Hokkaido University
      
School of Engineering 
       Course of Civil Engineering / Public Policy and Engineering
      Graduate School of Engineering
         Division of Field Engineering for the Environment

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  This is a brief introduction to our laboratory with a list of testing devices and tools.


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FACILITIES

Our group's experimental work takes place in three adjoining laboratories as well as in field. Below is a list of our tools for geotechnical research. You are more than welcome to come and see.








First of all, webcams monitor our lab!

Ever felt an anxiety when you run a test overnight? You ought to be so. Our laboratoy is monitored by six webcams at maximum, which can be  panned  remotely from PCs and smartphones from anywhere. This helps noticing any accident in the lab at the earliest opportunities. The webcams, being capable of capturing the PC displays in the lab, are also extremely convenient in tracking experiment progresses when you are running a long-term tests. The progres can be checked from your bed!




Monitoring experiments with a smartphone


Megatorque Motor-Driven Triaxial Apparatus
We have four pieces of triaxial apparatus driven by a Megatorque-Motor, with each own complete driving and monitoring system. All of them are run by home-grown Windows software with automatic control, data acquisition and real-time plotting capabilities. A Megatorque Motor allows ultra-precise control of the axial displacement, with a precision smaller than 0.00001mm. By installing local displacement transducers and bender elements, this apparatus is ideal in investigation stiffness over a wide range of strains, as well as ultimate strength of geomaterials. The pressure capacity of the cells is 700kPa in three of them, and 2,000kPa in one of them. The software, being home-grown, is being contantly updated to permits an ever wider range of loading conditions, such as K0-conditions by feedbacking and cyclic loadings with either stress or strain control prescriptions.

Stress/Strain-Controlled Triaxial Apparatus
We have three pieces of triaxial apparatus equipped with both stress-controlling (a Bellofam cylinder at the top) and stress-controlling (a motor-driven pedestal at the bottom) devices, which can be switchd from one to the other during a test. This apparatus is also controlled by home-grown Windows software which controls, monitors and records automatically. The stress-controlling device, though not as precise as the Megatorque Motor, is powerful enough to load cement-treated soils to failure.






Example of local instrumentation in triaxial apparatus



Hollow Cylinder Apparatus

HCA permits complex stress conditions to be applied to a soil specimen. With clever loading schemes, the direction of the three principal stresses and their individual magnitudes can be manipulated at our will. This is a unique advantage in investigating soil's anisotropy, for example. Characterisation of soil behaviour under general stress conditions through HCA testing is arguably one of the most advanced mechanical studies in geotechnical laboratory. Another notable feature of HCA is that it can simulate horizontal simple shear deformation, which is particularly relevant to soil deformation under seismic loadings. Our HCA is equipped with a set of local transducers to measure the shear modulus, G, very accurately over a wide range of strain.












Hollow Cylinder apparatus and its principle


Direct Shear Apparatus
Our pair of direct shear apparatus also have a Megatorque Motor for horizontal loading. The vertical loading is also computor-operated via EP regulators, allowing either constant-stress or no volume change condition by feedback control. Recently we have added an optional set of confining stack rings to achieve more uniform simple shear deformation modes. A newly designed pedestal allows installing a suction probe (tensiometer) when testing unsaturated soils (this project was undertaken in collaboration with Dr. Apiniti Jotisankasa of Kasetsart University, Thailand).




Direct shear apparatus



CRS Oedometers

Three oedometers in our laboratory all have a Megatorque Motor for  Constant-Rate-of-Strain (CRS) loading. They are capable of achieving extremely slow rates of compression, which are comparable to those observed in field. One of the oedometers has a chamber in which the temperature may be controlled between -30 and +80oC. These features of the oedometers are useful in investigating loading rate effects and thermal effects on soil's consolidation behaviour.










CRS oedometer


Swelling Pressure Test Apparatus with
Suction-Measurement

This machine is basically an altered form of the CRS oedometer introduced above. The machine has a high AEV (Air Entry Value) ceramic disc in contact with the soil specimen, through which the soil's suction is measured by means of the axis-translation technique employing air pressure. Either by fixing or controlling the movement of the ram, the swelling pressure or the compressibility can be measured while monitoring the suction.






