Close Menu
  • About Us
  • Services
    • House Plans/Views
    • Books
    • Videos
    • Softwares/Programmes
    • Job/Scholarship Adverts
  • Notes
    • Structural Engineering
    • Surveying
    • Geotechnical Engineering
    • Design Codes
    • Highway/Transportation Engineering
    • Environmental Engineering
    • Concrete Technology
    • Soil Mechanics
    • Mathematics
    • Strength of Materials
    • Fluid Mechanics and Hydraulics
    • Water Resources Engineering
  • Quiz
  • Privacy Policy
  • Terms and Conditions
  • Q&A
  • About Us
  • Services
    • House Plans/Views
    • Books
    • Videos
    • Softwares/Programmes
    • Job/Scholarship Adverts
  • Notes
    • Structural Engineering
    • Surveying
    • Geotechnical Engineering
    • Design Codes
    • Highway/Transportation Engineering
    • Environmental Engineering
    • Concrete Technology
    • Soil Mechanics
    • Mathematics
    • Strength of Materials
    • Fluid Mechanics and Hydraulics
    • Water Resources Engineering
  • Quiz
  • Privacy Policy
  • Terms and Conditions
  • Q&A
  • en
    • ar
    • zh-CN
    • nl
    • en
    • fr
    • de
    • it
    • pt
    • ru
    • es
Facebook X (Twitter) Instagram YouTube LinkedIn WhatsApp
Home»Geotechnics»How to Verify Adverse Conditions in Underground Water Retaining Structures (Worked Example)
Geotechnics

How to Verify Adverse Conditions in Underground Water Retaining Structures (Worked Example)

Mezie EthelbertBy Mezie EthelbertUpdated:
Facebook Twitter LinkedIn Telegram WhatsApp Pinterest Email Copy Link
Share
Facebook Twitter LinkedIn Pinterest Email Reddit Telegram WhatsApp
Reading Time: 5 minutes

Table of Contents

  • Introduction:
  • Verification for Adverse Conditions
    • A. Stabilizing actions (due to the weight of the pool components when empty)
    • B. Destabilizing actions (due to uplift pressure under the base of the pool)
    • A1. NEW Stabilizing actions

Introduction:

Prior to the design of underground water retaining structures such as tanks and swimming pools, preliminary sizing of the structural members must be done. However, these sizes must be verified to ensure that they satisfy some adverse effects which the structure would be exposed to in its service life. This verification involves the stabilizing actions that tend to keep the structure stable such as the weight of the structural components of the structure together with the weight of stored water and destabilizing actions that tends to unsettle the structure such as uplift forces from underground water etc.

Generally,  verification of stabilizing actions and destabilizing actions should be done in worst case scenario viz:
(1) When the structure is empty, to investigate the adverse effects of earth pressure and groundwater on the base and on the walls of the structure.
(2)
When the structure is full, to consider the effects of stored water on the base and walls of the structure without considering the beneficial effect of the near balance of earth pressure and groundwater on external walls.

The aim of the verification is to ensure that the structure is safe in the worst condition. If initial verification fails (i.e. the floatation is critical), maybe due to the fact that the effect of destabilizing forces is more than that of stabilizing forces, the thickness of the wall can be increased or the base of the slab extended (see Figure 1 below) such that the weight of the backfill earth on the extended portion contributes to stabilizing the structure. Another possible means is to lower the water table of the soil.

Verification for Adverse Conditions

Verify the adverse conditions of the swimming pool sections shown below and determine the suitable sizes of the members to satisfy adverse conditions.

A. Stabilizing actions (due to the weight of the pool components when empty)

i. Weight of the base (volume of base x unit weight of concrete)
-Area of base = (4.6 x 2.3) + (4.6 x 4.1) + (4.6 x 3.3) = 10.58 + 18.86 + 15.18 = 44.62 m2
-Volume of base = area x thickness = 44.62 x 0.3 = 13.386 m3
-Weight of base = 13.386 x 25 = 334.65 kN

ii. Weight of perimeter beams
-Depth of perimeter beams excluding part taken by slab = 600 – 300 = 300 mm = 0.3 m. Total length of perimeter beam = 4.6 + 4.6 + 2 + 2 + 4.1 + 4.1 + 3 + 3 = 27.4 m
-Thickness of perimeter beam = 300 mm = 0.3 m
-Volume of concrete due to perimeter beam = 0.3 x 27.4 x 0.3 = 2.466 m3
-Weight of perimeter beams = 2.466 x 25 = 61.65 kN

iii. Weight of longitudinal walls
-Volume of concrete wall at section A = (L x H x T) x 2 = 2 x 1.5 x 0.3 x 2 = 1.8 m3
-Volume of concrete wall at section B = (area of trapezium x thickness of section) x 2 = ½ (1.5 + 2.4)4 x 0.3 x 2 = 4.68 m3
-Volume of concrete wall at section C = 3 x 2.4 x 0.3 x 2 = 4.32 m3
-Total volume = 1.8 + 4.68 + 4.32 = 10.8 m3
Weight of longitudinal walls = 10.8 x 25 = 270 kN

iv. Weight of lateral walls
-Weight of lateral walls = (4.6 x 1.5 x 0.3 x 25) + (4.6 x 2.4 x 0.3 x 25) = 51.75 + 82.8 = 134.55 kN

Total weight, W = 334.65 + 61.65 + 270 + 134.55 = 800.85 kN

The load is for stabilizing action and it is considered favourable load and it is permanent. From Table 1, partial factor, γG = 0.9

