1 Introduction

Grouting is the process of enhancing the quality of the ground by injecting a substance with fluid-like properties. Grouting can be permeation grouting, compaction grouting, or hydraulic fracturing. Permeation grouting involves the free flow of grout into the soil voids with minimal effect. Grout materials may be solution grouts or suspension grouts. The permeation grouting technique is generally used to reduce ground permeability and control groundwater flow, but it can also be used to strengthen and stiffen the ground. Materials such as foams, polymers, and bentonite slurries are used as conditioning agents [1].

Each agent has unique characteristics that result in varying effects on the characteristics of the various soils. Their impact on various soils relies on their concentration, injection ratio, and, in the case of foam, their expansion ratio value, as well as whether they are employed singly or in combination. Commercial products containing various foams, polymers, and bentonite types are available as soil conditioning agents for usage in various ground conditions. As a soil-stabilizing substance, polyurethane foam has been introduced to geotechnical research. Since then, scientists have begun examining how such material affects the behavior of soils. Several businesses, including Uretek Ground Engineering, which provided the slide shown in Fig. 1, commercially use the impregnation process of polyurethane foam in soils [2].

Fig. 1
figure 1

Polyurethane foam impregnation technology (After Philip M., 2010) [2]

Full size image

Following an examination of the literature on this substance's properties, the following may be concluded about polyurethane:

  1. 1.

    Because polyurethane is waterproof, water resistant, and non-water soluble, it is the ideal material for underground applications in any environment.

  2. 2.

    Soil or moisture don't cause polyurethane to chemically react.

  3. 3.

    Polyurethane is environmentally neutral, inert, and does not contribute to the contamination of water. It does not leak harmful substances into the substrate.

  4. 4.

    Polyurethane solidifies up to 90% of its full strength in 15 min and cures quickly. Numerous uses for polyurethane can be modified to fit them. It can easily endure a range of temperatures, climatic factors, and soil types.

  5. 5.

    Minimal invasiveness is a benefit of polyurethane.

The foam expansion ratio (FER), which is defined as the ratio between the volume of foam to the volume of liquid used to form the foam, is the metric that typically characterizes the polyurethane foam characteristics.

The initial information on the compressibility of foamed soils comes from the impregnation behavior of foam in soils conducted by Quebaud et al. (1998) [3] in a consolidation cell.

Psomas (2001) [4] examines the basic soil characteristics of foamed sand, including compressibility, permeability, and shear strength. He employed two types of sand (fine and coarse), four different foaming agents, and a particular blend of polymers in his study. For the shear strength tests, a 60 mm direct shear box apparatus, a 75 mm Rowe cell apparatus, and a few permeability experiments were used. Also, to improve the gypseous soil behaviour so that it can be used to support shallow foundations. They found that 3% polyurethane foam can be recommended to improve the gypseous soil behaviour [5,6,7,8,9].

To investigate the physical characteristics of polyurethane foam, Abdelnaeem [10] carried out considerable experimental work. Using a plate load test, he also looked at how sand that had been impregnated with polyurethane foam behaved in three distinct locations. Additionally, he tested sand samples blended with various percentages of polyurethane foam in an unconfined compression test. When the sand has been impregnated or combined with such substance, all of his results have shown a noticeable positive influence on strength and settlement decrease.

According to [11] polyurethane (PU) foam is a lightweight material that can be utilized efficiently as a ground improvement method in treating excessive and differential settlement of soil foundation especially for infrastructures such as road, highway and parking spaces. Also, the use of effective thickness of PU will be able to reduce the cost of remedial measures.

Existing buildings and structures' foundations may be raised and strengthened, and settlement compensation may be achieved through the use of an expanding polyurethane resin in the soil injection process. Sabri (2021) [12] introduced review to evaluate the bearing capacity of the composite (soil-resin) and the settlement following the injection procedure, as well as to compute the strength and stiffness parameters using finite element analysis.

