Structure, basins and waterproofing

Structure, basins and waterproofing

From bed design and load control to execution of seams, penetration details and sealing test

The quality of a fountain is not measured only by the height of the fountains, the harmony of light and music, or the beauty of its facade. A large part of the real quality of the project lies in the components that are not seen after operation: the pond bed, the water retaining structure, the execution seams, the passing connections and the sealing system.

Defects in these parts can lead to continuous reduction of water level, increase in water supply cost, destruction of coatings, corrosion of metal components, damage to adjacent spaces and long stoppage of fountain. In fountains on the roof of a parking lot or inside a commercial center, the consequences of a leak may extend far beyond the perimeter of the fountain itself.

A successful design is formed when the structure, architecture, facilities and sealing are coordinated from the beginning of the project. The waterproofing cover must be implemented on a suitable substrate and all the possible paths of water passage, from the concrete seam to the cable sheath, have specific details.

23–1. What are the functions of the fountain structure?

The pond structure has three main tasks:

• Tolerating the imported loads and transferring them to the ground or the building structure;

• limiting deformation and cracking in operating conditions;

• Providing a stable platform for water storage, installation of equipment and implementation of coatings.

These tasks are interdependent. A tank with sufficient resistance may not have optimal sealing performance due to cracks or improper deformation.

In the official introduction of ACI 350-20, sealing, durability, crack control and deformation limitation are introduced as the main topics of liquid-retaining concrete structures. This reference also includes water, soil and vibrating equipment loads as design considerations. Official introduction of ACI 350-20 ^[141]

For each project, the basis of the design, applicable regulations on the site, supplementary references and the responsibility of the designers should be specified. Referring to international standards in this chapter does not mean that they are automatically applicable in all Iranian projects. Sample calculations are also educational; Determining the thickness, reinforcement and executive details requires a special design.

23–2. Bed survey; The first stage of pond design

Before determining the shape of the structure, it should be determined on what bed the pond will be placed:

The presence of concrete flooring in the area alone is not a sufficient reason for its suitability as a fountain foundation. Also, the water level observed in a short visit is not necessarily the highest possible groundwater level.

In long ponds or with irregular geometry, asymmetric settlement becomes more important; Because it can change the level of the overflow and the uniformity of the water curtain in addition to creating cracks.

23–3. loading modes; A full pond is not the only important situation

The design should cover the different life situations of the project.

The combination of loads and their coefficients should be determined according to the design basis. Summing up all loads with the greatest amount, regardless of the possibility of simultaneous occurrence, is not a substitute for engineering load combinations.

In buried ponds, the net pressure on both sides of the wall is important. In one situation, the internal water pressure can prevail, and in another situation, the external soil and water pressure.

23–4. Calculation example: water weight and pressure on the pond

Consider a hypothetical rectangular pond with the following specifications:

• Internal length: 10 meters;

• Internal width: 6 meters;

• Uniform depth of water: 0.60 meters;

• Density of water: 1000 kg/m3;

• Gravitational acceleration: 9.81 meters per square second.

a) Volume and weight of water

$V=L\times B\times h$

$V=10\times 6\times 0.60=36m^3$

The mass of water is equal to 36,000 kg and its weight is equal to:

$W=\rho gV=353.16kN$

Therefore, this shallow pond also holds about 36 tons of water. The weight of the structure, covers, pipes and equipment should be added to the calculations separately.

b) Water pressure in the floor

In still water and for open pond:

$p=\rho gh$

$p=1000\times 9.81\times 0.60=5.886kPa$

The pressure due to the water in the floor is approximately 5.89 kPa.

c) Lateral force of water on the wall

The hydrostatic pressure increases from zero at the free surface to the highest value at the foot of the wall. For each meter of vertical wall length, the result of internal water pressure is equal to:

$F\text{'}=\frac{\rho g{h}^2}{2}$

$F\text{'}=1.766kN/m$

This force acts at a height of one-third of the depth of the water from the floor, that is, 20 cm above the floor.

