Centrifuge model study on spudcan footprint interaction 7

Chapter – Dimensional Analysis for Spudcan-footprint Interaction Chapter Dimensional Analysis of Spudcan-footprint Interaction 6.1 Introduction It is apparent that spudcan-footprint interaction is a soil-structure interaction issue. Hence, the interaction is not only affected by the geotechnical condition but also the structure configuration. The influence of geotechnical condition on this problem was studied in detail in Chapters and 5. As the deployment of a jack-up rig at various sites depends on the rig availability, it is common to have different rigs to be deployed to a fixed platform for workover or drilling additional wells. The jack-up configuration is hence an important variable in the interaction between a footprint and a spudcan. In this chapter, an extensive series of centrifuge model tests results were analyzed focusing on the following: i) the effect of leg flexural rigidity, spudcan diameter and preload pressure on spudcan installation at 0.5 times spudcan diameter offset from the footprint centre; and ii) spudcan-footprint interaction at various offset distances. Dimensional analyses are conducted to generalise this complex problem. 206 Chapter – Dimensional Analysis for Spudcan-footprint Interaction 6.2 Footprint condition prior to future spudcan installation It is unquestionable that the footprint features affect its interaction with the spudcan installation in the vicinity of the footprint. Typically, a footprint has two main features: an uneven seabed and the soil shear strength variation. In Chapter 4, it has been established that the shear strength variation of soil beneath the footprint dominates the interaction in soft to firm clays. Shortly after a footprint is formed, the soil shear strength varies across the footprint having lower strength within the footing diameter and higher strength further from the footprint centre. This soil condition may cause a non-centric spudcan installation to have a tendency of sliding towards the footprint centre. Studies in Chapter revealed that the degree of the soil variation changes with time as the excess pore pressures generated by the previous spudcan installation dissipate. The behaviour of shear strength changes with time is dependent on the initial stress-history of the soil. However, when the time involved, either in operational period and elapsed time after a footprint is formed, is sufficiently short (negligible excess pore pressure dissipation), the soil condition beneath the footprint for both NC and OC clays is found to be similar. Previous findings in Chapter revealed that, above the initial spudcan penetration depth (de) in OC clay, the re-installed spudcan experiences higher moment and horizontal forces in the short-term than the long-term. This is because the soil that is previously heavily remoulded (within spudcan area) regains some strength in the long-term and these results in a less non-uniform soil profile across the footprint. All the tests presented in this chapter were conducted on clay samples with an over-consolidated profile. Only the short-term cases with nil 207 Chapter – Dimensional Analysis for Spudcan-footprint Interaction operational period (which yields higher horizontal force and moment) are considered. A generalised short-term soil condition of a footprint is produced based on five (5) tests (the test details are summarised in Table 6.1). Three tests were conducted on Malaysia kaolin clay, whereas the other two tests were conducted on UWA kaolin clay. It should be noted that the coefficient of consolidation for both clays and the spudcan used are not the same. Hence, the adjusted time factor,  is used to characterize the consolidation status of the soil after the extraction of spudcan (Table 6.1). Figure 6.1 shows the generalised short-term soil condition of a footprint formed in soft to firm clays for  < 0.002 and  < 0.2, where 1 and 2 are the adjusted time factors for soil consolidation during the operational period and during the elapsed time after a footprint is formed, respectively. 