Improvement of Gypseous Soils Using Different Types ...

Proceeding of 2nd International Conference Geosynthetics Middle East Dubai, UAE, 11-12 Nov. 2009

Improvement of Gypseous Soils Using Different Types of Geosynthetic Materials A.A.H. Al-Obaidi, College of Engineering – University of Tikrit, Iraq [email protected] S.S. Tawfeeq, College of Engineering – University of Tikrit, Iraq [email protected]

1. ABSTRACT Gypseous soils occupy about 1.865 million km2 in the world; the percent of gypseous in Iraq is 6.7% of the total world gypsiferous area and about 28.6% of the total area of this country. The gypsum percent may be reached 70% in some Iraqi soils. Many foundation failure problems that occur are associated with the percolation of water and dissolving of gypsum. The potential benefit of providing different types of Geosynthetic materials (geogrid – geonet – geotextile – geomembrane) reinforced gypseous soil have been investigated through a series of laboratory model tests on 100*100 mm footing model. The main phase of the experimental program is the bearing capacity pressure – settlement behavior that directed to investigate the performance of geosynthetic materials to improve the gypseous soils upon dry, soaking and leaching states. The results show an increment of bearing capacity ratio (BCR) between 4.25 to 1.18 times as compared with unreinforced models. Also, the results revealed an encouraging reduction in the settlement especially after leaching state, where using of geomembrane could be reduced settlement by approximately 73%. 2. INTRODUCTION Gypseous soils are those, which contain an appreciable amount of gypsum (CaSO4.2H2O) to change or affect construction adversely. They are present in dry arid to semiarid regions where sources of Calcium Sulphate exist. Gypsum has a specific gravity of (2.32) and its solubility is 0.2 %. Gypsum is found in many soils in amounts ranging from traces to several percents. Various authors have been described that gypsum accumulation occurs in two ways: by evaporation of mineralized groundwater and by the precipitation of the groundwater itself, (FAO, 1990). The problems of gypseous soils are associated with water seepage through this soil; the gypsum dissolves thus causing a subsidence of the ground level. The subsidence of phenomenon is irregular and erratic in nature and often leads to the collapse of the structures. The soluble gypsum may be leached out of the soil profile, which results in changing the soil properties. Failure by excessive leakage may take place when water infiltrates through cracks in structures and forming cavities in the surrounding regions, this behavior presents serious problems, (Alphen and Romero, 1971). Many engineering problems related to construction on or by gypseous soils were observed. Failure of different structures in various locations in Iraq has been reported. Several remedies have been suggested for the defaults generated by the presence of gypseous soils, these remedies are always focused towards the stability and serviceability of the structure, (Tawfeeq, 2009). In addition to Iraq, problems caused by gypseous soils have been reported in several areas in the world, i.e., the Arabian Peninsula, Russia, USA, and Spain, etc. (Nashat, 1990). To identify gypsiferous soils, Alphen and Romero (1971) used the value of 2% of gypsum content to define the gypsiferous soils. Jennings and Knight (1975) classified the gypseous soils according to the values of collapse potential (CP). Al-Barzanji, (1973) distinguished classes of gypsiferous soils based on the gypsum content as shown in Table (1). Many researchers studied the behavior of gypseous soils experimentally and theoretically. The gypsum content plays an important role in the determination of shear strength of gypseous soils, (Abbas, 1995). Soaking means previous saturation of the dry or partially saturated the soil with water without flow. This may happen when the site is flooded with water during heavy rainfall, irrigation or breaking of sewerage and water pipes. Therefore, soil containing gypsum as a cementing agent may be seriously affected by any change in water content. The soaking process has a great effect on shear strength, most of the researchers agreed that soaking of gypseous soil causes a great loss in the shear strength parameters (c & ϕ). The reduction in shear strength depends on a number of factors, the amount of loss in the