In 2023, Nimbalkar and Farooq [13] presented a study focuses on developing alternate sustainable base materials for a high-speed slab track. They found that The unconfined compressive strength of the soil specimen treated with PFA was significantly influenced by the duration of curing. However, compared to the concrete specimens, the polyurethane foam adhesive-treated specimen showed a noticeably higher early strength development.

An investigative method for examining the cyclic stress–strain properties of calcareous sands and their possible enhancement through the use of environmentally friendly Polyurethane Foam Adhesive (PFA), as researched by [14]. The result showed that the resilient modulus of the calcareous sand increased with the addition of PFA content and elevated confining pressure.

For the calcareous sand, which easily breaks under compression and causes unequal foundation settlement in real life, a new improvement technique is suggested.

The South China Sea calcareous sand was strengthened and improved by the use of PFA. The relationship between the calcareous sand strength index and the change in shear strength of PFA-solidified calcareous sand under various PFA contents and confining pressure levels was also examined using a large-scale triaxial testing apparatus. The peak strength progressively increased with pronounced strain hardening as the PFA level increased, suggesting that the healing effect of PFA on calcareous sand can nevertheless result in a brittle failure [15].

Innovative soil injection technology that stabilizes the soil by employing an expanding polyurethane resin is a solution for construction settlement problems. The report presents the findings of a full-scale experiment that was conducted in-situ to examine the impact of soil injection technology on the lifting of a concrete foundation and on the stiffness of the soil beneath the foundation (soil stabilization) at various soil depths [16].

To investigate the stabilizing effects of polyurethane foam on weak subgrade soil. [17] introduced study; it has been shown that strength of black cotton soil with liquid polyurethane foam increases its strength. It was found that following treatment with liquid polyurethane foam, the CBR values were saturated. Furthermore, the soil spaces had been filled and coated with foam. Initially, (P.U.) foam injection methods were designed to correct differential settling in foundations under constructions.

In the present work, a Finite Element investigation using PLAXIS 3D program was done to have more understanding of the behavior of polyurethane foam when used not as impregnating material but as an inclusion such as piles in clay and sand soils.

1.1 Aim of the current study

A) To analyze the performance of loose sand and soft clay soils which were injected by polyurethane foam as piles.

b) The effect of using different diameters of polyurethane foam piles on pile load-carrying capacity.

c) To study the effect of polyurethane foam piles length on pile load-carrying capacity.

d) This research paper is studying the use of a new type of materials (polyurethane foam) to improve the properties of sandy and clay soils, and the authors have used the engineering properties of this material according to the laboratory study conducted by Hassona and M. Abdelnaeem [10]. In this research, they have been thinking about how to benefit from this material in improving the soil capacity taking into consideration the effect of different diameters of polyurethane foam piles, polyurethane foam piles length. Instead of making laboratory models, The authors used numerical model (PLAXIS 3D software) which considered an important program in soil calculations, to simulate these cases as discussed in this study.

2 Validation of soil model using PLAXIS 3D finite element

Researchers commonly use the Alzey Bridge pile load test as an axially loaded validation example when examining new soil models. Near Frankfurt, the Alzey Bridge pile load test was conducted. To measure the loads immediately carried by the pile base, load cells were installed at the base. Figure 2 shows the configuration for the pile load test. The silt (loam) of the upper 4.5 m subsoil is followed to considerable depths by tertiary deposits. These tertiary deposits have variable degrees of overconsolidation and are composed of hard plastic clay akin to so-called Frankfurt clay. About 3.5 m below the top of the land is the groundwater table. The pile under consideration is 9.5 m long and 1.3 m in diameter. It is entirely within the clay that has been overconsolidated. The loads were applied gradually and kept at that level until the settling rate became insignificant. At the tested pile head, measurements were taken of the applied loads and the resulting displacements. The data for modeling the soil mass and pile are presented in Tables 1 and 2, which are taken from Engin et al. [18].

