TxDot San Antonio District
7 Miles off I-10 between La Cantera and FM 3351
San Antonio, Texas
Geotechnical engineering services were provided for a 7-mile stretch of I-10 between La Cantera and FM 3351 in San Antonio. The project included storm sewers, pavement, retaining walls, sign structures and bridges. The site is located in the Edwards Limestone of Fredericksburg Group. GES was aware that the geology contained caverns and known presence of federally protected endangered species. During the proposal phase GES informed TxDOT and our Client about potential difficulties in drilling. The project was on a fast-track. Accordingly, at contract start-up, GES agreed to a compressed schedule for data collection along the project corridor. However, NTP was significantly delayed because permits from the US Fish and Wildlife (USFW) took longer than the Client had expected. GES prepared boring location plans, traffic control plans and obtained TxDOT’s approval of said plans while the USFW permits were pending. Upon approval, GESI mobilized field crews to expedite data collection; mobilizing up to 5 drill rigs including various Ardco all-terrain, Mobil and CME 75 rigs.
Drilling production was slowed due to the presence of underground caverns and drill fluid losses. To resolve fluid losses, air-rotary drilling was employed. The air-rotary method was effective in dry boreholes where groundwater was not encountered. Where groundwater was encountered, air-rotary method could not be used. These boreholes took considerably more time and material (water, bentonite, etc.) to complete. To meet project milestones/deadlines and to recover time lost during the aforementioned delays, drill crews worked day, night and weekends when permitted. For real-time problem-solving during drilling activities a full-time geotechnical engineer was mobilized to site.
GES assigned extra personnel to speed up the laboratory testing. The report preparation task was divided based on the structure type (i.e. bridges, retaining walls and pavement) and multiple engineers were assigned to work on different portions of the report. GES delivered the report on time and within the budget. GES received an “excellent” feedback from the Client and TxDOT.