Subsurface data, SR 634 over Antler Creek, Sta. 40+00 to 70+00

CPTu reductions, SPT borings with rock core, and 111 rock probe and core holes were transferred from PDF into one compilation: su versus depth for each CPT, a combined depth plot at three locations, and top of rock along the alignment. Three items need the geotechnical engineer’s call before the data is used for the Antler Creek bridge foundations.

Sources: GDR and 2019 preliminary report, 6 filesSta. 40+00 to 70+00, up to 50 ft off centerlineNAD83(2011) Indiana East, US survey ft; NAVD 88Prepared Nov 5, 2026

Summary

CPT · CPT-07

CPT-07 was reduced with a different Nkt and reads 40% high

The 2019 preliminary report reduced CPT-07 with Nkt = 10 over the full depth. The other nine soundings use the project Nkt of 14, calibrated to field vane tests. Re-reduced with Nkt = 14, CPT-07 falls within −8% to +3% of CPT-06 and CPT-08 instead of 29% to 44% above.

Action: use the re-reduced values at End Bent 1 or have the geotechnical engineer confirm Nkt.

Source: AntlerCreek_Prelim_Geotech_2019.pdf, pp. 12–13

Cores and probes · weathered rock

5 to 12.5 ft of weathered rock below Pier 2, Pier 3 and End Bent 4

All nine holes at Pier 2 through End Bent 4 (Sta. 54+43 to 56+51) show a continuous zone directly below top of rock with probe drill times under 35 sec/ft or core RQD under 50%. At End Bent 1 the zone is 1.5 ft or less. Elsewhere only P-172 at Sta. 61+11 shows more than 3 ft.

Input for the geotechnical engineer’s choice of foundation tip elevations at Pier 2 through End Bent 4.

The 35 sec/ft and 50% RQD thresholds were chosen for this review and need the geotechnical engineer’s confirmation.

Sources: SR634_Rock_Probe_Logs.pdf, pp. 102–113; SR634_Boring_Logs_B-1_to_B-5.pdf, pp. 7–18

Probes · top of rock

Four probes logged as top of rock are likely boulders

P-183, P-188, P-190 and P-194 (Sta. 64+38 to 66+81) were logged as top of rock after 1.3 to 2.6 ft of hard drilling, short of the 10 ft confirmation in the investigation plan. They sit 7.7 to 13.0 ft above the rock surface interpolated from confirmed holes within 130 ft, in a stretch of thick glacial till.

Action: re-probe or core to the 10 ft criterion before these rock elevations are used.

The 6 ft threshold for a possible boulder was chosen for this review and needs the geotechnical engineer’s confirmation.

Source: SR634_Rock_Probe_Logs.pdf, pp. 168–191

Subsurface data

Three views of the same data. Pick CPT soundings and the reduction in the first tab, compare methods at one location in the second, and filter the probe and core holes in plan and profile in the third. Every value shows its file and page.

Reduction
Show soundings
    Active sounding Other selected Median of other selected

    Click a line to make that sounding active. Click in the plot to show a single value with its source.

    Sources and method

    Sources

    • SR634_AntlerCreek_GDR_AppC_CPT.pdfCPTu logs and su reduction, CPT-01 to CPT-06 and CPT-08 to CPT-10 (ASTM D5778)76 pages
    • AntlerCreek_Prelim_Geotech_2019.pdfEarlier CPTu CPT-07 and its reduction, pp. 11–1338 pages
    • SR634_Rock_Probe_Logs.pdf106 air-track probe holes with drill time per foot, scanned field logs215 pages
    • SR634_Boring_Logs_B-1_to_B-5.pdfSPT borings (ASTM D1586) with NQ rock core, recovery and RQD per run (ASTM D6032)22 pages
    • SR634_Subsurface_Investigation_Plan.pdfMethods and rock confirmation: 10 ft into rock by probe or core9 pages
    • SR634_Alignment.xmlAlignment in LandXML with stationing and bent locations1 alignment

    Method

    1. CPT. The reduction tables in Appendix C and the 2019 report were read row by row: depth, qt, u2, σvo, Nkt and su, with a page reference for each value. su was recomputed as (qt − σvo)/Nkt and checked against the reported value.
    2. Cone factor. Nkt was compared across soundings. CPT-07 was re-reduced with the project Nkt of 14 stated in the GDR. The reduction follows the general CPT approach in FHWA GEC 5, Geotechnical Site Characterization.
    3. Combined plot. SPT N-values, probe drill times and core RQD at three locations were digitized and plotted with the nearest CPT on a common NAVD 88 elevation scale. Background strata are interpreted at the centerline.
    4. Holes. For all 111 holes, ground elevation, depth to rock, length drilled or cored in rock, and drill time or RQD were read. Weathered rock is a continuous zone directly below top of rock with drill time under 35 sec/ft in probes or RQD under 50% in cores.
    5. Rock check. Each hole with less than 10 ft in rock was compared with the rock surface interpolated, inverse distance weighted, from confirmed holes and outcrops within 130 ft. More than 6 ft above is flagged as a possible boulder.
    6. Station and offset were computed from the hole coordinates against the LandXML alignment.

    Assumptions and limitations

    • This compilation is data for the geotechnical engineer’s evaluation. It is not a foundation design under AASHTO LRFD, and the rock elevations are not final.
    • The 35 sec/ft, 50% RQD and 6 ft thresholds were chosen for this review and should be confirmed by the geotechnical engineer.
    • The re-reduced su at CPT-07 assumes the project Nkt applies at that location.
    • Values read from scanned logs are accurate to about ±2 sec/ft for drill time and ±0.2 ft for elevations.
    • Hole coordinates as reported in the GDR, NAD83(2011) Indiana State Plane East (FIPS 1301), US survey feet. INDOT design survey and alignment data are in the county InGCS zone, so the alignment was transformed to State Plane before station and offset were computed. Elevations in NAVD 88.