Highway Construction And Sand Hazard Controlling Research In Active Dune Region In The Taklamakan Desert

The Taklamakan Desert is a represent of huge desert with migrating dunes, where the environmental conditions are extremely harsh. Through the center of the desert, the Taklamakan Desert Highway crosses various aeolian dune types from the north edge to the south.Because there is no precedent to build a desert highway all over the world, so we proposed series new techniques by generalizing the experiences, introducing the new technologies and testing the construction methods both in laboratory and field. In particular, considerable progress has been made on the dry compaction of aeolian sand by vibration, the resilience modulus of roadbed, the combination of different roadbeds and road surfaces, stability analysis of the geotextiles-strengthened roadbed, construction technologies of desert highway and the design of sand-controlling systems. The achievements of this research were successfully applied for the first time in the Taklamakan Desert. The results suggest that the construction of this highway was economical and that the simple construction methods produced a reliable highway. The resulting highway is believed to be the world's first long-distance graded highway running through a huge desert with migrating dunes.The achievements provided some necessary supports on constructing the desert highway, however, some problems are still not well solved and need a further research. These problems are restricted in desert regions, but it's very significant to solve these. To solve these problems, not only benefit to recognize the construction characteristics of aeolian sand and the law of sand drift, but also benefit to decrease the cost of constructing and maintaining the desert highway. In desert regions, the latter is especially important because that the poor-developed economy and the light road traffic make this region cannot bear the expensive cost.According to our research, some new progresses list below:<1> Under the rough maintenances of the engineering sand-controlling system, the roadbed type changed usually from low embankment to low cutting. The road cuttings are easily damaged by aeolian sand and very difficult to protect. So it's very necessary to increase the height of the embankments about 45-80cm, with an average about 60cm.<2> There is a long and deep cut section where the highway across a high compound sand ridge. On these conditions, the slope of the roadbed should be the steepest slip face.<3> In most of the Chinese deserts, the strength of aeolian sands is very higher. The design values of resilience modulus of roadbed are above 90MPa and usually more than current standards of sand soil and soil sand.<4> The density changes very little after soaking when the compactness of aeolian sand is above 90%. By increasing the times of sampling, the density measured by soaking and ring sampler is properly to use in highway roadbed design.<5> Under given conditions, sand accumulate amount around windbreaks are obviously related to the activities of blown sand. According to this, the blown sand activities estimated by the sand deposits on different dunes and positions in the central Taklamakan Desert are distinguishing, and the sand transport amount ranged from 3.25 m3 ? m'1 ? a'1 to 17.04m3 ? m'1 ? a"1. At some interdune depressions, the lower longitude ridges may be the sand transport corridors.<6> On the compound longitude ridges, both the sand transport and the types of roadbed impact the sand hazards along the highway. The most serious disaster happens on the mid of stoss slope, and relieved in turn on the crest, upper stoss slope, upper lee slope and interdune depressions;the most light happens at the lower lee slope. The engineering methods to control blown sand can be improved based on our findings.<7> There are many reasons induce the overestimation of sand hazards in sand-controlling design, which include the disagreement of disaster intensity with sand transport rates, different efficiencies of shielding and conducting sands around windbreaks, disequilibrium of sand deposits within the sand-fixed belts, different sand transport abilities along highways and various standards in estimating sand hazards. To avoid these confusions, a clearly standard to estimate sand hazards should be established firstly. Secondly, we should mention that the blown sand activities in diflferent dune positions are various. In addition, the engineering measures have a huge sand capacity more than our estimated usually. Only thus, we could control the sand hazard and minimize the cost.