Three people were arrested and a fourth hospitalised with leg injuries during a march by up to 300 protesters to the main gates of the Corrib gas terminal in Bellanaboy, Co Mayo yesterday.
The march was held to commemorate the 12th anniversary of the execution in Nigeria of writer and activist Ken Saro-Wiwa and eight comrades who were opposed to Shell activities.
It also marked the first anniversary of a demonstration when protesters clashed with gardaí.
Yesterday's protest, which began at 7am, was silent at first but gradually became more noisy as activists flung themselves on to the road in front of a truck carrying huge boulders which they believed was destined for the refinery site.
A large force of gardaí tried to keep the roadway clear but the protesters continued to block it. As a result, it took the lorry more than an hour to travel less than a mile.
Shell said later the lorry involved had nothing to do with its construction activities on the terminal site.
One man from Dublin was injured when the truck ran over his foot. He was taken by ambulance to Mayo General Hospital for treatment.
Feelings were running high after the march, with some protesters claiming they had been "manhandled". OisíÓ Dubhláin, who travelled from Cavan, said: "We have a right to walk these roads. People understandably get angry when they are prevented from going to a peaceful protest. To me that's not democracy."
Gardaí, however, defended their handling of the protest and said some of those involved in the demonstration had behaved in a very aggressive manner.
Supt John Gillan said he was "more than proud" of members of the force present as they had acted in a "very professional and controlled and proportionate way".
Willie Corduff, one of the five men jailed in 2005 for their opposition to the onshore gas pipeline, predicted even worse trouble in the future when Shell try to get on to people's property to secure a land corridor to the terminal.
"When they come into our land that is when the right trouble will start," said Mr Corduff, who was accompanied on the protest by his wife, Mary. He claimed Shell wasn't trying to resolve the dispute because it was "going to get the Government to do their dirty work".