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By Juan M. Pestana, Jeremy M. Gasser, Cuneyt Gokmen, Paul J. Sabatini, William Tanner, Daniel J. Woeste

An access pathway and working platform were designed and constructed for equipment access for a Deep Soil Mixing (DSM) pilot study over a coal combustion residual (CCR) surface impoundment (SI). The DSM pilot study was conducted to evaluate slurry mix designs and construction techniques for installing DSM columns up to 95 feet deep. Two-dimensional (2-D) limit equilibrium and 2-D finite element analyses were used to evaluate multiple failure mechanisms including: (i) bearing capacity, (ii) punching shear of mixed ground and underlying CCR, (iii) effect of fluidized DSM columns on working platform stability, and (iv) liquefaction. The analysis results were used to design ground improvement required to increase bearing capacity and stability of the CCR under the proposed equipment access route. A long-reach excavator was used to perform shallow bucket mixing and walk onto the CCR SI atop previously mixed cells following a minimum cure time and acceptance of quality control test results. Prior to mobilizing the DSM rig, a static load test was conducted to evaluate performance of the working platform. Both the access pathway and working platform demonstrated acceptable performance under the design loads during the DSM pilot study. This case study emphasizes the economic and safety benefits that can be realized by appropriately designing critical temporary work items such as access pathways and working platforms in difficult ground conditions. INTRODUCTION A Deep Soil Mixing (DSM) pilot study was conducted at a coal combustion residual (CCR) surface impoundment (SI) to evaluate slurry mix designs and construction techniques for closure design of the SI (Site). Sluicing of CCR at the facility ceased and closure will be initiated based on requirements in the final United States Environmental Protection Agency (USEPA) Rule for Disposal of Coal Combustion Residuals from Electric Utilities, 40 CFR 257, effective October 19, 2015. The proposed closure approach involves constructing a DSM containment structure (DSM Wall) to separate the SI into two areas: (i) a closure by removal area; and (ii) a consolidate and cap-in-place area. The proposed DSM Wall would retain the CCR within the consolidated closure footprint and provide a barrier between the two areas of the SI. The predominant CCR in the SI where the pilot study was conducted were fly ash and bottom ash. CCR materials in surface impoundments are generally soft and saturated as a result of being sluiced into place and can present stability and safety challenges when performing earthwork activities.

Jan 1, 2019

By Paolo Cavalcoli, Federico Pagliacci

"As opposed to the static functional recovery of existing structures, the construction of infrastructures in an urban environment, when combined with complex geological situations, often involves building foundation structures, whether circular or rectangular in section, through rock formations or chaotic strata (sand and gravel with cobbles). Until a few years ago, these formations or strata were sometimes an insurmountable constraint on traditional foundation installation techniques. The difficulty in overcoming these geological situations is sometimes added to the increasingly frequent need to reach depths that were unimaginable just a decade ago. These are real challenges for those carrying out these works and for those manufacturing the necessary equipment. There are two main methodological approaches to these problems, that can be summed up in the rhetorical figure of ""David and Goliath"": cunning versus force. In reference to the case studies in this article: the permanent retaining walls for the Copenhagen Metro, and the structural repairs to the Arapuni Dam in New Zealand and the Wolf Creek Dam in the U.S., we will describe the foundations constructed in presence of rock using combined small-diameter direction drilling solutions, associated with their enlargement up to the project’s size, at depths exceeding 300 feet. Finally, a case study will be presented on the implementation of a large cross-section of an excavation in the rock, at depths greater than 800 feet.IntroductionAs opposed to the functional recovery of existing structures, the construction of infrastructures in an urban environment, when combined with complex geological situations, often involves building foundation structures, whether circular or rectangular in section, through rock formations or chaotic strata (sand and gravel with cobbles).Until a few years ago, these formations or strata were sometimes an insurmountable constraint on traditional foundation installation techniques. The difficulty in overcoming these geological situations is sometimes added to the increasingly frequent need to reach depths that were unimaginable just a decade ago.These are real challenges for those building these works and for those manufacturing the necessary equipment. There are two main methodological approaches to these problems, that can be summed up in the biblical figures of ""David and Goliath"": cunning versus force. In the engineering field, the force is summarized in the use of ever-larger drilling equipment in terms of installed power, weight in working conditions, winch and rotary capacity."

