The primary methods utilized by Zebra Environmental Corp. for soil sample acquisition are done by utilizing the Macro-Core Soil Sampler, LB sampler, and the Dual Tube Method. These sampling devices work best in medium- to fine-grained cohesive materials such as silty clay soils or sediments. The Core Samplers can also be used successfully in sampling medium-to coarse-grained sandy materials with some fine to medium gravels when core catchers are used.
A major advantage of the Macro-Core Sampler is that it is one sampler with two sampling options. When sampling from the ground surface or continuous sampling from cohesive soils, ZEBRA utilizes the Open-Tube Method. If sampling from below the ground surface in a previously cored probe hole, or in unstable soils, ZEBRA utilizes the Closed-Piston Method.
The Macro-Core® Piston Rod Sampler is not designed for driving through undisturbed soil. A probe hole must be opened above the sampling interval either by removing continuous soil cores with an open-tube sampler, or by advancing a Macro-Core® Pre-Probe to depth.
Once a hole is opened to the appropriate depth, an assembled MC Piston Rod Sampler is advanced through any slough material to the top of the next sampling interval. Extension rods are inserted through the probe rod string and threaded onto the MC Stop-Pin Assembly. When unthreaded; the stop-pin is removed from the tool string with the extension rods. (MC Piston rod is removed with stop-pin if MC Stop-Pin Coupler is utilized). With the point assembly now released, the tool string is driven into the subsurface to fill the sampler with soil. The point assembly is later retrieved from the sampler with the liner and soil core.
Loose soils may fall from the bottom of the sampler as it is retrieved from depth. The MC Core Catcher alleviates this problem. Excellent results are obtained when the core catcher is used with saturated sands and other non-cohesive soils. A core catcher should not be used with tight soils as it may actually inhibit sample recovery. Constructed of PVC, the core catcher is suitable for use with all Direct Push liners.
The Large Bore Sampler
The LB Sampler is a solid barrel, piston sealed, direct push device for collecting discrete interval samples of unconsolidated materials at depth. This is a device that utilizes the Closed-Piston Method of sample extraction from the sub-surface. There are two different interval lengths for the LB Sampler...ZEBRA has both the 2' and the 4' LB Sampler available to any project.
The Large Bore (LB) is used primarily as a discrete interval sampler; that is, for the recovery of a sample at a prescribed depth. In certain circumstances, it is also used for continuous coring.
The assembled Large Bore Sampler is connected to the leading end of a probe rod and driven into the subsurface using a Direct Push Soil Probing Machine. Additional probe rods are connected in succession to advance the sampler to depth. The sampler remains sealed (closed) by a piston tip as it is being driven. The piston is held in place by a reverse-threaded stop-pin at the trailing end of the sampler. When the sampler tip has reached the top of the desired sampling interval, a series of extension rods, sufficient to reach depth, are coupled together and lowered down the inside diameter of the probe rods. The extension rods are then rotated clockwise (using a handle). The male threads on the leading end of the extension rods engage the female threads on the top end of the stop-pin, and the pin is removed. After the extension rods and stop-pin have been removed, the tool string is advanced an additional 24 inches. The piston is displaced inside the sampler body by the soil as the sample is cut. To recover the sample, the sampler is retrieved from the hole and the liner containing the soil sample is removed.
The Dual Tube Soil Sampling System
While the use of a sealed samplers (i.e. LB or Macro Core Sampler) has proven to yield representative samples, a considerable time investment is required when coring depths exceeding 20 feet. The Dual Tube Soil Sampling System offers an efficient method of collecting continuous soil cores with the added benefit of a cased hole.
Dual Tube Sampling Systems are efficient methods of collecting continuous soil cores with the added benefit of a cased hole. Dual tube sampling uses two sets of probe rods to collect continuous soil cores. One set of rods is driven into the ground as an outer casing. These rods receive the driving force from the hammer and provide a sealed hole from which soil samples may be recovered without the threat of cross contamination. The second, smaller set of rods are placed inside the outer casing. The smaller rods hold a sample liner in place as the outer casing is driven one sampling interval. The small rods are then retracted to retrieve the filled liner.
Dual Tube Sampling Benefits include:
-Continuous coring for faster sampling in intervals over 20-feet
-Cased hole eliminates cross contamination
-Optional solid drive tip seals system for driving to top of sampling interval or for split interval sampling
-Perform bottom-up pressure grouting while retracting outer casing
-Set monitoring wells through outer casing after collection of soil cores
The RS60 has a universal drive head that allows the sampler to work with either 3.25-, 2.125-, or 1.5-in. probe rods. A large liner profile allows these liners to be safely cut with minimal effort.
Option 1: Open Tube Sampling
The largest member of the Geoprobe soil sampler family, the RS60 sampler retrieves a soil core nearly 2.5 in. (60 mm) in diameter and is widely used where large soil cores are needed. A 3.25 in. probe rod serves as the sampler sheath. And, unlike all other Geoprobe sampling applications, the 3.25 in. probe rod is driven with the male end of the rod on the leading end of the sampler. A cutting shoe with a spacer ring is threaded on the male end of the probe rod, and a liner is inserted through the opposite end of the probe rod. The RS60 drive head is threaded onto the female end of the sampler and you’re ready to go!
If 2.125 in. or 1.5 in. probe rods are to your liking, simply thread the appropriate Macro-Core drive head into the ID of the RS60 drive head. The sampler is then operated as an open-tube sampler.
Option 2: Closed Piston Sampling
When “open hole” continuous soil sampling is hindered by slough or probe hole cave in, the RS60 sampler can be used with a closed piston option. This option simply utilizes a center probe rod which holds a Piston Point (18835) inside the Cutting Shoe (18891) preventing any soil from entering the sampler until the Piston Rod (1.25-in. probe rod) is removed. The RS60 Closed Piston Assembly also requires the RS60 Closed Piston Drive Head (18773), the RS60 Center Rod (19027) and a 1.25-in. Centering Drive Cap (12943).
With the use of 3.25-in. outer rods and 1.25-in. inner rods, the RS60 Closed Piston System is driven like a dual tube system – inner and outer rods are added as the tool string is advanced. Once the sampling depth has been reached, the inner rod string is removed, then the 3.25-in. outer casing is advanced to collect the sample material. After the sample fills the liner, the outer casing is retracted to retrieve the soil core. With the patent pending liner profile, the liner can be safely and easily cut for sample access
The MC5 system features a new, aggressive thread design which translates into longer tool wear for the most popular soil sampler in the Direct Push Industry.
Times have changed since the first Macro-Core tooling was developed in 1994. Machines are larger, hammers are more powerful, and field operators push tool strings deeper into the subsurface. The formula to meet these demands began with designing a larger MC Sampler Tube (increased the OD from 2.125 in. to 2.25 in.) which led to beefing up the thread design. These improvements to the already robust Macro-Core sampler make a great product perform even better in the field.