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Lagerungsdichte von nichtbindigen Böden aus Ramm- und Drucksondierungen: Eine aktualisierte Bewertung empirischer Beziehungen
Abstract
Der Einsatz von Rammsonden zur Abschätzung der Lagerungsdichte von nichtbindigen Böden ist in Deutschland sehr verbreitet. Die zugehörigen empirischen Korrelationen aus der inzwischen zurückgezogenen DIN 4094‐3 wurden teils in die DIN EN 1997‐2 und teils in die DIN 4094‐2 übernommen. Die Abhängigkeit der Schlagzahl von der Tiefe und somit vom Spannungsniveau wird dabei nicht explizit berücksichtigt und es wird lediglich zwischen Situationen über und im Grundwasser unterschieden. Der Einfluss des Überlagerungsdrucks wird auch bei den Drucksondierungen nicht berücksichtigt. Bedingt durch die verfeinerte Instrumentierung und die damit verbundene Möglichkeit einer differenzierteren Charakterisierung des Baugrunds gewinnen Drucksondierungen zunehmend an Bedeutung, so dass für diesen Sondierungstyp der Fundus von Korrelationen in der internationalen Fachliteratur groß ist. Im Rahmen einer Vergleichsuntersuchung werden die Anwendungsgrenzen und die Zuverlässigkeit der in den Regelwerken vorgeschlagenen empirischen Beziehungen kritisch bewertet und durch neue Ansätze erweitert. Besonderes Augenmerk wird dabei auf Korrelationen zwischen den Ergebnissen der beiden Sondierungstypen gelegt.
... With the vast body of soil parameter-related correlations and design methods available based on the penetration resistance of the CPT, a relationship between the results obtained from the DP and the CPT is beneficial. There are several sources in the literature which provide values or indications of such relationships for different soil types [4][5][6][7][8]. ...
... Since the only recent paper in Germany by Vrettos & Papamichael [6] focuses more on the derivation of state parameters from DP and CPT, the last significant advance on the understanding of correlations between CPT and DPH was provided in Placzek's paper from 1985 [9]. Since then, knowledge concerning the penetration of probes into the soil at different penetration rates has advanced considerably. ...
... and that k ranges between 0.75 and 1.25 for non-cohesive soils, whereby a mean value of k = 1 is typically used for correlating DPH to CPT values [10]. Alternative relationships for non-cohesive soils are provided in DIN EN ISO 22476-2 [11] and Vrettos & Papamichael [6]. Information provided by Hettler [7] and Prinz & Strauss [8] indicates a value for k between about 0.3 and 1.0 for cohesive soils. ...
Despite the widespread availability and superior information provided by the cone penetration test (CPT), dynamic probes like the DPH (dynamic probe heavy) remain an important soil investigation method under certain circumstances. In order to make use of the results of the DPH in the context of the vast body of interpretation and design methods developed for CPT tests, the drop count N 10 of the DPH is correlated to the tip resistance q c of the CPT. There are numerous correlations between both values available in the standards and in the literature. However, any soil‐related differences, limitations, and factors influencing those correlations are not necessarily obvious. The present paper presents a simple framework for the illustration of influencing factors and the interpretation of correlations between DPH and CPT. The proposed framework is based on the information provided in EN ISO 22476‐1 and published scientific literature. Linear correlation factors based on the proposed framework are derived. These factors are then compared with our own field data and information from the literature.
... wobei p a der atmosphärische Druck (100 kPa) ist. Für den Exponenten m wird in der Praxis meistens m = 0,5 angesetzt [18], was als ausreichend genau beurteilt wird. Bei kleinen Tiefen wächst C N überproportional an und muss begrenzt werden. ...
... der Überlagerungswirkungen in der Auswertung, analog zu Gl. (8), auch für die DPH vorgenommen wird. Die Normung sowie die gängige Praxis zur Abschätzung der In-situ-Lagerungsdichte sieht eine entsprechende Korrektur nicht vor [18,23]. In guter Näherung kann jedoch angenommen werden, dass die Überlagerungswirkungen bei beiden Verfahren DPH und CPT identisch sind. ...
