DESC:FIELD OF THE INVENTION:
The invention relates to the field of civil (Geotechnical) engineering.

Particularly, this invention relates to shear strength of in situ assessment of soil
Specifically, this invention relates to an in-situ torsional direct shear test device.

BACKGROUND OF THE INVENTION:
A direct shear test is a laboratory or field test used by (geotechnical) civil engineers to measure the shear strength properties of soil or rock material, or of soil or rock masses. In-situ shear tests are designed to check Coulomb’s shear strength parameters of in-situ soil.

One of the prior art practices for in-situ direct shear is mentioned in ASTM D4554-02 and IS code methods (IS 2720 part 39/sec 2). These methods are time consuming and not easy to perform ASTM D4554-02 method requires strong side support system for inducing required horizontal shear force on in-situ soil. IS code (IS 2720 part 39/sec 2) requires very heavy vertical loading arrangements. Also, these methods are stress controlled methods, thus time consuming.

Other method described in US patent No. 4480481, torque is applied for inducing shear stress while the sample, to be tested, is subjected to normal stress. However, the method involves manual application of normal and shear stress and can be useful only for soil particles less than 2mm due to very less size of shear area (2cm diameter only) It is difficult to apply shear stress at a constant strain; also, a normal load cannot be applied in a large quantity, such as 2 to 5 tons, as desirable for granular soils in which shear surface area should be large (such as about 30cm diameter)

Therefore, there is a need for a devise which obviates the problems associated with the prior art.

OBJECTS OF THE INVENTION:
An object of the invention is to provide a device which is used for in-situ torsional direct shear test on soil.

Another object of the invention is to provide an in-situ torsional direct shear test device which is configured to apply shear stress at a constant strain.

Yet another object of the invention is to provide a reliable in-situ torsional direct shear test device.

Still another object of the invention is to provide an in-situ torsional direct shear test device which is configured to work with all types of soil.

An additional object of the invention is to provide an in-situ torsional direct shear test device which is configured to work with large particle sizes.

Yet an additional object of the invention is to provide an in-situ torsional direct shear test device which is configured to allow dilation.

Still an additional object of the invention is to provide an in-situ torsional direct shear test device which is configured to measure soil cohesion (c) and angle of internal friction (?) of soil having small to large particle sizes.

SUMMARY OF THE INVENTION:
According to this invention, there is provided an in-situ torsional direct shear test device to evaluate shear strength parameters of in-situ soil, said device comprising:
- a cylinder, with its operative top side being covered by a top plate and its operative bottom side being open, said cylinder comprising vanes attached at right angles, inside said cylinder, said cylinder inserted in ground (that is to be tested) with peripheral soil outside said cylinder being removed;
- four quarter plates forming an operative top surface of said cylinder, each quarter plate separated by an adjacent vane that extends from underneath, each of said quarter plates, of said top surface, comprising a hemispherical slot at a pre-defined position for locating a corresponding spherical ball; and
- a top grooved plate which sits on said operative top surface of said cylinder to transmit normal load applied at the top of said plate directly to soil between said vanes underneath said cylinder, said top grooved plate resting on said four spherical balls which are sandwiched between said top grooved plate and said quarter plates, the underside of said top grooved plate comprising grooves which bifurcate said top plate’s underside into four quarters such that each groove receives a portion of a vane when said top grooved plate is placed over said spherical balls.

Typically, said cylinder is and open-ended circular with its open-end configured to be inside said ground that is to be tested.

Typically, said spherical ball being a steel spherical ball.

Typically, each of said quarter plates, of said top plate, comprising a hemispherical slot at a pre-defined position for locating a corresponding spherical ball, thus, each spherical ball being ensconced in a spherical groove formed by two corresponding hemispherical slots (one on the top surface of the cylinder and one on the underside of the top plate).

Typically, said device comprising:
- a vertical elongate column in order to apply normal load onto said device through the top grooved plate;
- a hydraulic jack to apply normal load to said top grooved plate through said vertical elongate column; and
- a bearing below said hydraulic jack to allow angular displacement of said vertical elongate column, while normal load is applied on the vertical elongate column.

