Slake Durability Test
The Slake Durability Test is a geotechnical procedure used to assess the resistance of rock samples, especially shales and other weak rocks, to disintegration when subjected to wetting and drying cycles. The test aims to simulate natural weathering processes and determine the durability of rock materials under cyclic environmental conditions. The results are crucial for evaluating the stability and longevity of rock masses in construction and engineering projects, such as tunnels, slopes, and foundations. The standard method for the Slake Durability Test is outlined in ASTM D4644.
Descriptions and Procedure
Apparatus Required
- Slake durability testing apparatus (including two drums with mesh sides, typically 2 mm openings)
- Balance with an accuracy of 0.01 g
- Drying oven
- Water bath
- Timer
- Sample preparation tools (e.g., hammer, chisel)
Procedure
1. Sample Preparation
- Obtain rock specimens from the field, ensuring they are representative of the rock mass.
- Break the rock samples into approximately equal-sized pieces, each weighing between 40 and 60 grams. Aim to have 10 pieces per drum, with a total mass around 500 grams for each set.
2. Initial Weighing
- Dry the rock specimens in an oven at 105°C for at least 48 hours or until a constant mass is achieved.
- After drying, allow the samples to cool to room temperature in a desiccator to prevent moisture absorption.
- Weigh the dry rock specimens collectively and record the initial mass (M1).
3. First Cycle
- Place the rock specimens in the slake durability testing drums. Each drum should have approximately 10 pieces of rock.
- Submerge the drums in a water bath at room temperature and rotate them at a speed of 20 rpm for 10 minutes.
- Remove the drums from the water bath and drain the water.
- Gently remove the rock fragments from the drums and dry them in the oven at 105°C to a constant mass.
- Cool the dried specimens to room temperature in a desiccator and weigh them. Record the mass after the first cycle (M2).
4. Second Cycle
Repeat the wetting and drying process for a second cycle:
- Place the dried rock specimens back in the drums.
- Submerge the drums in the water bath and rotate at 20 rpm for 10 minutes.
- Remove the drums, drain the water, and gently remove the rock fragments.
- Dry the specimens in the oven at 105°C to a constant mass.
- Cool to room temperature in a desiccator and weigh the dried specimens. Record the mass after the second cycle (M3).
Calculations
Slake Durability Index (SDI)
Calculate the slake durability index for each cycle as follows:
𝑆𝐷𝐼𝑛=(𝑀𝑛𝑀1)×100
where 𝑀𝑛 is the mass of the rock specimens after the 𝑛n-th cycle (e.g., M2 for the first cycle, M3 for the second cycle) and 𝑀1 is the initial dry mass.
First Cycle SDI (SDI1):
𝑆𝐷𝐼1=(𝑀2𝑀1)×100
Second Cycle SDI (SDI2):
𝑆𝐷𝐼2=(𝑀3𝑀1)×100
Data Interpretation
Slake Durability Classification
- The slake durability index is used to classify the durability of the rock. Higher SDI values indicate more durable rocks, whereas lower values indicate rocks more prone to disintegration.
Typical Classification Ranges
- SDI > 95%: Very high durability
- 85% < SDI ≤ 95%: High durability
- 60% < SDI ≤ 85%: Medium durability
- 30% < SDI ≤ 60%: Low durability
- SDI ≤ 30%: Very low durability
The second cycle SDI (SDI2) is typically used for classification because it gives a more realistic representation of the rock's durability under repeated wetting and drying conditions.
Summary Table
The Slake Durability Test is essential for assessing the weathering resistance of rock materials, providing valuable data for predicting the long-term stability and performance of rock structures in various engineering applications.