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cementation bonds, the original gypsum content, void ratio, the amount of added water to the soil and the condition of the test (Tawfeeq 2009). Also, the soaking period, the cyclic loading, and the compaction efforts may affect the amount of loss in cementation. Saaed et al. (1989) observed a reduction of the angle of internal friction from (40) to (29) in gypseous soils due to wetting. Most of the researchers recorded that the angle of friction (ϕ) suffered little reduction while the major reduction was in apparent cohesion (AlAlawee, 2001, Al-Amery, 2003, and Al-Dulaimi, 2004). The apparent cohesion is highly decreased upon wetting and diminished at saturation of most soils. The effect of soaking periods on the shear strength parameters (c & ϕ) of gypseous soil was investigated by Sulaiman et al, (1996); they found that the cohesion of soil is inversely proportional to the soaking periods while the effect on internal friction appears to be very small. Table 1. Classification of gypseous soils, (after Al-Barzanji, 1973) Gypsum content %

Classification

0 – 0.3

Nongypseous

0.3 – 3

Very slightly gypseous

3 – 10

Slightly gypseous

10 – 25

Moderately gypseous

25 – 50

Highly gypseous Gypseous soils to be described by the other fractions such as clayey or sandy gypseous soil.

>50

The leaching of soil, especially of those containing soluble salts causes changes in the engineering properties. These changes may create adverse problems for the structures founded on such soils. There is a general agreement that leaching of gypseous soils reduces the shear strength. Most of the researchers attribute the reduction in the shear strength parameters (c & ϕ) due to the removal of inter-particles cementing bonds during the leaching, which resulted in the loss of cohesion and friction, (Seleam, 1988, and Nashat, 1990). The improvement of gypseous soils means decreasing or eliminating the effect of water on the gypseous soils to ensure the safety and stability of the engineering structures. This treatment can be achieved chemically or physically. The details of these methods can be found in Al-Obaidi 2007 and Tafeeq 2009. Polymeric reinforcement materials are a subset of a much larger recent development in civil engineering materials. Geosynthetics may consider as one of the few developments that have had such a rapid growth and strong influence on so many aspects of civil engineering practice. These materials have been increasingly used in geotechnical and environmental engineering for the last four decades, (Palmeira et al, 2008). Due to the nature of polymeric materials, long-term behavior of the geosynthetic is a major concern for designers (Koerner 2005). Considerable focus has been given in recent years to establishing the long-term performance of geosynthetic reinforcement as a material, addressing such issues as installation damage, creep, and durability. Much research has been carried out to understand the beneficial effects of a planar form of reinforcement in sand using geosynthetic layers, such as (Venkatappa Rao et al. 2005, and Murthy, 2007). 3. TESTING EQUIPMENTS The testing apparatus comprises of four main parts, the model footing, the test box, the loading frame and the loading system. The model footing was square of side dimension equals to 100 mm and of thickness 30 mm, it was made from rigid Teflon material (Polytetrafluorethylene) having smooth faces and a notch at the center of the top face for mounting a calibrated proving ring. Two dial gauges, of accuracy 0.01 mm, were used to measure the footing vertical displacement. The soil beds were prepared in a steel box with inside dimensions 900 mm × 900 mm and 500 mm in height. The sides and the bottom were made of 6 mm thickness plate; at the lower part of the steel box, a valve was placed and connected by a rubber tube to drainage water at leaching test. The length of this tube was 600 mm, used to monitor the water level in the soil bed as a piezometer, and as indicate when the soil become at saturating stage. A proper

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geotextiles material, porous fabrics was used (at the lower part) as filtration devices, (Holtz, 2001). The general layout of the equipment is illustrated in figure (1)

Figure 1. Testing equipment for experimental setup The soil was brought from Tikrit city, which is located in Salah-Aldeen Governorate, in the middle of Iraq. The sand used in this study was a highly gypseous Dense poorly graded SAND with little fines, (SP) with a minimum dry unit weight of 10.50 kN/m3, the maximum dry unit weight of 16.30 kN/m3. The specific gravity of sand particles is 2.58. A designed the relative density was 78%. The determination of gypsum content is a very complicated problem. Many methods were suggested for this purpose according to the techniques by which the gypsum content may be estimated. Al-Azawi (2004) used seven methods to estimate the gypsum content. The tests results showed that the best method was that suggested by Lagerwerff. et al. in 1965, as compared with X-Ray diffraction. It was also found that (Al-Mufty and Nashat, 2000) method may be considered as the best method for gypseous soils with a high percentage of sand. The percent error does not exceed 5%. Table (2) shows the results of gypsum content by three different methods; each value represents the average of three trials. Table 2. Results of gypsum content using three different methods The Method Lagerwerff. Et. al. Method (1965) Al-Mufty and Nashat method, (2000) X-Ray Diffraction Test

