Hands-on precision paves way for engineering feats
Long before foundations are poured, surveyors trek into unmapped wilderness to ensure millimeter-perfect megaprojects
His teams, typically made up of three people, carry a gravimeter — a precision instrument with a spring-based sensor that detects minute variations in gravitational pull — along with satellite receivers, satellite phones and enough food for a full day. The gravimeter weighs about 10 kg in its protective case and demands careful handling at all times.
"It is a very delicate instrument. When we drive, we pad it with foam cushions and slow down for every bump," Zhao said. He added that in places accessible only on foot, they take turns carrying the instrument and need frequent rest.
A single measurement point can require a 10-kilometer round-trip hike through roadless terrain.
Although the automated observation takes less than 30 minutes, reaching the point and returning can consume an entire day. Zhao said that the team must return to base before nightfall because if the gravimeter's battery runs flat, all the data collected would be lost.
Before Zhao's teams measured gravity in the mountains, another kind of surveying and mapping had already unfolded along the same route.
Chen Chuan, a surveyor with the ministry's Third Geodetic Survey Brigade, spent years working on the Lhasa-Nyingchi section, which crosses three prefecture-level areas — Lhasa, Lhokha and Nyingchi. The railway corridor runs through farmland, pasture and village settlements, with sharply undulating terrain along the route. The work required not only technical precision but also close coordination with local communities.
Chen's team had to survey the entire route and mark boundaries section by section while assisting construction units with land-use approval procedures. Given the project's national significance and tight timeline, land-use permits for key tunnels and bridges were approved early to allow construction to begin, with full-line approvals completed progressively in phases. The work began around 2015 and continued through 2021.
He recalled times when boundaries were contested or compensation areas were in dispute, requiring village committees to mediate and surveyors sometimes to remeasure plots. During fieldwork, Chen picked up basic Tibetan, enough to ask for directions or find a meal in remote villages. Locals were mostly welcoming — sometimes they treated the surveyors to tsampa and other traditional foods.