1 is the operation duration of previous rig which depends on the type of work involved, whereas 2 is the elapsed time after footprints formed to a time of a new rig installation. Hence, 1 and 2 are independent from each other. The footprint generally consists of a crater with the lowest point of about 0.2D deep and a highly non-uniform soil beneath the crater surface. The degree of soil disturbance is classified by the shear strength ratio, Rsu, which is the ratio of the footprint su to the undisturbed su at the same elevation. Rsu = su_footprint/su_undisturbed (6.1) The strength ratio of less than 0.5 is categorised as heavily remoulded, which is basically confined within the spudcan area (Rd/Df ≤ 0.5). Df is the diameter of the spudcan used to form the footprint. The soil with strength ratio of 0.5 to 0.7 is classified as moderately remoulded, whereas a ratio range of 0.7 to 0.9 is 208 Chapter – Dimensional Analysis for Spudcan-footprint Interaction classified as less remoulded. The extent of radial soil disturbance varies with depth. As discussed in Section 5.3.1.1, the soil failure mechanism changes from shallow (or general) failure to deep (or localised) failure when the spudcan penetration depth increases. This defines the extent of soil disturbance as reflected in the su measurements across a footprint. At depths of up to 0.5Df, the radial disturbance is found to extend to Rd/Df of 1.5. Below this depth, the major radial disturbance (Rsu < 0.7) is found to be confined within Rd/Df = 0.75. In term of vertical extent, it is found that the soil is heavily remoulded to a depth of up to 1.1de, where de is the penetration depth to spudcan base level. Below this depth, a minor soil strength reduction (0.7 < Rsu < 0.9) extending up to 0.3Df is observed. In short, the above describes the soil condition prior to the future spudcan installation for all tests which will be presented later in this chapter. One of the important variables in this study is spudcan diameter, D. Each complete test involved two spudcan penetrations in which the first penetration was to form the footprint and the second penetration was to investigate the spudcan-footprint interaction. Df denotes the spudcan diameter for the first penetration, whereas Ds denotes the spudcan diameter for the second penetration. For all the tests presented in Sections 6.3 and 6.4, the same spudcan was used to perform the first penetration (to create a footprint) and the second penetration. Hence, D (= Df = Ds) is used to denote the spudcan diameter for both penetrations. A schematic diagram of the typical test arrangement is shown in Fig. 6.2. 209 Chapter – Dimensional Analysis for Spudcan-footprint Interaction 6.3 Effect of jack-up rig configuration The main interest of the study in this section is to investigate the behaviour of a spudcan installation partially overlapping with a footprint. The footprint problem is essential a soil-structure interaction problem. Both the footprint condition and the structural configuration can affect the manner of the interaction. Hence, in this problem, two conditions need to be considered: i) the footprint characteristics as discussed in Section 6.2; ii) the jack-up configuration such as the leg flexural rigidity, spudcan size and rig preload. In an ideal condition, a footprint should be axisymmetric in plane. When a cross-section through the footprint centre to the spudcan centre is considered, the interaction is symmetrical along the longitudinal axis. The probable soil failure mechanism during the spudcan re-penetration has been discussed in Chapter 4. As the leg-hull connection is modelled as fully rigid where no lateral displacement and rotational movement are allowed, the spudcanfootprint interaction is evaluated in term of three major ‘resultant’ load components (vertical force, V, horizontal force, H and moment, M) acting at spudcan level. These forces were measured by the strain gauges instrumented on the spudcan leg (see Appendix A for detail). 