**1. Introduction**

As a member of igneous rock family, granite is formed by magma inside the Earth. The main components of igneous rocks are quartz, feldspar, mica, and hornblende [1]. The features of granite include the full crystal-grain structure, hard texture and uniform material, and high compressive strength (120–200 MPa). Because joints exist in feldspar and mica, there are three groups of primary joints in granite. The significant difference (nearly doubled) between the expansion coefficients of quartz and feldspar causes granite surface to crack easily in the process of expansion and contraction. Hence, granite would weather easily, especially the one with coarse grain structure [2]. During the weathering process, granite is also influenced by long-term, geological tectonic movement, and climate changes in the specific geographical environment. Based on the different physical and chemical properties of granite mineral composition and the different degrees of weathering of granite, decomposed granitic soils are generally classified as weak weathering, weathering, strong weathering, and residual [3].

With further improvements to the civil infrastructure, more and more engineering construction projects (roads, railways, dams, etc.) will be built in complex mountainous areas. However, the shortage of building materials is an acute problem 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 characteristics [4–7].

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

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

**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

particle breakage characteristics of compacted weathered granite.

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

*Mineral composition of weathered granite samples.*

red-brown samples.

*Weathered Granite Soils*

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

**Figure 2.**

**Figure 3.**

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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 granite soils in engineering practice.
