their installation in a soft lightly overconsolidated clay and compared the field measurements with existing predictive methods. Abdrabbo and Gaaver (2011) collected field observation data from four different construction sites to study soil disturbance during construction of piles using continuous flight auger (CFA). They have found that the disturbed zone of soil by CFA has a conical shape and the excess pore pressure has no appreciable influence on the load capacity of the piles.Drilled screw pile (DS pile) is a kind of vibration-free, cast-in-place concrete pile. Because of the excellent bearing performance, low level of vibration pollution and negligible spoil, as well as its fast construction speed, DS pile has been widely accepted by many engineers around the world. As a new type of drilled displacement pile, the significant installation effects of DS pile on the adjacent soil have not been systematically and integrally investigated yet. Since a proper numerical simulation of the real installation process of DS pile is difficult to achieve, the investigation based on field measurements is necessary. This paper presents a field investigation of the installation effects of two DS piles on surrounding soils. Detailed horizontal soil displacement and pore pressure measurements during pile installation and subsequent soil consolidation have been conducted. Based on the monitoring data, variation of horizontal displacements and dissipation of excess pore pressures with depth and time have been analyzed. What's more, the construction machinery and technology used in DS pile installation are also simply introduced."

Jan 1, 2015

By Luca Pingue, Regine Jagow-Klaff, Franco Muratore, Carlandrea Albonico, Damiano Frontini, Rudolf Wernecké

This paper describes an artificial ground freezing (AGF) application carried out to ensure both watertightness and structural support for the safe excavation of four cross passages of the Forrestfield Airport Link (FAL) project in Perth. The line will deliver 8.5 km extension of the existing urban rail network connecting the growing eastern suburbs of Perth with the existing suburban rail network. The proposed soil improvement technique is adopted as a smart alternative to jet grouting from the surface since the use of heavy equipment with long vertical mast was not allowed due to the line underpassing an airport in operation. In this paper, details of the challenges and lessons learned during both design and construction phases are given. Furthermore, it is described the geometry and the installation of freeze pipes in presence of a massive steel frame, ventilation system and slurry pipes of the tunnel boring machine (TBM) in operation. It is also illustrated the web monitoring system to allow key personnel to follow in real time the development of soil temperatures, tunnel convergences and ground surface deformations as well as changes in the interaction between international parties involved due to the COVID-19 pandemic.

May 1, 2022

By Marwa Nabil, Alaa A. Ata

"Recent developments in the analysis of piled rafts has incorporated the load sharing of the raft and the piles to support the superstructure. In the piled-raft system, piles are cast monolithically with the raft and the load is partly transmitted by the raft to the soil directly below it, and partly by the piles to more competent deep soil. While these piles are effective in increasing the bearing capacity and reducing the settlements, they often lead to significant straining actions at the pile head-raft connection which may constitute the weakest link. An attempt to provide a more economical solution, that at the same time overcomes this weak link, is to disconnect the pile heads from the raft and introduce an intermediate cushion of compacted fill. In this case, the piles are considered as reinforcement to the subsoil and will also act as settlement reducers. This paper investigates the load transfers mechanism of the unconnected piled raft with cushion using ABAQUS finite elements Program. The main objective is to provide an in depth analysis of the raft–soil–pile interactions in multi-layered soil under static and seismic loads. The investigated system provides an economical alternative for traditional connected piled raft foundation, where there is no need to reinforce the piles, no need for pile head demolition or expensive waterproofing of the pile head connection. Cost analyses of unconnected versus connected piled raft systems confirmed a cost savings in the construction that may reach from 50 to 70 percent.INTRODUCTIONDesigners around the world have gained more confidence to use the piled-raft as a more realistic system where the raft and the piles share transferring the superstructure loads to shallow and deep soil layers. A further advancement is to use unconnected piled rafts as another practical and economical alternative to the traditional piled rafts. Unconnected piled raft is also synonymous to settlement reducing piles; or simply, soil improvement piles. Liang et al. (2003) has extended the concept of pile-raft-foundation to a new type of foundation called composite piled raft foundation or unconnected piled raft foundation. The foundation is composed of a sand/gravel cushion sandwiched between the raft and piles. The piles group may contain short and long piles. The short piles are constructed of flexible materials such as soil-cement columns or sand-gravel columns, and are used mainly to improve the bearing capacity of shallow soft soil; the long piles, which are made of relatively rigid materials such as concrete, and their main function is to reduce settlements. The cushion plays an important role in mobilizing the bearing capacity of the subsoil and in modifying the load transfer mechanism of the piles. In Shanghai, China, this system of unconnected piled raft has proved to be quite suitable and effective in coastal areas, where deep soft soil deposits exist."