Gypsum Content, % 51.1 52.5 52.0

Five types of standard geosynthetics were used to reinforce the gypseous soil specimens. I. High-density polyethylene Geogrid with 3825mm opening, (GG) II. High-density polyethylene Geonet 880 gm/m2 with 8mm opening (GN) III. High tenacity polyester, needle punched nonwoven Geotextile 230gm/m2, GX (1) IV. High tenacity polyester, multifilament woven Geotextile 480gm/m2, GX (2) V. Polyvinyl Chloride Geomembrane 1.0mm thickness (GM). The testing program comprised of two tests on unreinforced soil, five tests used the above types of geosynthetic in dry condition and five tests used the above types of geosynthetic in wet condition

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4. TEST PROCEDURE 4.1

Model Preparation for Unreinforced Soil

The soil was placed in the test box and compacted in 25 mm thick layers until the desired height was reached. For each layer, the height of drop of the hammer to achieve the desired density was determined. The relative density achieved was monitored by collecting samples in small cans of known volume placed at different locations near the side of the test box, (Sireesh, 2008). The difference in densities measured at various locations was found to be less than 1%. 4.2

Model Preparation for Reinforced Soil

The Same procedure was followed as for the unreinforced soil except that at the height of 320 mm from the base of the test box (figure 1). The first reinforcement layer was situated at the upper surface of the compacted soil. Compaction of the next layer of the fill material was followed and another reinforcement layer was placed. The procedure was repeated for all layers until placing the final layer. Five layers of reinforcement were used as effective layers to reach maximum benefit. The vertical distance between the reinforcement layers was 0.25B for all layers except the final layer (the layer near the footing) was 0.3B for all tests, (Ranadive and Jadhav, 2004), as the most effective spacing. The length of the reinforcement was chosen to be 9B. After the footing situated on the surface of the soil. The test started by applied the load, through a calibrated proving ring of 28 kN maximum capacity with recording settlement, this continued until the soil-filled. In soaking and leaching process tests the pressure of 100 kPa was applied to the dry soil, then the soaking process was started by opening the valve of the water tank to supply water until the saturation condition was reached. The soaking period was 72 to 216 hours depending on the type of geosynthetic used. The collapse of the model footing was recorded continuously by taking the dial gauge reading at different periods. The leaching process was started by opening the drainage valve at the lower part of the test box while the inlet valve of water tank was opened to supply water with a constant water level of 50 mm above the soil surface. The settlement was recorded at different periods of leaching test. In order to find the suitable leaching period, the relationship between gypsum content and time was studied. After 10 days the velocity of the interior and exterior water was high, it is believed that the mechanical piping occurs in the sample. Thus, the leaching period was decided to be 6 days for all tests. The pressure during the leaching process was keeping unchanged (100 kPa) and the collapse of the footing model was recorded at the different time. At the end, the supply of the water to the soil was stopped and the drainage allowed until all the water leave the soil. At this stage, the load was increased until the model footing was failed.

5. PRESENTATION OF RESULTS AND DISCUSSION To study the effect of geosynthetics on the behavior of footings in gypseous soils, two references tests were conducted on unreinforced soil, for the sake of comparisons, other tests were performed in the same manner but on the reinforced soil. 5.1

Behaviour of Footing Model in Dry Soil

Figure (2) represents the relationship between the bearing pressure applied on the footing in (kPa) and the vertical deflection of the soil (settlement) in (mm) for unreinforced soil and different types of geosynthetic reinforced soil foundation. In this figure, an early non-linearity of the curve is noticed in addition to the wide range of plastic yield prior to failure. The ultimate bearing capacity has been well defined by the point, where a fall-off load was observed as the deformation continued with a reduction in bearing pressure. This is clearly shown by the sharp bent in the bearing pressure-settlement curve. However, the mode of failure can be described as a general shear failure in this test. The ultimate bearing capacities and the corresponding settlements were presented in Table (3).

