3種類の代表的なタイプの節理を有する岩盤の応力伝達機構に関して数値解析および光弾性実験をおこないこれらの力学的特性のいくつかを明らかにした。又節理面の材料定数を変化させることにより岩盤の異方性効果を調べ, 均一弾性体との相違について論じた。
節理面が水平軸となす角θを0°≦θ≦90°の範囲で変化させた場合, 応力分布が急激に変化する遷移角度の存在が明らかとなった。この遷移角度近傍において数値解析は極めて不安定であり解の収束が悪く精度が低下する。又, 遷移点を越えた角度においては各節理タイプの応力分布性状はほぼ一致し遷移角度より小さな範囲においては節理形状の変化により応力分布は大きく変化する。
さらに節理面の引張強度についても, これがある限界値以下に低下した場合, 応力分布が急激に変化することが明らかとなった。これに対し粘着力および引張強度をある限界値以上に選び, 節理面のせん断剛性Gを弾性理論から得られる値G=E/2(1+ν)に選ぶことにより応力分布は均一弾性地盤の値と一致する。
ここで用いられた数値解析手法は連続体に対する解析から任意に発達した節理を有する岩盤の解析にまで適用可能であり, 強異方性を有する節理系岩盤の力学的特性を明らかにするのに極めて有効な方法であるといえよう。

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The continuity of cracks is one of the most important factors to determine many characters of rock mass such as ground water flow, strength and slope failure.
The crack continuity can be quantitatively estimated by the combined application of two stochastic process models; the branching process model and the percolation process model.
It goes without saying that detailed field data of crack system, particularly the ratios of the number of crack junctions to that of crack terminal points are indispensable for this kind of analysis.

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The relationship between rockfall and vibration of the ground has never been fully analyzed before in Japan because of several problems which fall within one of two categories which we have labelled “motivecause” and “primary cause”.
Problems falling within the “motive cause” category are concerned with characteristics of vibration whilethose problems falling within the “primary cause” category are concerned with the conditions of mountainslopes (e. g. morphometric parameters of slope; shape, size and depths at which blocks have been buried onslopes ; quality of weathered materials and surface soil).
In spite of these problems, it is quite important to analyze the relationship between rockf all and vibrationof the ground for some kinds of construction works such as railway and tunnel construction because shocksfrom blasting may cause rockfalls.
In our survey, two seismic tests were carried out-one involving a dynamite blast and the other involvinga shockwave caused by a passing train.The results of these tests can be summarized as follows:
1. The shock that was produced by the passing train did not cause a severe rockfalls. The maximum deformationof the ground was 7.6-10^-5 cmand occurred above 10 seconds. These results are too small tocause a rockf all.
2. The relationship among the amount of dynamite, the maximum displacement, the maximum accelarationand the transmissive velocity of vibration was studied to find the point at which a severe rockfall waslikely to occur during tunnelling work.In this test, 3 kg of dynamite were exploded 50 meters from the test site. As a result, the maximumdisplacement was 1.4-10^-3 cm. This value is also too small to cause a rockfall.

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In excavation of the Kan'etsu tunnel, rock burst occurred expectedly. Especially for about 1 year since July 1980, many broken pieces of rock had sprung out frequently. Rock burst should be classified into sometypes, such as springing of rocks, cracks on face without springing of rocks, and only breakdown noises onface or in bed rock. Those types seem to be a series of forms of rock burst. Some examples of occurenceprocess of rock burst are shown in figure-3, -4, -5, -6.
From our experiences of rock burst, it may be pointed out that those forms of rock burst have somecharacters. They are as follows:
(1) It occurred even under small overburden.
(2) It occurred in the formation of quartz-diorite, but not of hornfels.
(3) It occurred mostly at face, and few at backward and side wall.
(4) The existence of specific areas where rock burst occurred was recognized in the tunnel.
(5) At the areas with inflow of ground water, it did not occurred.
(6) It was related greatly to joint, fractured zone and so forth.
(7) The sizes of brocken rock pieces were various, but the shapes of them were all generally flat.
(8) It was closely related with working cycle of tunnel excavation.
Some investigations including measuring of initial stress in bed rock and its change during tunnel excavation, core discing in the horizontal bored and sampled core, acoustic emission survey, rock properties tests, andtemperature measuring of face and sidewall, were carried out at the rock burst areas.
As a result, significant informations on the behavior of bed rock related with tunnel excavation and onthe relation between rock burst and working cycle of excavation, were obtained.
The rock mass at the rock burst areas was elastic and high brittleness. And rock burst seemed to beclosely related to geological weak zone of bed rock.
For a countermeasure against rock burst, it was adopted as a keystone of tunnel excavation that many rockbolts were installed in working face. The tunneling method that we adopted by utilizing the above mentionedinvestigations of bed rock and analysis of our experiences of rock burst, may be appraised proper.
It is useful that the system of acoustic emission survey is composed completely in order to control tunnelexcavation work at the rock burst areas.

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