Design Of Bored Piles Research Articles

The use of piles with an adjustable operation mode to restraint the shaft sinking systems’ supporting structures

The article deals with the problem of ensuring the stability of grillages and pile foundations used to hold shaft sinking systems during the construction of vertical subway shafts. The features of such foundations’ operation in the process of shaft sinking are investigated, in contrast to similar structures that receive pressure from a building under construction. The importance of taking into account the mutual influence of shaft sinking and pile foundations of the shaft sinking systems’ supporting structures is shown. The design of bored piles and the technological scheme of mortar injection are proposed, which provide a change in the operating mode of pile foundations and regulation of its bearing capacity.

Comparison of Single and Group Bored Piles Settlement Based on Field Test and Theoretical Methods

Bored piles settlement behavior under vertical loaded is the main factor that affects the design requirements of single or group of piles in soft soils. The estimation of bored pile settlement is a complicated problem because it depends upon many factors which may include ground conditions, validation of bored pile design method through testing and validation of theoretical or numerical prediction of the settlement value. In this study, a prototype single and bored pile group model of arrangement (1*1, 1*2 and 2*2) for total length to diameter ratios (L/D) is 13.33 and clear spacing three times of diameter, subjected to vertical axial loads. The bored piles model used for the test was 2000 mm in length, and 150 mm in diameter has been constructed in soft clayey soils. Furthermore, different theoretical methods have been used for the estimation of bored pile settlement, such as Poulos and Vesic's methods and then their comparison with the pile load test data based on the quick pile load test as presented in (ASTM-D1143, 2007). In general, the theoretical method for estimation the bored pile settlement by Poulos and Vesic's gives higher value of the settlement for the single and group bored pile compared to the pile settlement results obtained from field pile load test data. Therefore, it is not recommended to be used for soft clayey soils. On the other hand, Hansen’s 90% and Butler and Hoy’s results may be considered reliable interpretation method to compute the settlement of single and group bored pile.

Comparison of field loading test results of bored piles with bearing capacity analysis based on various standards

AbstractICA Construction (Ictas ‐ Astaldi JV) is the general contractor of the WHSD ring road project in St. Petersburg and Section 7 & 8 of M11 Motorway project, which will be the toll highway between St. Petersburg and Moscow. WHSD ring road that has been constructed by ICA Construction passes through nearshore and offshore areas on viaducts and there are also two cable stayed bridges on the alignment. As a part of M11 motorway project, several bridges have been constructed overpassing various rivers. Since, all these structures have deep foundation systems, several axial pile loading tests have been performed on both projects. Soil in the vicinity of St. Petersburg consists of soft to medium dense silty, partially sandy clay layers at top levels. These layers are followed by Cambrian aged hard clay layers. In Russian Federation and some Eastern European countries, bored pile design is based on SNIP norms. In norms like AASHTO or Eurocode, pile bearing capacity calculations consider both contribution of the tip resistance and skin friction. On the contrary, in SNIP norms contribution of the skin friction to pile bearing capacity is very limited. Therefore, piles are generally extended to deep bearing layers. For piles where large axial bearing capacities are required, base enlargement is applied. In this paper, axial pile bearing capacities in the scope of the above mentioned projects are calculated based on SNIP, AASHTO LRFD and Eurocode 7, respectively and the calculated values are compared with the pile bearing capacities obtained from field tests. Total number of axial pile load tests gives the possibility to make a statistical comparison. Results of axial pile load tests have revealed that especially the bearing capacities calculated in accordance with SNIP norms underestimates bearing capacities of bored piles erected in clayey soils.

Characteristics of Gravelly Granite Residual Soil in Bored Pile Design: An In Situ Test in Shenzhen

Granite residual soil is widely distributed in south China and is treated as a special soil. Its design parameters in rotary drilling bored piles are a matter of debate due to lack of in‐situ pile load tests. Back‐analysis of test piles is a reliable means of studying the geotechnical capacity of granite residual soil for pile design. In this study, a series of in situ tests was conducted comprising six full‐scale instrumented test piles in gravelly granite residual soil in Shenzhen to consider the effects of different construction methods. The six piles were constructed with three different rotary drilling methods. Two commonly used design methods were investigated in the back‐analysis: the SPT and effective stress methods. The results of the loading tests and strain gauges were used to obtain the back‐analyzed parameters of the ultimate shaft resistance and ultimate base resistance for gravelly granite residual soil with these two design methods.

