Search Documents

By Wu Jie Mei, Li Yao Liang, Franz-Werner Gerressen, Arthur Bi

Diaphragm walls (D-walls) are known as underground structural elements commonly used for retention systems and permanent foundation elements. In addition, they are also quite often used as deep groundwater barriers, called Cut-Off-Walls (COW). Shanghai ranks third among the most densely populated metropolises in the world. In 1990, only eight million people lived there. Today, Shanghai has about25 million inhabitants. The increasing demand to accommodate the infrastructure of growing megacities like Shanghai pushes the required depth for subway, sewage and foundation projects to the limit. Future projects will demand excavation depths of more than 100 m (328 ft) on a regular basis. Already carried out reference projects will be described and a general outlook for upcoming projects will be given. The paper also explains the installation process in general focusing on the use of trench cutter technology. INTRODUCTION D- walls are known as underground structural elements, commonly used as retention systems for excavation pits and shafts as well as permanent foundation walls or elements. It is anticipated that, with the increasing trend of utilizing more and more underground space to accommodate environmental considerations and urban/suburban development, there will be an increasing requirement for diaphragm wall usage in even more difficult conditions and with increasing depth. The trench cutter is the most important tool for performing this work. The hydraulic grab, a well-known and valuable excavation tool for d-walls reaches its limits in terms of depth and when cutting rock. Therefore the trench cutter technology will be in the focus of this paper. The trench cutter itself is a reverse circulation excavation tool. It consists of a heavy steel frame with two drive gears attached to its bottom end, which rotates in opposite direction around the horizontal axis. Cutter wheels are mounted onto the drive gears. As they rotate, the soil beneath the cutter wheels is continuously broken up, removed, mixed with the bentonite slurry in the trench and moved towards the opening of the suction box of the pump? A centrifugal pump located right above the cutter wheels conveys the slurry via a hose system up to a desanding plant. There the slurry loaded with soil and rock particles is cleaned and returned into the trench.

Jan 1, 2018

By A. V. Shroff

The Indian Standards code of practice for design and construction of underreamed piles contains provision for installing such piles in expasive soils. In recent years, a large amount of research work has been carried out in the analysis, design, construction and performance of underreamed piles in expansive soils. This paper suggests that the results of this research field tests should be included in the code. Various additions and modifications as well as deletions that should be incorporated in the code are discussed.

Jan 1, 1996

By Zhou Lu-Jian

The Port of Shekou is situated at Shenzhen Bay on the east bank of Lingding Ocean. Its coastline is about 6 km long and the water depth near the shore is Favourable. Across the bay is the ' New Territories " of Hong Kong. The port is at a distance of 22-23 seamilesaway from center of Hong Kong and 80 seamiles to Huangpu Harbour of Guangzhou, its highway links with Shen-Guang Highay. Since 19 79 China Merchants Group of the Transportation Department, began to set up Shekou Industrial Zone, the port has been developing and flouri­shing in business. With 15 large or small berths in all, the present portline is 2600 m, and the annual cargo throughout is over 3,000,000 tons and the annual passenger traffic is about 2,000,000 persons. Equalling a medium-scale seaport, it has been officially approved as an oceangoing transit port by the ministry of Transportation. The construction of Shekou port is chara-terized by the self-collected funds and the short construction period. In view of this, the optional plan of the port structure must serve the requirements of simplicity in struture, economy in mate­rial and speed in construction. That accounts for the most application of the sheet piling type to the port in Shekou. Once the project was approved, the cons­truction started. Only within an average period of 7-8 months, a deep water pier was completed and put into operation, which covered series of processes from exploration, designing, tender for con­struction to completion.

Jan 1, 1991

By M. Mets

Pile foundations have been used in Estonia since the beginning of 1960's. To evaluate the capacity of piles nearly 2,500 pile tests and 1,800 pile loading tests Have been carried out. The pile foundations of nearly 150 houses are under settlement observations.

Jan 1, 2000

By Theo. A. M. Salet

The historic centre of one of the most beautiful cities in Northern Europe -Amsterdam - is being excavated to accommodate the new North/South metro line. This new line is due for completion in 2012, and will link the Buikslotermeerplein district north of the harbour, underneath the Central Station and the old city with its gables and picturesque canals, to the commercial centre in Amsterdam Zuid/WTC. Three underground stations are being construction in the old city at Rokin, Vijzelgracht and Ceintuurbaan. The logistics of working in the middle of an historic city are demanding -maintaining tram, vehicular traffic and pedestrian access along narrow streets, providing suitable protection for the public alongside the working areas, arranging adequate delivery routes, as well as monitoring the old and mostly historical buildings for potential settlement. Safety of both the public and adjacent properties is paramount. Diaphragm walling - 1.2m & 1.5m thick and up to 48m deep - was chosen as the support system for the three deep metro stations. Challenging engineering as well as state-of-the-art equipment to construct the diaphragm walls was needed in order to meet the tight working specifications, in the narrowest locations imaginable. Extreme conditions call for innovative solutions.