Fig. 2
figure 2

Layout of the pile load test (After Engin et al. 2007 [18])

Full size image
Table 1 Soil Properties for Validation
Full size table
Table 2 Pile Properties for Validation
Full size table

Using PLAXIS 3D software, the soil was modelled using Mohr–Coulomb soil model. The pile was modelled as an embedded pile. The top of the pile was subjected to a point load, and the soil was meshed. For meshing, medium mesh was used to reduce the run time. Figure 3 shows the soil and pile modelling developed with PLAXIS 3D.

Fig. 3
figure 3

Model of Embedded Pile and Point Load in PLAXIS 3D

Full size image

Figure 4 compares the pile load displacement behavior obtained experimentally with that found using the PLAXIS 3D software.

Fig. 4
figure 4

Comparison of experimental and numerical Soil Model

Full size image

It may be noted that, the load displacement behavior of piles is comparable between theoretical and field load test results. Thus, the PLAXIS 3D modelling of the soil and pile has been proven valid, and subsequent research can now proceed using the same technique. The difference in displacement values between numerical model results and field load test results may be due to one or more of the following factors:

  • Errors in field monitoring displacement measurements.

  • The use of traditional methods to calculate the settlement, which affects the accuracy of the results.

3 Numerical modelling using PLAXIS 3D

The production of a geometry model is the first step in the generation of a 3D finite element model. A workspace (x, y, and z space) and a borehole that represents the site circumstances make up a geometry model. To define geometry lines and structures, use the workspace. The ground surface, groundwater level, and soil stratigraphy are all determined via the borehole, if necessary. It is possible to generate and assign data sets of model parameters for the different layers of soil to the borehole. The parameters assigned in the current investigation are the modulus of elasticity E in kN/m2, density γ in kN/m3, Poisson's ratio ν, cohesion C, and angle of internal friction Ø for loose sand of 20º.

In the program's Structures mode, the structural components are built. The modelled structures in this instance are PU foam piles with various diameters and lengths loaded gradually as in the prototype pile load test. Figure 5 shows the stages that the numerical model went through. The application creates the finite element mesh after defining the preceding parameters. The choice of mesh size is dependent on the required accuracy of the results.

Fig. 5
figure 5

The stages followed in the numerical mode

Full size image

There are five different mesh sizes: extremely coarse, coarse, medium, fine, and very fine. The period of time needed to complete each run varies on the mesh size, with very fine mesh size requiring a significantly longer amount of time. In this experiment, a coarse mesh size is used to reduce runtime. The generation of the loading sequence, which is set to 2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 24, 28, 32, 36, 40, 44, 48, and 52 kN, is the final stage. By introducing the properties of both the confining soil and those for the pile material which are, as mentioned earlier, E, γ, ν, C, and Ø with the values given in Tables 3 and 4. The values of E in kN/m2 shown in Table 3 are given by Bowles [19].

Table 3 Input data for clay, sand and polyurethane foam in modelling program
Full size table
Table 4 Physical and mechanical properties of PU foam
Full size table

After doing this, the computer begins to determine the settlement values related to each loading or stress increment. A general view of the 3D model used in this experiment, which was used for constructing a soil block with the characteristics listed in Tables 3 and 4, is shown in Fig. 6. Additionally, polyurethane foam piles were modelled utilizing the characteristics listed in Tables 3 and 4. The Physical and mechanical properties of polyurethane foam employed in the present investigation are given in Table 4, Hassona and Abdelnaeem [10].

