A new method for the early detection and evaluation of post-construction settlement is presented by introducing the method of delayed loading test of pile-soil composite subgrade and using the method of probability statistical analysis. The residual settlement Sr and settlement rate Vt of the evaluation parameters were obtained by the delayed loading test. The evaluation index is obtained from the measured data of composite subgrade after construction by the method of probability statistical analysis. The results show that delay the load test under the condition of double bearing capacity design value, delay 48 hours can make more than 90% of the composite subgrade complete cushion of pile-soil stress ratio adjustment, can achieve the stability of the pile soil stress ratio under actual load. The maximum residual settlement of the delayed loading test follows logarithmic normal distribution when it is less than 7.0mm or greater than 12.0mm. It follows the inverse - distribution when it is greater than 7.0mm and less than 12.0mm. When the required value of post-construction settlement after 15 years is 100mm, 200mm and 300mm, the corresponding maximum residual settlement Srmax of the delayed load holding test is 4.5mm, 13.3mm and 35.41mm respectively, The corresponding Vt=48 is 0.021mm/h, 0.046mm/h and 0.055mm/h, respectively. The probability of satisfaction was 47.61%, 87.49% and 96.93%, respectively.The field example shows that the proposed evaluation index is in good agreement with the actual situation. The evaluation method is beneficial to the early evaluation of construction quality and the timely formulation of remedial measures.