... Dann nämlich kann das Bemessungsdiagramm Bild 2 direkt in Verbindung mit der DPH-Rammsondierung angewandt werden; es bedarf lediglich einer Umrechnung von q c auf N 10H . Vorschläge hierzu für rollige Böden sind in [18] zusammengestellt und bewertet. Darunter fi ndet sich auch der Vorschlag nach [24] für Sande (Gl. ...
de Die vorgenommene Neueinschätzung der Erdbebengefährdung für Deutschland im Rahmen der Erstellung des neuen Nationalen Anhangs zu DIN EN 1998-1 gab den Anlass, die in der geltenden DIN EN 1998-5 angegebene Nachweisführung zur Bodenverflüssigung zu bewerten und zu aktualisieren. In diesem Zusammenhang wurde für Gebiete mittlerer Seismizität ein leicht handhabbares Nachweisverfahren entwickelt, welches den aktuellen Stand der Technik berücksichtigt. Es basiert auf Ergebnissen von Drucksondierungen am Standort und erlaubt eine direkte Aussage zur potentiellen Gefährdung infolge Verflüssigung. Das Verfahren ist Bestandteil des neuen Nationalen Anhangs zu DIN EN 1998-5.
Abstract
en Approximate method for verification against ground liquefaction in regions of medium seismicity according to DIN EN 1998-5/NA:2021
The re-assessment of the earthquake hazard for Germany as part of the preparation of the new National Annex to DIN EN 1998-1 gave the reason to evaluate and update the verification against soil liquefaction specified in the applicable DIN EN 1998-5. In this context, an easy-to-use calculation method was developed for regions of medium seismicity, which takes into account the current state of the art. It is based on the results of cone penetration tests at the site and allows a direct determination of the potential liquefaction hazard. The procedure is part of the new National Annex to DIN EN 1998-5.
... Besides, the influence of other XBeach parameters was tested but found to have no influence (dryslp, critical avalanching slope above water, break = 3, wave breaking formulation according to Daly et al. (2011)) or to significantly reduce the erosion (wci, consideration of wave-current interaction). An initial porosity of 0.35 was additionally considered since a dynamic probing of the initial research dune was conducted and an increasing ground resistance (or storage) with increasing depth was observed (surface: loose, 1 m depth: very dense), which can be empirically related to the relative density and roughly to the porosity (DIN 18126 DIN 18126:1996-11;Vrettos and Papamichael, 2018). ...
The objective of this study was to evaluate the temporal and spatial performance of the XBeach model predicting storm surge induced erosion and breaching on the basis of a two-dimensional field case. Within the scope of a physical experiment, a large-scale artificial unvegetated research dune was built at the German Baltic Sea Coastline and surveyed before, during and after a surge event to generate high-resolution digital elevation models of the temporal and spatial failure process. The measured data was used to set-up and calibrate two-dimensional XBeach models. The numerical results showed that the default settings of the latest XBeach-X release lead to a very good agreement (BSS = 0.82) between the simulated and measured post-storm bed levels in the area of the research dune, while a higher agreement was observed on the overwash and inundation dominant eastern side than on the collision dominant western side. Evaluating the model accuracy during the storm surge using 44 digital elevation models of the seaside slope showed a spatially accurate prediction of the two observed breaches (±5 m) but also the occurrence of additional breaches. With respect to timing and breach width evolution, however, the results highly deviated from the observation and were found to be very sensitive to changes in grid resolution and to changes of default parameters. Exchanging the nearshore bathymetry with measurements one and two months prior to the physical experiment, where a 49% and 51% lower subaerial beach volume was observed, resulted in a significantly overestimated dune erosion (31% and 33%) and, hence, in a lower accuracy of the default model (BSS = 0.69). Overall, the XBeach model is capable of accurately predicting the evolution of storm-induced erosion during a sufficiently long and overwash/inundation dominant surge event when current high-resolution input data is available.
Der zukünftige Eurocode 7 wird ausdrücklich die Nutzung zuverlässigkeitsbasierter Methoden in der geotechnischen Planung und Bemessung erlauben. In Deutschland gibt es bisher kaum Erfahrung in der praktischen Anwendung derartiger Verfahren und entsprechend sind die Vorbehalte gegenüber diesen Methoden oft groß. Der neue DGGT‐Arbeitskreis (AK) 2.15 „ Zuverlässigkeitsbasierte Methoden in der Geotechnik “ hat sich zum Ziel gesetzt, durch praxisorientierte Anleitungen und Empfehlungen sowie begleitende Aus‐ und Weiterbildungsangebote den praktischen Zugang zu diesen Verfahren zu unterstützen. Ziel ist es, Möglichkeiten und Grenzen zu verdeutlichen sowie vor allem ihre Potenziale zu erschließen. In dem vorliegenden Beitrag werden allgemeine Grundlagen und die zukünftigen Arbeitsfelder des AK 2.15 vorgestellt. Ausgehend von der Einführung relevanter Fachbegriffe wird zunächst die Einbettung zuverlässigkeitsbasierter Verfahren in den aktuellen Normungs‐ und Regelungskontext aufgezeigt. Anschließend werden anhand des Lebenszyklus eines geotechnischen Bauwerks die Unsicherheiten in den geotechnischen Prognosen und Bewertungen beschrieben. Daran anknüpfend wird aufgezeigt, an welchen Stellen zuverlässigkeitsbasierte Methoden als mögliches Werkzeug sinnvoll genutzt werden können, um Ingenieur:innen, Bauherr:innen und Prüfer:innen in Nachweis‐ und Entscheidungsprozessen zu unterstützen. Zu den sich daraus ableitenden Arbeitsthemen werden durch den AK 2.15 zukünftig Empfehlungen erarbeitet und sukzessive veröffentlicht.
