Why Deep Foundation Testing is a Lifeline for Your Structure?
Have you ever wondered as to why Roman constructions are so captivating? While the structures built a few decades ago fade and faint, how is it that buildings constructed centuries ago still stand tall and attract the tourists? If these questions engage you, then Deep Foundation Testing concept is something you ought to know. The tenacity of structures built by Romans was predominantly because of the timber piles they used as foundations, which helped them construct strong structures within a short time especially while laying bridges during war times. This is a classic example of deep foundation but how did they test the soil –if it’s ideal for laying piles—is a question that remains unexplored though.
Before we understand the deep foundation, it is pertinent to know what shallow foundation is all about. Due to time, lack of expertise and budget constraints, a large number of contractors switch to the shallow foundation for the completion of the building. In a shallow foundation, the foundation (the base of the structure) will not penetrate the subsurface layer, which means that it’s just a slab foundation for one-storey building usually.
On the contrary, Deep Foundation penetrates the subsurface layers of the earth to give extra support for the buildings and other structures to ensure that they are strong enough to withstand the natural calamities. To be precise, a deep foundation is the transfer of structures’ complete load on to pillars that touch the deepest layers possible for extra durability.
If you are planning to have a two-storey building or skyscrapers, your engineer would surely suggest a deep foundation. However, before going with Deep Foundation, it is crucial to test the soil in the proposed construction site to ensure that deep foundation is carried out seamlessly. These tests—to ascertain whether Deep Foundation can be carried or not in the specific area—form the part and parcel of Deep Foundation Testing.
Types of Deep Foundation Testing:
These are some of the standard deep foundation tests that are carried out by any construction enterprise or an engineer if you have opted for Deep Foundation Testing.
- RIM-Cell Proof Test
- Top Down & Lateral Test
- Split Lateral Modulus Test
- Integrity Test
- Thermal Integrity Profiling
- Osterberg Cell (O-Cell) Static Load Test
- AFT Cell (proprietary service) Test
- Let us delve into each one of them.
O-Cell Bi-Directional Static Load Test:
This is the most sought after full-scale load testing as it is noiseless with near zero vibrations making it ideal in busy areas where other kinds of testing might require special permissions. The Osterberg Cell load test would help analyze the overall information about the drilled shafts/ barrettes. According to a survey conducted by the United States Federal Highway Administration (USHFA), at least 65% of engineers in the USA considered O-Cell as the preferable load testing in 1994 while it touched 90% by 2018. During its initial stages, O Cell method was tested on US 231 Highway Bridge Over the Ohio River in Kentucky. The bearing capacity of the bridge was to be determined and the engineers noticed that the load capacity of this device reached 7mm upward and 34mm downward, thereby giving an accurate and comprehensive picture of the shaft. How are the movements measured in O-cell test? Well, in the United States, electronic gauges are connected to the electronic/ computerized data systems where the results would be reflected and recorded. In an O-Cell test, side shear and end bearing components are separated by default that determines if the construction techniques worked well. Notably, O-cells need to be installed in advanced before the construction begins and cannot be installed on the wooden piles.
RIM-Cell Proof Test:
Touted to be one of the most sought-after technologies in civil engineering, RIM Cell Proof Test requires an engineer to ascertain the performance of the shaft through loading the required shafts at least 1.2 times to the actual design load. Based on the test results, engineers can reduce the impact of the detected source. Some of the advantages of RIM Cell test include reduction of uncertainty, improved reliability, cost-effective, low grout volume requirement, comprehensive verification of base, easy calculation of the load, to name a few.
Top Down and Lateral Test:
In the top-down test, the engineer would keep on exerting pressure on the pile to test as to how much weight the pile can load. In case the pile is destroyed, in the process, the load level would be calculated and a new pile would be installed. In Lateral Test, the pile would be tested by moving back and forth with extreme pressure to ensure that it can withstand the force from any direction. Often used in the deep excavation projects, the foundation structures used in this kind of test are for permanent use. This testing is used for tall structures with deep basements of two or three levels—essentially parking lots.
Split Lateral and Modulus Test:
Also referred to as full-scale modulus test, this test involves applying loads on to piles in a lateral direction wherein each cell is expanded into the rock or the soil. Each cell would be tested by applying the same loads but with designated intervals. Since the analysis in Split Lateral Test Module is complex, this is not so often used unless the proposed structure demands it.
SoniCaliper provides a comprehensive picture of the drilled shaft. After the pile is driven down, information or 3D profiling of the pile would be recorded for at least 10 to 12 inch through specially designed sensors that provide the temperature of the piles. In case, there’s an issue with any of the location of the concrete, it would be reflected in the SoniCaliper readings based on which the pile would be removed and the hole would be filled with concrete. SoniCaliper can be tested up to the depth of 300 inches.
Popularly known as Pile Integrity Test, the name speaks everything about this kind of testing. It is carried out to ascertain the quality of the pile, its integrity, and length of the existing piles of foundations if any. It is ideally carried out in the areas where the proposed construction is carried out in an area where other structures existed before. After the demolition of the previous structures, the length of the existing piles should be ascertained and pulled out before carrying out other deep foundation tests.