Jan 1, 2015

"TREVIICOS CorporationINTRODUCTIONThe Walter F. George lock and dam was constructed on the Chattahoochee River between 1955 and 1963 with the double function of improving navigation and generating power. Its 82 ft. by 450 ft. (25m x 137m) lock can accommodate large barge traffic and its four generating units with a plant capacity of 150 MW have an average energy output of 453,000 MWH. The dam consists of a 1,496 ft. (456m) long concrete structure housing the spillway, a non overflow portion, the power units and two earthen wing dams extending to the Georgia and Alabama sides, respectively 5,810 feet and 6,130 feet long (1770m and 1868m). As soon as the reservoir was impounded it became apparent that excessive seepage was occurring. From 1962 to 1985 a series of remedial works was performed using several techniques, but the problems continued under the dam, jeopardizing its generating potential and possibly undermining its stability.Finally, the decision was made to construct a deep cutoff primarily under the concrete portion of the dam to remedy the problem. PROCUREMENTOn July 5th, 2001 best and final offers were solicited by the Corps of Engineers (COE) for the construction of a deep cut-off to be built in front of the concrete portion of the dam from the bottom of the lake and tied into it. The cut-off had to cross an existing lock structure and an underwater retaining wall, as well as the remnants of a steel coffer cell left in place from the initial construction.The specifications required that the wall be built with a minimum thickness of 24” (600mm) and that it extended from the bottom of the lake to elevation -5 (1.52m) into the Providence formation, an impervious layer.While the land portions of the wall were on average 208 feet (63.4m) deep, the marine portion started from up to 90 feet (27m) of water and continued through different rock formations for another 100 feet (30m).Contractors were invited to propose their own method of constructing the cut-off and offers would be evaluated using several criteria, including technical, economical, organizational and experience.Three proposals were received and on August 14, 2001 an award was made to the Joint Venture (JV) of Treviicos and Rodio."

Jan 1, 2014

By R. Gerritsen, Erwin de Jong, E. van der Velde, C. te Boekhorst

"In recent years the market for Mixed-In-Place soil mix techniques in the Netherlands has been growing rapidly. Initially the technique was used to create cut-off walls near river dikes and as a vibration free method to create retaining walls for building pits. Studies have been undertaken and projects are executed in order to strengthen the dike itself by the use of Mixed-In-Place techniques. In February 2012 Bauer Funderingstechniek started the construction of the first polder in the Netherlands with their approved Mixed-In-Place cut-off walls. This article explains the background of the use of this cost-effective and durable construction method and discusses how the challenging requirements from the client were fulfilled, both in design and execution. The quality assurance and quality control consisted of preliminary soil and mixture investigations, extensive measurements during construction and leakage detection through geophysical methods. The information is presented in 3 case histories, all subprojects of a large infrastructural project ‘Leeuwarden Vrij-Baan’ in the Netherlands.INTRODUCTIONThe Netherlands have a worldwide reputation in creating their own country by reclaiming land from the sea. Since the 15th century the Dutch have been creating “polders”, areas of reclaimed land below sea level, surrounded by dykes and with a mechanically maintained water level. In the 20th century the use of artificial polders became an interesting construction method for creating underpasses below motorways and canals using watertight geomembranes to create an impermeable layer that separated the polder from its surroundings. These kinds of structures have one big disadvantage, they need a lot of space. The main idea of such a structure is that the upward water pressure under the geomembrane has to be in balance with the remaining soil on top of it. For this reason, the geomembrane has to be placed at a depth significantly deeper than the polder surface, depending on the hydraulic head in the aquifer. Slopes of 1:3 (1 vertical : 3 horizontal) are most commonly used, resulting in very large open excavations and massive earthworks, even for relatively small underpasses. Special measures can be taken to reduce the spatial use with vertical limits, but these measures will increase the building costs (Gerritsen et al. 2014)."