Fig. 6
figure 6

Modelling of a typical pile load test in clay

Full size image

4 Results and discussion

4.1 Loading response of piles embedded in the soft clay having different diameters

The adopted strength parameters for soft clay are: cohesion value of 40 kN/m2 and angle of internal friction Ø = 0º. The piles were loaded and the load settlement results were examined. A condensed study on load–settlement response of piles with a constant length of 15 m embedded in soft clay having different diameters of 40, 60, 80, and 100 cm. As mentioned before, C, Ø, and E are input data in the Plaxis3D program and are kept constant for each pile diameter as given in Table 3. The results of these runs are all shown in Fig. 7. It could be observed that the resistance to loading increases with the increase of the pile diameter. Another set of runs was performed, again, for sake of comparison, on piles having a length of 9.0 m and 3.0 m. Its results are shown in Figs. 8 and 9. Similarly, the load-settlement behavior of polyurethane piles embedded in soft clay when the length of piles was changed to 9 m and 15 m was shown in Figs. 8 and 9. Again, it could be noticed that, for each pile length, the loading capacity increases with the increase of pile diameter. Generally speaking, the load-carrying capacity of piles typically increases with the increase of their diameter with no distinct difference in behavior when pile length was increased. This means that the diameter increase is more influential on the load-carrying capacity of polyurethane piles than its length.

Fig. 7
figure 7

Load-Settlement behavior for piles with different diameter having L = 15.0 m, embedded in the soft clay

Full size image
Fig. 8
figure 8

Load-Settlement behavior for piles with different diameter having L = 9.0 m, embedded in the soft clay

Full size image
Fig. 9
figure 9

Load-Settlement behavior for piles with different diameter having L = 3.0 m, embedded in the soft clay

Full size image

4.2 Loading response of piles with different lengths embedded in the soft clay

Having seen the previous results, polyurethane foam piles having the same diameter of D = 100 cm embedded in soft clay. The length of these piles was changed between 3.0 and 15 m. The results of the aforementioned pile loading cases are shown in Fig. 10 and other loading runs were performed on piles having a diameter D = 40 cm for the sake of comparison. The results are shown in Fig. 11. It could be noticed that no clear trend of the results of both cases could be deducted with slight enhancement in piles with larger lengths.

Fig. 10
figure 10

Load-Settlement behavior for piles with different lengths having D = 100 cm, embedded in the soft clay

Full size image
Fig. 11
figure 11

Load-Settlement behavior for piles with different lengths having D = 40 cm, embedded in the soft clay

Full size image

A collective curve for the load at failure for piles with different diameters having 3 m and 15 m lengths embedded in soft clay is shown in Fig. 12. The results of both pile lengths were fitted with polynomial fitting curves with the having equation shown on the figure. The two curves coincide together which indicates that the load capacity of each pile increases with the increase of pile diameter while the pile length has no effect. These results suggest that polyurethane foam pile loading capacity is contributed only to its bearing and no contribution from its side surface friction.

Fig. 12
figure 12

Load at failure—pile diameter relationship, for piles embedded in the soft clay

Full size image

4.3 Loading response of piles embedded in the stiff clay having different diameters

The adopted strength parameters for stiff clay are: cohesion value of 75 kN/m2 and angle of internal friction Ø = 0º. The piles were loaded and the load settlement results were examined. A condensed study on load–settlement response of piles with a constant length of 15 m embedded in stiff clay having different diameters of 40, 60, 80, and 100 cm. As mentioned before, C, Ø, and E are input data in the Plaxis3D program and are kept constant for each pile diameter as given in Table 3. The results of these runs are all shown in Fig. 13. It is clear that when pile diameter increase, there is an increase in loading resistance. For comparison's sake, further runs on piles measuring 9.0 m and 3.0 m in length were made. Figures 14 and 15 display the findings of it. Similarly, the load-settlement behavior of polyurethane piles embedded in stiff clay when the length of piles was changed to 9 m and 15 m was shown in Figs. 14 and 15. Again, it could be noticed that, for each pile length, the loading capacity increases with the increase of pile diameter. In general, the load-carrying capacity of piles generally increases as the diameter of the pile increases, with no obvious change in behavior when the pile length increases. This indicates that the diameter increase has a greater impact than the length on the load-bearing capability of polyurethane piles.

