Journal of the Japan Society of Engineering Geology

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It has been pointed out by many previous authors that the creation of a small failure on slope such as a cluster of some small scarps or a small edge failure due to the intense rainfall acts as a trigger or a presage of large slope failure. It can be said that the fundamental study on the transient change of groundwater flow caused by the creation of a small failure is indispensable to clarify the outbreak mechanism of the large failure. The investigation presented here was intended to experimentally and theoretically clarify the characteristic nature of groundwater flow around a small failure on slope.
Experimental apparatus used was mainly composed of an inclined soil box of 92 cm wide, 78 cm long and 15 cm high and a reservoir to flow water through the soil box with constant head. Coarse sand of diameter of 2. 5 mm and mixture of bentonite and fine sand were filled in the box to model the slope which consists of two layers; high permeable upper layer and low permeable lower layer. Four models of slope having different types of failure at the end of them were prepared. The failure in each model was simulated by a small space filled with coarse sand of diameter of 2. 5 mm. Three dimensional patterns of groundwater flow in two of these models were numerically simulated by the use of Finite Element Method based on the Galerkin technique. After, the transient behavior of three dimensional flow of groundwater caused by a succession of two idealized rainfalls in two more appropriate models of slope were numerically simulated.
The obtained results are as follows;
(1) The numerical technique used in this investigation can well simulate the transient behavior of groundwater flow in slope.
(2) The upper end of the high permeable failure tends to converge the groundwater flow in slope.
(3) On the contrary, the lower end of the failure diverges the groundwater in the failure.
(4) Pore pressure significantly increases at the vicinity of the lower end of the failure.

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The authors are investigating the ground conditions concerning TBM excavation to make clear the geologic factors affecting TBM feasibility, to estimate the relation between rock mass properties and the rate of pene tration of TBM and also to establish the way how to proceed geologic survey for tunneling with TBM.
Few investigations have been reported to estimate TBM feasibility through variety of investigations considering the effects of discontinuities as well as strength and hardness of rock mass.
Artifitial factors affect considerably on tunneling with TBM, therefore the investigation and consideration on the TBM feasibility in relation to ground conditions seem to be very hard work.
Some basic relations between geologic factors and TBM feasibility are introduced here, and following reports will be published soon after to comment it in detail.

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