Ultimate Bearing Strength on Rectangular Footing Resting Over Geogrid Reinforced Sand Under Eccentric Load

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Ultimate Bearing Strength Over Geogrid Reinforced Sand Under Eccentric Load

Singh Avtar1

1,2Department of CE, (Geo3Civil Engineer, PWD Jammu and Kashmir

ABSTRACT There is number of works has been carried out for the evaluation of an ultimate bearing strength of shallow foundation, supported over geogrid reinforced sand and subjected to load on center. Some experimental has been study for calculation of the bearing strength of shallow foundation on geogrid reinforced sand under eccentric loading. However that the studies for strip footings. The main purpose of the research work is to conduct model tests under the laboratory with utilizing rectangular surface foundation rest over the reinforced sand. The true bearing capacity of eccentrically loaded rectangular footing resting over geogrid reinforced sand can be determined by knowing the ultimate bearing strength of rectangular footing resting over reinforced sand bed and subjected to central vertical load with using reduction factor (R kR). An equation for reduction factor for rectangular footing resting over geogrid reinforced sand is developed on based of the laboratory model test results KEY WORDS: Ultimate Bearing Strength,Load, Reinforced Sand Bed. INTRODUCTION Foundation is the lower part of any very important part of any structure onshore or offshore structure. Thatreceive very big amount of load from and transmitted the load on the foundation.the foundation should be strong sustain the load of superstructure. the structure is usually depends on thefoundation. Since it is very important part,be designed well. The main problembearing capacity is solved with helpanalytical experimental work. The first

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6470 | Volume - 3 | Issue – 1 | Nov – Dec 2018

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Ultimate Bearing Strength on Rectangular Footing RestingOver Geogrid Reinforced Sand Under Eccentric Load

Singh Avtar1, Anu2, Pershotam Singh3 1PG Student, 2Assistant Professor (Geo-tech) G.G.G.I Dinarpur (Ambala), Haryana

Civil Engineer, PWD Jammu and Kashmir

There is number of works has been carried out for the evaluation of an ultimate bearing strength of shallow

reinforced sand and subjected to load on center. Some experimental has been study for calculation of the bearing strength of shallow foundation on geogrid reinforced sand under eccentric loading. However that the studies for

se of the research work is to conduct model tests under the laboratory with utilizing rectangular surface foundation rest over the reinforced sand. The true bearing capacity of eccentrically loaded rectangular footing resting over

an be determined by knowing the ultimate bearing strength of rectangular footing resting over reinforced sand bed and subjected to central vertical load with using reduction factor (R kR). An equation for reduction factor for rectangular

er geogrid reinforced sand is developed on based of the laboratory model test

Ultimate Bearing Strength, Eccentric

structure, but whether it is

That part which superstructure

foundation. Therefore enough to The work of

the work of the part, so it should

problem of True help of both

first one can be

calculate using theory ofelement method, and the performing laboratory test survey of the subject shows thatultimate bearing capacity theoriesvertical load of the rectangularother hand if the load isdistribution below the footingcausing unequal settlement will result in the tilt of footing.with rise eccentricity to widthof eccentricity to width (e/B) edge of the footing away contact with the soil whichreduction of the effective widthreduction of true bearing strengthResearchers are introducing reinforcingmetal strip, geophone, geotextileenhance the true bearing strength EQUIMENTS AND MATERIALSThe basic purpose of this researchbearing capacity of reinforcedBiaxial geogrid is used to reinforcetank of dimension 1 X 0.504prepare for sand bed. MATERIAL SAND 1. Sample Collection: It is sand

work is collected from near byRiver) . That sand is washfrom of soil, grass roots,materials and then the washoven.

2. Characteristics of Sand: All theare conducted at same relative

Research and Development (IJTSRD) www.ijtsrd.com

Dec 2018

Dec 2018 Page: 840

Rectangular Footing Resting Over Geogrid Reinforced Sand Under Eccentric Load

, Haryana, India

of plasticity or finite second is reached by model, the literature that the majority of the

theories involve centric rectangular footing. On the

is eccentric, the stress footing will be no uniform

at two edges which footing. The title will rise

width ratio (e/B). The ratio is greater than 1/6, the

from load is lose its which will result on the width of footing and hence

strength of foundation. reinforcing material like

geotextile and geogrid to strength on foundation.

MATERIALS research is to discover the

reinforced sand bed. Tenser reinforce the sand. Test

0.504 X 0.655 m is used to

sand used for the research near by jammu (Tavi

wash and it use for free roots, and an other organic

wash specimen is dried in

All the practically work relative density of 69%.

International Journal of Trend in Scientific Research and Development (IJTSRD)


The overall average unit weight ofrelative density is 1.46g/cc and internal

angle is find out to be 40.90 bytest of the relative density.