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Bearing pressure ; (kPa) 0

400

800

1200

1600

2000

2400

2800

3200

3600

4000

0 Unreinforced Geomembranes

2

Geotextiles (1)

Settlement ; (mm)

4

Geotextiles (2) Geogrids Geonets

6

Dry soil 8 10 12 14 16

Figure 2. Bearing pressure–settlement curves of different types of geosynthetics reinforcement in dry soil From the data presented, it was found that provision of geosynthetic reinforcement in the dry gypseous soils leads to increase the ultimate bearing capacity; the amount of the increment depends on the type and properties of the geosynthetic materials. 5.2

Performance of Geosynthetic Materials in Dry Soil

The effect of reinforcement to increase the bearing capacity is further explained by introducing the nondimensional parameter called the bearing capacity ratio (BCRD), which is the ratio between ultimate bearing capacity or the allowable bearing capacity (at a given settlement) for reinforced and unreinforced soil in the dry state. Also, the degree of deformation in the settlement is expressed in terms of deformation ratio (S/B) %, which is the ratio of settlement to the width of the footing multiplied by 100 %. The values of (BCRD) at failure for a different type of geosynthetics reinforcement in dry state were presented in table (3). It was clear that the (BCRD) ranged from 1.51 to 4.25 for different types of geosynthetics reinforcement, the lower value was marked in geomembrane reinforcement, and this indicated that no important significant effects in comparison with the results of other materials were used. The reason attributes to a high smooth material used, cause no increase in friction between the soil particles and geomembranes reinforcement. A geotextiles (1) and geotextiles (2) respectively give more development in ultimate bearing capacity, that refer to best significant in bearing capacity in comparison with unreinforced and geomembranes reinforcement, especially for geotextiles (2), that will due to a rough palpable that cause to interaction with the soil particles, this was agreed with results achieved by residual (Das, 1999). On the other hand, the plastic group materials geogrid and geonet give a high increase was observed in bearing capacity as compared with the other types of dry tests, geonets was the first consequence and the greatest reinforcement, (BCRD=4.25). The reason behind these results refers to a high interface occurred and taken place between these materials with soil particles. Based on the shape of these materials and according to the function and purpose that was designed for it, all that was assisted in causing increases in friction and then generate rising in bearing capacity. The deformation ratio (S/B) % were also tabulated in the table (3) at ultimate bearing capacity, this improvement in ultimate bearing capacity occurred at deformation ratio range between (10 - 13.5) mm, for different types of geosynthetic reinforcement. However, a geotextiles reinforcement type gives high (S/B) % ratio. This is primarily because geotextiles are made of flexible materials, and sufficient settlement of the foundation will be necessary to give the layers of geotextile, a catenary’s shape and to develop the tension to resist the stress transmitted from the foundation.

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Table 3. Ultimate bearing capacity, BCRD, settlement, and S/B % for unreinforced and reinforced soil with different types of geosynthetics in dry soils. Geosynthetic reinforcement type Unreinforced soil Geomembrane Geotextile(1) Geotextile(2) Geogrid Geonet 5.3

