Modification of Peck Formula to Predict Ground Surface Settlement of Twin Tunnels in Low Permeability Soil

Xiaowu Tang,Yue Yu,Yuhang Ye,Wei Liu,Penglu Gan,Jiaxin Liang,Wenfang Zhao,Ma Jianjun

doi:10.1155/2021/6698673

Abstract

Accurate prediction of surface settlement induced by tunnel excavation is significant for preventing damage to existing structures under complex geological conditions. The Peck formula is currently considered as an efficient solution for surface settlement prediction. This paper proposes a modified Peck formula considering geological conditions to improve the accuracy of surface settlement prediction of twin tunnels. The asynchronization of the sinking rate and stability of the vault settlement and surface settlement within the river-affected area may attribute to the groundwater drawdown caused by cofferdam construction on the river. A modified Peck formula is put forward with soil permeability and width-controlling parameters involved. There is a small settlement at the center of the twin tunnels, making the settlement trough upward buckling, which is like a “W” shape. This situation can be accurately predicted by the modified formula with a significantly increased adjusted R-square. The modified formula can accurately predict the surface settlement of tunnels excavated in low permeability soil layers with a permeability coefficient between 10−4 cm/s and 10−7 cm/s, especially in the groundwater drawdown environment. The reliability of the modified Peck formula is verified by other cases in Nanjing and Singapore.

Highlights

Due to the rapid development and expansion of coastal cities around the world, underground traffic construction has been widely adopted to alleviate traffic pressure
Peck [1] considered the form of tunnel surface settlement as a normal distribution curve based on a large amount of measured data and first summarized an empirical formula to predict tunnel surface settlement under the assumption that the volume of the settlement trough is equal to the soil loss volume in undrained conditions
Many attentions have been paid to various influencing factors of surface settlement, e.g., space and time [4], the shape and depth of the tunnel [5,6,7,8], soil types and construction operation [9,10,11,12,13], reinforcement [14], and consolidation settlements [15, 16]. e prediction models in these studies greatly improve our understanding of tunnel settlement in different soils, whereas the utility of them cannot be extended to the tunnels in complex geological conditions, primarily owing to the ignorance of groundwater flow

Summary

Introduction

Due to the rapid development and expansion of coastal cities around the world, underground traffic construction has been widely adopted to alleviate traffic pressure. Is research presents a modification of the conventional Peck formula satisfying the “W” shape of twin tunnels’ monitoring data with proper depth and width of the settlement trough. E form of width modification of the Peck formula in this paper is proposed as follows: A. where Sw is the maximum settlement of the tunnel, f(x) is the function of the curve, x is the position of the central axis of the tunnel, A is the shape function parameter controlling the width of the profile, ks is the soil equivalent isotropic permeability, k0 10− 4 cm/s, bw is the width controlling parameter, iw is the width of settlement trough, Hm is the height of the mth layer of soil, and kv is the vertical permeability coefficient. Where TSS is the total sum of the square, RSS is the residual sum of the square, and dfError and dfTotal are the degree of freedom of Error and Total separately

Project Overview

Vault settlement Levels steel rulers