乔木的斜向支撑效能及其坡面稳定意义

以滇中地区的松林为例，初步定量探讨了乔木对顺坡有的浅层土壤的斜向支撑作用。研究，树根可能提供的锚固力可达０．６９ｋＮ；在有效的锚固作用下，单株树干的支撑力（抗滑力）最高为０．４２ｋＮ，平均为０．１７ｋＮ；受斜向支撑作用的影响，本来不稳定的浅层松散物质的稳定性系数Ｆ值，由０．５４提高到１．１０，使坡面成为稳定斜坡。如果在特定条件下，树根的锚固力全部转化为支撑力，坡面的Ｆ值可以达到２．８２。

LATERAL SUPPORTING OF TREES AND ITS SLOPE-STABLILZING SIGNIFICANCE

Lateral supporting of trees refers to the mechanic effect of trees on supporting and stabilizing shallow soil on problem slopes,through anchoring trunks which have certain strength into deeper and more stable soil layer by roots.It stops sliding soil and forces it piling up on the up_slope side of the trunks,hence curtailing soil moverment and stabilizing slopes.Ths presupposition of lateral supporting of trees is a firm anchorage into deeper soil layer by its root system.Based on the mechanical processes,lateral supporting could be divided into two sub_effects:buttressing and arching.Buttressing is a lateral restraint against shallow slope movement,provided by firmly anchored,rigid tree trunks.When taproot and sinker roots of many tree species penetrate into the deeper soil layers,they not only anchor them against down_hill movement of the upper protions of the soil.Where trees are sufficiently close together,the soil between the non_buttressed parts of the slope may gain strength by `arching'.By this ,it is meant that the shallow soil labyer may yield and arch between trees when soil attempts to move through and around a row of trees anchored in an unyielding layer.The magnitude of the lateral supporting is detemined by the diameters and strength of tree trunks and roots.the inclination of the yielding portion of soil profile,the spacing and shear strength properties of soil. The Yunnan pine trees closely spaced in the research areas are believed to perform buttressing and arching functions.It can often be observed that some trees restrain the downwards moving soil on steep slopes,leaving a difference in soil surface height between up_slope and down_slope sides immediately near the trunks.This paper takes a pine forest in central Yunnan as an example to conduct a preliminary and quantitative exploration into the mechanical effect mentioned.As shown by the results,the roots can provide an anchoring force of 0.69 kN.The lateral supporting force of a single tree may reach to 0.42 kN at its highest level and 0.17 kN at its average value.When the trees' space is within 1.4m,the arching force may reach to 0.38 kN.With inference by the lateral supporting effect,the safe factor (F ) of the shallow and engineered soil piled on the slope studied has been raised from 0.54 to 1.09,and the shallow waste soil has been stabilized to a certain extent.If under some special circumstances,the highest anchoring force is fully mobilized to supporting the sliding soil,the safe factor may reach up to 2.82.This study is the first of this kind on the lateral supporting in China. It indicates the results of the lateral supporting of the Yunnan pine,and shows a preliminary potential of the this effect.