FIELD OF THE INVENTION

The present invention relates to the devices/apparatus/systems/methods capable of carrying out direct and indirect accurate measurement of tensile strength of soil and other geomaterials. More particularly, the present invention relates to devices used with a load cell and/or a load frame (of the existing tensile strength testing assembly) for determining the direct tensile strength, indirect split tensile strength, and indirect flexural tensile strength of the soil/geomaterial specimen/sample. The present invention is advantageous in terms of research and development as well as for field applications, as it gives a useful insight in understanding the behaviour of soils and other geomaterials under tensile loading and indirect tensile stress conditions.

BACKGROUND OF THE INVENTION

Measurement of tensile strength of soil and other geomaterial is important for evaluation of soil susceptibility to cracking. Cracking causes several problems such as early failure of soil (including slopes) and higher settlement of soil due to ingress of water. Further, the effectiveness of soil stabilization for mitigation of cracking and improving stability of soil slopes; and better response of soil to wetting and drying cycles, depends on the improvement in tensile strength of soil. Hence, measurement of direct tensile strength of soil and other geomaterials (alternative materials such as flyash, pond ash, landfill mined soil like fraction and other materials, which can be used as replacement of soil) is important. Further, problems such as subsidence failure in dispersive and collapsible soils, failure of tunnels and soil arches would require evaluation of indirect tensile strength of soil, where tensile failure is either at other locations (direction/location of loading and failure are different) or tensile failure is due to flexural loading (bending).

A detailed prior art study has been carried out with respect to existing inventions that are related to tensile strength measurement for materials and are presented below:

US10408720B1 discloses the testing apparatus for tensile strength of soft rock and soil by using drawbars. Soft rock/soil specimen with central hole can be placed in the apparatus assembly and the lateral pull force is applied from the drawbars by making grip arrangement in hole of the soil specimen. However, patent US10408720B1 can be applicable for the rock/soft soil specimen which is facilitated with central hole. Direct tensile strength of intact specimen (without central hole), cannot be measured by using the patent US10408720B1. Further, flexural and split tensile strength, cannot be obtained by patent US10408720B1.

US5841019 discloses measurement of compressive strength by measuring the time interval of impact at which impactor touches the material surface and it stops moving/rebounding. Tensile strength is measured by recording the duration of the rebound phase (which is a time interval at which impactor stops moving, and rebounds until it loses the contact between body and surface). However, for soils and other geomaterials (which is relatively soft material, and that exhibits both brittle and ductile behaviour at different water content), the disclosed patent is not applicable.

US5905205 describes the biaxial test apparatus, in which the biaxial load carrying capacity of flat plate test specimen can be determined. The measurement of biaxial load is carried out by using load transfer frame (rhombus shape) with 4 members which take compression load and the tensile load is applied at the central portion of the frame. Test specimen is located at the central portion of the frame, however the measurement of tensile capacity of the relatively soft material such as soils and other geomaterials is not possible with the said patent.

US6560550B2 gives the indirect measurement of tensile strength of weak rock and hard soil, in which the device has to be inserted into the rock/hard soil specimen by making a hole in the weak rock/hard soil. The inflammation of the measuring device is carried out till failure of the weak rock/hard soil specimen. Tensile strength can be measured by monitoring the volume change and the maximum load which applied on the inner portion of the rock/hard soil. This patent cannot measure the tensile strength of intact soils/other geomaterials (without disturbance), which is possible with the present invention.

CN206095789U facilitates the measurement of uniaxial tensile strength of horizontal soil specimen using grips at edges connected with adhesive bonding material to the soil. This arrangement is very difficult for particulate materials such as soils, and cannot be utilized for measurement of tensile strength of relatively wet soil specimen. Further, the tensile stress distribution along length of specimen may be non-uniform due to restraint at the edges only. The present invention utilizes direct soil gripping arrangement with proper grip length, and can be utilized for tensile strength measurement of soils/geomaterials at different water conditions (relatively wet to dry conditions). Further, the present invention enables correlation between the direct and indirect tensile strength of soil and other geomaterials.