Table.1: Geotechnical Property

Property

Specific gravity (G) 2.64

Effective particle size (D10) 0.33mm

Mean particle size (D50) 0.455mm

(D60) 0.47mm

(D30) 0.42mm

Coefficient of uniformity (Cu) 1.424

Coefficient of curvature (Cc) 1.137

Maximum unit weight 14.87 kN/m

Minimum unit weight 13.42kN/m

Angle of internal friction (degree) 40.9

Maximum void ratio (emax) 0.929

Minimum void ratio (emin) 0.741

GEOGRID The shap of geogrids is the separategeosynthetics designed for reinforcement.Geogrids is the categorized by a relativelystrength and a same distributed groupopenings in between longitudinal and transverseThe openings are known aperture. Thatallow sand particle on both side ofgeogrid to come on the direct contact whichinteraction between the geogrid and base of strength direction, geogrids is Uniaxial and Biaxial while classified likeFlexible basis on rigidity. In present studygis used to model test is biaxial flexible geogridphysical characteristics is shown in Table

Figure 1 Flexible Geogrid



of sand on the internal friction

by shear direct

of Sand Value

2.64

0.33mm

0.455mm

0.47mm

0.42mm

1.424

1.137

14.87 kN/m3

13.42kN/m3

40.90

0.929

0.741

separate type of reinforcement.

relatively high tensile group of big transverse rib. That openings

of the mounted which rise the

sand.. On the classified like like Rigid and studyg geogrid geogrid whose

Table 3.2.

Geogrid

Table2. Properties of

Parameters

Polymer

Tensile strength at 2% strain

Tensile strength at 5% strain

Aperture size (W)

Aperture shape

Rib width (w)

Junction strength TEST TANK The size of the tank is madecode and from the result of some1962 said that lowest size shellthe wide of test plate to developzone without any interferencetank size, there is some scaleinfluence the ultimate bearingresting over geogrid reinforced(RKR ) is reduction factor is defined

(1- (

(

Where q uR(e) and q uR(e=0)bearing strength of reinforcedeccentric and centric loading EQUIPMENT USED STATIC LOADING UNIT A hydraulically operated staticused to apply the load overtest. The shaft is supportedwhich supply the reactionapplication of load. PROVING RING Proving ring of 20kN, 25kN,use during practically work applied load over the foundationpracticallyt work. The topconnected with the movable unit on the other hand the with the metallic ball whichfooting DIAL GAUGE Two number of dial gauge whichsettlement up to 50mm with is used during the practically

International Journal of Trend in Scientific Research and Development (IJTSRD) ISSN: 2456-6470

Dec 2018 Page: 841

of the geogrid

Value

Polypropylene Pp

strain 7 KN/m

strain 14 KN/m

39*39 mm

Square

1.1 mm

95%

made up on the base of IS some literature. IS 1888-shell be at least 5 times develop the full failure

interference to side. Due to the scale effect which will

bearing strength of footing reinforced bed sand. factor

defined as:

)

) )

uR(e=0) are the ultimate reinforced bed sand under

respectively.

static loading unit is

over the foundation during supported with horizontal beam

reaction on the shaft during

25kN, 50kN & 100kN are

to measure the actual foundation during the

top of proving ring is shaft of static loading

bottom is in connected which is resting over the

which is east to measure least count of 0.01mm

practically work. Needle of the



dial gauge is placed over the two adjacent corner of the footing. Magneticwhich is supported with test tank is usedthe dial gauge. MODEL FOOTING The thickness of Model test footing 3cmof mild steel are used for experimental1cm deep circular grove is made to holdball on one face of the footing at centereccentricity of 0.05B, 0.1B & 0.15B fromof the alone footings. Sand is use whilefooting with the helped of epoxy gluerough therefore that friction foundation and foot of soil can developedapplication ofload MODEL TEST AND METHODOLOGYTo study the bearing strength of eccentricallyfoundation, laboratory model test areover rectangular footing resting onreinforced with numbers of layers geogrid. Modeltest has performed over sand remoldedensity, foot and aneccentricity varied0.15B and number of reinforcement2, 3 & 4 PLACEMENT OF GEOGRID On the case of reinforced sand bed, it to decide the magnitude of u/B and b/Bmore benefit in the bearing strength sand. After then through many literature,been found that (u/B)cr for strip foundationsbetween 0.25 and 0.5, (b/B)cr is 8 andfooting and square foot respectively andbetween 0.25 to 0.4.