Jan 1, 2015

By Federico Pagliacci

"Many existing dams are subject to underwater seepage due to subsoil conditions, like deep alluvial deposits or pervious rocks or karst. Remedial works are necessary in order to install new cut-off walls to stop the water flow. In some cases the cut-off walls have to be executed at depths never reached so far, and difficult to reach with traditional foundation techniques. In many cases the Hydromill technology proved to be the best system to overpass rocky layers and ensure the required verticality. The maximum depth reached by the industry was in the range of 120-150 meters. This article describes the test performed to excavate and cast in place a 3.2x1.5 m panel to a depth of 250 m. The article will also describe the stratigraphy of the site down to 250 meters, as well as the technique adopted to achieve the said depth with deviations from verticality of 30 cm along the longitudinal axis (0.12%) and 20 cm along the transverse axis (0.10%), measured at the bottom of the excavation. The concreting of the panel, for about 1,100 m³, with plastic concrete in the lower portion and conventional concrete in the upper portion will be illustrated. Finally, the tests performed during the excavation and after concrete casting will be also described, with special attention to the continuous directional core drilling that was performed along the whole length of the panel to verify the results of the deviation from verticality, through the onboard instruments, and to control the quality of concrete at a depth never reached before. IntroductionMany existing dams are subject to underwater seepage due to subsoil conditions, like deep alluvial deposits or caves and cavities or acid solutions in the bedrock formations.Conventional remedial works generally consist in the construction of an additional cut-off wall throughout the dam body and the subsoil, in most cases being deeper than the original one. Today, many examples of successful remedial cut-off walls allow the engineers to design the most suitable solution according to the dam and subsoil characteristics and nature.The real difficulty stems from the depth at which the new cut-off wall has to be socketed in competent rock or soil, so as to eliminate underwater seepage. The maximum depth ever achieved with a cut-off wall is 122.5 m for the remedial work of Mud Mountain Dam, Washington, USA, in 1988-1990. This 0.85-1.0 m thick cut-off wall was realized by means of a Hydromill, by excavating single 2.8 m-wide secant panels."

Jan 1, 2017

By Allen B. Stanton, Parthiv Brahmbhatt, Michael Grimm, Stanley L. Worst

Constructing a circular shaft consisting of secant piles has its own complications which make it more difficult than typical drilled shaft construction. Add to that performing under low overhead powerlines and sitting inside of a 40-foot deep, 50-foot diameter shaft and it becomes more about logistics than the actual drilling. The complexities associated with the Romeo Arm Interceptor Segment 5 Lining project are the focus of this paper, delving into the details that made it work successfully.

Oct 1, 2022

By Lois G. Schwarz

I did a project (Sungai Piah) as a consultant to your firm in Malaysia, where we were faced with a similar situation as sketched out in your question. The following is what we did for the grouting of the primary holes, which were both located upstream of the plug as well as downstream: We used a hydrophobic MDI based semi-rigid polyurethane prepolymer in the first phase of the grouting operation when grouting under water flow conditions. Then in the second phase and also for the contact grouting we used a two component water compatible polyurethane elastomer. And then for deeper formation grouting, when all the water flow had been stemmed in the vicinity of the plug, we used a regular (balanced stable) cement based grout. So it may not exactly answer your question, but we first used hydrophobic grout because it is very efficient to grout a formation through which water flows. We didn't stop all the leaks day-lighting downstream of the plug or all water running through the formation near the plug, but the flow of water through the rock formation adjacent to the plug was reduced by 99.9%, after completing the urethane grouting. This facilitated the placement of cement based suspension grouts without wash-out.

Feb 10, 2003

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 Hayel M. El-Naggar, Marawan M. Shahien

