**2. Specimen preparation and test methods**

The weathered granite soil samples used in this chapter were obtained from a site near Mount Yunzhong (shown in **Figure 1**), a branch of the Lu-liang Mountains, on the eastern outskirts of Xinzhou City, Shanxi Province, China. The weathered granite soil was used as a part of the subgrade materials in the Xinbao highway (Xinzhou City to Baode City). There were three colors of the weathered granite in the field, red-brown, yellow-brown, and gray, as shown in **Figure 1**. The in situ dry unit weight and moisture content of the weathered granite were 17.82–18.22 kN/m<sup>3</sup> and 4.9–5.5%, respectively.

The excavation range of the filling materials used for Xinbao highway (Shanxi Province, China) was mined at a depth of less than 30 m on average under the

**Figure 1.** *Photograph of weathered granite samples.*

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

during constructing these infrastructures in mountainous areas. It is very important to study the engineering properties and applicability of special materials, e.g., weathered granite soil, in mountain area to solve the problem of shortage of building materials. Besides nonlinear stress-strain, elastic-plastic, dilatancy (shrinkage), and other properties, easy weathering and particle breakage are the distinctive and unique engineering property of weathered granite. The particle size distribution of the in situ soils is controlled by weathering process. Furthermore, the particle breakage characteristics of soils are affected by the particle size distribution. The particle size distribution of in situ weathered granite soil has been paid little attention in previous studies, but it is very important to have a full understanding of the particle size distribution of in situ weathered granite soil, because the particle size distribution has considerable influences upon engineering properties of weathered granite soil such as compatibilities, permeabilities, and strength-deformation char-

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

In this chapter, the weathering mechanism, particle breakage, mechanical properties (including compaction characteristic, bearing characteristics, strength characteristics, and shearing-dilatancy characteristics), and constitutive model of weathered granite soils from Shanxi, China, were investigated. The results can provide a basis for the comprehensive understanding of the engineering characteristics of weathered granite soils and references for the utilization of weathered

The weathered granite soil samples used in this chapter were obtained from a site near Mount Yunzhong (shown in **Figure 1**), a branch of the Lu-liang Mountains, on the eastern outskirts of Xinzhou City, Shanxi Province, China. The weathered granite soil was used as a part of the subgrade materials in the Xinbao highway (Xinzhou City to Baode City). There were three colors of the weathered granite in the field, red-brown, yellow-brown, and gray, as shown in **Figure 1**. The in situ dry unit weight and moisture content of the weathered granite were 17.82–18.22 kN/m<sup>3</sup>

The excavation range of the filling materials used for Xinbao highway (Shanxi Province, China) was mined at a depth of less than 30 m on average under the

acteristics [4–7].

granite soils in engineering practice.

and 4.9–5.5%, respectively.

**Figure 1.**

**144**

*Photograph of weathered granite samples.*

**2. Specimen preparation and test methods**

surface of the Lu-liang Mountains. This is a general practice in producing subgrade materials for highways. Because the red-brown and the yellow-brown weathered granites were located at depths of less than 30 m, the lab tests in this chapter are focused on these two kinds of samples. The embankment is mainly filled with redbrown weathered granite, so parts of the tests in this chapter were mainly aimed at red-brown samples.

Because the physical meaning of Fukumoto's weathering model [4] is clear and easy to use, this model was used in this chapter to evaluate the weathering process of granite. After the thorough investigation on the distribution of in situ weathered granite, numerous sieving tests on a large number of granite samples obtained from typical sections A and B (shown in **Figure 2**) were carried out. According to Fukumoto's grading model, geological year's parameter *m* and geometric progression constants *r* of granite samples at different depths were calculated. The experimental tests involved in this chapter, including X-ray diffraction, sieving, heavy compaction [8], and large-scale triaxial test [9], were investigated to research the particle breakage characteristics of compacted weathered granite.

**Figure 3** shows the composition of the rock samples in this study. **Figure 3** shows that the colors of the samples became gradually brighter with an increase in the quartz content. The increase in potassium feldspar or feldspar content was the

**Figure 2.**

*Photograph of field sampling: (a) section A and (b) section B.*

**Figure 3.** *Mineral composition of weathered granite samples.*

main cause of the brighter colors of the rocks. Geng et al. [10] noted that the amphibole was bluish-green, and the biotite was yellow in Mount Yunzhong. In addition, Geng et al. [10] described the main body of the granite as a coarse grain (porphyritic granite), with fine-grained granite on the edge. The three types of samples used in this chapter had quartz (mean 40.3%) and feldspar (mean 54.3%) as the dominant minerals present with smaller amounts of mica (mean 1.3%), amphibole (mean 2%), hematite (0.5%), vermiculite (1%), and unknown (1%) materials.