6.3.1 Leg flexural rigidity It has been suggested that leg flexural rigidity will influence the interaction between a spudcan and a footprint (Stewart and Finnie, 2001; Foo et al. 2003; Dean and Serra, 2004). Stewart and Finnie (2001) pointed out that if the jackup leg is fully flexible, the spudcan will tend to slide into the adjacent crater. On the other hand, if the leg is fully rigid, the spudcan will penetrate vertically 210 Chapter – Dimensional Analysis for Spudcan-footprint Interaction into the soil with large lateral force build-up. Foo et al. (2003) postulated that the infinitely stiff leg would take the most bending moment as compared to one that was fully flexible. To investigate the effect of leg stiffness on spudcan-footprint interaction; two tests, namely P1 and P2, were conducted on soil samples that having similar strength profiles. The model leg used in test P1 (Leg 1) has a flexural rigidity, EI, of 1.22×1012 Nm2 which is 15.6 times stiffer than the EI of the model leg used (Leg 2) in test P2. A 10 m diameter spudcan was used and the penetration depth required to achieve 460 kPa preload pressure was 8.7 m and 8.65 m for tests P1 and P2, respectively (Fig. 6.3a). The test details and results are summarised in Tables 6.2 and 6.3, respectively. Figs. 6.3b and c show the H and M profiles for Leg and Leg 2, respectively. For both legs, the induced H increases with penetration to a maximum of about 1.1 MN (Leg 1) and 1.08 MN (Leg 2). On the other hand, a larger M was obtained for Leg as compared to that of Leg indicating the leg flexural rigidity has a more significant effect on the M than the H. As it is not feasible to install the displacement transducer on the spudcan (to avoid influence to the spudcan measurements), the tip displacement (at L.R.P.) for both legs is computed using eq. (A.17) in Appendix A. The tip displacement plot is presented in Fig. 6.3d. It is apparent that Leg deflects with a much greater amplitude compared to Leg 1. Hence, the stiffer the leg is, the less deflection takes place under a similar loading condition. It is postulated that the horizontal force may be reverse of the horizontal displacement as the force induced decreases with increase in displacement (Stewart and Finnie, 2001; Jardine et al., 2001). In this case, the effect of tip displacement on the induced H is not obvious as 211 Chapter – Dimensional Analysis for Spudcan-footprint Interaction there is only a small deviation in H throughout the penetration depth up to d e. This may be due to the limitation of the experimental set-up where no horizontal displacement is allowed by the rigid connection between the leg and the vertical actuator. The tip displacement involved is potentially lower than the movement of a jack-up unit as a system and hence, the effect of horizontal displacement on this set-up is discounted. Similar observation was made by Cassidy et al. (2009) as they found no distinguished difference in the H profile for legs having different stiffness values using a similar experimental set-up (rigid connection). However, these findings may only be applicable to the range of leg stiffnesses and forces investigated. Beyond these stiffness and loading ranges, the penetration response may be different. It is also worth noting that the comparison in leg rigidity stiffness was made for the same boundary condition of fixed connection between the leg and the loading actuator. If the connection is not fully fixed, the induced horizontal force would be different. 6.3.2 Effect of spudcan diameter Early rigs had to 12 individual legs and each leg was supported by relatively small spudcan compared to modern-day rigs. Modern-day rigs are designed to have fewer legs, typically three legs, which lead to a trend of using larger spudcans (Poulos, 1988). According to the evolution of individual footings presented by McClelland et al. (1982), spudcan sizes can vary from 4.8 m (for Offshore No. 52 made in 1955) to 20.1 m (for Marathon Gorilla made in 1982). In this section, the effect of spudcan diameter will be studied. Two spudcan sizes, namely m and 10 m, were selected and four tests were conducted. The test details are summarized in Table 6.2. 