One worker, under the direction of an engineer dressed in a blue overall, pumps water over a small portion of the clay walls that stand erect upon the platform.

Rising 11-13 meters high, the walls, with holes in the middle at regular intervals, surround a rectangular area, 137 meters long and 17 meters wide.

Archaeological excavations at the site have yielded grains and other relics, which have shown that the site once served as a large army grain silo over 2,000 years ago. The regular holes were made for ventilation.

For five centuries starting probably in the year 114 BC, the grain silo, named Hecang Fortress, stored and supplied food for the soldiers in the army barracks there to safeguard the Silk Road, the traveling caravans and the local residents.

But two millenniums later, the silo has been reduced to broken walls. Fierce winds keep tearing at them. Rains have washed and cracked them, and continue to create and widen more crevices. Meanwhile, the clay, with a high sand and alkali content, loosens when water seeps in.

To prevent the ancient clay walls from further decay, Yang Tao, the engineer, is leading a team to buttress the walls.

Dipping a finger into the bucket from which the pump drew water, a visitor can feel that the water is sticky.

"It is what we call PS solution," said Yang Tao, who has worked with the Dunhuang Academy as a specialist in the protection of earthen ruins for 10 years.

Yang explained that the solution, a mixture of potash silicate, is being applied to reduce the high alkaline content in the clay and make it more resistant to rain and wind erosion.

The clay bricks are being laid in the areas that have caved in, at the base of the wall, to strengthen the foundations.

Although the team is small, Yang said, the job preserving the ancient army grain silo is one of a series of projects endeavoring to save thousands of ancient ruins of a similar nature in Gansu Province.

Great earthen ruins, such as the Hecang Fortress, are scattered across the Gobi desert in Gansu. Numbering more than 9,000, the ruins, most dating back more than 1,000 years, include large sections of the Great Wall, ancient military passes - such as the Jiayu Pass, and numerous tombs built of clay or mud bricks. Above all, tens of thousands of ancient murals painted on clay walls are now being preserved in Mogao, Yulin and Bingling grottoes, all located in Gansu Province.

"We should consider ourselves lucky because ancient earthen and clay constructions elsewhere in the country are long gone," said Liao Beiyuan, a local archaeologist now heading the department for the protection of cultural relics with the provincial bureau of cultural relics. "Only the remnants of the ones in Gansu and Xinjiang Uygur Autonomous Region are still visible."

However, thousands of earthen and clay ruins have posed grave difficulties for the local archaeologists, since few experts in the world are ready to offer advice on an undertaking so large.

But local archaeologists are ready to learn and to experiment. When Li Zuixiong, now deputy president of the Dunhuang Academy, learned of a Japanese experiment using a certain kind of solution to make clay stick, he talked with his Japanese colleagues and went to Japan to study their conservation techniques.

After he graduated as the first Chinese scholar to earn a doctorate in the conservation of relics from Japan in 1991, he returned and started his own experiments.

In nearly 10 years, Li and his colleagues have adopted different scientific methods to study the clay and earthen ruins. They have also carried out research on more common approaches to conservation, such as applying cement to deteriorating walls.

However, the more common methods all have their weaknesses. The cement and clay do not combine well. Clay walls behind cement continue to fall apart.

As a result, Li and his colleagues have come up with a series of PS solutions, according to the different mineral contents in the clay at different sites. The most successful application so far has been done at the Yulin Grottoes in Anxi.

Liao said that PS solutions also have shortcomings. For instance, the earlier solutions act as a plastic that does not let out air and water. And the solutions have not been effective in damp areas.

Others have worried that the clay surface may form a hard crust and peel off in large chunks.

Above all, the experiments cost money. A kilogram of PS solution costs 5,000 to 6,000 yuan (US$609-731).

Repair work at the Yulin Grottoes alone has cost 4 million yuan (US$490,000).

Li Zuixiong and his colleagues are taking all these points into consideration and they've also got support from both local and central governments.

"Whatever the shortcomings, experiments must go on," Liao Beiyuan said.

A frequently raised question is whether the ruins are worth saving.

When the question was put to Liao Beiyuan, he didn't answer right away.

"I felt a little fearful when I was left alone for a while in the middle of one such earthen ruin," Liao recalled of his first visit to a ruin in Wuwei, another important Silk Road town some 1,280 kilometers-drive to the east of Dunhuang. "I was reminded that human beings are so small in comparison with the universe all around us."

After working with the relics protection department for 16 years and visiting many earthen ruins, Liao said he now has a different feeling.

"I believe these ruins, as a group, contain more information about our past than we know of," Liao said. "In fact, we still know very little about these earthen ruins and about our past history. Our current knowledge may not be correct because we don't have advanced enough technology to acquire the knowledge.

"Thus, we try to preserve these ruins today and prolong their life so that future generations will have something to study and learn more with their advanced technology than we could," Liao said.

(China Daily)