Definition of Uplift Pressures in structures | Soil Mechanics

1964 Niigata - Japan

What Uplift pressure means?

An uplift pressure is any pressure exerted beneath a structure (e.g. A retaining wall) that has the potential to raise the structure higher relative to its surroundings.

Most common uplift pressures come from water pressures present around the structure. Permitting flow through a permeable stratum will reduce the hydrostatic pressure in the water due to energy losses.

Diagram represending Uplift = U

However, some of this water will remain under any impermeable structure and produce forces vertically to the structure (see picture below).

The excess pore water pressure remaining will produce an uplift beneath the structure and an uplift of the whole structure can occur.

However, if the structure has sufficient deadweight or appropriate anchorage system ( Eurocode 7 check required) the uplift pressures will be balance and no failure will occur.

How to calculate Uplift pressures.

Calculating Uplift pressures is much easier than you thought

Pore water pressure "u" is :

u = γwH

γw = Unit weight of water = 10 kN/m3

H = Height = in metres (m)

• Since pore water pressure acts equally in all directions ( hydrostatic pressure) uplift pressure equals the pore water pressure but at the underside of an impermeable structure.

Uplift Water Pressure = Pore Water Pressure (kN/m2)

---

Essential Books for Civil Engineering Students

Amazon's Choice

---

Retainning Wall diagram with acting forces

---

What does Eurocode 7 say about Uplift Pressure Failure Check?

Example of a design for a Retaining Wall

According to Eurocode 7 - BS EN 1997-1 (Part 1: General rules),

at Section 6.5.2.1 Bearing Resistance:

Where:

Vd: Shall include the weight of the foundation, the weight of any backfill material and all earth pressures, either favourable or unfavourable.

Rd: Soil Bearing Capacity calculated from the Geotechnical Investigation Report.

---

You May Also Like:

Concrete variable radius arch dam explained

An arch dam is a concrete dam that is curved upstream in a plan. The arch dam is designed so that the force of the water against it. Advantages of the arch dame are...

Read More...

---