Assessment of Air Pluviation Using Stationary and Movable Pluviators

Methods used for laboratory sample preparation should be able to produce uniform and highly repeatable sand beds of required density and to simulate field conditions. Air pluviation is a widely used method to prepare cohesionless soil samples in the laboratory. In the present study, two currently used air pluviation setups, viz, stationary/portable traveling pluviator (PTP) and movable/mechanized traveling pluviator (MTP), are investigated in terms of their ability to prepare uniform and repeatable sand beds of a wide range of relative densities. The PTP and MTP pluviation setups mainly comprise hopper, orifice, flexible hose, and rigid tube. Chain pulley and rail track are the additional features of MTP, which allow the hopper to travel smoothly in one direction. Pluviation studies are performed by using Indian standard sand (Grade II), and a California bearing ratio (CBR) mold is used to evaluate relative density (RD) and deposition intensity (DI) of samples. The effect of height of fall (HF), DI, and number of diffuser sieves on the RD of the sand sample is studied for both the PTP and MTP pluviation setups. A model tank is used to verify the uniformity of the sand samples with the help of miniature cone-penetrations tests. The test results reveal that a wide range of RD with uniform and repeatable sand samples can be prepared by using MTP compared with PTP. (C) 2016 American Society of Civil Engineers

In-house calibration of pressure transducers and effect of material thickness

Pressure transducers are increasingly used within soil mass or at soil-structure interface for appraisal of stresses acting at point of installation. Calibration of pressure transducers provides a unique relationship between applied pressure and voltage or strain sensed by transducer during various loading conditions and is crucial for proper interpretation of results obtained from pressure transducers. In the present study an in-house calibration device is used to calibrate pressure transducers and the study is divided into two parts: 1) demonstration of developed calibration device for fluid and in-soil calibration of pressure transducers; 2) effect of soil layer thickness on the earth pressure cell (EPC) output. Results obtained from the present study revealed successful performance of the developed calibration device, and significant effect of sand layer thickness on the calibration results. The optimum sand layer thickness is obtained as 1.5 times the diameter of EPC

Performance of a Rigid Retaining Wall with Relief Shelves

Earth pressure on a retaining wall decides the sectional dimensions of the wall, and there have been several attempts in the literature to reduce the earth pressures on the retaining walls, by using techniques such as lightweight backfill and placement of compressible inclusions at the wall-backfill interface, to name a few. A retaining wall with pressure relief shelves, though discussed for several decades, is one of the least practiced techniques to reduce the earth pressure on retaining walls, mainly because of its complex behavior and lack of distinct provisions. One such wall was constructed in the populated area in Hyderabad, India, however, it failed after a few years. This failure has motivated the authors to study the behavior of these walls and to understand the associated mechanism involved in earth pressure reduction, as well as what caused the failure in the previously mentioned wall. The work reported in this study presents static force analysis and numerical analysis of rigid nonyielding retaining wall retaining a dry cohesionless backfill with pressure relief shelves performed using three-dimensional numerical analysis. A parametric study is conducted to understand the influence of width and position of relief shelves on the contact pressure below the base slab, surface settlement profile of backfill, deflection of relief shelves, and reduction in lateral earth pressure. The present study reveals that relief shelves can reduce lateral thrust on the wall up to 23%, compared to that of a retaining wall without a relief shelf. The static force analysis suggests that the width of relief shelves should be increased from top to bottom of the wall, for achieving maximum reduction of earth pressure. Moreover, it is also noted that maximum allowable width of the relief shelf at any height of the wall is a function of the width of the relief shelf lying above it. (C) 2018 American Society of Civil Engineers

Assessment of portable traveling pluviator to prepare reconstituted sand specimens

Air pluviation method is widely adopted for preparation of large, uniform and repeatable sand beds of desired densities for laboratory studies to simulate in-situ conditions and obtain test results which are highly reliable. This paper presents details of a portable traveling pluviator recently developed for model sand bed preparation. The pluviator essentially consisted of a hopper, orifice plates for varying deposition intensity, combination of flexible and rigid tubes for smooth travel of material, and a set of diffuser sieves to obtain uniformity of pluviated sand bed. It was observed that sand beds of lower relative density can be achieved by controlling height of fall, whereas, denser sand beds could be obtained by controlling deposition intensity. Uniformity of pluviated sand beds was evaluated using cone penetration test and at lower relative densities minor variation in density was observed with depth. With increase in relative density of sand bed higher repeatability of uniform pluviation was achieved