Time changes every industry and the geotechnical sector is no different. Gone are the days in which drilling revolved around rough estimates and ‘that’ll do’ mentalities. In today’s geotechnical industry, the need for precision, accuracy and watertight results is paramount. One of the ways in which a geotechnical site investigation company such as Borehole Solutions can ensure this kind of quality, is through sample testing. There are various forms of sample testing, and each one best suits certain geotechnical investigations. One thing is for sure, however, and that’s that they’re vital.
In the blog below, the team here at Borehole Solutions are discussing all of the different situations that call for methods of sample testing. As a company, Borehole Solutions has carried out sampling in fields and cities alike; we have worked both here in the UK as well as abroad. Within this blog, we will also run through what the benefits of each of these sampling methodologies are.
Cone Penetration Testing (CPT)
Cone penetration testing is one of the more standard sample testing methodologies in the world of geotechnical drilling companies. It involves inserting an instrumented cone downwards through the ground at a controlled rate. This testing process is used to determine a soil’s characteristics. These characteristics include: the relative density of the soil, the stratigraphy of the soil and also other parameters such as pore pressure, both dynamic and static. The main benefits to CPT are that it is efficient both in terms of time and cost, and can provide accurate real-time data.
Standard Penetration Testing (SPT)
Standard penetration testing is the most common form of exploration and sampling test used in the drilling industry, worldwide. SPT works by hammering a thick-walled sample tube into the substrate at the bottom of a borehole. An N-value is calculated by looking at the number of hammer blows it takes to further the tube by a certain distance. The primary benefits of standard penetration testing, and part of why it’s gone on to see such widespread use, is that it provides an accurate relative density from sand and gravel deposits. The undisturbed nature of samples from these kinds of deposits, means that obtaining these relative density figures is virtually impossible unless you use SPT. Again, similar to cone penetration testing, this is a sample testing method that’s inexpensive and easy to carry out, whilst still returning incredibly useful data.
Vane Shear Testing
The vane shear test is another prominent in-situ method of sample testing. It’s especially widespread in Britain, the geology of which largely comprises clay-type formations. It’s used in fully saturated clays without disturbance. The purpose of this sample testing method is to provide an estimate of the sample’s shear strength (undrained). How does it work? The shear vane equipment itself is easy-to-use and highly portable. The test consists of inserting the vane into the ground and rotating it. The torque needed to cause soil failure is then recorded and subsequently converted into a shear strength reading. This test tends to be carried out in shallower formations. The vane shear test provides reliable data in a prompt and efficient manner.
Piston samples are used in the sampling of more cohesive soil-types; it is one of the sample testing methods that can be used in an open borehole setting. Piston sampling is used in the sampling of clays, silts and sands. The benefits of piston sampling are as follows: its operation is remarkably easy, made easier still by the lack of coring tubes, and it also provides profile descriptions very quickly. Piston sampling can also be used to carry out sample testing below the groundwater table.
The U100 sample testing system is used to take samples in softer formations (clays, gravels, sands and silts). The system typically comprises a steel body tube, a core catcher, a spacing ring and a hardened drive shoe (the edge of which can be either smooth or serrated). A PVC plastic liner is also often used in conjunction with the U100 sampler to obtain undisturbed samples from weak soils, and occasionally some rock formations. U100 sampling can be carried out to depths between 30m and 40m below the ground. Borehole also carries out UT100 testing, which as the name would suggest, is a similar sampling method. However, the UT100 sampling tube offers a thinner profile when compared with the U100 sampling system.
This sample testing method utilises a completely unique sample called the AquaLock. This sampler is used in conjunction with sonic drilling rigs (which is part of the reason why we’re such a big fan of this method) to return core samples of exceedingly good quality. The innovative water trap technology used within the AquaLock sampler ensures undisturbed samples are returned every time, without fail. The AquaLock sampler has a variety of uses and applications; it can be used to undertake mineral sampling, environmental sampling, archaeological sampling, within the installation of wells and many, many more.
You can quickly see just how many different samplers there are available to geotechnical drilling companies like Borehole Solutions. The methods mentioned above are by no means exhaustive, however they are some of the ones more that we more commonly use. Sample testing helps ensure the quality of both the site being investigated and the samples the investigation returns. For this reason, it’s very important. Even more important is that it’s carried out accurately. Knowing which one to use, when and where, requires serious expertise. A lack of proper testing can lead to serious consequences further down the line, and that’s no exaggeration. Especially if you’re sampling for construction purposes. So, if you’d like to find out more about how Borehole Solutions operate, and how we carry out our sample testing, then get in touch!