DNR Report 347: 2003; Analysis of Drilling and Sampling Techniques Used to Obtain Representative and Accurate Samples in Coarse Sand and Gravel Deposits

Introduction extracted from page 1 of the report:

Introduction  Drilling has traditionally been a cost effective means of evaluating sand and gravel deposits. It is used to collect samples that are representative of the deposit. These samples are typically sent to a material lab for sieve analysis to determine the particle size distributions. The particle size distributions of the samples help determine the overall texture of the deposit, which is a key factor in determining the value of the deposit. However, different drilling equipment specifications, sample collection techniques, and reduction techniques all affect the final results of the sieve analysis, which in turn can dramatically affect the final evaluation of the deposit.



This study was completed to analyze several different drilling and sampling techniques. The purpose was to determine the best methodologies to obtain representative and accurate samples in coarse sand and gravel deposits. Multiple samples were collected using several different sampling techniques to compare the effects of each technique on the material sampled (particle size distribution of the material). Five primary hypotheses were tested: (1) Drilling with larger diameter augers represents coarser sediment (> 1.5") more accurately than smaller diameter augers, (2) Channel sampling represents coarser sediment more accurately than drilling, (3) Large channels represent coarser sediment more accurately than small channels, (4) Sediment sampled directly off of the auger under-represents coarse sediment, and (5) Sample splitting techniques affect the final size distribution. A test site near Bayport, Minnesota, was selected where a sand and gravel pit provided a good exposure of a relatively homogeneous cobble-rich sand and gravel deposit. The site provided good accessibility for both drilling and channel sampling (Figures 1 and 2).


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Report 347: Analysis of Drilling and Sampling Techniques Used to Obtain Representative and Accurate Samples in Coarse Sand and Gravel Deposits
(40 pages, 8.5 x 11 inches, 3.23 MB)
Author: J. Ellingson

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