In Kap. 3 werden die notwendigen ingenieurgeologischen, hydrogeologischen, geophysikalischen, bodenmechanischen und felsmechanischen Untersuchungsmethoden dargestellt, um Boden und Fels für bautechnische Zwecke beschreiben, beurteilen und klassifizieren zu können. Des Weiteren werden für die geotechnischen Untersuchungen wichtige Aspekte wie z. B. Gesetzliche Grundlagen, Versorgungsleitungen oder Kampfmittel erläutert.
Vibrationsverdichtung wird oft zur Verminderung von Setzungen in rolligen Böden angewendet. Die Drucksonde CPT und der Flachdilatometer DMT eignen sich besonders zur Planung und Durchführung von Vibrationsverdichtungsprojekten, da sowohl die Bodensteifigkeit als auch die Änderung der Horizontalspannungen gemessen werden können. Der Spannungspfad bei der Vibrationsverdichtung beschreibt die permanente Erhöhung der Horizontalspannung und den dadurch entstandenen Vorbelastungseffekt. Ein Verfahren wird vorgestellt, wie aus der Erhöhung der Horizontalspannung der Vorbelastungsgrad abgeschätzt werden kann. Das Setzungsverhalten von normalkonsolidierten Böden wird beschrieben. Das Tangentenmodulverfahren kann zur Setzungsberechnung vor und nach der Verdichtung verwendet werden. Die Modulzahl sowie der Vorbelastungsgrad können aus Feldversuchen mit CPT und DMT abgeschätzt werden. Die Anwendung von CPT‐ und DMT‐Untersuchungen zur Festlegung von setzungsbezogenen Verdichtungskriterien wird beschrieben. Die Setzungsberechnung vor und nach der Vibrationsverdichtung wird anhand eines Fallbeispiels geschildert, bei dem ein schluffiger Sandboden mittels VibroWing‐Verfahren und Vibrationsplatte verdichtet wurde.
Das Kapitel behandelt die Baugrunduntersuchungen, die im Rahmen der Vorerkundung eines Bauprojekts ausgeführt werden. Grundlage für das Vorgehen bildet die europäische Norm EN 1997 Teil 2. Die Untersuchungen stützen sich auf den Baugrundaufschluss durch Schürfe, Bohrungen und Probenentnahmen, die es ermöglichen ein Baugrundmodell zu entwickeln. Während die EN 1997-2 die Planung und Auswertung behandelt, wird in der EN ISO 22475 die technische Durchführung beschrieben. Eine weitere Möglichkeit den Baugrund aufzuschließen, bilden die Sondierungen. Dazu zählen die Rammsondierungen (DP), der Standard Penetration Test (SPT), die Drucksondierung (CPT), der Flügelscherversuch (FVT) sowie die Gewichtssondierungen (WST) und aus Bohrlochaufweitungsversuchen können die Verformungseigenschaften abgeleitet werden. Zur Bestimmung der Dichte von nichtbindigen Lockergesteinen sind ebenfalls Felduntersuchungen erforderlich und geophysikalische Verfahren vervollständigen die Baugrundkenntnisse zwischen den Aufschlüssen und Sondierungen. Abgerundet wird das Kapitel durch ein Verzeichnis der wichtigsten Veröffentlichungen.
CPT and SPT field data from the Mediterranean Region comprising onshore and offshore sands, silts, clays and organic soils were analyzed and cross-correlated for the purpose of this research. Laboratory tests on retrieved samples were utilized to aid the evaluation of the applicability of CPT as a site investigation tool. Identification of soil types was carried out using different empirical diagrams and compared with laboratory classification. The applicability of existing empirical CPT-SPT correlations was examined and a site-specific correlation was proposed. The results show that the available empirical charts work well for the majority of soils. Nonetheless, a refinement is required for the transition zones. Robust correlations between the cone resistance of CPT and the N-value of SPT are still missing and available approximations should be applied with caution.
