Determination of Pile Driveability and Capacity From Penetration Tests, Volume I: Final Report

DTFH61-93-C-00047Research has been conducted on the potential improvement of dynamic wave equation analysis methodology using in-situ soil testing techniques. As a basis for this investigation, the literature was reviewed and a summary was compiled of efforts made to date on the development of models and associated parameters for pile driving analysis. Furthermore a data base was developed containing more than 150 cases of test piles with static load tests, dynamic restrike tests, soil information, driving system data and installation records. One hundred data base cases were subjected to correlation studies using both wave equation and CAPWAP. This work yielded dynamic soil model parameters which did not indicate a specific relationship with soil grain size. The in-situ soil testing device utilized was a Modified SPT which yielded data from both static and dynamic measurements. Either static uplift or torque tests yielded static ultimate shaft resistance, and uplift tests also indicated a shaft resistance quake. Static compressive tests on a special tip indicated ultimate end bearing and associated toe quake. Indirectly, by signal matching, soil damping parameters were calculated. These quantities were then used for the prediction of full-scale pile behavior. Data from the Modified SPT were gathered and analyzed on six sites with previous full-scale static pile tests and on three sites where static load tests were to be performed at a later date. Recommendations derived from these tests pertain to the current soil model and to proposals for future changes. In general, the current approach was found to yield, on the average, very reasonable results for end of installation situations. For restrike tests, standard parameters may be misleading. Any necessary modifications to the current approach, for example, the use of particularly large toe quakes or low toe damping factors, should be based on Modified SPT measurements. Differences between prediction and full-scale pile field behavior were attributed to soil strength changes over relatively small distances which cannot be detected with standard SPT spacings of 5 ft (1.5 m)

Determination of Pile Driveability and Capacity from Penetration Tests, Volume III: Literature Review, Data Base and Appendixes

DTFH61-93-C-00047Research has been conducted on the potential improvement of dynamic wave equation analysis methodology using in-situ soil testing techniques. As a basis for this investigation, the literature was reviewed and a summary was compiled of efforts made to date on the development of models and associated parameters for pile driving analysis. Furthermore a data base was developed containing more than 150 cases of test piles with static load tests, dynamic restrike tests, soil information, driving system data and installation records. One hundred data base cases were subjected to correlation studies using both wave equation and CAPWAP. This work yielded dynamic soil model parameters which did not indicate a specific relationship with soil grain size. The in-situ soil testing device utilized was a Modified SPT which yielded data from both static and dynamic measurements. Either static uplift or torque tests yielded static ultimate shaft resistance, and uplift tests also indicated a shaft resistance quake. Static compressive tests on a special tip indicated ultimate end bearing and associated toe quake. Indirectly, by signal matching, soil damping parameters were calculated. These quantities were then used for the prediction of full-scale pile behavior. Data from the Modified SPT were gathered and analyzed on six sites with previous full-scale static pile tests and on three sites where static load tests were to be performed at a later date. Recommendations derived from these tests pertain to the current soil model and to proposals for future changes. In general, the current approach was found to yield, on the average, very reasonable results for end of installation situations. For restrike tests, standard parameters may be misleading. Any necessary modifications to the current approach, for example, the use of particularly large toe quakes or low toe damping factors, should be based on Modified SPT measurements. Differences between prediction and full-scale pile field behavior were attributed to soil strength changes over relatively small distances which cannot be detected with standard SPT spacings of 5 ft (1.5 m)

Determination of Pile Driveability and Capacity From Penetration Tests, Volume II: Appendixes

DTFH61-93-C-00047Research has been conducted on the potential improvement of dynamic wave equation analysis methodology using in-situ soil testing techniques. As a basis for this investigation, the literature was reviewed and a summary was compiled of efforts made to date on the development of models and associated parameters for pile driving analysis. Furthermore a data base was developed containing more than 150 cases of test piles with static load tests, dynamic restrike tests, soil information, driving system data and installation records. One hundred data base cases were subjected to correlation studies using both wave equation and CAPWAP. This work yielded dynamic soil model parameters which did not indicate a specific relationship with soil grain size. The in-situ soil testing device utilized was a Modified SPT which yielded data from both static and dynamic measurements. Either static uplift or torque tests yielded static ultimate shaft resistance, and uplift tests also indicated a shaft resistance quake. Static compressive tests on a special tip indicated ultimate end bearing and associated toe quake. Indirectly, by signal matching, soil damping parameters were calculated. These quantities were then used for the prediction of full-scale pile behavior. Data from the Modified SPT were gathered and analyzed on six sites with previous full-scale static pile tests and on three sites where static load tests were to be performed at a later date. Recommendations derived from these tests pertain to the current soil model and to proposals for future changes. In general, the current approach was found to yield, on the average, very reasonable results for end of installation situations. For restrike tests, standard parameters may be misleading. Any necessary modifications to the current approach, for example, the use of particularly large toe quakes or low toe damping factors, should be based on Modified SPT measurements. Differences between prediction and full-scale pile field behavior were attributed to soil strength changes over relatively small distances which cannot be detected with standard SPT spacings of 5 ft (1.5 m)

