Abstract
The interaction between a waterproof curtain and withdrawal wells (or simply, the wall-well effect) is a key factor in controlling the environmental effects that occur during the dewatering of foundation pits. A series of laboratory investigations was conducted to study the changes in groundwater level during dewatering. The influence of the buried depth of the waterproof curtain placed in a dewatering confined aquifer (D), and the filter length of the pumping well (L), is investigated. Based on the laboratory test results, numerical simulations are used to analyse the ground settlement. The relationship between the approximate hydraulic gradients on both sides of the wall (Δi), or the ground settlement outside the excavation (S), using ratio RD (D divided by the thickness of the confined aquifer) or ratio RL (L divided by the thickness of the confined aquifer), can be simulated using a Boltzmann curve. The value of Δi increases while S decreases with an increase in RD, whereas Δi decreases while S increases with an increase in RL. The value of the contraflexure point of the Boltzmann curve is regarded as the effective value of RD or RL. Based on a comprehensive consideration, RD is suggested to be equal to or larger than the effective value, and RL is suggested to be equal to or lesser than the effective value.
Résumé
L’interaction entre un rideau étanche et les puits de pompage (ou simplement, l’effet de paroi) est un facteur essentiel dans la maitrise des effets sur l’environnement qui se produisent lors du dénoyage des excavations de fondation. Une série d’investigations de laboratoire a été conduite pour étudier les changements du niveau d’eau souterraine pendant le dénoyage. L’influence de la profondeur d’ancrage du rideau imperméable placé dans un aquifère captif en cours de dénoyage (D), et la longueur de crépines du puits de pompage (L), est étudiée. Basées sur les résultats d’essai en laboratoire, des simulations numériques sont employées pour analyser le tassement du sol. La relation entre les gradients hydrauliques approximatifs des deux côtés du mur (Δi), ou le tassement du sol en dehors de l’excavation (S), peut être simulée en utilisant une courbe de Boltzmann en utilisant le rapport RD (D divisé par l’épaisseur de l’aquifère captif) ou du rapport RL (L divisé par l’épaisseur de l’aquifère captif). Lorsque la valeur de Δ i augmente, S diminue avec une augmentation de RD, alors que lorsque Δ i diminue S augmente avec une augmentation de RL. La valeur du point d’inflexion de la courbe de Boltzmann est considérée comme la valeur efficace de RD ou de RL. Pour une considération complète, il est suggéré que RD pourra être égal ou plus grand que la valeur efficace, et RL égal ou moins grand que la valeur efficace.
Resumen
La interacción entre una pantalla impermeable y los pozos de extracción (o simplemente el efecto de los pozos) es un factor clave para controlar los efectos ambientales que se producen durante el drenaje de las excavaciones de una cimentación. Se llevó a cabo una serie de investigaciones de laboratorio para estudiar los cambios en el nivel del agua subterránea durante el drenaje. Se investiga la influencia de la profundidad de la pantalla impermeable colocada en un acuífero confinado con drenaje (D), y la longitud del filtro del pozo de bombeo (L). Basándose en los resultados de las pruebas de laboratorio, se utilizan simulaciones numéricas para analizar el asentamiento del terreno. La relación entre los gradientes hidráulicos aproximados a ambos lados de la pantalla (Δi), o el asentamiento del terreno fuera de la excavación (S), usando la relación RD (D dividido por el espesor del acuífero confinado) o la relación RL (L dividido por el espesor del acuífero confinado), puede ser simulada usando una curva de Boltzmann. El valor de Δi aumenta mientras que S disminuye con un aumento de RD, mientras que Δi disminuye mientras que S aumenta con un aumento de RD. El valor del punto de contraflexura de la curva de Boltzmann se considera el valor efectivo de RD or RL. Basándose en una consideración exhaustiva, se sugiere que la RD sea igual o mayor que el valor efectivo, y que la RL sea igual o menor que el valor efectivo.
摘要
止水帷幕与降水井的联合作用(以下简称墙井作用)是基坑降水中控制环境效应的关键因素。本研究为墙井作用对地下水渗流阻挡效应的基坑降水室内试验,试验中考虑了止水帷幕插入降水含水层中深度(D)及降水井滤管长度(L)对地下水位的影响。试验过程中降水引起的地面沉降则通过有限元方法进行模拟分析。研究结果表明,止水帷幕两侧的水力梯度(Δi)、坑外沉降(S)与止水帷幕插入深度比RD(D与降水含水层厚度之比)、滤管长度比RL(L与降水含水层厚度之比)之间的关系均可用Boltzmann曲线进行拟合。随着RD的增加,Δi增加而S减小;随着RL的增加,Δi减小而S增加。上述Boltzmann曲线的反弯点可视为RD和RL的优化值,为了控制降水引起的环境效应,RD建议大于等于该优化值,RL建议小于等于该优化值。
Resumo
A interação entre uma cortina à prova d’água e poços de bombeamento (ou simplesmente, o efeito de parede) é um fator chave no controle dos efeitos ambientais que ocorrem durante a drenagem de pontos de fundação. Uma série de investigações laboratoriais foi conduzida para estudar as mudanças no nível de água subterrânea durante a drenagem. A influência da profundidade enterrada da cortina impermeável colocada em um aquífero confinado drenante (D), e o comprimento do filtro do poço de bombeamento (L), é investigada. Com base nos resultados dos testes laboratoriais, são utilizadas simulações numéricas para analisar o assentamento do solo. A relação entre os gradientes hidráulicos aproximados em ambos os lados da parede (Δi), ou o assentamento do solo fora da escavação (S), usando a razão RD (D dividido pela espessura do aquífero confinado) ou a relação RL (L dividido pela espessura do aquífero confinado), pode ser simulado usando uma curva de Boltzmann. O valor de Δi aumenta enquanto S diminui com um aumento em RD, enquanto Δi diminui enquanto S aumenta com um aumento em RL. O valor do ponto de contraflexão da curva de Boltzmann é considerado como o valor efetivo de RD ou RL. Com base em uma consideração abrangente, o RD é sugerido como igual ou maior que o valor efetivo, e o RL é sugerido como igual ou menor que o valor efetivo.
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Funding
The research work described herein was supported by the National Nature Science Foundation of China (NSFC) (grant No. 41877213) and Key Laboratory of Land Subsidence Monitoring and Prevention, Ministry of Land and Resources in China (No. KLLSMP201502). This financial support is gratefully acknowledged.
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Xu, YS., Yan, XX., Shen, SL. et al. Experimental investigation on the blocking of groundwater seepage from a waterproof curtain during pumped dewatering in an excavation. Hydrogeol J 27, 2659–2672 (2019). https://doi.org/10.1007/s10040-019-01992-3
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DOI: https://doi.org/10.1007/s10040-019-01992-3