**4.2 Mineral content**

The red-brown, yellow-brown, and gray weathered granite samples were prepared with approximately the same particle size distribution. Standard heavy compaction tests were performed on the samples under optimum moisture content conditions [11]. The results of sieving before and after the test are shown in **Figure 6**.

The relationship between relative breakage and quartz (or feldspar) content was analyzed by calculating the relative breakage of different samples before and after

**Figure 6.** *Sieving curves of different samples before and after the test.*

**Figure 7.** *Relationship curve between mineral content and Br.*

that the rate of decrease of relative breakage of the red-brown sample was higher than that of the gray sample, reflecting that because the degree of weathering of red-brown weathered granite is higher than that of gray weathered granite, the strength of the red-brown sample was less than that of the gray sample. This shows that the sensitivity of the red-brown sample to particle heterogeneity was greater

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

The red-brown, yellow-brown, and gray weathered granite samples were prepared with approximately the same particle size distribution. Standard heavy compaction tests were performed on the samples under optimum moisture content conditions [11]. The results of sieving before and after the test are shown in

The relationship between relative breakage and quartz (or feldspar) content was analyzed by calculating the relative breakage of different samples before and after

than that of the gray sample [11].

**4.2 Mineral content**

**Figure 6**.

**Figure 6.**

**148**

*Sieving curves of different samples before and after the test.*

**Figure 5.** *Br-Cu curves.*

> the standard compaction test. **Figure 7** shows the relationship between relative breakage and quartz (or feldspar) content. It can be seen from the figures that *B*<sup>r</sup> decreased with the increase of quartz content, while *B*<sup>r</sup> increased with the increase of feldspar (=plagioclase feldspar + potassium feldspar). The results show that quartz and feldspar content have an obvious effect on the particle breakage characteristics of weathered granite [11].

> The main reasons that the *B*<sup>r</sup> of samples with high quartz content after compaction test was small are as follows: (1) the probability of breakage of samples with more quartz content is small because quartz has a high strength, (2) samples with high quartz content have strong ability to resist being weathered, and (3) there are few microcracks in samples with high quartz content. On the contrary, feldspar has little strength and is easily weathered, so the samples with higher feldspar content showed obvious particle breakage characteristics [11].

#### **4.3 Blows per layer (compaction degree)**

In order to analyze the effect of blows per layer of samples on the particle breakage properties of weathered granite, four red-brown weathered granite samples with the same initial particle size distribution were prepared, and four different heavy compaction tests were conducted, with blows per layer (BPL) of 30, 50, 75, and 98 [11]. The sieving results before and after the tests are shown in **Figure 8**.

As shown in **Figure 9**, the relative breakage increased with an increase in blows per layer, but the increasing level of relative breakage decreased. Furthermore, with the further increase of blows, *B*<sup>r</sup> tended toward a certain limit value. Considering the engineering practice, the compaction degree of samples was analyzed, and the compaction degrees of samples and corresponding relative breakage are depicted in **Figure 10**. It can be concluded from this figure that there is an approximate linear growth relationship between compaction degree and *B*r. It can be found that for the same weathered granite fillings, relative breakage can be used to reflect the compaction performance indirectly on the basis of the relationship between compaction effect and compaction performance. Excessive compaction may lead to excessive particle breakage of soils and is not conducive to the long-term stability of subgrade [11].

characteristics of compacted weathered granite soil under different stress levels, particle size analysis tests were conducted on the samples before and after consolidated drained large-scale triaxial tests, and the relationship between relative break-

Because specimens for the triaxial test must be prepared by the vibrating forming method, particles of the specimens may be partially crushed. In order to improve the accuracy of the experiment, two specimens for the large-scale triaxial test under the same confining pressure were artificially prepared with approximately the same particle size distribution before vibrating compaction. One of the samples was sieved after vibrating compaction and before the triaxial test. The results of the sieving test for this sample were used as the initial gradation of the

From the stress-strain curve of samples in this study, it can be seen that when the axial strain reached 15%, the residual strength of the specimen under different confining pressures reached its constant value. Therefore, when the axial strain reached 15%, the triaxial tests were forced to stop, and then the sieving tests were performed. **Figures 11** and **12**, respectively, show variations in relative breakage

As indicated in **Figure 11**, at the end of the triaxial test, the relative breakage of samples increased with the increase of confining pressure, while the increasing amplitude of relative breakage decreased slightly with the increase of confining

age and confining pressure (or stress ratio, *q*/*p*) was analyzed [11].

