*Paul Janzé – Advanced Biomass Consulting Inc.*

For many reasons, people need to know how much material is present in a biomass storage pile. Accurate volume measurement is relatively easy, but to determine the amount of dry fibre actually present, the compacted density and moisture content are required. In fact, the greatest number of queries I receive at this website are with regard to biomass pile density and compaction. This is because compaction is the most difficult pile parameter to determine with any consistent accuracy.

Biomass is highly compressible both through artificial and natural means. Every material is different and every pile is different. The amount of compaction depends upon the species, the form of the material, the relative amounts of bark, wood and foliage present, the grind size, particle size distribution, moisture content, weather conditions, the shape of the pile, how the pile is constructed, how long it has been sitting, the amount of decomposition, the amount of contamination with dirt, grit or stones, etc. So, it is just an educated guess as to how much compaction there will be in any one pile.

To my knowledge, there are no tables you can consult that will help you determine the amount of compaction, the average density and the consequent amount of material in any biomass pile. It is something that must be determined by a combination of measurement, calculation and over time, historical record.

If you are not artificially compacting the pile by driving on it with mobile equipment or using another form of densifier, most of the resulting compaction will likely occur as the pile is being constructed; the material at the bottom will be compressed by the weight of the material resting on top. Also, over time you will get some consolidation and decomposition which further reduces pile volume. Natural compaction in a biomass pile varies within the pile depending upon the height of the pile, with the least dense material on top and the most dense on the bottom of the pile.

With a bit of work you can approximate the average amount of compaction in small, naturally compacted biomass piles.

Method 1

- Create a test pile that has a representative cross-section of your normal storage piles.
- Measure the pile immediately after it is created and calculate the volume.
- Measure the pile after (1) week and calculate the volume.
- Measure the pile after (X) weeks and calculate the volume.
- Compare the results to determine relative compaction over time.
- To make volume calculation easier, I suggest that you create the pile between vertical walls 12’-15′ apart to make the total volume you are measuring, smaller and easier to handle.

Method 2

If the above method is not practical, you could simulate and estimate the compaction by the following method:

- Determine the average bulk density of freshly ground material taken from the top surface of the pile by filling a 1.0ft³ container with material and weighing it. Take (10) different samples from different areas on the pile and calculate an average bulk density (e.g. 20 lb/ft³).
- Multiply the average bulk density by the pile height to determine the load seen by the material at the bottom (e.g. 12’ h x 20 lb/ft³ = 240 lb/ft²).
- Place 1.0 ft³ (12 x 12 x 12 in) of freshly ground material in a container and place the equivalent weight on top (240 lb), which will compact the material somewhat.
- Remove the weight and measure the new height of the compacted material and calculate the volumetric compaction (%).
- Repeat steps 2-4 for each foot of pile height.
- If the stockpile has a tapered top, then repeat this sequence for every foot of width of the pile, using the relative pile height in the calculation.
- Calculate the average of the compaction calculations.
- To determine the amount of natural compaction occurring over time, repeat steps 1-6 for: a freshly ground pile, a 1-week old pile and for an (x)-week old pile and compare the results.
- You could use the same process to compare compaction values for piles of different grind sizes or materials.

Note: Neither of these methods are suitable for determining the compaction of artificially compacted biomass piles.

Attached is an Excel spreadsheet based on method 2 that I developed to approximate the natural compaction of a small biomass pile. You are welcome to use it if you need to determine an overall average compaction, but be aware that the result from one pile constructed today could be different from a similar pile constructed next week. Pile Compaction Calculation,2

If you do choose to attempt to calculate pile compaction this way, let me know how it works out.

For long-term, on-going biomass pile inventory control, read the following articles, titled “Chip / Biomass Pile Inventory Measurement” and “Biomass Storage Pile Basics” located elsewhere on this website.

Copywrite © 30 November 2014

Paul can be reached at: *Advanced Biomass Consulting Inc*., tel: 604-505-5857, email: pjanze@telus.net

The following email string is between the website author and a client that I have chosen not to identify. I thought the discussion may be of interest to others.

From: Jeff H__________

Sent: Wednesday, December 9, 2015 8:03 PM

To: pjanze@telus.net

Subject: Calculating Wood Pile Space Requirements

Found your spreadsheet for calculating compaction on advancedbiomass.com. I’m working on a project where we need to calculate the space required to store 7500 tons of wood chips (3/4 to 3 in size). I looked at your table spreadsheet, but don’t think it will help me. Any ideas on where I could get data/formulas to calculate this?

Take care…

Jeffrey __________

Hi Jeff,

I apologize for taking so long to answer your query.

The footprint required to store a given amount of material depends upon several factors, including:

• Material density and moisture content.

• Material angle of repose

• The need (or not) to consider compaction from mobile equipment.

• Method of building the pile.

• Shape of the pile; conical, flat-top, oblong, symmetrical, radial-conical, etc.

• Maximum allowable pile height.

• Method for reclaiming the pile.

• Is the pile bottom flat or inclined.

• Consider if the pile has retaining walls.

• Effective fill percentage; i.e. – allowance for road to top of pile

• Available space for the pile.

Example

Bulk Material Density: 10 BDlb/ft³ non-compacted

Moisture Content: 50%

Angle of repose: 45°

Compaction: Mobile equipment driving on the pile, so assume 15% average

Quantity to be stored: 7500 tons = 750,000 ft³ non-compacted or 637,500 ft³ compacted

Effective Fill Percentage: 80%

Loading Point: Single drop point

Retaining walls: None

Pile Shape: Truncated conical pile, with a flat horizontal base.

Maximum Pile Height: 60’

Reclaimer: Mobile equipment working from the pad

So, using simple geometry a truncated conical pile for storing 7,500 tons of compacted wood chips would have:

• A base diameter of 185’

• A top diameter of 65’

• A pile height of 60’

• An effective fill of 80%

If the pile had a rectangular base, then the calculation would be different.

I’ve visited your website, and it appears that this is your first foray into wood and biomass handling. I have extensive experience with wood and biomass handling, primarily in Canada and the USA. I am very interested in learning about your project and in submitting a proposal to provide engineering assistance; anything from high-level feasibility and definition studies, through design review, detail design or trouble-shooting. If this is of interest to you, please contact me per the following.

Paul Janze

Advanced Biomass Consulting Inc., Langley, BC, Canada

tel: 604-505-5857

pjanze@telus.net