Based on the prior art it is observed that, the similar information regarding direct and indirect tensile strength measurement of soils and other geomaterials (as proposed in the present invention) is not available.

OBJECT OF THE INVENTION

The object of the present invention is to allow easy and direct/indirect tensile strength measurement of soils and other geomaterials using simple and compact device, which would be beneficial in both research work and field applications.

It is another object of the present invention to provide a device for direct tensile strength measurement of soils and other geomaterials along the drying and wetting paths (soil undergoes drying during summer and wetting during monsoon and its properties varies during the drying and wetting paths). Additionally, evaluation of effectiveness of crack mitigation/soil stabilization at different water contents is possible by measurement of tensile strength before and after treatment.

It is another object of the present invention to provide device(s) for indirect split tensile strength measurement and indirect flexural tensile strength measurement of soils and other geomaterials. Additionally, the present invention allows development of corelation between direct and indirect tensile strength of soils/geomaterials. This would allow prediction of tensile strength of soils/geomaterials for field problems such as crack propagation in soils/geomaterials after crack initiation (e.g. soil slopes), and simulation of complex problems such as tunnels, soil arches, subsidence failures due to cavity formation in soils.

It is a further object of the present invention to provide a low-cost device(s), easy and quick measurement of tensile strength of soils and other geomaterials.

SUMMARY OF THE INVENTION In one aspect, the present invention provides a device/apparatus to be used with a load frame and load cell for determining direct tensile strength of soils/geomaterials. The device comprises a gripper assembly having a gap therein to hold a soil/geomaterial specimen; two tension plates mounted at opposite sides within the gap of the gripper assembly; and two tension hooks coupled with the tension plates at the opposite sides through connecting rods. The gripper assembly comprises a pair of top and a pair of bottom grip plates, which have open slots through which positioning of the tension plates are adjusted as per the specimen thickness. The top grip plates are aligned in a first plane at a defined distance therebetween, and the bottom grip plates are aligned in a second plane parallel to the first plane at the defined distance therebetween.

In another aspect, the present invention provides a device/apparatus to be used with a load frame and load cell for determining indirect tensile strength of soil/geomaterial. The device comprises soil/geomaterial specimen holder/container as a lower part to be placed within a load frame (with motorised/hydraulic/pneumatic load application facility) connected with the load cell; and a loading pad as an upper part adapted to apply force/reaction to the specimen. The loading pad having a top groove for receiving a load/reaction from the load frame, which is measured by the load cell, and a downward apex point contoured to apply upward compressive force to the specimen. The specimen holder comprises of guide walls, and a fixed bottom base plate having an upward apex point contoured to apply downward compressive reaction to the specimen causing splitting of the specimen therein. For split tensile strength measurement the fixed bottom base plate is used; whereas for flexural tensile strength measurement, the specimen holder also comprises an adjustable base assembly in place of the fixed bottom base plate.

Other aspects, advantages, and salient features of the present invention will become apparent to those skilled in the art from the following detailed description, which delineate the present invention in different embodiments.

BRIEF DESCRIPTION OF DRAWINGS

These and other features, aspects, and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying figures. Fig. 1, 2 and 3 are top view, side view and isometric view of the direct tensile strength measuring device respectively, in accordance with an embodiment of the present invention.

Fig. 4 is a side view of the indirect split tensile strength measuring device, in accordance with an embodiment of the present invention.

Fig. 5 is a side view of the indirect flexural tensile strength measuring device, in accordance with an embodiment of the present invention.

Fig. 6 illustrates pulling/compressive force application using the devices with the load frame and load cell (of the tensile strength testing assembly), in accordance with an embodiment of the present invention.

Fig. 7 is a flow chart illustrating simulation of different field problems where soils/geomaterials experience either direct or indirect tensile stresses.

