Soil mechanics surface sampler experiment for Surveyor

The arrangement of an apparatus designed to measure the mechanical properties of the lunar surface from the Surveyor spacecraft is described. The experiments that may be made with this device are discussed and examples are given

The calculation of horizontal accelerations from seismoscope records

The seismoscope is a simple instrument designed originally to give a largely qualitative indication of the strong ground motions produced by an earthquake. It consists of a smoked watch glass attached to a two-degree-of-freedom pendulum with a period of Formula sec and damping about 10 per cent of critical; a pen records the pendulum motions on the watch glass. One point on the displacement spectrum of the recorded ground motion at this period and damping is obtained from the measurement of the maximum pendulum excursion. An examination of the seismoscope record obtained on the east abutment of the failed Lower San Fernando dam during the 1971 San Fernando earthquake showed a high-frequency vibration superimposed on the general oscillations. It did not seem likely that this was solely an earthquake vibration component, and shaking table tests of seismoscopes revealed the presence of a seismoscope vibration mode at frequencies of 15 to 18 Hz depending on the instrument. The oscillations due to this mode on the abutment seismocope record have, therefore, been used as timing marks, to enable the seismoscope equation to be solved for the input acceleration components. The results of the calculations are presented along with analyses of the seismoscope response to indicate the range of applicability. One other record, obtained on a seismoscope alongside a strong-motion accelerograph, was also analyzed for comparison with the recorded accelerations, to demonstrate the validity of the technique. The timing vibration appears on a number of seismoscope records

The density of the lunar surface soil

Until the landing of the Surveyor 1 spacecraft on the moon, it had been inferred from earth-based optical, thermal, radio, and radar observations that the surface f the moon consisted of material of low-bulk density (less than 1 g/cm^3) and high porosity. Recently, a change in this belief, at least with respect to the optical data, has occurred, although a low density continues to be postulated on the basis of radiometric data

An Ultraviolet-Excess Optical Candidate for the Luminous Globular Cluster X-ray Source in NGC1851

The intense, bursting X-ray source in the globular cluster NGC 1851 was one of the first cluster sources discovered, but has remained optically unidentified for 25 years. We report here on results from Hubble Space Telescope WFPC2 multicolor images in NGC 1851. Our high spatial resolution images resolve ~200 objects in the 3'' radius Einstein X-ray error circle, 40 times as many as in previous ground-based work. A color-magnitude diagram of the cluster clearly reveals a markedly UV-excess object with B~21, (U-B) ~ -0.9 only 2'' from the X-ray position. The UV-excess candidate is 0.12'' distant from a second, unremarkable star that is 0.5 mag brighter in B; thus ground-based studies of this field are probably impractical. Three other UV-excess objects are also present among the ~16,000 objects in the surveyed region of the cluster, leaving a ~5% probability that a UV-excess object has fallen in the X-ray error circle by chance. No variability of the candidate is seen in these data, although a more complete study is required. If this object is in fact the counterpart of the X-ray source, previous inferences that some globular cluster X-ray sources are optically subluminous with respect to low-mass X-ray binaries in the field are now strengthened.Comment: 13 pages including 1 table and 3 figures in AASTeX 4.0; To appear in The Astrophysical Journal Letters, volume 472 (1996 December 1). Preprint with full-resolution figures available at http://www.astro.washington.edu/deutsch/pubs/pubs.htm

Centrifuge modeling of earthquakes

The major problem in scale modeling of crustal tectonic processes, namely, the requirement for a brittle modeling material of extremely low strength (∼0.1 bar) can be overcome by doing model tests under artificial gravity in a centrifuge. When conditions of dynamic similarity are observed, scale modeling, because of its controlled nature, can be an important tool supplementing field investigation, theoretical study, and numerical simulation of crustal tectonic processes. Fracture events by simulated tectonic stress loading in a model thrust fault (model dimensions: 20 cm depth × 25 cm × 27 cm) have been generated when the model is subject to 50 g in a centrifuge of 1.53 m radius. Measurements obtained are: the total loading force, the stress change at one location inside the fault zone, and model seismic signals recorded on the model top surface. With use of a scaled brittle model material, the model scales up to a prototype approximately 2.2 km depth × 2.8 km × 3.0 km in dimensions

Axially-loaded centrifuge pile tests

This report concerns investigations of the behavior of piles under axial loading using centrifugal modeling and t-z analysis. The results of five centrifuge model pile tests on instrumented piles are presented. The present chapter puts this work into perspective, both with relation to current practical concerns with pile performance and existing analytical techniques

A New Soil Testing Apparatus

Green (1967) has effectively stated the case regarding certain serious deficiencies of the Authors' new soil test box. Ko and Scott mention that small volumes of the sample at the corners and along the edges of the box may not be in a homogeneous stress state but did not consider this to be important. This would appear to represent simply an error in judgement. The Writer agrees with Green (1967) that the soil cube was appreciably restrained by the relatively stiff stainless steel spacing frame. The Authors offer insufficient evidence to support the conclusion that the stress state generated in the sample contained within the new soil test box was found to be uniform or the opinion that the present equipment measures the true deformational behaviour of the soil tested. The opinions of Green (1967) and those of the Writer can easily be verified analytically or through the performance of simple experiments. The following brief and approximate analysis based on the theory of elasticity analytically demonstrates the possible importance of edge restraint for a particular stress path and a cylindrical specimen. Fig. 1 (a) represents a free cylinder with homogeneous triaxial compression while Fig. l (b) represents the same cylinder subjected to identical vertical loads but laterally fixed at four vertical edges

Fault motions at the Baldwin Hills Reservoir site

A distinction is made between the damaging potential of rapid fault motions associated with earthquakes and those having a relatively slow creep type motion. Information is given on nonseismic movements that have been occurring on faults passing through the Baldwin Hills Reservoir during the past 10 years. The relationship between those faults and the Inglewood fault system is described, and correlations are presented with local elevation changes, horizontal ground movements, and seismic activity. Comparisons are made with similar slow fault motions occurring at other places in California, and attention is drawn to the potential damaging effects of such movements

Analysis of wedge penetration in clay

A variety of devices designed to penetrate soil is used in soil engineering practice to measure soil properties or to emplace instrumentation, although the mechanics of the steady state penetration process is not well understood. Consequently the two-dimensional problem of steady state wedge penetration is examined. Solutions are obtained for wedge penetration in an ideal rigid plastic medium representing a clay. It is found that the solution requires the presence of a cavity behind the wedge, and the geometry of this cavity is established. A lower limit of the soil/wedge friction coefficient is derived, above which the wedge is considered rough. The force required to push the wedge is calculated as a function of wedge point angle and is shown to reach a minimum for a rough wedge at a point angle of about 67°. For axisymmetric penetration some finite element solutions were obtained and show that cone and wedge penetration mechanisms are similar. The mechanism and patterns of flow movement past the wedge for different point angles are demonstrated. Practical implication of the results and their extension to axisymmetric cone penetration are discussed