This example only calculates the static charge of water. External pressure, support conditions, structure geometry, earthquake and crack control have not been investigated yet; Therefore, it is not possible to directly determine the thickness of the wall or the amount of reinforcement from these numbers.

Figure note from the source manuscript

Instead of picture 23-1

Suggested image: training section of a pool with a depth of 60 cm, triangular diagram of pressure on the wall, pressure on the floor and the place of effect of lateral force. The image should be prepared schematically and not have armature details.

Caption: "Water pressure increases with depth; In the design of the structure, the net pressure on both sides of the wall should be checked."

23–5. lifting force; Why can an empty pool be critical?

If the groundwater exerts pressure below the bottom of the pond, an upward force is created. By emptying the pond, the weight of the water inside is removed; While the groundwater pressure may remain.

To illustrate the point, suppose:

• Effective area under the foundation: 70 square meters;

• The height of underground water pressure compared to the floor: 0.80 meters;

• Total effective permanent weight attached to the structure: 500 kilonewtons;

• The pond is empty and the resistance of the restraints or the soil is not included in the calculation.

Assuming uniform pressure under the horizontal floor:

$U={\gamma }_w\Delta hA$

$U=9.81\times 0.80\times 70=549.36kN$

Simple ratio of resistant weight to lifting force:

$\frac{W}{U}=\frac{500}{549.36}\approx 0.91$

In this example, even before the design factors are applied, the lifting force exceeds the resistive weight. This ratio is just an educational comparison and the required safety factor is not considered as a regulation.

The solution may include changing the geometry and weight of the foundation, proper structural connection, use of designed restraints or groundwater management system. Its selection depends on geotechnical and structural conditions.

A waterproof coating cannot compensate for the lack of stability against lift. Also, relying on active drainage requires checking its reliability, maintenance and damage status. Groundwater conditions should also be checked before draining the pond for repairs.

23–6. Concrete, cracking and durability

For a concrete pool, determining the compressive strength is only one of the design decisions. The quality of the mixing plan, compaction, processability, rebar coating, concreting order and deformation limitation also play a role in the final performance.

In the executive specification, the task of the following should be clear:

• Contact conditions with water, cleaning materials and external environment;

• The quality and characteristics of concrete according to the exposure conditions;

• How to concrete and compact around the buried parts;

• Premature drying treatment and protection program;

• Shrinkage control and thermal changes;

• The method of evaluation and repair of wormholes and cracks.

For all ponds, a fixed number cannot be determined as the allowed crack width. The acceptance criteria should be in harmony with the design reference, environmental conditions and sealing system.

Permeability reduction additives may be part of the solution; But they are not a substitute for seam design, proper density or correct processing.

23–7. Types of seams and their roles

Seams must be designed before execution. An accidental stop of concreting should not become a permanent joint without investigation.

The three important groups are:

executive seam: the connection point of different stages of concreting; Its details should provide power transmission and sealing according to the plan.

Movement joint: It is predicted to accept relative displacement caused by factors such as temperature, settlement or movement of structural components.

Joint seam: the place where the pool meets another member or structure that may behave differently.

Separation of operational, movement and connection seams is also mentioned in the Sika seam sealing technical guide. Guide for sealing seams - Sika ^[142]

The type of movement expected, the components of the waterproofing, its continuity at the corners and the way to pass through the final layers should be specified in the plan of each seam. The distance of the seams should also be obtained from the design; A fixed distance is not suitable for all fountains.

