Monitoring and Process Control of Vibratory Driving
K. R. Massarsch1 and C. Wersäll2
ABSTRACT: Vibrators are used increasingly in the foundation industry, primarily for installation of piles and sheet piles, but also for deep vibratory compaction. Fundamentals of vibratory driving are described that make it possible to choose vibrator performance parameters based on field monitoring and performance control. Variable frequency and amplitude vibrators have become available that make it possible to adapt the driving process to project-specific requirements. The components of modern electronic measuring systems are detailed that can be used to monitor, control, and document different aspects of vibratory driving. Two examples are presented—vibratory driving of sheet piles and resonance compaction—which show how the performance of vibrators and sheet piles can be analysed and adapted to meet specific requirements. By using the advanced monitoring and process control systems, the efficiency of vibratory driving is enhanced. From the retrieved parameters, a better understanding of the vibratory driving process is gained, which can be used to develop a valuable database.
KEYWORDS: Vibrator, Pile, Sheet pile, Compaction, Ground vibration, Monitoring.
Load-movement Response by t-z and q-z Functions
Bengt H. Fellenius1 and Mohammad Manzur Rahman2
ABSTRACT: A static loading test provides more than a single-point value, “capacity”. The primary use of a loading test is to show the load- movement response of the pile-and-soil system in order to assist in analysis of the transfer of a supported load to the soil. A pile is composed of a series of short lengths (elements) that are affected by shaft shear or toe stress, expressed as a relation of stress (load) versus movement for the element. The response of the soil around a pile element is expressed in load-transfer functions. The response of a pile head, that is, the actual pile load-movement curve, is the sum of the response of a series of individual pile elements. Fitting the theoretical load-movement response to actual test results by trial-and-error applying a series of shaft (t-z) functions and a toe (q-z) function, enables a calibration of a pile and site that serves to establish the load-transfer conditions of a piled foundation needed for determining what short and long-term settlement the foundation will experience. Thus, a crude “capacity” assessment will not do. Eight functions for modeling strain-hardening and strain- softening response are presented in the paper and their use in fitting theoretical to actual results is illustrated.
KEYWORDS: Load-movement response, t-z and q-z function, Test simulation.
Common Mistakes in Static Loading-test Procedures and Result Analyses
Bengt H. Fellenius1 and Ba N. Nguyen2
ABSTRACT: Static loading tests on piles are arranged in many different ways ranging from quick tests to slow test, from constant-rate-of- penetration to maintained load, from straight loading to cyclic loading, to mention just a few basic differences. Frequently, the testing schedule includes variations of the size of the load increments and duration of load-holding, and occasional unloading-reloading events. Unfortunately, instrumenting test piles and performing the test while still using unequal size of load increments, duration of load-holding, and adding unloading-reloading events will adversely affect the means for determine reliable results from the instrumentation records. A couple of case histories are presented to show issues arising from improper procedures involving unequal load increments, different load-holding durations, and unloading and reloading events—indeed, to demonstrate how not to do. The review has shown that an instrumented static loading test, be it a head-down test or a bidirectional test, performed, as it should, in a series of equal load increments, held constant for equal time, and incorporation no unloading-reloading event, will provide data more suitable for analysis than a test performed with unequal increments, unequal load-holding, and incorporating an unloading-reloading event. No useful information is obtained from prolonging the holding time for the maximum load.
KEYWORDS: Pile, Load test, Strain, Extensometer, Tangent stiffness, Load cycle.
Stiffening Effect on End Bearing Granular Piles
M. R. Madhav1, Jitendra Kumar Sharma2 and Vaibhaw Garg3
ABSTRACT: The performance of ground improement using granular piles (GP) is limited by its low strength and stiffness. If GPs are partially strengthened and stiffened near the ground surface, their overall performance gets enhanced several fold. Stiffening of GP can be achieved by replacing partially the upper portion of GPs with material having higher strength and deformation modulus, e.g. by geo-synthetic encased columns, SDCM (stiffened deep cement mixing), etc. Analyses of a single and group of two partially stiffened end bearing GPs is presented in terms of top settlement influence factor, settlement interaction factor for two-pile group, settlement reduction factor, percentage load transferred to the base, variation of normalized shear stress distribution along the length of the pile. Settlement influence factor decreases while the percentage load transferred to the base of increases with increase in the relative stiffness factor and the relative length of stiffening from top of the partially stiffened GP, both for single as well as for two pile group.
