**5.2 Bearing characteristics**

pressure. It can be considered that the higher confining pressure limited the further compaction and movement of soil particles in soil samples and resulted in producing microcracks and fracture within a single particle. The data in **Figure 12** illustrate that at the end of the experiment (*ε*<sup>1</sup> = 15%), both relative breakage *B*<sup>r</sup> and the amplitude of *B*<sup>r</sup> increased with the increase of the stress ratio *q*/*p*. These results indicate that under the same axial strain conditions, more particles were broken due to the increased strain confinement caused by higher confining pressure [11].

*Geotechnical Engineering - Advances in Soil Mechanics and Foundation Engineering*

**Figure 13** shows the compaction curves for the red-brown and yellow-brown samples with different clay contents. It can be seen from **Figure 13** that the peak maximum dry density (MDD) values occur most significantly when the clay contents are in the range of 7.5–10%. The peak MDD of the red-brown and the yellow-

results of the tests clearly show that as the clay content increases, the MDD tends to be considerably reduced after it reaches the peak MDD. Therefore, the experimental results show that the clay content of weathered granite soil has a remarkable influence on its compaction characteristics. Furthermore, at peak MDDs, the clay content of red-brown weathered granite soil is 1% larger than that of yellow-brown weathered granite soil. Because the particles of the red-brown samples were smaller than the ones in the yellow-brown samples, the yellow-brown samples mixed with clay could be easily formed into the suspended-dense structures in the process of compaction. The red-brown samples mixed with clay could be easily formed into the skeleton-dense structures. Consequently, the peak MDD of red-brown samples was smaller than that of yellow-brown samples. In addition, the higher the clay content, the larger is the optimum moisture content, and this relationship is approximately linear. These results also indicate that because the gradation of redbrown samples is finer than yellow-brown, the optimum moisture content (OMC) of red-brown samples is 0.1% smaller than yellow-brown. It is noted that the

, respectively. The

brown samples of weathered granite soil is 2.32 and 2.38 g/cm<sup>3</sup>

*Compaction curves for weathered granite samples with differing clay content.*

**5. Mechanical behavior**

**Figure 13.**

**152**

**5.1 Compaction characteristics**

**Figure 14** represents the relationship of clay contents and CBR (California Bearing Ratio) obtained from different compaction tests, with the blows per layer of 30, 50, and 98, respectively. As shown in **Figure 14**, the CBR comes to a peak value when the value of blows per layer is 50 or 98. Because the compaction power is not enough to make rock material in a dense state when compacted under 30 blows, the CBRs of the samples with 30 blows do not arise to a peak value. However, with the increase of clay content ratio, the samples with 30 blows will eventually arise to a peak CBR. The experimental results show that the peak value of CBR increases with the increase of blows per layer. But the results also show that as the blows per layer increase, the clay content ratio at the point of peak CBR decreases. It is noted that the clay content ratio at the point of peak CBR with 98 blows per layer is approximately 4%, which is 4% less than the clay content ratio at the point of peak maximum dry density. The cause of the above results is mainly because that when clay content ratio exceeds a certain value (i.e., 4%), the interlocking structure of the compacted weathered-granite would be opened by the clay in the material, the internal friction angle (*φ*) would be decreased, and the penetration resistance subsequently would be declined. Finally, the clay content ratio at the point of peak CBR is larger than that the ratio at the point of peak maximum dry density [17].
