Leaved probe experiment is used for determinating undrained shear strength uncracked and totally concentrated clay in situ. This experiment is especially suitably for soft clay studying, whose structure can be disturbed in process of taking sample. It is also used for undrained strength clay until 100kPa. Leaved probe is made of four thin steel sheet on the end of steel rod.
The probe length is two times bigger than its wide, typical dimensions are 150x75mm and 100x50mm.
The probe is depressed with rod in ground, into the borehole, to the depth three times bigger than borehole’s radius. The experiment in soft clay can be passed directly from the site, without boring. Through the adequate mechanism, the torsion moment is happened step by step to the upper end of rod. That way, probe rotation brings the shear fracture of clay. Shearing is extended upon an envelope, and bases cylinder. The rotation speed is between 6° and 12°in one minute. When the torsion moment gets its maximum, we have undrained cohesion.
The leaved probe can be used for sensibility definition too. Except described ground apparatus, we also use minor leaved probes, and by that way we can research parts of clay layer on the territory or to the lab samples.
Results are presented in probes profile of every borehole, as it’s shown on the picture. The depth marks and ground sort is reviewer in profile, and also information’s about examination in borehole and lab. That is base for geotechnical profile of ground.
SPT is escorted like this: on the boring rod, after decaying of the sample, we fix particular cylinder, which is pressed in the ground by beetle stroke. We clean the borehole first on the destinated depth, and then we press cylinder to the depth of 30 cm by the standard weighted stoke (63,5 kg) which falls from the height of 76 cm.
The number of hits needed for cylinder to be pressed to the destinated depth (30 cm) is registered.
Rod penetration resistance and spire (which is pressed into the ground by static force) resistance is being tested.
Main components of static penetration plugging-up machine are:
- probe pressing and squeak tool-box
- force testing machine
- outer rod and thin gib
An examination fazes are:
It is also called as an experiment with an enabled side spreading
This trial give us approximate values of internal friction angle, also the values of cohesion and the compressibility module.
How it works: the sample is getting imported under a load cylinder, after that we closing the machine and putting under saddle in determinate time spacing. After every saddle we are reading from a comparator the values of a subsidence. And after that we are inflicting experiment results on the diagram.
By saddling we are getting the diagram of the subsidence which shows us that the very first subsidence is pretty proportionally as a same saddle.
By downloading we are getting the swelling diagram, which shows us that the sample is particularly getting back in the primary position. If we repeat saddle of a sample we going to get diagram of a recovered subsidence.
Sample is saddled with a vertical force, normal stress and after that with a horizontal force which induce the shear stress in a middle of the sample.
We have two kinds of machines:
1. Modern machine – there are inflicted the relatively moving between lower and upper part of a sample with a controlled velocity, and the shear forces which produced that moving are registered.
2. Older machine – where is sample submitted with a controlled shear force by adding weight step by step, and the shearing movements are registered between upper and lower part of the sample.
For the complete direct share experiment we usually take three samples with a different value of normal stresses. Pressure drifts in two fazes.
1. Faze one: normal force drifts which is constant for one sample during the whole experiment.
2. Faze two: shear force is being enlarged till it cracks, or 10-15% of the sample dimensions in shearing way.
From this research method there are three standard procedures:
1. Slow experiment or drained experiment (D experiment)
2. Fast experiment or undrained experiment (U experiment)
3. Reversible drained experiment (R experiment)
Perhaps the most familiar illustration of shear is the movement of rocks on opposite sides of a fault as shown here. Because this type of shear is the easiest to visualize, it is called simple shear.
We can define shear strain exactly the way we do longitudinal strain: the ratio of deformation to original dimensions. In the case of shear strain, though, it's the amount of deformation perpendicular to a given line rather than parallel to it. The ratio turns out to be tan A, where A is the angle the sheared line makes with its original orientation. Note that if A equals 90 degrees, the shear strain is infinte.
A test in which a relatively thin test specimen of a solid circular or annular cross section, usually confined between rings, is subjected to an axial load and to shear in torsion.
Triaxial Compression test
- it is done by a triaxial machine
- we put cylindrical earthen template into the rubber pouch and move it into the machine between bleeding spike and the filter stone. Template is being closed hermetically by the cylinder and the space between template and cylinder is becoming solid by the water or oil
- under the undermost filter stone, the glass bulb for water drainage from the template is being turned on, and the other bulb is turned on with the tang unto the manometer (water compression into the template test).
- The spike bleeding is written on the other manometer, and the shrug on the comparator.
- The experiment can be done in two ways:
1. Slow consolidation experiment
2. Quick experiment (without consolidation)
The simple shear device at UBC
is a modified NGI type. A cylindrical soil specimen is laterally confined by a
steel reinforced rubber membrane. The reinforced membrane enforces an
essentially constant cross sectional area, therefore if vertical displacement
is prevented, constant volume conditions are simulated.
The simple shear apparatus applies plane strain loading in one direction, and enforces zero extension in the other perpendicular horizontal direction. It also imposes uncontrolled rotation of principle stress during loading while the sample is being sheared under plane strain. The ability to simulate principle stress rotation is common to many geotechnical problems, including earthquake loading.
The device has extensively been used to study the static and cyclic stress-strain response of sands and silts.
The integrated True -Triaxial Test Cell Platen and Seal System is designed for large strain deformation (4% to 8%) and to date has been built to accommodate 80mm cube and 80x160mm prism samples. Designs have been produced to a accommodate a 240mm cube The unique three element Seal System compensates for the large movements whilst maintaining a gas tight seal between the TTSCP Test Rig containment pressure vessel and the cube/prism under testing.
1. Axial "Telescopic" Anti-Extrusion Rods in Engineering Plastic
2. Soft Deformable rubber - 12 Off 3d Mitred Strips
3. Flexible Rubber Integrally Bonded To Stress Support Platen
The platens of the TTT cell are made of two elements:
1. Stress support platens made in high tensile stainless steel (17/4-PH Condition H1150) to spread the applied load by the 3D hydraulic jack system
2. Interposing sample platens made in aluminium alloy (6082 -T6) for Modulus compliance and for interchangeability in case of damage during the testing
The six platens of the test cell are held together by precision machined "L" elements using ISO 12.9 M5 button head socket head fasteners which can be backed out during 3D straining. The X2, Y2 and Z2 platens were also fitted with sliding spherically seated plates made in hard tool steel. This was incorporated to compensate for a potential skewing of the loading by the original three-jacks on three faces (X1, Y1 and Z1) only of the test specimens. The spherical seats were incorporated to allow tilting of the X1/X2 and Y1/Y2 platen sets due to the pressure drop between Z1 and Z2 platens during permeability determinations.
Dynamic triaxial test
The need to analyze dynamically the behavior of soils and earth structures in seismic zones has encouraged the development of new testing techniques to obtain the necessary parameters to model the behavior of granular and cohesive soils.
On the other hand, research into the changes in the mechanical properties with temperature of deep clay formations is attracting more attention, since these materials can be suitable for the storage of radioactive wastes due to their plasticity, impermeability and cation retention capacity.
One of the existing techniques for the execution of these studies is the dynamic triaxial test with control of temperature; it permits the material to be tested under dynamic loads and it also reproduces the high equilibrium temperature and the strong overloading expected in underground storages for radioactive products.