KEYWORDS: Relative stiffness of bearing stratum, Relative stiffness of granular pile, Setlement influence factor, Settlement interaction factor, and Settlement reduction factor
Long-term Behaviour of Piled Raft with DMW Grid on Reclaimed Land
K. Yamashita1, T. Tanikawa2 and A. Uchida3
ABSTRACT: This paper offers a case history of a friction piled raft, supporting a four-story parking garage on reclaimed land. The subsoil consists of filled sand and alluvial loose sand which have the potential for liquefaction. Hence, grid-form cement deep mixing walls were employed as a countermeasure of liquefaction with the piled raft. Below the sand layers, there are very-soft to medium alluvial clay layers, which are normally consolidated or under-consolidated, and the depth of the dense sand layer changes markedly near the center of the site. To reduce the differential settlement due to consolidation of the clay, 152 friction piles of different length were employed. To corroborate the foundation design, field monitoring on the foundation settlement and the load sharing between the piles and the raft was performed. The measured settlements and the maximum angular rotation of the raft about 12 years after the end of the construction were within acceptable limits. Furthermore, at the time of the 2011 off the Pacific coast of Tohoku Earthquake, no significant change in effective contact pressure between the raft and the unimproved sand was observed after the event, which confirms that the effectiveness of the grid-form DMWs as a countermeasure of liquefaction.
KEYWORDS: Piled raft, Grid-form DMWs, Consolidation settlement, Monitoring, Liquefaction, The 2011 Tohoku Earthquake
In-situ Full Scale Load Tests and Estimation Method of Pile Resistance for Nodular Diaphragm Wall Supporting High-rise Tower
K. Watanabe1 and T. Sudo2
ABSTRACT: In recent years, the height and weight of buildings have increased; a trend noticeable especially in the central urban areas of Japan. Additionally, overturning moments from earthquakes and wind loads cause tensile and compressive forces to occur in pile and wall foundations. These situations result in the development of new types of foundations for high-rise superstructures. The nodular diaphragm wall is one type of such foundation; the nodular part is located at the middle depth. The study presented here was to evaluate the applicability of the nodular diaphragm wall for high-rise towers. A review of foundations similar to the nodular diaphragm wall was first made, followed by an outline description of the high-rise tower. The tension and compression load tests performed on the foundation elements are then presented, and finally a discussion of the design formula for the nodular diaphragm wall.
KEYWORDS: Nodular diaphragm wall, High-rise tower, In-situ full-scale load test, Tension resistance, Compression resistance
Three-dimensional Finite Element Analyses of Barrette Piles under Compression and Uplift Loads with Field Data Assessments
D.W. Chang1, C. Lin2, T.Y. Wang3, Y.K. Lin4, F.C. Lu5 and C.J. Kuo6
ABSTRACT: This paper presents the three-dimensional finite element modeling of barrette piles in clayey and sandy soils, in which the piles are subjected to statically compressive and uplift loads. Load displacement curves and load transfers were monitored and compared to solutions from one-dimensional finite difference analysis. Capacities of the barrette piles were examined by interpretation methods and bearing capacity equations. Pile load test data of barrette piles located in Xingyi District, Taipei Basin was used for simulation. It was found that the conventional bearing capacity equations are applicable to barrette piles. The interface elements between pile and soils were found to significantly affect the results. Finite element analysis can provide more complete solutions when compared with finite difference analysis. It was also found that the soil frictions due to pile uplift in soft clays at Taipei Basin were underestimated when using common strength reduction ratios.
KEYWORDS: Barrette pile, Finite element analysis, Finite difference analysis, Pile load test, Interpretation method
AUT: Geo-CPT & Pile Database
Updates and Implementations for Pile Geotechnical Design
A. Eslami1, S. Moshfeghi2, S. Heidari3, F. Valikhah4
ABSTRACT: Due to uncertainties in geomaterial properties and modelling, a detailed and precise data source can significantly improve reliability indices. Accordingly, to facilitate quantifying the uncertainties, there are currently several databases in the realm of piling and CPT. AUT (Amirkabir University of Technology): Geo-CPT&Pile Database was initially developed in 2015 by 466 case records including pile and CPT records. At present, it is updated to the total number of 600 case records which is partly accessible online. Aiming at pile performance- based design, risk analyses and evaluation of optimum safety factor have been examined based on value engineering by Wasted Capacity Index (WCI). Subsequently, the performance of direct and indirect CPT methods for pile bearing capacity estimation has been assessed focusing on reliability-based approaches. In addition, a methodology was employed to predict the load-displacement and bearing capacity of driven piles interactively. Finally, an algorithm is implemented for pile geotechnical performance-based design through a selected database considering probabilistic, reliability and risk assessments.
