不同砾石覆盖度床面蚀积过程的野外风洞实验研究

Field Wind Tunnel Simulation of the Process of Aeolian Erosion and Deposition of Gravel Beds with Different Coverage

野外风洞实验表明,砾石床面具有捕沙和过沙的双重功能,砾石床面的输、阻性质是不同覆盖度与风动力耦合的结果。当砾石盖度小于20%时,床面基本以风蚀作用为主;当砾石覆盖度在30%～50%时,低风速条件下(<10 m/s),床面以强烈风积作用为主,高风速条件下(>12 m/s),床面以强烈风蚀为主,其间[(10～12)m/s]床面趋于蚀积平衡状态;当砾石覆盖度大于60%时,随着风速的增大,床面蚀积量变化不大。研究结果可应用于莫高窟顶沙砾质戈壁的风沙防治,为风沙工程增添新的思路和新技术。

Results of field wind tunnel simulation reveal that gravel beds exist three types of states： aeolian erosion, balance of aeolian erosion and deposition, aeolian deposition. Under certain wind velocity, there is a type of gravel bed reaching the balance. At this time, sand accumulation is saturated. Processes of aeolian erosion and deposition can be fitted by a polynomial function, which can be usedto predict the changing process of sand accumulation of gravel beds with different coverage. Gravel beds have dual function of sand trapping and transporting. Properties of erosion a^d deposition of gravel beds are the results of the coupling of gravel cover- age and the impetus of wind. Gravel beds are mainly eroding when gravel coverage is below 20%; gravel beds are mainly intensively depositing under low wind velocities （〈 10 m/s）, while under high wind speeds （〉 12 m/s） gravel beds change into eroding intensively. Aeolian erosion and deposition balance approximately be- tween wind velocities with 10-12 m/s. When gravel coverage is larger than 60%, with increasing wind veloci- ty, aeolian erosion and deposition amount of gravel beds changes little. The ratio of gravel space to height （SJ H） and the airflow property are main factors influencing on erosion/deposition state of gravel beds. When the value of SJHranges from 5 to 3, the airflow of gravel beds is isolated roughness flow, and gravel beds are erod- ing or intensively eroding. When the value of Sill ranges from 3 to 1, the airflow of gravel beds is wake coher- ence flow, and gravel beds are intensively depositing or intensively eroding. When the value of SJH is smaller than 1, the airflow of gravel beds is boating flow. Because of the wind-blocking effect the gravel beds are de- positing, balance between depositing and eroding or eroding. These results can be applied to the wind-blown sand control projects at the top of Mogao Grottoes. The artificial gravel surface with a coverage of 30% is ide- al both in sand trapping and depositing, thereby decreasing sand damages on the murals at utmost, which offers some new thought and techniques to the wind-blown sand control project.