23–8. Waterstop and seam sealing continuity

Waterstop limits the passage of water through the seam. Its selection depends on the type of joint, water pressure, expected movement, chemical conditions and the possibility of correct execution. Waterstop systems - Sika ^[143]

Three implementation issues must be carefully controlled:

1. Correct position: Waterstop should remain in the designed place during concreting.

2. Condensation around it: Cavities and wormholes around it can create a leak path.

3. Continuity: connecting parts at corners and intersections must be done with the approved method of the same system.

Inflatable waterproofing tapes and injection systems also have specific applications, but the possibility of replacing them with a single movement waterstop should be considered separately. Types of seam sealing system - Sika Canada ^[144]

Figure note from the source manuscript

Figure 23-2 instead

Suggested image: two close-up photos of waterstop before concreting; One at the junction of the floor and the wall and the other at the intersection or corner. The anchorage location, the connection status and the space required for concreting should be clear.

Caption: "Continuity of waterstop and density of surrounding concrete should be checked and recorded before covering."

23–9. Passing pipes and cables through the floor and wall

Every facility crossing is a critical point in the water retaining shell. Its details must be coordinated with the structure plan before concreting.

On the GSO website, "water fountain wall and floor transition connections" are introduced among the equipment; These parts should be considered in the initial coordination of facilities and structures. Urban fountain equipment - GSO ^[145]

For example, Crystal Fountains introduces the IWS connection to create a watertight passage of supply and discharge lines through concrete slabs. This example shows that the passage of the pipe has a detail independent of the piping itself. IWS - Crystal Fountains water seal connection ^[146]

In the map of each crossing, it should be specified:

• The piece is buried directly or passes through the casing;

• How is the sealing between the concrete and the part provided;

• How is the gap between the sheath and the tube closed?

• How to connect the waterproof cover to the part;

• Repair or replacement is possible from which side;

• How is the movement of the pipe and the forces caused by it controlled.

For cable, sealing around the sheath and sealing the path inside the sheath are two separate issues. Details should be compatible with the cable type, cross-section and electrical requirements.

Post-implementation drilling should also be done by checking reinforcements, buried components and sealing repair method.

23–10. Choosing a sealing system

Sealant selection should be based on the actual conditions of the pond, not just the brand name or the word "waterproof".

These groups may complement each other in a plan; Their juxtaposition must be verified in terms of compatibility.

For example, Sikalastic-1K product information lists applications including concrete ponds and tanks and sealing under pool tiles. Such a characteristic is related to the same product and its conditions of use and should not be generalized to all cement coatings. Specifications Sikalastic-1K - Sika ^[147]

The decisive questions are: Is the product suitable for permanent immersion? From which side does the water pressure enter? What is the moisture content of the basement? How is the contact with purification materials and sunlight? How much movement or crack opening does the coating accept?

The water pressure behind the inner cover can create different conditions than the water pressure inside the pool; Therefore, verification of performance in one pressure direction is not necessarily verification of the other direction.

23–11. Floor, corners, overflow and final coating

Tiles, stones and wainscoting should be part of the complete details of the pond. Their healthy appearance alone does not prove the sealing of the underlying shell.

In the design of the floor and wall, the following must be coordinated:

• Water movement path to the discharge points;

• Final alignment of nozzles and lights;

• details of the corners according to the sealing system;

• Connecting the cover to the floors and overflows;

• Continuation of movement seams in necessary layers;

• Sealing protection against equipment foundation and repair operations.

The slope of the floor should be determined by the geometry, the type of cover, the place of discharge and the need of operation. Using a constant slope for all ponds can conflict with equipment alignment or optimal water depth.

In linear overflows, the accuracy of edge alignment is particularly important; Because the difference in height can cause uneven distribution of flow and discontinuity of water effect.

23–12. Dry fountain and fountain on the building

In a dry fountain, the traversable floor is usually an architectural covering, passageway, and part of the facility's access. Its design should examine the plate, foundations, connections and the underlying structure in an integrated manner.

The declared resistance of a screen or grating alone is not sufficient to confirm that a vehicle will pass through the complex. The load of the wheel, the place of application of the load, the distance of the supports and the capacity of the underlying components should also be known.

