Classification of Engineering Properties of Tropical Boulder in Completely Weathered Granite in Johor, Malaysia

Engineering properties of tropical weathered granite mass have been widely investigated and classified for engineering purposes. However, the engineering properties of tropical boulder in weathered granite profile is poorly understood and not well classified. This study aims to examine and classify the physico-mechanical properties of granite boulder in completely weathered zone. A total of 34 in-situ boulders were examined from two granite quarries located in Southern Johor, Malaysia. Microstructure-mineralogical alterations were analyzed based on petrographic analysis and scanning electron microscopy (SEM). The mechanical properties were including dry density, porosity, point load strength, uniaxial compressive strength and permeability. Three properties were identified as significant indicators to differentiate between tropical boulder and completely weathered granite when it is evaluated from the soil investigation drilling work namely; texture characteristics, discolourations and degree of weathering. Analysis revealed that the alteration of microstructures and minerals such as feldspar, biotite, and plagioclase from corestone (Grade I/II) to saprolite (Grade IV/V) zone were significantly reduced the dry density, point load strength, uniaxial compressive strength and permeability with 32%, 99.5%, 98.6% and 84.8%, respectively. It has also significantly increased the porosity up to 11.6 times or 1065% from corestone to saprolite. The significant different of physico-mechanical properties of material surrounding boulder due to weathering can be classified and useful in evaluation of geotechnical design and geological engineering applications.

Optimizing the Grouting Design for Groundwater Inrush Control in Completely Weathered Granite Tunnel: An Experimental and Field Investigation

Groundwater and mud inrush disaster from completely weathered granite presents a huge difficulty for tunnel construction, which requires the grouting measurement with favorable performance. To propose the optimal material parameters for grouting, numerous tests, including strength, permeability, and anti-washout, were conducted to evaluate the effects of grouting filling ratio (GFR), curing age and water velocity on the grouting effect. The test results show that: (1) The hydraulic property of completely weathered granite can be significantly improved by increasing the grouting volume and curing age. In particular, when GFR ≥ 48%, the cohesion and internal friction angle increased to about 200 kPa and 30°, which were more than three and ten times of that pre-grouting. (2) With the increase of GFR, the permeability exhibited three stages: Slowly decreasing stage, sharply decreasing stage and stable stage. When increased from 32% to 48%, the permeability coefficient sharply decreased two orders of magnitude, namely from 4.05 × 10−5 cm/s to 1 × 10−7 cm/s. (3) The particle erosion rate decreased sharply to below 10% in the low water velocity (v ≤ 0.2 m/s) when GFR ≥ 48%, but still exceeded 50% when v ≥ 0.4m/s. The results indicated that the grouting volume of GFR = 48% was a suitable grouting parameter to reinforce the completely weathered granite, particularly in the low water velocity condition. The field investigation of hydraulic-mechanical behaviors in the Junchang tunnel indicated that the grouting effect can be improved markedly.

Effects of Initial Porosity and Water Pressure on Seepage-Erosion Properties of Water Inrush in Completely Weathered Granite

In order to investigate the water inrush mechanism in completely weathered granite, a large-scale triaxial testing system is designed and manufactured, which can induce the mass transfer and monitor the flow properties. Using this system, the effects of water pressure and initial porosity on the mass transfer and flow properties were determined, and the relative critical conditions for water inrush were proposed. The results indicate that (1) the particle transfer could cause an increase in porosity, permeability, and water inflow, which is the essential reason for water inrush in completely weathered granite. (2) Due to the effect of particle transfer, the flow properties may change from a Darcy to a non-Darcy flow, which is a key signal for water inrush. (3) With the increase of water pressure, the mass transfer, permeability, and water inflow increased gradually, and a critical value (p=0.6 MPa) that caused the water inrush was obtained. Furthermore, with the decrease of initial porosity, the mass transfer and flow properties were suppressed rapidly, and a critical porosity (0.23) to anti-inrush was observed. The results obtained can provide an important reference for understanding the mechanism, forecasting the risk, and taking the effective control measures for water inrush.