Flat push method rock mass direct shear tester

HTSZ-1Flat push methodRock direct shear tester

1Objective of the test

This experiment is used to determine the in-situ shear strength of the contact surface between dam concrete and rock mass, the interlayer bonding surface of roller compacted concrete, and the roller compacted concrete body.Meet national industry standards（SLT264-2020) Rock Testing Code for Water Resources and Hydropower Engineering.

IITechnical specifications

1*Large loading range:0-100T*Large displacement:0-150mm

2Hydraulic cylinder:2A

3Displacement sensor:4a

4Transmission rod:1a

5Gauge bracket:4a

6Pad and Ball Row:1set

IIIThe preparation before the experiment and the preparation of the test piece should meet the following requirements:

1Select representative parts and test layers on the structure, preferably on the construction test section or dam body, and the selected test area should not be less than2m×8mThe test specimens should be arranged on the same level, in terms of quantity4~5Block.

2The shear area of each specimen should not be less than500mm×500mmThe net distance between specimens should not be less than the minimum side length of the specimen1.5Twice.

3The height of the specimen above the shear plane should be slightly greater than the side length of the specimen2/3，

4When arranging the experiment, the horizontal thrust direction applied to the test surface should be consistent with the direction of the structural force.

4、 The preparation and maintenance of specimen excavation shall be carried out in accordance with the following regulations:

1The excavation age of the specimen should not be less than21dManually excavate and chisel the concrete around the specimen in the test area to prevent disturbance to the specimen.

2The excavation depth of the test specimen should reach the test layer, but the test layer subjected to horizontal thrust should be excavated below the layer and leave sufficient space for installing jacks. The jack should be strictly positioned, and the centerline should be parallel to the predetermined shear plane, and the distance from the shear plane should not be greater than the side length of the specimen in the shear direction5%The allowable deviation of the size of the excavated specimen should be±20mm， And use cement mortar with similar strength to the test block to smooth it out. When making layer joint shear resistance, leave a shear joint about 10mm wide around the shear surface.

3. After completing the excavation of the test specimen and experimental area, the test pit should be filled with water or backfilled with wet sand, and the test specimen should be well maintained and protected until the specified age. When the installation of instruments and equipment begins, it should be removed. At the same time, measures should be taken to maintain the specimen and its shear surface in a water saturated state.

5、 The installation of the normal load system should meet the following requirements:

1Lay a layer of cement mortar on top of the specimen and place a cushion plate. The cushion plate should be lightly tapped to make it parallel to the predetermined shear surface. Rubber or fine sand can also be laid on top of the specimen before placing the cushion plate.

2Place the roller row, pad, jack, transmission column, top pad, and reaction device on the pad in sequence.

3When it is not possible to use the roof of the cave as a reaction force in an open field or when it is not possible to use the cave roof as a reaction force, the pile cutting method or ground anchor can be used as a reaction force device. When the normal load is small, the compression method can also be used.

4After installation, the jack can be started with a little pressure to make the entire system tightly integrated.

5All components of the entire normal load system should be kept on the same axis in the loading direction and perpendicular to the predetermined shear plane. The resultant force of the normal load should pass through the center of the predetermined shear plane.

6The normal load system should have sufficient strength and stiffness. When the shear plane is inclined or the load system exceeds a certain height, the normal load system should be supported.

7The hydraulic jack piston should start a partial stroke before installation.

6、 The installation of the shear load system should meet the following requirements:

1. When conducting direct shear tests using the flat push method, cement mortar should be applied to adhere the stress surface of the specimenA cushion plate should be perpendicular to the predetermined cutting surface. After the cushion plate, the transmission block, hydraulic jack, and cushion plate should be placed in sequence. Concrete (or mortar) should be filled between the cushion plate and the reaction seat.

2When sticking a pad to the stress surface of the specimen, a space should be reserved between the bottom of the pad and the shear surface1cmGap.

3When installing a shear load jack, the shear direction should be aligned with the predetermined thrust direction, and the projection of its axis on the shear plane should pass through the center of the predetermined shear plane. The axis of the shear load applied by the flat push method should be parallel to the predetermined shear plane, and the distance between the axis and the shear plane should not be greater than the length of the specimen in the shear direction5%.

7、 The installation of the measurement system should meet the following requirements:

1The installation of the displacement measuring instrument bracket for the measuring body should be firmly placed on the fulcrum, and the fulcrum of the bracket should be outside the deformation influence range.