Low-pressure loading machines:
Triaxial Apparatus for Creep Monitoring
/Large Oedometer for Extremely Soft Soils
We have two pieces of very simple triaxial apparatus whose loading devices are a hydraulic pot for providing cell presure and dead weights for providing axial loads. Though this may sound primitive, this set-up is ideal in performing stable long-term creep tests for soft  soils such as high-water-content clays and peats. The deformation may be measured by conventional instrumentation such as dial gauges but we normally adopt digital camera monitoring and image analysis to save the cost of instrumentation. We have an oedometer designed with a similar principle. It can house large diameter specimens and so are suitable for testing peats.





Low-pressure, large-diameter  oedometer


Rheological tesing tools:
Viscometer/Ultra-Low Capacity Vane

To characterise the strength and rheological properties of high-water content clay slurry (1-3 times the liquid limit), we have a suite of equipment ranging from a general-purpose industrial viscometer to originally designed bench-top, ultra-low capacity vane shear machine. The research subjects include dredged surplus clays occurring from marine contruction work.












PC-operated viscometer


Ultra-low capacity vane shear machine



1G-Model Test Equipment

Although much of our effort goes to specialised laboratory mechanical tests, model tests are also constantly conducted to obtain insights into soil-structure interactions as part of boundary value problems. We have round and plane-strain containers which allow reduced-size model tests under 1G field. An instrumentaion frame to mount transducers and PIV software to analyse model ground movements by image analysis have also been developed.











Example of 1G model tests: Long-term observation of sand backfill settlement in peat (above: snapshot, below: displacement vectors obtained by PIV analysis)


Getechnical Centrifuge
Our arm-type geotechnical centrifuge, with its effective radius of 1.5m, is just the right size for routine testing. The maximum attainable acceleration is 150 G. Introduced in the 2000s, new capabilities have been added for each new projects, including a rainfall simulator.







Geotechnical centrifuge



Field Equipment

We have a suite of field testing tools. They include an electric 3-component cone (also known as CPTu), seismic cone, conventional Dutch cone, field vanes, penetration balls of two different sizes. Our portable rig (old-fashined Dutch cone rig) allows our team to reach depth of 30m in soft clay on our own, without renting heavy machinery.
















BPT (Ball Penetration Test) in field


Field shear wave velocity measurement by seismic CPT: Hitting an anvil to generate shear wave


Shear Wave Velocity Measurement System
This consists of a pair of bender elements, a function generator and oscilloscope. The bender element is a small plate made of a semi-conductor material, which generates electric voltage when deflected, and vice versa. This special property makes it a convenient transmitter and receiver of minute shear waves in a solid. By measuring the shear wave velocity, we can estimate the shear modulus of soils based on the wave equation. Our students (and professors) coat it with epoxy resin themselves by using purpose-made moulds to make it water-proof and use it in mechanical test machines such as triaxial apparatus.







Shear wave velocity measurement system with bender elements



XRD Machine

X-Ray Diffraction machine is capable of indentifying mineral compositions of soils. By scanning a soil sample, fundamental information concerning the soil's physical properties and geological origin is obtained.




X-Ray diffraction machine


HU Soils PIV (Particle Image Velocimetry)
We also produce home-grown software for geotechnical experiments. Our PIV software is a very basic, no-frill  program but does a good job; it can perform subpixel high-resolution analysis, both Eulerian observation and Lagrangean tracking, and, if combined with a Wi-Fi SD card, it can even perform the analysis real-time by receiving images from a digital camera via ad-hoc network. Being home-grown, it can be modified/altered to suit our needs at any time.





Sceenshot from HU Soils PIV



HU Soils RealTimeGraph
Observing an experiment through real-time plots is an extremely important activity. Our home-grown plotting software works as an auxiliary program and can be added to any of the Windows testing programs that have been developed here. By observing the plots by the webcams, we keep an eye on tests even from our bedrooms and assure safe and successful tests.





Screenshot from HU Soils RealTimeGraph

    ... And, there are lots more of bits and pieces!






Copyright © 2011 Laboratory of Soil Mechanics, Hokkaido Univerisity