Assessment of Direct Cone Penetration Test Methods for Predicting the Ultimate Capacity of Friction Driven Piles

This paper evaluates the applicability of eight direct cone penetration test (CPT) methods to predict the ultimate load capacity of square precast prestressed concrete (PPC) driven friction piles. Analyses and evaluation were conducted on 35 driven friction piles of different sizes and lengths that were failed during pile load testing. The CPT methods, as well as the static α and β methods, were used to estimate the load carrying capacities of the investigated piles (QP). The Butler–Hoy method was used to determine the measured load carrying capacities from pile load tests (Qm). The pile capacities determined using the different methods were compared with the measured pile capacities obtained from the pile load tests. Four criteria were selected as bases of evaluation: the best fit line for Qp versus Qm, the arithmetic mean and standard deviation for the ratio Qp/Qm, the cumulative probability for Qp/Qm, and the histogram and log normal distribution for Qp/Qm. Results of the analyses showed that the best performing CPT methods are the LCPC method by Bustamante and Gianeselli as well as the De Ruiter and Beringen method. These methods were ranked number one according to the mentioned criteria.     

Axial Load Tests on Bored Piles and Pile Groups in Cemented Sands

The behavior of bored pile groups in cemented sands was examined by a field testing program at a site in South Surra, Kuwait. The program consisted of axial load tests on single bored piles in tension and compression and compression tests on two pile groups each consisting of five piles. The spacing of the piles in the groups was two- and three-pile diameters. Soil exploration included standard penetration tests, dynamic cone tests, and pressure meter tests. Laboratory tests included basic properties and drained triaxial compression tests. Test results on single piles indicated that 70% of the ultimate load was transmitted in side friction that was uniform along the pile shafts. The calculated pile group efficiencies were 1.22 and 1.93 for a pile spacing of two- and three-pile diameters, respectively. Since settlement usually controls the design of pile groups in sand, the group factor defined herein as the ratio of the settlement of the group to the settlement of a single pile at comparable loads in the elastic range was determined from test results. A comparison between the measured values and calculated values based on a simplified formula was made.     

Horizontal Bearing Capacity of Piles in a Lateritic Soil

The behavior of pile foundations subjected to horizontal loading is typically evaluated using horizontal load tests. Although load tests are valuable to understand site-specific soil-structure interaction phenomena, validated predictive methods are also useful during the design phase. In this study, the results from horizontal load tests are compared with methods which predict the horizontal bearing capacity of piles using in situ measurements of soil behavior. Specifically, several horizontal load tests were performed in order to evaluate the behavior of two 12-m long Strauss piles and four bored piles with similar length, all installed in a lateritic soil profile. Two prediction methods were evaluated using p-y curves computed from the results of Marchetti’s dilatometer test (DMT) results. The predictive methods using the p-y curves from the DMT showed good agreement with the behavior observed in the pile loading test.     

Estimation of Axial Load Capacity for Bored Tapered Piles Using CPT Results in Sand

Tapered piles in comparison to cylindrical piles can be beneficial in terms of the load capacity. In this paper, estimation of the load capacity for tapered piles using cone penetration test (CPT) resistance was investigated. Fourteen calibration chamber load tests using different pile types and six CPTs were conducted under various soil conditions. From the calibration chamber test results, the total, base, and shaft load capacities were analyzed in terms of soil conditions and taper angle. To evaluate CPT-based load capacity of tapered piles, normalized base and shaft resistances were obtained from normalized unit load-settlement curves. Based on the normalized base and shaft resistances, design equations that can be used to evaluate the base and shaft resistances of tapered piles were proposed. The proposed method is valid for sands of medium to dense conditions, while it may result in unconservative predictions for loose sands. To check the accuracy of the proposed method, field load tests using both cylindrical and tapered piles were conducted and compared with the predictions using the proposed method. A simplified approach using an equivalent cylindrical pile was also investigated and compared.     