Settlement prediction of the rock-socketed piles through a new technique based on gene expression programming

The settlement design of bored piles socketed into rock has received considerable attention. Although many design methods of pile settlement are recommended in the literature, proposing new/practical technique(s) with higher performance prediction is of advantage. A new model based on gene expression programming (GEP) is presented in this paper for predicting the settlement of the rock-socketed pile. To do this, 96 piles socketed in different types of rock (mostly granite) as part of the Klang Valley Mass Rapid Transit project, Malaysia, were studied. In order to propose a predictive model with higher performance prediction, a series of GEP analyses were conducted using the most important factors on pile settlement, i.e. ratio of length in soil layer to length in rock layer, ratio of total length to diameter, uniaxial compressive strength, standard penetration test and ultimate bearing capacity. For comparison purpose, using the same dataset, linear multiple regression (LMR) technique was also performed. After developing the equations, their prediction performances were checked through several performance indices. The results demonstrated the feasibility of GEP-based predictive model of settlement. Coefficients of determination (CoD) values of 0.872 and 0.861 for training and testing datasets of GEP equation, respectively, show superiority of this model in predicting pile settlement while these values were obtained as 0.835 and 0.751 for the LMR model. Moreover, root mean square error (RMSE) values of (1.293 and 1.656 for training and testing) and (1.737 and 1.767 for training and testing) were achieved for the developed GEP and LMR models, respectively.

Comparison between empirical and experimental ultimate bearing capacity of bored piles—a case study

In this paper, several pile load tests are conducted for the evaluation of the actual axial compressive bearing capacity of bored piles casted beneath rear crane beams in Shahid Rajaee Port Complex Development Project (SRPCDP) in south of Iran (case study). Different methods of pile load test interpretations are employed to achieve the actual bearing capacity of piles. Moreover, the result of pile load tests are compared with empirical relations based on American Petroleum Institute (API) and American Association for State Highway and Transportation Officials (AASHTO) recommendations. Undrained parameters for cohesive layers and SPT-N value or relative density of cohesionless materials are employed for the estimation of the bearing capacity based on API and AASHTO proposals. It can be observed that in most of cases, the empirical prediction based on API and experimental data are coherent. This coherency is more obvious when the pile tip is overlain on a sandy layer. Hence, notwithstanding the common use of API recommendation for the steel offshore pile design, it can also be employed for the design of bored piles.

A database to ensure reliability of bored pile design in Egypt

A new electronic database has been developed to house reliable results for more than 318 load tests of large-diameter bored piles in Egypt, including comprehensive records of soil profile, in situ tests and pile characteristics. Using information from the database, the load and resistance factor design reliability-based calibration approach was applied to established pile design methods and another two local methods. Resistance factors were developed using the Monte Carlo simulation, covering several nominal capacity determination criteria from the pile load–displacement response. The analysis was then extended to assess the reliability of the load test results, which represent the key construction control measure for bored piles. This was achieved by connecting the number of load tests conducted per-site basis with an indicative level of soil variation.

Appraisal of reliable skin friction variation in a bored pile

The design of bored piles in Malaysia is usually based on the results of the standard penetration test. It is important to predict the geotechnical capacity of a designed bored pile through the multilayer soil strata. The back-analysis of a test pile is a reliable means of obtaining the range for the ultimate skin factor (Ksu) and the ultimate end-bearing factor (Kbu). In this research, two case histories of maintained load tests on single bored piles (PTP-1 and 2) under full-scale static load (up to twice designed load) are examined. Measurements are taken using various embedded transducers, including both conventional instrumentation and a state-of-the-art global strain extensometer. The results show the rates of the pile base and pile head load mobilisation with settlement, the variation of the skin friction factors and stresses along the pile, and their proportion in relation to the total pile capacity. The Ksu and Kbu factors for both tested piles are obtained and compared using a conventional vibrating-wire global strain gauge and a global strain extensometer. It is also observed that for the stiff soil layers the skin friction is significant. However, the increase in the applied load increases the proportion carried by the end-bearing.