#### **3. Weathering process**

Based on the geometric fractal theories and some assumptions, Fukumoto [4] proposed a gradation equation for decomposed granite soils by using mathematical statistics method and made it possible to quantificationally describe the weathering process of granite by using a certain mathematical model to evaluate the particle breakage of weathered rock. Because Fukumoto's model is more scientific and easier to use, this model has been widely used in describing the process of rock weathering. Thus, this model was also used in this chapter to describe the weathering process of in situ weathered granite.

**Figure 4** shows changes of parameters *m* and *r* for the samples at different depths of mountain profile, *h*.

The results of statistical analysis indicate an approximate power function relationship between *h* and *m* (or *r*), and the correlation of relationship was relatively good. The power function relationships between *h* and *m* (or *r*) in section A are shown as follows:

$$m\_{\rm A} = \text{3.324}h^{-0.706} \tag{1}$$

*<sup>r</sup>*<sup>B</sup> <sup>¼</sup> <sup>0</sup>*:*269*h*0*:*<sup>168</sup> (4)

where *m*<sup>B</sup> is the geological year's parameter in section B and *r*<sup>B</sup> is the geometric

Actually, the geological year's parameter, *m*, reflects the degree of geological actions (including physical actions and chemical actions) [11]. The deeper the granite is buried, the less the geological action will affect it. The above results indicate that *m* was close to zero at a depth of 20–25 m under the surface of the mount in sections A and B, which indicate that the physical and chemical actions on the granite in this research can be negligible at this depth. The geometric progression constant, *r*, represents the integrality of rock. The *r* of section A and section B studied in this chapter was close to a certain value at a depth of 25 and 20 m, respectively, which indicates that the granite in Mount Yunzhong was close to the

It can be found from the results that the *m* of section A was larger than that of section B at the same depth, indicating that the ability of section A to resist geological and climatic environment was worse than that of section B. On the other hand, the *r* of section A was smaller than that of section B at the same depth, which illustrates that the integrality of granite in section A was worse than that in section B [11]. Although section A and section B are under the same geological and climatic environment, the values of *m* (or *r*) are different between these two sections. The main reason for the difference was the difference in internal properties (e.g., the mineral composition of rocks) of weathered granite between these two sections. Of course, some external factors could not be excluded; for example, the probability of

Many aspects, such as particle gradation, mineral composition, blows per layer, and stress level, can influence the characteristics of particle breakage of compacted

Hardin [12] proposed the concept of relative breakage (*B*r), which was achieved

from the variation in particle size distribution curves before and after loading. Relative breakage can embody the overall change in particle size distribution before and after loading and overcomes the shortcoming of using single index of sieving

Standard heavy compaction tests on four red-brown samples and four gray samples of weathered granite with different gradations under optimum moisture content conditions were investigated. Sieving tests were implemented on the samples before and after compaction, and the uniformity coefficient (*C*<sup>u</sup> = *d*60/*d*10) and relative breakage (*B*r) of the samples before and after the compaction test were calculated. The relationship between *C*<sup>u</sup> and *B*<sup>r</sup> is shown in **Figure 5** [11]. The test results show that *B*<sup>r</sup> decreased with the increase of *C*<sup>u</sup> which indicates that as the *C*<sup>u</sup> of weathered granite increased, the degree of particle breakage was reduced because of the enhancement of the intergranular locking effect. In addition, it can be seen

test results (percentage of particles passing a given sieve size or sieve size corresponding to a given percentage passing) as the evaluation index for particle breakage [13–16]. In view of the above, *B*<sup>r</sup> has been widely used in evaluating soil particle breakage characteristics, because it can represent the basic attribute of the

soil material and is more scientific and reasonable to use.

progression constant in section B.

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

*Weathered Granite Soils*

complete unweathered state at a depth of 20–25 m.

**4. Particle breakage characteristics**

weathered granite.

**4.1 Particle gradation**

**147**

fracture distribution of section A is larger than that of section B.

$$r\_{\rm A} = 0.243h^{0.153} \tag{2}$$

where *h* is the depth of granite samples, which was measured from the surface of mount, *m*<sup>A</sup> is the geological year's parameter in section A, and *r*<sup>A</sup> is the geometric progression constant in section A.

The power function relationships between *h* and *m* (or *r*) in section B are shown as follows:

$$m\_{\rm B} = \text{3.729h}^{-0.747} \tag{3}$$

**Figure 4.** *Change of parameters m and r for samples at different depths: (a) section A and (b) section B.*

main cause of the brighter colors of the rocks. Geng et al. [10] noted that the amphibole was bluish-green, and the biotite was yellow in Mount Yunzhong. In addition, Geng et al. [10] described the main body of the granite as a coarse grain (porphyritic granite), with fine-grained granite on the edge. The three types of samples used in this chapter had quartz (mean 40.3%) and feldspar (mean 54.3%) as the dominant minerals present with smaller amounts of mica (mean 1.3%), amphibole (mean 2%), hematite (0.5%), vermiculite (1%), and unknown (1%)