KEYWORDS: AUT: Geo-CPT & Pile Database, Pile Capacity, CPT-based Methods, Performance-Based Design (PBD)
Drilled Shaft Grouting Effectiveness in Mekong Delta
Hai M.N.1, Anand J.P.2, Long D.P.3 and Trung T.N.4
ABSTRACT: In recent years, the post shaft-grouting technique has been used prevailingly for improving the drilled shaft bearing capacity of the high-rise building foundation projects in Mekong River basin of Vietnam. However, the effectiveness of the post shaft-grouting works for the drilled shafts is rarely obtained as expected. This paper will present results of bidirectional tests on the non-grouted and grouted shafts of the Lancaster Lincoln high-rise building project in Ho Chi Minh City, Vietnam, performed in 2016. The test shafts had diameter of 1.5 m and were constructed to 85 m depth below ground surface. The shaft grouting was performed along about 49 m above the drilled shaft toe level. The bidirectional load test results and the analysis shows that the unit shaft resistances of the sand and clay layers were increased about 150 and 300 percent after grouting, respectively.
KEYWORDS: Shaft grouting, Bidirectional load test, Movements, Strain, Shaft resistance, load distribution, Elastic Shortening
Design of Axially-loaded Piles: Experimental Evidence from 400 Field Tests
A. Mandolini1 and R. Di Laora2
ABSTRACT: This work is aimed at furnishing an experimental support to the design of axially-loaded piles, taking advantage of an extensive database of pile load tests carried out in different sites nearby Napoli, in South Italy. Experimental data consist of nearly 400 full-scale pile load tests, some of them reaching large values of settlement. Different construction methods, including Non-Displacement, CFA and Displacement piles, have been used. The main results of the work consist in furnishing experimentally-derived rules and indications for pile design. With regards to failure loads, mobilization curves relating properly normalized values of load and settlement are proposed as function of the installation technique; indications on the bearing capacity of piles as function of geometry and technology are also provided. Initial stiffness of piles is investigated, identifying a rule of thumb for a rapid assessment, function solely of pile diameter and valid regardless of length and specific properties of pile and soil material.
KEYWORDS: Piles, Load test, Full-scale experiment, Axial stiffness, Axial bearing capacity
The Use of Equivalent Circular Piles to Model the Behaviour of Rectangular Barrette Foundations
H.G. Poulos1, H.S.W. Chow2 and J.C. Small3
ABSTRACT: Barrettes having rectangular cross-sections can be analysed using finite elements, but this requires a three-dimensional non- linear computation which can be time consuming. Therefore, in this paper, the use of simple means of analysis based on conventional piles of circular cross-section is examined. Equivalent dimensions are chosen for the circular piles to represent the barrette, and the behaviour of the equivalent piles is compared to finite element results for the barrettes. It is shown that for single barrettes and groups of barrettes under either vertical or lateral load, it is possible to model barrette behaviour approximately but adequately using equivalent circular piles.
KEYWORDS: Barrettes, Equivalent pile, Finite element analysis, Pile groups, Vertical load, Lateral load
Analysis of Thermo-Mechanical Behaviour of Energy Piles
G. Russo2, R.M.S. Maiorano1and G. Marone2
ABSTRACT: The use of pile foundations as heat exchangers in combination with heat pump conditioning systems are becoming increasingly popular. Quite a large number of small scale laboratory tests and field scale experiments are available and allow to gain an insight in the mechanisms governing pile-soil interaction under thermo-mechanical loading. In the paper, numerical FEM simulations are carried out on published experimental small scale laboratory tests. The paper focus is on the load-settlement relationship and on the load-transfer curves with depth. The tests show that under purely cyclic thermal loading reversible strains are predominant, while the preliminary application of an axial load causes the development of irreversible deformations during the thermal loading. Numerical FEM simulations carried out with two different constitutive soil models confirm such a finding. A simple procedure to calibrate the model’s parameters is proposed and validated.
KEYWORDS: Energy piles; Finite element modelling; Pile testing; Thermo-mechanical behaviour.
A Method to Estimate Shaft and Base Responses of a Pile from Pile Load Test Results
Madhav Madhira1and Kota Vijay Kiran2
ABSTRACT: A practical method for estimating initial shaft and base stiffnesses and ultimate shaft and base resistances of a pile from pile load test results has been proposed. The method employs hyperbolic relationships for the non-linear responses of shaft and base resistances, which are solved using iterative procedures to arrive convergence. A large number of empirical correlations are reported in the literature but many-a-times they either under-estimate or overestimate the pile response. Similarly, numerical tools that can predict shaft and base resistances typically would depend on the expertise of the engineer and also based on various input parameters. Thus, the applicability of the tools therefore too is uncertain. The present method discussed in this paper, would help engineers to estimate shaft and base responses of the actual site using the initial Pile load test results. The analytical solutions of the method are discussed in detail and the proposed method is applied to few load – displacement data available from pile load test results to illustrate its efficacy.