Ultimate bearing capacity, (kPa) 664 996 1453 2332 2585 2827

BCRD 1.00 1.51 2.19 3.51 3.89 4.25

Settlement, (mm) 10.2 10.5 12.2 13.5 10.8 11.1

S/B% 10.2 10.5 12.2 13.5 10.8 11.1

Behaviour of Footing Model in Soaking and Leaching States

Same materials (geosynthetics) used in dry soil tests will be used, and the effect of soaking and leaching of water will be studied. In these test, the load was applied in increments up to a pressure of (100) kPa. After this stage, the soil was soaked with water, and then the leaching process started by opening the drainage valve and lets the water dispossess from the soil bed. The main results of these tests are presented in two forms, the first as a relationship between settlement versus the applied load, and the second form related the deformation ratio (settlement/ width of the footing *100%) versus time during the soaking and leaching periods. Figure (3) illustrates a plot of the bearing pressure versus settlement for models tested. Three segments can be identified for this curve. The first one represents the settlement of the soil at dry state, where the load increases up to 100 kPa; this state continues only a few minutes. The second segment which indicates no transfer in bearing pressure value and continuous settlement that occurred due to the collapse of the sample as the water percolation begins during soaking and leaching. The last segment represents the effect of increasing the load until the model reaches to the failure state. The ultimate bearing capacity was considered at the failure state. For unreinforced soil, it can be observed that a high decreasing in bearing capacity after soaking and leaching when compared it with the dry state. This may be due to the high dissolution rate of gypsum content and generating voids, which lead to decrease the friction area between soil particles and reduces the shear strength. In addition, to increase the ability of soil structure to roll and slide and deform to a new structure. Figure (4) represents the deformation ratio (S/B) % versus time during the soaking and leaching periods. For the unreinforced curve, the results indicate that rapid increase in the deformation ratio was observed especially at the hours of soaking state (approximately 1.66 hours). This rapid, which hardly controlled settlement, was developed due to the loosening of the cementing bonds between the individual soil particles, followed by a slower rate of deformation developed during the rest of soaking period. After 72 hours, the soaking state finished, when the level of the water in the piezometer became at same in with soil box, and the leaching process began. High rate settlement was observed during the first 2 hours, this behavior may be attributed to the high departure of dissolved gypsum, after that the dissolution of the residual undissolved gypsum from the previous soaking state started, leads to more settlement but with a low rate. The total settlement was recorded 43.5mm which is the accumulated of 0.3mm in a dry state, 34.7mm in soaking state (72 hours), 5.3mm in leaching state (144 hours), and 3.2mm during loading to failure. That means 80% of the settlement occurs in the soaking state. (Table 4). However, the results show that the reduction in ultimate bearing pressure was 62.35% and the increment of the settlement was 326.5% as compared with dry test results. The behaviors of the gypseous soils reinforced with different types of geosynthetics, in general, are similar in trend to the unreinforced soil. The nylon materials geomembrane reinforcement was provided the best and maximum bearing capacity in the wet test, due to the smaller settlement as compared with the unreinforced and with the other types. The geomembrane is impermeable liquid barriers material, for this reason, the water was prevented from reaching through soil and seepage between soil particles so that dissolution of gypsum inside the gypseous soil was prevented. The settlement was only noticed in the first layer beneath the footing (Table 4) which is not entrenched with geomembranes.

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Bearing pressure ; (kPa) 0

100

200

300

400

500

600

700

800

900

0 Unreinforced Geomembraines Geotextiles (1) Geotextiles (2) Geogrids Geonets

4

8

12

Settlement ; (mm)

16

20

24

28

32

36

40

44

48

Figure 3. Bearing pressure – settlement curves for unreinforced and different types of geosynthetic reinforcement in soaking and leaching soil. Time ; (min) 0

1

10

100

1000

0 5

Deformation ratio , S/B ; ( % )

10 15 20 25 30 35 40 45

Unreinforced Model Geomembrane Geotextile (1) Geotextile (2) Geogrid Geonet

50

Figure 4. Deformation ratio S/B% - time for unreinforced and different types of geosynthetic reinforcement soils in three periods (dry, soaking and leaching) Geotextile (1) was the second to follow types in improving the bearing capacity in wet test and was given a good reinforcement when it compared with the unreinforced and with other types. The degree of woven material (like the needle or are matted together) in geotextile (1) makes it a temporary waterproof layer that prevents the water from infiltrating easily between the soil particles and late the dissolution of gypsum,

