PSI - Issue 70

Ashutosh Kumar et al. / Procedia Structural Integrity 70 (2025) 175–182

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4. Results and Discussion 4.1 Influence of Sequence ff Sand Layer Thickness

The typical uplift stress-anchor displacement (d/B%) relationship obtained from numerical model tests placed at an embedment ratio (H/B) of 1, 2, and 3 having equal thickness of Layer 1 and Layer 2 (h 1 =h 2 ), are presented in Fig. 4, 5, and 6, respectively. In these tests, Layer 1 (h 1 ) consists of loose (RD = 30%) and layer 2 (h 2 ) consists of dense sand (RD = 75 %), or vice versa. The results indicates that the pullout load is significantly increases with an increase in the embedment ratio. Furthermore, the uplift stress for the loose soil (RD = 30%) over dense soil (RD = 75%) configuration is higher than that for the dense soil (RD = 75%) over loose soil (RD = 30%) configuration for all H/B ratios of 1, 2, and 3. For instance, in Fig. 4, the uplift stress for loose soil over dense soil and dense soil over loose soil are found to be 9.75 kPa and 8.64 kPa respectively, at H/B of 1. However, the uplift stress for single-layered loose soil (RD = 30%) and dense soil (RD = 75%) are 7.55 kPa and 10.24 kPa, respectively. Similarly, in Fig. 5, the pullout capacity corresponding to loose soil over dense soil and dense soil over loose soil are 25.12 kPa and 21.98 kPa, respectively, at H/B of 2, while those for single-layered loose soil and dense soil are 19.89 kPa and 27.54 kPa, respectively. In Fig. 6, the uplift capacity for loose soil over dense soil and dense soil over loose soil are 65.07 kPa and 55.10 kPa respectively, at H/B of 3, while those for single-layered loose soil and dense soil are 47.58 kPa and 81.57 kPa respectively. The percentage increase in uplift stress from H/B = 1 to H/B = 3 is 40.86 % higher for the loose soil over dense soil configuration as compared to the dense soil over loose soil configuration with equal layer depths. This observation cab be explained by the fact that the uplift stress of a plate anchor embedded in layered soil is influenced by the soil's shear strength, density, and layer sequence. In the dense soil over loose soil configuration, the anchor is embedded in the weaker loose soil (RD = 30%), which has lower shear strength and stiffness. When uplift force is applied, the failure mechanism involves the development of a failure surface primarily within the loose soil above and around the anchor. This surface mobilizes limited frictional resistance. Consequently, the uplift stress is lower as the loose soil dominates the resistance. Conversely, in the loose soil over dense soil configuration, the anchor is embedded in the stronger dense soil (RD = 75%), which has higher shear strength and stiffness. The failure mechanism here involves a failure surface of greater resistance around the anchor, mobilizing significant frictional forces resulting higher uplift stress. Hence, from the above observation it can be clearly stated that the anchor performance is very dependent on the sequence of the layer soil system. These results are summarized and presented in Table 3.

4.2 Uplift capacity factor Fq

To express the uplift capacity of the plate anchor, a dimensionless quantity, termed as dimensionless uplift capacity factor is used (Ilamparuthi et al., 2002; Bhattacharya and Kumar, 2016). Mathematically, the dimensionless uplift capacity factor, Fq, in single-layered soil and two-layered soil are defined as follows: F q = Q p /A ϒ H (1) F q = Q p /A ( ϒ 1 h 1 + ϒ 2 h 2 ) (2)

Where, Q p is the peak uplift stress A is the area of the plate anchor ϒ is the unit weight of the soil for single-layered soil

H is the embedment depth of an anchor plate placed in a single-layered soil ϒ 1 , and ϒ 2 are the unit weight of the soil for layer 1 and layer 2 respectively d 1 , and d 2 are the depth of thickness of the layer 1 and layer 2 respectively

The results shows that the uplift capacity factor “F q ” for loose soil over dense soil is185.19, 238.56, and 411.97, while for dense soil over loose soil, it is 164.10, 208.74, and 348.84, corresponding to H/B of 1, 2, and 3, respectively. Notably, the “F q ” lies within the range of values obtained for single-layered loose and dense soil at the respective embedment depths. For example, for H/B of 1, the “F q ” , for dense soil over loose soil and loose soil over dense soil is 164.10 and 185.19, respectively. These values fall within the range of single-layered loose soil (RD =30%) and