EVALUATION OF PARAMETERS INVOLVED IN THE EROSION OF LIMESTONE BY SOLID PARTICLE IMPACTION

The effect of solid particle impact on limestone was investigated in a laboratory setting, using Silurian limestone samples gathered from near Columbus, Ohio. A staining method revealed that the tested samples are dolomitic fossiliferous limestone with various amounts of organic material. 1 × 2 inch slabs of the limestone sample were polished and placed in a simple water circulation tank to test the effects of erosion from suspended solid particles. The solid particles used were quartz, feldspar and clays taken from soil in New Concord, Ohio. The particles were separated by size into four categories: fine sand, coarse silt, fine silt, and clay. The sample rock slab was held perpendicular to the current. During the test, average flow speed, duration of impact, density of suspended sediments, and net weight loss of the rock slabs were measured. The surface texture of limestone after the impact was examined under an SEM.

The single major factor of uncertainty in this experiment is the turbulent flow created by the water circulation. Due to the turbulence, solid particles were not uniformly distributed and the effect of the sample’s orientation on the rate of erosion could not be accurately measured. However, the effect of turbulence on erosion rate was minimized by taking the average flow speed over 30 seconds or longer and by monitoring the concentration of suspended sediments before and after each run in the water tank. The samples were in the tank with the suspended sediments for 8 hours to 72 hours.

In spite of the limitations, our experiment has indicated that limestone is eroded by solid particle impact at a rate of 0.01 gram to 0.02 gram per 12 hours under the impact of fine silt particles at a flow speed of 0.5 m/s. This is equivalent to an erosion of 0.25 cm to 0.50 cm per year, provided that the limestone surface is unprotected and is under continuous impact. Using the SEM observations of the eroded limestone surfaces, it can be suggested that the rate of erosion also depends on the texture, structure and composition of the limestone. Limestone made of mixed grain sizes such as a mixture of organic materials, micrite and microspars tend to be eroded at a faster rate.