Load Deformation Analysis of Bored Piles in Residual Weathered Formation

The current design practice of single bored piles in residual weathered formations is based mainly on stability consideration against shear failure, and pile deformation analysis is rarely carried out. However, the acceptance criteria of single piles during pile load tests during construction is based mainly on the permissible settlement criteria as specified in the specifications∕codes. In this study, a reliable method of predicting the load deformation and load distribution curves is proposed for bored piles in a residual weathered formation (Kenny Hill Formation) in Kuala Lumpur based on: (1) considerations of the weathering profiles and the engineering characteristics of this formation; (2) field performance data of fully instrumented bored pile load tests; and (3) load transfer design characteristics of the load deformation behavior. In this deformation analysis, the pile installation methods and the nonlinear behavior of the pile material are incorporated. The proposed load deformation analysis was carried out on both the instrumented and noninstrumented piles, producing good results. Therefore, this proposed method can be used to predict the load deformation characteristics of single bored piles in weathered formation during the design stage.     

Investigations of Pile Foundations in Brownfields

“Brownfields” are real estate properties with subsurface or surface contamination. The redevelopment of Brownfields is required to clean, improve, and protect the environment. Pile foundations are often used in Brownfields and other contaminated site situations to support structures. Regulators are concerned about the environmental safety of pile foundations in Brownfields sites, since piling in Brownfields may lead to transport of contaminants from the contaminated region to underground aquifers. This investigation is an extension of previous research programs on pile foundations in Brownfields or contaminated sites conducted at the University of New Orleans. The purpose of the overall investigation is to evaluate the potential for contaminant transport due to pile foundations in Brownfields. The current paper summarizes the research carried out to ascertain the potential for contaminant transport from concrete piles of different shape, depth of penetration, and method of installation. The results of bench scale model tests and numerical studies are presented. Under full penetration conditions, the square shaped and circular cast-in-place piles were found to have a higher potential for contaminant transport than circular driven piles. There is a low potential for contaminant transport in the case of piles penetrating less than 95% of an aquitard. Selected results from a previous program on wooden and steel piles are summarized for comparison.     

Case History Evaluation of Laterally Loaded Piles

This paper examines seven case histories of load tests on piles or drilled shafts under lateral load. Since the current design software to estimate lateral load resistance of deep foundations requires p-y curves. The first approach used was correlative whereby soil parameters determined from in situ tests [standard penetration test (SPT) and cone penetration test (CPT)] were used as input values for standard p-y curves. In the second approach p-y curves were calculated directly from the stress deformation data measured in dilatometer (DMT) and cone pressuremeter tests. The correlative evaluation revealed that, on the average, predictions based upon the SPT were conservative for all loading levels, and using parameters from the CPT best predicted field behavior. Typically, predictions were conservative, except at the maximum load. Since traditionally SPT and CPT correlation-based p-y curves are for “sands” or “clays,” this study suggests that silts, silty sands, and clayey sands should use cohesive p-y curves. For the directly calculated curves, DMT derived p-y curves predict well at low lateral loads, but at higher load levels the predictions become unconservative. p-y curves derived from pressuremeter tests predicted well for both “sands” and “clays” where pore pressures are not anticipated.     

Centrifuge Modeling of Large-Diameter Bored Pile Groups with Defects

In this research, centrifuge model pile-load tests were carried out to failure to investigate the behavior of large-diameter bored pile groups with defects. The model piles represented cast-in-place concrete piles 2.0?m in diameter and 15?m in length. Two series of static loading tests were performed. The first series of tests simulated the performance of a pile founded on rock and a pile with a soft toe. The second series of tests simulated the performance of three 2×2 pile groups: One reference group without defects, one group containing soft toes, and one group with two shorter piles not founded on rock. The presence of soft toes and shorter piles in the defective pile groups considerably reduced the pile group stiffness and capacity. As the defective piles were less stiff than the piles without defects, the settlements of the individual piles in the two defective pile groups were different. As a result, the applied load was largely shared by the piles without defects, and the defective pile groups tilted significantly. The rotation of the defective pile groups caused large bending moments to develop in the group piles and the pile caps. When the applied load was large, bending failure mechanisms were induced even though the applied load was vertical and concentric. The test results confirm findings from numerical analyses in the literature.     

