Wellpoint systems

Step 1 of 6 - slide through the snapshots.

STEP 1

Design from the GI

Extract permeability, standing water level and seasonal variation from the ground investigation.

STEP 2

Install the wellpoints

Points are jetted in with a high-pressure water lance or bored, the screen set at design depth, and the annulus sand-packed where the ground needs a filter -…

STEP 3

Connect, seal and commission the header

The header ring is laid level around the dig, connected to the vacuum-assisted pump, and every joint checked - air leaks are the silent killer of vacuum…

STEP 4

Prove drawdown before trusting it

Observation wells or dip tubes inside and outside the ring confirm the water level is actually falling to target - the pump running proves nothing except the…

STEP 5

Dig dry, in stages for deep excavations

Excavation proceeds inside the depressed water table, keeping formation comfortably above it.

STEP 6

Run continuously, then decommission in order

The system runs 24/7 with duty/standby changeover, alarms and weekend cover until the works resist flotation or are backfilled.

How does Wellpoint systems work, step by step?

1. 1

   Step 1: Design from the GI

   Extract permeability, standing water level and seasonal variation from the ground investigation. Set the target drawdown - at least 0.5–1 m below formation - and compute flows to size wellpoint spacing (often 1–2 m in sands), header diameter and pump duty. Deep digs are staged: draw the section with berms and check the geometry of each suction lift against the 4–5 m limit.

   
2. 2

   Step 2: Install the wellpoints

   Points are jetted in with a high-pressure water lance or bored, the screen set at design depth, and the annulus sand-packed where the ground needs a filter - the sand pack is what stops the point pumping fines. Risers connect to the header with a valve per point so each can be tuned or isolated. In silty ground, installation quality decides whether the system works for weeks or clogs in days.

   
3. 3

   Step 3: Connect, seal and commission the header

   The header ring is laid level around the dig, connected to the vacuum-assisted pump, and every joint checked - air leaks are the silent killer of vacuum systems. Commissioning is a tuning exercise: run up, watch the vacuum gauges, walk the line listening and feeling for leaks, and balance flows point by point. Discharge runs through silt control to the consented outfall.

   
4. 4

   Step 4: Prove drawdown before trusting it

   Observation wells or dip tubes inside and outside the ring confirm the water level is actually falling to target - the pump running proves nothing except the pump. Digging proceeds only when monitoring shows drawdown at or beyond the requirement across the dig area. A point or zone lagging behind gets investigated: blocked screen, air leak or a permeability surprise.

   
5. 5

   Step 5: Dig dry, in stages for deep excavations

   Excavation proceeds inside the depressed water table, keeping formation comfortably above it. For staged systems, the first-stage ring runs while the dig forms the berm, then the second-stage header is installed on the berm and commissioned before digging on. Berms are cut and points relocated in the designed sequence - never dug away while still doing their job.

   
6. 6

   Step 6: Run continuously, then decommission in order

   The system runs 24/7 with duty/standby changeover, alarms and weekend cover until the works resist flotation or are backfilled. Decommissioning reverses the logic: confirm the structure is safe, then pull points, grout or backfill the holes, close the discharge consent formally, and monitor recovery briefly to confirm it is benign for the neighbours.