Fig. 8 is a flow chart illustrating working of the devices (method steps employed using the devices) for determining both direct and indirect tensile strength of soil/geomaterials, in accordance with an embodiment of the present invention.

List of reference numerals:

100 Tensile strength testing assembly

13 load cell

13a load display

13b pulley

13c pulling rope for applying pulling force on the specimen

13d tension hook connecting points

33 load frame

34 load

14 Direct tensile strength measuring device

1 gripper assembly la top grip plates lb bottom grip plates 2 tension hooks

3, 11 open slots of top and bottom grip plates respectively

4, 6, 8, 9 screw assembly

5 tension plates

12 connecting rods between tension hooks and tension plates

7 connection points between tension plates connecting rods

10 gripping base provided on internal side of grip plates

35 Indirect split tensile strength measuring device

23 soil/geomaterial specimen

29 specimen holder

24 guide walls

26 fixed bottom base plate

25 upward apex point

20 loading pad

22 top groove

21 downward apex point

36 Indirect flexural tensile strength measuring device

30 adjustable base assembly

31 top plates

31a downward proj ections

32 bottom plate

32a grooves

33 frame of load cell

34 load

DETAILED DESCRIPTION OF THE INVENTION

Various embodiments described herein are intended only for illustrative purposes and subject to many variations. It is understood that various omissions and substitutions of equivalents are contemplated as circumstances may suggest or render expedient, but are intended to cover the application or implementation without departing from the scope of the present invention. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of terms “including,” “comprising,” “consisting,” or “having” and variations thereof herein are meant to encompass the items listed thereafter and equivalents thereof as well as additional items. Further, the terms, “an” and “a” herein do not denote a limitation of quantity, but rather denote the presence of at least one of the referenced item.

As shown in Fig 6, the present invention proposes a holistic approach/solution in form of interlinked assemblies/devices (14, 35, 36) which are compatible to be used in an existing tensile strength testing assembly (100) for measuring both direct and indirect tensile strength of a soil/geomaterial specimen/sample carried within the devices (14, 35, 36). Preferably, the tensile strength testing assembly (100) is known to have a load cell (13), a load frame (33) and a load (34) to be applied to cause cracking/breaking/splitting/bending of the specimen [as shown in Fig. 6(a), Fig. 6(b)], Further, the tensile strength testing assembly (100) may have a provision of horizontal or vertical manual/motorized pulling arrangement including pulling rope (13c) passing over pulley (13b) coupled with tension hook (device) connecting points (13d) [as shown in Fig. 6(a)], Furthermore, the load frame (33) has a motorised/hydraulic/pneumatic or other mechanism/assembly, for applying pulling (tensile) /compressive force on the specimen carried within the devices (14, 35, 36), while the load cell (13) enables the measurement of applied tensile/compressive load/reaction force value to be displayed in a load display (13a); so that the desired tensile strength of the specimen is calculated by using the following formula/equations. > Formula (1) where is direct tensile strength of soil/geomaterial; P is failure tensile load (pulling load); A is cross-sectional area of failure section of the specimen > Formula (2) where cr _t ( _spI£t ) is split tensile strength of soil/geomaterial, P is failure load from split tensile test, D is diameter of specimen, t = thickness of specimen. > Formula (3) where Otfjiexure) is flexural strength of soil/geomaterial, P is breaking load; L is unsupported length of soil/geomaterial, t is thickness of specimen; B is the width/diameter of the specimen.

Accordingly, a correlation among the direct tensile strength and the indirect (split and flexural) tensile strength can easily be established for better understanding of behaviour of the specimen under different types of loading conditions (that occur in the field).

