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Title:
SOIL REINFORCEMENT WITH DISCRETE FIBERS
Document Type and Number:
WIPO Patent Application WO/2018/021981
Kind Code:
A1
Abstract:
The present invention proposes a composition for soil reinforcement which is comprising soil, at least one binder and polyamide66 or polyamide 6. Such a composition provides high load bearing strength, flexural strength and good compatibility of said fibers into the mixture.

Inventors:
OZBORA TARHAN, Adile Asli (Kordsa Global Endustriyel Iplik Ve Kord Bezi Sanayi Ve Ticaret Anonim Sirketi, Alikahya Fatih Mahallesi Sanayi Caddesi No:90, Kocaeli, TR)
ERDAL, Burak (Kordsa Global Endustriyel Iplik Ve Kord Bezi Sanayi Ve Ticaret Anonim Sirketi, Alikahya Fatih Mahallesi Sanayi Caddesi No:90, Kocaeli, TR)
IZMIT, Ilhan (Kordsa Global Endustriyel Iplik Ve Kord Bezi Sanayi Ve Ticaret Anonim Sirketi, Alikahya Fatih Mahallesi Sanayi Caddesi No:90, Kocaeli, TR)
GUNER CANTEKINLER, Pinar (Kordsa Global Endustriyel Iplik Ve Kord Bezi Sanayi Ve Ticaret Anonim Sirketi, Alikahya Fatih Mahallesi Sanayi Caddesi No:90, Kocaeli, TR)
Application Number:
TR2016/050234
Publication Date:
February 01, 2018
Filing Date:
July 25, 2016
Export Citation:
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Assignee:
KORDSA TEKNIK TEKSTIL ANONIM SIRKETI (Alikahya Fatih Mahallesi Sanayici Caddesi No:90, Izmit/Kocaeli, TR)
International Classes:
E02D3/12
Attorney, Agent or Firm:
ANKARA PATENT BUREAU LIMITED (Bestekar Sokak No:10, Kavaklidere, Ankara, 06680, TR)
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Claims:
CLAIMS

A reinforced soil mixture characterized in that, said reinforced soil mixture comprising; polyamide66 or polyamide6 micro fibers in an amount of 0.1-1% by weight and at least one binder material in an amount of 2-9% by weight into said reinforced soil mixture.

A reinforced soil mixture according to claim 1 wherein said polyamide66 or polyamide6 micro fibers have a length ranging between 6-30 mm.

A reinforced soil mixture according to claim 1 wherein said polyamide66 or polyamide6 micro fibers have a diameter at most 30 μιη.

A reinforced soil mixture according to claim 1 wherein said binder is cement.

A reinforced soil mixture according to claim 1 wherein said binder is

Pozzolanic cement.

A reinforced soil mixture according to claim 1 wherein said soil is constituted of 1% of gravel, 68% of sand, 29% of silt and 2% of clay.

A reinforced soil mixture according to claim 1 wherein said soil is constituted 4% of gravel, 83% of sand, 12% of silt and 1% of clay.

Description:
SOIL REINFORCEMENT WITH DISCRETE FIBERS

Technical Field of the Invention

The present invention is related to the compositions of reinforced soil which is comprising micro polyamide66 or polyamide6 fiber and at least one binder material.

Background of the Invention

The engineering properties of soils are improved by soil improvement techniques. These techniques vary by the application methods and soil types that can be improved. In general, the aim of soil improvement methods is improving the shear strength of soils and increase the bearing capacity of shallow foundations, reducing the shrinkage and swelling of soils, decreasing the settlement of structures and increasing the factor of safety for possible slope failure of embankments and earth dams.

Various materials has been mixed with soil to improve its properties. Soil and rocks were blended to have more stable roadbed with better performance in early highway constructions. For example, to reduce the swelling potential and the plasticity of clay and silty soils, lime has been used. Portland cement has been incorporated into several types of soils to have improved highway base material.

Geosynthetic materials have been used for numerous purposes such as improving load bearing capacity, providing resistance to lateral deformation, controlling erosion, etc.

As explained in US3934421, a matting of continuous thermoplastic filaments which are bonded together at intersections increases the vertical load bearing capacity and resistance to lateral deformation.

US4002034 provides a multi-layered composite matting, anchored to the ground to prevent erosion. US4329392 discloses a layered matting designed to inhibit soil particles rearrangement. The matting is composed of melt-spun synthetic polymer filaments with macrofibers forming a web, a filter layer of finer fibers bonded thereto and an intermediate layer of other fibers therebetween. The purpose is to control erosion below water level.

Another configuration of geotextile material is explained in US4472086. The material is used as a reinforcement for the construction of road ways and on slopes and river banks to control erosion.