Calibrating cross-site variability for reliability-based design of pile foundations

The cross-site variability (i.e., variability from site to site) makes the statistics of the bias factor of a design model vary from site to site. How to characterize the cross-site variability of the model bias factor is important for design of pile foundations based on site-specific load test data. In this study, a probabilistic model that allows for explicit modeling of the cross-site variability is suggested. An equation is derived based on Bayes’ theorem to calibrate the suggested model with load test data from different sites, which is applicable even when the number of load tests at each site is small. A procedure based on hybrid Markov Chain Monte Carlo simulation is employed to solve the Bayesian equation. How to update the statistics of the model bias factor, when applied to a future site, with site-specific load test data is also described. As an illustration, the probabilistic model is applied to the design of bored piles in Shanghai, China. It is found that, given a certain number of site-specific pile load tests, the effect of updating depends on the mean and the COV of the measured model bias factor. With the assistance of regional experience, a small number of load tests can significantly reduce the uncertainty associated with the design model, and further increase in the number of load tests may not change the site-specific statistics of the bias factor and hence the resistance factor substantially.

Discussion: Bored pile design in stiff clay I: codes of practice

Paul J. Vardanega MEngSc, PhD, MIEAust, M.ASCE Research Associate, Department of Engineering, University of Cambridge, UK Ekaterina Kolody MSc Geotechnical Engineer, Arup, London, UK Stuart H. Pennington BEng, BSurv, CEng, MICE Senior Geotechnical Engineer, Arup, London, UK Paul R. J. Morrison MSc, DIC, PhD, CEng, MIEI Director, Arup, London, UK Brian Simpson OBE, FREng, MA, PhD, FICE Arup Fellow, Arup, London, UK Nick O’Riordan PE CEng Arup, London, UK Brandon Kluzniak PE Arup, San Francisco, USA

Corrigendum: Bored pile design in stiff clay II: mechanisms and uncertainty

Corrigendum: Bored pile design in stiff clay II: mechanisms and uncertainty

Bored pile design in stiff clay I: codes of practice

The assessment of the allowable bearing load of bored piles ‘floating' in stiff clay is a standard engineering task. Although the soil mechanics is universal, engineers designing structures in different parts of the world will need to take into account the pertinent codes of practice. It will be helpful to compare such codes, especially in relation to their treatment of uncertainty in the design of bored piles. This paper presents a series of design calculations for a real set of geotechnical data using four international codes of practice: the Australian, American, European and Russian codes. The National Annexes of Ireland, the Netherlands and the UK are used in conjunction with the European code. This selection of countries covers the three Eurocode 7 design approaches (DA1, DA2 and DA3). A non-codified design method is used to provide a base case for comparative purposes with the six codified calculations. A companion paper investigates the issues of soil mechanics in pile design methods, uncertainty in soil parameters and settlement criteria.

Bored pile design in stiff clay II: mechanisms and uncertainty

The soil mechanics related to pile design in clay has been the subject of substantial engineering research. In a companion paper, various codes of practice were reviewed showing the effect on pile capacity of the different global factors of safety that emerge from the various partial factor combinations for the ultimate limit state. Factors of safety are generally specified based on the opinions of experts. In this paper an assessment will be made of various objective procedures that can be used to reduce uncertainty in the design process, especially regarding the adoption of a pile resistance model and the selection of a soil strength profile as part of a ultimate limit state check, and the estimation of pile head settlement in the context of a serviceability limit state check. It is shown that both total stress and effective stress calculation methods are applicable in London Clay. Estimates of settlement using a non-linear soil stress–strain relationship are made and compared with published data. It is shown that the compression of the concrete dominates the settlement of long piles. Given the low settlements observed, recommendations are made for a reduction in standard factors of safety for bored pile design in stiff clays.

