Technical Papers

Technical Papers

Field experience of the piezoball in soft clay

C. Colreavy & C.D. O’Loughlin – Institute of Technology Sligo, Ireland
M. Long
– University College Dublin, Ireland
N. Boylan
– University of Western Australia, Australia
D. Ward
– In Situ SI, UK

ABSTRACT: This paper presents the results of a series of piezoball penetration and dissipation tests carried out at two well characterized soft soil sites in Ireland. Piezo-ball data are compared with piezocone data, in addition to other in situ and laboratory test results. Using the standard N factor of 10.5 resulted in an undrained shear strength profile which is in very good agreement with Tbar profiles from previous studies. Interestingly, results of dissipation tests show that dissipation around the pie-zoball is faster than around the cone, when the different diameters are accounted for.

Interpretation of CPTU and SDMT in organic, Irish soils

A. Bihs – NTNU, Trondheim, Norway
M. Long – UCD, Dublin, Ireland
D. Marchetti – Studio Prof. Marchetti, Roma, Italy
D. Ward – In Situ Site Investigation, UK

ABSTRACT: The Limerick South Ring road project started in August 2006 and connects the N7 Dublin Road to the N18 Ennis Road. An extensive laboratory and field soil investigation program was carried out. The soil consists of alluvial (mostly organic) fine clays and silts with thicknesses up to 13m. This paper presents the re-sults of CPTU and seismic dilatometer tests (SDMT) carried out by In Situ Site In-vestigation (In Situ SI) at two locations along the new embankment in November 2008. It is the first time that the research DMT including shear wave velocity meas-urements was tested on Irish soils. Effective stress based models developed at the NTNU have been used among several others to interpret the data from the CPTU. The results obtained are compared to the findings from the SDMT.

Cone penetration testing on liquefiable layers identification and liquefaction potential evaluation

E. Anamali – In Situ Site Investigation, Balkans
L. Dhimitri & D. Ward – In Situ Site Investigation, UK
J.J.M. Powell – Geolabs Limited, UK

ABSTRACT: This paper presents the results of liquefaction potential evaluation for various sandy sites, with high seismic risk, where soil liquefaction is a major concern for all structures supported on these kinds of soils. There are many methods available for these calculations, based on different site investigation techniques. The Cone Penetration Test (CPTU) provides ideal data for this purpose, due to its repeatability and reliability. CPTU based methods on soil liquefaction assessment are important not only to identify liquefiable layers, but also their state in situ. This paper looks at results of liquefaction analyses on different sites susceptible to liquefaction, using CPTU based methods and also compares them with methods that are Standard Penetration Test (SPT) based, but using SPT data derived from correlations to CPTU results.

Evaluation of Liquefaction Potential by CPTU and SDMT

E. Anamali – In Situ Site Investigation, Balkans
L. Dhimitri & D. Ward – In Situ Site Investigation, UK
Neritan Shkodrani – Faculty of Civil Engineering, Polytechnic University, Albania

ABSTRACT: This paper deals with the evaluation of liquefaction potential of the soils at the marsh of Porto Romano, located in the western central part of Albania, where will be constructed the Energetic Park of Porto Romano. These analyses are performed based on the data taken from different in situ testing techniques. Piezocone tests (CPTU) were carried out during the two different site investigations (before and after the ground improvement) for the characterization of soil layers and determination of soil properties. In addition, during the first phase of site investigation a full seismic study was performed to estimate the shear wave velocity, Vs, and the peak ground acceleration. During the second site investigation two seismic dilatometer Marchetti tests (SDMT) were also carried out very close to the CPTU locations. The paper shows the results of the liquefiability assessment by CPTU and SDMT tests carried out during the two site investigations.