An updated CPT soil classification chart is presented based on a new cone penetrometer resistance normalization techniques
In Tanzania, standard penetration test (SPT) is the most commonly used in situ test for foundation design site investigations. In an effort to increase the amount of geotechnical information at low cost, the quicker and much cheaper dynamic probing of light (DPL) hammer is sometimes performed along with SPT to supplement the expensive SPT. Nevertheless, the information gathered with DPL has been applicable only for site stratification. Recently, the static cone penetration test (CPT) has also been introduced in the country with a view to combining these methods in site investigations. In this study, side by side testing was performed with the three in situ methods and correlations established through regression analysis and arithmetic mean methods. Results indicate that DPL data correlate better with CPT than SPT data, with lower magnitudes of transformation uncertainty. The local SPT-CPT correlations compare fairly well to those in the literature. The established correlations extend the function of DPL data to analysis and design.
Hungarian experience about the correlation of CPT and DPH results is summarized. A historical review of CPT-DPH and CPT-SPT correlations is presented, and the reliability of the published CPT-DPH correlations is analyzed using recent data from Hungarian geotechnical practice. Based on these data the paper defines soil types where reliable correlation exists and proposes formulas describing the relationships between the CPT and DPH results, because in the case of hard state clays and soils containing gravel an acceptable relationship cannot be stated.
The paper summarises the experience gained by the writers in the interpretation of the cone penetration test (CPT) and flat dilatometer test (DMT) for the assessment of the geotechnical properties of sands. In the first part of the paper, the problem of determining the relative density (DR) as function of the penetration test results and ambient stress (σ'), for silica sands, is dealt with. In the second part of the paper, the assessment of the peak angle of shearing resistance (φ'p) is dealt with. The attention is given to the use of the Bolton's (1986) strength-dilatancy theory in order to estimate φ'p. Engineering correlations, based on Bolton's (1986) work, are proposed allowing estimation of φ'p as function of penetration resistance and σ', taking into account the compressibility and the curvilinear shear strength envelope.
Following disastrous earthquakes in Alaska and in Niigata, Japan in 1964, Professors H. B. Seed and I. M. Idriss developed and published a methodology termed the "simplified procedure" for evaluating liquefaction resistance of soils. This procedure has become a standard of practice throughout North America and much of the world. The methodology which is largely empirical, has evolved over years, primarily through summary papers by H. B. Seed and his colleagues. No general review or update of the procedure has occurred, however, since 1985, the time of the last major paper by Professor Seed and a report from a National Research Council workshop on liquefaction of soils. In 1996 a workshop sponsored by the National Center for Earthquake Engineering Research (NCEER) was convened by Professors T. L. Youd and I. M. Idriss with 20 experts to review developments over the previous 10 years. The purpose was to gain consensus on updates and augmentations to the simplified procedure. The following topics were reviewed and recommendations developed: (1) criteria based on standard penetration tests; (2) criteria based on cone penetration tests; (3) criteria based on shear-wave velocity measurements; (4) use of the Becker penetration test for gravelly soil; (4) magnitude scaling factors; (5) correction factors for overburden pressures and sloping ground; and (6) input values for earthquake magnitude and peak acceleration. Probabilistic and seismic energy analyses were reviewed but no recommendations were formulated.
In situ ground freezing with liquid nitrogen can be an excellent technique for obtaining high quality undisturbed samples from a wide range of loose sand deposits, with their in situ conditions preserved. This paper describes the techniques used during the CANLEX project to carry out in situ ground freezing and undisturbed sampling of the loose sand deposits encountered at six test sites. Specific details, with respect to the effects of difficult subsoil or ground-water conditions encountered at the sites, are provided. Modifications made to the ground freezing and sampling system to accommodate difficult ground conditions are described. The actual advance of the freezing front and the consumption of liquid nitrogen are compared with theoretical predictions. The dry coring technique utilized to recover undisturbed frozen sand samples is described. The void ratios measured for the frozen core samples are compared with void ratio measurements obtained using geophysical logging in boreholes located within a 5-m radius of the freeze pipe. The costs associated with in situ ground freezing utilizing liquid nitrogen and coring of the frozen sand at six test sites are presented.
