1. General

Loading test is a procedure that checks the real carry capacity of a foundation under real load.

As the vertical load applying on a foundation is basically static and long last – the loading test has to use static load for long period of time.

What is “Static” and how much time is “long Period” - are often asked questions.

For us, “static load” is a load, which varies by less than 10% in few minutes interval.

As the load is vertical and points to the ground, an upwards pointed reaction is needed. That reaction may be realized by dead weight or by anchored to the ground structure.

Both above mentioned techniques are expensive and time consumer.

Our solution is to split the foundation (pile) into two parts, and to use each part as the reaction to the other’s force. We call that technique “TOMER Loading Test”.

We started using TOMER Loading Test at the early seventies and patented it at the year 1978. At the year 1982 we introduced our TOMER Loading Test internationally.

By now, we run more than 2,000 TOMER Loading Tests, using various types of load cells and several configurations.

2. The Structure

In order to create a load, a reaction has to be supplies. In order to avoid an external reaction, we split the pile into two pieces. Each part serves as the reaction to the other part’s load.

The common structure of TOMER Loading Test is described in drawing No. 1. The pile was divided into a Lower Part and an Upper Part. In between them there is Inflatable device.

Applying hydraulic pressure to the Inflatable device, pushes the Upper Part upwards and, at the same time, pushes the Lower Part downwards.

By that, the Upper Part serves as a reaction to the Lower Part, and vice versa.

The Lower Part is loaded like “normal” pile – from the top downwards.

The Upper Part behaves like an anchor – loaded from the bottom upwards.

There are situations in which it is important to load the Upper Part downwards. In such a case, we invert the directions of the forces by using steel rod. Drawing No. 2 describes the arrangement.

3. The Load Cell

The load cell is the inflatable device. It creates the load while pressurized by hydraulic liquid.

Any hydraulic piston may be used. The only restriction is the ability to create the needed load.

usually, high load capacity hydraulic piston is very expensive. As we bury the piston in between the two parts of the loaded pile – there is no way to recover it for reuse. In order to reduce the price of TOMER Loading Test, we developed some non-expansive solutions.

The most popular loading cell we use, is the Flat-Jack. That device is light weight and non-expensive but, at the same time, reliable and high capacity.
Refer to Drawing No. 4.

Drawing No. 5

4. Load Measurements

The load is calculated by multiplying the hydraulic pressure by the effective area of the inflatable device.

The effective area may be calculated or measured.

For a better preciseness, a calibrating procedure may be done.

If autonomous load measurement is needed – an electronic measuring tool may be placed between the inflatable device and the Upper (or Lower) Part of the tested pile.

5. Load regulation

The load is regulated by keeping the pressure in the load cell. An electronic pressure gauge measures the pressure and transmits that information directly to the main computer. The computer controls that pressure by starting and stopping the hydraulic pump or by controlling the pressure regulator.

The computer performs the load according to any standard, rising and decreasing the load at any needed rate and timing.

6. Settlement (movement) Measurements

The settlements of the Upper and Lower parts of the loaded pile are measured using Tell-Tales.

The settlement of each part may be measured at some points. By that, the elastic compression of the pile can be detected.

The measures are done by electronic gauges, which are directly connected to the main computer.

Tensioned Tell-Tales (left) and a reference beam (right)

7. Strain Measurement

The strain of the pile, at any place, may be measured using electronic strain gauges or vibrating wires.

We like to use a full bridge of electronic strain gauges with integral power supply and signal condition. Each bridge has 4-20 mA output. That design assures long time stability, prissiness and simple use.

All the strain measurements are directly connected to the computer.

8. Extensometers

Extensometers may be used at any needed length. The readout may be done by LVDT or any other electronic device.

The measurements are directly connected to the computer.

9. End Bearing Gauge

The End Bearing Gauge measures the force at the foot of the pile.
Refer to drawing No. 6.

10. The Computer

The computer may be any member of our TomTech III family (including TomNet), or any laptop equipped with our add-on hardware and software.

