珠江三角洲地区竖向排水体施工扰动初探

竖向排水体施工具有挤土效应，按照平面应力问题，应用圆柱孔扩张理论分析表明，竖向排水体周围土体孔隙水压力显著增大，应力变化明显，形成瓶状塑性区。地面以下一定深度Zo范围内，塑性区半径取决于土体初始应力和不排水强度，并随深度增大；Zo以下，塑性区半径不再变化，其大小与土体初始应力、不排水强度，割线模量、排水体类型、间距、长度、导管类型等有关。施工扰动以塑性区为主，塑性区地面发生隆起，珠江三角洲地区，在饱和软粘土基中施工竖向排水体时，实测表明土体强度显著降低，最终沉降增大。计算表明扰动区半径可取塑性区半径的1.2倍，扰动区半径约为竖向排水体导管半径的9倍。

PRELIMINARY STUDY ON CONSTRUCTION DISTURBANCE OF VERTICAL DRAINAGE BODIES IN THE PEARL RIVER DELTA

The construction of vertical drainage bodies causes compacting effect. The stress change in soft clay and the range of construction disturbance zone due to construction of vertical drainage bodies are analyzed using the column cavity expansion theorem in the light of a plane stress problem. The increment of pore water pressure and the stress change in soft clay are prominent. The plastic zone around a vertical drainage body is like a bottle. Within the depth of Z0, the radius of plastic zone depends on the initial stress and undrained shear strength of the soft clay, and increases with the depth. Below Z0, the radius of plastic zone is invariable, and its value depends on the initial stress, undrained shear strength, secant modulus of soft clay, the types of vertical drainage bodies and the guide tube, length of and distance between vertical drainage bodies, etc. The construction disturbance mainly occurs within the plastic zone with the heave of ground surface as a byproduct. In-situ soil test reveals that in comparison with the untreated soft clay ground, the shear strength of the soft clay in the ground treated with vertical drainage bodies decreases greatly in the Pearl River Delta and the settlement of treated soft clay ground increases. Theoretical analysis shows that the radius of construction disturbance zone in the soft clay ground is about 1.2 times of that of the plastic zone and 9 times of that of the guide tube of vertical drainage bodies.