# Numerical Modeling of Single Pile Behaviors Due to Groundwater Level Rising
## 1 Introduction  
A decrease in groundwater extraction due to industrial decentralization and the restriction or prohibition of groundwater pumping has led to rising groundwater levels. It has been observed in several cities, including London (England) [1], Jeddah (Saudi Arabia) [2], Naples and Milan (Italy) [3, 4], Wuxi (China) [5] and Bangkok (Thailand) [6] for half of a century. The rising groundwater levels can change the water pressure in the aquifer, and effective stresses in the soil layers can be reduced. An upward movement of the ground [7, 8], underground structures [1, 9] and a loss in foundation bearing capacity [10, 11] were then observed. Several studies investigated the pile-soil behavior and the capacity change of pile foundations with rising groundwater level. For example, the full-scale tests on ten driven piles in sand and gravel under controlled water pressure within neighborhoods of wells were proposed by [PERSON] and [PERSON] [11]. The results showed that the ground movements corresponded to the water level fluctuations, whereas pile movements with the working load of more than 50% of the ultimate load continuously settled with increasing pore pressures. The behavior of four driven piles in clay with increasing pore water pressure was investigated by small scale model test measured. A 25 mm diameter pile at 230 mm depth was installed in compacting clay in a test container for investigating stresses and movement of the pile. A significant loss in pile load capacity resulted from an increase in soil moisture content (comparable to a reduction in effective stress) and the movement of a floating unloaded pile increased with soil movement ([PERSON] and Poulos [12]). In a series of centrifuge model experiments, [PERSON] and [PERSON] examined the effect of increasing pore water pressures on the behavior of pile foundations buried in reconstituted Speswhite kaolin clay. The results showed that the pile foundations moved less than the surrounding ground surface and reduced the ultimate capacity [13, 14]. Bangkok, Thailand experienced land subsidence from 1960 to 1997 due to excessive groundwater extraction [15; 16]. Consequently, the government strictly controlled groundwater pumping and the groundwater level in the underlying aquifers, slightly recovered [6]. The rising groundwater led to reduction in effective stress, which affected existing deep pile foundations, installed prior to groundwater recovery. Some research investigated the changing of pile capacity, due to rising groundwater levels in Bangkok subsoils, for example simple static analytical methods evaluated the loss in pile capacity, due to the reduction in effective stress [6; 17]. [PERSON] and [PERSON] tested the load distribution of a single pile in the centrifuge test, and found that it was less than manual calculations, but it still showed the same trend. Due to complicated multiple many boundary values, it was not possible to derive closed form solutions and numerical methods, within a theoretical framework, were used [18]. [PERSON] et al., using numerical methods for evaluating capacity in deep foundations, with change in groundwater level, derived the load-settlement curve and the axial load capacity of the piled-raft foundation, indicating that the static groundwater level affected the depth at which piled rafts were controlled [19]. Although the capacity in a deep foundation was evaluated, the soil deformation and the groundwater levels did not take into account changes in time, as in real situations. Recently, [PERSON] and [PERSON] used fully coupled finite element (using Abaqus code [20]) to simulate land deformation, pore water pressure and effective stress change induced by long term groundwater drawdown and recovery in the Bangkok aquifers, but the pile structure was not integrated into their numeric model.