Evaluation of bearing capacity of cast in place piles from in situ tests based methods

E. Anamali – In Situ Site Investigation, Balkans
L. Dhimitri & D. Ward – In Situ Site Investigation, UK
Neritan Shkodrani – Faculty of Civil Engineering, Polytechnic University, Albania

ABSTRACT:
Different in situ based methods are used for determining the bearing capacity of a single pile. For this reason, this paper aims to deal with evaluation of bearing capacity of a single cast in place pile, by using various methods based on three different in situ testing techniques: Standard Penetration Test (SPT), Cone Penetration Test (CPT) and Dilatometer Marchetti Test (DMT). These tests are used in this study to identify the soil profile and also to characterize the strength parameters of the soils, which are further used to estimate the bearing capacity. The tests are carried out in different locations in Albania, including also some coastal areas. The soil profile identified in all the sites is non homogeneous. From site investigations are determined various sandy and clayey layers, but in the coastal sites also organic material is present. The considered cast in place pile diameters, in this paper, range from 0.5 m through 2.0 m and embedment lengths range from 10 m, 20 m and 32 m. At the end of our study, the results of bearing capacities by different methods are compared. Some conclusions are highlight related to the use of in situ tests during the pile foundation design.

Small Strain Stiffness assessments from in situ tests – revisited

E. Anamali – In Situ Site Investigation, Balkans
L. Dhimitri & D. Ward – In Situ Site Investigation, UK
A.P. Butcher –
Consultant, UK
J.J.M. Powell
Geolabs Limited, UK

 

ABSTRACT: The increasing trend to model the behaviour of the ground requires more detailed soil properties that include small strain data. These data can be obtained from both field and laboratory tests to measure shear wave velocities from which the shear modulus at small strains can be calculated. However, such measurements are only specified for large projects and so smaller projects have to rely on correlations from other in situ tests. In 2004 Powell & Butcher presented and discussed some correlations between the small strain stiffness of the ground in different orientations measured by geophysical tests and parameters measured by the Cone Penetrometer (CPT) and the Marchetti Dilatometer (DMT). Since that time the database of information has grown and this paper reviews and updates the findings of the earlier paper. Anisotropy of stiffness is shown to be a major factor in the correlations especially in ‘aged’ clays.

Review of CPT testing and pile design parameters derived from glacial deposits in Perth

D.R Illingworth – Piledesigns, UK
L. Dhimitri  – In Situ Site Investigation, UK

ABSTRACT: This paper identifies a glacial meltwater deposit beneath Perth town centre which provides a suitable bearing stratum for piled foundations. Geotechnical testing shows the material to be mainly a laminated silt with a reasonably consistent profile in depth and lateral extent. Site investigation using Cone Penetration Testing (CPT) is shown to provide a better assessment of the in-situ characteristics of the material compared to more conventional techniques. The paper also reviews the results of several pile tests, installed using Continuous Flight Auger (CFA) techniques, and back analysis shows a fairly consistent range of derived parameters. This paper shows the importance of obtaining an accurate assessment of geotechnical characteristics. This is demonstrated with regards to pile design parameters. It is also shown how CPT testing is a valuable technique to assess in-situ geotechnical characteristics in fluvio-glacial deposits.

Full-scale tests on laterally loaded railway overhead line equipment mast foundations

David J Richards
William Powrie

Anthony P Blake

ABSTRACT: Pile foundations for masts supporting overhead line equipment (OLE) on railways in Western Europe have traditionally been designed using empirical formulae derived from tests carried out in the 1950s under the auspices of the Union Internationale des Chemins de fer (UIC). Recent application in the UK of ostensibly more analytical approaches led to significantly increased pile lengths, which contributed to the high-profile cost over-run on the Great Western electrification programme. Further, the loads associated with some newer designs of mast are greater than those covered by the original field tests, and hence are outside the evidence base for the empirical approach. To address this, full-scale field tests were carried out on three, 610 mm dia. circular hollow-section steel piles installed in a railway embankment at the High Marnham test track (Nottinghamshire, UK). Each pile was designed according to the empirical OLE master index (OLEMI) method for a different form of modern OLE mast, and instrumented using Shape accelerometer arrays (SAAs) to determine pile deformations. The results provide valuable insights into the mechanisms of deformation of piles of different lengths, both at and beyond the expected in-service loads. p–y curves derived from the SAA measurements compare reasonably well with curves constructed using the American Petroleum Institute method for undrained clay soils. The tests also demonstrate the suitability of the OLEMI approach for large structures and loads; and that the Eurocode 7 partial factors on load and undrained shear strength applied to an undrained (total stress) limit equilibrium calculation are likely to be sufficient to meet serviceability requirements for standard single-and twin-track cantilever structures.