According to an embodiment of the present invention, as shown in Fig. 1-3 and Fig. 6(a), the device (14) is to be mounted in the load frame with the load cell (13) having a pulling arrangement adapted for applying pulling force from opposite sides of the soil/geomaterial specimen held within the device (14). The load cell (13) has the display (13a) to show the pull load/force applied thereon. The pulling arrangement (with calibrated known weights or mechanical/motorized pulling arrangement) that includes two opposite facing device connecting hooks (13d) between which the device (14) is to be mounted. The device (14) comprises a gripper assembly (1) having a gap therein to hold a soil/geomaterial specimen; two tension plates (5) mounted at opposite sides within the gap of the gripper assembly (1); and two tension hooks (2) coupled with the tension plates (5) at the opposite sides (i.e. connection points 7) through connecting rods (12). The gripper assembly comprises a pair of top grip plates (la) detachably attached above a pair of bottom grip plates (lb) at a gap therebetween to hold a soil/geomaterial specimen. The grip plates (la, lb) are provided with open slots (3, 11) through which positioning of the tension plates (5) are adjusted as per the specimen size. The top grip plates (la) are aligned in a first plane at a defined distance therebetween, and the bottom grip plates (lb) are aligned in a second plane parallel to the first plane at the defined distance therebetween. Alternatively, this direct tensile strength measurement device (14) may be used with the load cell in the load frame (motorized/hydraulic/pneumatic) which is used for the indirect tensile strength measurement devices (35, 36) for application of tensile loading, instead of the pulley assembly (as shown in Fig. 6(b).

In a preferred embodiment, in the device (14) the top grip plates (la) are coupled with the bottom grip plates (lb) through screw assembly therebetween to adjust positioning and gripping of the specimen therein. The grip plates (la, lb) are internally provided with gripping bases (10) to grip the specimen with sufficient strength. The screw assembly comprises two pairs of oppositely facing clamping screw plates (4) provided on outer edges between the gap region; two inner clamping screw plates (6) provided near the tension plates (5); bottom screws (8) provided underneath the bottom grip plates; and clamping screws (9) provided between the top and bottom grip plates (la, lb).

In a preferred embodiment, the device (14) is to be held between the device connecting hooks (13d), and with the load cell (13) using the tension hooks (2) to apply pull force at the opposite sides till the specimen cracks, thereby enabling to determine direct tensile strength as a ratio of pulling load at which the specimen cracks and cross-section area of the specimen (using Formula 1).

According to an embodiment of the present invention, as shown in Fig. 4 and Fig. 6(b), the device (35) is to be mounted in the tensile strength testing assembly (100) that has a housing/load frame (33) and a top load (34) adapted for applying compressive force on the soil/geomaterial specimen (23) held within the device (35) placed within the housing frame (33). The device (35) comprises a soil/geomaterial specimen holder/container (29) to be placed within the housing frame (33) of the load frame, along with load cell (for measurement of load); and a loading pad (20) adapted to apply force into the specimen holder/container (29). The loading pad (20) has a top groove (22) for receiving the load/reaction (34) from the load frame assembly, and a downward apex point (21) contoured to apply downward compressive load/reaction (point load application) to the specimen (23). The specimen holder (29) comprises guide walls (24), and a fixed bottom base plate (26) having an upward apex point (25) contoured to apply upward compressive force to the specimen (23) causing splitting of the specimen (23) therein. The compressive force is applied by the load (34) with the loading frame (33) and measured by the load cell (13) till the specimen (23) splits, thereby enabling to determine indirect split tensile strength using Formula 2.

According to an embodiment of the present invention, as shown in Fig. 5 and Fig. 6(b), the device comprises a soil/geomaterial specimen holder (29), to be placed within the housing frame (33) of the tensile strength testing assembly (100); and a loading pad (20) having a top groove (22) for receiving the load (34) of the tensile strength testing assembly (100), and a downward apex point (21) contoured to apply bending force to the specimen (23). The specimen holder/container (29) comprises guide walls (24), and an adjustable base assembly (30). Further, the adjustable base assembly (30) comprises a pair of top plates (31) having a gap with downward projections (31a) therebetween; and a bottom plate (32) provided thereon with a plurality of grooves (32a) through which the downward projections (31a) of the top plates (31) movably coupled to adjust the gap therebetween according the specimen size or unsupported length requirements. The compressive force is applied by the load (34) from the load frame till the specimen breaks (due to bending at the gap or unsupported region between the top plates 31), thereby enabling to determine indirect flexural tensile strength using Formula 3.