Jan 1, 2006

By M. Hesham El Naggar, Osama F. E. Drbe

"Abstract: The use of micropiles has greatly increased the last twenty years, including applications involving low capacity micropile networks, seismic retrofitting, underpinning of existing foundations and high capacity foundations for new structures. This paper presents a field study of the behaviour of single hollow core micropiles in firm to stiff lean clay. Eight micropiles were installed using hollow bars (76 mm OD and 48 mm ID) with air/water flushing technique and advanced to a depth of 5.75m: six micropiles were installed using 228 mm (9 in) drill bit and two micropiles were installed using 178 mm (7 in) drill bit. All micropiles were instrumented with linear potentiometers to measure the vertical displacement of the micropile head and vibrating wire strain gauges to measure the axial strain at three points along the micropile length. Twelve full scale tests were conducted on the eight micropiles, four monotonic compression, four cyclic compression and four tension tests. Only the results of micropiles tested under monotonic compression is presented in this paper. The full scale load tests and a comparison of the performance of the micropiles with 228 mm and 178 mm drill bit are presented and discussed in terms of load-displacement curves, bond strength and tip resistance. The results showed that the proposed values of bond strength in FHWA give a conservative design of the hollow core micropiles. The micropiles constructed with 228 mm drill bit performed marginallybetter than the micropile with 178 mm drill bit in terms of the ultimate capacity.IntroductionMicropiles have been defined in a variety of ways, but can universally be classified as small diameter (less than 300mm), bored, and grouted in place piles (FHWA, 2005; Bruce et al., 1999; and Scherer et al., 1996). They can sustain axial (compression and tension) and/or lateral loads. Dr. Fernando Lizzi used micropiles in 1952 for underpinning of historic buildings damaged during World War II (Bruce D. A., 1988). Since then, micropile applications have expanded rapidly to include underpinning for existing foundations, in situ reinforcement, and seismic retrofitting and foundations for new construction. In particular, micropiles have graduated from use in low-capacity micropile networks toapplications as single high-capacity foundation.Micropiles capacity is affected by the construction technique, which involves drilling, placing reinforcement, and placing or pressurizing the grout. For example, the drilling method influences the degree of bonding between the grout and the ground, and the placement of reinforcement and the choice of grouting method have an impact on the development of the bonding. Bruce et al. (1997) showed that grout/ground bond is most affected by the grouting method. Based on the type of pressure applied during the grouting process, micropiles are classified as follows (FHWA, 2005): Type A: grout is placed under gravity pressure only using either sand-cement mortars or neat cement grout. Type B: pressures typically in the range of 0.5 MPa to 1 MPa are applied in order to inject the neat cement grout into the drilled hole while the temporary drill casing is withdrawn. Type C: involves two-step process; neat cement grout is first placed in the hole under gravity pressure head only as in type A, and prior to the hardening of this primary grout, a similar grout is then injected via a preplaced sleeved grout pipe at a pressure of at least 1 MPa. Type D: like type C, this type is a twostep process: neat cement grout is placed in the hole under gravity pressure head only (but pressure could be applied in some cases), additional grout is injected via a sleeved grout pipe at a pressure of 2 MPa to 8 MPa once the primary grout has hardened. In some cases, a packer is used inside the sleeved pipe, enabling specific horizons to be treated. Recently, Type E micropile is proposed, which involves"

