Soil Compaction Testing

nuclear density gauge test

Soil Compaction Testing is a crucial step in the construction process. Ground that has not been properly compacted can be detrimental to the structural integrity of buildings, retaining structures, roads and pavements, just to name a few. Essentially, proper soil integrity could make or break your structure. Since soils are so critical to a structures reliability you will find that soil compaction testing is required most cases. For instance, most regulatory agencies such as, the Department of Transportation and American Society for Testing and Materials all require laboratory testing. Additionally, you will find that the California and Uniform Building Codes, the geotechnical engineer, and structural engineers will also require soil compaction testing.

Why Compaction Testing is Important

There is a very good reason for all the necessity. Basically, if soil tests are not conducted you risk shifting, cracking, and even the collapse of your building. Roadways could also result in disaster by cracking, sagging, potholes, or even sinkholes. In the end, it’s vital for the success of your structure to ensure you have reliable soil compaction testing. Moreover, having a company that has a seasoned and knowledgeable staff, as well as testing facility, is critical. Not only will a more experienced staff save you time, it will also save you money.

How soil Compaction Testing Works

A soil compaction test begins with samples. After excavation a field technician will collect soil samples. An experienced field technician will gather samples from several locations to attain representative samples of various soil types that may be on site. Each soil type, or mixture thereof, has different properties and can act in different ways. A skilled lab technician will be able to recognize the potential properties of each, and be able to determine best spots for soil extraction. It can also be valuable to take a sample from the stockpile. This is usually done if the technician notices that the stockpile soil has different properties than the other site soil, or because several soil types are being blended together.

Once at the laboratory the process of determining the optimum moisture content and maximum dry density will occur. A lab technician will start by sifting and moisture conditioning of the soil. Once the soil is prepped the soil will go into a cylindrical mold to be compacted at various moisture contents and weighted.

The test is to see how much of the material can be compacted into the same volume at the various amounts of moisture. When a material is too dry it can not compress very tightly. As more water is added, it is able to compact in better and better, so it’s dry density (unit weight calculated removing the water weight) is increased. Once it hits the limit that the material will allow, the water starts displacing the material and the dry density will start dropping, creating a “curve”. The peak of this “curve” is considered the maximum dry density and the optimum moisture for that specific material. Again, it is of vital importance to have an experienced lab for this process.

Nuclear Gauge Testing

The last key step in soil compaction testing involves the use of a soils nuclear gauge. Back at the job site, a field technician uses a nuclear gauge that has two radioactive isotopes (roughly the same mass as the head of a pin), and emits extremely small amounts of radiation into the soil. Inside of the machine there are sensors that detect how much of the radiation makes it back to the machine. One of the sources is for detecting the hydrogen content, which is a direct correlation with the moisture content. The other source is for detecting the wet density.

Using both of these readings, the nuclear gauge calculates the in-place dry density. This number is compared to the maximum dry density that was determined by the lab testing and is expressed in the form of a percentage. Typical requirements are between 90% and 95% of the maximum dry density. If the material changes even slightly, it could drastically affect the results indicating failure. An experienced field technician will notice the change and pull another sample for a curve rather than have the contractor keep trying to work the material wasting time and money.

To find out more about soil compaction requirements in California click here.

Why BSK Associates

Soil Compaction Testing

As mentioned previously, having seasoned field and laboratory technician is key in this process. BSK Associates has been in the industry for over 53 years. Our history in the industry ensures that our clients receives accurate results in a timely manner. We are a dedicated team focused on developing practical, cost-effective solutions for our clients, and working toward constant improvement within our profession.

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BSK strongly believes in giving back to the communities in which we work. We make sure our community involvement goals have a positive impact on the communities which we serve; because, in the end it’s all about community.

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BSK: Gem Lake Dam Project.

BSK: Gem Lake Dam Project.

We are excited to announce that BSK conducted a Geotechnical Engineering Investigation for Gem Lake Dam!

Gem Lake is located on the eastern side of the Sierra Nevada mountain range near June Lakes. This rural area is a hiker’s paradise with beautiful trees and lush vegetation.

Gem Lake Dam was originally built in the 1920’s and is a key element of the Rush Creek Hydroelectric System. In fact, Hydroelectric Dam Systems produce 8-12% of the nations power, making these dam systems all the more important. Additionally, this particular hydroelectric system is considered an eligible renewable energy resource! Hence, all the more reason that BSK is so proud to be a part of this project.

Part of the Federal Energy Regulatory Commission (FERC) requirements is to have the ability to control water levels of these lakes. Thus, ensuring that in the case of a natural disaster, the public will be safe. Southern California Edison (SCE), who own the 3 dams that make up the Rush Creek hydroelectric system, is in the process of retrofitting these dams to guarantee the safety of the residents who live downstream of the dam.

How Are We Helping.

Gem Lake Dam is a reinforced concrete Arch Dam which consists of several arches. BSK’s responsibilities included the Geotechnical engineering investigation for the proposed valve replacement for Arch 8. This consists of; field exploration, laboratory testing, and engineering analysis. Basically, BSK will be assessing the condition of the soil below the new valve. Additionally, we will provide recommendations to the project designers for moving forward. Field exploration on this project began October of 2019. Site reconnaissance included geological survey, rock sampling, and ground resistivity testing. In addition, we conducted laboratory testing on the samples. These tests included; unconfined compression testing of rock; basically measuring how much force is needed to crush the rocks.

Gem Lake History and Findings.

BSK: Gem Lake Dam Project.

This will not be the first time the dam has seen work over its almost 100 years of existence. In fact, shortly after its conception, the dam began to show signs of deterioration. Upon investigation it was found that a high water/cement ratio was used, causing the efflorescence and deterioration. This finding, along with other concrete studies, is why the American Concrete Institute now recommends a water/cement ratio of no more than 0.45 for poured concrete. In turn, these types of regulations and findings led to the conception of what we do at BSK.

Why We Love It.

Earthquakes, floods, fires, and other natural disasters have taught us what needs to be done to keep the public safe. We have learned what our soil, buildings, water, and roads need to withstand natural disasters. Due to this, we have enacted rules and regulations. BSK has Engineers and Geologists that are trained and educated to know how buildings need to be erected; what soil/foundation standards need to be in place. We have inspectors that are licensed to know if a buildings weld joints will react accordingly in an earthquake. We have laboratories that can test if the water system has been exposed to an outside contaminant. In essence, our work at BSK deals with keeping the public safe. Above all, we take pride in knowing that what we do on a daily basis at BSK makes our communities safer and stronger!

BSK has Engineers and Geologists that are trained and educated to know how buildings need to be erected.

BSK: Gem Lake Dam Project.

Lastly, don’t forget to take a look at the view of Gem Lake Dam from a helicopter here.

Follow Us and Like Us:

Want to be in the “know” on upcoming BSK events, community service, and projects?

Like us on Facebook.
Follow us on LinkedIn and Twitter.

Have a question about the services we offer? Check out our webpage @bskassociates.com.

Looking for a Great Places to Work? You’ve found it! We are proud to be Great Place to Work certified. Check out our job opportunities page for more details.

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