## 1 Introduction  
The development and utilization of underground space engineering (such as subways, underground stores, and underground parking, etc.) has become an important way of urban construction in China to achieve sustainable urban development. Deep excavations are an important part of urban underground space engineering construction, which is usually high-risk construction project because of great difficulty and danger during excavation. Even worse, there are Marine and Continental sediments of Quaternary Period with a large thickness that is below the water table in China's coastal areas (e.g., Tianjin, Shanghai, and Fuzhou, etc. ), which are mainly composed of miscellaneous fill, silt, clay, sand, and gravel, etc. Occasionally, the aquitards (e.g., silt, clay, etc.) are discontinuous, which results in close hydraulic relation among the aquifers. Besides, the confined aquifers usually have a high piezometric head in these areas. In these cases, groundwater control is a rather difficult work for deep excavation in these coastal areas. Dewatering must be carried out prior to the excavation in order to prevent water inflowing towards the excavation during the excavation. Water-isolation techniques are generally applied to reduce the adverse impact caused by excavation dewatering when dewatering may cause damage to the surrounding environment (e.g., buildings, roads, underground pipelines). The water-isolation techniques are mainly the use of waterproof curtains (completely or partially penetrating curtains) to cut off groundwater around the excavation,such as deep cement mixing piles, steel pipe sheet piles (SPSP), diaphragm walls, jet grouting columns, and steel cement-soil mixing walls (SMW) [1; 2; 3; 4; 5]. The issue on the calculation and design of excavation dewatering has attracted the attention of many researchers [6; 7; 8; 9], especially a great deal of literature on dewatering for deep excavations with partially penetrating curtains has been published in recent years [10; 11; 12; 13; 14; 15; 16]. Deep excavations are conducted in China's coastal cities, where the aquifers have a very large thickness (sometimes as large as 60-70 m). For such deep excavations surrounding complex urban environment where land subsidence needs to be strictly controlled, the partially penetrating curtains are perhaps not able to effectively cut off groundwater. In this case, sometimes the success of dewatering is difficult to be achieved, and simultaneously large-scale dewatering may also induce adverse effect on the environment around the excavation. However, when the completely penetrating curtains are employed for these deep excavations, the construction cost is very expensive and the construction is also difficult. Although, in this way, groundwater can be completely blocked, defects in underground enclosures at construction site are frequent [17; 18; 19; 20], which result in groundwater inflow towards the excavation and inevitably induce high drawdowns and settlements (or even collapse sinkholes) outside the excavation. In order to solve the problem on groundwater control for a deep excavation in deep aquifers, sometimes massive horizontal bottom-sealing barriers made of partially overlapping jet grouting columns [21; 22; 23] are performed for the excavation. When combined with the partially penetrating curtains (diaphrag walls), a waterproof curtain system that is enclosed on all the sides and at the bottom is formed. In this way, groundwater inflow towards the excavation can greatly decrease, so as to reduce or eliminate the drawdown outside during pumping groundwater inside an excavation. In spite of playing an effective role of jet-grounded bottom sealing barriers to groundwater control for deep excavations, there is still considerable uncertainty in the design phase in China, owing to the lack of reliable methods for the design of jet-grounded bottom sealing barriers.