Jan 1, 2014

By Elizabeth Varghese, Sanket Rawat, Prachuryya Kaushik, Ravi Kant Mittal

"Geo5 Software is gaining popularity worldwide due to its expediency in analysis and design of pile foundation. The analysis is based on various theoretical, empirical and semi-empirical methods available in existing literature and various country standards. Moreover, the ultimate resistance of pile in the software is based CSN 73 1002, Fellenius method, NAVFAC DM 7.2 and Tomlinson method. Due to the specificity in calculation of ultimate resistance, it becomes necessary to validate the results arrived using the software for better accuracy. Furthermore, the above-mentioned methods are not necessarily popular in every design offices. Therefore, an attempt has been made to predict the efficiency of Geo5-v15 software to analyze the pile foundation by comparing it with the results obtained using the analysis based on Indian Standard IS 2911:2010, performed with spreadsheet specifically designed for the same purpose. The accompanying outcome of the comparison and several shortcomings found in the design part associated with the software has been highlighted in the later part of the paper. Besides, the optimization tool present in the software is also described for the more efficient and economic design of pile foundation, hence contributing as practical aid to structural engineers.INTRODUCTIONThe analysis of individual pile foundation and pile in groups can be said to include the three main important parameters – Ultimate bearing capacity, Settlement and Structural Design. The first two parameters are to be evaluated to check the reliability of foundation against ultimate limit state and serviceability limit state. The third parameter includes the analysis of pile against both horizontal and vertical load. This parameter mainly intends to evaluate the size of foundation and the amount of reinforcement. Geo5 is a software which can expediently compute the above mentioned three parameters just by the mere input of the necessary factors. The ultimate bearing capacity analysis in Geo5 is based on various theoretical, empirical and semi-empirical methods available in existing literature and various country standards depending upon the drained and undrained condition of soil (Bowles, 1968; CSN 73 1002,1987; Felenius,1991; NAVFAC DM 7.2,1984; Tomlinson,1977). However, the method mentioned in IS 2911 (2010) is not the same and have slight variations in way of evaluating the parameters which affect ultimate bearing capacity. Therefore, it becomes necessary to evaluate the efficiency of Geo5 with respect to the value of ultimate bearing capacity and therefore, asserting the confidence in the software based method for the convenience of the designs in Indian Scenario. The present study aims to evaluate the efficiency of Geo5 v-15 software in predicting the ultimate bearing capacity of pile foundation. The results of the software are compared with the bearing capacity calculated using IS 2911 (2010) with the help of excel sheet. Moreover, as the software is frequently put under revision, therefore a comparison of this version has also been made with the latest version of Geo5 (2017) to check whether the latest revision has accounted for the discovered shortcomings. The design steps performed in the software is also shown. As Geo5 make use of IS 456 (2000) for the design purpose, hence it can be considered as reliable with respect to the estimate of the third parameter. Furthermore, the optimization process is also shown in the later part of the paper to emphasize the simplicity of the software in economizing the design cost."

Jan 1, 2017

By O&apos, M. W. Neill

Mini-piles have been found to be a practical, technically correct remedial underpinning method. They can be constructed in limited access areas with very little disruption. Experience indicated that mini-piles installed using a down-the-hole soil displacement hammer would be particularly effective in the "bottomless" Beaumont Clay formations in the Houston, Texas, U.S.A. area. The University of Houston Foundation Testing Facility was ideally suited to perform tests on mini-piles. The availability of extensive geotechnical data and previous pile test results was invaluable in evaluating the mini-pile test data. As expected, the mini-pile test results were consistant with test results from large sized driven piles in the same soil formation.

Jan 1, 1989

By Ryan Higbie, King Chin, Matthew Anderson, Mike Huggins, Rian Johnson, Dave Sinsheimer

"The Permanent Canal Closures and Pumps (PCCP) project is the capstone piece of New Orleans’ extensive hurricane risk-reduction system constructed following Hurricane Katrina. The project consists of three discrete pump stations and flood gates on the shore of Lake Pontchartrain which provide a storm surge barrier and pump rainwater from the City of New Orleans’ primary drainage canals. The depth of the pump station structures ranged between 39 and 45 feet below sea-level. USACE developed the PCCP project for design-build delivery; granting the project team latitude to develop innovative, cost effective solutions for the project. The use of OPEN CELLTM cofferdams to construct the pump station structures was one such innovation. OPEN CELL structures utilize the strength of the retained soil to anchor cellular sheet pile face arcs; allowing a free-field of construction within the cofferdam. This cofferdam design did not require ground improvement or dewatering around the perimeter of the cofferdam. The free-field cofferdams streamlined construction and large equipment installation within the structures with no encumbrance from internal bracing. Meticulous force-based design, soil-structure numerical modeling, and physical testing were all techniques used to present and gain USACE acceptance of the design on this vital element of the work.PROJECT DESCRIPTIONThe Permanent Canal Closures and Pumps (PCCP) project is the capstone piece of the City of New Orleans’ extensive hurricane risk-reductions system constructed following Hurricane Katrina in 2005. The project encompasses three separate pump stations and floodgate structures located at the mouths of three outfall canals (17th Street, Orleans, and London) on the south shore of Lake Pontchartrain. These three canals, running from the south to north, act as the primary conduits for discharging water from the New Orleans area. Prior to Hurricane Katrina, these canals were operated with pump stations two to three miles upstream of the mouths at Lake Pontchartrain. This left long stretches of levee on each side of the canals exposed to storm surges entering from the lake. Three levee failures occurred along these canals during Katrina; two at London Canal and one at 17th Street Canal. The failures resulted in major flooding of the surrounding neighborhoods, significant damages, and loss of life.Following initial canal levee repairs after Hurricane Katrina, USACE, in partnership with the Louisiana Coastal Protection and Restoration Authority (CPRA), took action to move the line of flood protection to the mouths of these three canals at the edge of the lake. By cutting off the storm surges from Lake Pontchartrain at the entrance to the canal, over ten miles of canal levee would no longer be exposed to storm surge water elevations, significantly decreasing the risk of failure."

