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By Michael W. Neill, O&apos

The performance of foundations that combine the high bearing capacity of rafts (mats) with the settlement reduction capability of piles is described through a summary of 24 case histories. Structures included are high-rise commercial office buildings, governmental buildings, industrial facilities and residential buildings, and subsurface conditions range from soft clay to stiff soil overlying rock. Pile types are bored, augered and driven. Since piled rafts are not commonly used in the United States, most of the case histories are from overseas. In all cases the performance of the foundations was monitored during and after construction. Particular emphasis is placed on measured settlements of the piled-raft foundations, distribution of resistance between piles and raft, and general analysis methods that were used by the designers for various geotechnical circumstances. Finally, patterns of behavior are summarized. In most cases, the piles were not designed to mobilize their full capacities under sustained loading of the foundation; therefore, under long-term loading conditions, the piles typically carried more load than the raft. This paper is the result of a study conducted by ITC-18 (Deep Foundations, Willem Van Impe, Chair) of the International Society for Soil Mechanics and Geotechnical Engineering by a subcommittee chaired by the author.

Jan 1, 2003

By Andrew Baxter

The Crystal Bridges Museum of American Art in Bentonville, Arkansas is a beautiful glass and concrete structure cut into a valley that mingles with water ponds spanned by multiple bridges with suspended roofs. Or, at least it will be when completed in 2009. At Crystal Bridges, most of the proposed buildings involve cuts up to 50 ft high to be retained by the building structures. This requires the construction of retaining walls adequately founded to support lateral loads of up to 70 kip/ft. To add to this difficulty, the site is within a karst region with all the variability and irregularities associated with solutioning and erosion of the parent rock in this environment. The irregular rock profile made it virtually impossible to conceive a predictable arrangement of shallow footings and shear keys for the retaining walls. The existence of layers of soft soils within a hard rock formation made a caisson foundation impractical. The authors developed an innovative solution based on micropiles, which proved to be invaluable from a cost and schedule point of view. In areas where rock was shallow, micropiles were used as ?shear pins? to transfer the horizontal loads to the rock. In areas with significant overburden, a system of vertical and battered micropiles was devised to carry vertical and horizontal loads from the retaining walls. This paper presents a detailed description of the design and installation of the micropiles used as shear pins, and includes the results of lateral load tests performed on full-scale models of the grade beams on shear pins. The work performed shows that micropiles in rock can be effectively utilized for support of significant lateral loads provided that an adequate arrangement of suitably sized micropiles is provided, and that micropiles used as shear pins may develop significant tensile stresses when loaded laterally.

Jan 1, 2008

By C. W. Sheng

In this paper conventional construction procedure is briefly described for the installation of stone columns in soft ground in China. A viewpoint concerning the mechanism of ground improvement by use of stone columns is presented for discussion. Based on the information obtained from field measurement and observation three important problems relating to the construction and design of stone columns are discussed. Finally, a case history is given to show that short stone columns floating within the weak soil layers may in some instance be used to improve the weak strata of great thickness.

Jan 1, 2010

By George Burke

Of the three projects, particularly the extensive Nimitz II (downtown) project, a single system, which was part of the operation, was used to control the spoil. Spoil control was continuous with the work since a vacuum truck and crew was used to suck up the spoils as they came out of the borehole. So, the whole job was kept clean both during operations and at the end of the shifts. On the Sand Island project, a double system was used. Larger spoil quantities were contained within the shaft limits during the work and the cleanup or disposal of the spoils was performed during excavation.

Feb 10, 2003

By Sepideh Damavandinejad Monfared

In recognition of the practicality of using inclined micropiles as elements for foundation support to resist static and seismic loading conditions, specifically in retrofitting projects, this study presents an investigation into the beh avior of an inclined micropile subjected to simultaneous lateral load and bending moment. Three-dimensional numerical simulations are performed using the finite element method to assess the influence of micropile geometrical parameters such as angle of inclination, length, and diameter on the response of micropile-soil system. The Mohr-Coulomb failure criterion is used to define the behavior of soil and stabilized soil around micropile materials and the micropile, constructed of concrete and steel, is assumed to be elastic. The interaction between soil and micropile is taken into account by defining interaction elements covering both tangential and normal behavior. The study is carried out using nonlinear FEM analyses. The results of these simulations indicate that negative micropiles, in which slip surface deflects downward, have higher lateral load capacity than positive micropiles with slip surface deflecting upward. The conducted research also shows that increasing the diameter and the length of micropile increases the lateral load capacity. Increasing micropile diameter is more effective in increasing lateral load capacity. A relationship is developed from statistical regression analysis of the finite element modeling computations to estimate the lateral displacement of a micropile inclined at an angle of 30o in silty sands.

