Instrumented Test Piles Research Articles

Discussion of “Distribution of residual load and true shaft resistance for a driven instrumented test pile”1Appears in the Canadian Geotechnical Journal,48(4): 583–598 [doi: 10.1139/t10-084

The authors have presented a well-documented case study of the load test interpretation of prestressed high-strength concrete (PHC) piles, which are very popular in the Far East and are often favoured over steel piles on the basis of cost. Despite their popularity, well-analyzed load test case histories are rare and hence the authors’ paper is a valuable contribution to the technical knowledge base. Although the authors’ have considered the geotechnical aspects in detail, the discussers believe that this case study also would benefit from a fuller analysis of the structural conditions of the piles. This is because the authors have identified that the key design aspects for this site are actually the maximum load in the pile and the pile structural strength, but not the pile capacity. Based on the load test results, the authors concluded that the long-term maximum load in the pile will approach the pile structural strength and hence grouting the central void should be considered. The discussers have carried out an assessment of the pile strength using a different approach and compared the results with the current design guidelines. It was found that even with the central void grouted, the PHC piles are still not sufficiently robust and a different pile size or type may need to be considered. The discussers’ assessment and, where appropriate, comparisons with the authors’ results are described as follows.

Newly Developed Test Pile Intended to Improve Pile Design

A reusable instrumented test pile may help engineers improve the design of their pile foundations.

Distribution of residual load and true shaft resistance for a driven instrumented test pile

Foundation conditions are studied for a series of apartment buildings in a shore area reclaimed from the Nakdong River estuary delta west of Busan, South Korea, in full-scale field tests on two 600 mm, post-driving grouted, concrete cylinder piles instrumented with strain gages, driven through compressible layers and a short distance into underlying dense sand at depths of 56 m (Shinho) and 35 m (Myeongji). One test pile was provided with an O-cell so that after an initial O-cell test, a subsequent head-down test only affected pile shaft resistance. The purpose was to evaluate drivability of the piles, magnitude of the drag load due to consolidating soils, and potential settlement (downdrag) of the piled foundations. Early in the study, it became apparent that the internal process of heating and cooling of the grout during the hydration process and swelling from absorption of water affected the strain records and the assessment of residual load in the test piles during the wait time before the static loading test. The paper reports the measurements, analyses, and method for determining residual load, strain-dependent modulus of test piles, and actual load distribution in the test piles. The results are correlated to cone penetration test (CPTU) sounding data and effective stress analysis.

Pile Load Test and Implementation of Specifications of Load and Resistance Factor Design

An instrumented pile load test was performed as part of the foundation design for the Caminada Bay Bridge project in south Louisiana. Both static and dynamic load tests were performed. The load-transfer curve of the test pile was obtained from strain measurements by using sister bar strain gauges at six locations along the pile shaft. The test pile resistance was determined by the Tomlinson method for cohesive soils and by the Nordlund method for cohesionless soils. The dynamic and the static load testing results indicated the test pile did not achieve the desired design resistance. The static analysis model was calibrated on the basis of observations of the pile load testing program. The design pile length was revised to benefit from the shallower scour depths for the revised pile design. The low resistance of the test pile resulted in the engineer's decision to use dynamic testing on the production piles to ensure adequate resistances. Taking advantage of the static load test of the instrumented test pile instead of simply using the smaller resistance factor from dynamic tests, the engineer combined the results of the two test methods and used a combination of resistance factors from both the static and dynamic load tests. This paper presents the evaluation of load test results and the rationale used for the selection of the resistance factor.

An Empirical Method for Analysis of Load Transfer and Settlement of Single Piles

An empirical method is developed for estimating the load transfer and deformation of drilled, in situ formed piles subjected to axial loading. Firstly, governing equations for soil–pile interaction are developed theoretically, taking into account spatial variations in: (a) shaft resistance distribution and (b) ratio of load sharing between the shaft and base. Then generic load transfer models are formulated based on examination of data from 10 instrumented test piles found in the literature. The governing equations and load transfer models are then combined and appropriate boundary conditions defined. Using an incremental-iterative algorithm whereby all the boundary conditions are satisfied simultaneously, a numerical scheme for solving the combined set of equations is developed. The algorithm is then developed into an interactive computer program, which can be used to predict the load-settlement and axial force distribution in piles. To demonstrate its validity, the program is used to analyse four published case records of test piles, which other researchers had analysed using the following three computationally demanding tools: (a) load transfer (t–z), (b) finite difference and (c) finite element methods. It is shown that the proposed method which is much less resource-intensive, predicts both the load-settlement variation and axial force distribution more accurately than methods: (a–c) above.

