Numerical simulation for regular drainage in peat soil

21st International Scientific Conference on Advanced in Civil Engineering "Construction - The Formation of Living Environment"

土木建筑工程

Zaborskaya, Olga^1 ; Nikitin, Andrey^1

Northern Federal University Named after M.V. Lomonosov (NArFU), Severnaya Dvina Emb. 17, Arkhangelsk

163002, Russia^1

关键词: Analytical method;    Drainage designs;    Field observation data;    Ground water depths;    Perforated pipes;    Permeability factor;    PLAXIS softwares;    Step approximations;   

Others  :  https://iopscience.iop.org/article/10.1088/1757-899X/365/4/042069/pdf
DOI  :  10.1088/1757-899X/365/4/042069

学科分类：土木及结构工程学

来源: IOP

【 摘 要 】

The development of wetlands requires lowering considerably the water table. This objective used to be achieved by arranging regular drainage. As practice shows, the preset depression of the water table has not been achieved in many cases. It is caused by decrease of the peat water permeability due to its compression under the removal of water hydrostatic uplift and by clogging processes in the peat. The analytical methods used to ignore the above factors for drainage design. This article suggests an algorithm of numerical simulation for regular drainage using PLAXIS 2D software. Its verification has been made in accordance with the field observation data, which had being collected for 1.5 years in Arkhangelsk within 500x600 m site built up with low-rise flat blocks. The thickness of the least decomposed peat layer is from 3.0 to 4.2 m within the site. The peat from the top is loaded by the construction and household debris layer with up to 0.6 m thickness mixed with decomposed organic matter. The peat is under laid by impermeable stiff clay. The stratification and properties of the soils are taken in accordance with the survey results. The regular drainage was constructed in the seventies of the last century out of 300 mm diameter asbestos-cement perforated pipes placed with 140 m spacing with the drain filter made of crushed stone. The pipes were buried with its bottom at the depth from 3.3 to 3.4 m from the daylight surface. The drainage trenches were backfilled with sandy soil. The position of the depression curve was being monitored within the studied site. With this aim, we drove piezometers into the soil at the distance of 6, 18, 30 and 45 m from the drainage pipes. The water level in the piezometers was measured with periodicity of 30-60 days. The results of monitoring showed that the difference of ground water depth values in the piezometers reach 2.3 m with the distance increase from the drain. The variation of the water table within an annual cycle as per an individual piezometer is from 0.21 to 0.37 m. It is shown that the results of drainage design by way of analytical methods give considerable deviations from the actual ground water levels. The numerical simulation for water level depression with the PLAXIS software is performed by step-by-step approximation. The first step considered the decrease of the peat permeability factor due to removal of the water hydrostatic uplift and the second step considered the change of the permeability with time due to clogging. Considering the peat permeability with time allows to get ground water depression curve closer to the data obtained by site monitoring.