Database Assessment of CPT-Based Design Methods for Axial Capacity of Driven Piles in Siliceous Sands

Numerous cone penetration test (CPT)-based methods exist for calculation of the axial pile capacity in sands, but no clear guidance is presently available to assist designers in the selection of the most appropriate method. To assist in this regard, this paper examines the predictive performance of a range of pile design methods against a newly compiled database of static load tests on driven piles in siliceous sands with adjacent CPT profiles. Seven driven pile design methods are considered, including the conventional American Petroleum Institute (API) approach, simplified CPT alpha methods, and four new CPT-based methods, which are now presented in the commentary of the 22nd edition of the API recommendations. Mean and standard deviation database statistics for the design methods are presented for the entire 77 pile database, as well as for smaller subset databases separated by pile material (steel and concrete), end condition (open versus closed), and direction of loading (tension versus compression). Certain methods are seen to exhibit bias toward length, relative density, cone tip resistance, and pile end condition. Other methods do not exhibit any apparent bias (even though their formulations differ significantly) due to the limited size of the database subsets and the large number of factors known to influence pile capacity in sand. The database statistics for the best performing methods are substantially better than those for the API approach and the simplified alpha methods. Improved predictive reliability will emerge with an extension of the database and the inclusion of additional important controlling factors affecting capacity.     

Development of Residual Forces in Long Driven Piles in Weathered Soils

A large-scale field-monitoring program for studying residual forces in long-driven piles is described. Eleven steel H-piles, 34.2–59.8?m in embedded length, were instrumented with vibrating-wire strain gauges, installed and subjected to static loading tests in a building site in Hong Kong. The residual forces in these piles during and after pile installation were recorded. The development of residual forces as it relates to the pile penetration depth during construction, and in time after the piles were installed, is presented. The measured load transfers in the piles from static loading tests are reported and the effect of the residual forces on the interpretation of load-transfer behavior is studied. The field measurements show that residual forces increase approximately exponentially with penetration depth. The residual forces continue to increase with time after pile driving due to secondary compression of disturbed soils around the pile shaft and other factors. The large residual forces in the long piles significantly affect the interpretation of the pile load distributions. The effect of residual forces on the shaft resistance is significant at shallow depths. Bearing-capacity theory tends to overpredict the true toe resistance of the long piles founded in weathered soils.     

Observed Performance of Long Steel H-Piles Jacked into Sandy Soils

Full-scale field tests were performed to study the behavior of two steel H-piles jacked into dense sandy soils. The maximum embedded length of the test piles was over 40?m and the maximum jacking force used was in excess of 7,000?kN. The test piles were heavily instrumented with strain gauges along their shafts to measure the load transfer mechanisms during jacking and the subsequent period of static load tests. Piezometers were installed in the vicinity of the piles to monitor the pore pressure responses at different depths. The time effect and the effect of installation of adjacent piles were also investigated in this study. The test results indicated that, although both piles were founded on stiff sandy strata, most of the pile capacity was carried by shaft resistance rather than base resistance. This observation implies that the design concept that piles in dense sandy soils have very large base capacity and small shaft resistance is likely to be inappropriate for jacked piles. It was also found that the variation in pore pressures induced by pile jacking was closely associated with the progress of pile penetration; the pore pressure measured by each piezometer reached a maximum when the pile tip arrived at the piezometer level. A nearby pile jacking was able to produce large tensile stresses dominating in the major portion of an installed pile; both the magnitude and distribution of the induced stresses were related to the penetration depth of the installing pile.     

Response of Laterally Loaded Large-Diameter Bored Pile Groups

This paper presents results of full-scale lateral load tests of one single pile and three pile groups in Hong Kong. The test piles, which are embedded in superficial deposits and decomposed rocks, are 1.5 m in diameter and approximately 30 m long. The large-diameter bored pile groups consist of one two-pile group at 6 D (D = pile diameter) spacing and one two-pile and one three-pile group at 3 D spacing. This paper aims to investigate the nonlinear response of laterally loaded large-diameter bored pile groups and to study design parameters for large-diameter bored piles associated with the p-y method using a 3 D finite-element program, FLPIER. Predictions using soil parameters based on published correlations and back-analysis of the single-pile load test are compared. It is found that a simple hyperbolic representation of load-deflection curves provides an objective means to determine ultimate lateral load capacity, which is comparable with the calculated values based on Broms' theory. Lateral deflections of bored pile groups predicted using the values of the constant of horizontal subgrade reaction, suggested by Elson and obtained from back-analysis of the single pile load test, are generally in good agreement with the measurements, especially at low loads.     

