Field and Equipment Problems and Recovery

Transcription

1 Field and Equipment Problems and Recovery

2 In theory pile driving is simple. There are three physical components: Hammer Pile Theoretical Soil Profile And a fourth component: Specifications Problems may occur in each of these areas and sometimes in combinations

3 Hammers Three types of hammers commonly used in the market place Air/steam (Drop) Diesel Are ones commonly seen on construction projects Hydraulic; infrequently

4 Air/Steam hammers have few moving parts, relatively trouble free, easy to determine the energy delivered in each stroke. And are being replaced in the industry by diesel hammers.

5 Diesel hammers have varying strokes depending on soil resistance and fuel settings. More moving parts Combustion chambers with seals Require more maintenance. They also have more versatility by using different fuel settings.

6 The most often seen problems with diesel hammers involves maintenance. Including: Head cushion replacement Proper injector operation Compression seal The next significant problem area is Appropriate sizing of the hammer

7 Piles Pile types used in DOTD projects include Timber, Steel Pipe, Post Tensioned Concrete Cylinder and the most predominant by far Square Pre stressed Concrete.

8 The two most likely causes of pile defects are: Strand pattern Poor fabrication procedures. Including: Bed Removal Curing Storage Transportation

9 Soil Profile The third physical aspect is the theoretical soil profile. Borings, cone penetrometers, test and monitor piles Cost limits the amount of geotechnical investigation Assumptions are made

10 Problem prevention Geotech works to prevent pile issues through the use of: WEAP Analysis hammer adequacy Monitoring permanent piles PDA; Pile driving analysis PE and Contractor need to review and understand the borings prior to starting

11 What are the most usual field problems?

12 Most field problems manifest themselves through the piles. It won t go in (refusal) It goes in too easy (low resistance) It cracks or breaks

13 Someone will ask what is refusal

14 It Won t Go In Possible factors 1. Is the hammer working correctly? Check maintenance records Check stroke 2. Is the soil profile correct? Hard to check Does the soil profile provide an explanation?

15 If the hammer is working properly and there is nothing in the soil information that can explain the hard driving additional Geotechnical information may be needed. This takes time. The initial action will be a PDA

16 Depending on the pile behavior and the believed soil profile we May alter the size or depth of preboring Attempt to redrive after a delay (pour pressures) Action is very specific to a specific project.

17 It goes in too easy This has the potential to be the worst problem. It could require redesign of the cap and/or bridge.

18 What to do Over drive the pile and buildup Redesign the cap Change the Bridge grade

19 Prevention Be prepared Review the borings Have an idea of what should be happening as the pile drives Be conservative on the first pile Treat the first pile as a test pile.

20 Leave the pile high. How high? Depends To evaluate set up requires about 2 inches. Count the blows per inch. The longer it sets the higher the set up value, generally. A rule of thumb is that a pile can be overdriven 2 inches without having to buildup the pile. Another rule of thumb is that we design for about 5 foot of penetration into a tip layer. If over driving is required the pile will need to be built up using the CS 216 Pile Standard.

21 The pile cracks or breaks Vertical cracks and spalls Vertical cracking in the body of the pile is an unusual event. Spalling is not that unusual. Broken piles are rare.

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25 Horizontal cracking Will occur occasionally for no determinable reason. If a sequence of piles cracks something is wrong. The best way to trouble shoot is using a PDA. Often the pile cushion is involved. Corrective action Epoxy injection or sealant

26 There is no such thing as a perfect specification or a perfect set of plans. Slowdowns and problems are not beneficial to the contractor or the dept When a contractor brings a question or problem to the PE attention it deserves to be taken seriously. Do what the specs say maybe the right answer; it should not be an automatic answer.