连云港海相软土固结状态及地质成因

CONSOLIDATION STATE AND GEOLOGICAL ORIGIN ANALYSIS OF LIANYUNGANG MARINE SOFT SOIL

软土的固结状态是分析其沉降变形的一个重要指标。为了研究连云港海相软土的固结状态,进行了多组原位十字板剪切(FVT)试验、标准固结试验和金属基索状光缆的沉降监测。结果表明:由于表层作用,导致浅部和深部软土显示出不同的固结状态,固结状态存在一个临界深度(5~6 m)。原位土抗剪强度与埋深的拟合曲线表明视超固结比(OCR_(1))大于1,但这包含了土体结构强度,不能反映土体在地质历史上曾经受过的最大有效应力,临界深度(5m)以上OCR_(1)平均值为1.74,临界深度以下OCR_1平均值为1.01,整体均为轻微超固结土。基于标准固结试验,采用塑状样试验数据计算临界深度以下软土超固结比(OCR_(2)),OCR_(2)小于1,表明其为欠固结土,在地质历史上所遭受的最大有效应力小于现在土体上覆有效应力。FVT试验得出的OCR_(1)值大于标准固结试验得出的OCR_(1),这与室内试验样的扰动和土体应力状态的改变有关,基于室内压缩试验的数据会低估OCR_(1)。基于金属基索状光缆的软土沉降监测数据在深度上的分布规律与软土OCR_(1)分布规律基本一致,OCR_(1)虽不是真正的超固结比,但这一指标直接与工程建设有关。

The consolidation state of soft soil is an important index to analyze its settlement and deformation.In order to study the consolidation state of Lianyungang marine soft soil,several sets of standard consolidation tests,field vane test(FVT)and settlement monitoring by metal-based cable-like cables were used.Due to the surface layer,the shallow and deep soft soils show different consolidation states,and there is a critical depth(5~6m)in the consolidation state.The fitting curve of in-situ soil shear strength and buried depth shows that the apparent overconsolidation ratio(OCR_(1))is greater than 1,but this includes the structural strength of the soil and cannot reflect the maximum effective stress,which the soil has experienced in the geological history.The average value of OCR_(1)above the depth(5m)is 1.74,and the average value of OCR_(1)below the critical depth is 1.01,both of which are slightly over-consolidated soils.Based on the standard consolidation test using the plastic sample test data,the OCR 2(over-consolidation ratio)of the soft soil calculated is less than 1 below the critical depth,which indicating that it is an under-consolidated soil,and the maximum effective stress suffered in the geological history is less than the current soil effective stress on the body.The OCR_(1)value by the FVT test is greater than the OCR_(1)by the standard consolidation test,which is related to the disturbance of the indoor test sample and the change of the soil stress state.The data by the indoor compression test will underestimate the OCR_(1).Although OCR_(1)is not a true over-consolidation ratio,this indicator is directly related to engineering construction,and it is necessary to make good use of the structural strength of the soil.Finally,the distribution law of soft soil settlement monitoring data by metal cable-like cable is consistent with the distribution law of soft soil OCR_(1).