Typically, said vertical elongate column is a telescopic vertical elongate column.

Typically, an additional spherical ball is provided which rests in between said top grooved plate and said vertical elongate column in order to transfer load normally to said other four spherical balls where, again, said load is transferred normally, the use of said arrangement of spherical balls ensuring a 2-level distribution of force, normally.

Typically, said top grooved plate comprising two blocks, protruding outwardly, on its operative top surface such that when said vertical elongate column is angularly displaced by means of a pulling horizontal beam, extending horizontally from a segment of said vertical elongate column, it provides torsional force to the vanes.

Typically, a flange is attached at the bottom of said vertical elongate column.

Typically,
- said top grooved plate comprising two blocks, protruding outwardly, on its operative top surface such that when said vertical elongate column is angularly displaced by means of a pulling horizontal beam, extending horizontally from a segment of said vertical elongate column, it provides torsional force to the vanes;
- load cells are placed in between the flange and the blocks so that shear load can be measured directly. The flange is angularly displaced when the torsional force is applied and upon its displacement it hits the blocks, thereby causing measurement of load in load cells placed between the radial ends of the flange and the blocks; and
- a horizontal beam is pulled with the help of a wire attached to a motor or a manual winch, the shear load being measured by attaching a proving ring or spring balance at a wire rope which is attached to said horizontal beam and said motor, the load cell / spring balance, measuring the force required to angularly displace said vanes, from which torque can be calculated, said calculated torque having a direct relationship with the shear strength of said soil.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS:
The invention will now be described in relation to the accompanying drawings, in which:

Figure 1 illustrates details of vane;
Figure 2 illustrates vane with porous quarter plates;
Figure 3 illustrates top plate with grooves;
Figure 3a illustrates inserted vanes in to soil;
Figure 3b illustrates quarter plates resting on soil surrounded by vane;.
Figure 3c illustrates steel balls resting on the top of quarter plate;
Figure 4 illustrates device set-up with hydraulic jack;

Figure 5 illustrates another view of the device set-up with hydraulic jack;
Figure 6 illustrates the flange fixed on vertical column and block fixed on the top plate; and
Figure 7 illustrates hydraulic jack and bearing, fixed at bottom part of horizontal jack.

DETAILED DESCRIPTION OF THE ACCOMPANYING DRAWINGS:
According to this invention, there is provided an in-situ torsional direct shear test device to evaluate shear strength parameters of in-situ soil

Figure 1 illustrates details of vane.

In at least an embodiment, the apparatus of this invention comprises an open-ended circular cylinder (2), with its operative top side being covered by a top plate (shown in Figure 3 of the accompanying drawings) and its operative bottom side being open. The vanes (1) are attached at right angles, inside the cylinder (2). This cylinder with vanes, as shown in Figure 1 of the accompanying drawings, is inserted in the ground (that is to be tested) and peripheral soil outside the cylinder (1) is removed. The operative top surface of the cylinder is formed of four quarter plates (3), each quarter plate separated by an adjacent vane (1) that extends from underneath.

In at least an embodiment, each of the quarter plates (3), of the top surface, comprise a hemispherical slot at a pre-defined position for locating a corresponding steel ball (4).

Figure 2 illustrates vane with porous quarter plates.

Figure 3 illustrates top plate with grooves.

Figure 3a illustrates inserted vanes (1) in to soil.
Figure 3b illustrates quarter plates (3) resting on soil surrounded by vane (1).
Figure 3c illustrates steel balls (4) resting on the top of quarter plate.

In at least an embodiment, there is provided a top grooved plate (5) which forms the operative top surface of the cylinder (1). Its function is to transmit normal load applied at the top of the plate (5) directly to the soil between the vanes (1) underneath the cylinder (2). The top plate (5) rests on the four steel balls (4) which are sandwiched between top plate and quarter plates, the underside of the top plate comprises grooves which bifurcate the top plate’s (5) underside into four quarters such that each groove which a portion of a vane (1) when top plate is placed over the steel balls. Due to grooves, vanes can be rotated by top plate, without transmitting any normal load to vanes (i.e. all the normal load is transmitted to soils resting between vanes only). Each of the quarter plates allow dilation effect of soil during shearing.