Study of Pile Setup

A new growth-rate–based model is proposed for pile setup prediction. Together with the Skov–Denver model, it has been developed for southern Louisiana clayey soils by using the pile driving analyzer database provided by the Louisiana Department of Transportation and Development from the construction of Phase 1B of the LA-1 relocation project in Leeville, Louisiana. The data used for this study include 115 restrike records from 95 production piles and the records of restrikes, static, and statnamic load tests of nine fully instrumented test piles. The models were developed with the average unit skin friction or normalized pile shaft resistances, which were obtained from the case pile wave analysis program analyses and the pile load test results. The growth-rate–based model can predict the capacity increase with time and can estimate the ultimate pile resistance. For the Skov–Denver model, selection of the reference time was investigated and distribution of the setup parameters A was studied. Predictability of the rate-based model was evaluated and validated by comparing it with the conventional Skov–Denver model.

Development of Design Practice for Piles in Stiff Glacial Till

AbstractDesign practice for piles installed in Irish glacial till has developed in an ad-hoc manner, based on the results of un-instrumented load tests. This had led to designers using similar design parameters for both CFA and displacement piles. To address the concerns of industry a series of instrumented pile tests were performed by two Irish Universities. These tests summarized herein, revealed that CFA piles develop higher shaft resistance than piles driven in glacial till. However, they exhibit low base stiffness and the end bearing resistance that can be mobilized at acceptable pile settlement is low. The use of simple non-linear elastic design approaches to predict the load-displacement response is considered. The methods are used to predict the capacity of two large diameter CFA piles installed in glacial till. While the predictions were reasonably accurate at predicting the initial load-displacement of the piles, signifi cant creep settlement developed at higher load levels. The cause of the cre...

CFA pile behaviour in very stiff lodgement till

The design of CFA piles in the stiff/hard lodgement till that underlies most of Dublin is usually based on published experience from similar piles in other soils that lack the high density and stiffness of this till. The results of load tests on two instrumented test piles are presented, one 450 mm in diameter and 12·3 m long and the other 600 mm in diameter and 11 m long, which were loaded to 3·15 MN and 4·5 MN respectively. A 1 m long instrumented dummy pile was formed at the same time as the prototype and was tested in the laboratory to confirm the calibrations for use in interpreting the instrumentation. The instrumented piles showed that high average shaft resistances of 230 kPa and 270 kPa were mobilised, which were of similar magnitude to those recorded on an instrumented driven pile in this lodgement till that was reported previously. The pile load tests indicate an estimated Nc value of about 7 for the bearing capacity factor in ultimate end resistance, which is less than the value of 9 normally used and considerably less than a value of about 55 estimated from the tests on the driven pile. The results also indicate a change in the load–pile-head deflection curves with time, which could be related to disturbance of the ground caused by the construction process.

Design and Construction of Three Instrumented Test Piles to Examine Time Dependent Pile Capacity Gain

Abstract Three heavily instrumented test piles were designed, constructed, and installed at a bridge reconstruction site in Newbury, Massachusetts as part of a research initiative into time dependent pile capacity gain. Pile instrumentation consisted primarily of an alternating pattern of piezometers and strain gages, allowing for correlation between pile capacity gain and excess pore pressure dissipation along discrete pile segments. Additional instrumentation within the piles included accelerometers, telltales, and radial pressure cells, allowing monitoring of total pressure at the pile wall. Standard dynamic gages (strain gages and accelerometers) were also attached to the piles during dynamic testing. A total of 86 vibrating wire, 17 electrical resistance, 17 telltales, and 4 piezo-resistive gages were installed within the test piles to record strain, displacement, pressure, and acceleration. This paper describes (i) the initial installation location of the test piles, (ii) the design and layout of the individual test piles, (iii) the selection and installation design of the individual instrumentation within the test piles, and (iv) assembly of the test piles. Sample measurements of the various instruments and a summary of the instrumentation performance are also presented.