Potential of the Cone Pressuremeter Test for obtaining stiffness degradation for offshore wind turbine monopile foundations

G W Tucker, CT Leth,  L Krogh, P Ladefoged – Orsted
T Lunne – Norwegian Geotechnical Institute
M Taylor –
In Situ Site Investigation
 

ABSTRACT: The piezocone (CPTU) offers a quick and repeatable investigation tool with instantly available high-resolution data. For these reasons it is both technically and commercially attractive to further instrument the CPTU to acquire additional measurements with more sensors either within the cone itself or as add-on mod­ules behind the cone. Many ideas for further instrumentation of the CPTU have been conceptualised or tested but one that could offer direct benefit for offshore wind turbine foundation design is the Cone Pressuremeter (CPM). This in situ tool includes a pressuremeter module behind the standard cone that can measure ground displacement or expansion as a function of pressure applied during the loading, unloading and reloading of the surrounding soil when penetration is paused. From these measurements a number of soil parameters may be interpreted including the stiffness degradation (G/G0) of the soil when combined with reliable in situ or labora­tory measured G0 values. With increasingly larger wind turbines being used and deeper water sites selected for construction, soil stiffness is an increasingly critical input for the design of many offshore wind turbine founda­tions. CPM testing has been trialed in the field onshore at a glacial till site and a medium to very dense sand site. The results of the CPM are compared in this paper to site specific results for the self-boring pressuremeter and advanced laboratory-based alternatives. The practical considerations of using the CPM offshore in seafloor mode are also reviewed.

The use of CPTU for driven piles designed in a backfilled opencast ‘marlhole’ in an important post-industrial revolution area within the UK

D. Illingworth & C. Burton – Piledesigns Limited, UK
L. Dhimitri & D. Ward – In Situ Site Investigation, UK
P. Shelton –
Phil Shelton Geotechnical Consultancy Limited, UK 

ABSTRACT: The Etruria Formation has historically been an important resource for the pottery and brick-making industry in the Stoke-on-Trent area and was mainly exploited using opencast methods – or ‘marl holes’ as they were commonly known. These ‘marl holes’ some of which have been reported to be more than 100m deep, have been subsequently backfilled generally with non-organic pottery, brickmaking and domestic waste. This paper explores the redevelopment of land over a backfilled ‘marl hole’ at a site in Hanley, Stoke­on-Trent, Staffordshire, UK, for residential properties. The development posed a number of challenges for the design of the foundations due to the historical legacy of the site. Driven steel tubular piles were chosen as a suitable system as there is precedent with this foundation solution, which has been frequently adopted for buildings within the area. However, some of the key challenges for this site included the presence of ‘high walls’ along the edges of the opencast works where driven piles could be deviated off the sides along with the uncertainty regarding socket lengths of piles driven into the underlying solid strata. To establish a 3D ground model for the ‘marl pit’, underlying strata, piezocone tests (CPTU) were seen as the most cost-effective and practicable method of site characterisation. Using this data, piles were installed, test/production piles were installed, driven to a set/penetration into the bedrock criteria and then compared to this ground model.

Watch out for the use of global correlations and “black box” interpretation of CPU data

J.J.M. Powell  – Geolabs Limited, Watford, UK
L. Dhimitri – In Situ Site Investigation, UK
 

ABSTRACT: Many people interpret soil properties from CPTU measurements based on correlations embed­ded in software packages without ever questioning the validity of those correlations. This could be termed the ‘black box’ approach! This paper aims to show how dangerous this can be but also the power of the CPTU in helping to show the variations in soil properties within profiles. Based on correlations properties can be both over and under-estimated, which can of course result in both unsafe design and over design. Too often one correlation must be used to derive a soil property required in another correlation, further compounding the potential for errors. A range of sites will be examined with a range of soils varying from very soft clays and silts to stiff clays, sands and soft rocks.

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