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 26, 20203 min read

What is an OSHA-compliant Trench Box System?

Updated: Aug 6, 2021

Shield or sometimes referred to as “trench box” or “trench shield” prevents workers from being trapped inside a trench or excavation in event of cave-ins. They also protect workers from any material falling apart from excavation faces and from possible collapse of adjacent structures. Shield is recommended by the Occupational Safety and Health Administration (OSHA) as a Trench and Excavation Protective System besides Sloping/Benching and Shoring Solutions. Trench Boxes, from OSHA’s stand point, are characterized as follows.

DESIGN AND MANUFACTURE

According to OSHA Standard 1926.650, shields can be either pre-manufactured or job-built in accordance with 1926.652(c)(3) or (c)(4).

(C) (3)-Designs using other tabulated data. Tabulated Data are tables and charts approved by a registered professional engineer and used to design and construct a protective system.

(C) (4)-Design by a Registered Professional Engineer (RPE). Designs shall be in written form and shall include: A plan indicating the sizes, types, and configurations of the materials to be used in the protective system; and the identity of the RPE approving the design.

MATERIALS AND EQUIPMENT

Under OSHA Standard 1926.652(d), materials and equipment used shall be free from damage or defects that might impair their proper function. They shall be used and maintained consistently with manufacturer recommendations, and in a way that will prevent employee exposure to hazards. When damaged, a competent person shall examine the material or equipment and evaluate its suitability for continued use. If the competent person cannot assure its ability to support the intended loads or is otherwise unsafe to use, such material or equipment shall be removed from service. It will be evaluated and approved by a registered professional engineer before being returned to service.

LIMITS OF APPLICATION

Trenches 5 feet (1.52 m) deep or greater require a shield unless the excavation is made entirely in stable rock. If less than 5 feet deep, a competent person may determine that a protection not required. (OSHA 1926.652(a)(1)(I & ii)).
Trenches 20 feet (6.1 meters) deep or greater require that the shield is designed by an RPE or be based on tabulated data prepared and/or approved by an RPE in accordance with 1926.652(c).
A trench box can be combined with other protective systems, such as sloping and benching. In this scenario, the trench box must extend 18 inches above the vertical part of the excavation walls. If the top of the trench box is at ground level, trench box does not have to extend above grade.

https://www.osha.gov/dts/osta/otm/otm_v/otm_v_2.html

Photo Credit: OSHA Technical Manual Section V: Chapter 2

INSTALLATION AND RETRIEVAL

Conditions provided in OSHA 1926.652(g) are summarized as below:

Shield systems shall not be subjected to loads exceeding those which the system was designed to withstand.
Shields shall be installed in a manner to restrict lateral or other hazardous movement of the shield in the event of the application of sudden lateral loads. The space between the excavation sides and the trench box should be minimized or backfilled in any circumstance.
Employees shall be protected from the hazard of cave-ins when entering or exiting the areas protected by shields. A stairway, ladder, ramp or other safe means of egress shall be located in trench excavations that are 4 feet (1.22 m) or more in depth so as to require no more than 25 feet (7.62 m) of lateral travel for employees.
Employees shall not be allowed in shields when shields are being installed, removed, or moved vertically.
The maximum distance between the bottom of the shield and the bottom of the trench should be 2 feet (0.61m). Excavation of not more than 2 feet below the bottom of a shield is allowed, only if the shield is designed to resist the forces calculated for the full depth of the trench. Also only if there are no indications of loss of soil from behind or below the bottom of the shield.

To facilitate proper stacking in deep excavations, a design or system should be used to prevent the boxes from being misplaced or misused in the excavation when boxes of different ratings are employed. Boxes can be designed in a manner that they will fit together only one correct way, or using a marking system that readily identifies the maximum depth each individual box can be placed.

Photo Credit: OSHA Technical Manual Section V: Chapter 2

ESC Trench Boxes

In need of Professional Assistance for your Excavation and Trenching Projects? Contact ESC Group Please visit us at: www.esctrenchsafety.com email: escglobal@escpile.com

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What is an OSHA-compliant Trench Box System?

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