Prediction and analysis of foundation pit support deformation for ultra-large dock chambers based on CNN-LSTM-Attention model
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摘要: 某超大型船坞坞室基坑采用锚碇式组合钢板桩围护体系。为研究基坑变形规律,对坞墙承台、组合钢板桩、锚碇墙等围护结构进行沉降、水平位移和受力监测,分析其变化趋势、原因及时空关联性。结果表明,采用无内支撑组合钢板桩的船坞坞室围护设计,受软土特性和降水影响,其围护结构顶部沉降和水平位移、组合钢板桩深层水平位移在开挖过程中变形较大,各监测项目数据变化具有较强的时空关联效应。建立了一种可以提取监测时序数据关键特征的CNN-LSTM-Attention组合神经网络模型,以不同监测项目的监测数据作为模型输入,经过CNN神经网络卷积运算、LSTM神经网络回归预测、Attention注意力权重分配、全连接层等操作输出预测值,并与实测数据对比分析。根据试验结果,引入注意力机制的CNN- LSTM-Attention的组合模型,比LSTM模型和BiLSTM模型预测精度更高,且在相邻监测点的预测中,该模型适用性良好,验证了监测点数据变化趋势具有较强的空间相关性。Abstract: The foundation pit of an ultra-large dock chamber adopts the anchor type composite steel sheet pile retaining system. To study the deformation law of foundation pit, the settlement, horizontal displacement and stress of retaining structures such as dock wall bearing platform, composite steel sheet pile and anchor wall were monitored, and their change trend, causes and temporal and spatial correlation were analyzed. The results show that the top settlement and horizontal displacement of the retaining structure and the deep horizontal displacement of the composite steel sheet pile are large in the excavation process due to the influence of soft soil characteristics and precipitation, and the data change of each monitoring item has a strong spatio-temporal correlation effect. A CNN-LSTM-Attention combined neural network model which can extract the key features of monitoring time series data is established. The monitoring data of different monitoring items are taken as the model input, and the predicted values are output through CNN neural network convolution operation, LSTM neural network regression prediction, Attention weight distribution, full connection layer and other operations, and compared with the measured data. According to the experimental results, the combined model of CNN-LSTM-Attention with attention mechanism has higher prediction accuracy than LSTM model and BiLSTM model. In the prediction of adjacent monitoring points, the model has good applicability, which verifies that the change trend of monitoring points’ data has strong spatial correlation.
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表 1 土层主要物理力学参数
层号 土层名称 重度$ \gamma $/(kN·m−3) 内摩擦角$ \varphi $/(°) 黏聚力c/kPa 渗透系数k/(cm·s−1) ①1-1d 吹(冲)填土 17.6 29.5 4 5.0×10−4 ①1-2a 灰褐色淤泥质粉质黏土夹粉性土 17.9 21 11 8.0×10−5 ①1-2b 灰黄色黏质粉土 18.6 26.5 8 4.0×10−4 ①1-2c 灰褐色淤泥质粉质黏土夹粉性土 17.9 18.5 12 5.0×10−5 ②1 灰黄色粉质黏土 18.4 20.5 19 3.0×10−6 ②2 灰色淤泥质粉质黏土夹黏质粉土 18.1 20.5 13 2.0×10−5 ②3-1 灰色砂质粉土 18.7 27 8 5.0×10−4 ②3-3 灰色黏质粉土夹淤泥质粉质黏土 18.1 23.5 10 7.0×10−4 ④ 灰色淤泥质黏土 16.9 11.0 12 3.0×10−7 ⑤1-1 灰色黏土 17.3 13.0 14 5.0×10−7 ⑤1-2 灰色黏土 17.8 16.0 16 5.0×10−6 ⑤3-1 灰色粉质黏土夹粉性土 18.2 20.5 20 5.0×10−6 ⑤3-2a 灰色粉质黏土夹粉性土 18.4 22.5 21 5.0×10−6 ⑤3-2b 灰色粉质黏土夹粉性土 18.9 30.5 6 5.0×10−6 表 2 监测相关技术要求
监测项目 点位间距 设计报警值 监测频率 承台顶竖向位移 20 m ±50 mm 1次/d 承台顶水平位移 ±250 mm 1次/d 锚碇墙顶竖向位移 20 m ±100 mm 1次/d 锚碇墙顶水平位移 ±250 mm 1次/d 钢板桩深层水平位移 40 m ±250 mm 1次/d 锚拉杆受力 40 m 1200 kN 1次/d 表 3 监测点处施工过程及日期
位置 工况施工时段(年-月-日—年-月-日) 基坑开挖 垫层及底板施工 底板完成及结构施工 W40,W41 2022-11-05—
2023-03-102022-03-11—
2023-04-102023-04-11—
2023-06-10W42,W43 2022-10-09—
2023-02-172023-02-18—
2023-03-152023-03-16—
2023-05-12W45,W46 2022-09-30—
2022-12-162022-12-17—
2023-01-162023-01-17—
2023-03-06W47,W48 2022-08-25—
2022-10-152022-10-16—
2022-11-182022-11-19—
2023-02-05表 4 不同预测模型RMSE值
点号及监测项目 LSTM RMSE BiLSTM RMSE CNN-LSTM-Attention RMSE 训练集 测试集 训练集 测试集 训练集 测试集 W48沉降/mm 2.25 0.98 2.45 2.01 1.54 0.65 W48水平位移/mm 2.86 3.97 2.27 1.73 1.74 0.47 QX25深层水平位移/mm 9.08 2.65 7.45 3.14 6.23 1.11 ML6锚杆拉力/kN 13.44 17.28 12.33 14.72 11.79 13.83 表 5 相邻点预测RMSE值
W47沉降
/mmW47水平
位移/mm深层水平
位移/mmML5锚杆
拉力/kN1.45 2.03 2.66 24.11 -
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