KEYWORDS: Pile capacity, Load test, Compressive load, Settlements, Shaft and base responses
Technical Issues on Static Load Tests on Barrettes and Bored Piles
K. Watanabe1, T. Hosoi2, S. Matsushita3, A. S. Balasubramaniam4, and R. N. Hwang5
ABSTRACT: This paper addresses to 1) Characteristic of slurry and mechanism of forming cakes, 2) Effects of the shapes of piles on load capacities, and 3) Modulus of elasticity of concrete. The results of laboratory tests on the strengths of mud cakes formed of bentonite slurry and polymer slurry are discussed. Also discussed are the results of loading tests on bored piles and barrettes with and with nodules. It has been found that the mud cakes formed of polymer slurry offer larger frictional resistance to shearing than bentonite slurry. It has also been found that nodules on piles will increase the load capacities of piles drastically. Furthermore, equations are proposed for calculating the moduli of elasticity of concrete based on the axial loads and stains obtained in pile load tests.
KEYWORDS: Slurry effect, Polymer slurry, Friction resistance, Cake, Slurry management, Shape effect, Non-uniform shaft pile, Under-reamed piles, Elastic modulus
Piled Raft on Sandy Soil- An Extensive Study
V. Balakumar1, Min. J. Huang2, Erwin Oh3, Richard Hwang4 and A. S. Balasubramaniam5
ABSTRACT: In recent years, designers have recognized that in addition to bearing capacity, settlement of foundations must be taken into account. To reduce settlement of buildings, piled raft appears to be a solution for structures found on soft ground. To investigate the performance of piled rafts, model tests have been conducted on circular, square and rectangular raft supported on piles with different spacings between piles. Numerical analyses were carried out to verify the results obtained in the model tests. The performance of a 14-story building was analysed to compare with the settlement readings obtained. The results of numerical analyses appear to be very encouraging as the results of the analyses well agree with the results of model tests, as well as the settlement readings collected in 790 days for this 14-story building. The value of numerical analyses in back analyses and in prediction of settlement of buildings has thus been confirmed.
KEYWORDS: Piled raft, ANSYS, Compressible layer
Finite Element Modelling of a Bidirectional Pile Test in Vietnam
Phung Duc Long1 and B. William Cheang2
ABSTRACT: Static loading test on single piles for verification is commonly required, yet very expensive and difficult to perform, especially for the large-diameter bored piles. The bidirectional test, also-called Osterberg cell test, is nowadays very common in Vietnam. The Finite Element Method (FEM), which is a reliable tool for simulating loading tests, can also be used to model a bi-directional pile test. In this paper, FEM is used for modelling a bidirectional test on a 2.5m-diameter, 80m long bored pile at the Cao Lanh cable-stayed bridge in the Mekong Delta, Vietnam. The FEM results are compared with the monitored data obtained from the bi-directional test. The comparison showed that FEM can be an effective and reliable tool in this case. The FEM is performed using PLAXIS 2D.
KEYWORDS: Numerical analysis, Bidirectional test, Axial bearing capacity, Single pile, FEM
A FEM Assessment on the use of t-z and q-z Functions for Deep Foundations
Q.J. Ong1, S.A. Tan2
ABSTRACT: Load-movement t-z and q-z functions have been established and widely accepted as a tool to characterise pile shaft and toe resistances respectively. The functions are best used to represent a short element along the pile. But the question remains whether these functions depend on pile diameter and pile depth. This paper discusses the soil-structure interaction and load transfer mechanisms of a single pile and reviews the theoretical basis of the t-z and q-z functions. The bearing behaviour of a single circular footing under various conditions was also investigated and compared against the toe behaviour of piles. Linear elastic and Mohr-Coulomb soils are used for this study to investigate stress versus normalized movement curves for pile behaviour.
Keywords: Shallow foundation, Deep foundation, Piling, t-z, q-z
Shaft Resistance of Shaft-grouted Bored Piles and Barrettes Recently Constructed in Ho Chi Minh City
T.D. Nguyen1*, V.Q. Lai2, D.L. Phung3, T.P. Duong4
ABSTRACT: Recent years, several high-rise buildings have been constructed in Ho Chi Minh city, the largest and most dynamic city in Vietnam. The city is located in the Saigon-Dongnai River delta, where, especially in the central districts, bored piles and barrettes for the high- rise buildings need to be large and socketed in alluvial deposits at large depths. Shaft-grouting technique has been recently applied to increase shaft resistance of the bored piles and barrettes. This paper briefly presents latest shaft grouting technique applied to bored piles and barrettes in the city. A database of head down and bidirectional tests on well-instrumented grouted and not-grouted bored piles and barrettes was analysed to evaluate the enhancement of shaft resistance. Correlations between the ultimate unit shaft resistance (ru) with the SPT N60 value indicated that the ru-value of grouted piles in both clayey and sandy soils was on average two times larger than that of not grouted piles. Estimated ru- values obtained from b-method recommended in practice compared well with those obtained from the instrumented piles.
KEYWORDS: Bored piles, Barrettes, Shaft Grouting, Shaft resistance