Jan 1, 2016

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 Lu Yitan, Frances Badelow, Manish Tiwari

"Large ‘design and construct’ projects often present significant geotechnical risks. However, these also present significant opportunities for value engineering in design. These opportunities can be realised through systematic site investigation and close collaboration with the Contractor to dovetail the design solutions to suit construction methods. This paper presents a case study of a large infrastructure project in Singapore which involved design optimization of an earth retention system for a deep excavation in a constrained urban environment. The project also required installation of over one thousand bored piles in highly variable ground conditions - identified as a key risk. Systematic site investigation was undertaken to develop a reliable ground model. A detailed value engineering exercise identified opportunities for design optimization by changing the retention systems and construction sequence in some segments. An innovative low cost ground improvement method was used in some areas to reduce the forces on the retention system. An extensive instrumentation and monitoring plan was implemented for verification of design and to mitigate the remaining risks. This paper includes the lessons learnt on this challenging project, which are relevant to a wide range of construction projects.INTRODUCTIONSingapore has been rapidly expanding its underground Mass Rapid Transit (MRT) network over the past two decades. The Thomson-East Coast Line (TEL) forms part of this expansion and is 43 km long and fully underground comprising 31 stations. This paper describes the value engineering and design optimizations undertaken during detailed design of the earth retaining and support structures (ERSS) for one of the underground stations along TEL. The station, currently under construction, is up to 24m deep and 350m long. The edge of the station excavation is less than 10m away from the existing MRTviaduct. The proposed station is surrounded by high-rise residential and commercial structures, somewithin 2m of the excavation. Land Transport Authority (LTA) of Singapore imposes stringent technical and contractual requirements on MRT construction works to ensure high quality and safety standards. These include minimum requirements for embedment of retaining walls, groundwater control, additional site investigation, instrumentation and monitoring, and compliance to LTA’s Civil Design Criteria (CDC). Any deviations from the minimum requirements can only be approved by LTA after detailed calculations, analysis and field testing are completed and additional monitoring and control measures are proposed."

Jan 1, 1900

By Aaron L. Sacks, David R. Good, Srinivas Yennamanda, Joseph K. Carey

Construction of Parcels 6 and 7, the second phase of The Wharf, began in 2019 and geotechnical construction was completed by December 2020. The overall project consisted of horizontal site, parks, and office buildings. The Wharf’s Phase 2 development includes approximately 1.2 million ft2 (110,000 m2) of above-grade construction including five multi-story, mixed-use buildings constructed over up to three levels of underground parking. The site is located between the WMATA Green Line Tunnels to the north and the Washington Channel to the south; it is bisected by a 108-in. (2740-mm) diameter DC Water outfall pipe. This arrangement, along with very difficult ground conditions, created challenges in the geotechnical design and construction. The support of excavation for this complex project required several different methodologies, including sheet piles, soldier piles, displacement piles, tiebacks, deep foundation anchors, jet grouting, and internal bracing with multi-tier rakers. Ground improvement was also required for support of spread footings in soft soils over the garage footprint. Underpinning of the active 108-in. (2740-mm) diameter DC Water outfall pipe running on a north/south alignment through the center of the site between the two garage structures was also performed. Since portions of the support of excavation are below the groundwater table, an extensive pre-excavation dewatering program was necessary and was separate from the foundation package. On the north side of the project, support of excavation (SOE) was required on a curved alignment, offset approximately 10 ft (3 m) from the outbound Green Line tunnel. Due to the proximity of the tunnel, a stiff, near-zero displacement wall was required. A portion of the buildings extend over the tunnels, imparting load to the tunnels to approximately restore original overburden loads excavated for the basement space. The building foundation is a 3 to 4-ft (0.9 to 1.2-m) thick mat slab anchored into the Potomac clay formation. Continuous movement monitoring of the tunnels was performed by an automated system. This paper describes the design and construction of the SOE and foundations for this high-profile project, which required collaboration between the Owner, Engineer, Construction Manager, and Specialty Geotechnical Contractor to solve many challenges.

