In the Phase I-a, following development of the engineering technology is carried out for deep underground.
examine the basic concept of the MIU Project design
extract investigation items carried out in and after the Phase II by referring to domestic and overseas precedents and requirements for underground research laboratory by Atomic Energy Commission (1994)¹⁾
examine the layout of the research drifts

Upon the examination of the research drifts, following must be taken into consideration.
Unlike the other underground structures, excavation itself is considered as a part of research. Also, various investigations are carried out during the excavation.
The investigations follow a series of procedures of surveys -> simulation -> prediction -> verification. In case unexpected geological environments are encountered, the initial design should be flexible enough to cope with the unexpected geological environments by avoiding them or accepting them as new study objects. This is called "DESIGN AS YOU GO" in overseas precedents and is accepted as a means to get excellent results¹⁰⁰⁾.

Geoscientific researches carried out in the MIU Project consist of geological investigations, hydrogeological investigations, hydrochemical investigations, solute transport, rock mechanical investigations, investigation techniques and equipment, engineering technology for deep underground and seismological observations, etc.
As such a variety of investigations are complexly related to each other, it is important to design an appropriate layout which allows achieving goals of the entire project and each Phase. Upon designing the layout, mutual effects among investigations must be taken into consideration.

Basic concepts of designs are examined from the above-mentioned points of view. Besides, domestic and overseas precedents and requirements for underground research laboratory by Atomic Energy Commission (1994)¹⁾ are examined and investigation items carried out in and after the Phase II are extracted. Also, the layout of research drifts are examined¹⁰¹⁾.

1) Basic design concept

Basic design concept examined in the Phase I-a is as follows (Fig.4.81).

Firstly, based on the expected investigation results in the MIU Project, investigation items are extracted. Afterward, master plan is examined for constructing underground facilities. Also, detailed shape and size of facilities are examined. Requirements for these examinations are as follows.

Investigation items allow the above-mentioned goals to be attainable.
Synthesis of the investigation results are taken into consideration.
Probable restrictions on construction are taken into consideration.

Based on the data obtained in the Phase I and the investigations items, the layout of the research drift takes concrete shape.

Details of the above-mentioned three requirements are as follows.

Investigation items allow the above-mentioned goals to be attainable
This requirement should take the following into consideration.

Conditions of geological environment needed for individual investigations
For example, fracture (zones) serving as water paths and intersections between fault and research drift are necessary for investigations in and after the Phase II

The number of reiterations of individual investigations
Prediction carried out in the Phase I and methodology could be evaluated twice by using the Sub stage (500m in depth) and Main stage (1,000m in depth) of the research drifts. For depth-dependence investigation, reiteration is required at as many depths as possible using above-mentioned stages and supplementary stages. Here, supplementary stages (horizontal, hood-shaped, 3m3m) are planned to be constructed every 100m in depth to install drainage equipment for maintenance of research drifts. On the other hand, the number of reiteration carried out after encounters with the unexpected geological environments will be decided by the investigation results in the future.

Period required for individual investigations
Approximate periods must be set properly.

Synthesis of the investigation results are taken into consideration
With the purpose of establishing comprehensive investigation techniques for geological environments, it is important to synthesize various investigations so as to construct comprehensive methodologies of "geosynthesis". For this requirement, aimed objects for individual investigations (e.g. fractures, fracture zones, faults, etc.), aimed areas and periods must be taken into consideration.

Probable restrictions on construction are taken into consideration
It is important to specify various conditions interrelated to construction schedule, method and facilities required by the investigation items. Research drifts are constructed throughout Phases II and III. Investigations in the both Phases are carried out simultaneously with the related construction works. Therefore, the order and timetable exert a great influence on the whole project. The construction itself might be suspended to continue investigations without any effect. (e.g. when drifts are expected to cross fractures (zones) or faults or when unexpected geological environments are encountered.)

2) Example of research drift layout

Domestic and overseas precedents and requirements for underground research laboratory by Atomic Energy Commission (1994)¹⁾ are examined and investigation items carried out in and after the Phase II are extracted. Also, the layout of research drifts is examined. However, the investigation items are not finilized yet. They will be finalized with the progress of the investigations in the Phase I.

An example of the layout is as follows.

The MIU consists of ground facilities, main shaft (1,000m in depth), ventilation shaft, spiral gallery and two groups of research drifts (Sub stage and Main stage) for investigations in the Phase III. The spiral ramp is designed to avoid the Tsukiyoshi Fault expected at about 950m in depth. The current layout is shown in Fig.4.82.

The Shobasama site is underlain by the rock mass with a lower fracture density (400700m in depth) and the rock mass with a higher fracture density due to the effects of the fault (deeper than 800m). To secure investigations in both types of rock mass, research drifts are planned at around 500m and 1,000m in depth. Also, the spiral ramp is constructed to avoid the fault for the reason that the penetration of the Tsukiyoshi Fault by the main shaft incurs a large-scale water inflow to greatly disturb the hydrogeological field in the Shobasama site. Thus, an advantage is expected that transportation of construction machinery and drilling of horizontal observation boreholes at several depths become more easily.

The ground facilities are composed of a research/administration facility, a sample storage, an equipment maintenance facility, a well-head facility, a muck deposit and a wastewater treatment facility.