Inputs
Example Data
| Foundation Length (m) | Pin Length (m) | Gap (m) | Stages | Crews | Pins/Crew/Day | Curing Days | Expected Pins |
|---|---|---|---|---|---|---|---|
| 24.00 | 1.20 | 1.20 | 2 | 1 | 2.0 | 2 | 10 |
| 36.00 | 1.50 | 1.00 | 3 | 2 | 1.5 | 3 | 14 |
Formula Used
- Pitch: pitch = pin_length + gap
- Pin count (conservative): n = floor((foundation_length + gap) / pitch)
- Pin position: start(i) = (i−1)×pitch, end(i) = start(i)+pin_length
- Stage assignment: stage(i) = ((i−1) mod stages) + 1
- Stage days: days(stage) = ceil(pins_in_stage / (crews × pins_per_day))
- Total duration: sum(stage_days) + (stages−1)×curing_days
How to Use This Calculator
- Measure the underpinning run length along the foundation wall.
- Enter the planned pin length and the gap between pins.
- Choose the number of stages to avoid adjacent excavation.
- Set crews, productivity, and curing days for time estimates.
- Click Calculate Plan to generate the sequence table.
- Use the CSV or PDF export for briefings and records.
Sequencing intent and risk control
Underpinning is normally executed in discrete pins to protect load paths and limit ground disturbance. This planner assigns pins to stages so adjacent locations are not excavated within the same run. Staging improves stability where masonry, shallow strip footings, or variable soils require careful excavation and timely concrete placement.
How the planner builds the pin layout
The calculator uses the foundation run length, pin length, and gap to create a repeating pitch. It then places each pin start and end along the run and labels it with a stage using a rotating sequence. Direction selection mirrors the plan so supervisors can start from the preferred access point.
Production and curing assumptions
Construction duration is estimated from the number of pins in each stage and the total daily capacity based on crews and productivity. Curing days are applied between stage runs to reflect typical waiting periods before adjacent excavation. These values are planning aids and must be aligned with mix design, temperature, and approvals.
Interpreting the plan table
Each row shows stage, pin identifier, and chainage values for start and end. “OK” indicates the staged assignment avoids immediate adjacency; warnings appear if two neighboring pins share the same stage due to extreme input combinations. Use the exported table for briefings, inspection records, and method statements.
Example data for quick validation
Example: foundation length 24.00 m, pin length 1.20 m, gap 1.20 m, and 2 stages typically yields 10 pins with alternating stage allocation. With 1 crew producing 2.0 pins/day and 2 curing days between stages, the plan provides a practical baseline schedule for coordination and permits.
FAQs
1) What does “stage” mean in the plan?
A stage is a pass along the foundation where selected pins are excavated and concreted while leaving separation. Later stages fill the remaining pins after curing and checks confirm stability.
2) How do I choose the number of stages?
Use more stages when ground is weak, structures are sensitive, or tighter controls are required. Fewer stages can work for robust conditions, but only if the design and method statement allow it.
3) Why is there a gap between pins?
The gap keeps unexcavated material between active pins, reducing the chance of loss of support. Gap size should follow design drawings and ground behavior observed during trial excavations.
4) Does the schedule include inspections and approvals?
No. The duration is a planning estimate using productivity and curing days. Add allowances for hold points, inspections, utility checks, access constraints, and any client or engineer approvals.
5) What should I do if I see an adjacency warning?
Increase stages, increase gap, or adjust pin length so neighboring pins fall into different stages. Also review whether the run length and dimensions reflect the actual underpinning set-out.
6) Can I use this for stepped or irregular foundations?
Use it as a baseline only. Irregular geometry often needs segmented runs, different pin sizes, and bespoke sequencing. Split the wall into sections and plan each section separately.
7) Is the output suitable for a method statement?
It supports a method statement by providing a clear sequence table, but it does not replace engineering design. Confirm loads, temporary works, excavation support, and concrete specifications.