Thermal Integrity Profile:
First developed at the University of South Florida, it’s a permanent and non-destructive/ positive test method that is mandatorily used along with along deep foundation testing. During Thermal Integrity Profiling, engineers would record the heat that’s generated by the concrete and the time taken for effective cooling to ensure that the concrete has set in, and it’s ideal to carry out the construction. This test is often followed by Sonic testing and integrity testing. An engineer would understand the issue with the concrete when an average temperature of some depth significantly varies from the average temperature at the other depth. In case of a potential problem, reinforcing cage would be aligned properly.
Based on the above tests and your soil type, your engineer might adopt one or more of these tests to ensure that your structures or skyscrapers are built to withstand natural calamities. Apart from them, AFT has developed its own proprietary testing called AFT testing by leveraging the trending technology coupled with the strong expertise of professional engineers working with profound experience in civil engineering.
Merits of Miniature Shaft Inspection Device
Out of all the civil engineering technologies, Miniature Shaft Inspection device enjoys a unique position. Founded and first implemented in one of the major projects in Florida in 1986 by the Florida Department of Transportation, this dynamic device helped the structural engineers in finding out the depths of the subsoil that helped in the seamless construction of the Sunshine Skyway Bridge. Since then, this device has become part and parcel in the construction of significant projects. Read on to find the benefits of the Miniature Shaft Inspection.
By leveraging this new technology, it is possible to understand the extreme bottom surface of a drilled shaft or a bored pile for that matter. Several other benefits come bundled with the miniature device.
Holistic view: The constructions of skyscrapers and other massive structures are said to be sound when their foundation is ideal. To ensure that the foundations are perfect, it is pertinent for the geotechnical engineers to ensure the quality of the soil underneath. Earlier, civil engineers used to assess based on extracting the soil from the bottom, but still, it would only provide the picture of the soil type. By fixing a camera to this miniature device, the engineers send it down through a shallow shaft until the desired level is reached. Every minute detail is visible on the connected devices, thereby providing a holistic view of the bore.
Ruling out cracks: A sonics sensor would also be embedded in the miniature shaft inspection device. When the device emits sensors, it will record the condition of the soil and alert the engineer in case of any cracks anywhere along the shallow shaft.
Measures thickness: This device is also helpful in measuring the width of the debris.
Easy Transportation: Given that the size of the camera and the entire equipment is small, it’s portable to carry to any remote location without any friction.
Time-Saving: To blindly go ahead with the piling without having the 360-degree view of the sidewall shear, shaft bottom, and settlement, it would be risky, time-consuming and costly affair for the vendors and contractors. Imagine what would be the situation if the pile fails in a particular location? The entire pile needs to be removed, and testing should be done in another area, which is undoubtedly expensive. The miniature shaft inspection device eliminates these issues with ease.
Achieves Greater Depths: This device is entirely reliable and safe as it can reach a depth of 200 feet and above without frictions making it an ideal for gigantic constructions.
Fast Analysis: It would take a few minutes for the device to reach the expected depth, thereby providing the overall scenario of the soil in a jiffy.
Feasibility to Save Images: As the camera is directly linked to the computers, the footage can be recorded and viewed as a future reference when a contractor or vendor or customer want to explain their efforts involved in constructing a project right from scratch, which starts with the inspection of the subsurface.
Multiple Bores-Holes that Help Your Structures
As we plunge into the depths of civil engineering, bored pile foundations catch our attention as they are deeply rooted in the soil to support the gigantic structures.However, to ensure that these foundations are laid down in the right area where the soil is healthy, a civil engineer drills a bore in multiple areas, which is referred to as multiple bores.
Types of Multiple Bores:
Displacement Boring: This type of boring is generally not suitable in the sand areas. It is carried out to understand the soil character through penetration resistance. Usually, 25mm to 75mm holes are made through displacement bore.
Wash Boring: Often carried out by the limited equipment, its inexpensive approach makes it one of the most sought-after ones by the vendors and contractors. A pipe—usually of 5cm diameter—is driven into the soil and then filled with water. When the pressure is applied, slurry soil comes out of the tube. Based on the color of the soil, its quality and type are ascertained.
Auger Boring: Ideal for soft to stiff soil types, Auger Boring is widely used for piling for both small and significant structures. The auger that’s equipped with the steel casing will rotate to collect the soil. Compared to other types, auger boring is efficient and saves time.
Rotary Drilling: As the name suggests, in rotary drilling, a sharp machine is drilled into the soil that even cleaves through the rock. The broken hard soil or rocks are then removed for examination. It is suitable when the designed hole diameter is not exceeding 20cm. It is the robust and conventional method of bore drilling, although it’s often expensive.
Percussion Drilling: When auger boring and water boring don’t work due to hard soil and the presence of rocks, percussion drilling comes to the forefront as a rescue. Percussion drilling is a manual process wherein the hammer is attached to the rope that will be descendent into the soil through the temporary casing with the help of a tripod. Since the stick is at cutting end, it will easily break through the stones and can reach depths of several hundred feet. Earlier, China-based engineers reached a whopping 4000 feet through multiple bores.
Benefits of Multiple Bores:
• Stable structures that can have strong foundations
• Less economical as foundation repairs would not crop up in the future
• Can get the holistic view of the subsurface soil type
• Extensive excavations can be significantly minimized
• Engineers can construct Caissons of high capacity seamlessly by expanding the base of the soil
• Piles can be extended beyond and below the seasonal moisture variation
• Minimal or zero disruption to the surrounding soil