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as compared with the unreinforced one which has a sharp curve in this state time. Geonets and geogrids respectively were found in third and fourth consequence types in increments of the bearing capacity but with very high settlement values at wet tests as compared with the unreinforced and with other types, the attributed of this behaviour for these materials despite high friction that had been generated due to interaction with soil particles which was observed in dry tests but with high permeable character which allows water to flow easily through it to soil and this causing to dissolve a high percent of gypsum. On the other hand geotextile (2) as last to follow types effect in bearing capacity and remark a high results in settlement when it compared with unreinforced and other types, the reason refers of that in spite of geotextile (2) had a rough surface enough to improve the bearing capacity but in balance not impermeable enough to prevent or late dissolved of the gypsum. The time needed for soaking and the corresponding settlement for each type of geosynthetic materials, besides the settlement in leaching state and total settlement were recorded in the table (4). 5.4

Performance of Geosynthetic Materials in Soaking and Leaching Soil

Soil reinforcement performs necessary juncture due to significant development in bearing capacity until soaking and leaching, which cause many problems in gypseous soil produce of the water. Geosynthetic was provided this momentous advance in the gypseous soil. Table (5), shows the development of the ultimate bearing capacity due to the use of geosynthetic materials especially in geomembrane, which gives the greater value of bearing capacity ratio in wet (BCRSL) reach to 2.42 inverse that occurred in the dry test. The range of (BCRSL) in this table between 1.18 to 2.42, since the lower bearing capacity ratio was recorded with geotextile (2) reinforcement. On the other hand, the deformation ratio decreases during the wet test by employing these materials as shown in the table (5). It can see a high decrease was marked in deformation ratio due reinforcement tests compression with unreinforced and dry models tests, the range of deformation ratio in this bar chart between 11.8% to 36.5%. From all tests whether in dry and wet conditions, it must mention from the behavior of curves in figures that reinforcement was not affected in the initial stages of the test. This may be due to non-development of proper friction mechanism between soil and reinforcement in the initial stages, and reinforcement starts to work after a quantity of settlement occurred. As further settlement takes place, and this behavior was agreement with behavior reported by (Ranadive and Jadhav, 2004). Table 4. Settlement and time for (dry, soaking and leaching states and ultimate bearing pressure in unreinforced and different types of geosynthetic reinforcement.

Dry state Type of reinforcement

Unreinforced soil Geomembran e Geotextile(1) Geotextile(2) Geogrid Geonet

Soaking state

Tim e (hrs)

Settl . (mm )

Tim e (hrs)

Settl . (mm )

-

0.30

72

-

0.14

-

0.2 0.16 0.10 0.12

Leaching state

Test to failur e

Total settlemen t (mm) or S/B%

Ultimate bearing pressur e (kPa)

BCRS

Tim e (hrs)

Settl . (mm )

Settl. (mm)

34.7

144

5.3

3.2

43.5

250

1.00

216

8.96

-

-

2.7

11.8

605

2.42

120 90 76 81

18.8 22.5 22.7 21.9

144 144 144 144

2.60 4.34 3.20 2.98

4.1 5.0 10.5 3.7

25.7 32.0 36.5 28.7

501 296 421 451

2.00 1.18 1.68 1.80

L

Now a comparison is made depending on a new bearing capacity ratio (BCRD/SL), which is the ratio between the ultimate bearing capacity of reinforced soil in the wet state and the ultimate bearing capacity of unreinforced soil in a dry state, as mentioned in Table (5).

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The surprise was in geomembrane reinforcement type, the values of (BCRD/SL) was more than one, and the settlement was very little as compared with unreinforced tests, and this reflects the performance of geosynthetic materials to improve the gypseous soil.