In at least an embodiment, each of the quarter plates, of the top plate (5, comprise a hemispherical slot at a pre-defined position for locating a corresponding steel ball (4). Thus, each steel ball is ensconced in a spherical groove formed by two corresponding hemispherical slots (one on the top surface of the cylinder and one on the underside of the top plate).

In at least an embodiment, a vertical elongate column (6) is provided in order to apply normal load onto the device through the top plate. A hydraulic jack (7) is provided so as to apply normal load to the top plate through the column (6). Typically, the vertical elongate column (6) is a telescopic vertical elongate column (6). A bearing is provided below hydraulic jack to allow rotation of vertical column, while normal load is applied on the vertical column.

An additional steel ball is provided which rests in between the top plate and the vertical elongate column. The function of steel ball is to transfer the load normally to the other four steel balls where, again, the load is transferred normally. Thus, the use of steel balls ensures a 2-level distribution of force, normally.

Normal load is applied with the help of a vertical column (6) and a hydraulic jack (7) shown in Figure 4 of the accompanying drawings.

In at least an embodiment, the top grooved plate (5) has two blocks (16), protruding outwardly, on its operative top surface such that when the vertical column (6) is angularly displaced by means of a pulling horizontal beam (9), extending horizontally from a segment of the vertical column (6), it provides torsional force to the vanes (1).

In at least an embodiment, a flange (10) is attached at the bottom of the vertical column (6). Load cells (15) are placed in between the flange (10) and the blocks (16) so that shear load can be measured directly. The flange (10) is angularly displaced when the torsional force is applied and upon its displacement it hits the blocks (16), thereby causing measurement of load in load cells (15) placed between the radial ends of the flange (10) and the blocks (16).

The horizontal beam (9) is pulled with the help of a wire(14) attached to motor (13) or a manual winch; the shear load can also be measured by attaching a proving ring or spring balance at a wire rope (14) which is attached to the horizontal beam (9) and the motor (13). The load cell / spring balance, measures the force required to angularly displace the vanes (2), from which torque can be calculated. The calculated torque has a direct relationship with the shear strength of the soil. By plotting the measured shear strength under different normal loads, Coulomb’s shear strength parameters can be calculated like in a direct shear test.

Figure 4 illustrates device set-up with hydraulic jack.

Figure 5 illustrates another view of the device set-up with hydraulic jack.

In this method, normal load up to 5 T or more can be applied easily with the help of the hydraulic jack (7). Hydraulic jack has been connected with the bearing (18) so that while the angular movement of the entire assembly, the hydraulic jack should be at rest position. Also, the shear stress can be applied at a constant and desirable strain with the help of the geared motor (13). Two square strips (17) have been fixed on the vertical column (6) on which sliding block (8) can slide. The block is connected to horizontal beam (9), in this way horizontal beam also can be fixed any desired location on the vertical column. Torque can easily be calculated with the help of readings from the load cells or spring balance. The applied shear stress at various degrees of shear displacements can be plotted and peak shear stress can be easily obtained. Thus, the apparatus is very useful for measuring accurately the Coulomb’s shear strength parameters of the in-situ soil (for both cohesive as well as non-cohesive soils). Also, the same apparatus can be used for conducting a plate load test up to 5 T or more normal loads.

1 Vane
2 Cylinder
3 Four numbers of porous quarter plates
4 Steel ball position for quarter plates
5 Top plate with bottom groove
6 Telescopic Vertical column
7 Hydraulic jack with bearing arrangement
8 Connection of vertical column with horizontal beam.
9 Horizontal beam
10 Flange
11 Inner vertical column
12 Outer vertical column
13 DC motor
14 Wire rope
15 Load cell
16 Blocks
17 Vertical square strips
18 Bearing

The apparatus, of this invention, is configured to measure soil cohesion (c) and friction angle (?) of field soil. Horizontal beam arrangement is provided for giving torsional load. There is provision of a normal (axial) load by means of a hydraulic jack. The top plate with a groove arrangement is provided in order to transfer whole normal load to the soil (no normal load transfer on walls of vane) and also allows angular displacement of vanes. The top plate comprises a two blocks' arrangement in order to transfer torque applied on vertical column to the top plate and thus to the vane. There is provision of four quarter plates (with ball arrangement) between soil and top plate to allow dilation of soil during shearing action. There is confined vane arrangement in order to keep shearing area constant. Using this apparatus, particle size up to 25 mm can be tested; as diameter of vane is 300 mm, which is 12 times greater than particle size (as required as per standards). Also, more than 25 mm particle size can be tested by simply modifying the size of vane and length of horizontal beam.