Integrity Problem of Large-Diameter Bored Piles

Bleeding is known to occur in bored piles (drilled pier). The generally accepted view is that bleeding in piles is confined to the upper part of the pile only. Under certain conditions during bleeding, channeling may happen. Practising engineers believed that the associated problems with bleeding and channeling in bored piles can be overcome by overcasting the piles. A case study of extensive integrity tests consisting of cross-hole sonic logging tests and dynamic load tests on bore piles, as well as continuous corings from top to bottom of the piles carried out, revealed that some bored piles have channeling of concrete at various depths. Most of them were larger diameter piles. The finding that bleeding and channeling are not confined to the upper part of the pile is contrary to the generally accepted view. This paper attempts to develop a theory for the bleeding and channeling of concrete to explain the mechanics of the occurrence of channeling in bored piles. The proposed theory is verified by the close correlation of the predictions of the theory with field observations of the case study. Based on the proposed theory, recommendation with regards to the quality of concrete will be made to avoid the occurrence of channeling of concrete in large-diameter bored piles. The implications on the structural performance pertaining to axial capacity, compressibility and durability of bored piles with channels will be investigated.     

Prediction of Ground Movements due to Pile Driving in Clay

This paper evaluates theoretical predictions of ground movements caused by the installation of driven (or jacked) piles in clay. The predictions are based on an approximate analysis framework referred to as the shallow strain path method that simulates undrained pile penetration from the stress-free ground surface. Large strain conditions close to the pile are solved numerically, and closed-form analytical expressions are obtained from small strain approximations at points further away. These results show that, for closed-ended cylindrical piles of radius R and embedment L, the normalized displacements δL∕R2 are functions of their dimensionless position x∕L. In contrast, for a planar sheet pile or unplugged open-ended pile, the far-field soil displacements at x∕L depend only on the wall thickness w; i.e., δ∕w = f[x∕L]. The proposed analyses show favorable agreement with data from a variety of available sources including field measurements of (1) building movements caused by installation of large pile groups; (2) uplift of a pile caused by driving of an adjacent pile within a group; and (3) spatial distributions of ground movements caused by installation of a single pile (both cylindrical closed-ended and sheet pile wall), including a particularly detailed set of measurements in a large laboratory calibration chamber. The comparisons show that the proposed analysis is capable of reliably predicting the deformations within the soil mass but generally underestimates the vertical heave measured at the ground surface. Further investigation suggests that this discrepancy may be related to the occurrence of radial cracks observed at the ground surface during pile installation and is consistent with tensile horizontal strains computed in the shallow strain path method analyses.     

New Failure Load Criterion for Large Diameter Bored Piles in Weathered Geomaterials

In the literature, various “failure criteria” or methods of estimating the failure load in pile loading tests have been proposed. The criteria, based on varying assumptions, were intended for different methods of pile testing and were verified on tests of a variety of pile types and sizes. Most of the criteria were not developed for slow maintained loading tests of large-diameter (greater than 0.6 m) and long bored piles. Piles of this kind have considerable resistance, and it is often impractical to reach failure load as defined by the various criteria. In this paper, a total of 38 large-diameter bored piles (drilled shafts) that were tested, ranging from 0.6 to 1.8 m in diameter, varying from 12 to 66 m in depth, and founded in weathered geomaterials (rocks and saprolites), are critically reviewed and studied. Among them, a selection of seven pile load tests is examined in detail by using different existing failure criteria and specifications. The tests were chosen for their high degree of mobilization of pile capacity and the availability of reliable load-movement relationships. Specific aspects of pile behavior, such as the mobilization of toe resistance and shaft shortening, are also investigated using 31 loading tests to develop a new failure load criterion. The writers were heavily involved with the construction, testing, and analysis of 15 of the 38 piles. From the results of the study, a new nonsubjective, semiempirical method is proposed for estimating the approximate interpreted failure loads for piles founded in weathered geomaterials. The method is based on a moderately conservative estimation of the movement required to mobilize toe resistance and incorporates observations of shaft shortening from pile loading tests. Generally, the new method may allow more effective and consistent designs for large-diameter bored piles in weathered geomaterials.     