Figure 4.1 Cross-section showing sand bed andmultiple number of reinforcement



diagonally at Magnetic basis

used to support

3cm made up

experimental work. A hold the metallic

center and an from the centre

while the side of glue to make it

in between developed on

METHODOLOGY eccentrically loaded

are performed on bed sand geogrid. Model

remolde on one varied from 0 to

reinforcement varied as 0,

is an essential b/B to take the of reinforced

literature, it has foundations vary and 4.5 for strip and (h/B)cr lies

section showing sand bed and

reinforcement

Figure 4.2 Placement ofexperiment.

RESULTS AND ANALYSISLoad tests have been completelyrectangular of size footings9cmx28cm resting over unreinforcedreinforced sand bed with eccentricity0.0 to 0.15B. The true bearingis determined from load settlementtangent intersection method. BEARING STRENGTH OFSAND MODEL TEST RESULT Results of load test have beensettlement curve as shown infooting size 10x18 cm (B/L=0.55)(B/L=0.32 respectively. Fromobserved that true bearingeccentricity width ratio (e/B the total settlement at failureeccentricity width ratio (e/B)the graph shown in Figure 5.1be concluded that the Ratio ofdecreases, load carrying capacity

Figure4. Load-settlement curve ofunreinforced sand bed (B/L=0.55)


Dec 2018 Page: 842

of geogrid during

experiment.

ANALYSIS completely on model

footings like 10cmx18cm and unreinforced as well as eccentricity varying from

bearing capacity for each test settlement curve using

OF UNREINFORCED

been draw in term of load

in Figure 5.1 and 5.2 for (B/L=0.55) and 9x28 cm

From graph, it is bearing capacity less like

)and also increases in failure load decreases as

(e/B) increases. By compare 5.1 and 5.2, it can also of width to length (B/L)

capacity of footing increases

settlement curve of bed

unreinforced sand bed (B/L=0.55)



Figure5 Load-settlement curve of unreinforced sand bed (B/L=0.32)

BEARING STRENGTH OF REINFORCED SAND MODEL TEST RESULT The Laboratory model tests have beenwith using rectangular foot with B/L=0.55resting over the geogrid reinforced sand.reinforced by place multilayer (N=2, 3,with df /B ratio equals to 0.6, 0.85 & 1.1,the depth of lower most geogrid layer fromfooting and B is the width of footing.applied centrally as well as eccentricallymodel foot use static loading machine.Settlement corresponding to each loadhave been write down and load settlementhave been plotted.

Figure6. Load-settlement curve for B/L=0.55 & N=2 and different e/B ratio

Figure7. Load-settlement curve for B/L=0.55 & N=3 and different e/B ratio



settlement curve of unreinforced

GEOGRID

been preform B/L=0.55 & 0.32

sand. This sand is 3, 4) geogrids 1.1, where df is

from bottom of footing. Thae load is eccentrically on the

machine. The load increment

settlement curve

settlement curve for B/L=0.55 &

N=2 and different e/B ratio


ratio

Figure 8 Load-settlement curve for B/L=0.55 & N=4 and different e/B

SUMMARIZED RESULTSFUTURE WORK There is a number of laboratoryconducted to find the ultimateof rectangular model footingsreinforced sand and subjectedeccentric load. All the tests hasfooting resting over the surface. Following is the summarizedresearch work. An ultimate bearing

foundation for un-reinforcedsoil decreases with the increaseratio i.e. e/B.

An ultimate bearing strengthincreases with the increasereinforcement layer.

Reduction factor for the footing0.32 has been derived combined toget a simple reduction factor for rectangularEquation 5.11. SCOPE OF FUTURE WORKOn the present study the researchultimate bearing strength ofrectangular footing with B/L =reinforced sand bed. During timeaspects similar to shallow foundationsstudied. The work for shouldmentioned points: REFERENCES 1. Terzaghi, K. (1943). Theoretical

Wiley, New York.MeyerhofInvestigation for the FoundationsDense Sand.” Proceedings


Dec 2018 Page: 843


N=4 and different e/B ratio

RESULTS AND SCOPE OF

laboratory model tests has been ultimate load bearing capacity

footings resting on geogrid subjected to vertical an

has been conducted for surface.

summarized results of present strength of the

reinforced and reinforced increase in eccentricity

strength of the foundation increase in number of

footing with B/L=0.55 & alonely and then general equation to

rectangular footing as shown in

WORK research work is related to

of eccentrically loaded = 0.55 & 0.32 resting on time constraint, another foundations can not be

should consider the below

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7. Khing, K. H., Das, B. M., Puri, V. K.,Yen, S. C. (1993). “The bearing strip foundation on geogridsand.” Geotextile and Geomembranepp351-361

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on Soil Engineering, 2, pp.

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Education

Ultimate Bearing Strength on Rectangular Footing Resting Over Geogrid Reinforced Sand Under Eccentric Load