Figure 6 illustrates the flange (10) fixed on vertical column and block fixed on the top plate (5).

Figure 7 illustrates hydraulic jack (7) and bearing, fixed at bottom part of horizontal jack.

The TECHNICAL ADVANCEMENT, of this invention, lies in providing a device for assessment of in-situ shear strength of soil using axial load and torsional load; on all types of soil, including soils with large particle sizes, such as up to 25 mm.
The TECHNICAL ADVANCEMENT, of this invention, also lies in the fact that due to grooves, vanes can be rotated by top plate, without transmitting any normal load to vanes (i.e. all the normal load is transmitted to soils resting between vanes only). Each of the quarter plates allow dilation effect of soil during shearing.
The in-situ torsional direct shear test can be used for obtaining the Coulomb’s shear strength parameters of the in-situ sandy or gravelly soil, which can be more reliable as compared to the laboratory obtained shear strength parameters.

When compared with prior art, related to shear test on soil using torsional load. the following observations can be made:
Sr. No. PARAMETERS Field Vane Shear test
(Prior Art) US Patent Application No. 04/480,481
(Prior Art)
Torvane Shear
ASTM D2537
(Prior Art) DEVICE OF THIS INVENTION INVENTIVE STEP
1 Type of soil test Soft Cohesive soil All types of soil Soft Cohesive soil All types of soil The device of this invention is compatible for all soils
2 Way of application of normal load Normal load is not applied Normal load is applied by use of dead loads Normal load is applied by hand pressure Hydraulic jack with bearing arrangement is used In the device of this invention, normal load can be applied by up to 5 T or more. The vertical column can be rotated due to bearing fixed by using hydraulic jack
3 Torsional load By gear and spring arrangement Spring arrangement Spring arrangement Applied by horizontal beam In the device of this invention, horizontal beam is pulled with motor or winch. Also, beam can move in vertical direction so that test can be conducted at any depth. This arrangement is provided as large torque is required for rotation of vanes.
4 Particle size which can be tested Particle size of fine particles (< 75 ?) Up to 1mm Up to 1mm Up to 25mm Mould size should be 12 times more than particle size which is to be tested. In the device of this invention, soil having higher particle size can be tested by just increasing the diameter of vane and length of the horizontal beam. The current arrangement has been made to test up to 25mm particle size.
5 Dilation No provision No provision No provision Allows dilation Four porous plates have been used in the device of this invention. This allows dilation of soil, during shearing action.
6 Confinement of vanes using circular cylinder fixed to vanes No confinement No confinement No confinement Confined vane Confined vane keeps shearing area constant throughout the test, thus shearing and normal stress can be calculated easily.
7 Results Only c is obtained and ? assumed as a zero. c and ? can be obtained but verification of results are not available, only for particle size 1mm Only c is obtained and ? assumed as a zero. c and ? can be obtained up to 25 mm size particles c and ? from T-DST are comparable to that obtained from laboratory large box direct shear test. In the usual cases most of the soils
from TDST about 1.5 times c from DST, and TDST is almost equal to ? from DST.

While considerable emphasis has been placed herein on the particular features of this invention, it will be appreciated that various modifications can be made, and that many changes can be made in the preferred embodiments without departing from the principles of the invention. These and other modifications in the nature of the invention or the preferred embodiments will be apparent to those skilled in the art from the disclosure herein, whereby it is to be distinctly understood that the foregoing descriptive matter is to be interpreted merely as illustrative of the invention and not as a limitation.

