A surveying device that works with surveying prisms mounted on the masonry and measures any horizontal or vertical movement in the walls

A year after the MBTA suspended a construction project that caused a crack from the foundation to the roofline of Old South Church, the jackhammers are back in operation, thudding away and sending small tremors through the 136-year-old National Historic Landmark across from Copley Square.

Despite the clamor that echoes through the ornate sanctuary, MBTA and United Church of Christ congregation officials said the hallowed building is structurally sound.

Working with a team of structural engineers, restoration architects, stained-glass consultants, and an organ conservator, the contractor has installed an array of sophisticated subsurface devices to monitor the soil and the foundation to ensure there is no further damage to the church’s distinctive Roxbury puddingstone façade, its signature Gothic campanile, or its 6,500-pipe organ.

“We’re satisfied that they’re being extremely careful and that the foundation is not in jeopardy,’’ said Lois Corman, who is monitoring the construction for Old South Church.

The $45 million construction project, which is expected to take another year, was suspended last December during excavation work by an MBTA contractor hired to make the Copley Square subway station accessible to the handicapped. Framingham-based J.F. White Contracting Co. is installing an elevator shaft and replacing the station’s old brick entrance on Dartmouth Street.

MBTA officials said the work is monitored 24 hours a day by automated instruments in the ground and on the church’s walls that provide “real-time’’ data to reflect any shifts in the building or defects in the foundation.

“The automated instruments allow the project to monitor the building nearly continuously [several times an hour] in real time, and the data are uploaded to a project office site so that key parties can track the response of the building to construction activities,’’ said Lydia Rivera, a spokeswoman for the MBTA.

She said the equipment enables “rapid reaction to correct or mitigate undesirable impacts to the building.’’

The equipment includes a theodolite, a surveying device that works with surveying prisms mounted on the masonry and measures any horizontal or vertical movement in the walls. There also are seismographs to monitor vibrations from the construction and automated meters that track ground movement, groundwater changes, and any opening or closing movement in the large crack on the wall facing Dartmouth Street, which will be repaired after the elevator shaft is fully excavated and backfilled.

Neither MBTA nor church officials know how much it will cost to repair the damage, which they said will be covered by J.F. White’s insurance company. They expect the crack, still visible inside and outside the church, will be repaired by the end of next summer.

Reverend Nancy S. Taylor, the senior minister at the church, said she is comfortable with the new safety measures.

“We have investigated the current condition of the wall, foundation, and timber piles, and the MBTA and its contractor have redesigned the current and future construction activities with the purpose of ensuring no further damage to the church,’’ she said.

The project is complicated because the area around the church is built on fill and all the buildings are supported by wooden pilings, making them vulnerable to damage from excavation and drilling. The contractor also has to deal with the concerns of neighbors, some of whom filed an unsuccessful lawsuit against the MBTA because of aesthetic concerns about the project.

The Old South congregation traces its history back more than three centuries, to 1669, when it was established as Third Church in Boston.

It was later renamed Old South Church and moved from downtown to its current location in the Back Bay in 1875.

The building, an example of Ruskinian Gothic architecture, was designed by Charles Amos Cummings in the 1870s and updated by the Tiffany firm in 1905. It was renovated in the mid-1980s by Shepley Bulfinch Richardson and Abbott.

With Jersey barriers blocking off much of the corner of Dartmouth and Boylston streets, large earth-moving equipment and jackhammers have filled the area with piles of rubble.

While church officials have to schedule musical events and other meetings around the construction, they said they’re happy to see work underway again.

“Old South is as eager to see the newly renovated and accessible Copley T Station as we are eager to ensure that our building is not damaged any further in the process,’’ Taylor said. “We believe that with good will and good care, these two things are not incompatible.’’