Following disastrous earthquakes in Alaska and in Niigata, Japan in 1964, Professors H. B. Seed and I. M. Idriss developed and published a methodology termed the ''simplified procedure'' for evaluating liquefaction resistance of soils. This procedure has become a standard of practice throughout North America and much of the world. The methodology which is largely empirical, has evolved over years, primarily through summary papers by H. B. Seed and his colleagues. No general review or update of the procedure has occurred, however, since 1985, the time of the last major paper by Professor Seed and a report from a National Research Council workshop on liquefaction of soils. In 1996 a workshop sponsored by the National Center for Earthquake Engineering Research (NCEER) was convened by Professors T. L. Youd and I. M. Idriss with 20 experts to review developments over the previous 10 years. The purpose was to gain consensus on updates and augmen- tations to the simplified procedure. The following topics were reviewed and recommendations developed: (1) criteria based on standard penetration tests; (2) criteria based on cone penetration tests; (3) criteria based on shear-wave velocity measurements; (4) use of the Becker penetration test for gravelly soil; (4) magnitude scaling factors; (5) correction factors for overburden pressures and sloping ground; and (6) input values for earthquake magnitude and peak acceleration. Probabilistic and seismic energy analyses were reviewed but no recommen- dations were formulated. a
During routine site investigations, high-quality sampling and laboratory testing of sands are not feasible because of inevitable sample disturbance effects and budgetary constraints. Herein, a select database is compiled for calibration of cone penetration test (CPT) interpretative methods, primarily from undisturbed frozen sand samples at 15 sites in Japan, Canada, Italy, Norway, and China. The database is used to evaluate the peak secant friction angle in terms of the normalized cone tip resistance using two analytical approaches: (i) spherical cavity expansion theory with an operational rigidity index , and (ii) a limit plasticity formulation with appropriate angle of plastification . Backfigured values of and are found correlated to the normalized small-strain stiffness . Thus, with measurements taken of both the initial shear modulus and shear strength, seismic cone tests offer the opportunity to derive the entire stress–strain–strength response of sands at all depths.
This manual focuses on the needs of engineers involved in the geotechnical design of foundations for transmission line structures. It also will serve as a useful reference for other geotechnical problems. In all foundation design, it is necessary to know the pertinent parameters controlling the soil behavior. When it is not feasible to measure the necessary soil parameters directly, estimates will have to be made from other available data, such as the results of laboratory index tests and in-situ tests. Numerous correlations between these types of tests and the necessary soil parameters exist in the literature, but they have not been synthesized previously into readily form in a collective work. This manual summarizes the most pertinent of these available correlations for estimating soil parameters. In many cases, the existing correlations have been updated with new data, and new correlations have been developed where sufficient data have been available. For each soil parameter, representative correlations commonly are presented in chronological order to illustrate the evolutionary development of the particular correlation. The emphasis is on relatively common laboratory and in-situ tests and correlations, including those tests that are seeing increased use in practice.
Effective overburden stress can have a significant influence on cone penetration test CPT measurements. This influence can lead to an incorrect assessment of soil strength/resistance for such purposes as liquefaction triggering analysis. For an accurate measure-ment of tip and sleeve resistance, unbiased by overburden stress, it is essential to normalize these index measurements appropriately. Presented herein is a comprehensive study reviewing all aspects of CPT normalization. A result of this study is a variable normalization procedure for the CPT that is based on both empirical results and theoretical analysis. This paper presents these results in the form of an improved normalization scheme and discusses its application in practice.
The Standard Penetration Test (SPT) is critically examined with respect to its ability to estimate relative density in situ. SPT's were performed using field drilling equipment at three overburden pressures on 4-ft (1.22-m) diam by 6-ft (1.83-m) high test specimens constructed using Platte River and Standard Concrete sands at three relative densities. The results are presented as a family of curves correlating relative density with SPT N values for the three testing pressures. This research was an extension of a previous SPT test series on Reid-Bedford Model and Ottawa sands. The results of testing the four sands were compared and a statistical analysis produced an empirical equation relating relative density to effective overburden pressure, N value, and coefficient of uniformity. Comparisons are also made between this work and the previous work of Gibbs and Holtz at the Bureau of Reclamation and Bazaraa at the University of Illinois.
The Standard Penetration Test (STP) is critically examined with respect to its ability to estimate relative density in situ. Twenty-six test specimens, 4-ft in diameter by 6-ft high, were constructed using Reid Bedford Model sand and Ottawa sand. Using field drilling equipment, the SPT was performed at three overburden pressures on test specimens built to various densities. The results are presented as a family of curves correlating relative density with the SPT N-values at the testing pressures. It is concluded that the SPT is fairly repeatable in homogeneous deposits; however, variations in density, structure, or lateral stress within the test medium will produce widely scattered N-values. Thus, estimates of in-situ relative densities from N-values should be considered gross values or trends and should not be interpreted as accurate determinations for any specific case.
