砂層内局部沈下部にかかる垂直土圧

Abstract

If one part of the horizontal support in a sand layer or a local section of mass ofsand lowers while the remainder stays in place, the earth pressure on the yielding sectiondecreases from the initial earth pressure corresponding to the overlaid sand layer.In order to study such earth pressure, two-dimensional model tests were performedby using the trap door set beneath alminium rod mass. Investigating the results of thesetests, assumptions and conditions necessary to set up the earth pressure problems mathe-matically are determined as follows:Sand mass above the trap door can be devided into 3 zones separated by 2 slidingsurfaces.Inner sliding surface is assumed to consist o.f 2 symmetrical logarithmic spirals whichstart from a point on the center line of the door making angle of (π/4-Φ/2) with thehorizontal line respectively and reach both edges of the door intersecting there at rightangle with it. Therefore, earth pressure acting on the inner sliding surface can beobtained by K~tter-Massau's theory.The outer sliding surfaces are assumed as surfaces rising vertically from both edgesof the door land the vertical 'earth pressure in' 'the zone between these surfaces is assumedto be calu~ulated as similar as that in the silo with vertical walls.Therefore vertitiat earth 'pressure on the trap door is expreased by the sum of theresultant of vertical component of tbe earth pressure on the inner sliding surface and theweight of sand existing sn the' zone ~urrattnded b~ this sliding surface. The amount ofthe earth pressure thus calculated shows~ well ~gr, ~ement with that obtained experimentallyby the model test.