Before utilizing mass rocks for foundation construction, it is crucial to investigate their properties thoroughly. This is because these properties play a significant role in determining the behavior of the foundation structure and can have a substantial impact on any future issues that may arise.
Exploring the various properties of rock mass is necessary to ensure a solid foundation for any construction project. These properties are essential in understanding how the rock mass will interact with the foundation structure and can help anticipate any potential issues that may arise.
Investigating the properties of rock mass can provide crucial insights into its suitability for foundation construction. By understanding these properties, engineers can determine the strength and stability of the rock mass and how it may affect the foundation structure in the long run.
In summary, investigating the various properties of rock mass is a crucial step in ensuring the successful construction of any foundation. By thoroughly exploring these properties, engineers can anticipate potential issues and develop solutions to ensure the safety and stability of the foundation structure.
Fig.1: Rock Massfor Foundation Construction
Investigation of Rock Mass Properties for Foundation Construction
1. Rock Mass Weathering
Weathering is the process of degradation and disintegration of intact rocks, leading to a reduction in their ultimate strength. Several factors can cause weathering, including environmental influences, leaching of ground water, and chemical attacks. The material that undergoes weathering is often removed from its original location due to erosion, resulting in the formation of cavities, fissures, and joints in rocks. This can increase the compressibility and permeability of the rock mass, which may not be desirable for construction of foundation structures. The extent of weathering can vary depending on the location, with some claims suggesting an influence up to 100 meters. Weathered mass rock can sometimes provide false indications of soil bearing strength, for example when small cores are drilled in partially weathered sandstone, generating loose debris that gives inaccurate results. The resistance of rocks to weathering depends on their type and mineral composition, with limestone (except for chalk) generally exhibiting greater resistance compared to mudstone, siltstone, and shale. Fluctuations in ground water can also lead to degradation of mass rocks containing pyrite, such as shale and mudstone, due to chemical and bacterial reactions. However, certain chemical solutions can also create fissures and caverns in limestone, which may be difficult to investigate if covered by younger rock layers. Geophysical methods can be used to explore such features to some extent. Cavities in limestone rock mass are often filled with loose materials, resulting in low bearing capacity and making them unsuitable for spread and pile foundations. If foundation placement on such rock mass cannot be avoided, design measures should be taken to bridge across the cavities.
2. Faulting of Rock Mass
In regions that are susceptible to earthquakes, it is important to conduct specific investigations into the faulting of rock formations. While some may argue that movements along fault planes may have ceased over time, it remains necessary to consider faulting during the design of foundation structures in such areas. This is particularly important in regions that are prone to mining subsidence or experience seismic activity.
One of the key features of rock masses that requires investigation in earthquake-prone regions is faulting. Faulting refers to the movement or displacement of rock along a fault plane. While it may be tempting to assume that such movements have ceased over time, it is important to conduct thorough investigations to better understand the nature and extent of faulting in a given area.
This is particularly important when designing foundation structures, as faulting can have a significant impact on the stability and safety of such structures. Furthermore, faulting is of particular concern in regions that are prone to mining subsidence or experience seismic activity, as these factors can exacerbate the effects of faulting and increase the risk of damage or collapse. Therefore, it is crucial to conduct comprehensive investigations into faulting in such areas to ensure the safety and stability of infrastructure and buildings.
Fig.2: Faulting of Rock Mass
3. Jointing in Rock Mass
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Joints are fractures that occur in rock masses and can result in small relative movements of rocks on either side of the joint plane. The compressibility of a rock mass, which is loaded under a foundation, is influenced not only by the spacing of the joints but also by the width of the joints. Additionally, if the joints are inclined towards an excavation and filled with loose material like weak clay, it can jeopardize the stability of the excavation and potentially lead to the failure of the foundation bearing on an irregular rock surface. Therefore, it is necessary to conduct examinations and explorations of the rock core to determine parameters such as joint spacing, width, and inclination for proper assessment and design of foundations on rocky terrain.
4. Strength of Intact Rock
The bearing strength and compressibility of a jointed rock mass may play a role in determining the strength of intact rock. Furthermore, values derived from splitting tests and uniaxial compression tests can help determine if explosive excavation is feasible for a foundation, or if excavated materials can be used for construction purposes.
References
The book “Foundation Design and Construction” by MJ Tomlinson was published in 1999 and is currently in its 6th edition. It is a widely used reference for engineers and architects involved in designing and constructing foundations for various types of structures. The book covers topics such as site investigation, soil mechanics, foundation types, and construction techniques.
In a research article published in PLoS ONE in 2015, Qiang Xu, Jianyun Chen, Jing Li, Chunfeng Zhao, and Chenyang Yuan presented a study on the constitutive model for jointed rock mass. The research aimed to develop a better understanding of the behavior of jointed rock masses, which are commonly encountered in engineering projects involving rock structures. The researchers developed a new constitutive model for jointed rock mass based on laboratory testing and numerical simulations. The proposed model was found to accurately predict the deformation and failure behavior of jointed rock masses under different loading conditions. The study’s findings are expected to have significant implications for the design and construction of structures in rock formations.