Vibratory Plate Research Articles

Vibratory Plate Loading of Compacted and Instrumented Field Soil Beds

Abstract Field scale studies of foundation and plate vibrations, particularly in the nonlinear domain, are vital to improving understanding and validating analytical and numerical efforts. This paper describes the development of an experimental program to investigate the dynamic signature of a rigid plate and of the soil during surface plate vibration of compacted soil beds. Nineteen testing sequences were performed on 1.2-m deep prepared soil test beds embedded with miniature triaxial accelerometers. Various vibratory loading frequencies (10–60 Hz) and amplitudes (up to 220 kPa contact stress) were applied via a 0.45-m-diameter plate to the prepared test beds. The paper describes the load testing frame, the preparation of free field partially-saturated sand test beds, and the placement of triaxial accelerometers within the soil. Plate and soil acceleration profiles are presented for the range of applied forcing frequency and amplitude levels involved. The nonlinear soil-compactor system response is analyzed and presented in both the time and frequency domains to present key features observed during testing.

Use of Dynamic Cone Penetrometer to Control Compaction of Granular Fill

Granular material is commonly used as backfill and embedment material for buried structures, including thermoplastic pipe. Proper compaction of this material is crucial to the successful performance of the pipe. However, the commonly used Proctor density approach cannot be used for the field compaction control of these materials because it does not provide a well-defined moisture-density relationship. An alternative method used by the authors for compaction control of such materials is described. This method involves a device known as the dynamic cone penetrometer (DCP). Findings are presented from a series of DCP tests conducted on a range of granular backfill materials that belong to ASTM D 2321 Classes I and II. These materials were compacted using ( a) an impact rammer and ( b) a vibratory plate compactor. The level of compaction energy was varied by changing the number of passes. The data obtained from these tests are presented in the form of DCP blow count profiles, which are then used as the basis for comparison between different materials, compaction equipment, and levels of compaction energy. A series of full-scale load tests conducted on high-density polyethylene (HDPE) pipe installations is also described. An overview is provided of how the DCP data may be combined with load-deflection data from full-scale load tests to establish guidelines for compaction control of pipe backfill.

Cement Treated Marginal Aggregates for Roads

Low-grade laterite and pit-run gravel aggregates available in abundance in eastern India may be turned into a cost-effective base for low-volume roads when ordinary portland cement, river sand, and aggregates are mixed in a 1:6:12 proportion by weight. 152 × 152 × 152 mm3 cubes were cast at several water-cement ratios and the mix was compacted by a vibratory plate compactor. The compressive strength test was determined for different water-cement ratios, and the one that gave the maximum strength was used to prepare 102 × 102 × 508 mm3 beam specimens. A number of cubes and beams were kept inside airtight polyethylene bags for accelerated curing at a temperature of 50°C. Modulus of rupture and flexural fatigue tests were carried for the evaluation of pavement design parameters. A methodology of design of a lightly cemented pavement along with an example are also presented.

Field Tests of Buried Pipe Installation Procedures

Full-scale field tests to evaluate pipe-soil interaction during backfilling were conducted on the campus of the University of Massachusetts at Amherst. The program consisted of 14 tests, with each test including concrete, plastic, and metal sections. In addition to pipe type, installation variables included in situ soil conditions, trench width, backfill material including controlled low-strength flowable material, haunching effort, and compaction methods. Test trenches were excavated under undisturbed in situ soil conditions. Eleven installations were conducted with 900-mm (inside diameter) pipe, and three installations were conducted with 1500-mm (inside diameter) pipe. Pipe and soil behavior was monitored during backfilling. Measurements included pipe shape, pipe strains, pipe-soil interface pressures, soil density, soil stresses, and soil strains. The pipes were buried to a cover depth of 1.2 m and were then excavated to inspect the pipe bedding and haunches. The results indicated significant variations in pipe behavior caused by installation practices. The rammer compactor produced greater backfill density than did the vibratory plate compactor with the same number of coverages and produced higher residual lateral soil stresses that contributed to better overall pipe performance during backfilling. The silty sand backfill tripled the peaking deflection during sidefill compaction compared with that with angular crushed rock backfill, but the former was more sensitive to deviations from good installation practice. Backfill compaction in the region from the spring line to 30 degrees below the spring line has a significant positive effect in mitigating poor bedding and haunching conditions. Pipe tests with controlled low-strength material for backfill performed very well.