Fig. 13
figure 13

Load-Settlement behavior for piles with different diameter having L = 15.0 m, embedded in the stiff clay

Full size image
Fig. 14
figure 14

Load-Settlement behavior for piles with different diameter having L = 9.0 m, embedded in the stiff clay

Full size image
Fig. 15
figure 15

Load-Settlement behavior for piles with different diameter having L = 3.0 m, embedded in the stiff clay

Full size image

4.4 Loading response of piles with different lengths embedded in the stiff clay

Following the previous findings, polyurethane foam piles with the same D = 100 cm diameter were embedded in stiff clay. These piles' lengths ranged from 3.0 to 15 m. The outcomes of the aforementioned pile loading cases are depicted in Fig. 16, and further loading runs on piles with a diameter of D = 40 cm were carried out for comparison. The outcomes are displayed in Fig. 17. It was apparent that neither case's data showed a distinct trend, notwithstanding a minor improvement in piles with greater lengths.

Fig. 16
figure 16

Load-Settlement behavior for piles with different lengths having D = 100 cm, embedded in the stiff clay

Full size image
Fig. 17
figure 17

Load-Settlement behavior for piles with different lengths having D = 40 cm, embedded in the stiff clay

Full size image

Figure 18 shows a collective curve for the load at failure for piles with various diameters and lengths of 3 m and 15 m sunk in soft clay. With the equation given on the figure, polynomial fitting curves were used to fit the findings for both pile lengths. The two curves are converging, indicating that while pile length has no bearing, an increase in pile diameter enhances each pile's load capacity. These findings imply that side surface friction has no bearing on the polyurethane foam pile loading capacity and only increases to its bearing.

Fig. 18
figure 18

Load at failure—pile diameter relationship, for piles embedded in the stiff clay

Full size image

4.5 Loading response of piles with different diameters embedded in loose sand

The load response of polyurethane foam piles having lengths 3, 9, and 15 m embedded in the loose sand is performed to compare the results with those done for piles with D = 100, 80, 60, 40 cm and lengths of 3, 9, and 15 m. Both results were compared and presented in Figs. 19, 20, and 21. It could be noticed that consistently piles having bigger diameters showed higher resistance to loading for any pile length.

Fig. 19
figure 19

Load-Settlement behavior for piles with different diameter having L = 15.0 m, embedded in the loose sand

Full size image
Fig. 20
figure 20

Load-Settlement behavior for piles with different diameter having L = 9.0 m, embedded in the loose sand

Full size image
Fig. 21
figure 21

Load-Settlement behavior for piles with different diameter having L = 3.0 m, embedded in the loose sand

Full size image

4.6 Loading response of piles with different lengths embedded in the loose sand

Polyurethane foam piles having the same diameter of D = 100, 40 cm embedded in the loose sand with the same angle of internal friction Ø = 20º were loaded and their results were examined. The length of these piles was changed between 3.0 and 15 m. The results of the aforementioned pile loading cases are shown in Figs. 22, and 23. Generally speaking, and from the output figures, the deformations are mainly concentrated in the top part of the pile generated from the compressibility of the foam material with more resistance when pile length increases. It should be mentioned here that the endpoint of the failure process during the program run was defined as the point at which the program stops working.

Fig. 22
figure 22

Load-Settlement behavior for piles with different lengths having D = 100 cm, embedded in the loose sand

Full size image
Fig. 23
figure 23

Load-Settlement behavior for piles with different lengths having D = 40 cm, embedded in the loose sand

Full size image

Figure 24 shows a collective curve for the load at failure for piles with various diameters and lengths of 3 m and 15 m embedded in loose sand. The results for both pile lengths were fitted with polynomial fitting curves using the equation shown in the attached figure. The two curves align. This indicates that the load capacity of each pile improves with the increase in pile diameter. However, the pile length does not seem to influence it. These findings imply that the polyurethane foam pile's loading capacity is solely dependent on its bearing and does not depend on the friction on its side surfaces.