Table 5. (BCR) and (S/B) % of different types of geosynthetic reinforcement for dry and wet tests. Geosynthetics reinforcement type Unreinforced soil Geomembrane Geotextile(1) Geotextiles(2) Geogrid Geonet 5.5

Dry test BCRD S/B, % 1.000 10.20 1.505 10.50 2.187 12.20 3.510 13.50 3.893 10.80 4.256 11.10

Wet test BCRSL S/B, % 1.000 43.50 2.420 11.80 2.004 25.70 1.184 32.00 1.684 36.50 1.804 28.70

BCRD/SL 0.377 0.911 0.755 0.446 0.634 0.679

Comparison with Other Results

In order to investigate the performance of geosynthetic materials to improve gypseous soils, the results obtained from this study are compared with the results obtained by many investigators carried their studies in the same field or used a different type of soil. Al-Alawee (2001), Al-Barzangi (2003), Al-Ani (2003), and Al-Ameery (2003). All these studies, which were carried during the last two decays, are directed to investigate the proper and the most effective technique of improvement of gypseous soils. All the used methods, test conditions, and variables of test conditions are summarized in Table (6). It is worth to mention that each testing technique whether it is chemical or physical was carried under different conditions. It is well pronounced that the soaking stress and the initial moisture content for each treated laboratory model used, was different. For example, the laboratory model tested by Al-Alawee (2001) using the Emulsified Asphalt was tested at the same soaking stress of this study (100 kPa). The difference was only in the dry unit weight=16.25 kN/m 3 and the initial moisture content=12.6%. While in the case of laboratory model reinforced with traditional stone columns by Al-Barzangi (2003), was tested at soaking stress=40 kPa which is lower than the used soaking stress for this study. Because of the different procedures, only the amount of reduction in the settlement was compared, the results in Table (7) show that the amount of reduction in the settlement was significantly high when the geosynthetic material is used as a treatment method compared with other types of treatment. Table 6. Laboratory models improved with various physical and chemical techniques Al- Alawee 2001 Emulsified Improvement type Asphalt X=5B, Improvement variables t=2B Gypsum content% 72 Density kN/m3 16.25 Initial water content% 12.6 Soaking pressure (kPa) 100 Reduction in 2.2 settlement% Authors

Al- Ameery 2003 Stabilized stone columns 25% sand, 7.5% Cement , w/c=0.6 66 12.88 6.5 40 9.92

Al-Ani 2003

Al- Barzangi 2003 Stone Bentonite columns 7.5% mix Traditional

Current study

67 12.9 9 80

66 14.6 2.63 100

Geosynthetic materials Type of reinforcement 52 14.56 2.7 100

4.63

10.37

12-25.6

CONCLUSIONS Based on the results obtained it can be proved that the inclusion of the geosynthetics as reinforcement materials improves the bearing capacity of the gypseous soil, which depends on the type of geosynthetics, The plastic materials (geonets and geogrids) reinforcement are the best type of geosynthetic materials in dry state, When the water permeates this soil in soaking and leaching states The bearing capacity of the gypseous soil reduced about 62% and the collapse settlement increased 326%. Geosynthetic materials provide a better solution, where using this material increased the bearing capacity ratio and reduced the