Jan 1, 2017

By Emöke Imre

A point-symmetrical linear coupled consolidation model with displacement boundary condition is suggested for the description of the consolidation around the pile tip after pile penetration. Analytical solution is given. Main features of the solutions are predicted by the analysis of the system of differential equations and, the boundary conditions.

Jan 1, 2002

By Yu Zhenquan

At the construction site of Bao Shan Iron &. Steel Mill in Shanghai, lots of RC driven piles with length of 50 to 60m were applied. The most unfavourable distribution of stress along the pile shaft was known by measuring the compressive and tensive stresses. With analysing the test results a phenomenon of impact fatigue of RC pile was discovered, the range of impact fatigue and its critical zone can be distinguished. Finally some countermeasures are presented to avoid the impact fatigue of RC long pile.

Jan 1, 1991

By Ken Andromalos

Continued population growth combined with limited water resources in the Denver area has resulted in the conversion of a number of mined out gravel pits in the area into municipal water storage facilities. The use of slurry walls provides a cost effective means of isolating groundwater to convert these pits into efficient water storage facilities. Design considerations include: stability, underlying bedrock conditions, backfill mix design and earthwork requirements. Installation issues during construction include: trench stability considerations when excavating through relatively clean sand and gravel deposits in potentially high groundwater conditions; keying into three to ten feet of fractured claystone, siltstone or sandstone that makes up part of the Denver formation, and quality assurance procedures to assure a proper groundwater barrier is constructed. The paper concludes with two brief case histories to illustrate how these considerations are applied

Jan 1, 2007

By Wesley Schmutzler

The Deep Mixing Method (DMM) was employed to raise and support the LPV (Lake Pontchartrain and Vicinity) -111 Levee in New Orleans. Even using innovative technologies, the tight schedule to achieve the 100 year elevation by June 1, 2011 was a daunting endeavor. The size and scope of DMM proposed for LPV-111 was on a scale never attempted outside of Japan. Over 1.65 million cubic yards of DMM was installed. LPV-111 is adjacent to the Bayou Sauvage Wildlife Refuge, which is the largest urban National Wildlife refuge in the United States. By utilizing DMM to control settlement and improve stability of the taller levee, side slopes were steepened from the conventional 1V:4H to 1V:2.85H, thus avoiding encroachment into the Bayou Sauvage and reducing the amount of clay needed for the completed levee. The COE utilized Early Contractor Involvement (ECI) for this contract. The ECI process allowed for input from the DMM contractor, TREVIICOS South, in order to optimize equipment resources and material requirements. This paper gives an overview of the extensive DMM requirements for LPV-111 and explains the benefits of the ECI process.

By Jay A. Berger

Nondestructive testing of deep foundations for integrity problems made great strides in the late 1980's. Inexpensive portable computers have allowed the immediate and rapid processing of field measured acceleration records which can provide insight into the relative structural integrity of a previously installed foundation member. Although the gathering, processing and displaying of the data is now straightforward, interpretation remains at times rather challenging. This paper provides a brief introduction into the theoretical basis for data interpretation and the hardware necessary for data acquisition. Five case studies are discussed which demonstrate the varied applications of low strain integrity testing of deep foundations and the efficiency at which they are completed. BACKGROUND One dimensional wave mechanics, when applied to a linear elastic pile with a length that is an order of magnitude greater than its width, provides a straightforward basis for the interpretation of motion measurements made at a pile top. When impacted, a stress wave travels through the pile at a wave speed, c, which is a function of the elastic modulus, E, and mass density p (i.e., E=pc2). The applied load F, and particle velocity v, at a point are related by the equation F=Zv. For a cross-sectional area A, the proportionality constant Z is equal to EA/c. Because Z is a measure of the pile's resistance to change in velocity it is called the pile impedance.