Working of the Invention:

As illustrated in Fig. 7, various evaluation and simulation of different field problems, wherein soils/geomaterials experience either direct or indirect tensile stresses are carried out. If the direct tensile strength is required to be measured, then the user may use the device (14) with the existing tensile strength testing assembly (100) (using Formula 1). If the indirect tensile strength is required to be measured, then the user may use the devices (35, 36) with the existing tensile strength testing assembly (100); where the device (35) helps in determining split tensile strength (using Formula 2), and the device (36) helps in determining flexural tensile strength (using Formula 3).

In an exemplary embodiment, as illustrated in Fig. 8, three circular soil specimens of 5 cm diameter are selected for determining tensile strength. One specimen is intact/untreated undisturbed soil directly obtained from the site. Two other specimens are treated (remoulded or slurried [after some drying]).

The undisturbed, remolded or slurried (after some drying) soil and other geomaterial specimen can be tested in the first embodiment device (14) for determining direct tensile strength (caused due to pulling load). Specially design grip facilitates proper holding the soil/geomaterial specimen between the top and bottom grip plates (la, lb). The pull force can be applied through the tension hooks (2) and the direct tensile strength can be measured as the ratio of failure load and cross-section area at failure plane. The undisturbed, remolded or slurried (after some drying) soil and other geomaterial specimen can be tested in the second embodiment device (35) for determining indirect split tensile strength (caused due to compressive load). By application of point load from bottom and top of the soil specimen can be split into two parts and the indirect tensile strength can be measured. This device (35) is useful when failure in soil is tensile failure but induced due to loading in other direction (e.g., indirect tension failure in slopes).

The undisturbed, remolded or slurried (after some drying) soil and other geomaterial specimen can be tested in the third embodiment device (36) for determining indirect flexural tensile strength (caused due to bending/flexural load). The soil is unsupported in some region between the top plates of the adjustable base assembly (the unsupported span can be adjusted as required), then it may undergo bending/flexure and fail by indirect tension due to bending. For example, failure of tunnels and soil arches under very heavy loading, subsidence failure due to internal erosion in embankments due to washing away of particles with water flow, etc. The specimen in the device (36) can be placed above the central portion of adjustable base support (30) and the tensile strength can be indirectly determined by measuring failure load of the specimen.

The present invention provides the following advantages over the prior arts, including but not limited to:

• The invention enables obtaining the stress-strain curve and elastic modulus under tensile loading for soils/geomaterials. The invention also allows evaluation of variation in tensile strength of the specimen at different water content along the drying and wetting paths.

• The invention allows direct and indirect measurement of tensile strength of soils/geomaterials without disturbing the structure of the specimen (intact specimen can be tested with the present invention). Insitu soil specimen (with intact structure), can be extracted to desired shape/size and tested with the present invention.

• Correlation between direct tensile strength, flexural tensile strength and split tensile strength of soil and other geomaterials is also possible with the present invention, which consists of three devices that enables measurement of direct and indirect (split and flexural) tensile strength. The foregoing descriptions of exemplary embodiments of the present invention have been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the invention to the precise forms disclosed, and obviously many modifications and variations are possible in light of the above teaching. The exemplary embodiment was chosen and described in order to best explain the principles of the invention and its practical application, to thereby enable the persons skilled in the art to best utilize the invention and various embodiments with various modifications as are suited to the particular use contemplated. It is understood that various omissions, substitutions of equivalents are contemplated as circumstance may suggest or render expedient, but is intended to cover the application or implementation without departing from the scope of the claims of the present invention.