(*B*r) with confining pressure (*σ*3) and stress ratio (*q*/*p*) [11].

other sample for the triaxial test [11].

*DOI: http://dx.doi.org/10.5772/intechopen.86430*

*Weathered Granite Soils*

**Figure 11.** *Br-σ<sup>3</sup> curves.*

**Figure 12.**

**151**

*Br-q/p (ε<sup>1</sup> = 15%) curves.*

**Figure 8.** *Sieving curves of samples under different blows per layer. BPL: blows per layer.*

**Figure 9.** *Relationship curve between blows per layer and Br.*

**Figure 10.**

*Relationship curve between degree of compaction and Br.*

#### **4.4 Stress level**

The breakage of soil particles in a sample of rockfill under moderate stress will be quite evident [11]. For the purpose of studying the particle breakage

#### *Weathered Granite Soils DOI: http://dx.doi.org/10.5772/intechopen.86430*

characteristics of compacted weathered granite soil under different stress levels, particle size analysis tests were conducted on the samples before and after consolidated drained large-scale triaxial tests, and the relationship between relative breakage and confining pressure (or stress ratio, *q*/*p*) was analyzed [11].

Because specimens for the triaxial test must be prepared by the vibrating forming method, particles of the specimens may be partially crushed. In order to improve the accuracy of the experiment, two specimens for the large-scale triaxial test under the same confining pressure were artificially prepared with approximately the same particle size distribution before vibrating compaction. One of the samples was sieved after vibrating compaction and before the triaxial test. The results of the sieving test for this sample were used as the initial gradation of the other sample for the triaxial test [11].

From the stress-strain curve of samples in this study, it can be seen that when the axial strain reached 15%, the residual strength of the specimen under different confining pressures reached its constant value. Therefore, when the axial strain reached 15%, the triaxial tests were forced to stop, and then the sieving tests were performed. **Figures 11** and **12**, respectively, show variations in relative breakage (*B*r) with confining pressure (*σ*3) and stress ratio (*q*/*p*) [11].

As indicated in **Figure 11**, at the end of the triaxial test, the relative breakage of samples increased with the increase of confining pressure, while the increasing amplitude of relative breakage decreased slightly with the increase of confining

**Figure 12.** *Br-q/p (ε<sup>1</sup> = 15%) curves.*

**Figure 11.**

**4.4 Stress level**

**Figure 10.**

**150**

**Figure 8.**

**Figure 9.**

*Relationship curve between blows per layer and Br.*

*Relationship curve between degree of compaction and Br.*

The breakage of soil particles in a sample of rockfill under moderate stress will

be quite evident [11]. For the purpose of studying the particle breakage

*Sieving curves of samples under different blows per layer. BPL: blows per layer.*

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

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].

increase of OMC slowed down slightly when the clay contents of the samples were

**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].

**Figure 15** shows the typical stress-strain relationship of the CD tests on four representative red-brown samples of pure weathered soil under four different confining pressures, where *σ*<sup>1</sup> is the axial stress, *σ*<sup>3</sup> is the confining pressure, and *dε*<sup>1</sup> is the axial strain. **Figure 16** shows this typical *ε*v-*ε*<sup>1</sup> relationship of the CD tests,

It can be found in **Figure 15** that the peak deviator stress increases as the confining pressure increases. The internal particles of weathered granite soil could be overturned, stridden, and dislocated under lower confining pressure and could

more than 8% [17].

*Weathered Granite Soils*

**5.2 Bearing characteristics**

*DOI: http://dx.doi.org/10.5772/intechopen.86430*

**5.3 Strength characteristics**

where *ε*<sup>v</sup> is the volumetric strain.

*Change in CBR for soils with differing clay content.*

**Figure 14.**

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## **5. Mechanical behavior**

#### **5.1 Compaction characteristics**

**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 yellowbrown samples of weathered granite soil is 2.32 and 2.38 g/cm<sup>3</sup> , respectively. The 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

**Figure 13.** *Compaction curves for weathered granite samples with differing clay content.*

increase of OMC slowed down slightly when the clay contents of the samples were more than 8% [17].