Oct 1, 2022

"The Morris Island Lighthouse (MIL) is located between the jetties leading to the Charleston Harbor and Folly Beach, S.C. The present structure is the third lighthouse to occupy this location. The first navigational aid was erected in 1673, and consisted of a raised pan filled with pitch, which was set afire at night to guide early ships. The next structure was built in 1767, and constituted the first real lighthouse, standing 42 ft (12.8 m) in height. In 1838, a second lighthouse was built on the site, and it measured 102 ft (31 m) in height and featured a revolving light. This structure lasted until 1862 when Confederate troops, during the Civil War, destroyed it to deny its use to Union troops.Navigators steered these waters without a lighthouse for nearly a decade until 1876, when the current structure was built under the direction of the U.S. Army Corps of Engineers (USACE). In 1886, the Charleston area suffered a M7.6 earthquake. Significant damage was caused throughout much of the area, including a slight “list” of the lighthouse to the northeast. As a result, the cast of the beacon was reduced from 18 mi (29 km) to about 6 mi (9.7 km), causing much distress to navigators until the beacon platform was releveled and remains at this list to the present day.Conditions for ConcernThe current lighthouse was originally constructed about 1,200 ft (366 m) from the shoreline. Over the years, USACE has undertaken several programs to meet the increased shipping and navigation demands in the Charleston Harbor. Around the turn of the last century, two jetties were constructed, which drastically changed the approach direction for ships entering the harbor. In subsequent years, the harbor began to experience accelerated siltation."

Jan 1, 2017

By Harald Vogel, Johannes Lachenski, Friedemann Koetzel, Sebastian Schnell

In this paper, a digital subsoil approach, a work-in-progress, will be presented describing the transformation from a classical 2D to digital 3D thinking process in the design of geotechnical structures. Certain pitfalls as well as lessons learned are described, and the reader can understand that the digitalization process of the design of geotechnical structures is always a problem-focused approach by creating systems for certain processes rather than setting rules or regulations. Three project examples are presented. Two of the presented project examples feature a heterogeneous geology distribution and made it necessary for the design of the foundations to work with 3D subsoil and 3D calculation models. However, the digital 3D design process in the third project, an inner-city excavation pit, is driven by the complicated boundary conditions making it necessary to work in a parametric 3D design space. All projects have in common, that new processes had to be developed. The paper concludes with a flow chart describing the process of the elaborated digital subsoil approach.

May 1, 2022

By Wu Jian-tao, LI Guo-wei

"The Cement Mixing Pile (CMP) quality assurance assessment is an important programme in evaluating the efficiency of foundation improvement. Coring is the current specified method of quality assessment in China which has the shortcomings of long cycle, high cost and low efficiency. The field and laboratory test show that the regular cone penetration test can only detect maximum of 4m of effective detection depth in CMP. In contrast, the method of cone penetration test in the reserved hole can detect the quality continuously along the pile at any depth. The tip resistance of reserved hole penetration in the 7th day has good linear relationship with unconfined compressive strength in the 28th day. The slope of linear relationship decreases with the increasing of clay particles content.INTRODUCTIONThe method of Cement Mixing Pile (CMP) is often used to improve soft soil foundation in highway construction, with the major purpose of reducing settlements under embankments (Bruce et al., 2000),which is a form of what is known as the Deep Mixing Method (Bruce et al., 2013). The CMP technology spread quickly in China in the 1980s. CMP quality assurance assessment is an important programme in evaluating the efficiency of foundation improvement. Coring is the current specified method of quality assessment in China (China Academy Of Building Research, 2002). The method of Coring is perceived in some quarters that samples will provide lower strengths given the distress caused to the core during drilling and extraction (Bruce et al., 2002).The cone penetration test CPT can provide continuous measurements of the penetration resistance, sleeve friction at the tip of the probe, which has advantages of simple operation, low cost and high efficiency compared with coring. However, CPT tests have not been established to assess CMP in Sweden because of difficulties in maintaining verticality (Larsson, 2005). In Finland and Norway, however, CPT tests are commonly used (Halkola, 1999). One of the disadvantages of CPT is the tendency of the cone to steer out of the column (Porbaha et al., 2003). Darya Mokrousova (2010) states this tendency to deviate can be overcome by pre-boring and starting the penetration test from the base of the pre-bored hole. Sheng Haiyang (1999) found that probes may be deflected out, sometimes even at small penetration depths, and may not give a complete inspection of the pile. Liu Songyu et al. (2003) suggested that the Standard Penetration Test (SPT) is an effective way to evaluate the strength and quality of stabilized soil-cement columns. In general, Regular CPT can’t test the full length of CMP, and SPT still needed drilling which causes discontinuous detection. From the existing standard of China, core sampling compressive strength test is the main method, evidently, coring displays a longer test cycle, high cost and low efficiency. Therefore, an improvement of CMP quality assessment, by conjuring a fast and reliable detection and evaluation method, is necessary. The aim of this paper is to research the feasibility of using CPT in assessing the quality of CMP and presents an improved CPT method."

Jan 1, 2015

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