212 Chapter – Dimensional Analysis for Spudcan-footprint Interaction 6.3.2.1 Tests P2 (D = 10 m) versus Test P3 (D = m) Tests P2 and P3 were conducted in soil samples having similar undisturbed shear strength profiles. The same leg (Leg 2) was used in tests P2 and P3. The spudcan was re-installed at an offset of 0.5Df from the footprint centre. It is worth to highlight that both spudcans have the same base angle. There are two scenarios: i) the same preload level for different spudcan sizes, the larger spudcan will yield lower preload pressure; and ii) the same preload pressure for different spudcan size (e.g. the rig with smaller spudcans will have more legs than that with larger spudcans). In this study, the scenario ii) is considered. The VHM plots for tests P2 and P3 are shown in Figs. 6.3 and 6.4. The bearing response of a foundation is influenced by the degree of nonhomogeneity, kD/sum, where k is the rate of increase in shear strength with depth in kPa/m, D is the foundation diameter and sum is the shear strength at mudline. Although the undisturbed soil conditions for both tests are similar, owing to different footing diameters, the m spudcan required less penetration depth than the 10 m spudcan in order to achieve the same penetration resistance. It is observed that the penetration depth required for the m spudcan was about 1.5 m shallower than the 10 m spudcan to achieve preload pressure of 460 kPa. For test P3, H increases with depth to a maximum value of 0.71 MN at a depth of m. Similarly, M increases with depth to a maximum value 2.36 MNm at a depth of 6.3 m. At the same depth, the magnitude of the VHM for m spudcan is lower compared to those obtained for 10 m spudcan as a smaller footing area is involved. Two dimensionless parameters, namely load inclination angle  and normalised load eccentricity e/Ds are used to evaluate the resultant soil 213 Chapter – Dimensional Analysis for Spudcan-footprint Interaction reaction. The angle indicates how much the resultant soil reaction is inclined relative to the vertical and it is a ratio of H to V at the corresponding depth. The e/Ds, on the other hand, represents the eccentricity e of the vertical soil reaction from the spudcan centre. The derivations of these two parameters are presented in Appendix A. Figs. 6.5a & b show the load inclination,  and the normalized eccentricity, e/Ds for tests P2 and P3. The corresponding penetration depth, d is normalised with de. A high can be either due to a high H or a low V. In shallow depth penetration or low depth ratio, d/de = – 0.2, because of the existence of the crater and the partial support of the spudcan (attributed to low V), a high  results. For depth ratio of 0.2 – 0.8, an almost constant  is obtained for both tests. This implies that H increases at a similar rate as V. On the other hand,  decreases at depth d/de ≥ 0.8. As the initial shear strength profile increases linearly with depth, V for re-penetration also increases with depth. The decreasing below d/de of 0.8 is attributed by the decreasing H. This indicates that less sliding force is produced when the penetration is beyond the heavily remoulded zone. The higher  is obtained for the m spudcan compared to the 10 m spudcan. Similar to , high e/Ds is observed at d/de of up to 0.4, which is attributed by the partial support of the spudcan that results in a high M and a low V. After this depth, the e/Ds of both tests is almost constant with a value of about 0.025 before it decreases to nil. 6.3.2.2 Test P4 (D = 10 m) versus Test P5 (D = m) Similar to tests P2 and P3, the effect of spudcan size using m and 10 m spudcans is examined in tests P4 and P5 but in relatively softer soil samples. 214 Chapter – Dimensional Analysis for Spudcan-footprint Interaction The results of VHM are presented in Fig. 6.6. The m spudcan requires 9.0 m penetration (measured from the mudline to the spudcan base level), whereas the 10 m spudcan requires 11.66 m to achieve preload pressure of 460 kPa for the initial penetration. Details of the tests are tabulated in Table 6.2. For both tests, the H profile increases with penetration depth to a maximum value of 1.3 MN for the 10 m spudcan and 0.685 MN for the m spudcan. A typical ‘double-humped’ M profile is obtained where the upper hump is due to the partially supported spudcan. whereas the lower hump (and also the maximum M) is due to the soil strength variation. The test results are summarised in Table 