Site Investigation — Worked Examples

A 1000 mm run yields sound full-diameter pieces of 120, 80, 250 and 100 mm, an unsound full-diameter piece of 150 mm, and fragments with an equivalent recovered length of 100 mm. Calculate the three indices using the lesson's logging convention.

Enlarge

A 150 cm run has sound full-diameter pieces of 12, 8, 25, 5, 14, 9, 32, 11, 4 and 18 cm. Validate recovery, calculate RQD and classify the unrounded value. Would a separate sound piece exactly 10 cm long qualify?

A complete SPT record has already been corrected to $N_{60}=24.0$. An applicable interpretation supplies $C_N=1.25$ for this layer. Find $(N_1)_{60}$ and state what the number establishes.

A 100 cm run yields sound full-diameter lengths of 5, 6, 24, 9 and 40 cm. The driller and logger document that the 5 and 6 cm pieces broke during handling, and the pieces fit as one original piece. Other breaks are natural. Determine RQD with the documented rejoining and the error if that pair is left separate.

Enlarge

A log lists a 120 cm drilled run, 56 cm of qualifying pieces and another 90 cm of nonqualifying recovered material, without overlap. Should the logger publish an RQD of $56/120\times100\%=46.7\%$?

Two valid runs have lengths of 100 and 200 cm and RQD values of 80.0% and 50.0%, respectively. Calculate their combined RQD.

Three complete 150 mm increments require 6, 12 and 18 blows. Measured $ER=75\%$ and the adopted factors are $C_B=1.00$, $C_R=0.85$ and $C_S=1.00$. Calculate field $N$ and $N_{60}$.

A log records 8 blows for 150 mm seating, 12 blows for the next 150 mm, then 50 blows for only 50 mm before termination under the governing procedure. What should be retained, and can ordinary field $N$ or $N_{60}$ be reported from this record?

Enlarge

A complete test has field $N=24$, corrected $N_{60}=27.0$, and supplied $C_B=C_S=1.00$, $C_R=0.90$. What energy ratio is implied by this calculation, and does the result replace energy measurement?

A 300 cm run yields 180 cm recovery, including 150 cm of qualifying sound pieces. An analyst incorrectly divides the qualifying length by recovered length. Find the true RQD, the incorrect value, their percentage-point difference and the relative overestimate.

A preliminary profile suggests saturated soft clay below cobbly overburden. The project needs consolidation information from the clay and confirmation of the deeper material. Select an investigation response without assuming perfect samples or a particular proprietary drilling system.

Two boreholes 20 m apart recover limestone and breccia, respectively. An intervening geophysical anomaly has no direct confirmation. Historical records also suggest nearby old workings. Does this prove an active karst cavity or establish that a proposed public park is safe?

Enlarge