Pile foundation in karstic limestone terrain: a geotechnical constraint and its solution

ABSTRACT
 The karstic limestone terrain poses complex geotechnical problems, as there are many uncertainties in terms of position and dimension of cavities, sinkholes, pinnacles, and overhangs developed in it. The study deals with the 6.5 km long Ampang­ Kuala Lumpur Elevated Highway over the rivers Kelang and Ampang in Malaysia. The large-diameter bored piles and cast in-place piles were constructed for this purpose.
 The toll plaza area is underlain by karstic limestone. In that area, the piles were located in rows extended as columns connected by crosshead whereas they were provided in pile groups of 2, 3, 4, or 5 connected by a rigid pile cap elsewhere. An instrumented test pile was load tested using static method and calibrated with site investigation results. To design the friction piles and end bearing piles, direct methods (viz. exploratory drilling and rock probes) and indirect methods (viz. resistivity survey and transient electromagnetic survey) were adopted. Based on lithologs, the piles were designed using the safety factor of 2 and 3. The rock probe results were used for designing the rock socket length of the end bearing piles.
 There was much variation between the designed and encountered rock head levels as revealed during the time of excavation. In such cases, the geotechnical design of end bearing piles was reviewed. As in most of the cases, rock probe holes were inclined (as they slid over a rock cliff, overhang, or pinnacle) giving rise to wrong information of rock head levels. To solve this problem at site, a new integrated approach was evolved considering the 3D subsurface topography of rock head level of the area, position and dimension of karstic features, rock mass classifications, and bearing capacity calculation. Based on the above parameters and other measures (underpinning, micropiling, grouting etc.), the piles were designed and load tested.

Closure to “ Mechanisms of Shaft Friction in Sand from Instrumented Pile Tests ” by B. M. Lehane, R. J. Jardine, A. J. Bond, and R. Frank (January, 1993, Vol. 119, No. 3)

Closure to “ <i>Mechanisms of Shaft Friction in Sand from Instrumented Pile Tests</i> ” by B. M. Lehane, R. J. Jardine, A. J. Bond, and R. Frank (January, 1993, Vol. 119, No. 3)

Discussion of “ Mechanisms of Shaft Friction in Sand from Instrumented Pile Tests ” by B. M. Lehane, R. J. Jardine, A. J. Bond, and R. Frank (January, 1993, Vol. 119, No. 3)

Discussion of “ <i>Mechanisms of Shaft Friction in Sand from Instrumented Pile Tests</i> ” by B. M. Lehane, R. J. Jardine, A. J. Bond, and R. Frank (January, 1993, Vol. 119, No. 3)

Behaviour of instrumented test piles under horizontal loadins (In French) : Frank, R; Zervogiannis, H; Christoulas, S; Papadopoulos, V; Kalteziotis, N A Can Geotech J V30, N1, Feb 1993, P1–11

Behaviour of instrumented test piles under horizontal loadins (In French) : Frank, R; Zervogiannis, H; Christoulas, S; Papadopoulos, V; Kalteziotis, N A Can Geotech J V30, N1, Feb 1993, P1–11

Mechanisms of shaft friction in sand from instrumented pile tests : Lehane, B M; Jardine, R J; Bond, A J; Frank, R J Geotech Engng Div ASCEV119, N1, Jan 1993, P19–35

Mechanisms of shaft friction in sand from instrumented pile tests : Lehane, B M; Jardine, R J; Bond, A J; Frank, R J Geotech Engng Div ASCEV119, N1, Jan 1993, P19–35

Mechanisms of Shaft Friction in Sand from Instrumented Pile Tests

Comprehensive measurements of the effective stresses developed during the installation, equalization, and load testing of displacement piles in a loose to medium dense quartz sand are presented. The results shed new light on the mechanisms that control shaft friction in sand. First, it is demonstrated directly that the stresses developed at any given soil horizon depend strongly on both the distance of that horizon from the pile tip and the soil's initial state. Second, pile loading is shown to induce radial effective stress changes associated with the soil fabric set up by installation and dilation phenomena at pile‐soil interface. Thirdly, the operational angles of interface friction are found to be constant volume values that correlate well with the results from laboratory interface shear tests.