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

Based on the geometric fractal theories and some assumptions, Fukumoto [4] proposed a gradation equation for decomposed granite soils by using mathematical statistics method and made it possible to quantificationally describe the weathering process of granite by using a certain mathematical model to evaluate the particle breakage of weathered rock. Because Fukumoto's model is more scientific and easier

**Figure 4** shows changes of parameters *m* and *r* for the samples at different

The results of statistical analysis indicate an approximate power function relationship between *h* and *m* (or *r*), and the correlation of relationship was relatively good. The power function relationships between *h* and *m* (or *r*) in section A are

where *h* is the depth of granite samples, which was measured from the surface of mount, *m*<sup>A</sup> is the geological year's parameter in section A, and *r*<sup>A</sup> is the geometric

The power function relationships between *h* and *m* (or *r*) in section B are shown

*Change of parameters m and r for samples at different depths: (a) section A and (b) section B.*

*<sup>m</sup>*<sup>A</sup> <sup>¼</sup> <sup>3</sup>*:*324*h*�0*:*<sup>706</sup> (1) *<sup>r</sup>*<sup>A</sup> <sup>¼</sup> <sup>0</sup>*:*243*h*<sup>0</sup>*:*<sup>153</sup> (2)

*<sup>m</sup>*<sup>B</sup> <sup>¼</sup> <sup>3</sup>*:*729*h*�0*:*<sup>747</sup> (3)

to use, this model has been widely used in describing the process of rock weathering. Thus, this model was also used in this chapter to describe the

weathering process of in situ weathered granite.

materials.

**3. Weathering process**

depths of mountain profile, *h*.

progression constant in section A.

shown as follows:

as follows:

**Figure 4.**

**146**

$$r\_{\rm B} = 0.269h^{0.168} \tag{4}$$

where *m*<sup>B</sup> is the geological year's parameter in section B and *r*<sup>B</sup> is the geometric progression constant in section B.

Actually, the geological year's parameter, *m*, reflects the degree of geological actions (including physical actions and chemical actions) [11]. The deeper the granite is buried, the less the geological action will affect it. The above results indicate that *m* was close to zero at a depth of 20–25 m under the surface of the mount in sections A and B, which indicate that the physical and chemical actions on the granite in this research can be negligible at this depth. The geometric progression constant, *r*, represents the integrality of rock. The *r* of section A and section B studied in this chapter was close to a certain value at a depth of 25 and 20 m, respectively, which indicates that the granite in Mount Yunzhong was close to the complete unweathered state at a depth of 20–25 m.

It can be found from the results that the *m* of section A was larger than that of section B at the same depth, indicating that the ability of section A to resist geological and climatic environment was worse than that of section B. On the other hand, the *r* of section A was smaller than that of section B at the same depth, which illustrates that the integrality of granite in section A was worse than that in section B [11]. Although section A and section B are under the same geological and climatic environment, the values of *m* (or *r*) are different between these two sections. The main reason for the difference was the difference in internal properties (e.g., the mineral composition of rocks) of weathered granite between these two sections. Of course, some external factors could not be excluded; for example, the probability of fracture distribution of section A is larger than that of section B.

## **4. Particle breakage characteristics**

Many aspects, such as particle gradation, mineral composition, blows per layer, and stress level, can influence the characteristics of particle breakage of compacted weathered granite.

Hardin [12] proposed the concept of relative breakage (*B*r), which was achieved from the variation in particle size distribution curves before and after loading. Relative breakage can embody the overall change in particle size distribution before and after loading and overcomes the shortcoming of using single index of sieving test results (percentage of particles passing a given sieve size or sieve size corresponding to a given percentage passing) as the evaluation index for particle breakage [13–16]. In view of the above, *B*<sup>r</sup> has been widely used in evaluating soil particle breakage characteristics, because it can represent the basic attribute of the soil material and is more scientific and reasonable to use.

#### **4.1 Particle gradation**

Standard heavy compaction tests on four red-brown samples and four gray samples of weathered granite with different gradations under optimum moisture content conditions were investigated. Sieving tests were implemented on the samples before and after compaction, and the uniformity coefficient (*C*<sup>u</sup> = *d*60/*d*10) and relative breakage (*B*r) of the samples before and after the compaction test were calculated. The relationship between *C*<sup>u</sup> and *B*<sup>r</sup> is shown in **Figure 5** [11]. The test results show that *B*<sup>r</sup> decreased with the increase of *C*<sup>u</sup> which indicates that as the *C*<sup>u</sup> of weathered granite increased, the degree of particle breakage was reduced because of the enhancement of the intergranular locking effect. In addition, it can be seen

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

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 than that of the gray sample [11].

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 charac-

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

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

teristics of weathered granite [11].

*Relationship curve between mineral content and Br.*

**Figure 7.**

*Weathered Granite Soils*

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

showed obvious particle breakage characteristics [11].

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

of subgrade [11].

**149**
