Mistakes in data recording have never been more costly. Spatial data helps aircraft fly safely, money is stored on a server and reflected as numbers on a screen, and the odometer reading on a vehicle helps determine its value. Society generally accepts those coordinates, figures and numbers as truth, so when they differ from reality it can lead to chaos and unwise decisions.
By comparison, recording soil sampling data accurately and using proper sampling equipment may seem insignificant. But whether it’s choosing the location for a new home or rotating crops that feed an entire country, this data helps people make important, long-lasting decisions.
Thankfully, the world of soil sampling is not as time sensitive as a plane midflight. We have ample opportunities to use collection equipment precisely and record, check and recheck data. With soil quality judged by data derived from the sample, it’s extremely important to record data and practice accurate collection procedures at every opportunity. Properly implementing a few fundamental pieces of equipment and recording basic elements during sampling can save time, reduce costs and streamline operations for experienced geotechnical engineers and those just breaking into soil sampling.
The Minnesota Pollution Control Agency and the U.S. Environmental Protection Agency have established guidelines and data crucial to an accurate and thorough soil sampling project. Much of this data can be recorded in the field before sending the sample for lab testing. Establishing a recording system, including a dedicated soil sample log and pre-labeled containers, prior to entering the sample site is crucial. Preparing materials beforehand can allow a contractor to focus on recording data accurately and implementing the proper sampling equipment — from cathead kits and safety hammers to split-spoon samplers — instead of fumbling through the process. Here’s how to begin.
Start by assigning the overall sample area a unique identifier such as SA-1 — Sample Area One. From there, the terrain layout and soil sample requirements will largely dictate the labeling method used, but sample areas can be broken down further into sample sites, like SS-1, SS-2, and so on. Borings can then be assigned to specific sample sites within the overall sample area. For example, SS-1 can contain borings 1-12, or B-1, B-2, etc., with the individual boring containers — as well as the logbook — being labeled with this information.
Referencing and recording data will be much more fluid after establishing an identification system like the one above. From there, the contractor can decide what specifics to record on individual sample containers and which to detail in the logbook. It’s good practice to record some data, like boring coordinates, dates and times, in both locations.
Date and Time
Once contractors label containers, set up the logbook and establish data recording priorities, they should note the date and time they arrive at the sample area and the times for every boring within a sample site. For example, a contractor arrives at SA-1 at 9 a.m. They take their first boring, B-1, at the first sample site, SS-1, at 9:15 a.m., the second boring at 9:20 a.m., etc. Be sure to record the last boring time along with the time range for the sample site, SS-1, before moving on to SS-2 and starting the process over. With soil conditions constantly changing, the tiniest detail from time of year to time of day can have an impact on the results and their interpretation.
Soil and Weather Conditions
Take note of the weather conditions upon arriving at the sample area and consider how these may change during the collection process. Note the soil conditions. A contractor may divide a sample area into sample sites based on soil type or conditions, but individual boring conditions can still vary. Soil color may also be important to note, as it can give clues to the mineral content and soil condition.
Soil condition descriptors can be anything that seems relevant: smooth, gritty, sand, clay and more. At this point, soil conditions can also allude to specialty equipment requirements and techniques that may be needed.
Sampling Techniques, Drill Type, Boring Depth and More
If soil is determined to be sandy and loose, this may call for switching to a hollow-stem auger. Hollow stem augers create a natural casing in the soil and protect the sample from possible contamination by unstable surrounding soil. The center rod and plug of a hollow stem auger can be removed, providing a clean path to insert a soil sampler. If the environment makes this equipment change necessary, be sure to record it in the notes.
A sandy and confined environment may also call for a more maneuverable drill, such as a hydraulic earth drill or post hole digger. These drills can be paired with tripod kits to ensure accurate sampling down to 35 feet. More robust drills can sample in tough clay and still remain maneuverable and compact by utilizing stabilizing legs, tower kits, cathead kits and manual safety hammers to reach depths down to 100 feet. Truck- and trailer-mounted drill options can reach similar depths. These may come with automatic hammers to ensure accuracy and make quick work of tough soils in more easily accessed sample sites. Look for manufacturers that make soil sampling OEM accessories that pair with their drills to ensure compatibility, straightforward setup and smooth operation.
Record any equipment changes due to changing soil conditions, whether that’s just switching augers, using hand sampling tools or bringing in an entirely different drill rig. This will make a good reference for later to trace irregular sample results back to possible equipment-soil mismatches.
Equipment model names and drill types are also important to note. This may be the same for an entire sample area or may change from site to site based on the soil conditions and sample requirements. For example, a contractor may use a hydraulic earth drill to reach a target depth and then use a manual or automatic safety hammer to drive in a split-spoon sampler. These are all essential aspects of the sampling process that should be recorded. This helps in case of sampling anomalies or user errors. That might include forgetting to discard the top few inches of a sample from a split spoon taken without the use of a hollow-stem auger, as that part of the sample commonly contains material dislodged from the walls of the borehole.
Additionally, note the borehole depth and size of the soil sampler: “B-1 taken at a borehole depth of 20 feet with a 24-inch split-spoon sampler.” At this point in data recording, consider noting the blow counts needed to drive in the soil sampler to the desired depth. This should be noted for every borehole.
Photos, Photos, Photos
Photos are an important part of the documentation process. While a smartphone camera will do, a dedicated field-ready camera with proper weather sealing and a removable memory card is ideal for collecting photos throughout the sampling process. Take landscape shots of the sample area to have on hand for cross-referencing with a map and boring coordinates. This can often provide confirmation or answers to questions that may arise after testing. Pictures of the sampling process at every borehole can also be useful and shed light on mistakes when reviewed later. Additionally, the surrounding soil, entire soil sample and any individual sections chosen from the sample should be photographed for later reference and note-taking confirmation. The camera used for site photography can also provide an excellent third source for referencing soil date and time, in addition to the logbook and containers.
Handling the Sample
Different industries and contractors establish their own standard operating procedures for handling and storing samples. Contractors usually follow overall guidance to not do anything to alter the sample’s chemical properties, based on which properties are of interest. However, an airtight container for storage in the field is essential. From there, place samples in the shade, preferably in a cooler, until they can be refrigerated or sent to a lab. Individual labs may offer further shipping and storage recommendations.
While the impact of soil sampling may seem to rely solely on the trusted systems set in place — like a testing lab — to provide reliable data, it’s important to remember that the person in the field is still flying the plane. A contractor’s actions determine how closely the soil sample arriving at the lab represents the soil at the jobsite. A well-constructed soil-sample log, diligent note taking and proper sampling equipment ensure every borehole counts and any decisions made will be wise.