6.3. From Fig. 6.7a, it is found that the profile of  is similar to those obtained in tests P2 and P3 where the high value at shallow penetration depth is followed by an almost constant value before steadily decreasing with depth. However, due to different soil strength profiles and the de, the magnitude of  is different for both sets of test (P2 and P3 versus P4 and P5). For e/D, similar profiles for tests P2 and P3 are observed. The e/D decreases from a maximum value near the surface to a narrow range of 0.025 – 0.035 from d/de = 0.4 to 1, before finally decreases to nil. 6.3.3 Effect of preload pressure For earlier rigs, the average bearing pressure lies within a range of 200 to 350 kPa (Le Tirant, 1979). For modern rigs, the average vertical bearing pressures can be in excess of 400 kPa for a fully embedded spudcan (Randolph et al., 2005). Some rigs have considerable preload pressure in the range from 575 to 960 kPa (Poulos, 1988). It can be seen that the preload pressure is a variable that depends on the rig type. Two tests, namely P6 and P7, were conducted to 215 Chapter – Dimensional Analysis of Spudcan-footprint Interaction hdeg) 0 0.2 0.4 0.6 0.8 de/D 1.2 1.4 1.6 1.2 1.4 1.6 Fig. 6.14 Plot of load inclination angle, h versus de/D 0.14 T5 0.12 T4 em/D 0.1 0.08 0.06 0.04 0.02 0 0.2 0.4 0.6 0.8 de/D Fig. 6.15 Plot of normalized load eccentricity em/D versus de/D 249 Chapter – Dimensional Analysis of Spudcan-footprint Interaction 1.5m or 0.25Df m Footprint & Spudcan Repenetration m Footprint m Spudcan Diameter of Spudcan, Ds Diameter of Footprint, Df a) Test OA1 m or 0.5Df c) Test OA3 m or 1Df e) Test OA5 b) Test OA2 4.5 m or 0.75Df d) Test OA4 m or 1.5Df f) Test OA6 Fig. 6.16 Test arrangement for tests OA1- 250 Chapter – Dimensional Analysis of Spudcan-footprint Interaction su (kPa) 20 40 60 80 100 Depth (m) su = 25 + 5z su = 30 + 5z 10 12 14 Fig. 6.17 The undisturbed su profile of the soil samples 251 Chapter – Dimensional Analysis of Spudcan-footprint Interaction 600 200 400 -0.2 d/d Depthe (m) d/de Depth (m) 0.6 1.4 Initial Re-penetration 10 V (MN) 12 1.6 0.8 1.2 1.4 1.6 16 1.8 10 10 V (MN) 12 16 b) 0.25D 200 400 200 400 0.4 d/de Depth (m) 0.8 1.2 1.6 0.8 1.2 d) 0.75D 12 16 -0.2 0.2 0.4 0.6 0.8 1.2 1.4 1.4 1.6 1.6 1.8 1.8 10 V (MN) -0.4 0.6 1.8 10 600 0.4 1.4 400 0.2 0.6 200 -0.2 0.2 16 -2 -0.2 12 Preload Pressure (kPa) 600 -2 V (MN) c) 0.5D Preload Pressure (kPa) 600 -2 0.6 1.6 Preload Pressure (kPa) 0.4 1.4 a) 0D 0.2 1.2 1.2 0.8 d/de Depth (m) Depth (m) 0.4 0.8 -0.2 0.2 0.4 0.6 600 0.2 400 -0.2 200 -2 -2 -2 Depth (m) 600 d/de 400 10 V (MN) e) 1.0D 12 16 d/de 200 Preload Pressure (kPa) Preload Pressure (kPa) Preload Pressure (kPa) V (MN) 12 16 f) 1.5D Fig. 6.18 Preload pressure for the initial penetration and re-penetration at various offset distances 252 Chapter – Dimensional Analysis of Spudcan-footprint Interaction 20 Reduction in V (%) 40 60 80 100 0.2 d/de 0.4 0.6 0.8 OA1 - 0D OA2 - 0.25D OA3 - 0.5D OA4 - 0.75D OA5 - 1D OA6 - 1.5D Fig. 6.19 Percentage of V reduction for the re-penetration at various offset distances 253 Chapter – Dimensional Analysis of Spudcan-footprint Interaction 10 Nco = Nc 0 0.2 0.4 d/D 0.6 0.8 Fig. 6.20 Bearing capacity factor for the initial penetration, Nco for tests OA1 – OA6 10 Ncf OA1 - 0D OA2 - 0.25D OA3 - 0.5D OA4 - 0.75D OA5 - 1D OA6 - 1.5D 0 0.2 0.4 0.6 d/D 0.8 1.2 1.4 Fig. 6.21 Bearing capacity factor for the re-penetration, Ncf for tests OA1 – OA6 254 Chapter – Dimensional Analysis of Spudcan-footprint Interaction -2 H (MN) 0.2 0.4 0.6 0.8 0D 0.25D 0.5D 0.75D 1.0D 1.5D Depth (m) 10 Fig. 6.22 The induced horizontal force, H during the spudcan re-penetration at various offset distances -2 M (MNm) Depth (m) 0.5 1.5 2.5 0D 0.25D 0.5D 0.75D 1.0D 1.5D 10 Fig. 6.23 The induced moment, M during the spudcan re-penetration at various offset distances 255 Chapter – Dimensional Analysis of Spudcan-footprint Interaction  (deg) 0.2 0.4 d/de 0.6 0.8 1.2 0D 0.25D 0.5D 0.75D 1.0D 1.5D 1.4 1.6 1.8 Fig. 6.24 The load inclination angle,  for re-penetration at various offset distances e/D = M/DV 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.2 0.4 d/de 0.6 0.8 1.2 1.4 1.6 1.8 0D 0.25D 0.5D 