In the water fountain on the roof, in addition to the total weight, the following are important:

• Load concentration under foundations and equipment;

• short-term and long-term deformation of the roof;

• relative movement of the pond and the building;

• Continuity of structural seams;

• Emergency overflow and evacuation route;

• Ability to detect and access the location of the leak.

Adding a shallow water fountain to an existing building should also be accompanied by an examination of the actual capacity of the structure.

Figure note from the source manuscript

Instead of picture 23-3

Suggested image: Cross-section of a dry fountain showing removable floor, bases, nozzle, bottom basin, sealing layer and access point. The path of load transfer is indicated by an arrow.

Subtitle: "In a dry fountain, the bearing capacity must be checked all the way from the floor to the underlying structure."

23–13. Quality control points in execution

Quality control is effective when it is done before components are worn.

For sensitive points, the photo, exact location, date and approval of the control officer should be recorded. It is not possible to register a waterstop or a buried connection after concreting; Therefore, documentation should be done simultaneously with implementation.

23–14. sealing test; Measurement instead of appearance judgment

The test program must be clear before the start of implementation: which part will be tested, at what stage, to what water level, for how long and with what acceptance criteria.

ACI 350.1-22 is one of the specialized references for the sealing test of liquid retaining structures. Its official introduction and preview explains the scope of related tests; The duration and limits of project acceptance should be determined from the selected reference text and approved specifications. Introduction and preview of ACI 350.1-22 ^[148]

The suggested process of preparing the test program:

1. Ensuring that concrete, repairs, and coatings reach the permitted water intake conditions; 2. Determination of test boundary and controlled isolation of related lines; 3. Investigating the condition of underground water and the safety of filling and emptying; 4. Dewatering according to approved procedures; 5. Record water level, time, rainfall, environmental conditions and observations; 6. Visiting seams, penetrations and accessible surfaces; 7. Analysis of volume change and comparison with acceptance criteria; 8. Fixing the defect and repeating the test of the affected part.

For a pond with a constant free surface:

$\Delta V=A_s\Delta h$

But the observed volume loss is not necessarily all leakage; Evaporation, precipitation, water withdrawal and changes in test conditions should be investigated.

For example, in a hypothetical pond with a surface of 60 square meters, a drop of one millimeter is equivalent to a volume change of 60 liters. This calculation only shows the measurement sensitivity and does not determine the leakage limit.

The pond shell test and piping test should also have clear boundaries so that the source of water loss can be identified. Success in the sealing test is not a substitute for verifying the strength and stability of the structure.

Figure note from the source manuscript

Figure 23-4

Suggested image: photo of the pool during the test, along with the fixed level measurement index, the numbered locations of the visit, and a sample of the results record sheet.

Caption: "The sealing test must be measurable, repeatable, and have a predetermined acceptance criterion."

23–15. Delivery, repairability and lasting documents

The operator should be able to identify years later what was implemented under the final coating. Delivery documents must include at least the following:

• Maps such as construction of the structure, seams and penetrations;

• Specifications of the sealing system and compatible components;

• Photo of the buried components before being covered;

• Records of concrete control, repair and sealing test;

• Drainage, washing and repair instructions;

• Restriction of drilling and installation of new equipment;

• Access to replaceable components and monitoring points.

If a leak is observed, the cause must be checked first: is the crack active or stable? Is the leak from the shell or the pipe? Does the pressure come from inside or outside? Does the seam continue to sit or move?

The choice of repair method is done after answering these questions. Covering the leak, without identifying the path and cause, may only change the location of the leak.

The value of the structure and proper sealing becomes apparent over the life of the project: the fountain works with less downtime, more predictable maintenance and better protection of the surrounding spaces.

In Chapter 24: mechanical installations and fountain plumbing, the path of water from the tank and pump suction to the collectors, valves, nozzles and return lines will be examined; Focusing on selection of pipe material and diameter, pressure drop, support, discharge and access for maintenance.