ASSESSMENT OF DIFFERENT METHODS FOR DESIGNING BORED PILES / SKIRTINGŲ METODŲ VERTINIMAS PROJEKTUOJANT GRĘŽTINIUS PAMATUS

This work concerns the design of bored piles on the site of Elektrenai Power Plant in Lithuania. Equipment for supporting bored pile foundation in the power plant consists of a gas turbine, a steam turbine and a generator. The foundation not only endures high loads but also sustains a strong dynamic impact due to the vibration of equipment in the power plant under working conditions. A solution to the pilling problem was adopted for the following reasons: i) the insufficient capacity of soil to support acute stresses; ii) high requirements of slab settlements and bearing capacity with regard to the main equipment used in the power plant. The objective of this work is to assess the methods used for estimating immediate settlement and carrying capacity of the pile considering cone penetration tests conducted in Elektrenai power plant. For settlement estimation, four methods, including Bowles (Bowles 1997) and Schmertmann methods (Schmertmann 1978) as well as the methods described in EN 1997-2 and NEN 6743 (NEN 6743:1991/A1:1997) were employed. A carrying capacity of the pile was evaluated with the help of direct methods that utilize data on the cone penetration test (CPT). The following direct methods such as the Schmertmann method (Schmertmann 1978), the de Ruiter and Beringen method (de Ruiter, Beringen 1979), the Bustamante method (LCPC) (Bustamante, Gianeeselli 1982) and the methods described in EN 1997-2 and NEN 6743 (NEN 6743:1991/A1:1997) were applied. Pilling foundation was evaluated performing immediate settlement analysis and included the examination of soil data received from cone and dynamic penetration tests, boreholes and laboratory tests. Soil properties were estimated taking into account investigation into the site of Elektrenai power plant and a soil exploration program developed according to Lithuanian standards. Pile settlement analysis showed that settlement value made 13.6 mm (pile toe settlement) and the settlement value of an elastic deformation of the pile from vertical compressive loads was 2.3 mm, for the most conservative situation. For such structure, foundation settlement should not exceed 16 mm. Elektrenai power plant has high reliability requirements, and therefore the pile having the diameter of 800 mm with a pile length of 27 m was adopted to endure overall loads. Santrauka Straipsnyje nagrinėjami įvairūs skaičiavimo metodai, skirti gręžtiniams pamatams projektuoti. Lietuvos elektrinės teritorijoje projektuojant kombinuoto ciklo dujų turbinos bloko pamatus, dėl ypatingų statinio reikalavimų polių nuosėdžiams bei laikomajai gebai buvo parinkti gręžtiniai poliai. Pagrindinis darbo tikslas – įvertinti gręžtinių polių nuosėdžių ir laikomosios gebos skačiavimus pagal statinio zondavimo duomenis bei analitinius sprendimus, taikant skirtingus skaičiavimo metodus. Polio nuosėdžiams ir laikomajai gebai vertinti buvo taikyti šie metodai bei standartai: Bowles, Schmertmann, de Ruiter ir Beringen, Bustamante (LCPC), EN 1997-2 ir NEN 6743 standartų metodika. Remiantis statinio ir dinaminio zondavimo bei laboratorinių tyrinių duomenimis, suminio nuosėdžio reikšmė buvo gauta lygi 16 mm, iš jų 2 mm sudaro nuo vertikaliosios apkrovos gniuždomo polio deformacija. Tokio tipo statinių pagrindo nuosėdis negali būti didesnis nei 2 % polio skersmens. Atlikti skaičiavimai parodė, kad 800 mm skersmens ir 27 m ilgio polio visiškai pakanka statinėms ir dinaminėms apkrovoms atlaikyti.

Performance of bored piles with different construction methods

The design of bored piles in residual soil is usually based on empirical correlation with the results of the standard penetration test, regardless of the construction method of the bored pile. This paper presents the pile load test results of two bored piles with different construction methods. A preliminary bored pile of 1000 mm diameter was constructed using a wet method with bentonite as the stabilising fluid. The static pile load test result shows that the shaft friction could be overestimated by the empirical method. A 1200 mm diameter bored pile was constructed about 5 m away from the preliminary bored pile but using the dry method. The static pile load test result shows that higher shaft friction can be obtained. The empirical method could underestimate the shaft friction in this case.

