The nickel ore from Boakaine, which contains comparatively higher proportion of large particles as shown in Fig. 2, was used for the experiment. Fig. 5 shows the results of the experiment. In the figure, the abscissa and ordinate denote experiment number and maximum cone penetrating force, respectively. The black and white circles denote measured data for samples at 23.0 and 24.5 % in average moisture content, respectively. The moisture content of sample is represented by the wet base one, , as following:
where, WT is total weight and WS is dry weight.
Fig. 5. Maximum cone penetrating forces
The superscript 105 denotes the drying temperature in Celsius. "D < 19 mm" means that the maximum grain size of the sample was reduced to 19 mm. The thinner solid lines denote the minimum value in three data including the former and the latter data in the experiment number. The thicker solid lines, similarly, denote the minimum value in five data. It can be said that the difference between the minimum values in three data and in five data is not significant, in particular in the case that the maximum cone penetrating forces are small. Thus we determined the number of repetition of cone penetration tests for single sample at three.
3. Determination of criterion for judgment
3.1. Outline of determination of the criterion
The criterion of representing cone penetrating force for judgment on prevention of sliding failure is determined by the following steps:
(1) Determination of primary criteria of moisture content, i.e., upper bound of moisture content of the samples for shear tests, based on the measurement of the relations between moisture content and shear strength and the analyses on the relations between moisture content and slope stability;
(2) Conversion of the primary criteria of moisture content to the moisture contents of samples for the new test procedure;
(3) Measurement of the relations between moisture content and representing cone penetrating force; and
(4) Determination of the criterion of the representing cone penetrating force based on the representing cone penetrating forces corresponding to the moisture contents from step (2).
3.2. Determination of primary criteria of moisture content
We carried out the direct shear tests 3), 5) for the five samples changing moisture content to obtain the relation between moisture content and shear strength. Table 5 shows the specification of the tests. The maximum grain size of the samples for the tests was 6.7 mm.
Table 5. Specification of direct shear test
Fig. 6. Shear strength of a sample