Jan 1, 1990

By C. J. Kirkland

For two thousand years and more, we insular Britons have been grateful for the existence of the narrow strip of water that separates us from mainland Europe. It has given us a sense of security against invaders, though it has been breached many times. The first recorded serious consideration of a fixed crossing of the English Channel was in around 1802, when it was suggested to Napoleon I. The motive was not entirely peaceable and the British Navy, who saw themselves as defenders of our shores, were decidedly unenthusiastic A whole series of imaginative schemes were proposed in the course of the nineteenth century, embracing viaducts, immersed tubes, artificial islands as resting places for the horses which were to draw carriages, as well as mechanically bored tunnels. The first Channel Tunnel Company was formed in 1872, and an application for permission to construct a tunnel was made to the British parliament. A Colonel Beaumont, of the Corps of Royal Engineers designed and constructed a machine which, in around 1882, bored over a mile of tunnel out to sea from Britain which exists to this day.

Jan 1, 1991

By Matthew Janes

Statnamic load testing is becoming widely accepted as a method to quickly and economically determine the load-deflection behaviour and ultimate static resistance of high capacity deep foundations. Strain instrumented large diameter bored shafts were tested at four locations for the federal and state Departments of Transportation in the United States. Tests were conducted vertically (to 30 MN) and laterally on the shafts and, in some cases, testing was completed over water. Instrumented shaft test results provided shaft load distribution with depth and shaft shear transfer stress throughout the soil stratum. Shaft end bearing and ultimate end bearing stress values were provided. On two projects, Osterberg load cells provided comparative static data for skin friction and end bearing. Correlations between Statnamic derived static load-displacement results and Osterberg load-deflection results are very good. Statnamic lateral load test results were correlated with static lateral results in addition to providing useful dynamic response and damping data.

Jan 1, 1996

By Shahid Islam, Lucian Bogdan

There is a rapid expansion of world’s infrastructure and simultaneously existing infrastructure is aging. The maintenance of infrastructures has been of particular concern to the engineering community. Monitoring and evaluating the structures have become more significant than ever. Ground anchor is an important part of the structure where it is installed. Unfortunately there are limited testing methods available to assess the force in the pre-stressing steel. High cost, complicated equipment and limitation of space often prevent these methods from being implemented. DYNA Force sensors have been developed to measure the force in the pre-stressing steel during construction and at any time during the lifetime of the structure. These sensors make use of the magneto-elastic properties of ferrous materials. A readout unit is designed to magnetically energize the steel through the sensor and measure the response of the steel to the process. The readout unit then converts the response into a direct force reading. They can be used for bare, epoxy- coated, galvanized and greased-sheathed steel in the bonded, un-bonded, grouted or un-grouted length of the tendon. It measures the force of the steel element at the location where it is installed and can be recorded manually, automatically, or remotely. The sensor is robust, requires no maintenance and it is expected to have a similar service life to that of the surrounding structure. Sensors have received attention in terms of accuracy, performance, ease in installation, durability, and cost effectiveness. Sensor readings provide a second measurement, in conjunction with the jack pressure gauge, of the post tensioning force during initial testing procedure for ground anchors. This paper describes its application in tie-back and tie-down anchors and force monitoring of retaining walls, bridge abutment and dams where the data were collected manually, automated and remotely. INTRODUCTION Our infrastructure is expanding and the existing infrastructure is aging. Some structures are expensive to maintain and some occasionally fail. There is a large demand for implementing health monitoring of structures. Many tie-backs, retaining walls, dams and other geotechnical structures are post-tensioned and many of them need repair using a post-tensioned system. On many occasions during construction and service life of the structure, it is useful to know the force in the post-tensioning and anchor system. Many piles and drilled shafts are designed using reinforcing steel and the compressive forces in reinforcement are unknown. Although there are many methods to measure the tendon force, most of them are cumbersome, expensive, and the accuracy varies depending on the method used.

