Insitu-ch7.ppt
Chapter 7 In-Situ Tests 第七章 原位测试,绪 论,Definition： In-situ test is to obtain the engineering mechanical properties of subsoil under undisturbed (in-situ) conditions.,Advantages： 1. Can obtain the engineering mechanical properties of subsoil under undisturbed (in-situ) conditions . 2. Can avoid the negative effects of sampling disturbance. 3. Can minimum the negative effects of boundary conditions. 4. Saving time for geological investigation.,Disadvantages： 1. Special limitations for the application of different in-situ techniques. 2. All the empirical relations between measuring parameters and mechanical properties of subsoil are based on statistical results. 3. Influencing factors are complicate.,Techniques 7.1 Loading Test (静载荷试验) 7.2 Cone Penetration Test (静力触探) 7.3 Standard Penetration Test(标准贯入) 7.4 Shear Vane Test (十字板剪切),7.1 Loading Test,Plate loading test provides valuable information by which the bearing capacity and settlement characteristics of a foundation or pile can be assessed.,Such test is carried out in a trial pit, usually at excavation base level. Plates can be round or square. The size of the plate varies from 0.5 m2 to the size you want. The plate should be properly bedded and the test carried out on undisturbed materials so that reliable results may be obtained.,Loading Test,The load is applied by a jack, in increments of one tenth of the proposed bearing pressure.,a jack,Technical Requirements 1.承压板：Plate should with high rigidity 2.试坑宽度：Width of the testing pit(3d) 3.加荷方法：loading way(快速法与慢速法) 4.稳定标准：Standards(0.1mm/h) 5.荷载分级：loading increments(1/10-1/8) 6.破坏标准：Failure limits(土体侧向挤出或裂纹;沉降等速增加within 24h;P增加很小,但s急剧增加,P-s出现陡降),Three phases： I： Linear II：Non-linear III：Failure,Purposes： To determine critical pressure(临塑荷载)，ultimate load(极限荷载) To Estimate the modulus of deformation (变形模量E0) To determine un-drained shear strength Coefficient of sub-grade reaction (基床反力系数) Results： Ps curve，slogt curve.,Testing results,Determination of bearing capacity,Pu,Determination of bearing capacity,Disadvantages 1. Limited plate size controls the influencing depth. Loading process does not last for enough time. 2. Stiff shell of subsoil pays a negative effects on the tests.,Loading Test,Bulb of pressure beneath a foundation as compared with one beneath a plate load test,Penetrometer,7.2 CPT Test,Cone head,Cone head,Cone sleeve,Cone rod,The ratio of sleeve resistance to that of cone resistance is higher in cohesive than in cohesion-less soils. The ratio of penetration resistance: Ps=P/A P: net penetration resistance; A cross-sectional area of cone.,Cone penetrometer traces,Suitable conditions： 1. Soft soil: Clay, silts and sands 2. Penetration capability can cover soil properties, depth 3. Anchoring resistance not less than net penetration pressure,Applications 1. To Classify soil strata 2. To estimate physical and mechanical properties of subsoil 3. To evaluate bearing capacity of subsoil 4. To choose bearing stratum for pile foundation, to estimate ultimate bearing capacity of signal pile and to evaluate the possibility of pile driving 5. To evaluate possibility of soil liquefaction under earthquake,7.3 Standard Penetration Test SPT test (标准贯入),标准贯入试验,A kind of dynamical penetration test, this empirical test consist of driving a split-spoon sampler, with an outside diameter of 50mm, into the soil at the base of a borehole. Driving is accomplished by a trip hammer, weighing 63.5kg, falling freely through a distance of 750mm onto the drive head, which is fitted at the top of the rods.,标准贯入试验,During the test, the split-spoon is driving 150mm into the soil at the bottom of the borehole. Then a further 300mm is driven and the number of blows required to drive this distance is recorded. The blow count (击数)is referred to as the N (N63.5) value from which the relative density of the soil can be assessed.,标准贯入试验,A difference to CPT is the penetrometer that it is a pipe instead of cone, which can be used for sampling during penetration. It is designed to determine the relative density of cohesion-less soils.,Split-spoon sampler,Trip hammer,Advantages For obtaining dynamical properties Can take samples for diagnosis and lab tests Applications For evaluating : 1. Density and relative density of sands 2. State of clay,3. Shear properties of sands 4. Un-drained shearing strength of clay 5. Mudulous of deformation and compressive for soils 6. Bearing capacity of foundation 7. Bearing capacity of single pile 8. Liquefaction of sands,Disturbance to sample Unreliable lab testing results in-situ undrained shear strength. Shear Vane Test,7.4 Shear Vane Test,Shear Vane Test,十字板剪切试验,优点： A more efficient and reliable in-situ testing technique Scope： Homogeneous saturated soft clay Applications ： 1. Un-drained shear strength 2. Estimate degree of sensitivity (灵敏度) of soft clay,Chapter 8 Site investigation 第八章 工程地质勘察,Contents,General objectives 勘察的主要目的 Basic requirements 勘察的基本要求 Working steps 勘察阶段的划分 Investigation works 主要的勘察工作内容 Site investigation reports and figures 勘察报告书和图件,General objectives,To assess the suitability of a site for the proposed structure. Should attempt to foresee and provide against difficulties that may arise during construction due to ground and/or other local conditions. Investigation should not cease once construction begins.,Basic requirements,1. To find out the geological conditions for proposed buildings, according to different investigation steps. 2. To evaluate geological conditions properly and use it as basic information for design and construction.,Main tasks,To chose construction site. To propose suitable foundation form, determine depth of foundation, determine bearing capacity of subsoil, predict potential settlement and stability for proposed buildings etc. To find out the geological conditions at the construction site and nearby areas, and evaluate its influences to the proposed buildings as well as their attachments,Working steps 勘察阶段的划分,In China: Suitable construction site choosing Preliminary reconnaissance Site exploration program construction investigation,Basic techniques,Engineering geological survey Engineering geological exploration and sampling (pit, trench explorations ) Field testing (in-situ tests) Lab tests (soil tests and rock tests) Testing results analysis and reports,Site investigation reports and figures,Site investigation literature reports : It should make clear geological conditions, explore geological problems and reach conclusions.,Contents of investigation reports,（一）literature reports 1. General information：information about the proposed project, objective and requirements of investigation, problems to be solved. 2. Exploration techniques and works: exploration techniques, instruments and devices have been used, investigation works.,Contents of investigation reports,（一）literature reports 3. Site engineering geological conditions: site topographic characters, subsoil layers and their distributions, physical and mechanical properties of subsoil, zoning of engineering geological conditions, hydrological conditions, site stability evaluations and the analysis and evaluation of subsoil (choosing of bearing stratum, bearing stratum for pile foundation, bearing capacity of pile foundation, settlement calculation etc.) 4. Key conclusions and proposals.,Figures,1. layout of exploration points 勘探点平面图 2 Engineering profile工程地质剖面图 3 Profile 钻孔柱状图 4 Table of results of insitu tests原位测试成果图表 5 Results of lab soil tests 室内土工试验成果图表 6 Special figures 专门性图件（暗浜分布图，工程地质分区图，各种分析图）,