Fig. 24
figure 24

Load at failure—pile diameter relationship, for piles embedded in the loose sand

Full size image

4.7 Loading response of piles embedded in the clay having different strength

To have more knowledge on the behavior of such piles when embedded in firm clay instead of soft clay. A pile with D = 100 cm, L = 15 m having L/D = 15 and D = 60 cm, L = 15 m having L/D = 25 was numerically loaded. The input parameter of firm clay was as follows: E = 21,000 kN/m2, C = 75 kN/m2, γ = 18 kN/m3, Ø = 0, and the value of ν was set by the program to 0.49 for undrained condition.

Again, the pile with D = 100 cm, L = 7 m having L/D = 7.0, and D = 60 cm, L = 7 m having L/D = 11.7 was numerically loaded for both stiff and soft clay. The results are compared with that embedded in soft clay as shown in Figs. 25, 26, 27 and 28. It is clearly noticed that the pile in firm clay showed higher loading capacity and less settlement. This result showed a clear-cut result of the effect of confining media. As the confining stress resulting during the loading process from clay strength increases, the polyurethane pile load-carrying capacity increases too. Also, the results indicated that the polyurethane pile load-carrying capacity increases when L/D decreases for both soft and stiff clay.

Fig. 25
figure 25

Load-Settlement behavior of piles embedded in the stiff and soft clay, (L/D = 15)

Full size image
Fig. 26
figure 26

Load-Settlement behavior of piles embedded in the stiff and soft clay, (L/D = 25)

Full size image
Fig. 27
figure 27

Load-Settlement behavior of piles embedded in the stiff and soft clay, (L/D = 7)

Full size image
Fig. 28
figure 28

Load-Settlement behavior of piles embedded in the stiff and soft clay, (L/D = 11.7)

Full size image

4.8 Comparison between the loading responses of piles in soft clay with that in loose sand

If we recall the results of loading polyurethane piles (having the same diameter and length) embedded in loose sand where Ø = 20° from the companion paper (Hassona and Abdelnaeem 2022) and compared with that of piles embedded in soft clay which are presented as shown in Fig. 29.

Fig. 29
figure 29

Loading-settlement response of polyurethane piles embedded in soft clay and loose sand

Full size image

The results of the load-settlement response of piles having the same diameter of D = 100 cm and length of L = 15 m which are embedded in soft clay and loose sand shown in Fig. 29 indicate that pile embedded in loose sand is more resistant to loading than that in soft clay. This result could be attributed to the higher skin friction resulting from sand particles while in soft clay, as mentioned before; skin friction has no contribution to pile resistance to loading.

4.9 Comparison between the loading responses of polyurethane piles with concrete piles embedded in soft clay

To have more knowledge on the behavior of polyurethane piles with concrete piles when embedded soft clay. A pile with D = 100 cm, L = 15 m having L/D = 15 and D = 60 cm, L = 15 m having L/D = 25 was numerically loaded. The results are compared as shown in Figs. 30, and 31. It is clearly noticed that the concrete pile showed higher loading capacity and less settlement than polyurethane piles. Also, figs. indicated that; the percentage of loading capacity of concrete piles to that of polyurethane piles (Pcp /Ppp) = 4.51 for (L/D = 15), (Pcp /Ppp) = 4.8 for (L/D = 25).

Fig. 30
figure 30

Load-Settlement behavior of polyurethane and concrete piles embedded soft clay, (L/D = 15)

Full size image
Fig. 31
figure 31

Load-Settlement behavior of polyurethane and concrete piles embedded soft clay, (L/D = 25)

Full size image

4.10 Comparison between the loading responses of polyurethane piles with concrete piles embedded in stiff clay

Again, the pile with D = 100 cm, L = 15 m having L/D = 15, and D = 60 cm, L = 15 m having L/D = 25 was numerically loaded for stiff clay. The results are shown in Figs. 32, and 33. It is clearly noticed that the pile in firm clay showed higher loading capacity and less settlement, (Pcp /Ppp) = 7.0, (Pcp /Ppp) = 8.0 for ( L/D = 15), and ( L/D = 25), respectively.