The computer completely controls the loading process. It maintains the load while measuring the gauges at pre-set time intervals. Normally, no one has to interfere along the loading procedure, but if it is needed – any setting may be changed “on the fly” including a switch to manual operation.

The needed hardware is depended on the kings and number of gauges installed. There is no “standard” as there are a lot of possibilities and requests.

The software monitors, at real time, all the readings of the gauges. In parallel, the information is stored in solid state memory and even may be transmitted to your office by the GSM network.

The software is very friendly. You have complete control on the flow of the loading process including the number of cycles, the max. load of each cycle,the time interval between the loading stapes and even conditional decisions.
You may swap from numerical information to graphic presentation at any time.

In order to compensate for the potential movement of the ground surrounding the loaded pile, a remote reference has to be used. That reference device may be any surveying tool which has one mm. vertical accuracy at a distance of at least 50 m.
Normally, we do not connect the remote reference to the computer.

12. Coverage

The international standards request that the loaded pile, include all the instrumentation and references will be covered and protected against sun radiation, rain and snow.

The easy way is to use a tent but any other solution is well-come.

13. Documentation

The software includes a module, which automatically produces reports and documents. The reports may be produced on the spot – while loading, or later on - in the office.

The information in side the solid state memory is fully opened. It is written in pure ASCII format.

If you want to make your own reports – you may use virtually any available, off the shelf software package.

14. Safety

Unlike “conventional” loading test, the TOMER Loading Test is fully safe. The loading energy is accumulated in the Load Cell which is deeply buried in the ground.

There are no stressed structures, nor huge dead load. There is no possibility for buckling nor for collapsing.

People may be any where, including near, or even on, the Upper Part - during the entire loading process.

From the safety point of view, there is no need for fences nor for warning signs.

Collapsed structur after anchor's failure

15. Installation

The installation procedure is sharply depended on the drilling technique.
Basically the process starts at the bottom and continue upwards.

The process for wet or dry drill and cast pile:
    • Drill the complete pile.
    • Insert the end bearing cell (if apply) and push it all the way down.
    • Insert the Lower Part reinforcement including the needed gauges.
    • Cast the Lower Part.
    • Insert the Inflatable device.
    • Insert the Upper Part reinforcement including the needed gauges.
    • Cast the Upper Part.
    • Wait the time needed for the concrete to consolidate.

Inserting the Load cell

The process for CFA (Auger Cast) pile:
    • Drill and cast the complete pile. (Use supper plastisizer to keep the viscosity of the concrete low for one hour).
    • Insert the end bearing cell (if apply) and push it all the way down.
    • Insert the Lower Part reinforcement including the needed gauges.
    • Insert the Inflatable device.
    • Insert the Upper Part reinforcement including the needed gauges.
    • Wait the time needed for the concrete to consolidate.

Balancing the Load Cell

16. Loading Process

In most cases, the loading process follows the ASTM 1143 standard. You may use any standard you want and even design your own.

Complete set for TOMER Loading Test

17. Part’s List

In order to perform a TOMER Loading Test, you need to have a written license from TOMER SYSTEMS BV. for each to be load pile.
    TLT-1 License for one TOMER Loading Test.
    TLT-2 Flat-jack Load Cell (You have to specify Diameter and Displacement).
    TLT-3 Piston style Load Cell (You have to specify Diameter and Displacement).
    TLT-4 End Bearing force gauge (You have to specify Diameter).
    TLT-5 Strain Gauge bridge.
    TLT-6 Vibrating Wire gauge.
    TLT-7 Extensometer (You have to specify length).
    TLT-8 Tell-Tale (you have to specify length).
    TLT-9 Remote Reference.
    TLT-10 Hardware set for Laptop.
    TLT-11 Software for Laptop.
    TLT-12 Manuel operated hydraulic pump.
    TLT-13 Electric operated hydraulic pump.
    TLT-14 Reference beams for tensioned Tell-Tales.
    TLT-15 Covering Tent.
    TLT-16 Working day of a technician.
    TLT-17 Accommodation day.
    TLT-18 Flying tickets.
    TLT-19 Freight costs.