Formation of suprathermal electron distributions in the quiet solar corona

Context.Solar wind electron velocity distribution functions (VDFs) show enhanced levels of suprathermal electrons as compared to a Maxwellian distribution. Previous studies show that the suprathermal tails of solar wind VDFs can be fitted by kappa distributions, and that a coronal origin of the suprathermal electrons is possible. Aims.The generation of suprathermal electrons by resonant interaction with whistler waves in the corona is investigated under quiet solar conditions without any flare activity. The magnetic field geometry is that of a closed magnetic loop. The electron-whistler interaction is described within the framework of quasilinear theory, that leads to pitch-angle diffusion of the electrons in the reference frame of the waves. Methods.A study of electron VDFs requires a kinetic description of the electrons. The model used in this paper is based on a numerical solution of the Boltzmann-Vlasov equation for the electrons, considering Coulomb collisions and wave-electron interaction. The waves are assumed to enter the simulation box with a given power-law spectrum, which evolves inside the box due to wave propagation and absorption by the electrons. Starting from a nearly Maxwellian initial electron VDF, the temporal evolution of the VDF is calculated until a final steady state has been reached. Results.The results show that a population of suprathermal electrons develops in a closed coronal loop. The electron VDF can be approximated by a power-law in the energy range of 4–10 keV. The power-law index is in agreement with the solar wind observations. For lower energy, the electrons are thermalized in the dense model coronal loop, and the efficiency of the acceleration mechanism decreases for higher energies. The energy range of the simulation box has to be chosen sufficiently large, and the influence of the loop geometry on the results is also studied. Conclusions.These numerical studies show that the quiet solar corona is capable of producing suprathermal electron VDFs with similar characteristics to those observed in the solar wind. This study is focused on a closed region in the solar corona, but if such an electron population is present in the corona, it should also appear in the solar wind

Radio burst from converging separatrices

Context.In a previous paper on the X17 flare October 28, 2003, we found, among other radio flare sources, one displaced at ≈0.2 $R_\odot$ north of the flaring AR 10486, away from the main Hα and hard X-ray flare emission. The source came to our attention due to its timing, its spatial displacement from the flaring active region, and due to the behavior of the radio spectral fine structure sources which are embedded in the continuum emission. We speculated that the source is situated at a separator of coronal magnetic flux systems. Aims.Here we analyze the topology of the potential coronal magnetic field extrapolated from SOHO-MDI data near the source site of this meter-decimeter radio continuum. Methods.Using the Source Method for magnetic field modeling, and the displacement gradient of the field lines as a connectivity measure, we give a description of the critical field structure. We compare it with the Nançay Radio Heliograph source positions of the continuum which have been classified by the spectral data of Astrophysical Institute Potsdam. Results.We find that the radio source occurs near the contact of three separatrix surfaces between magnetic flux cells. There are other separatrix surfaces in the field which are not distinguished by a strong radio source during the analyzed flare. Conclusions.This is the first evidence for the occurence of a strong coronal radio burst continuum source at such coronal magnetic field structures