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collapse settlement, and the geomembrane materials represent the best reinforcement that develops the bearing capacity and reduces the collapse settlement during soaking and leaching process. Comparing the results obtained with those found in the literature using different types of improvement; reveal that the geosynthetics reinforcement materials may be the best for using in gypseous soils. The low cost of these materials and its durability may consider as another function added for encouraging of using these materials. REFERENCES Abbas H.O. (1995), Effect of Gypsum on the Engineering Soil Properties, M.Sc. Thesis, Civil Eng. Dept., University of Baghdad, Iraq. Al-Alawee, A.B.J. (2001), Treatment of Al-Therthar Gypseous Soil by Emulsified Asphalt Using Model Tests, M.Sc. Thesis, Dept. of Building and Construction, University of Technology, Baghdad, Iraq. Al-Ameery, A.A. (2003), Traditional and Stabilized Stone Columns in Gypseous Soils, M.Sc. Thesis, Building and Construction Department, University of Technology, Baghdad, Iraq. Al-Azawi, N.H. (2004), Comparison of Gypsum Content in Soil by Different Methods, M.Sc. Thesis, Dept. of Building and Construction, University of Technology, Baghdad, Iraq. Al-Barzanji, A.F. (1973), Gypsiferous Soils of Iraq, Ph.D. Thesis, Dissertation, State University of Ghent, Belgium. Al-Dulaimi, N.S. (2004), Characteristics of Gypseous Soils Treated with Calcium Chloride Solution, M.Sc. Thesis, Civil Eng. Dept. University of Baghdad, Iraq. Al-Mufty, A.A., and Nashat, I.H. (2000), Gypsum Content Determination in Gypseous Soils and Rocks, 3rd International Jordanian Conference on Mining, pp. 500-506. Al-Ani, A.K. (2003), Improvement of Gypseous Soil Below Foundations Using Bentonite, M.Sc. Thesis, Dept. of Building and Construction, University of Technology, Baghdad, Iraq. Al-Obaidi, A.L.M. (2007), Gypsiferous Soil Behaviour by Finite Element Method, Ph.D. Thesis, Civil Eng. Dept., University of Baghdad, Iraq. Alphen, J.G.V., And Romero, F.D. R. (1971). Gypsiferous Soils Notes on their Characteristics and Management, Int. Institute for Land Reclamation and Improvement, Wageningen, Netherlands. FAO (1990), Management of Gypsiferous Soils, Food and Agricultural Organization of United Nations, Rome, The Internet, Http.//Fao.Org/Doc Rep/To 323e/Ro323e03.Htm. Holtz, R.D. (2001), Geosynthetics for Soil Reinforcement, 9th Spencer J. Buchanan Lecture, College Station Hilton, University Drive, College Station, pp1-20. Jennings, J.E., and Knight, K. (1957), The Additional Settlement of Foundation Due to a collapse of Structure of Sandy Subsoil on Wetting, Proceedings of 4th International Conference on Soil Mechanics and Foundation Engineering, Vol. 1, PP. 316-319. Koerner, R.M. (2005), Designing with Geosynthetics, 5th Edition, Pearson Prentice Hall, USA 796p. Murthy, V.S. (2007), Effects of Reinforcement Form on the Behaviour of Geosynthetic Reinforced Sand, Geotextiles, and Geomembranes, Vol.25, pp.23-32. Nashat, I.H. (1990), Engineering Characteristics of Some Gypseous Soils in Iraq, Ph.D. Thesis, Civil Eng. Dept. University of Baghdad, Iraq. Palmeira, E.M., Tatsuoka, F., Bathurst, R.J., Stevenson, P.E, and Zornberg, J.G. (2008), Advances in Geosynthetics Materials and Applications for Soil Reinforcement and Environmental Protection Works, EJGE Special Vol. Bouquet 8. pp 1-38. Ranadive, M. S., and Jadhav, N. N. (2004), Improvement in Bearing Capacity of Soil by Geotextiles-An Experimental Approach, 5th Int. Conf. on Ground Improvement Techniques, Malaysia, G104. Saaed, S.A., Al-Omary, R. and Nazhat, N. (1989), Shear Behaviour of Gypsiferous Soils, Proc, of the 2ed Int. Symposium on Environmental Geotechnology, Shanghai, India. Seleam, S.N. (1988), Geotechnical Characteristics of Gypseous Sandy Soil Including the Effect of Contamination with Some Oil Products, M.Sc. Thesis, Dept. of Building and Construction, University of Technology, Baghdad, Iraq. Sireesh, S., Sitharam, T. G. and Dash, S. K. (2008), Bearing Capacity of Circular Footing on Geocell-Sand Matters Overlying Clay Bed with Void, Geotextiles, and Geomembranes, Vol.27, pp. 89-98. Sulaiman, R.M., Al-Obaydi, A.A. and Hussain, A.A. (1996), Study of the Engineering Properties of AlQadisiyah Hai, Tikrit City, Scientific Journal of the University of Tikrit, Iraq, Vol.3, No.1. Tawfeeq, S.S. (2009) Performance of Geosynthetics to Improve gypseous Soils, M.Sc. Thesis, Department of Civil Eng., University of Tikrit, Iraq. Venkatappa Rao, G., Dutta, R.K., Ujwala, D. (2005), Strength Characteristics of Sand Reinforced with Coir Fibers and Coir Geotextiles, EJGE, Vol.10.

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