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原文传递 Use of Walk Opportunities Index to Quantify Local Accessibility.

题名：	Use of Walk Opportunities Index to Quantify Local Accessibility.
作者：	Kuzmyak-JRichard; Baber-Charles; Savory-David
关键词：	Boreholes-; Clay-soils; Cohesive-soils; Diameter-; Earth-pressure; Finite-element-method; Horizontal-directional-drilling; Hydraulic-fracturing; Pipe-laying; Pressure-; Slurry-; Stresses-; Two-dimensi
摘要：	Hydraulic fracturing during horizontal directional drilling can permit drilling mud to travel to the ground surface, to collect under overlying pavements, or to be released into the riverbed during river crossings. These events can decrease drilling efficiency, damage adjacent infrastructure, and cause environmental damage. Current design equations for maximum drilling pressure focus on shear failure around the borehole drilled to house the new pipe. The present research examines, instead, the potential for tensile fracture of cohesive soils surrounding the borehole. Two-dimensional nonlinear finite element modeling is used to study the effectiveness of closed-form solutions for calculation of the drilling slurry pressures that fracture the surrounding soil. Tangential stresses are calculated for a borehole with a 0.2-m diameter in an undrained clay soil with various K sub 0 values, construction depths, and drilling slurry pressures. Elastic plate theory is found to provide effective values of (a) tangential crown and spring line stresses when the soil responds elastically and (b) the decreases in tangential crown stress that occur as drilling slurry pressures increase. Closed-form plasticity solutions provide good values of tangential stresses once the soil yields. Following yield, increases in mud pressure result in increases in tangential stress, so hydraulic fracture from tension is no longer an issue. The study indicates that mud loss in low-strength clays or those with K sub 0 close to unity is most likely the result of unconfined plastic flow (blowout). Mud loss for stiff clays and those with other K sub 0 values is more likely the result of tensile fracture.
总页数：	Transportation Research Record: Journal of the Transportation Research Board. 2006. (1976) pp172-180 (9 Fig., 1 Tab., 13 Ref.)
报告类型：	科技报告