Fiber bursts as 3D coronal magnetic field probe in postflare loops

Fiber bursts appear in some complex solar radio bursts as a continuum fine structure in the frequency range of 150$\cdots$3000 MHz. We present and test a new method to use fiber bursts as a probe of the magnetic field strength and the 3D field structure in postflare loops. Thereby we assume that fiber bursts are driven by whistler waves ascending in the postflare loops which act as magnetic traps for nonthermal flare electrons. For a selected event (1997 April 07) we derive from dynamic radio spectra (Potsdam) and Nançay Radio Heliograph imaging data of fiber bursts the coronal magnetic field strength within the fiber burst source. We compare the fiber burst source positions and field strength estimates with the extrapolated potential magnetic field above the flaring active region NOAA 8027 using SOHO-MDI photospheric field data. The field strength from fiber bursts are within a factor of 0.6 to 1.4 of the field strength of the selected subset of potential field lines and give preference to a 3.5 times Newkirk (1961, ApJ, 133, 983) coronal density model within the evolving postflare loops. We find independent proof of the physical significance of considering selected potential field lines as postflare loop field information regarding topology and field strength over a time interval of one hour after the impulsive flare phase. We conclude that radio decimeter and meter wave spectra and radio imaging at two representative frequencies are sufficient for a reliable estimate of the (otherwise not measurable) coronal magnetic field strength in postflare loops. This can be an important field sounding method using the forthcoming FASR (Frequency Agile Solar Radiotelescope) instrument

The GLE on Oct. 28, 2003 – radio diagnostics of relativistic electron and proton injection

Timing discrepancies between signatures of accelerated particles at the sun and the arrival times of the particles at near-earth detectors are a matter of fundamental interest for space-weather applications. The solar injection times of various components of energetic particles were derived by Klassen et al. (2005, JGR, 110, A09S04) for the October 28, 2003, X-class/γ-ray flare in NOAA AR 10486. This flare occured in connection with a fast halo coronal mass ejection and a neutron monitor-observed ground level event (GLE). We used radio (Astrophysikalisches Institut Potsdam, \emph{WIND}, Nançay Multifrequency Radio Heliograph), Hα (Observatorium Kanzelhöhe), \emph{RHESSI}, \emph{SOHO} (EIT, LASCO, MDI), and \emph{TRACE} data to study the associated chromospheric and low coronal phenomena. We identify three source sites of accelerated particles in this event. Firstly, there is a source in projection 0.3 $R_\odot$ away from AR 10486, which is the site of the reconnection outflow termination, as revealed by a termination shock signature in the dynamic radio spectrum. Secondly, there is the extended current sheet above a giant coronal postflare loop system in the main flare phase. Thirdly, there is a source situated on a magnetic separatrix surface between several magnetic arcades and neighbouring active regions. This source is 0.2 $R_\odot$ away from AR 10486 and acts during onset and growth of high energy proton injection in space. It is not clear if this source is related to the acceleration of protons, or if it only confirms that energetic particles penetrate a multistructure magnetic loop system after being previously accelerated near the main HXR- and γ-ray sources. The result is in favour of energetic particle acceleration in the low corona (<0.5 $R_\odot$ above the photosphere) and in contrast to acceleration of the relativistic particles at remotely propagating shock waves.

A microflare with hard X-ray-correlated gyroresonance line emission at 314 MHz

Context. Small energy release events in the solar corona can give insights into the flare process which are regularly hidden in the complex morphology of larger events. For one case we find a narrowband radio signal well correlated with the hard X-ray flare. We investigate wether these signals are probes for the flare current sheet. Aims. We aim to establish the relation between narrowband and short-duration features (<1% of the observing frequency in the spectral range 250–340 MHz, and some 5 s until 2  min, respectively) in dynamic radio spectral diagrams and simultaneously occuring HXR bursts. Methods. We use dynamic radio spectra from the Astrophysical Institute Potsdam, HXR images of RHESSI, TRACE coronal and chromospheric images, SOHO-MDI high resolution magnetogram data, and its potential field extrapolation for the analysis of one small flare event in AR10465 on September 26, 2003. We point to similar effects in e.g. the X-class flare on November 03, 2003 to demonstrate that we are not dealing with a singular phenomenon. Results. We confirm the solar origin of the extremely narrowband radio emission. From RHESSI images and the magnetic field data we identify the probable site of the radio source as well as the HXR footpoint and the SXR flare loop emission. The flare loop is included in an ongoing change of magnetic connectivity as confirmed by TRACE images of hot coronal loops. The flare energy is stored in the nonpotential magnetic field substructure around the microflare site which is relaxed to a potential one. Conclusions. We conclude that the correlated HXR footpoint/narrowband radio emission, and the transition to a second energy release in HXR without associated radio emission are direct probes of changing magnetic connectivity during the flare. We suppose that the narrowband radio emission is due to gyroresonance radiation at the second harmonic of the local electron cyclotron frequency. It follows an upper limit of the magnetic field in the radio source volume of less than 50% of the mean potential field in the same height range. This supports the idea that the narrowband radio source is situated in the immediate surroundings of the flare current sheet