Field Tests of Buried Pipe Installation Procedures

Full-scale field tests to evaluate pipe-soil interaction during backfilling were conducted on the campus of the University of Massachusetts at Amherst. The program consisted of 14 tests, with each test including concrete, plastic, and metal sections. In addition to pipe type, installation variables included in situ soil conditions, trench width, backfill material including controlled low-strength flowable material, haunching effort, and compaction methods. Test trenches were excavated under undisturbed in situ soil conditions. Eleven installations were conducted with 900-mm (inside diameter) pipe, and three installations were conducted with 1500-mm (inside diameter) pipe. Pipe and soil behavior was monitored during backfilling. Measurements included pipe shape, pipe strains, pipe-soil interface pressures, soil density, soil stresses, and soil strains. The pipes were buried to a cover depth of 1.2 m and were then excavated to inspect the pipe bedding and haunches. The results indicated significant variations in pipe behavior caused by installation practices. The rammer compactor produced greater backfill density than did the vibratory plate compactor with the same number of coverages and produced higher residual lateral soil stresses that contributed to better overall pipe performance during backfilling. The silty sand backfill tripled the peaking deflection during sidefill compaction compared with that with angular crushed rock backfill, but the former was more sensitive to deviations from good installation practice. Backfill compaction in the region from the spring line to 30 degrees below the spring line has a significant positive effect in mitigating poor bedding and haunching conditions. Pipe tests with controlled low-strength material for backfill performed very well.

Evaluation of vibratory plate compactors : Proc 4th Australia-New Zealand conference on geomechanics, Perth, Western Australia, 14–18 May 1984 V2, P450–455. Publ Barton: Inst of engineers, 1984

A study has been undertaken to obtain quantitative data on the energy outputs from vibratory plate compactors. Data have been obtained for four compactors of various sizes operating on a thick layer of Perth sand of medium density. It has been shown that the peak particle velocity measured near the surface is highly dependent upon the operating frequency of the machine and decays approximately in proportion to the inverse of the distance from the source. The transmitted vibration has been compared in terms of human and structural response with limits found in the literature. (Author/TRRL)

On the dynamics of homogeneous, isotropic, electrically conductive elastic bodies subjected to a magnetic field. Case of vibratory plates

With reference to previous own works, the author deals more fully with the vibratory motion of a homogeneous, isotropic perfectly electric conductive elastic body, subjected to a uniform magnetic field, and highlights the possibility of asymmetrical stresses. He applies the results obtained to the case of transversal vibrations of a plane homogeneous plate whose thickness is very small compared to its area, subjected to a uniform magnetic field, perpendicular to its plane.

THE FEEDING AND SWIMMING OF CONCHOECIA (CRUSTACEA, OSTRACODA)

1. The swimming and feeding of living Conchoecia is described. In general, the observations reported support conclusions arrived at by Iles from anatomical studies.2. Freshly caught animals swam constantly, except during feeding. Apparent running over the bottom was achieved by beating of the antennal exopods, as in swimming, and was not the result of any action by the more leglike appendages.3. The food consisted almost entirely of dead crustaceans. Formed masses of detritus were also eaten. Living Crustacea were generally ignored, although one attack on a possibly moribund specimen was observed.4. There was much shifting and rotation of the food by the mandibular palps, the exopods of the maxillae and first trunk limbs, and the caudal furca. This manipulation served to press different parts of the food against the mandibular gnathobases. Loss of food was prevented by the sticky secretion of the marginal carapace glands.5. The dorsal condyle of the mandible seemed to be more loosely articulated than would appear from the description by Iles.6. There was no significant filtration of particles from the current produced by the beating of the vibratory plates.7. Swirls caused by the more leglike appendages brought in particles which became trapped in the sticky secretion of the marginal carapace glands. Resulting boluses of Sepia ink particles were pushed to the mouth and swallowed. However, there are reasons to doubt the significance of this mechanism in the natural habitat.

Diffractions of flexural waves by a cavity in an elastic plate

Based on Mindlin's theory of flexural motions of plates, which takes into account the rotatory inertia and shear effects, diffractions of flexural waves by a circular inclusion in an elastic plate are investigated. An incident plane flexural wave passing through the inclusion is scattered into three types of flexural waves. From the combined incident and scattered waves, moment and shear on the boundary of the cavity are computed. They are the dynamical moment and shear concentrations in a vibratory plate with a cavity. Moment concentration factors are found to be lower in the dynamic case than in the static case.