How many chinese laborers were brought to the us to dig through the sierra nevada mountains?

Between 10,000 and 20,000 Chinese workers were brought to, through the rock, trace the Summit Tunnel, a key stretch of the first transcontinental train. They were hired because they were the only ones to accept the low payments, were hard workers and  only drank tea, something that Californians did not do, since they got drunk and missed work almost every day.