Das Kapitel behandelt die Baugrunduntersuchungen, die im Rahmen der Vorerkundung eines Bauprojekts ausgeführt werden. Grundlage für das Vorgehen bildet die europäische Norm EN 1997 Teil 2. Die Untersuchungen stützen sich auf den Baugrundaufschluss durch Schürfe, Bohrungen und Probenentnahmen, die es ermöglichen ein Baugrundmodell zu entwickeln. Während die EN 1997-2 die Planung und Auswertung behandelt, wird in der EN ISO 22475 die technische Durchführung beschrieben. Eine weitere Möglichkeit den Baugrund aufzuschließen, bilden die Sondierungen. Dazu zählen die Rammsondierungen (DP), der Standard Penetration Test (SPT), die Drucksondierung (CPT), der Flügelscherversuch (FVT) sowie die Gewichtssondierungen (WST) und aus Bohrlochaufweitungsversuchen können die Verformungseigenschaften abgeleitet werden. Zur Bestimmung der Dichte von nichtbindigen Lockergesteinen sind ebenfalls Felduntersuchungen erforderlich und geophysikalische Verfahren vervollständigen die Baugrundkenntnisse zwischen den Aufschlüssen und Sondierungen. Abgerundet wird das Kapitel durch ein Verzeichnis der wichtigsten Veröffentlichungen.
For more than 30 years, there has been considerable interest in using CPT also to evaluate the liquefaction resistance of soils. Unfortunately, most of the simplified methods used for liquefaction resistance evaluation only require in situ measurements from electrical cone penetrometers even if they are frequently applied using measurements from mechanical CPTs that are still preferred by current engineering practice in many countries. Erroneous estimates of liquefaction resistance and relevant non-conservative results are obtained by applying electrical CPT-based methods to mechanical CPT data without any form of correction. This study focuses on the developing of an appropriate procedure for correcting mechanical CPT data and provides modified equations for liquefaction resistance estimation by means of electrical CPT-based simplified methods. A dataset of more than 3900 pairs of measurements of cone tip resistance and sleeve friction were obtained from 44 sites selected in Northern and Central Italy and processed by means of statistical analyses. Suitable adjustments to CPT mechanical data were proposed for determining corrected liquefaction potential.
The Standard Penetration Test (SPT) is critically examined with respect to its ability to estimate relative density in situ. SPT's were performed using field drilling equipment at three overburden pressures on 4-ft (1. 22-m) diam by 6-ft (1. 83-m) high test specimens constructed using Platte River and Standard Concrete sands at three relative densities. The results are presented as a family of curves correlating relative density with SPT N values for the three testing pressures. This research was an extension of a previous SPT test series on Reid-Bedford Model and Ottawa sands. The results of testing the four sands were compared and a statistical analysis produced an empirical equation relating relative density to effective overburden pressure, N value, and coefficient of uniformity. Comparisons are also made between this work and the previous work of Gibbs and Holtz at the Bureau of Reclamation and Bazaraa at the University of Illinois.
Granted that good site control is exercised in carrying out the standard penetration test the energy delivered to the sampler, and therefore the blow count obtained in any given sand deposit at a particular effective overburden pressure, can still vary to a significant extent depending on the method of releasing the hammer, on the type of anvil and on the length of rods (if less than 10 m). For consistency it is essential to correct the observed blow count N to the value which would have been measured using a specified rod energy. A recommended value, which should be recognized internation- ally, is 60% of the free-fall energy of the standard hammer weight and drop. The corrected blow count is then designated as N60 and the normalized value (N1)60 at unit effective pressure (1 kg/cm2 or 100 kPa) may be regarded as a basic characteristic of the sand. Factors controlling the rod energy ratio are examined in detail and methods of deriving N60 values are developed. An examination of selected field and laborat...
It has been known that the penetration resistance depends on the grain size of soils, and that fines-containing sands have smaller SPT N-values than clean sands. Previous investigations on the link between the penetration resistance and relative density have indicated that the ratio between the normalized N-value and the square of the relative density, N1/D2r, is dependent on the grain size of sands. While this dependence has not been properly quantified, it has been customary to utilize the well-known expression of Meyerhof with N1/D2r being fixed at 41. In this paper, an attempt was made to correlate the penetration resistance and relative density by accounting for the grain size properties of soils. The void ratio range (emax-emin) was used as a measure indicative of the grain size and grain size composition. It was found that N1/D2r is highly dependent on the value of (emax-emin) and that this ratio gradually decreases with increasing void ratio range from a value of about 100 for gravels to a value of about 10 for silty sands. This dependence is mathematically formulated and used to establish an empirical correlation between the SPT N-value and Dr that is applicable to various kinds of soils ranging from silty sands to gravels. The correlation is developed by using data of high-quality undisturbed samples and results of SPT measurements on natural deposits of sandy soils and gravels.
A critical review of field performance of sandy soil deposits during past earthquakes is conducted with special emphasis being placed on Standard Penetration Test N-values and fines content. The field relationship between adjusted dynamic shear stress ratio and normalized SPT N-values together with laboratory tests on undisturbed sands indicate that (1) sands containing more than 10 percent fines has much greater resistance to liquefaction than clean sands having the same SPT N-values, (2) extensive damage would not occur for clean sands with SPT N1-values (N-values normalized for effective overburden stress of 1 kgf/cm²) greater than 25, silty sands containing more than 10 percent fines with SPT N1-values greater than 20, or sandy silts with more than 20 percent clay, and (3) sands containing gravel particles seem to have less resistance to liquefaction than clean sands without gravel having the same SPT N-values.