"Large capacity piles are important type of foundation elements that are needed in case of high column loads such as in tall buildings with large span between columns. In many projects, especially if the designer uses the concept of one pile supporting one column (Hamza, 2003a & b). The axial capacity of the large bored deep foundations can be further increased by grouting the shaft skin and the base of the pile. The increase in the capacity of the piles due to grouting can be tremendous. Thus grouting appears as an ideal solution for achieving more reliable foundation and greater savings (Littlechild et al., 2000). A data base of pile load tests of instrumented grouted piles is under development in a major study aiming to propose a simple method to estimate the axial capacity of large bored grouted piles. The data base include pile load tests from projects constructed in Egypt and abroad. The main goal of this paper is to analyze pile load test(s) from one project. The tested deep foundations included 1.2 m diameter and 1.5 m diameter piles and a barrette of size 1.0mx2.8m. The instrumentation of the tested piles and barrette allowed for the separation of skin friction and base contributions to the axial load. Further, the contribution of the skin friction of every layer along the pile shaft could be identified. The results of the analysis clarified how base and shaft grouting increased the axial capacity of the pile and decreased the settlements for certain load level compared to conventional un-grouted piles installed under similar conditions.INTRODUCTIONIn recent years, significant research has been carried out to develop new techniques which are suitable to withstand problems in major projects such as high applied loads in high rise building, large spans structures projects and structures designed using the concept one pile supporting one column (Hamza, 2003a & b). Base and shaft grouting of piles are one of these new techniques which aim at decreasing the settlements and increasing the capacity of the pile under axial load that became major requirements in large projects (Stocker, 1983; Mullins et al., 2001; and Hamza, 2015).Base grouting consists of injection grout under pressure at the base of the pile after the concrete is sufficiently hard. Field evidences showed that the ultimate end bearing of base-grouted piles could be as high as 1.5 that of non-base-grouted bored piles (Suckling and Eager, 2001). Further, field evidences was provided by Shahien and El-Naggar (2015) that showed an increase in end bearing resistance due to base grouting reached to 2 to 3 times that of non-base-grouted bored pile. On the other hand, shaft-grouting causes increase in the soil density in the zone which had been disturbed by the pile construction and thereby improves the shaft resistance of the pile. Field measurements by Gouvenot and Gabaix (1975), Stocker (1983), Robson and Wahby (1994), Troughton and Stocker (1996), Byrne et al. (1998), Joer and Randolph (1998), Hamza and Leoni (1998), Littlechild et al. (2000), Hamza and Ibrahim (2002), Hamza (2003 a&b), Hamza (2015) and Shahien and El-Naggar (2015) showed that the shaft resistance of grouted piles could be nearly 1.5 to 5 times that of non-grouted piles."

Jan 1, 2017

By Guo Qian, Du Guangyin, Deng Yongfeng, Liu Songyu, Wang Ningping

"Metakaolin (MK) can efficiently enhance the strength and the impermeability of concretes and mortars. However, it has rarely been attempted in admixtures of cement-stabilized soils until presently. As deep mixing method is wildly used in ground improvement, the strength of cemented soils (soilcrete) and the applicability of the MK should be considered. This paper focuses on the macro-strength development of cement-stabilised silty soil mixed with MK. The result shows that the addition of MK can enhance the unconfined compressive strength of the soilcrete, which attributes to a combination of the rates of OPC hydration and the MK-CH reaction. Note that the strength of soilcrete was influenced by the properties of soil, water-to-binder mass ratio (W/B) in admixtures, which needs to be reconsidered since the binder mass composes that of cement and MK totally.INTRODUCTIONCement was used in ground modification techniques, such as the jet grouting, deep mixing method (DMM) which was put into practices in Japan and Nordic countries in the middle of the 1970s, and then spread to China, South East Asia[1]. For last decades, fly ash, slag or silica fume was mixed with cement to form the new cement base stabilizing agent in the view of economy and performance improvement. The mechanical behavior of these soil-binder admixtures (nominated as “soilcrete”), was investigated. But the soilcrete modified with the metakaolin (MK) was still not investigated much and lots of further work needs to be conducted.Some laboratory experiments of the soilcretes modified with MK have been taken[2~4]. Kolovos et al. (2013) indicates that the unconfined compressive strength has a more significant improvement when W/B equals 0.4 than that when W/B equals 1.20 concerning the water-to-binder mass ratio (W/B). Sonebi et al. (2013) investigates the mechanical behaviors of cement grouting containing MK with W/B equals 0.4, and also found the effectiveness of the addition of MK. Zhang et al. (2014) performed the studies on Lianyungang marine clay improvement showed that MK obviously enhanced the quality of cemented soils.In this paper, the strength of soilcrete modified with MK is further investigated, where the unconfined compressive strength at different curing time, the content of MK and cement (w/w) in lab conditions was discussed."

