# Settlement Prediction and Differential Settlement Criterion for Heightening and Thickening Leveee
###### Abstract  
Owing to the pavement cracking of heightening and thickening levees (HTL) caused by differential settlement, it is necessary to study the settlement prediction and differential settlement criterion for HTLs. In this study, an HTL was taken as the study object. First, leveling observation and layered settlement observation were adopted, and a generalized settlement prediction model (GSPM) that can describe both S-shaped and hyperbolic settlement-time curves was proposed. The physical meanings of GSPM parameters were analyzed. Moreover, the effectiveness of the GSPM was verified using field monitoring data. Second, finite element analysis based on a viscoelastic constitutive model was used to reveal the quantitative relationship between the differential settlement and horizontal stress of the pavement. On this basis, the differential settlement criterion was obtained. The results showed that the GSPM can unify the logistic model and hyperbolic model by introducing two morphological change parameters. In addition, the GSPM can be more widely used, more accurate, and more stable than the traditional logistic model and hyperbolic model. When an asphalt concrete pavement (whose ultimate tensile stress is 0.12 MPa) is used, the corresponding differential settlement criterion is approximately 4.3 cm. The research results can provide a reference for reasonable differential settlement control for HTLs in order to prevent pavement cracking.  
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the boundary conditions. However, deducing methods based on field monitoring data can overcome these issues. For deducing methods, there are mainly seven types: 1. Hyperbolic model [13; 14]; 2. Exponential curve model [15; 16; 17]; 3. Three point method [18; 19; 20]; 4. Asaoka method [21; 22]; 5. Logistic curve method [23]; 6. Grey theory method [24; 25]; and 7. Neural network [26; 27; 28].  
In fact, the settlement-time curve of the HTL shows variation. The settlement-time curve variation of the HTL may be due to factors such as seepage, erosion, groundwater changes, freeze-thaw deformation, and the initial time-point of monitoring. In addition, settlement-time curve variation has also been shown in a previous study [29] involving an expressway. Hence, the traditional logistic model and hyperbolic model are inadequate to describe the settlement-time curve variation, which may result in settlement prediction errors, such as final settlement error and settlement stability time error. Therefore, finding a settlement prediction model with strong adaptability and strong stability is still a challenge.  
However, the differential settlement of the HTL is unavoidable in practical engineering. It must be pointed out that differential settlement that does not cause pavement cracking is acceptable. Regrettably, the control criterion of the differential settlement for the HTL is still unclear at present, which leads to uncertainty in settlement control. Therefore, it is necessary to identify the differential settlement control criterion for the HTL from the point of view of the pavement cracking mechanism.  
This paper can be divided into two parts. First, a generalized settlement prediction model (GSPM) describing an S-shaped and hyperbolic settlement-time curve is proposed. In the first part, the physical meaning of the model parameters is analyzed, and the effectiveness of the GSPM is validated using field monitoring data. For the second part, the differential settlement control criterion is presented based on the finite element method. The two parts, which are closely related, can provide a reference to achieve reasonable differential settlement control of the HTL in order to prevent pavement cracking.