Unconsolidated sands provide zones of high porosity and permeability important for freshwater aquifers, hydrocarbon production, and CO₂ sequestration. An understanding of the acoustics of unconsolidated sands enables the characterization of such formations using ultrasonics, borehole acoustics, and seismic methods. Inversion of ultrasonic compressional and shear velocities measured for unloading as a function of confining pressure for room-dry unconsolidated sands allows information on the mechanical properties of the grain contacts to be obtained using an approach based on the divergence theorem. This allows the effective compliance of sand to be written as the sum of the compliance of the pores and of the grain contacts, and it does not assume that the grains are identical spheres, in contrast to previous approaches. Grain contacts are found to be more compliant under shear than under normal compression, and the ratio of the normal-to-shear compliance decreases with decreasing confining pressure, implying that the shear compliance increases faster with decreasing confining pressure than the normal compliance. This is of importance in understanding the role of shear in the failure of unconsolidated sands, such as occurs in shallow water flow, sanding, and failure around injectors, where the change in stress is a function of the normal-to-shear compliance ratio of the grain contacts.

中文翻译：

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非固结砂中颗粒接触的机械性能

未固结的砂提供了高孔隙度和渗透率的区域，对于淡水含水层，碳氢化合物生产和CO ₂非常重要隔离。对未固结砂土的声学的理解使得能够使用超声波，钻孔声学和地震方法来表征这种地层。测得的用于卸载的超声压缩速度和剪切速度与室温下未固结砂土的围压成函数关系，从而可以使用基于发散定理的方法获得有关晶粒接触机械性能的信息。与以前的方法相比，这可以将有效的沙子柔度写为孔隙和颗粒接触的柔度之和，并且不假定颗粒是相同的球体。发现谷物接触在剪切力下比在正常压缩下更顺应，随围压的减小，法向剪切柔度的比值减小，这意味着随着围压的减小，剪切柔度的增大比正常的柔度要快。这对于理解剪切在未固结的砂土破坏中的作用非常重要，例如在浅水流动，打磨和注入器周围的破坏中发生的情况，其中应力的变化是法向剪切屈服比的函数。谷物接触。