Trial Pitting Frequently Asked Questions: Normally undertaken using a JCB backhoe excavator, a concrete hammer is available to break out hardstanding if required. What depths will Trial Pitting Achieve? Depths achieved vary depending on the plant used, typically a JCB backhoe excavator can reach depths of approximately 3.5m to 4.5m below ground level, depending on the space available at surface. The bigger the excavator the deeper the trial pit can progress – a 20 tonne 360° excavator can been used to trial pit to about 6.0m Why choose Trial Pitting Techniques? Trial pitting is a relatively inexpensive method of intrusive investigation and allows good coverage of a site to be achieved over a period of one day. Shallow samples can be retrieved for laboratory contamination and geotechnical analysis. Sample size is not limited. If soakage potential is required, the trial pit is filled with clean water, and measurements made to calculate the change in water volume over time are taken, allowing infiltration rates to be calculated. The Engineer also has the opportunity to see the changes in ground conditions with depth and in some cases lateral changes can be observed. How is Trial Pitting Undertaken? Trial pits are progressed by stripping thin layers of soil from ground level to slowly form a short trench. Each stripped layer is examined in detail and samples representing the strata encountered are recovered for further detailed analysis and laboratory testing. Will there be a mess left? During the digging of a trial pit, arisings are placed on the ground next to the hole. Upon completion the arisings will be placed back into the hole and lightly compacted. There is usually an excess of arisings that can be mounded over the excavation or placed in a skip for removal from site. Will there be an open hole left in the ground? Trial pits will be backfilled upon completion to make safe. Surface depressions at the trial pit location can occur over time. Where reinstatement to “as found” is required we can arrange for a specialist contractor.

Are there access restrictions? Trial pitting is generally undertaken using a JCB backhoe excavator therefore vehicular access of 2.5m is required, the working area required is approximately 7m x 4m

Pros

• Good site coverage per day

• Varied sample size

• Allows soakage testing

• Visual perspective of the “living ground”

• Allows contamination source to be “chased”

• Relatively inexpensive

Cons

• Depth restrictions

• Monitoring pipes cannot be installed

• Disturbed sample recovery/No in-situ sampling

• Mess