Jan 1, 2015

By George Gazetas, Sissy Nikolaou, Fani Gelagoti, Irene Georgiou, Rallis Kourkoulis

"The need to shift geotechnical design from a “factor of safety” to a “performance based” design (PBD) approach has increased rapidly in the past years following examples from structural engineering. PBD supports sustainable engineered systems that target project-specific geotechnical behavior objectives and results in more rational and, in most cases, less conservative solutions. Resiliency, efficiency, risk optimization, and cost-effectiveness are key components of this approach. For design of retaining walls, the concept of mechanically stabilized earth (MSE) systems combines these attributes, while being environmentally friendly and adaptive to variable construction conditions. Natural hazards, such as earthquakes, may drive the design of MSE systems whose reliability depends on their performance under extreme events. In this paper, the authors compare the seismic response of an MSE steel-reinforced vs. concrete-reinforced retaining wall. The MSE system is composed of a grid of longitudinal and transverse ribs which internally enhances the capacity of the soil backfill. Results of fully non-linear twodimensional (2-D) numerical finite element analyses using two commercial programs with emphasis on the interface conditions are presented. The pull-out resistance of the grid used in the numerical simulation was evaluated from actual pull-out experiments. The results demonstrate a superior performance of the MSE system as compared to the concrete one, especially when subjected to strong seismic excitations.INTRODUCTIONThe idea of performance-based geotechnical engineering is not new, and has been evolving as our perception for ‘good’ performance has also evolved (Kramer, 2008). In early practice, the only criterion for achieving good performance was to avoid failure; designers had only to ensure that the available capacity of the geotechnical system is sufficiently higher than the expected demand (i.e. Load and Resistance Factor Methodologies). Yet, even when the key design requirements against collapse are satisfied, the system may still be placed into a condition in which the deformation constraints are not met (Bolton, 2012). To address these issues, geotechnical design has been developing into a predominantly performance-based approach that correlates deformation considerations to the severity of the experienced loading. As such, in earthquake-related problems, the definition of good performance of a geotechnical system is no more unique; for a low intensity earthquake the system should remain serviceable (i.e., the developed deformations should remain low), whilst for the design earthquake the maintenance of lifesafety is the single performance criterion."

Jan 1, 2016

By Prasanta Paul, Aminul Islam

"Nhava Sheva (India) Gateway Terminal Private Limited proposed to construct a container terminal yard, comprising a back-up area at Jawaharlal Nehru Port Terminal (JNPT), Uran, Maharashtra. The proposed container terminal yard is located on a recent reclamation on the Thane Creek, which was developed by land-based reclamation method. The underneath soft marine clay was treated, using vertical band drains and placement of surcharge upon.Settlement of the reclamation during its construction was monitored using settlement plate installed at +4.8m CD elevation which was above the highest high water level.This paper examines the settlement behaviour of the reclamation during the ground improvement works. The geotechnical parameters are back-analyzed by the authors from the field settlement results and the concerned preloading details. The back analyzed coefficients of consolidation due to horizontal flow (Ch) are compared with laboratory determined parameters and the estimated value, using Asaoka Method (1978). The authors also studied field compression ratio [CR= Cc/(1+e0)] vs. the compression ratio determined by laboratory test using back-analysis method.1. INTRODUCTIONNhava Sheva (India) Gateway Terminal Private Limited proposed to construct a container terminal yard, comprising a back-up area of approximately 27 hectares, complete with associated buildings and services on a part brownfield/ greenfield site. The back-up area shall include a heavy duty block paved pavement with band beams for electric Rubber-Tyred Gantry Crane (eRTGC) alongwith surface water drainage system and other services including area lighting, provision of fire-fighting facilities , sources for potable water and power.Based on the Employer’s Requirement and the available geotechnical investigation report, ground improvement scheme is designed by the construction contractor. Ground improvement works included the installation of prefabricated vertical drains and subsequent placement of surcharge for accelerating the consolidation of the underlying soft marine clay."