Residual strength characteristics of Bothkennar clay

The Paper describes a series of ring shear experiments which were performed to assist the interpretation of instrumented pile tests carried out at Bothkennar. Data are presented from soil-soil and soil-interface experiments. The interface used was a sand blasted annulus of stainless steel and tests were made at a variety of displacement rates. The large displacement shearing behaviour was found to be turbulent, despite the soil's high clay fraction and plasticity index, with slow residual ' ~ 30°. There was no sign of the large difference often seen with high' clays between soil-soil and soil-interface tests. Marked reductions in shearing resistance were found (post-peak) in high-speed tests. These were transitory and probably associated with a change in the basic mechanisms of shearing, rather than the creation of highly ordered residual soil fabric. L'article présente une série d'essais à l'appareil de cisaillement à couronne cylindrique qui ont été réalisés pour faciliter l'interprétation des résultats d'essais de pieux instrumentés à Bothkennar. Des résultats sont présentés pour des essais sol-sol et sol-interface. L'interface utilisée était un anneau d'acier inoxydable décapé à la sableuse, et les essais ont été faits pour un grand nombre de vitesses de déplacement. Le comportement au cisaillement sous grands déplacements était du type turbulent malgré une teneur en argile et un indice de plasticité élevés, avec un angle de frottement résiduel lent 4&gt;' = 30°. On n'a pas noté la différence élevée souvent rencontrée pour les argiles à ' élevé entre les essais sol-sol et sol-interface. Des réductions marquées de la résistance au cisaillement (passé le maximum) ont été trouvées dans les essais à grande vitesse. Ces réductions étaient passagères et probablement associées à un changement du mécanisme de base du cisaillement plutôt qu'à la création d'une structure résiduelle du sol très ordonnée.

Frequency response problems to instrumented pile tests : Ground Engng V24, N4, May 1991, P28–39

Frequency response problems to instrumented pile tests : Ground Engng V24, N4, May 1991, P28–39

Bearing capacity of friction piles in marine clay

A full-scale investigation with two instrumented test piles was carried out at the St Alban test site, to study the increase in bearing capacity with time of short friction piles jacked into an over-consolidated soft sensitive marine clay. It is shown that the increase in shaft bearing capacity with time is significant and reaches about 12 times the initial shaft supporting capacity. The maximum skin friction is developed when the excess pore pressures generated during driving are fully dissipated after about 600 h. The results of load tests strongly suggest that effective stress parameters govern the behaviour of friction piles during the reconsolidation phase. The shaft bearing capacity is underestimated by approximately 45% with an effective stress approach in which the Ko, value is inferred from 1 – sin φ. However, if the measured values of Ko are taken, the calculated load carried by shaft friction is 70–90% of the actual shaft capacity. It is shown that the ultimate toe bearing capacity is strain rate dependent. For strain rates less than 5 × 10-4/s, which corresponds to pile penetration rates less than O·1 cm/s, the behaviour of tbe clay surrounding the toe is partially drained. Thus, the prediction of toe resistance for load testing conditions, i.e. a penetration rate of about 0·0001 cm/s, is complex and cannot be carried out with the undrained characteristics of the clay. Un essai en vraie grandeur a été effectué sur deux pieux instrumentés au centre d'expéiences de St Alban afin d'étudier I'accroissement dans le temps de la portance des pieux flottants courts vérinés dans une argile marine tendre surconsolidée sensible au remaniement. L'article démontre que la portance s'accroît de façon significative dans le temps et atteint environ 12 fois la valeur originale. Le frottement maximal est atteint lorsque les surpressions interstitielles créées au cours du battage des pieux se dissipent complètement après environ 600 h. Les résultats des essais de chargement montrent que les paramètres de contrainte effective régissent le comportement des pieux flottants pendant la phase de reconsolidation. La portance est sous-estimée d'environ 45% avec une méthode employant la contrainte effective dans laquelle la valeur Ko, est prise égale à 1 – sin ø. Cependant, si on prend les valeurs mesurées de Ko la charge calculée portée par le frottement représente entre 70% et 90% de la capacité réelle. On démontre que la force portance limite de pointe dépend dutaux de déformation. Pour des taux de déformation inférieurs à 5 × 10-4'/s, ce qui correspond à des vitesses de pénétration inférieures à 0, l cm/s, le comportement de l'argile entourant la base du pieu est partiellement drainé Il est ainsi très dificile de prédire la réistance de pointe pour des conditions d'essais de chargement, c'est-à-dire un taux de pénétration d'environ 0,001 cm/s, et aucune prédiction ne peut se faire sur la base des caractéristiques non-drainées de l'argile.

