Recently many large-scale land use projects are being developed on hill, where many kinds of soft rocks are widely distributed in Japan.
The excavations of these soft rocks, such as, sand stone, mud stone, their alternations and tuffs, belonging to Neogene or Quartenary Period, are performed by the large-scale mechanical works. Nowadays, the earth work machineries become bigger and bigger, and accordingly the efficiency of the machines become higher and higher.
On the non-blast cutting works of these Soft rocks, the efficiency of the rippig machine is often away from the predicted that is bassed on the seismic wave velocity (Vp1),which is usually lower than 2,5 km/s. in p-wave. The refractional wave method applied to these low velocity rocks has some problems.
The authors measured the true seismic wave vehlocity(Vp2)on the cutting surfaces by the direct wave method, and the ripping work efficiency(R.W.E.)at the same points, in order to examine the relations between Vp1, Vp2 and R.W.E. The predicted values of velocity(VP1)are often different from the true velocity(Vp2).
In using the output materials for embankments big blocks must be broken to a suitable size for transportation, Spreading work at the filling yard and for effective compaction work. The percentage of big blocks (P.B.B.) is measured by a conventional method at the cutting yard. The authors show that R.W.E. can be classified by Vp2 reasonably at a field, but not be a general rule. And P.B.B. can be classified rather by the number of ripping pick, than by Vp2.
In cases of non-blast excavation work the reasonable. and effective selection of machines and the decision of cost are carried out only by these observation at the cutting yard. This can be said to be one of the effective application of the observational method.
Two places for the test fields were chosen at where the typical and simple geological layers are distributed(Table 1).
The predictional field investigations were performed by the seismic exploration (refractional method),borings and loggings. The characteristics of rock-fragments were defined by laboratory tests (Table 2). The typical geological sections are shown in Figs.1.and 2.
(Table in full paper)
Geology of field-A shows an uniform weathed tuff, originated with Tokachi volcanic eruptions in Quarternary. Being weathered from the surface, the upper top of the layer was changed to silty fine sand of 20 to 100 cm in thickness. Under the top soil, there is a thin layer that has been intensely fractured. The fractured zone of 20 to 100 cm in thickness, does not contain matrix. Then the seismic wave is very much dumped and it makes very low velocity zone. The unconfined compression strength of the rock-fragment is 55 to 190 kg/cm2.
Alternations of both muddy tuff and sandy tuff, each layer being 5 to 10 m in thickness, are distributed in this field. There can be seen complex geotechtonics, some faults and foldings. The muddy layers has been intensely fractured and thickly weathered, but the 'sandy layers are not so much.