Although polymer filaments are widely used in fabrics, matting, geogrids, etc. as soil reinforcers, the use of randomly distributed fibers in soil is limited.

The tensile behaviour of soil plays a significantly important role in various engineering applications such as slopes, dams, embankments and hydraulic barriers, where tensile cracks are likely to occur but compared with compressive or shear strength, tensile strength of soil is basically insignificant in geotechnical engineering practice because of its relatively low value. Also,the material used to reinforce soil has to be durable enough to satisfy the design life. In case of soil reinforcement with geosynthetics such as geogrid, the application on site has to be carefully performed to minimize the possible installation damages which could negatively affect the long-term design strength of the geosynthetics. As explained in W09914288A1, some fibers may be effective in improving the strength properties of soil-cement such as glass fibers but glass fibers if they are not alkali resistant, are detrimental to durability.

Another potential problem with randomly distributed fibers is the agglomeration of the fibers.

Synthetic fibers have been used for over 40 years to reinforce cementitious materials such as concrete but research works on discrete fiber reinforced soil are not so numerous. Limited number of examples of the soil reinforcement by fibers have been described in the patent literature. It was known from the prior art that fibers such as polypropylene, polyester fibers, fiberglass are used into soil to improve the punching shear resistance, the total angle of internal friction, the average total cohesion and the average initial tengent modulus. However, inadequate homogenity of fiber in soil mixture depending on lack of physical and chemical adhesion property of widely used fiber materials such as polypropylene, polyacrylonitrile, fiberglass exc. causes nonhomogenous load bearing capacity for a reinforced soil. Objects of the Invention

Compared to conventional methods, the advantages of discrete fibre reinforcement which is a relatively newly developed technique to improve soil mechanical behaviour are as follows; the discrete fibres are directly added and mixed randomly with soil in one process, similarly to soil mixed with cement, lime, or other additives, potential planes of weakness that can develop in the direction parallel to the conventionally oriented reinforcement are limited by randomly distributed fibres, fibres increase thoughness of the soil and provide three dimensional reinforcement which can increase the load bearing capacity in all dimensions especially required for slope stability, earth quake reinforcement and weak soil reinforcement, the inclusion of fibre is sustainable solution which only changes the physical properties of soil and has no adverse effect on the environment. For all these reasons, an increasing interest in mechanical behaviours of fibre reinforced soils has been shown.

The main object of the present invention is to provide homogeneous, compatible reinforcement material for soil to improve its load-deformation behavior by interacting with the soil particles, thus, increase the load bearing capacity of the soil in all dimensions.

A further object of the present invention is to provide thoughness of the soil and provide three dimensional reinforcement.

Another object of the present invention to prevent embankment failures and settlement problems of soil. A further object of the present invention is to provide energy efficiency, low maintance costs and increase sustainability by enabling the use of the soil in most of the layers in earthworks which will be the State of the Art of Earthworks.

Brief Description of the Invention

The present invention proposes composition to provide reinforced soil which have high load bearing capacity by proposing the usage of specified amount of polyamide66 or polyamide6 fibers and at least one binder material together in the mixture.

Brief Explanation of the Figures The figures brief explanation of which are herewith provided is solely intended for providing a better understanding of the present invention and are as such not intended to define the scope of protection or the context in which said scope is to be interpreted in the absence of the description. Figure 1 shows the graph of relative stress deflection curve for specimens with and without fibers.

Figure 2 shows the graph of relative compressive stress-axial strain curve for specimens with and without fibers.

Figure 3 represents the effect of polyamide66 on cement stabilized soil specimen fracture.

Detailed Description of the Invention

The present invention proposes a reinforced soil composition which includes random distributed fibers provides strength isotropy to the soil. Fiber reinforcement of soil increases structure stability security improving the residual strength and toughness of the reinforced soil.

As the fibers can improve the average angle of friction, steeper side slopes for embankments are possible. Additionally, as fill dirt decreases, transportation costs may be reduced and energy efficiency is achieved. Fiber reinforced soil providing improved engineering properties, permits to reduce volume change or settlement in high fills. Greater cohesion and angle of internal friction values or shear strength provide to improve the long term strength of backfill soils behind walls, retaining structures producing lower earth pressures thus, reducing the potential for lateral movement.

The present invention provides for the reinforcement or stabilization of soil by proposing a composition of reinforced soil mixture which provides high load bearing capacity, improved toughness and adequate flexural strength.

Type of the soils includes but are by no means limited to; silty sand and clayey sand. To classify the soils, necessary tests are carried out to determine the grain size, liquid limit and plastic limit.