Behaviour of a sensitive clay during pile driving

A full scale investigation with six instrumented test piles has been carried out on the Saint-Alban test site in order to study the behaviour of friction piles in soft sensitive soils. The first part of this investigation, reported in this paper, deals essentially with the effects of pile driving on the induced pore pressures and their dissipation and on the disturbance of the clay around the pile.It is shown that the induced pore pressures at the pile tip ΔuT, and at the pile surface Δus, correspond to 1.6σvo and 0.8σvo respectively. If the failure pattern developed during driving is interpreted by means of the theories of expansion of cavities, it is shown that the induced pore pressures calculated at the pile–soil contact agree well with the measured values; these pore pressures are fully dissipated after 600 h.Immediately after driving, a decrease in the undrained shear strength varying between 0 and 30% was observed in a zone of 3 diameters around the pile. The strength in that zone was nearly fully recovered after the pore pressures had dissipated.The tip resistance measured during driving was quite in excess of the static zone penetration resistance qc, indicating possible scale effects. The average unit skin friction was observed to decrease from a value in the order of cu to about 0.10σvo′ and to be directly related to the pore pressures, i.e., to the effective stresses in the clay around the pile.

Pullout Tests of Piles in Sand

Three pullout tests on two instrumented 24-in. -diameter, steel-pipe piles were performed in a deep sand deposit at Mustang Island, Tex., to determine the tension capacity of a pile and to assess the effects of lateral loading on pullout resistance. Test equipment and procedures are described and results of strain data and load vs pile-top movement are presented. Skin friction parameters are determined from these results. Introduction Pullout tests on open-steel pipe piles in sand were run at Pullout tests on open-steel pipe piles in sand were run at the Shell Oil Co. Tank Battery on Mustang Island, Tex. The map in Fig. 1 indicates the test site. About 5 ft of fill was excavated at the site so that the water table would be at ground surface. Two instrumented test piles were driven and pullout tests were performed before and after lateral loading. Test Equipment and Test Piles Test Setup and Test Piles The test setup and test piles are shown in Fig. 2. Two reaction beams, one on each side of the test pile, rested on timber mats. Two hydraulic jacks with pumping units and pressure gauges rested on the reaction beams. A 10-ft pressure gauges rested on the reaction beams. A 10-ft section of 24-in.-diameter pile was specially made and welded to the top of the test pile. Two small-diameter piles were driven to support deflection gauges used to piles were driven to support deflection gauges used to measure movement of the pile top. Cables from deflection and strain gauges were run from the pile to the instrumentation system housed in a van parked beside the excavated area. Two test piles were manufactured from seamless steel pipe (ASTM A-53, Grade B) with 24-in. OD. The wall pipe (ASTM A-53, Grade B) with 24-in. OD. The wall was 3/8-in. thick and weighed 94.6 lb/ft. The piles were composed of a 10-ft loading section, a 32-ft instrumented section, and 38-ft anchor section (Fig. 2). The instrumented section was sealed off by diaphragms at the top and bottom of the section to prevent moisture from damaging the strain gauges. Wires from these gauges were passed through pressure-packing glands in the diaphragm at the top of the instrumented section. Each pile had 40 strain gauges - 34 active and 6 unstrained dummies. The 120-ohm strain gauges were 0.50- x 0.50-in. metal foil. Strain-gauge spacing in the 32-ft section is indicated in Fig. 2. Both test piles were driven with a Delmag-12 diesel hammer. The 38-ft open-ended, uninstrumented section was driven until its top was about 3 ft above the soil surface. Next, the soil plug inside the section was augered out completely to keep it from driving against the diaphragm in the bottom of the 32-ft instrumented section. After welding the 32-ft section to the 38-ft section, driving was resumed and the pile was driven to grade, with the pile flange approximately I ft above the soil surface. The pile was embedded 69 ft. Measurement of Load, Strain, and Deflection During the pullout tests, readings were taken of the applied load, the deflection of the top of the pile, and the axial strain along the pile. The applied load was obtained by reading bourdon-tube pressure gauges that measured the hydraulic pressure in the jacks. The pile deflection was obtained from dial indicators and by use of lineardisplacement transducers. Output from the displacement transducers and from strain gauges was recorded with a digital recording system. JPT P. 343