Research On The Risk Stone Under Wind Loding With Wind Tunnel Test In The Minjiang River Valley

The valley in Upper reaches of Minjiang River, which is located in minshan-longmenmountain on the west side of south-to-north tectonic belt, has a strong tectonic activity aswell as a complicated terrain. Therefore when air flow over the study area, the deep valleywill significantly change the wind-speed vertical distribution of wind flow in stratum andturbulent structures and thus forming a unique ravine wind and over-mountain wind. After"5.12" earthquake, shattered mountain in study area become extremely loose. A largenumber of debris in the state of limit equilibrium remains in the surface of a slope. it willbe unstability easily on the condition of a strong wind，forming a “wind-blowing-stone”geological disasters. On the basis of scene investigation in the valley of Minjiang River,integrating valley model and rolling stones model with wind tunnel test, cooperating withadvanced particle imaging technology at the same time，we study the wind speeddistribution of the Minjiang River Valley, the flow structure in the asymmetric valley,rolling stones surface forces under wind loads and start-up mode. Research has made majorachievements are as follow:(1) Minjiang River Valley is mainly affected by the southwest monsoon from theIndian Ocean circulation warm and wet. Because of the deep valley terrain thermal factors,the prevalence of the monsoon in the following form large valley winds and localcirculation. As airflow being held hostage by the deep valley terrain orientation, the winddirection is roughly consistent with the strike of the valley.(2) Maximum wind speed appeared at grade change point of the slope. Differentproportions of narrow valley and wide valley affects the location of level ofgrade change point. So it turns into key areas of concern in slope geological disasters.When wind direction outside is in a small angle intersection with the valley, windspeed will be strengthened in the valley; otherwise being weakened. Valley asymmetryaffects symmetrically distribution of wind speed on both sides of each elevation valley.When the valley is asymmetrical, the two sides occurred different wind speed, steepshore wind is slightly larger than the slow shore (3) Vertical distribution of wind flow of deep valley is as follows:①wind speed is notlogarithmic or exponential growth from bottom to up. Maximum speed appears in themountainside location.②“narrow pipe effect” have differences from each elevation. Theunderlying has the most significant narrow pipe effect, followed by grade change point ofthe slope, the upper is weaker.③underlying fundamental airflow goes along the rivervalley straight forward being held hostage by the deep valley. With elevation increasing,terrain is weaken in hostage role.④When Airflow direction turn out to be a big Angleintersection towards the valley, Valley model on the leeward side will show thephenomenon of air separation and reattachment and return vortex. There will be asignificant difference between both sides of the wind speed.(4) Collapse rock failure model can be divided into sliding type, toppling type androlling type. Square risk stone is slippage instability. Elongated risk stone is topplinginstability. Due to the different positions of the relationship between risk stones and theirmother rock, it can be divided into forward and sideward toppling instability s. Ellipsoidrisk rock is rolling instability.(5) Based on results of field investigations and test, We point out the key preventionand control department and principles in the Minjiang River Valley for“wind-blowing-stone” geological disasters. Control measures are studied at the same time.We can flexibly take some useful measures to prevent and control it according totopography and vegetation coverage.