0.75D 1.0D 1.5D Fig. 6.25 The normalized load eccentricity, e/D for re-penetration at various offset distances 256 Chapter – Dimensional Analysis of Spudcan-footprint Interaction 0.4 NUS Stewart and Finnie (2001) Cassidy et al. (2009) de/D_avg = 0.88 Hmax/suDs2 0.3 de/D_avg = 0.48 0.2 de/D_avg = 0.39 0.1 0 0.25 0.5 0.75 Rd/Df 1.25 1.5 Fig. 6.26 Plot of Hmax/suDs2 versus Rd/Df 0.2 de/D_avg = 0.88 Mmax /s uDs 0.16 de/D_avg = 0.39 0.12 0.08 0.04 NUS Cassidy et al. (2009) 0 0.25 0.5 0.75 Rd /Df 1.25 1.5 Fig. 6.27 Plot of Mmax/suDs3 versus Rd/Df 257 Chapter – Dimensional Analysis of Spudcan-footprint Interaction h NUS Stewart and Finnie (2001) Cassidy et al. (2009) 0 0.25 0.5 0.75 Rd/Df 1.25 1.5 Fig. 6.28 Plot of h versus Rd/Df 0.12 NUS Cassidy et al. (2009) em /Ds 0.08 0.04 0 0.25 0.5 0.75 Rd /Df 1.25 1.5 Fig. 6.29 Plot of em/Ds versus Rd/Df 258 Chapter – Dimensional Analysis of Spudcan-footprint Interaction 1m 3.1 m m Footprint m Footprint m Spudcan Re-installation m Spudcan Re-installation Diameter of Spudcan, Ds Diameter of Footprint, Df a) Test OA7 b) Test OA8 5.2 m m Footprint 7.0 m m Spudcan Re-installation m Footprint c) Test OA9 m Footprint 1.0 m m Spudcan Re-installation d) Test OA10 10 m Spudcan Re-penetration 8m Footprint e) Test OA11 6.6 m 10 m Spudcan Re-penetration f) Test OA12 Fig. 6.30 Test arrangements for tests OA7 – OA12 259 Chapter – Dimensional Analysis of Spudcan-footprint Interaction Preload Pressure (kPa) 200 400 Preload Pressure (kPa) 600 -2 Depth (m) Depth (m) 10 10 a) Test OA7 b) Test OA8 Preload Pressure (kPa) 200 400 Preload Pressure (kPa) 600 200 400 600 -2 Test OA10 Initial (8 m Spudcan) Re-penetration (6 m) Test OA9 Initial (8 m Spudcan) Re-penetration (6 m) Depth (m) Depth (m) 600 Test OA8 Initial (8 m Spudcan) Re-penetration (6 m) 400 -2 Test OA7 Initial (8 m Spudcan) Re-penetration (6 m) -2 200 10 10 c) Test OA9 d) Test OA10 Fig. 6.31 Preload pressure measured during the initial penetration and repenetration for tests OA7 – 10 260 Chapter – Dimensional Analysis of Spudcan-footprint Interaction 0.2 0.4 H (MN) 0.6 0.8 1.2 -0.2 Test No Rd/Df OA7 0.12 OA8 0.39 OA9 0.65 OA10 0.88 0.2 d/de 0.4 0.6 0.8 1.2 1.4 1.6 Fig. 6.32 The induced H for tests OA7 – 10 0.5 M (MNm) 1.5 2.5 -0.2 0.2 3.5 Test No Rd/Df OA7 0.12 OA8 0.39 OA9 0.65 OA10 0.88 d/de 0.4 0.6 0.8 1.2 1.4 1.6 Fig. 6.33 The induced M for tests OA7 – 10 261 Chapter – Dimensional Analysis of Spudcan-footprint Interaction Preload Pressure (kPa) -2 400 Preload Pressure (kPa) 600 -2 T est OA1 Initial (8 m Sp udca n) Re-pen etratio n (10 m ) Depth (m) Depth (m) 200 400 600 800 T est OA1 Initial (8 m Sp udca n) Re-pen etratio n (10 m ) 10 10 12 12 14 14 a) Test OA11 200 b) Test OA12 Fig. 6.34 Preload pressure measured during the initial penetration and repenetration for tests OA11 and OA12 262 Chapter – Dimensional Analysis of Spudcan-footprint Interaction 0.2 0.4 H (MN) 0.6 0.8 1.2 -0.2 0.2 0.4 d/de 0.6 0.8 1.2 1.4 1.6 Test No R d/Df OA11 0.13 OA12 0.83 1.8 Fig. 6.35 The induced H for tests OA11 – 12 M (MNm) 10 -0.2 0.2 0.4 d/de 0.6 0.8 1.2 1.4 1.6 1.8 Test No R d/Df OA11 0.13 OA12 0.83 Fig. 6.36 The induced M for tests OA11 – 12 263 Chapter – Dimensional Analysis of Spudcan-footprint Interaction 0.6 D f/Ds = 0.8 D f/Ds = 1.0 D f/Ds = 1.33 0.5 Hmax/suDs2 0.4 0.3 Df/Ds = 1.0 0.2 0.1 0 0.25 0.5 0.75 Rd/Df 1.25 1.5 Fig. 6.37 Effect of Ds/Df on Hmax/suDs2 at various offset distances 0.3 D f/Ds = 0.8 D f/Ds = 1.0 D f/Ds = 1.33 Mmax/suDs 0.2 Df/Ds = 1.0 0.1 0 0.25 0.5 0.75 Rd/Df 1.25 1.5 Fig. 6.38 Effect of Ds/Df on Mmax/suDs3 at various offset distances 264 . spudcan-footprint interaction is a soil-structure interaction issue. Hence, the interaction is not only affected by the geotechnical condition but also the structure configuration. The influence. – Dimensional Analysis for Spudcan-footprint Interaction 206 C C h h a a p p t t e e r r 6 6 Dimensional Analysis of Spudcan-footprint Interaction 6.1 Introduction It is apparent that spudcan-footprint. Spudcan-footprint Interaction 2 07 6.2 Footprint condition prior to future spudcan installation It is unquestionable that the footprint features affect its interaction with the spudcan installation in the vicinity