Jan 1, 2018

By Robert R. Morrison

Alberta Piling Contractors very rarely are required to perform major marine construction in the prairies, so it became as a big surprise to AGRA Foundations Limited to be invited by Transalta Utilities Corporation to bid on a major marine project for the Sundance Cooling Pond Expansion at Lake Wabamun, Alberta. Even more of a shock, the work had to be undertaken during Alberta's harsh winter conditions with temperatures plunging to -30 C. Not a happy situation for prairie construction workers to be in, working from barges in the middle of a lake in the dead of winter. However, it is well known that prairie boys make the best sailors.

Jan 1, 1997

By Minna Karstunen, Patrick Becker

"Abstract The deformation behaviour of a foundation on deep mixed columns in a natural soft soil is a three-dimensional problem, which has to be considered adequately in numerical modelling. However, simplifications are often made due to the computational costs of fully coupled 3D analyses by either modifying geometry of the problem or material parameters in 2D for plain strain analyses or by modelling the problem as 2D axisymmetric case. The volume averaging technique (VAT) is an enhanced 2D FE technique that enables mapping the 3D problem in two-dimensions, yet modelling the two constituents (column and soft soil) with appropriate different constitutive models within a homogenized material. The performance of the volume averaging technique is demonstrated by considering unit cell simulations of floating and end bearing columns in soft soil. The results with VAT are compared and validated against conventional 2D axisymmetric and fully coupled 3D finite element analyses.IntroductionThe properties of very soft clays, silts and organic soils can be improved by stabilizing agents, such as lime and/or cement that are mixed into the soil in situ by using auger-type mixing tools in situ. Deep mixed columns are extensively used to reduce deformations and to improve the overall stability of embankments and foundations on soft soils. Whilst the most typical applications are embankments, increasingly the method is used under foundations. The first category of applications is very common in Scandinavian countries, whilst the latter application has been pioneered in Poland, as an environmentally friendly (low CO2) and cost effective alternative for piling. Due to economic and environmental reasons there is an increasing interest in the technique elsewhere in Europe. With deep mixing, the strength and deformation properties of the soft soil can be improved, and the risk of unwanted deformations is substantially reduced.Numerical methods, such as finite element (FE) analysis, can be used as an alternative to conventional design methods. They are particularly suitable when considering serviceability limit state, i.e. deformation analyses under working loads. FE analyses allow using advanced constitutive models that take account of the complex stress-strain behaviour of natural soil and stabilized columns, respectively. The problems that involve a grid of circular columns under an embankment or a strip footing are fully three-dimensional problems. As 3D analyses are very laborious and expensive, an enhanced 2D technique using the so-called volume averaging technique (VAT) is utilised. The basic idea is to describe the column-improved ground as a homogenized composite material, and using clever mathematics to map the true 3D problem into 2D. Once the constitutive relations of both composites are defined, the response of the column-improved ground can be simulated in 2D subject to arbitrary loading and boundary conditions."

Jan 1, 2014

By James Su

The Green River Valley in Kent, Washington, is a fast growing area containing retail facilities, warehouse factories and industrial businesses, including the Boeing Space Center. Traffic from Interstate - 5 to the West Valley Highway is highly congested. Accordingly, a new corridor, including a bridge across the Green River, was designed and constructed between 1996 and 1997. This paper presents a case history of the design elements and issues associated with the construction of the pier foundations of the bridge. Subsurface conditions were evaluated using both deep test borings and CPT soundings to evaluate the strength and consolidation properties of the supporting soils. Subsurface conditions consisted of alternating layers of loose and medium dense silty sand and sandy silt. Engineering analysis included an assessment of liquefaction as well as pier supporting capacity and associated settlement. The constructed foundations included 6-foot-diameter piers cased to a depth of 120 feet below the ground surface. The pier casings were driven to the design tip elevation and the soil inside the casing was removed by drilling. Despite performing borings and CPT soundings at specific pier locations, occasional trees, buried thousands of years ago through geologic processes, were surprisingly encountered during pier construction. This presented unique and difficult driving and drilling conditions. During drilling, the water level inside the piers was maintained near the ground surface to create a balance of hydrostatic pressure and prevent boiling of soils the bottom of the casing. After the casings were installed, the soil inside the casing was excavated, the rebar cage was installed and the pier was filled with concrete using treme techniques. Construction of the piers is complete and the completed piers have experienced negligible settlement. Owner: City of Kent Engineering Department Timothy La Porte, Project Manager Kent, Washington General Contractor: Mowat Construction Company, Kirkland, Washington Foundation Contractor: Condon - Johnson & Associates, Inc., Tukwila, Washington

Jan 1, 1998