One type of the soil is constituted of 1% of gravel, 68% of sand, 29% of silt and 2% of clay. Liquid limit is 33%, plastic limit is 18 and plasticity index is 15%. The dry density, γ, varies from 19.10kN/m 3 to y=19.60kN/m 3.

The other type of the soil is constituted of 4% of gravel, 83% of sand, 12% of silt and 1% of clay. Liquid limit is 0%, plastic limit is 0, this soil type is constituted of non- plastic fine grains. The dry density, γ, varies from 20.30N/m 3 to y=20,65kN/m 3. Typical soil binders known in the art are made from a variety of materials: Portland cement, lime, quicklime, hydrate lime, gypsum, ground blast furnace slag, fly ash type "C", fly ash type F", fly ash type F"— lime, fly ash-gypsum-lime, cement-fly ash, cement-slag, and slag-fly ash. The binder, which acts as a chemical stabilizer, is added to the soil and intermixed with it, the preferred binders according to the present invention are cement and Pozzolanic cement but should not be limited to that.

To achieve the maximum compaction, water is included into the binder-fiber-soil mixture. The amount of water to be incorporated depends on the soil type. Simple tests such as (modified) proctor are carried out to determine the amount of water to be added to give the optimum dry solid density following compaction for any particular type of soil. The optimum water content, w op t, ranges between 12-12,5% for the first type of soil and this value ranges between 9-9,5% for the second type.

Preliminary visual tests are performed to determine the most appropriate fibers without any agglomeration problem for two types of soil.

In a preferred embodiment of the invention fibers are polyamide6 or polyamide66, more preferably, polyamide66. Fiber material are selected for flexibility, elasticity, durability, ductility and compatibility into the soil mixture. Taking into consideration these first visual results, mixes are prepared to evaluate the effect of fiber with different aspect ratios based on mechanical test results.

The preferred embodiment of the present invention, for soil reinforcement application of the above described two type of soil, the most suitable fiber material has been invented as polyamide66 or polyamide6 depending on its above mentioned characteristics, visual results because of its outstanding water absorbence capacity, stronger bonds into the soil particles form. As a result of those, a homogeneous soil mixture is obtained while the structure stability security increases, residual strength and toughness improves at the same time.

The reinforced soil mixture according to the present invention comprises polyamide66 or polyamide6 micro fibers in an amount of 0.1-1%, by weight and at least one binder material in an amount of 2-9%, by weight into said reinforced soil mixture.

Preferably, a reinforced soil mixture is obtained by mixing a quantity of soil to be stabilized with 2-9% (w/w) of at least one binder; mixing a quantity of stabilized soil with 0.1-1% (w/w) polyamide66 or polyamide6 fibers to a substantially homogeneous mixture according to the present invention.

The micro fibers according to the present invention are added to the binder stabilized soil. Preferably, the diameter of the micro fiber filaments varies at most 30 μιη to provide higher surface contact area between fibers and soil particles, if the diameter of the filaments is higher than this value, the surface contact area between fibers and the soil particles decreases .The fiber length can range from about 6 to 30 mm for the micro fibers. The fibers are intermixed by hand until they appear to be homogenously distributed throughout the binder stabilized soil mass.

Fiber with suitable length is chosen based on the preliminary laboratory test results. The length has to be determined in such a way that adequate tensile strength is provided to the material but the fiber has not to be too long which could cause the balling problem during the mixing process at laboratory scale or on site.

An exemplary of the present invention is obtained with a polyamide6.6 micro fiber which has 24 mm long with a round cross-section and is cylindrical in design. A special spin finish is applied during the production of 24 mm micro fiber (Kratos ® ), which allows the fiber to be homogeneously distributed within cement stabilized soil during the application.

To assess the effects of fiber reinforcement on the engineering properties of binder stabilized soil, numerous cylindrical and prismatic specimens are prepared with varying fiber quantities for unconfined compressive strength and flexural tensile tests. The results are compared against the same binder stabilized soil without fiber accepted as control specimens. As seen in Figure 1, the cement stabilized soil gains ductility with improved thoughness and residual strength values when polyamide fibers are added into the mixture according to the present invention.

Similarly, the unconfined compressive strength test results show that the fiber incorporation improves the ductility of the soil according to the present invention as given in Figure 2. In the present invention, discrete fibre reinforcement is proposed to improve soil tensile behaviour while providing a homogeneous reinforced soil mixture depending on the good water absorbency of polyamide66 or polyamide6. To evaluate the effect of the fibers on thoughness and residual strength of binder stabilized soil, a flexural tensile apparatus normally used for concrete is adopted for soil tests. Using this apparatus, series of flexural tensile tests are performed on fibre reinforced binder stabilized soil to determine the flexural tensile strength characteristics.