The pile-soil shear displacement has a significant influence on the development of negative skin friction of piles. Based on current research

a calculation method of plie-soil shear displacement was established by the monitoring results of the pile strain and the soil settlement in the field test. This method was used to analyze the monitoring data of pile and soil in the shallow middle layer

and then the shear displacement of pile and soil was determined to be 4?5 mm under the condition of free pile top in the test. However

the negative skin friction was unavailable to reach its extreme value when the shear displacement of deep pile and soil did not reach the above value. In addition

according to the development characteristics of negative skin friction

its calculation in the specifications was improved by considering both the vertical effective stress of soil around piles and the pile-soil shear displacement. The negative skin friction calculated by this improved method has a good correspondence with the test results. The obtained dragload can achieve a safe

economical effect

which can offer references for engineering design.