By Y. W. Mou

In order to improve the construction of pile foundations and deep foundations of largo sizes, the paper deals with the method of installing square or rectangular bored-piles for annular foundation as well as large-sized hollow or solid foundation.

Jan 1, 2010

By Manish Kumar

One of the recent advances in the field of testing of concrete piles is the Non-Destructive testing (NDT) of piles. This paper deals with a specific project where this technique was employed along with an extensive program of conventional testing methods to cross check the results. Conventional testing of the Bored, cast-in-situ piles involved taking full length concrete cores from piles to check physical properties such as core recovery, RQD, crushing strength and density of concrete. Additionally, a number of questionable piles were exposed and inspected and actual load tests were performed on selected piles. Concrete pour cards were used to compare actual Vs theoretical consumption of concrete. A direct comparison of the conclusions drawn from both these testing methods provided an excellent opportunity to better understand the intricacies of NDT technique. The study undertaken clearly indicated a need for developing clear guidelines and specifications for the use of this method of non-destructive testing of piles before the .method can be accepted as a useful quality control tool at the construction sites.

Jan 1, 1996

By Sepideh Damavandinejad Monfared

"In recognition of the practicality of using inclined micropiles as elements for foundation support to resist static and seismic loading conditions, specifically in retrofitting projects, this study presents an investigation into the behavior of an inclined micropile subjected to simultaneous lateral load and bending moment. Three-dimensional numerical simulations are performed using the finite element method to assess the influence of micropile geometrical parameters such as angle of inclination, length, and diameter on the response of micropile-soil system. The Mohr-Coulomb failure criterion is used to define the behavior of soil and stabilized soil around micropile materials and the micropile, constructed of concrete and steel, is assumed to be elastic. The interaction between soil and micropile is taken into account by defining interaction elements covering both tangential and normal behavior. The study is carried out using nonlinear FEM analyses. The results of these simulations indicate that negative micropiles, in which slip surface deflects downward, have higher lateral load capacity than positive micropiles with slip surface deflecting upward. The conducted research also shows that increasing the diameter and the length of micropile increases the lateral load capacity. Increasing micropile diameter is more effective in increasing lateral load capacity. A relationship is developed from statistical regression analysis of the finite element modeling computations to estimate the lateral displacement of a micropile inclined at an angle of 30o in silty sands. IntroductionMicropiles are small diameter (typically less than 300 mm), cast-in-place, drilled, and grouted replacement piles with steel pipes which after being conceived in Italy (Lizzi,1978), were originally developed for underpinning existing structures (Bruce et al.,1990) to arrest and prevent structural movement, upgrade loadbearing capacity of existing structures, repair or replace deteriorating or inadequate foundations or raise settled foundations to their original elevation."

Jan 1, 2017

By Sam Messina

[Project: Job Number: Date: Superintendent: Person Making Inspection: Note: The following checklist shall be used on a regular basis as an overall assessment of the jobsite. The checklist is not all-inclusive. All applicable Federal, State, and local regulations, standards, and ordinances pertinent to the jobsite conditions must be evaluated on a continuous basis. Column A - Adequate Column I ? Inadequate]

Jan 1, 1998

By Jeffery L. Ottesen

Early construction delays can jeopardize timely completion of subsequent work. As an early construction activity, and due to many unforeseen issues, deep foundation work inherently bears great potential for impacting the critical path of a planned construction schedule. This article describes two construction projects where delays related to deep foundation work forced the Contractor to consider various schedule recovery alternatives to mitigate those delays. Specifically, deep foundations on Vancouver BC's Millennium SkyTrain light rail extension and on a Mill Facility in the United States are discussed. This article cites examples of permitting delays, alleged design changes, differing subsurface conditions and changed construction methodology, the effect each problem had on the project, the mitigation means implemented by the Contractor to minimize adverse impacts of the problem, and Lessons Learned for each scenario.