,CLAIMS:WE CLAIM,

1. An in-situ torsional direct shear test device to evaluate shear strength parameters of in-situ soil, said device comprising:
- a cylinder (2), with its operative top side being covered by a top plate (Figure 3) and its operative bottom side being open, said cylinder comprising vanes (1) attached at right angles, inside said cylinder (2), said cylinder inserted in ground (that is to be tested) with peripheral soil outside said cylinder (1) being removed;
- four quarter plates (3) forming an operative top surface of said cylinder, each quarter plate separated by an adjacent vane (1) that extends from underneath, each of said quarter plates (3), of said top surface, comprising a hemispherical slot at a pre-defined position for locating a corresponding spherical ball (4); and
- a top grooved plate (5) which sits on said operative top surface of said cylinder (1) to transmit normal load applied at the top of said plate (5) directly to soil between said vanes (1) underneath said cylinder (2), said top grooved plate (5) resting on said four spherical balls (4) which are sandwiched between said top grooved plate and said quarter plates, the underside of said top grooved plate (5) comprising grooves which bifurcate said top plate’s (5) underside into four quarters such that each groove receives a portion of a vane (1) when said top grooved plate (5) is placed over said spherical balls (4).

2. The device as claimed in claim 1 wherein, said cylinder is and open-ended circular with its open-end configured to be inside said ground that is to be tested.

3. The device as claimed in claim 1 wherein, said spherical ball (4) being a steel spherical ball (4).

4. The device as claimed in claim 1 wherein, each of said quarter plates, of said top plate (5), comprising a hemispherical slot at a pre-defined position for locating a corresponding spherical ball (4), thus, each spherical ball being ensconced in a spherical groove formed by two corresponding hemispherical slots (one on the top surface of the cylinder and one on the underside of the top plate).

5. The device as claimed in claim 1 wherein, said device comprising:
- a vertical elongate column (6) in order to apply normal load onto said device through the top grooved plate (5);
- a hydraulic jack (7) to apply normal load to said top grooved plate (5) through said vertical elongate column (6); and
- a bearing below said hydraulic jack (7) to allow angular displacement of said vertical elongate column (6), while normal load is applied on the vertical elongate column (6).

6. The device as claimed in claim 5 wherein, said vertical elongate column (6) is a telescopic vertical elongate column (6).

7. The device as claimed in claim 5 wherein, an additional spherical ball is provided which rests in between said top grooved plate (5) and said vertical elongate column (6) in order to transfer load normally to said other four spherical balls where, again, said load is transferred normally, the use of said arrangement of spherical balls ensuring a 2-level distribution of force, normally.

8. The device as claimed in claim 5 wherein, said top grooved plate (5) comprising two blocks (16), protruding outwardly, on its operative top surface such that when said vertical elongate column (6) is angularly displaced by means of a pulling horizontal beam (9), extending horizontally from a segment of said vertical elongate column (6), it provides torsional force to the vanes (1).

9. The device as claimed in claim 5 wherein, a flange (10) is attached at the bottom of said vertical elongate column (6).

10. The device as claimed in claim 5 wherein,
- said top grooved plate (5) comprising two blocks (16), protruding outwardly, on its operative top surface such that when said vertical elongate column (6) is angularly displaced by means of a pulling horizontal beam (9), extending horizontally from a segment of said vertical elongate column (6), it provides torsional force to the vanes (1);
- load cells (15) are placed in between the flange (10) and the blocks (16) so that shear load can be measured directly, said flange (10) being angularly displaced when the torsional force is applied and upon its displacement it hits the blocks (16), thereby causing measurement of load in load cells (15) placed between the radial ends of the flange (10) and the blocks (16); and
- a horizontal beam (9) is pulled with the help of a wire (14) attached to a motor (13) or a manual winch, the shear load being measured by attaching a proving ring or spring balance at a wire rope (14) which is attached to said horizontal beam (9) and said motor (13), the load cell / spring balance, measuring the force required to angularly displace said vanes (2), from which torque can be calculated, said calculated torque having a direct relationship with the shear strength of said soil.

Dated this 04th day of December, 2019

CHIRAG TANNA
of INK IDEE
APPLICANT’s PATENT AGENT