- Problem Definition
Working volume is important element for established the cost besides unit price. Currently there are many standards of volume measurement for project quantity surveying. One of them is CESMM [Civil Engineering Standard Method of Measurement] published by The Institution of Civil Engineers. For blog W12, I am trying to compare earthwork volume calculation for shallow foundation following CESMM section E [Earthwork] with traditional method in accordance with OSHA standard.
Figure 1 Excavation Work
- Identify the Feasible Alternative
There are four soil types according to OSHA: a. stable rock, b. type A, c. type B and d. type C soil with their slope configurations. I will take the basic excavation with maximum depth of 20 feet (equal to 6 m1) configuration.
- Development of the Outcome for Alternative
A. Safe Slope Configuration
Present in Figure 2 OSHA safe slope configurations:
Figure 2 OSHA Safe Slope Configurations for Single Layer
B. CESMM Section E-Earthwork
CESMM measurement rules stated that “the quantity of earthwork shall be computed net using drawing dimension with no allowance for bulking, shrinkage or waste”. The calculation model present in Figure 3 compare with traditional method:
Figure 3 OSHA Calculation Model for Single Layer
- Selection Criteria
It is interesting to see reduction volume from traditional method in order to find compensation in working unit price if CESMM applied as the measurement regulation in project contract.
- Analysis and Comparison of the Alternative
Figure 3 gives reduction volume per length of foundation excavation. For stable rock CESMM result is same with traditional method but decrease rapidly for weak soil with lower slope angle (power function). There is negative correlation between average width factor [B] relevant with soil type and the reduction volume as present in Figure 4:
Figure 4 Correlation Between Soil Type and Volume Ratio
If along the depth [D] there are many layers with weak soil type, then the reduction volume will be greater compare with strong single layer. For example the reduction volume from combination layer of type A and B will be less than single layer type A, part of layer A replace with layer B which has higher volume reduction.
- Selection of the Preferred Alternative
It can be seen from Figure 3 that reduction ratio vary from 57% to 40% correspond with soil type. If data from site investigation shows weaker soil other than type C, then I should proposed in early stage to have bracing method instead common excavation method because is not safe for the worker and cost will be more expensive and not efficient.
- Performance Monitoring and the Post Evaluation of Result
Unit price adjustment should be made if CESMM applied in the project to cover the reduction volume, otherwise Contractor will lose their profit which will impact for project completion. The compensation unit price should be higher for weak soil compare to strong soil layer.
safety.duke.edu. (2009). Guide to OSHA Excavations Standard. Retrieved from http://www.safety.duke.edu/OHS/Documents/ig14.pdf
Oakley. H.R. (1991). CESMM3 Civil Engineering Standard Method of Measurement. London, United Kingdom: Thomas Telford.
Brassard, Michael., Ritter, Diane. (2010), The Memory Jogger 2nd Edition (pp.190-191). New Hampshire, United States: GOAL/QPC.