Jan 1, 2002

By Naim Noori Samie

Lateral force rsistance of piles is analytically investigated by dividing the pile length to 3 segments. The first segment (Zone I) models the load eccentricity with respect to the soil and the pile-deck connection, using a third degree differential equation representing the shear variation along the pile. The soil is assumed to be uniform, homogeneous with an elastic-perfectly plastic behavior. The Top soil layer (Zone II) is assumed to be stressed beyond the elastic limit. A simple 4th degree differential equation represents this zone. The soil resistance is assumed to vary linearly with depth (or surcharge). The pile deformation and soil behavior determines the plastic zone length. In zone III the soil is assumed to behave elastically, hence its resistance is proportional to its deformation. A linear 4th degree differential equation is employed in this zone. The compatibility conditions are satisfied on each boundary. Maximum allowable moment and shear are investigated throughout the pile as the basic limiting criteria on lateral force capacity. In this paper the soil coefficients are taken from a proposal by ref(3), and the results are compared with the soil response as determined by the P-Y method as recommended by ref(2).

Jan 1, 1996

By Ryan Law

Ground energy systems are being installed in increasing numbers in the United Kingdom. This is particularly true in London where planning regulations require larger scale developments to provide at least 10% of their entire energy demands from renewable sources. A common approach has been to use the groundwater from the Chalk aquifer as a source of energy. This paper explains the potential long and short term sustainability problems with groundwater based systems sited in central London (or any other urbanized area). It also outlines an approach to site testing and numerical modelling to ensure that the system functions well throughout its lifetime. This approach is then applied to a project located in central London.

Jan 1, 2008

By Paul W. Mayne

The axial load-displacement-capacity and load-transfer response of deep foundations can be conveniently assessed by geophysical piezocone tests that provide four independent readings with depth, including tip stress (qt), sleeve friction (fs), porewater pressures (ub), and shear wave velocity (Vs). The penetration data (qt, fs, and ub) of the CPT are utilized to obtain the pile side friction (fp) and end bearing capacity (qb) while the shear wave measurements provide the initial stiffness. Within an elastic continuum framework, the axial pile deflections are calculated and an approximate nonlinear response is obtained by modulus degradation from small-strain response (G0) to intermediate- and large-strains (G). The continuum solution permits separation of load transfer along the sides and proportion to the base. Applications are shown for case studies involving an end-bearing drilled shaft, two friction-type drilled shafts in Alabama and Georgia, and a "Class A" prediction involving driven pipe piles in residuum of the Atlantic Piedmont geology. Load-transfer data were available for the drilled shaft foundations.

Jan 1, 2002

By Wei Tu

A grade separation was required to allow uninterrupted traffic crossing for a busy rail spur and a county road. The grade separation was achieved by creating a 30-foot (9-meter) high embankment that incorporates two multiplate tunnels and allows the passage of a rail spur and an existing county road. The site is located in an abandoned meander channel in the floodplain of the Mississippi River, near Osceola, Arkansas, and is underlain by more than 40 feet (12 meters) of soft clay and interlayered clays, sands and silts. Without soil improvement, the post-construction settlement would exceed 3 feet, slowly crushing the proposed tunnel structure and cutting off the railroad. Preloading, combined with vertical drains, was used to accelerate the consolidation of the underlying soil layers and to reduce the post-construction settlement under working loads. Six settlement plates were installed to monitor the progress of consolidation under surcharge load. The Asaoka observational method and the hyperbolic fitting method were used to analyze the measured settlement data to predict the end of primary settlement. The in-situ consolidation coefficient, ch, was back calculated from the measured settlement data. The stress release caused by the removal of the preloading surcharge load and the tunnel installation was determined using a Plaxis 3-D finite element model. The measured and predicted settlement using Hansbo's analytical solution demonstrated reasonable agreement. Early removal of the surcharge and construction of the tunnel prior to reaching the end of primary settlement was accomplished by analyzing the post-excavation stress reduction achieved via tunnel construction.

