Abstract:In practical construction， there are usually some foundation pits with large scale， long construction period and are overwintering. Therefore， the work of proper cold-insulation and protection needs to be done. Based on a deep foundation pit project of a building in Ulaanbaatar， the capital of Mongolia， this paper studies the cold-insulation and protection technology for safety wintering of deep foundation pits. B2 grade polystyrene board is used to insulate and prevent freezing of the soil at the bottom of the pit. Greenhouse was built to keep the leakage area on the side wall of the foundation pit warm. Measures of electric heat tracing and insulation with rock wool are adopted to ensure normal dewatering of the foundation pit. The actual construction situation confirmed the effectiveness of the above technology， which can provide reference for the insulation and protection of safe overwintering of foundation pit projects in the future.

Abstract:To date， the commonly used BIM software lacks foundation pit engineering related families， making it difficult for designers to create complex foundation pit models. Based on Autodesk Revit software， this paper supplements and develops Revit families related to foundation pit engineering， and tries to provide convenience for designers to apply BIM technology in foundation pit engineering. The foreign family of foundation pit engineering is constructed， the design and creation of foreign family models are carried out， and a plan is proposed for model construction and construction process simulation for various stages of foundation pit engineering . Relying on the actual project， the families developed in this paper are used to create the foundation pit support model， and the feasibility of the modeling scheme is verified. Finally， the simulation of the foundation pit construction process is realized via the Fuzor software. The result shows that BIM technology can be better applied to foundation pit engineering by the developed Revit families.

Abstract:The deep and large foundation pit project of an international financial building in Shanghai is adjacent to the operating rail line interval with the shortest distance of only 7.87m on the north side， and the clearance of 2.0 to 3.0m from the pipe ditch of World Expo on the south side. Because of the high sensitivity of the surrounding environment， the deformation control of the foundation pit is quite demanding； meanwhile， the project is located on the bank of the Huangpu River. The shallow layer at the site is a typical silty soft soil layer， while the lower part is a soil layer rich in confined ground water. Moreover， the micro-confined aquifer is connected to the first and second confined aquifers， and the sealing curtain cannot cut off the confined aquifers. All these factors constitute complex geological conditions. Considering the situation， the project adopted various technical measures. The final measurement results showed that the maximum deformation of the tunnel is 6.52mm， and the maximum deformation of the pipe ditch is 15.3mm， which meet the deformation control requirements， ensuring the safe operation of the tunnel and the pipe ditch.

Abstract:Part of the foundation pit of the Zone A2 commercial and residential buildings of Taiyuan Wanda Plaza is composed of coarse sand and gravel stratum， where the deep mixing piles cannot be used effectively for the water cut-off curtain of the foundation pit； therefor， high pressure jet grouting piles were put forward for the water cut-off curtain in coarse sand and gravel stratum. With the jet grout technology， the double casing anchor drill pre-bored the grout hole with the single pipe high pressure jet grout process for grouting to complete the project successfully. Inspection indicated that the jet grouting elements interlocked well with each other with even cement content across the effective pile diameter and free of blocky inclusions； thus， providing good sealing effect.

Abstract:In this paper, the causes of leakage to the foundation pit is illustrated in detail by the example of a construction site in Wenzhou City, where drainage and plugging technology was used to treat leakage to the foundation pit. A diversion pipe was used to drain the leakage outlets to relieve the water pressure in the soil layer of the leakage site and some surrounding areas, and to improve the success rate of leakage stoppage. Then, double liquid grouting was used to cut off part of the water flow path so as to reduce the water flow from the leakage outlets; and to reinforce the foundation pit. The results showed that drainage and plugging provided efficiency, accuracy and effectiveness in the field, with 57 leakage points in the foundation pit effectively treated.

Abstract:In order to ensure that the recharge water in the foundation pit dewatering project meets the water quality requirements of the spring groundwater system in Jinan, an integrated dewatering and recharge apparatus for foundation pit projects has been developed. The apparatus consists of two parts: recharge engine and water collection tank. The main components are water pump, filter, pressurizing tank, electronic control system, water collection tank and recharge well tubing. The working principle and technical characteristics of the recharge apparatus are introduced. Through the successful application in the foundation pit dewatering project of Dayangzhuang Station on Line R1 of Jinan Rail Transit, the integrated dewatering and recharge apparatus for the foundation pit project has achieved good environmental and social benefits.

Abstract:The surrounding ground settlement in the process of the foundation pit construction is directly related to the safety of the surrounding buildings. In this paper, the ground settlement surrounding the foundation pit was monitored and predicted according to the historical monitoring data, the construction conditions and the surrounding stratum parameters of a foundation pit project in Qiantan district of Shanghai. Based on PSO-BP neural network, this paper compares the network model based on the time series with that based on the settlement influence factors. It is found that the prediction error of these 2 models is small and the prediction precision of neural network based on the time series is higher, which means that PSO-BP neural network can be used to analyze and predict the ground settlement surrounding the foundation pit. In order to comprehensively consider the time effect and space effect, the historical monitoring data is added as the input layer of prediction model for optimization on the basis of prediction model of settlement influencing factors. The results show that the optimized PSO-BP neural network model has a smaller relative error range and a higher prediction precision, and it has good application prospect in the prediction of ground settlement surrounding the foundation pit.

Abstract:Currently, there are no mature design and optimization methods of recharge for foundation pit tube well. Through the analysis on different types of deep foundation pit recharge, the design principle and process are presented and the discussion and analysis are made on the well recharge parameters and maximum recharge pressure. Based on the calculation of 285 sets of hydro-geological model of deep foundation pit, different permeability anisotropy parameters, recharge well types, well locations and seepage featrues under the buildings (structures) being protected are comparatively analyzed to provide the comprehensive index of recharge well design. From the angles of economic, technique and construction difficulty, the comprehensive evaluation are made on double effect of recharge to the buildings (structures) protection and pit dewatering to guide the integration design of pumping and recharging.

Abstract:The formation conditions are complex in an intercity railway station of Zhengzhou to Xinzheng, lens of sandy soil and cohesive soil exist interacted. The excavation range is in poor permeable loess formation with silt, silty sand silty clay, so the dewatering well construction quality is very important. The formation conditions and characteristics of enclosure structure should be fully considered in dewatering design to ensure water level lowering below the excavating surface and avoid the sand flow, piping and gushing. The dewatering scheme is designed on the baisis of the analysis on hydrogeology seepage in the field by 3D numerical simulation, and with the effective dewatering construction measures being used, good dewatering effect has been proved by practice.

Abstract:For the design and application of tube well recharge in deep foundation pit engineering, the analysis is made on the particularity of recharge well design for deep foundation pit engineering based on environmental control, the comparison is carried out on dewatering recharge seepage of different recharge filters for hanging curtain and the discussion is made on the key factors affecting plane layout of recharge wells and the design of tube well filter. Aiming at the recharge particularity of deep foundation pit engineering, design principles of “two points flow state” control and determination methods of the lift pump pressure control are put forward, the paper also present 3 principles that the injection water quality should meet.