Only the installation of water pipes, electric conduit, or drainage systems come close to having universal requirements for backfilling. This is an important step that is facilitated by delivery of sand from banks.Sand delivery from banks facilitates this important step, as it helps to protect the installed utilities and restore stable ground conditions above them.
Backfilling may seem like a trivial operation of filling a hole, but there are several concerns to consider when installing the soil compaction method, material characteristics, and protection of the utilities below. The use of suitable material does make a real difference to long term performance and durability in this application.
The importance of selecting materials for trench backfill.
The surrounding and overlying material should be placed above and around the utilities to support them properly without forming pressure points or settling problems that may cause damage to the pipes or cables in the long-term. The properties of the sand used in utility trenches as a backfill material make it useful for such a protective purpose.
The following is a list of some of the factors to consider when choosing trench backfill material:
- Good compaction characteristics with low settling or fines content
- Protection from sharp edge or debris striking utilities.
- Moisture conditions that favour long term stable moisture conditions.
- Adaptability to the surrounding soil and rehabilitation requirements
The problems with bad backfill
Poorly chosen or poorly placed backfilling soil in trenches, or poor compaction technique, can cause settlement problems months or years after the work is finished. Settling frequently manifests itself as surface lows near the trench line that can cause tripping hazards, drainage issues or even stress buried utilities over time.
These can be prevented if Bank sand delivery is used and is compacted adequately during backfilling which reduces the risk of these types of delayed settling problems occurring after the project has been completed and the site is in other phases.
The implementation of the Backfilling Process.Implementation of the Backfilling Process in Practice.
The typical backfilling process for a trench is as follows:
- Installation of utilities in the open trench is completed
- Initial planting material is installed immediately adjacent to the utility of concern.Initial planting material is installed immediately adjacent to the utility of concern.
- Compacting is done between each layer of bank sand added.
- Surface restoration is completed when the backfilling is at grade level.
Layered Compaction is important because…
The backfill material dumped into a trench at one time is not likely to compact adequately throughout the trench. Rather, experienced crews generally backfill in layers, compacting each layer before adding the next layer, which helps to assure uniformity of density in the trench rather than pockets of loose material that might settle unevenly over time.
This multi-layered method requires slightly more time than a single pour, but the added stability over time is normally worth the extra time spent when backfilling.
How this safeguards the investment of infrastructure.
From a single house connection to a major development, utility lines are a large investment in infrastructure. Proper backfilled trenches help preserve this investment by helping to maintain stable conditions around buried utilities and help limit damage caused by ground movement or settling which could result in expensive repairs later.
Before backfilling, Contractors should verify the following:
To ensure smooth backfilling operations, it's useful to confirm a few practical details prior to the commencement of backfilling:
- That utilities are correctly located and if necessary, inspected.
- If specified that bedding material has already been correctly placed.
- That the volume of sand delivered to that bank is equal to the volume of the trench that is measured.
- That there is suitable and available compaction equipment for the trench depth.
Final Thoughts
One of the most common and useful uses of bank sand for Houston construction is trench backfilling. This process, if done correctly with the right materials and compaction technique, does benefit buried utilities and helps to avoid settling delays that can cause significant problems long after a project is complete.