CPT-DMT Correlations

Although the cone penetration test (CPT) and flat-plat dilatometer test (DMT) have been used for over 30 years, relatively little has been published regarding comprehensive correlations between the two in situ tests. This paper presents preliminary correlations between the main parameters of the CPT and DMT. The key to the proposed correlations is the recognition that the main DMT parameters are normalized and hence, should be correlated with normalized CPT parameters. The suggested correlations are developed and evaluated using published records and existing links to various other parameters as well as comparison profiles. The suggested correlations may guide future more detailed correlations between these two in situ tests.     

黏土中静压沉桩离心模型

采用西澳大学室内鼓轮式离心机,在预先固结的高岭黏土中开展不同离心力场(50g,125g及250g,g为重力加速度)条件下的模型压桩试验、T-bar试验和静力触探试验,分析了模型桩在贯入过程、静置稳定过程中桩身径向应力(σ_r)的变化规律,并对后期桩体拉伸载荷阶段的径向应力变化值(Δσ_r)及桩侧摩阻力变化情况行了探讨,揭示了在不同超固结比(OCRs)黏土中静压桩侧摩阻力的演变特性.在此基础上,通过两种经验公式方法对桩侧摩承载力进行了预测计算和对比分析.研究结果表明:沉桩过程中桩端相对高度(h/B)对桩身径向应力的发展变化有很大的影响,桩身不同位置(h/B)的总径向应力对同一贯入深度而言,存在桩侧径向应力退化现象;基于静力触探试验提出的经验方法,能有效考虑静力触探锥端阻力(q_t)和桩端相对高度(h/B)因素的影响,将其应用于黏土沉桩时桩侧摩阻力的预测,可取得与试验实测结果较吻合的结果.研究成果对软土地区静压桩施工与承载力设计具有一定的工程指导意义.      

Behavior of Axially Loaded Pile Groups Driven in Clayey Silt

This paper presents a case history describing measurements made during the installation and load testing of groups of five, closely spaced, precast concrete piles in a soft clay-silt. The test results extend the presently limited set of reported high-quality data for pile groups at field scale and allow assessment of the reliability of existing numerical and analytical predictive approaches. Full scale maintained compression and tension load tests on groups as well as tests on single (reference) piles and an individual test on a pile within a pile group enable the effects of multiple pile installations and interaction between piles under load to be assessed. The results are compared with existing simple methods of pile group analysis and with other case histories reporting results on small pile groups. A simple expression to evaluate pile group stiffness efficiency is proposed.     

Analysis of Load Tests on Piles Driven through Calcareous Desert Sands

The ultimate bearing capacity of short, precast concrete piles driven into calcareous sands was examined by pile-load tests carried out at two sites in Kuwait. The piles had a 0.3 m × 0.3 m square cross section and extended to a maximum depth of 12 m. They were driven through a loose-to-compact calcareous surface sand layer underlain by a competent dense-to-very-dense siliceous cemented sand deposit. The pile tips and part of the pile shafts were embedded in the lower layer. The base resistance and shaft friction were calculated using the Meyerhof method for a layered soil profile. The method employs the standard penetration test N values. The results indicate that a great portion of the pile capacity is due to base resistance. The skin friction mobilized is small and consists of two components corresponding to the two layers penetrated along the pile shafts. The calculated pile capacities were very close to the measured values. The unit skin friction is not constant along the pile shafts.     

Assessment of the Axial Load Response of an H Pile Driven in Multilayered Soil

Most of the current design methods for driven piles were developed for closed-ended pipe piles driven in either pure clay or clean sand. These methods are sometimes used for H piles as well, even though the axial load response of H piles is different from that of pipe piles. Furthermore, in reality, soil profiles often consist of multiple layers of soils that may contain sand, clay, silt or a mixture of these three particle sizes. Therefore, accurate prediction of the ultimate bearing capacity of H piles driven in a mixed soil is very challenging. In addition, although results of well documented load tests on pipe piles are available, the literature contains limited information on the design of H piles. Most of the current design methods for driven piles do not provide specific recommendations for H piles. In order to evaluate the static load response of an H pile, fully instrumented axial load tests were performed on an H pile (HP?310×110) driven into a multilayered soil profile consisting of soils composed of various amounts of clay, silt and sand. The base of the H pile was embedded in a very dense nonplastic silt layer overlying a clay layer. This paper presents the results of the laboratory tests performed to characterize the soil profile and of the pile load tests. It also compares the measured pile resistances with those predicted with soil property- and in situ test-based methods.