Thus, Gstb,d = W x γG = 800.85 x 0.9 = 720.765 kN

B. Destabilizing actions (due to uplift pressure under the base of the pool)

i. Section A (head of groundwater above the base = 1.1 m)
Uplift pressure = 10 x 1.1 = 11 kN/m2
Udst,d = factor for unfavorable permanent action (Table 7) x area of zone A  x uplift pressure = 1.1 x 10.58 x 11 = 128.018 kN

ii. Section B (average head of groundwater above the base = 1.55 m)
Uplift pressure = 10 x 1.55 = 15.5 kN/m2
Udst,d = 1.1 x 18.86 x 15.5 = 321.563 kN

iii. Section C (head of groundwater above the base = 2 m)
Uplift pressure = 10 x 2 = 20 kN/m2
Udst,d = 1.1 x 15.18 x 20 = 333.96 kN

Total Udst,d = 128.018 + 321.563 + 333.96 = 783.54 kN

Gstb,d (720.765 kN) < Udst,d (783.54 kN) –  this is not satisfactory.

Decision: Let us increase the base thickness to 400 mm and the depth of the perimeter beam to 750 mm

A1. NEW Stabilizing actions

Total weight of the pool when empty comprises

ai. Weight of the base
-Volume of base = area x thickness = 44.62 x 0.4 = 17.848 m3
-Weight of base = 17.848 x 25 = 446.2 kN

aii. Weight of perimeter beams
-Depth of perimeter beams excluding part taken by slab = 750 – 400 = 350 mm = 0.35 m.
-Volume of concrete due to perimeter beam = 0.35 x 27.4 x 0.3 = 2.877 m3
-Weight of perimeter beams = 2.877 x 25 = 71.925 kN

aiii. Weight of longitudinal walls
-Volume of concrete wall at section A (L x H x T) x 2 = 2 x 1.5 x 0.3 x 2 = 1.8 m3
-Volume of concrete wall at section B (area of trapezium x thickness of section) x 2 = ½ (1.5 + 2.4)4 x 0.3 x 2 = 4.68 m3
-Volume of concrete wall at section C = 3 x 2.4 x 0.3 x 2 = 4.32 m3

Total volume = 1.8 + 4.68 + 4.32 = 10.8 m3

Weight of longitudinal walls = 10.8 x 25 = 270 kN

aiv. Weight of lateral walls
-Weight of lateral walls = (4.6 x 1.5 x 0.3 x 25) + (4.6 x 2.4 x 0.3 x 25) = 51.75 + 82.8 = 134.55 kN

Total weight, W = 446.2 + 71.925 + 270 + 134.55 = 922.675 kN

The load is for new stabilizing action and it is considered favourable load and it is permanent. From Table 7, partial factor, γG = 0.9

Thus, Gstb,d = W x γG = 922.675 x 0.9 = 830.4075 kN

Gstb,d (830.4075 kN) > Udst,d (783.54 kN) – this is satisfactory

Thus, the final dimensions of the components of the pool are;

Thickness of walls = 300 mm

Thickness of slab = 400 mm

Depth of external perimeter beams only = 750 mm including thickness of base slab.

Share this:

  • Click to share on Facebook (Opens in new window) Facebook
  • Click to share on X (Opens in new window) X

Related

Share. Facebook Twitter Pinterest LinkedIn Email Telegram WhatsApp Copy Link
Previous ArticleStability and Indeterminacy of Civil Engineering Structures
Next Article Type of Geosynthetics and their Applications
Mezie Ethelbert

An inquisitive engineer with considerable skills in analysis, design and research in the field of civil engineering.

Related Posts

Common Rules of Thumb in Geotechnical Engineering

Important Tests Required in Tunnel Construction

Concise Notes on Bearing Capacity and Settlement of Soils (PDF)

Add A Comment

Leave a ReplyCancel reply

June 2025
M T W T F S S
 1
2345678
9101112131415
16171819202122
23242526272829
30  
« Dec    
INTRO VIDEO OF OUR SERVICES
https://mycivillinks.com/wp-content/uploads/2022/01/Lemarg-Consulting-Services-Intro-Video.mp4
CLICK ON THE BOOK COVER TO SEE CONTENT
theory of structures
CLICK ON THE BOOK COVER TO SEE CONTENT
BLOG SUBSCRIPTION

Get the latest posts on this blog

MOST RECENT POSTS

Common Rules of Thumb in Geotechnical Engineering

Important Tests Required in Tunnel Construction

Concise Notes on Bearing Capacity and Settlement of Soils (PDF)

MOST VIEWED POSTS
  1. Differences between University and Polytechnic Education System in Nigeria (Example of Civil Engineering Syllabus) (9,988)
  2. COREN Past Interview Questions for different Engineering Divisions in Nigeria (8,208)
  3. Standard Rules for Setbacks in Nigeria for Structures (8,085)
  4. COREN professional interview (COREN P.I.) (7,610)
  5. Structural Analysis and Design of Sawtooth or Slabless Staircase (7,328)
  6. Analysis and Design of Sheet Piles (PDF) (6,904)
POSTS CATEGORIES
© {2025} Mycivillinks. All rights reserved
  • About Us
  • Services
    • House Plans/Views
    • Books
    • Videos
    • Softwares/Programmes
    • Job/Scholarship Adverts
  • Notes
    • Structural Engineering
    • Surveying
    • Geotechnical Engineering
    • Design Codes
    • Highway/Transportation Engineering
    • Environmental Engineering
    • Concrete Technology
    • Soil Mechanics
    • Mathematics
    • Strength of Materials
    • Fluid Mechanics and Hydraulics
    • Water Resources Engineering
  • Quiz
  • Privacy Policy
  • Terms and Conditions
  • Q&A

Type above and press Enter to search. Press Esc to cancel.