Construction monitoring

What construction monitoring is

Building the works to the drawings and specification is the constructor’s responsibility, and monitoring does not take that over. What it does is put the designer back on site during construction, so that the design is interpreted correctly, the methods used do not undermine it, and the finished work is checked before it is covered up.

The point about being covered up is the practical one. Reinforcement, subgrade, a founding surface, a wall drain: each is verifiable for a few hours and then it is not. Monitoring is largely about being there in those windows.

The five levels, CM1 to CM5

The levels are defined in Construction Monitoring Services, published by Engineering New Zealand. That document is the authority and the summary below is our paraphrase of it, not a substitute for reading it.

• CM1 reviews the outputs of somebody else’s quality assurance programme, with visits at an agreed frequency. The document is explicit that this is a secondary service, appropriate when another party holds the higher-level monitoring or when performance testing is being done and monitored by others.
• CM2 reviews a sample of each important work procedure, material and component, and a representative sample of completed work before it is enclosed. It suits smaller routine projects with a competent, experienced constructor where a higher than normal risk of non-compliance is acceptable.
• CM3 reviews random samples of important work procedures to an extent agreed with the client, plus important completed work. It suits medium-sized routine projects with an experienced constructor at normal risk.
• CM4 moves from random to regular sampling and reviews the majority of completed work. It applies where a lower than normal risk of non-compliance is required.
• CM5 keeps personnel on site reviewing work constantly. It is for major projects, projects where the consequences of failure are critical, and projects using innovative or complex construction methods.

The step from CM2 to CM5 is a step in coverage, and coverage costs money. Higher is not automatically better; it is a purchase of reduced risk, and the right level is the one that matches the risk actually carried.

Choosing the level

Four factors drive the choice: the size of the project, its importance, how complex the construction work is, and the constructor’s experience and demonstrated skill in quality management. The Engineering New Zealand document turns those into a scoring method, assigning a value to each factor and reading the appropriate level off a table from the total.

In practice the constructor is the factor people underweight. The same structure built by a certified contractor with a working quality system and by a crew doing it for the first time genuinely does not need the same level of review.

Councils often have a view on the level they expect before they will accept the work, so it is worth settling the level with the client and the council together, at design stage.

What LDE does on site

LDE monitors its own designs and reviews work designed by others, across geotechnical, civil and structural scopes. On the geotechnical side that usually means founding surfaces, subgrade, fill placement and compaction testing, retaining and drainage before backfill, and the records that support earthworks certification.

Each visit produces a dated record of what was reviewed and what was found, including what was not accepted. That record is the deliverable. A file of site memos that only says things were fine is not evidence of monitoring.

Monitoring sits inside the wider project management service, and the investigation work that precedes it is on the geotechnical investigation page.