On the basis of the above findings, an improved empirical chart separating liquefiable and non-liquefiable conditions is presented in terms of dynamic shear stress ratio, SPT N-values, fines content, and shear strain amplitude.
The applicability of three previous empirical correlations proposed for estimating relative density of sandy soils based on the SPT N-value, effective overburden stress and soil gradation characteristics was investigated in the present study by using a data base of relative density obtained from high quality undisturbed samples of fine to medium sand with F-c <= 20%, D-50 <= 1.0 mm and D-max <= 4.75 mm. All undisturbed samples were recovered by in-situ freezing method. The relative density estimated by Meyerhof's method (1957) was in the range of + 15 % similar to - 45 % of the measured values. Meyerhof's method (1957) was modified by Tokimatsu and Yoshimi (1983) by considering the effect of fines content on the SPT N-value. The relative density estimated by Tokimatsu and Yoshimi's method (1983) is in the range of + 25 % - - 20% of the measured values. The underestimation of relative density of Meyerhof's method (1957) was modified. On the contrary, the overestimation of relative density is more significant than Meyerhof's method. The relative density estimated by the method proposed by Kokusho et al. (1983) is in the range of + 20% to - 35% of the measured values even for dense sand with a relative density larger than 60%. Meyerhof's method (1957) and the method proposed by Kokusho et al. (1983) have a common disadvantage that they will extremely underestimate the relative density of fine to medium sand for SPT N-value lower than about 8. The errors in estimation of relative density by these methods are large. A simple empirical correlation (Eq. (10)) was proposed in the present study to estimate the relative density of fine to medium sand based on the normalized SPT N-value, N-1. The relative density estimated by the proposed method is in the range of + 15% to - 30% of the measured values for N-1 in the range between 0 and 50. As a whole, the proposed method is less in errors for estimating relative density compared with those estimated by Meyerhof's method (1957) and the method proposed by Kokusho et al. (1983). Based on a data base of undisturbed samples with data of fines content obtained from the SPT spoon samples, the method proposed by the authors is again compared with the three previous methods. The relative density estimated by the proposed method based on the above data base is in the range of + 15% to - 10% of the measured values. Among four methods, as a whole, the proposed method shows the least errors in estimation of relative density. The proposed method was also modified (Eq. (16)) by taking into account of the effect of fines content of SPT samples. The relative density estimated by the modified method based on the fines content is almost in the range of + 10% to - 10% of the measured values. Two empirical correlations proposed in the present study are less in errors of estimating, relative density compared with three previous methods. The range of relative density estimated by the proposed method is well consistent with the range of the measured values (40% to 90%). The empirical correlations proposed in the present study should be applied to fine to medium sand with F-c <= 20%, D-50 <= 1.0 mm and D-max <= 4.75 mm.
Several formulae and charts have been published for correcting the results of the standard penetration test (SPT) performed in sands for the effects of overburden pressure. However, depending on which published correction factor is used, very different interpretations may result. This paper attempts to clarify and resolve some of these differences, and proposes a simple correction factor as a tentative standard, contingent on data from future research.
Characteristics of the maximum and minimum void ratios of sands and their possible use for material characterization have been investigated in this study. Data of over 300 natural sandy soils including clean sands, sands with fines and sands containing small amount of clay-size particles have been used to examine the influence of fines, grain-size composition and particle shape on emax, emin and void ratio range (emax - emin). A set of empirical correlations are presented which clearly demonstrate the link between these void ratios and material properties of sands. The key advantage of (emax - emin) over-conventional material parameters such as Fc and D50 is that (emax - emin) is indicative of the overall grain-size composition and particle characteristics of a given sand and that it shows off the combined influence of relevant material factors. The void ratio range provides a general basis for comparative evaluation of material properties over the entire range of cohesionless soils.
Important issues related to the laboratory procedures used for determination of emax and emin as well as their applicability to fines-containing sands are also addressed. Three distinct linear correlations were found to exist between emax and emin for clean sands, sands with 5-15% fines and sands with 15-30% fines respectively, thus illustrating that the standard JGS procedures for minimum and maximum densities of sands can provide reasonably consistent emax and emin values for sands with fines content of up to 30%. The importance of the grain-size distribution and presence of gaps in the grading of composite soils or mixtures of sands with fines produced in the laboratory is also discussed.
