What is flow net in soil mechanics?

What is flow net in soil mechanics?

A flow net is a graphical representation of two-dimensional steady-state groundwater flow through aquifers. Construction of a flow net is often used for solving groundwater flow problems where the geometry makes analytical solutions impractical.

How many flow lines flow net?

A flow net consists of two sets of lines which must always be orthogonal (perpendicular to each other): flow lines, which show the direction of groundwater flow, and equipotentials (lines of constant head), which show the distribution of potential energy.

Why flow net is important?

Flow nets provide a general knowledge of the regional groundwater flow patterns that the hydrologist can use to determine such information as areas of recharge and discharge. Freeze and Cherry (1979, pg. 168) have stated that flow nets are an important concept of hydrology.

What is NF and ND?

Nd = number of potential drops Nf = number of flow channels h = total head loss q = total quantity of unit flow.

What are uses of flow net?

To determine the amount of seepage and upward lift pressure below hydraulic structure. Once the flow net is constructed, the same one applies to flows at different discharges. A flow net analysis assists in the design of an efficient boundary shapes.

Which is the most commonly used method of construction of flow net?

But for that first we need to solve the laplace equation, which is not a very easy task to do. So, we try to obtain our flow net for two dimensional flow using next method. This is the most commonly used method of flow net construction because it is easy and it provides nearly accurate results.

What is potential drop in flow net?

Hence, in a flow net, where all the figures are square, there is the same quantity of unit flow through each figure and there is the same head drop across each figure. Nd = number of potential drops Nf = number of flow channels h = total head loss q = total quantity of unit flow.

What is exit gradient?

The disturbing force at any point is proportional to the gradient of pressure of water at that point (i.e. dp/dl). This gradient of pressure of water at the exit end is called the exit gradient. In order that the soil particles at exit remain stable, the upward pressure at exit should be safe.

What is NF in seepage?

2.12 Calculation of seepage quantities from a flow net. Nd = number of potential drops Nf = number of flow channels h = total head loss q = total quantity of unit flow.

What are the characteristics of flow net?

Properties of flow net are as follows:

• The angle of intersection between each flow line and an equipotential line must be 90o which means they should be orthogonal to each other.
• Two flow lines or two equipotential lines can never cross each other.
• quantity of seepage occurs in each flow channel.

How to design a sheet pile?

Designing a sheet pile consists of the following two steps: 1. Calculation the depth of penetration (D). 2. Determining the section Modulus (S) where: S= Q c W n ¢ W b b M k _ v=maximum moment along sheet pile σ _ j j=maximum allwable flexural stress (for sheet pile material). Always in this chapter we will use Rankine LEP theory.

How to draw a flow net correctly?

The first step is to draw in one flow line, upon the accuracy of which the final correctness of the flow net depends. There are various boundary conditions that help to position this first flow line, including:

What is the depth of penetration of sheet pile?

The line at which the sheet pile starts penetrating in soil from both sides is known by dredge line, and the depth of penetration of sheet pile under this line is D: depth of penetration. Designing of sheet piles mainly is to calculate the depth of penetration D and determining the section of sheet pile as will be discussed later.

How to calculate seepage from a flow net?

2.12 Calculation of seepage quantities from a flow net Nd = number of potential drops Nf = number of flow channels h = total head loss q = total quantity of unit flow. .’. Total unit flow per unit length (q) — kh —- A soft pencil, a rubber and a pair of dividers or compasses are necessary.