Jan 1, 2015

By Stephen Buttling

The construction of a water treatment plant in Dandenong, Victoria, required detention tanks and a pumping well. The design provided by the Engineer used conventional rectangular cast-in-situ reinforced concrete walls within a sheet piled cofferdam. It was decided to construct the tank and shaft using the diaphragm walling technique as an alternative and, for the shaft in particular, this involved a “circular wall”. Except where cutters are used, joints in diaphragm walls have to be made between colinear panels, with waterproofing provided by dumb-bell water stops held within trapezoidal forms. This means that the circle has to be approximated by a number of straight sides, which in this case was twelve. The requirement was to design the reinforcement for the strange shaped panels. Finite element analysis was used, in the first stage using an axisymmetric model to determine the profile of lateral earth pressures with depth. In the second stage a horizontal slice was modelled, without gravity which normally operates from the top to the bottom of the page. By considering appropriate possible earth pressures at different depths, a range of bending moments was calculated, which was used by the structural engineers to design the rebar. The tanks were successfully constructed, and inclinometers were installed in both the tank and the shaft. Measured deflection profiles show that the design was moderately conservative.

Nov 1, 2022

By Matt Fenwick, Douglas R. Schwarm

Stringent underwater noise limits at the Fairview Ave. N. bridge replacement on Seattle's Lake Union required an innovative approach to supporting the 470-ft long drill trestle. Screw-in foundations would reliably mitigate noise, but the required 500-kip bearing resistance were an order of magnitude higher than typical helical piles. This paper describes the process of designing, installing, monitoring, and testing 22-inch dia. helical piles 80 feet long with 36- and 42-inch dia. helices. A static load test confirmed that the conventional k-factor design method can be extended to capacities of up to 800 kips. A 375 ft-kip drive mechanism had to be fabricated because no North American equipment could supply the necessary installation torque. Real time installation monitoring and later "re-torque" tests confirm that helical piles gain capacity with time, analogous to driven piles under restrike. Underwater and on-land measurements confirmed very low noise, suggesting the possibility of widespread adoption where similar limits are imposed. Overall, this case history illuminates the need for innovative deep foundation types in response to ever-increasing regulatory constraints.

Sep 8, 2021

By Gerry Houlahan

The east span of the 3.5 km long SF-Oakland Bay Bridge is supported by different types of foundations along its span. Starting from the west, its first 460 m section comprising twin concrete box-girders is supported by sands and rock on Yerba Buena Island. A 620 m long steel suspension span then bridges a 25 m deep channel that is formed in sediments overlying rock. Twin concrete box girder structures, each 2.4 km long, complete the stretch over the remainder of San Francisco Bay to the engineered earth fill landing at its east end. For most of its length, the Skyway bridges water 3 to 10 m deep over soft surficial Young Bay Mud. The foundation types include spread footings with hold-downs, steel and concrete piles that are set in drilled rock sockets up to 3 m in diameter and 2.5 m diameter steel tubular piles driven to penetrations of up to 100 m. The design and construction-related considerations are presented. The different foundation types, influences of the site geology and earthquake demands on the substructures are discussed. The seismic motions of the bridge superstructures and substructures, as well as the depth-varying soil motions, influenced the foundation design. Together with performance-based design criteria, including post-earthquake footing displacement limits, these seismic demands influenced various aspects of the foundation design, including the use of battered and vertical piles.