The purposes of in situ testing are set out, and the difficulties of the interpretation of the observations are emphasized. These difficulties are due to the complex behavior of soils together with the lack of control and of choice of the boundary conditions in any field test. One notable exception is the pressuremeter test, from which soil properties can be derived directly without recourse to empirical correlations. The discussion is concentrated on the measurement of undrained shear strength. The results obtained from different tests (triaxial, plane strain, direct simple shear, pressuremeter and vane) are compared by expressing them in terms of the undrained strength ratio S//u/ sigma //v//0 prime as a function of the friction angle phi . Special attention is paid to tests in which the principal axes of stress and of strain increment are free to rotate. Refs.
Granted that good site control is exercised in carrying out the standard penetration test the energy delivered to the sampler, and therefore the blow count obtained in any given sand deposit at a particular effective overburden pressure, can still vary to a significant extent depending on the method of releasing the hammer, on the type of anvil and on the length of rods (if less than 10 m). For consistency it is essential to correct the observed blow count N to the value which would have been measured using a specified rod energy. A recommended value, which should be recognized internation- ally, is 60% of the free-fall energy of the standard hammer weight and drop. The corrected blow count is then designated as N 60 and the normalized value (N 1 ) 60 at unit effective pressure (1 kg/cm ² or 100 kPa) may be regarded as a basic characteristic of the sand. Factors controlling the rod energy ratio are examined in detail and methods of deriving N 60 values are developed. An examination of selected field and laboratory data shows that the relation between blow count, effective overburden pressure σν′ (kg/cm ² ) and relative density D r is given to a close approximation by an equation of the form proposed by Meyerhof: N 60 = (a + bσν′)D r ² or (N 1 60 = (a + b)D r ² where a and b are constants for a particular sand within the range 0·35 < D r < 0·85 and 0·5 kg/cm ² < σν′ < 2·5 kg/cm ² .‖ The parameters a and b, values for which are given for all the cases studied, tend to increase with increasing grain size, with increasing age of the deposit and with increasing over-consolidation ratio. The long-standing apparent discrepancy between field and laboratory tests is resolved when the effects of differing rod energy ratios and of ‘ageing’ are taken into account. Also, the Terzaghi-Peck limits of blow count for various grades of relative density, as enumerated by Gibbs and Holtz, are shown to be good average values for normally consolidated natural sand deposits, provided that the blow counts are corrected to (N 1 ) 60 values.
Pourvu que le chantier soit bien controle lors de ‘standard penetration test’ l'energie transmise à l'appareil de prise de chantillon et done le nombre de coups donnés dans un dépôt de sable à une pression effective de terrain de couverture spécifique peuvent encore varier de facon importante selon la méthode de déclanchement du marteau, le type d'enclume et la longueur des tiges (si moins de 10 m). Pour être correct il est essentiel de corriger le nombre de coups observe N pour obtenir la valeur qui aurait été mesurée si une énergie de tige spécifique avait été employée. Une valeur recommandée, qui devrait étre acceptée sur le plan international, est 60% de l* énergie de chute libre du poids normal du marteau. On appelle alors le nombre de coups corrigé N 60 et on peut considérer la valeur normalisée (N 1 ) 60 à la pression effective spécifique (1 kg/cm ² ou 100 kPa) comme une caractéristique fondamentale du sable. L'article examine de facon détaillée les facteurs qui contrôlent le rapport de l'énergie de la tige et preśente des méthodes pour calculer des valeurs N 60 . Des données sélectionnées obtenues in situ et en laboratoire indiquent que le rapport entre le nombre de coups, la pression effective du terrain de couverture σν′ (kg/cm ² ) et la densité relative D r est doneé à peu près par une équation de la forme proposée par équation de la, forme proposée par Meyerhof: N 60 = (a + bσ‘ν′) D r ² où a et b sont des constantes pour un sable spécifique dans l'intervalle 0·35 < D r < 0·85 et 0·5 kg/cm ² < σν′ < 2·5 kg/cm ² . Les paramètres a et b, dont les valeurs sont données pour tous les cas étudiés, tendent à s'accroître au fur et à mesure que le diamétre des grains, l'âge du depot et le rapport de surconsolidation augmentent. Le désaccord apparent trouvé depuis longtemps entre les essais in situ et en laboratoire disparait lorsqu'on tient compte des effets des rapports differents de l'énergie de la tige et du ‘vieillissement’. On démontre aussi que les limites du nombre de coups donnees par Terzaghi et Peck pour differentes fourchettes de densités relatives, comme mentionnées par Gibbs et Holtz, représentent de bonnes valeurs moyennes pour des dépôts naturels de sable normalement consolides, à condition que les nombres de coups soient corrigés pour obtenir les valeurs (N 1 ) 60 .
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