Construction Effect on Load Transfer along Bored Piles

The load transfer behavior along bored piles is affected by details of pile construction particularly those imposing stress and moisture changes to the surrounding soils. An investigation involving moisture migration tests, in situ horizontal stress measurements, and borehole shear and pressuremeter tests shows clear effects of construction that lead to subsequent changes in soil properties. The construction of bored piles in Singapore and the region often involves casting of concrete either in unsupported dry boreholes or in wet boreholes filled with water. It is necessary to differentiate these two extreme construction conditions in bored pile design. Based on triaxial compression and pressuremeter tests on the residual soil of the Jurong Formation in Singapore, the variation of soil modulus with shear strain can be described by a hyperbolic function. A procedure is recommended for assessing the combined effect of stress relief and soaking on soil modulus by introducing a modulus reduction factor. Modulus degradation curves from pressuremeter tests with the borehole conditions properly simulated are found capable of producing load transfer curves that are comparable to those deduced in the field.

Investigation and Analysis of a Well Instrumented Small Displacement Pile Founded on Rock

The construction of driven piles on rock has been practiced for years in Hong Kong. However, detailed field studies to investigate the performance of this type of foundation are still limited. A well instrumented driven H-pile was recently installed and founded on granite. The load transfer mechanism and the pile performance are studied based on comprehensive pile tests. Analyses show that the pile design is controlled by the structural capacity of the pile section but not the engineering properties of the bedrock. The pile toe resistance back-calculated from strain gauges is found to be considerably higher than the allowable values for bored pile design. The Hiley formula commonly used in Hong Kong is found to underestimate the ultimate pile capacity of the pile founded on rock. A more rational wave equation analysis is performed and shows consistent results with PDA tests and the CAPWAP analysis.

Instrumented load tests in mudstone: pile capacity and settlement prediction

The present work stems from the design of a viaduct in South Wales, U.K., where full-scale pile testing was carried out to assess whether the proposed design methods would meet the required load capacity and settlement criteria for the working piles. Five fully instrumented large diameter bored cast in situ piles, up to 30 m deep, were installed in weathered mudstone and tested under vertical loading. A sixth pile, which had no shaft instrumentation, was formed with a voided toe. In conjunction with vast soil data from 218 site investigation boreholes, the extensive data produced from the load tests were analyzed to quantify the key parameters considered to influence load transfer and settlement behaviour. Each pile was first calibrated using four methods to establish the as-built stiffness, taking into account the nonlinearity of concrete and the effect of partial steel encasement. It is demonstrated that the current national norms for bored pile design in cohesive soil – soft rock are overconservative for South Wales ground conditions. To ameliorate this, alternative methods are proposed, which lead to improved reliability and accuracy in shaft and base capacity assessment. In addition, a numerical model is developed that can be used to predict the complete load-settlement variation up to the ultimate state. The model is sufficiently expounded to allow its immediate application in pile design by geotechnical engineers.Key words: piled foundations, load tests, bearing capacity and settlement, Mercia mudstone.

Design of bored piles in residual soils based on field-performance data : Chang, M F; Broms, B B Can Geotech JV28, N2, April 1991, P200–209

Design of bored piles in residual soils based on field-performance data : Chang, M F; Broms, B B Can Geotech JV28, N2, April 1991, P200–209

Design of bored piles in residual soils based on field-performance data

The current practice for the design of large-diameter bored piles in residual soils in Singapore is based on the calculated static capacity of the piles. Insufficient consideration of the load-transfer mechanism and overreliance on pile load tests have led to conservative designs. A better alternative is to adopt a load–displacement analysis method that provides information on the load distribution along the pile and the complete load–displacement relationship. Results of full-scale load tests on instrumented piles indicate that bored piles in residual soils in Singapore behave in the same way as in stiff clay and weak rocks elsewhere in that the load transfer at the working load is dominated by shaft friction. Simple correlations exist between the standard penetration resistance and the load-transfer parameters. An example illustrates that the proposed design procedure that uses these simple correlations and the load-transfer method is an improvement over present design methods. Key words: bored piles, cast-in-place piles, design, drilled piers, field test, load transfer, residual soil, shaft resistance.