What is the proper vinyl sheet pile driving method for different soil types?

“Pitch and drive” method is the most practical way of pile driving in loose soils especially when using short piles. Also called “set and drive”, this method installs piles one by one. However, with only one interlock in control, sheet piles have high tendencies of rotating from the axis and leaning forward or backward. Panel driving is recommended for the dense deposit of sands and compact cohesive soils such as heavy clay or in presence of obstructions. In this method, a number of piles are interlocked together before driving. The panel of piles is supported by guide frames and driven gradually in sequence, sometimes in a staggered manner. The method can achieve installations of longer piles in more difficult ground conditions with better results in sheet pile alignment and verticality. In cases of difficult ground conditions such as hard strata and the presence of obstructions, driving assistance is employed along with a proper selection of driving method and equipment. Jetting and drilling help by loosening or eliminating obstructions by creating pressure right under the tip of the sheet pile being driven. Long and slender PVC sheet piles require steel mandrels as supports when driven in such conditions. Mandrel, which shape is similar to sheet pile profiles, increases the rigidity of Plastic Sheet Pile and supports the weight of the driving equipment such as a vibro-hammer.

What is the proper machine to drive piles in different conditions?

Impact driving is suitable for all soil types but appears to create the highest degree of stress to sheet piles. It is more appropriate to cohesive soils and soft soils such as silts and peats, loose medium to coarse sand, and gravels free of rock inclusions. Drop hammers such as the hydraulic hammer are the common types of impact-driving machinery. Driving using vibratory hammers is ideal for non-cohesive or granular soils such as soft soils and round-grained sand or gravel. It has also shown satisfactory performance in sandy, silty, or softer clay soils. It is less effective in angular-grained materials and soils with a firm consistency. With the introduction of vibration, however, the sub-soil can be further compacted, increasing penetration resistance and ultimately-refusal. If this is the case, driving aids like jetting and drilling might be necessary.

What are the pvc sheet pile selection criteria for soil condition of different hardness?

General rule of the thumb: “the harder the soil, the stronger and stiffer sheet pile section should be used”. Driveability of a pile section is a consequence of its cross-sectional properties (thickness, depth, and width), designed shape, length, grade, and the applied load. Hardness of soil strata characterized by SPT or CPT values is used to predict soil resistance which is essential in the calculation of driving force to be applied. Knowing the range of force from the selected driving machine, corresponding sheet pile sections can be picked according to their yield strength and elastic modulus.

How should I choose a sheet pile section for soils with, say, SPT Value, N=30? Can I still consider using vinyl or shift to steel?

Every sheet pile material has a design purpose, strengths, and areas of improvement. The availability of different materials denotes the need for a special material for a specific application. Plastic or synthetic sheet piles for example are known for being light and corrosion-resistant; Steel sheet piles are recognized for their extraordinary strength and versatility; and so on.

ESC Group
- Nov 6, 2022
- 3 min read

Difference Between Cast Iron vs Cast Steel Bollard

Mooring bollard is a vital component of any mooring system. It is usually the short post and is used as the anchor point for mooring lines to be fixed to secure the vessel alongside jetties/quay, berths, wharves and dolphins in ports and harbors.

Mooring Bollards Catalogue

Since the beginning of maritime history, people have been using wooden posts or iron structures for this purpose. With the advancement of manufacturing technology, engineers and manufacturers of today have considered the strength and durability of materials while also providing a safety factor as a safety cushion.

Mooring bollard is a simple and essential mooring device. However, not all bollards are created equal. Different design profiles, sizes and mooring line capacities are considered to adjust in each port. The suited mooring system applications considers the physical conditions, and the type of ships it will serve.

Designing and choosing the right components are a big part in marine construction. It is crucial to know what type of material to be utilized. Ductile cast iron, cast steel and stainless steel are some of the main materials used to make marine mooring bollards. They each have advantages in their applications.

In this article, we will focus mainly on the difference of cast iron vs cast steel.

Carbon content is the main difference

Iron and steel are both ferrous metals composed primarily of iron atoms. Pure elemental iron is too soft to be useful but when mixed with carbon, it gets harder, and therefore more useful. In fact, the carbon composition is the main distinction between cast iron and steel. Cast iron typically contains more than 2 percent carbon, while cast steel often contains between 0.1–0.5 percent carbon.

Impact resistance

Steel is excellent at withstanding sudden impacts without bending, deforming, or breaking due to its ability to withstand high stress and strain forces.

Strength without ductility results in a brittle material that is highly susceptible to fracture—and cast iron is one good example of strength without ductility. Because of its brittleness, cast iron has a limited range of application.

While iron may be easier to work with in most casting applications, steel has an optimal mix of both strength and ductility for many applications, and it is extremely tough. Steel is the most widely used metal in the world due to its impact-resistant qualities and all-around load-bearing nature making it desirable for many mechanical and structural applications.

Corrosion Resistance

Iron has better corrosion resistance than steel. Both metals oxidize in the presence of moisture, but iron develops a patina to prevent deep corrosion of the metal's integrity.

The mooring bollards have long been exposed to a highly corrosive marine environment, which is easy to rust, so the mooring bollards require a durable coating system. Due to the wear and abrasion from the ropes, the mooring bollards need to be regularly maintained. The steel mooring bollards need to be painted often to maintain all intensity because it is more susceptible to the cast iron mooring bollards.

Wear Resistance

Cast iron has better resistance to mechanical wear than steel, specifically in friction-wearing situations.

Steel wears more readily than iron but may still be resistant to certain types of abrasion. This can be resolved by adding certain alloys that can help improve its abrasion qualities.

Cost

Cast iron is cheaper than cast steel due to its lower material costs, energy, and labor required to produce the final product. Raw steel is costlier to purchase, and it requires more time and attention to cast.

Alloys can be added to both iron and steel to engineer desired properties. For example, Manganese increases toughness, while chromium improves corrosion resistance and may also affect the cost of the material.

To summarize :

Materials	Advantages	Disadvantages
Ductile Cast Iron	- Long service life - High strength - Good impact resistance - High corrosion resistance	The most expensive among the 3 types of materials.
Grey Cast Iron	- Low cost per weight - Excellent corrosion resistance	- Low strength - Low impact resistance
Cast Steel	- High strength - High impact resistance - Good cost per weight	Needs regular maintenance to prevent corrosion.

Mooring bollards play an important role in ship mooring and the choice of the right material will greatly affect the operation of the marine facility. Ultimately, the right selection should also consider the factors such as the most demanding load combination possible, the type of marine structure and the adhesion of the surface into account. This will determine the most suitable shape, size and material of the bollard to ensure maximum quality and strength.