Jan 1, 2013

By Marco Fellin, Van E. Komurka

Significant cost and construction benefits were obtained from performing a bi-directional static load test prior to construction on the Russell Street Bridge Replacement project in Missoula, Montana. The project utilized 24 drilled shafts to support two three-span bridges across the Clark Fork River. A bi-directional static load test (“BDSLT”) was performed on a large-diameter production shaft to demonstrate construction methods and confirm design assumptions. Subsurface conditions consisted of gravel with sand to a depth of 20 feet (6.1 m), underlain by gravel with sand, silt, cobbles, and occasional boulders. The test shaft had a nominal diameter of 5.9 feet (1.8 m), and an embedded length of 75.5 feet (23.0 m). The geotechnical engineer of record and the BDSLT test engineer collaborated to optimize the BDSLT jack assembly location within the test shaft, determine appropriate instrumentation locations, and plan the test protocol. The maximum applied test load was 10,707 kips (47.6 kN). Significant benefits were obtained from performing the BDSLT test, including 1) reducing each production shaft’s length by using a higher LRFD resistance factor allowed by having performed the testing, 2) using test-determined unit shaft resistances to evaluate and accept two production shafts that may have otherwise required remediation, and 3) providing the Montana Department of Transportation (and other designers) with increased presumptive unit resistance values in the gravel/cobble/boulder deposits. PROJECT DESCRIPTION The project was constructed in Missoula, Montana for the Montana Department of Transportation (“MDT”). The original bridge was approximately 60 years old, and consisted of a two-lane, 420-foot-long (128-m), four-span, riveted steel plate girder design spanning the Clark Fork River. The bridge was due for replacement owing to its deteriorated state, and the need for increased traffic volume capability afforded by a four-lane structure. HDR was the structural engineer. The preferred bridge alternate was a 459-foot- long (140-m), three-span, welded steel plate girder design. The new bridge was designed to meet current standards in accordance with MDT bridge design and AASHTO LRFD criteria. The new bridge was constructed in phases to keep traffic open during construction.

Jan 1, 2019

By William M. Tanner, Daniel C. Brahana

"A drilled pier foundation was originally designed to support the proposed G. Wayne Clough Undergraduate Learning Commons on the campus of Georgia Tech in Atlanta, GA. Reflective of the site geology, the original drilled pier foundation was divided into a Northern and Southern portion with an allowable end bearing capacity of 60 ksf and 100 ksf, respectively. After initial pricing on the original design, several value engineering options were submitted that featured changes to the original design capacity and construction method. The project team selected the value engineering option that involved conducting an Osterberg Load Cell test to assess end bearing of the site bedrock and skin friction. Results of the Osterberg Load Cell test justified increasing the allowable end bearing capacity of the site bedrock to 100 ksf in the Northern portion and 125 ksf in the Southern portion. Considering the final foundation design and Osterberg Load Cell test program, a net savings of approximately $259,000, or approximately 34%, was obtained over the original design.Project BackgroundThe G. Wayne Clough Undergraduate Learning Commons (CULC) is a 5-story academic building on the Georgia Tech campus in Atlanta, Georgia. The CULC was completed in 2011 and consists of a concrete frame structure supported on a drilled pier foundation.After pricing of the original drilled pier foundation design, several value engineering (VE) analyses were performed by the foundation contractor in an effort to demonstrate the potential for a reduced foundation cost. The VE analyses focused on variations in design assumptions, as well as construction techniques. This paper presents a case study that demonstrates how the value engineering process can be used to reduce foundation costs.Site Investigation and Subsurface ConditionsThe CULC building site is located within the Southern Piedmont Physiographic Province, an area underlain by metamorphic and igneous rocks. McConnell and Abrams (1984) indicate that the site is located at the boundary between two distinct geologic formations. The Northern portion of the site is underlain by the Wahoo Creek Formation while the Southern portion of the site is underlain by the Stonewall Formation. The following paragraphs briefly describe the geotechnical investigations performed by the project geotechnical engineer (GE) for the CULC."

