app.py

import streamlit as st
import math

st.set_page_config(page_title="Geotech Engineering Solver", layout="wide")
st.title("🧱 Geotechnical Engineering Solver")
st.markdown("Built using **American Standards** (ASTM, NAVFAC, Terzaghi, Meyerhof, Coduto).")

# Tabs for modules
tabs = st.tabs([
    "Phase Relationships",
    "Soil Classification (USCS)",
    "Bearing Capacity (Terzaghi & Meyerhof)",
])

# Constants
WATER_DENSITY = 1.0  # g/cm³


# PHASE RELATIONSHIPS TAB
with tabs[0]:
    st.header("Phase Relationships")
    st.markdown("Enter known values. Leave unknowns blank.")

    col1, col2 = st.columns(2)
    with col1:
        rho_wet = st.number_input("Wet Density (g/cm³)", step=0.01, format="%.3f")
        w = st.number_input("Moisture Content (as decimal, e.g. 0.12)", step=0.01, format="%.3f")
        Gs = st.number_input("Specific Gravity Gs", step=0.01, format="%.3f")
    with col2:
        rho_dry = st.number_input("Dry Density (g/cm³)", step=0.01, format="%.3f")
        e = st.number_input("Void Ratio", step=0.01, format="%.3f")
        S = st.number_input("Degree of Saturation (decimal)", step=0.01, format="%.3f")

    if st.button("Calculate Phase Relationships"):
        results = {}

        if rho_dry == 0 and rho_wet and w:
            rho_dry = rho_wet / (1 + w)
            results["Dry Density"] = f"{rho_dry:.3f} g/cm³"

        if e == 0 and Gs and rho_dry:
            e = (Gs * WATER_DENSITY / rho_dry) - 1
            results["Void Ratio"] = f"{e:.3f}"

        if e and not S and Gs and w:
            S = (w * Gs) / e
            results["Degree of Saturation"] = f"{S*100:.2f} %"

        if e:
            n = e / (1 + e)
            results["Porosity"] = f"{n*100:.2f} %"
        if e and S:
            Av = (e / (1 + e)) * (1 - S)
            results["Air Voids"] = f"{Av*100:.2f} %"

        st.subheader("Results:")
        if results:
            for k, v in results.items():
                st.success(f"{k}: {v}")
        else:
            st.warning("Not enough data to compute results.")

# SOIL CLASSIFICATION TAB
with tabs[1]:
    st.header("Soil Classification (USCS)")
    st.markdown("Based on **ASTM D2487 - Unified Soil Classification System**.")

    gravel = st.number_input("Gravel (%)", 0.0, 100.0, step=0.1)
    sand = st.number_input("Sand (%)", 0.0, 100.0, step=0.1)
    fines = st.number_input("Fines (Silt + Clay) (%)", 0.0, 100.0, step=0.1)
    LL = st.number_input("Liquid Limit (LL)", 0.0, 100.0)
    PL = st.number_input("Plastic Limit (PL)", 0.0, 100.0)

    if st.button("Classify Soil"):
        if fines > 50:
            PI = LL - PL
            if PI > 7 and LL > 50:
                soil_type = "CH (Fat Clay)"
            elif PI > 7 and LL <= 50:
                soil_type = "CL (Lean Clay)"
            elif PI <= 7 and LL <= 50:
                soil_type = "ML (Silt)"
            else:
                soil_type = "MH (Elastic Silt)"
        elif fines <= 50:
            if fines > 12:
                soil_type = "SM or SC (Silty/Clayey Sand)"
            elif sand > gravel:
                soil_type = "SP or SW (Poorly or Well Graded Sand)"
            else:
                soil_type = "GP or GW (Poorly or Well Graded Gravel)"
        else:
            soil_type = "Unclassified"

        st.success(f"USCS Soil Classification: **{soil_type}**")

# BEARING CAPACITY TAB
with tabs[2]:
    st.header("Bearing Capacity (Terzaghi & Meyerhof)")
    st.markdown("Formulas from **Terzaghi (1943)** and **Meyerhof (1951)** for shallow foundations.")

    φ = st.number_input("φ (Friction Angle, degrees)", 0.0, 45.0, step=0.1)
    c = st.number_input("Cohesion (kPa)", step=1.0)
    gamma = st.number_input("Soil Unit Weight (kN/m³)", 10.0, 30.0, step=0.1)
    B = st.number_input("Footing Width B (m)", step=0.1)
    D = st.number_input("Depth of Foundation D (m)", step=0.1)
    shape = st.selectbox("Footing Shape", ["Strip", "Square", "Circular"])

    if st.button("Compute Bearing Capacity"):
        φ_rad = math.radians(φ)

        Nq = math.exp(math.pi * math.tan(φ_rad)) * (math.tan(math.radians(45) + φ_rad / 2) ** 2)
        Nc = (Nq - 1) / math.tan(φ_rad) if φ > 0 else 5.14
        Nγ = 2 * (Nq + 1) * math.tan(φ_rad)

        if shape == "Strip":
            sc = sq = sγ = 1
        elif shape == "Square":
            sc = 1.3
            sq = 1.2
            sγ = 0.8
        elif shape == "Circular":
            sc = 1.3
            sq = 1.2
            sγ = 0.6

        q_ult = c * Nc * sc + gamma * D * Nq * sq + 0.5 * gamma * B * Nγ * sγ
        FS = 3
        q_allow = q_ult / FS

        st.subheader("Results")
        st.success(f"Ultimate Bearing Capacity q_ult = {q_ult:.2f} kPa")
        st.info(f"Allowable Bearing Capacity (FS={FS}) = {q_allow:.2f} kPa")