2The measuring instrument should be installed on the bracket through a magnetic gauge holder. Shear and normal displacement gauges should be installed separately at the symmetrical parts of the specimen, and the number of each gauge should not be less than2Only.

3According to the needs, a measuring table can be arranged between the specimen and the surface of the cornerstone to measure the relative displacement of the test specimen.

4All measuring instruments and punctuation points should be oriented, and should be perpendicular or parallel to the predetermined shear plane.

5Maintain the cement mortar and concrete poured during installation.

8、 The preparation for the experiment should include the following items:

1The applied loads and pressure gauge readings should be calculated based on the hydraulic jack calibration curve and the shear area of the specimen.

2Check the working status of each meter and read the initial reading value.

9、 The application method of normal load should meet the following requirements:

1Different normal loads should be applied to each specimen, which can be divided into equal parts of the maximum normal load. The maximum normal stress on the shear plane should not be less than the predetermined normal stress.

2For each specimen, the normal load should be divided into1level~3Grade application, grading can be determined by the magnitude and lithology of the normal stress.

3Loading is time controlled and should be done every time5minApply a first level load, and immediately measure the normal displacement under each level load after loading,5minAfter reading once, the next level of load can be applied. After applying the predetermined load, every5minRead once, when the difference in normal displacement between two consecutive readings is not greater than0.01mmAt this time, shear loads can be applied.

4During the shearing process, the normal stress should always be kept constant.

10、 The application method of shear load should meet the following requirements:

1Before applying shear loads, the shear load system and measuring instruments should be checked and adjusted if necessary.

2It should be divided according to the estimated maximum shear load8level~12Level applied. When the shear displacement caused by the application of shear load increases significantly, the shear load grading can be appropriately increased.

3The application method of shear load should be time controlled. each5minApply one level, and read each displacement meter before and after applying each level load. When approaching the cutting point, it is necessary to closely monitor and measure the changes in load and corresponding displacement, and the load and displacement should be observed synchronously.

4After the specimen is sheared, the shear load should continue to be applied until a stable shear load value is measured.

5Slowly reduce the shear load to zero, observe the rebound of the specimen, and the shear test is completed. During the process of shear load zeroing, the normal stress should still be kept constant.

6As needed, after the shear test is completed, the normal stress can be kept constant, and the equipment and measuring instruments should be adjusted according to the provisions of this article2Payment to clause6Conduct shear (friction) tests along the cut surface. The shear load can be applied in stages according to the final stable value of the shear test.

7After the shear test is completed, repeated friction tests can be conducted under different normal loads as needed, namely single point friction tests.

11、 During the experiment, provide detailed descriptions and records of the operation of the loading equipment and measuring instruments, the noise that occurs during the experiment, the loosening or falling of the specimen and rock mass, and the development of cracks.

12、 The equipment should be dismantled promptly after the experiment is completed. After cleaning the test site, flip the specimen and describe the shear surface. The description of the cutting surface should include the following:

1Measure the shear surface area.

2The damage situation of the shear surface, the distribution, direction, and length of scratches.

3The location and area of local shear in rock or concrete specimens.

4The properties and distribution of debris material on the shear surface.

13、 The compilation of experimental results shall comply with the following regulations:

1Using the flat push method, the normal stress and shear stress under each normal load are calculated according to the following formulas:

a=

Ⴀ =

Where: a-Normal stress acting on the shear plane（MPa）

Ⴀ-Shear stress acting on the shear surface（MPa）

P-Total normal load acting on the shear plane（N）

Q-The total shear load acting on the shear surface（N）

A-Shear surface area（mm²）

2The relationship curves between shear stress, shear displacement, and normal displacement under various normal stresses should be plotted. The peak shear strength under each normal stress should be determined based on the relationship curve.

3The relationship curve between the normal stress and its corresponding shear peak should be plotted according to Coulomb-Determine the corresponding shear strength parameters using the Navier expression（ƒThec）. The estimated shear (friction) strength should be determined as needed.

4Other shear stage characteristic points should be determined on the shear stress displacement curve as needed, and corresponding shear strength parameters should be determined based on each characteristic point.

14、 The direct shear test record of the contact surface between concrete and rock mass should include the project name, test section location and number, specimen arrangement, specimen number, test method, description of specimen and shear surface, concrete strength, shear surface area, jack and pressure gauge numbers, gauge arrangement and number, normal displacement and shear displacement at each level of shear load under various normal loads.

HTSZ-1Flat push methodRock direct shear tester