Fig. 32
figure 32

Load-Settlement behavior of polyurethane and concrete piles embedded stiff clay, (L/D = 15)

Full size image
Fig. 33
figure 33

Load-Settlement behavior of polyurethane and concrete piles embedded stiff clay, (L/D = 25)

Full size image

4.11 Comparison between the loading responses of polyurethane piles with concrete piles embedded in loose sand

Figures 34 and 35 show load-settlement behavior of polyurethane and concrete piles embedded loose sand, (L/D = 15, L/D = 25, respectively). Also, the (Pcp /Ppp) = 7.9, (Pcp /Ppp) = 5.3 for (L/D = 15), and (L/D = 25), respectively.

Fig. 34
figure 34

Load-Settlement behavior of polyurethane and concrete piles embedded loose sand, (L/D = 15)

Full size image
Fig. 35
figure 35

Load-Settlement behavior of polyurethane and concrete piles embedded loose sand, (L/D = 25)

Full size image

From the previous results, to obtain the best case for polyurethane pile vs. concrete pile, the pile with D = 100 cm, L = 5 m having L/D = 5 was embedded in soft, stiff clay, and in loose sand. The results of these cases are shown in Figs. 36, 37, and 38.

Fig. 36
figure 36

Load-Settlement behavior of polyurethane and concrete piles embedded soft clay, (L/D = 5)

Full size image
Fig. 37
figure 37

Load-Settlement behavior of polyurethane and concrete piles embedded stiff clay, (L/D = 5)

Full size image
Fig. 38
figure 38

Load-Settlement behavior of polyurethane and concrete piles embedded stiff clay, (L/D = 5)

Full size image

The results of the load-settlement response of piles having the same diameter of D = 100 cm and length of L = 5 m which are embedded in stiff, soft clay and loose sand shown in Figs. 35,36, and 37 indicate that the (Pcp /Ppp) = 1.9, (Pcp /Ppp) = 1.3, and (Pcp /Ppp) = 3.07 for soft, stiff clay, and loose sand, respectively. `Hence, the best case for all above cases is the pile length = 5.m with diameter = 100 cm.

5 Conclusions

From the above-mentioned results the following conclusions can be drawn:

  1. 1-

    A Finite Element investigation using PLAXIS 3D program was done to study the behavior of polyurethane foam when used not as impregnating material but as an inclusion such as piles in clay and sand soils.

  2. 2-

    The results of loading the same diameter polyurethane foam piles embedded in soft clay having different lengths (3, 5, 7, 9, 11, and 15 m) showed an increase in the ultimate load with the increase in pile length.

  3. 3-

    The settlement values corresponding to the failure loads for 40 cm diameter piles are approximately four time that for 100 cm diameter piles for each pile length of loading capacity.

  4. 4-

    It was noticed that consistently piles having bigger diameters sustained higher resistance to loading for any pile length.

  5. 5-

    The results indicated that the polyurethane pile load-carrying capacity increases when L/D decreases for both soft and stiff clay.

  6. 6-

    The concrete pile showed higher loading capacity and less settlement than polyurethane piles. Also, the percentage of loading capacity of concrete piles to that of polyurethane piles embedded in soft clay (Pcp /Ppp) = 4.51 for (L/D = 15), (Pcp /Ppp) = 4.8 for (L/D = 25).

  7. 7-

    Also, for the polyurethane piles embedded in stiff clay, (Pcp /Ppp) = 7.0, (Pcp /Ppp) = 8.0 for (L/D = 15), and (L/D = 25), respectively.

  8. 8-

    The (Pcp /Ppp) = 7.9, (Pcp /Ppp) = 5.3 for (L/D = 15), and (L/D = 25), respectively for polyurethane piles embedded in loose sand.

  9. 9-

    The best case for using polyurethane is the pile length = 5.m with diameter = 100 cm for soft, stiff clay, and loose sand.

  10. 10-

    When the loading results of polyurethane foam embedded in loose sand are compared with the loading results of piles in soft clay, the ultimate capacity of piles in loose sand, was much higher than that in soft clay.