LƯU ĐỐI VỚI giếng Đối với một số phương pháp phân tích lý thuyết của dòng chảy ngầm tính toán có sẵn, phân tích hoặc số. Nghiên cứu dòng chảy nước ngầm là rất quan trọng cho vấn đề cơ học đất, bởi vì ảnh hưởng của nước ngầm vào hành vi của một cấu trúc đất là rất lớn. Nhiều tai nạn đáng kể đã được gây ra bởi áp lực nước lỗ cao hơn so với dự kiến | Chapter 11 FLOW TOWARDS WELLS For the theoretical analysis of groundwater flow several computational methods are available analytical or numerical. Studying groundwater flow is of great importance for soil mechanics problems because the influence of the groundwater on the behavior of a soil structure is very large. Many Figure Single well in aquifer. dramatic accidents have been caused by higher pore water pressures than expected. For this reason the study of groundwater flow requires special attention much more than given in the few chapters of this book. In this chapter one more example will be presented the flow caused by wells. Direct applications include the drainage of a building pit or the production of drinking water by a system of wells. The solutions to be given here apply to a homogeneous sand layer confined between two impermeable clay layers see Figure . This is denoted as a confined aquifer assuming that the pressure in the groundwater is sufficiently large to ensure complete saturation in the sand layer. In this case the groundwater flows in a horizontal plane. In this plane the cartesian coordinate axes are denoted as x and y. The groundwater flow is described by Darcy s law in the horizontal plane qx - k h dx dh qy - -kdy and the continuity equation for an element in the horizontal plane dqy -0 dx dy 68 Arnold Verruijt Soil Mechanics 11. FLOW TOWARDS WELLS 69 It now follows if it is assumed that the hydraulic conductivity k is constant that the partial differential equation governing the flow is d2h d2h ỡx2 dy2 This is again Laplace s equation but this time in a horizontal plane. The problem to be considered concerns the flow in a circular region having a radius R to a well in the center of the circle. This is an important basic problem of groundwater mechanics. The boundary conditions are that at the outer boundary for r R the groundwater head is fixed h ho and that at the inner boundary the center of the circle a discharge
