The development of a direct experimental SPT and CPT method is shown in Table 1.  
Considering the high cost of in-situ tests, artificial intelligence (AI) combining mathematics, algorithm, and creativity, has been introduced to establish AI-based predictive models of bearing capacity of piles in the last decade [4; 35; 36; 37; 38; 39]. With the CPT results, two artificial neural networks (ANNs) and a nonlinear multiple regression model for predicting pile resistance were set up to predict pile resistance [2]. It has been proved that the application of artificial intelligence and predictive models are practical, feasible, and they can be regarded as fast tools in solving engineering problems [40]. Apart from that, a new on-site camera method based on node displacement with the biological mechanism of phagocytosis to correlate continuous images was developed to calculate the settlement of piles [41]. Apart from the in-situ test, numerical simulation methods have also been applied to study the bearing capacity. [PERSON] et al. used a discrete element model (DEM) to assess the pile-sand interactions at the micro-scale [9]. [PERSON] et al. used the finite element model (FEM) to calculate bearing capacity at the tip of the pile for different slope angles [10]. [PERSON] et al. also adopted the FEM to obtain the pile bearing capacity and pile settlement of the soil-pile system [42]. For a broad group pile foundation, the field load test combined with numerical analysis are usually applied to estimate the ultimate performances of the pile foundation [43]. The pile properties are also of considerable significance to better evaluate the bearing capacity of the pile foundation. A new type of offshore oil and gas platform mixed pile was explored with the laboratory test program and the FEM, and the results show that the novel offshore foundation type is suitable for a wide range of sand conditions [44]. The impact of sand piles on improving the bearing capacity of soil foundations as well as controlling the settlement is studied by partially replacing sand piles with constraints [45]. Moreover, there are still many factors affecting the bearing capacity of the pile foundations, such as external sulfate attack, effective radius, and the elastic modulus of a pile. The ultimate bearing capacity (UBC) and failure characteristics of the pile are related to the shape of the pile cap and the strength of the pile body [46]. The degree of soil-plugging should be considered when the bearing capacity of the open-ended pile is studied [47]. The plugging effect of open-ended piles is highly influenced by the pile driving condition, soil condition, and pile geometry conditions [48]. Much work has focused on the prediction method and influence factors of pile bearing capacity; however, it remains challenging to accurately estimate the ultimate bearing capacity (UBC) of a single pile, especially in consideration of complex geological conditions in practice. The purpose of this paper is to analyze the ultimate bearing capacity (UBC) of PHC piles embedded in saturated sandy layers. Three in-situ tests, including SPT, CPT, SLT, and the corresponding calculation methods of the ultimate bearing capacity of a single pile with data from various tests, are described to demonstrate the differences between in-situ results and values recommended in the survey report. The mechanism for these differences is also explored.