Jan 1, 2009

By Safwan Labanieh

An experimental set-up is specially designed to study the behavior of a friction pile of 3 cm diameter in contact with the soft clay of Mexico City in a small calibration chamber (CC) of 30 cm diameter and 50 cm height. The consolidation of this compressible clay is accomplished using a special system adapted to the CC itself to insure a good knowledge of the initial state. Loading results of the pile under a consolidation pressure of 50 kPa indicate an elastic mobilization of shear stresses at the shaft of the pile (?3 kPa for 1mm displacement) followed by a hardening plastic type behavior. Unloading-reloading results indicate a mobilization of shear stresses of the same type and of the same order of values obtained from the virgin loading stress path. Cyclic loading (?40 cycles) between 0 and 1 kPa (1/3 of the failure value) give similar results to those obtained from virgin loading.

Jan 1, 2002

By Jiun-Yih Chen

Pile load tests are regularly used to verify pile capacities. Sometimes, they are used to optimize pile designs. This paper presents a case study based on a real project, in which the information obtained from load tests during construction was used to shorten the design pile lengths without a formal decision analysis. In this study, a simple probabilistic model was used to assess the probabilities of failure based on design information. The Bayesian approach was used to update the probabilities given the additional information from load tests. These probabilities were then used in a formal decision analysis to determine the optimal pile lengths based on design information and based on the additional information from load tests. The optimal pile lengths are different from those implemented in the project without a formal decision analysis. The value of the formal decision analysis is illustrated by its ability to optimize the pile length in a transparent and defendable way.

Jan 1, 2009

By X. L. Chen

The diaphragm walling has been recently adopted in one of the largest excavation of deep foundation engineerings in Shanghai, China with dimension of 90m in length, 50m in width and 13m in depth to solve its stability problem. In this paper the field test for monitoring the stability of the diaphragm wall is discribed, in which the excess pore water pressure and the horizontal displacement of the clay layers were monitored during the period of the excavation. The data measured in the field test are efficient for the safety during construction.

Jan 1, 2010

By J. L. Liu

Long-term maintained load test on the bored pile group in unsaturated silty soil has been carried out. And the research on the time effects of bearing behavior of pile group has been done by the method of installing pressure cells and reinforcement stress gauges for measuring the soil reaction beneath the cap and the pile bottom as well as the shaft resistance. The test shows that, within a certain duration after loading, the soil reaction beneath the cap and the pile point resistance increase with time; but the shaft resistance decreases. The load distribution among the pile tops in the group tends to be even with time. The shaft resistance redistributes along the pile shaft with time, that is, getting less in the upper part, getting larger in the middle. The redistribution does not tend to stop till the distribution in both upper and middle part becomes to be uniform. The load-bearing conditions of soil beneath the cap of pile group and the variation in time effects with related factors also have been discussed.

Jan 1, 2010

By Dhanvin B. Mehta

Pile testing is generally understood as static load test. It is our common experience that for high capacity, large diameter bored piles, static testing is expensive and time consuming. It is practically impossible to test large number of piles by traditional testing methods. The escalating cost in carrying out a static load test, as well as incomplete information derived therefrom compelled researchers in United States to look for an alternative method of testing for both bored and driven piles. The original research work was carried out at Case Western Reserve University in early 70's, under the funding of Federal Highway Administration as well as several State Depts. of transportation in United States. The outcome of the research was the development of a state of art field computer for capacity determination, based onOne Dimensional Wave Mechanics.

Jan 1, 1996

By Jesús E. Gómez

A recent bridge underpinning project provided a unique opportunity to obtain information on the load-deflection response of 260 hollow-core bar micropiles. All production micropiles were proof-tested to a maximum load of 125 percent of the design load. In addition, four verification tests were performed on sacrificial micropiles to at least two and a half times the design loads. This paper presents the results of the verification and proof tests performed for this project, and provides recommended values for design of hollow core bar micropiles in soils similar to those encountered. This work shows that hollow core bar micropiles provide a significant unit bond capacity in both granular and fine soils, which may be greater than that typically expected in pressure-grouted (Type B) micropiles. The hollow core bar system allows faster installation rates in the soil types encountered than other traditional micropile techniques, and can be installed with relatively simple quality control procedures.

Jan 1, 2007