Jan 1, 2015

By John P. Turner, Steven S. Dapp, Dan A. Brown

"The Goethals Bridge Replacement (GBR) spanning the Arthur Kill Waterway between Elizabeth, NJ and Staten Island, NY is supported on over 200 drilled shaft foundations ranging in diameter from 4.5 ft to 10 ft and socketed into Passaic Formation siltstone. Four drilled shafts, two on each side of the bridge (NJ and NY), were load tested using the bi-directional axial load method. Axial test results demonstrate that RQD, taken by itself, is not necessarily a reliable indicator of side or base resistance. High recovery with low RQD can be a function of horizontally bedded siltstone and shale where the individual pieces of core do not exceed four inches, but may still provide very high side and base resistance. Axial testing was followed by a lateral rapid-load test (Statnamic) on each of the same four shafts. In addition, one of the shafts was subjected to a static lateral load test to validate the rapid-load method as being representative of static loading conditions. Results of the axial load tests provide the basis of unit side and unit base resistances used in the LRFD design of the rock sockets for axial loading, while results of the static and Statnamic lateral load tests were used to calibrate p-y curve parameters used for design under lateral and moment loading. This paper describes implementation of the load testing program and its role in the design process.INTRODUCTIONDesign of drilled shaft foundations for the Goethals Bridge Replacement (GBR) required load testing in order to validate the parameters used for calculating geotechnical axial and lateral resistances. The bridge, including foundations, was designed in accordance with the AASHTO LRFD design specifications, 6th Edition (2012). The bridge owner is the Port Authority of New York and New Jersey (PANYNJ). One of the PANYNJ project requirements was stated as follows:“Perform a minimum of two (2) separate axial compression load tests (one [1] in New York and one [1] in New Jersey) for each demonstration shaft of different size and construction methodology to verify the design assumptions and construction procedures. At a minimum, one (1) demonstration shaft is required to be representative of production shafts with a diameter within one (1) foot above or below the demonstration shaft diameter.Conduct a minimum of two (2) lateral load tests (one [1] in New York and one [1] in New Jersey) for each demonstration shaft of different size and construction methodology. At a minimum, one (1) demonstration shaft is required to be representative of production shafts with a diameter within one (1) foot above or below the demonstration shaft diameter.”"

Jan 1, 2016

By Ronnie Melker, Joel Webster, Daniel Belardo, Thomas Hyatt

Quality assurance of drilled shafts is highly dependent upon the construction practices used during the excavation and concrete placement process. When performed under slurry, challenges are presented in maintaining borehole stability and placing a uniform and continuous concrete column. An integral part of the construction operation is to evaluate the as-built integrity to verify the drilled shaft is capable of safely transferring the required loads to the subsurface. One such case is exemplified by a project involving the expansion of an existing public transit rail line. The expansion required the construction of a new bridge bent supported by seven 5-ft diameter drilled shafts of various lengths. The specifications for the project required both Cross-Hole Sonic Logging (CSL) and Thermal Integrity Profiling (TIP) for drilled shaft integrity evaluation. Both of these post-construction non-destructive tests (NDT) are designed to detect anomalies or the presence of regions with reduced concrete quality. However, the implementation and methodologies of performing each of these NDT methods are significantly different. Cross-Hole Sonic Logging uses ultrasonic signals emitted from a transmitter in one access tube to a receiver in another access tube. Thermal Integrity Profiling measures elevated concrete temperatures during the curing process using embedded thermal wires. Both test methods require different access details and therefore have different costs associated to the contractor or owner to perform. This paper provides a detailed comparison of these NDT methods as performed on these seven drilled shafts. The associated financial and time costs to perform each method are compared and the results are discussed in detail. INTRODUCTION Drilled shafts are a fundamental deep foundation element that can be designed to resist large bending moments as well as to transfer large compressive axial loads through weaker upper soils to competent soils or rock below. Often times when the upper soils are very soft, lateral support by casing or slurry, or a combination of both, may be used to hold back the softer soils from collapsing into the hole before concrete has been placed. Due to the blind nature of drilled shaft construction and the qualities issues that may arise during the placement process, it is essential for design engineers to specify non-destructive testing (NDT) to assess the quality of the as-built drilled shaft. CSL and TIP testing are two NDT methods designed to detect areas of lower quality concrete or soil inclusions throughout the length of the drilled shaft and determine its overall quality. Each method uses different technologies and methods to achieve the results required to determine the as-built condition of the drilled shaft.

Jan 1, 2019

By Jim Bruce

No answer required. From the drilling equipment suppliers, but the specifications must be tailored to be project-specific. Yes, the sonic technique is very interesting as we said, and it is not so much as an issue of the magnitude of power, it's about the efficient use of the power. The efficiency of the machine is not necessarily related to size so it is best to talk to the two contractors that supply the service about that. I think it can be scaled down but it is quite a big head, so therefore there are practical limitations on the size of the door it can walk through and also the size of the casings and rods that it can use. You might defeat the economic advantages if you were to use too short casing lengths. Boart Longyear have a low head room machine that can work within an 8 foot verical clearance.

Feb 10, 2003