In this study, the elastic modulus along a borehole for the construction of a national highway tunnel in ground consisting of volcanic and pyroclastic rocks was estimated by using dynamic elastic modulus. The data used in estimating the elastic modulus were the P-wave velocity measured in the velocity logging during the boring and the P- and S-wave velocities, wet density, Poisson's ratio, and unconfined compressive strength of cores measured in the laboratory. As the results of analysis, in-situ elastic modulus along the borehole wall is used to assume the rough value of deformation modulus in the ground classification for a tunnel. And predicted tunnel deformation by in-situ strain along the borehole wall based on in-situ elastic modulus along the borehole wall is useful for setting the continuous control standard values of displacement in tunnel excavation.

1 Introduction

In conducting numerical analyses and reviewing the rock mass classification for a tunnel construction, physical property data that reflect the conditions of the site ground as much as possible and evaluation based on the mechanical strength of the site ground are necessary. Because of such necessities, a horizontal boring investigation (advanced boring) at the excavation tunnel face may be conducted during a construction. The ground conditions immediately adjacent to the excavation ahead of tunnel face are evaluated based on the P-wave velocities obtained in velocity loggings in advanced borings, deformation moduli obtained in the horizontal loading test, and the P-wave velocities obtained in the laboratory test. In the velocity logging, the S-wave velocity ahead of the tunnel face is not measured; however, the S-wave velocity ahead of the tunnel face is able to be estimated based on the P-wave velocity measured in-situ and P- and S- waves obtained in the core test. The continuous in-situ elastic modulus for the total length of the advanced borehole is able to be obtained by using the estimated S-wave velocity, wet density, and Poisson's ratio. This in-situ elastic modulus along the borehole obtained in this way enables evaluation of the ground at the construction site based on values that appropriately reflect the in-situ conditions. These elastic moduli are able to be applied to estimation of the strain in the ground around the advanced borehole and in setting the control standard displacement values that associate with the excavation of a tunnel.

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